Skippy: Good morning Buzz! The last go around, we talked about feed throat cooling.
Buzz: Right; it is more important than many operators give credit to to have a feed throat temperature control ‘plan’ that is measurable and repeatable for this key area on an extrusion since it can impact
a) Zone One (feed section) of the barrel overall temperature variation and the machines controls for (potential over) compensation and
b) Moisture content of hopper flood fed In-rush of material – aka too cold in a humid production environment could sweat out moisture to end up falling into the feed stream
Skippy: The generic improvement suggested was adding a gallons per hour meter to the feed throat cooling loop. It could be necessary depending on larger machinery for say sheet etc running thousands of pounds per hour to require a gallons per minute meter, but that will be rate dependent.
Buzz: Yes, make an observation(s) at the line running in control as to water flow at various usage rates and select a gage that has the RANGE of use occupying same about the middle 50% of the gages working range.
Skippy: Let’s not forget safety issues –
Buzz: Of course, it’s a good idea to start the water flow at a small rate at start up so as not to flood the feed throat with water (which will turn to STEAM – OUCH) if you heat up the line and forget to have the feed throat coolant on until the barrel has potentially over-heated that area. Your set up procedure should include having the gage OPEN at start up to allow pressure relief as the system is started up then closed down to the range of coolant flow necessary for operation.
Skippy: also, as a reminder, remember to add a measurement process to your processing records for each rate requirement which can be impacted by incoming material temperatures (from cold boxes off of freezing trucks in the winter to preheated and dried materials) and shear generated during extrusion.
Buzz: Again, it is important to measure the flow OUT of the feed loop – keeping the loop filled, and at a constant temperature pulling out only a given amount of heat once equilibrium is achieved is key –
Skippy: ok, so having dealt with the feed throat area, what is this we continue to hear about “Hammer Rash”?
Buzz: You mean “hoppers that have been terribly abused and mercilessly beaten” in the interests of improving flow?
Skippy: Exactly.
Buzz: Well, we’ve always tried to avoid “reinventing the wheel”. There IS a lot of good information out there on the internet and discussions about material handling always get around to HOPPER FLOW.
In a general search on the internet for some good information about hopper flow, we’ve found a number of good sources and among them, found AJAX EQUIPMENT’s site at
http://www.ajax.co.uk/index.htm
Where there are a number of excellent articles and videos describing typical problems with feed related issues. For anyone interested in improving flow related issues in hoppers for plastics - check it out!
Skippy: Great - With a good grounding on hopper related issues and potential corrections, we can turn to another big element in feed related surging – material presentation to the screw –
Stay tuned –
Skippy and Buzz
Friday, December 11, 2009
Thursday, December 3, 2009
Feed Throat Cooling - Surging
Buzz: Good morning Skip - we've been having some discussion in other formums about "screw and barrel wear and it's possible affect(s) on surging". To that end, we have gotten a lot of good feedback, and are in process of organizing it into a better report out format and to give credit where we should.
In going over the material, I couldn't help noting that the overlap of experience will indeed be of great value to the "newer" extrusion techs.
Skippy: - Well, there IS a lot of good training material out there, but sometimes in the editing process it can become so terse, abbreviated, or worse situational as to be little to no help to our "newer" team mates.
Buzz: - right; for instance, one of the thoughts central to the surging discussion comes back to the simple "feed throat cooling". This important area should be cool enough to allow material not to stick in the feed throat on the way into the feed section of the screw, but not so cold as to
a) be cooler than the dew point in the plant resulting in water condensation on and in the throat being carried down into the extruder and
b) be cold enough to impact temperature sensing devices on zone one controls.
c) warm enough not to pull heat unnecessarily out of pre-conditioned (heated or dried or both) hopper materials.
Skippy: you bet. I remember once dealing with a problem on a particular make of extruder that used TWO thermocouples per barrel zone - one in the approximate center of the barrel, and one a scant few thousands of an inch from the barrel wall. The idea was that the comparison between the net change of the two was call for 'control intervention'.
Buzz: what happened?
Skippy: It was the darnest thing - in real operation, with regrinds in the material mix and a drying system in place (and feed throat water not under very good control,) we were finding that the net temperature of the mix delivered was moment to moment changing in the feed section and disturbing the thermocouple nearest the wall only a couple of degrees. However, with this 1-2 degree change happening so fast, the machine interpreted huge swings in temperature average range occurring. The machine controls in response would apply heat and then (water) cooling in a progressively expanding band of ripples which would throw the machine into real dismay. The output eventually would surge (at best) or stop with melt blockage on the screw (at worst).
Buzz: Was there a fix?
Skippy: - you bet. We put a small 1/2" long metal dowel in the bottom of the hole, and THEN the thermocouple to move it out just a bit from the wall. In this way, the mass of the measured area was not so quick to be "affected" by a momentary change in the mix. The problem was solved and never occurred again. This repair was actually applied to all additional similar equipment in the plant to overcome the same problem.
Buzz: what about the feed throat water?
Skippy: Well, the material was CAB and very hydroscopic. We used a lot of cold water cooling baths, and found that under the right circumstances, our chilled water could be applied too liberally to the feed throat and actually sweat water out of the air into the feed section. Water in clear materials ends up looking like "moisture" trapped in the material, so you can mistakenly be looking for a dryer problem where none really exists. Water driven out in the feed section as steam ends up going up the hopper stack and re-hydrating dried materials and can come back down through the throat again etc - all in all not a good process to support.
Buzz: what was your approach?
Skippy: The global answer was to equip each feed throat with a gallons per hour meter on the OUTPUT side of the loop. In other words, you want to trap the water in the feedthroat and only let out enough volume at what ever temperature you are putting in at what ever rate you are running (since many plants approach it differently) to yield a net temperature that is measured (on the same place of the feed throat each time)as part of the operations once or twice a shift after start up and steady state.
The temperature of the feed throat can be different for different materials and will be affected by different hopper dryer temperatures, rates and shear heat curve in the barrel etc. of course, so a "once size fits all" temperature isn't correct, but a one process variable fix to get to a repeatable measurable temperature is -
Buzz: - good stuff.
Anyway, over the next day few days, we will be consolidating more of this excellent input from the various groups for a report out for all how have contributed - stay tuned
Skippy and Buzz
In going over the material, I couldn't help noting that the overlap of experience will indeed be of great value to the "newer" extrusion techs.
Skippy: - Well, there IS a lot of good training material out there, but sometimes in the editing process it can become so terse, abbreviated, or worse situational as to be little to no help to our "newer" team mates.
Buzz: - right; for instance, one of the thoughts central to the surging discussion comes back to the simple "feed throat cooling". This important area should be cool enough to allow material not to stick in the feed throat on the way into the feed section of the screw, but not so cold as to
a) be cooler than the dew point in the plant resulting in water condensation on and in the throat being carried down into the extruder and
b) be cold enough to impact temperature sensing devices on zone one controls.
c) warm enough not to pull heat unnecessarily out of pre-conditioned (heated or dried or both) hopper materials.
Skippy: you bet. I remember once dealing with a problem on a particular make of extruder that used TWO thermocouples per barrel zone - one in the approximate center of the barrel, and one a scant few thousands of an inch from the barrel wall. The idea was that the comparison between the net change of the two was call for 'control intervention'.
Buzz: what happened?
Skippy: It was the darnest thing - in real operation, with regrinds in the material mix and a drying system in place (and feed throat water not under very good control,) we were finding that the net temperature of the mix delivered was moment to moment changing in the feed section and disturbing the thermocouple nearest the wall only a couple of degrees. However, with this 1-2 degree change happening so fast, the machine interpreted huge swings in temperature average range occurring. The machine controls in response would apply heat and then (water) cooling in a progressively expanding band of ripples which would throw the machine into real dismay. The output eventually would surge (at best) or stop with melt blockage on the screw (at worst).
Buzz: Was there a fix?
Skippy: - you bet. We put a small 1/2" long metal dowel in the bottom of the hole, and THEN the thermocouple to move it out just a bit from the wall. In this way, the mass of the measured area was not so quick to be "affected" by a momentary change in the mix. The problem was solved and never occurred again. This repair was actually applied to all additional similar equipment in the plant to overcome the same problem.
Buzz: what about the feed throat water?
Skippy: Well, the material was CAB and very hydroscopic. We used a lot of cold water cooling baths, and found that under the right circumstances, our chilled water could be applied too liberally to the feed throat and actually sweat water out of the air into the feed section. Water in clear materials ends up looking like "moisture" trapped in the material, so you can mistakenly be looking for a dryer problem where none really exists. Water driven out in the feed section as steam ends up going up the hopper stack and re-hydrating dried materials and can come back down through the throat again etc - all in all not a good process to support.
Buzz: what was your approach?
Skippy: The global answer was to equip each feed throat with a gallons per hour meter on the OUTPUT side of the loop. In other words, you want to trap the water in the feedthroat and only let out enough volume at what ever temperature you are putting in at what ever rate you are running (since many plants approach it differently) to yield a net temperature that is measured (on the same place of the feed throat each time)as part of the operations once or twice a shift after start up and steady state.
The temperature of the feed throat can be different for different materials and will be affected by different hopper dryer temperatures, rates and shear heat curve in the barrel etc. of course, so a "once size fits all" temperature isn't correct, but a one process variable fix to get to a repeatable measurable temperature is -
Buzz: - good stuff.
Anyway, over the next day few days, we will be consolidating more of this excellent input from the various groups for a report out for all how have contributed - stay tuned
Skippy and Buzz
Wednesday, November 25, 2009
Worn screws/barrels and extruder surging
Buzz: Oh yes, Skippy; another thought on the discussion so far about extrusion screw and barrel wear and "surging".
As you know, we have been involved with extrusion companies in two broad camps -
a) those that religiously measure and rebuild screws and replace barrels when they expect wear to be too much of an impact on reliable extrusion, and
b) those that have machines that you can rattle the screws around in worn barrels to a good degree
and yet because they can continue with process updates and changes produce product profitably, these companies couldn't care less about the thought of "measuring the wear" and moving directly to repair/replacement.
Skippy: - but how can this be? If both can achieve steady state extrusion with a wide variety of virgin and regrind materials in new and worn equipment, and both can exhibit machine conditions where "surging" exists - there must as Paul Harvey says be a "the rest of the story" -
Buzz: well yes. We have some thoughts on this that we would like to share with our readers and use to develop some discussion on solutions as well as discuss why this TYPE of question is so difficult - once we've had a little tryptophan er um TURKEY to help marshall our thoughts, we shall continue.
Skippy: - what direction is the discussion likely to go?
Buzz: well, I'd like to see us confirm that there is essentially no right or wrong answer here, but due to the system or environment in which it is answered, it could go either way.
BECAUSE of that, perhaps it is time for us to spend a few sessions in a much more compressed time span talking about a number of the other extrusion variables that can contribute to "surging" as well, how to spot them, how to eliminate or at least control them, and certainly the importance of being aware of them. In this way, our readers hopefully will jump in with additional thoughts and our dialog will be that much more productive -
Skippy - can't wait - see you in a day or two . . . Happy Thanksgiving to all!
(to be continued)
As you know, we have been involved with extrusion companies in two broad camps -
a) those that religiously measure and rebuild screws and replace barrels when they expect wear to be too much of an impact on reliable extrusion, and
b) those that have machines that you can rattle the screws around in worn barrels to a good degree
and yet because they can continue with process updates and changes produce product profitably, these companies couldn't care less about the thought of "measuring the wear" and moving directly to repair/replacement.
Skippy: - but how can this be? If both can achieve steady state extrusion with a wide variety of virgin and regrind materials in new and worn equipment, and both can exhibit machine conditions where "surging" exists - there must as Paul Harvey says be a "the rest of the story" -
Buzz: well yes. We have some thoughts on this that we would like to share with our readers and use to develop some discussion on solutions as well as discuss why this TYPE of question is so difficult - once we've had a little tryptophan er um TURKEY to help marshall our thoughts, we shall continue.
Skippy: - what direction is the discussion likely to go?
Buzz: well, I'd like to see us confirm that there is essentially no right or wrong answer here, but due to the system or environment in which it is answered, it could go either way.
BECAUSE of that, perhaps it is time for us to spend a few sessions in a much more compressed time span talking about a number of the other extrusion variables that can contribute to "surging" as well, how to spot them, how to eliminate or at least control them, and certainly the importance of being aware of them. In this way, our readers hopefully will jump in with additional thoughts and our dialog will be that much more productive -
Skippy - can't wait - see you in a day or two . . . Happy Thanksgiving to all!
(to be continued)
Saturday, November 14, 2009
Worn Screw/Barrel - Extruder Surging - more thoughts
Skippy: Our first stab on this question was put out there and a question came back on our preliminary thoughts below - concerning whether this was seen on single or twin screws. Others have observed more wear at the start of the life cycle on singles -
Buzz: Oops, engaged fingers faster than brain. The intent is not to be aggregating total screw and barrel wear as being a one side or the other phenomenon; regret it appearing to be so one sided - to continue;
In singles, we did see wear in a brief spike at the beginning of each screw and barrel rebuild for a short duration while all of the items "wore in" so to speak (remember, we were looking at situations where multiple screws and materials went into each machine).
Skippy: What happened after this initial break in period?
Buzz: We would observe a long period of wear which would be fairly predictable when on lines committed to more or less one material, and then accelerate nearer the end as the wear began to accumulate enough to cause significantly greater changes to process 'output' and we applied more and more resultant torsion to the screw and barrel interfacial region with other process variables. Our feeling was that since the screws were captive at the hub and near the gate, the torsion resulted in a greater arc in the "bend" to the screws and opened up the clearances at an accelerating rate in the 'middle' of the processing area.
Skippy: Did machine size or rate expectations play into this at all?
Buzz: Other factors coming into play did include the over-all rate as a percentage of "top end" capability since the observations were made on 2 1/2 and 3 1/2" machines and our goals did include increasing rates to "gain contribution per hour." I guess the anecdotal way to communicate this concept is the same as saying that when painting, using an 18" roller versus a 9" doesn't double the output at the same intended quality with out other factors being affected.
The other major difficulty area for our data may have been the constant change from one material to another, the various screw designs with and without various mixing elements in differing locations down the screw. Rather than having to overcome "wear" in one part of the screw and barrel with ONE screw and barrel, things were changing up and down the inter-facial area probably from just after the feed section until well into the metering sections from a number of the combinations.
Skippy: so in the end, wear begins to accumulate and . . .
Buzz: Well, once we began to be confronted with the results of leakage back over the flights, and the corresponding reduced outputs etc, the natural tendency was to try to put a toe or two out over the edge without leaping into the abyss - increase screw speed.
Skippy: Hmm. Most find that dealing with the resultant increased shear, and "residence" time for a portion of the material along with the general increase in melt temperature requires rethinking how to pump the material down a screw and barrel (with increasing wear) in differing manners versus suffering the resultant degradation, adhesive versus cohesive, flow related and sometimes aesthetic issues related to a hotter melt.
Buzz: Right. This tug of war over the abyss was generally continued until we would be delivering sufficiently high rate, continual output in terms of rate but dealing with stratified material coming out of the metering section in the 'plug flow' transformation at the breaker plate after the screw tip with a lower level of melt homogeneity. Instead of relying on the breaker plate and screens to simply help move ribbon to plug flow, we found ourselves relying on these to play an increasing role in melt mix distribution as well.
Sorry, all this once again is beyond the scope of this discussion. The short course was that it was (well past?) time for a screw and or barrel rebuild or replacement; and remember first that as processors, we need to look holistically at all the the interelated variables and manage them as just that - a whole.
Skippy: What about twin screws?
Buzz: A couple of things; on twins - yes we saw the most amount of wear at the end of the process since the forces exerted in the conveying mechanism were significantly different and other control options like screw tempering and differing feeds like starve versus flood feeding in combination with screw rpm and fusion rate modifications with the raw material supplier on formulations gave us a good many more options over the life of the screws and barrels -
Just our two cents
Buzz: Oops, engaged fingers faster than brain. The intent is not to be aggregating total screw and barrel wear as being a one side or the other phenomenon; regret it appearing to be so one sided - to continue;
In singles, we did see wear in a brief spike at the beginning of each screw and barrel rebuild for a short duration while all of the items "wore in" so to speak (remember, we were looking at situations where multiple screws and materials went into each machine).
Skippy: What happened after this initial break in period?
Buzz: We would observe a long period of wear which would be fairly predictable when on lines committed to more or less one material, and then accelerate nearer the end as the wear began to accumulate enough to cause significantly greater changes to process 'output' and we applied more and more resultant torsion to the screw and barrel interfacial region with other process variables. Our feeling was that since the screws were captive at the hub and near the gate, the torsion resulted in a greater arc in the "bend" to the screws and opened up the clearances at an accelerating rate in the 'middle' of the processing area.
Skippy: Did machine size or rate expectations play into this at all?
Buzz: Other factors coming into play did include the over-all rate as a percentage of "top end" capability since the observations were made on 2 1/2 and 3 1/2" machines and our goals did include increasing rates to "gain contribution per hour." I guess the anecdotal way to communicate this concept is the same as saying that when painting, using an 18" roller versus a 9" doesn't double the output at the same intended quality with out other factors being affected.
The other major difficulty area for our data may have been the constant change from one material to another, the various screw designs with and without various mixing elements in differing locations down the screw. Rather than having to overcome "wear" in one part of the screw and barrel with ONE screw and barrel, things were changing up and down the inter-facial area probably from just after the feed section until well into the metering sections from a number of the combinations.
Skippy: so in the end, wear begins to accumulate and . . .
Buzz: Well, once we began to be confronted with the results of leakage back over the flights, and the corresponding reduced outputs etc, the natural tendency was to try to put a toe or two out over the edge without leaping into the abyss - increase screw speed.
Skippy: Hmm. Most find that dealing with the resultant increased shear, and "residence" time for a portion of the material along with the general increase in melt temperature requires rethinking how to pump the material down a screw and barrel (with increasing wear) in differing manners versus suffering the resultant degradation, adhesive versus cohesive, flow related and sometimes aesthetic issues related to a hotter melt.
Buzz: Right. This tug of war over the abyss was generally continued until we would be delivering sufficiently high rate, continual output in terms of rate but dealing with stratified material coming out of the metering section in the 'plug flow' transformation at the breaker plate after the screw tip with a lower level of melt homogeneity. Instead of relying on the breaker plate and screens to simply help move ribbon to plug flow, we found ourselves relying on these to play an increasing role in melt mix distribution as well.
Sorry, all this once again is beyond the scope of this discussion. The short course was that it was (well past?) time for a screw and or barrel rebuild or replacement; and remember first that as processors, we need to look holistically at all the the interelated variables and manage them as just that - a whole.
Skippy: What about twin screws?
Buzz: A couple of things; on twins - yes we saw the most amount of wear at the end of the process since the forces exerted in the conveying mechanism were significantly different and other control options like screw tempering and differing feeds like starve versus flood feeding in combination with screw rpm and fusion rate modifications with the raw material supplier on formulations gave us a good many more options over the life of the screws and barrels -
Just our two cents
Breaker Plate clean up suggestion
Buzz: - Hey Skippy, the holidays continue to close in on us and we had a quick question on breaker plate maintenance -
[Flex PVC user] "Is there an energy efficient way to clean breaker plates?"
Skippy: As a big believer in (M)inimum (N)ecessary (C)hange or correction should be applied for (M)aximum (D)esired (R)esult, how about this -
Assuming that you are pulling and tidying them up "hot" after running flex PVC (even highly loaded), an operator with sufficient vocational prep time should be able to use compressed air and have them spic and span by simply pulling them clean most of the time. This does require a little practice with experienced personnel and the appropriate non scratching tools - most houses make brass tooling available specifically for this type of clean up. Once fully cleared, they should be dipped in an acid neutralizing solution, rinsed, air dried to remove moisture and either stored with/in a light lubricant, or preheated and reused on the next line -
Buzz: there are of course all sorts of other cleaning methods - (old) salt baths, fluidized beds, ultrasonics, etc . . .
Skippy: Yes of course. Generally plants with processes requiring breaker plates to convert ribbon to plug flow also have a supply of compressed air on hand as part of the operations, and may need to avoid the extra expense of these additional energy consuming devices. You may need to re-engineer your tooling with one or more die "swing gates" or multiple breaker plate positions on a push through system to keep the line up and running again during clean up/change over with a minimum of lost time. The activity to avoid appears to be pulling the plates out and leaving them to cool down, then trying to "clean them" in an "energy efficient manner"; which seems like the start of a wasteful process -
Just our two cents -
[Flex PVC user] "Is there an energy efficient way to clean breaker plates?"
Skippy: As a big believer in (M)inimum (N)ecessary (C)hange or correction should be applied for (M)aximum (D)esired (R)esult, how about this -
Assuming that you are pulling and tidying them up "hot" after running flex PVC (even highly loaded), an operator with sufficient vocational prep time should be able to use compressed air and have them spic and span by simply pulling them clean most of the time. This does require a little practice with experienced personnel and the appropriate non scratching tools - most houses make brass tooling available specifically for this type of clean up. Once fully cleared, they should be dipped in an acid neutralizing solution, rinsed, air dried to remove moisture and either stored with/in a light lubricant, or preheated and reused on the next line -
Buzz: there are of course all sorts of other cleaning methods - (old) salt baths, fluidized beds, ultrasonics, etc . . .
Skippy: Yes of course. Generally plants with processes requiring breaker plates to convert ribbon to plug flow also have a supply of compressed air on hand as part of the operations, and may need to avoid the extra expense of these additional energy consuming devices. You may need to re-engineer your tooling with one or more die "swing gates" or multiple breaker plate positions on a push through system to keep the line up and running again during clean up/change over with a minimum of lost time. The activity to avoid appears to be pulling the plates out and leaving them to cool down, then trying to "clean them" in an "energy efficient manner"; which seems like the start of a wasteful process -
Just our two cents -
Friday, November 13, 2009
Plastics in the news - cutting through the noise -
Welcome one and all - our list of visitors is growing, and we are always interested in new discussion topics.
Interested in keeping up with a wide varitey of plastics information worth investigating?
Check out Matt Defosse's blog at Plastics Today!
http://www.plasticstoday.com/blog/4942
Skippy and Buzz -
Interested in keeping up with a wide varitey of plastics information worth investigating?
Check out Matt Defosse's blog at Plastics Today!
http://www.plasticstoday.com/blog/4942
Skippy and Buzz -
Thursday, November 12, 2009
Worn extrusion equipment and surging
Skippy: Hey Buzz - happy almost Thanksgiving - we saw an interesting question in another plastics forum -
"Can a worn extruder screw cause surging? I've heard this for years but can't see how a linear variation with a period of a minute or two can be caused by a slow radial change over many weeks or months or even years. If anyone can come up with a reasonable and technically sound explanation, I would like to see it. ALG"
Buzz: - Well Skippy, I tend to agree with most that the slow evolution of “wear” is not likely to create a situation where we have good melt pumping on Tuesday, only to have it fall apart on Wednesday. Screw melt pumping conditions DO change over time with wear, and particularly when aggressive screw and screw tip cooling are employed to “throw material around” in profile tools.
Skippy: To be fair, don't we have to acknowledge here that there are a number of critical process areas that contribute perhaps as much to "surging" based on material delivery (aspect ratio of material components, mix of materials, conveying method/stability, existence of fines, drying temperature, air flow, residence time in the dryer, feed throat temperature control, zone 1 and or 2 temperature control, etc etc etc) to the feed section of a screw that are ignored or not very well understood in too many shops?
Buzz: Of course, although that conversation is way beyond the scope of this particular discussion and will be investigated more fully in the future. On the other hand, in custom plant environments where screw and barrel wear were faithfully measured by quarter on extrusion lines that ran a variety of materials from week to week (aka not just one material from beginning to end of each screw/barrel rebuild life) we observed the following –
The most amount of wear from quarter to quarter occurred at the END of the screw and or barrel life measurement period, not at the beginning. (by production hours)
R&D staff tend to prefer to “run in new items on new screws and barrels” and in short order, the “process” is/was not as "stable" to established run conditions in future runs and required “tweaking”
Many US firms have gotten caught in the trap of increasing rates to “increase contributions per hour” (false economy of course if no new sales fill the new empty machine time) at the expense of significantly closing the ‘window of process ability’ with any particular brand of elements
Skippy: I'm wondering whether the economic climate we're experiencing contributes in any way as well -
Buzz: well, we have observed that batch to batch variation in raw materials from manufacturers quite frankly (despite their “certifications” on lab materials) DO exist, sometimes in great measure and
Business conditions (and perhaps lack of cash flow?) in custom extrusion in poorly run shops affects the run to run use of varying raw material virgins and regrinds –
Skippy: How does that affect running an extrusion line?
Buzz: Well sometimes, rather than running a standard mix of regrinds back into product from the beginning of the run until the end, some houses accumulate and “rev the meter” from nearly 0 to nearly 100% which further requires "tweaking" in general to re-achieve proper melt thixotropy with varying amounts of regrind.
This can result in some rather aggressive approaches to achieving a stable melt pumping mechanism at the correct melt temperature and pressure to have the material “be one” with the intended tooling flow paths –
Skippy: So all that translates to what?
Buzz: In the case(s) above, we find that the requirements for process adjustment in a process where we KNOW that all else (listed in the opening above) is in good working order and under “control” end up being “justified” due to “changing outputs”. The bottom line is that although a good deal of data can be accumulated in “screw and barrel wear” verus "surging" it is meaningless, unless the contribution to wear can some how be tied back to the requirements for any number of the destabilizing run approach problems above in the plant as well.
Your question is an excellent one, because many shops quite frankly do not do a very good job of monitoring, mixing, drying etc the input of raw materials and then “change the process and blame the extruder” aka worn barrel and screw.
Skippy: is this likely to be a standard answer for extrusion in general?
Buzz: Quite frankly, we would guess that the pipe folks who will routinely rebuild screws and change out barrels on an “X” pounds schedule on lines running the same product 24/7 for months on end would have a totally different answer than the “custom gang” but that's just our two cents
"Can a worn extruder screw cause surging? I've heard this for years but can't see how a linear variation with a period of a minute or two can be caused by a slow radial change over many weeks or months or even years. If anyone can come up with a reasonable and technically sound explanation, I would like to see it. ALG"
Buzz: - Well Skippy, I tend to agree with most that the slow evolution of “wear” is not likely to create a situation where we have good melt pumping on Tuesday, only to have it fall apart on Wednesday. Screw melt pumping conditions DO change over time with wear, and particularly when aggressive screw and screw tip cooling are employed to “throw material around” in profile tools.
Skippy: To be fair, don't we have to acknowledge here that there are a number of critical process areas that contribute perhaps as much to "surging" based on material delivery (aspect ratio of material components, mix of materials, conveying method/stability, existence of fines, drying temperature, air flow, residence time in the dryer, feed throat temperature control, zone 1 and or 2 temperature control, etc etc etc) to the feed section of a screw that are ignored or not very well understood in too many shops?
Buzz: Of course, although that conversation is way beyond the scope of this particular discussion and will be investigated more fully in the future. On the other hand, in custom plant environments where screw and barrel wear were faithfully measured by quarter on extrusion lines that ran a variety of materials from week to week (aka not just one material from beginning to end of each screw/barrel rebuild life) we observed the following –
The most amount of wear from quarter to quarter occurred at the END of the screw and or barrel life measurement period, not at the beginning. (by production hours)
R&D staff tend to prefer to “run in new items on new screws and barrels” and in short order, the “process” is/was not as "stable" to established run conditions in future runs and required “tweaking”
Many US firms have gotten caught in the trap of increasing rates to “increase contributions per hour” (false economy of course if no new sales fill the new empty machine time) at the expense of significantly closing the ‘window of process ability’ with any particular brand of elements
Skippy: I'm wondering whether the economic climate we're experiencing contributes in any way as well -
Buzz: well, we have observed that batch to batch variation in raw materials from manufacturers quite frankly (despite their “certifications” on lab materials) DO exist, sometimes in great measure and
Business conditions (and perhaps lack of cash flow?) in custom extrusion in poorly run shops affects the run to run use of varying raw material virgins and regrinds –
Skippy: How does that affect running an extrusion line?
Buzz: Well sometimes, rather than running a standard mix of regrinds back into product from the beginning of the run until the end, some houses accumulate and “rev the meter” from nearly 0 to nearly 100% which further requires "tweaking" in general to re-achieve proper melt thixotropy with varying amounts of regrind.
This can result in some rather aggressive approaches to achieving a stable melt pumping mechanism at the correct melt temperature and pressure to have the material “be one” with the intended tooling flow paths –
Skippy: So all that translates to what?
Buzz: In the case(s) above, we find that the requirements for process adjustment in a process where we KNOW that all else (listed in the opening above) is in good working order and under “control” end up being “justified” due to “changing outputs”. The bottom line is that although a good deal of data can be accumulated in “screw and barrel wear” verus "surging" it is meaningless, unless the contribution to wear can some how be tied back to the requirements for any number of the destabilizing run approach problems above in the plant as well.
Your question is an excellent one, because many shops quite frankly do not do a very good job of monitoring, mixing, drying etc the input of raw materials and then “change the process and blame the extruder” aka worn barrel and screw.
Skippy: is this likely to be a standard answer for extrusion in general?
Buzz: Quite frankly, we would guess that the pipe folks who will routinely rebuild screws and change out barrels on an “X” pounds schedule on lines running the same product 24/7 for months on end would have a totally different answer than the “custom gang” but that's just our two cents
Friday, August 7, 2009
More on Vacuum Tank help -
Skippy: Say, we thought a bit more about the response in the last post, and hadn't realized we didn't ask a couple more 'broad brush stroke" questions -
a) are you using a color concentrate with the PE and PP that is being exuded out from the melt and being deposited/captured/coating the calibration unit or plugging vacuum holes and slots? This could be insulating the calibration unit and preventing efficient heat transfer - may need to be checked on a regular basis if the colorant system and or process can't be modified to eliminating this "plate out" effect. A rubberbanding or thinning/stretching effect in the calibration unit due to this insulating of the calibration could intermittently look like folding at the front of the calibration unit - rather than a constant haul off down the line -
b) we didn't really discuss the travel method, and assumed that the take off unit was capable of overcoming the normal calibration drag and pulling the part at a constant rate of speed - without belt/cleat slippage or obvious motor speed problems. Depending on the drive makeup, one thing to check is that the take off is operating at approximately 70-80 percent of it's rated motor speed in the correct gear reduction range if applicable at the correct haul off rate.
c) is the output of the extruder constant? as we had assumed; - if not could be a host of issues - check by cutting off 10 to 60 second pieces of hot melt at the die -several in a row, cool the mass and weigh on an accurate (gram?) scale to see what if any variation is occuring at the extruder. It is important that the sample size be large enough to overcome the inherent error in your "by hand" cut off of the samples -
Buzz: and d) we were also assuming that the calibration unit had previously been checked for obvious damage, nicks, blocked ports, correct coolant and vacuum hook ups etc. and that the Vacuum tank itself was in correct running order with adequate coolant into and out of the system - sorry for not thinking of those items as well earlier -
Good luck -
a) are you using a color concentrate with the PE and PP that is being exuded out from the melt and being deposited/captured/coating the calibration unit or plugging vacuum holes and slots? This could be insulating the calibration unit and preventing efficient heat transfer - may need to be checked on a regular basis if the colorant system and or process can't be modified to eliminating this "plate out" effect. A rubberbanding or thinning/stretching effect in the calibration unit due to this insulating of the calibration could intermittently look like folding at the front of the calibration unit - rather than a constant haul off down the line -
b) we didn't really discuss the travel method, and assumed that the take off unit was capable of overcoming the normal calibration drag and pulling the part at a constant rate of speed - without belt/cleat slippage or obvious motor speed problems. Depending on the drive makeup, one thing to check is that the take off is operating at approximately 70-80 percent of it's rated motor speed in the correct gear reduction range if applicable at the correct haul off rate.
c) is the output of the extruder constant? as we had assumed; - if not could be a host of issues - check by cutting off 10 to 60 second pieces of hot melt at the die -several in a row, cool the mass and weigh on an accurate (gram?) scale to see what if any variation is occuring at the extruder. It is important that the sample size be large enough to overcome the inherent error in your "by hand" cut off of the samples -
Buzz: and d) we were also assuming that the calibration unit had previously been checked for obvious damage, nicks, blocked ports, correct coolant and vacuum hook ups etc. and that the Vacuum tank itself was in correct running order with adequate coolant into and out of the system - sorry for not thinking of those items as well earlier -
Good luck -
Thursday, August 6, 2009
Need Help Extruding Rigid Tubing Using a Vacuum Tank
Buzz: You know Skip, we are working on extrusion materials from the last NPE show, but we often get questions that show the need for making sure just the basics are covered as well - like this one:
"We just got a vacuum tank and have had several jobs tool really well on it. On the past few jobs, we are getting a fold in the wall of the tubing that we cannot seem to work out. Materials are PP, PE and Nylon. I know that we are probably missing something simple. Any suggestions or resources that can help me trouble shoot?"
Skippy: Oh boy, I hope that our 30 years of extrusion experience can be of some benefit. We do this for a living, and would be glad to come in and help - Note these comments are not meant to criticize, but we will assume nothing -
Mentioned in your post:
"We just got a vacuum tank and have had several jobs tool really well on it. On the past few jobs, we are getting a fold in the wall of the tubing that we cannot seem to work out. Materials are PP, PE and Nylon. I know that we are probably missing something simple"
Buzz: Let's talk about a couple of these elements to see if you are in fact "missing something".
Skippy, ok, A) You got a new vacuum tank. Was this the only addition to the line, or did you get some new tooling with it to make particular parts as well? You mention the first few jobs ran "well" - were they in the same materials? Using the same tooling? Do you have a program in place to tear down the machine from job to job and a set up sheet that has been gone over to be sure that all processing conditions are "correct"? Are you running more or less lines now that in the past (see calibration - aka water)
Buzz: right, then B) Suddenly, you are having problems with the extrudate folding over in the wall of the extrudate - is it in one area only, or all around the tube - A fold usually indicates one of several things -
1) The wall balance versus the "draw down" is not correct.
When you shear off some material coming out of the die at rate, the parison (tube shape) pushed out should flow out roughly horizontally for a small way (until gravity kicks in).
Question? Do you clean the machine up totally from material to material (clean means all plastic out of the tooling to bare metal, pull the screens, pull the screw and clean all down to the metal?) If not, you might have material hung up in the barrel or at the tip of the screw, in the screens or breaker plate that isn't moving. Since the screw is imparting ribbon flow that must be converted into plug flow through the breaker plate, if you interrupt this plug, erratic and generally uneven flow through the balance of the tooling may occur. You might also have material caught up in one or more spider legs - causing whacked out flow that an operator is trying to correct with pin/shell relationships -
Once the material flows through the gate adapter in plug flow, through the spider and pin/shell in even distribution and assuming that your tooling is approximately 5 degrees above the correct melt temperature, then you should be delivering a "tube" out of the tooling that is ready for draw down and calibration -
Skippy: Good point, but it also might be
2) Die Gap - this is the distance between the Die Face and calibration. Assuming that the wall is even, then we would want the Die Gap to be even from every point on the die to every point on the calibration. Since the tooling is larger than the calibration, you need to back the tank AWAY from the die so that "draw down" can occur. The correct distance away will be somewhat variable based on
a) the melt temperature and "stiffness" of the melt"
b) the wall thickness versus the cross sectional area
c) the lot of material - yes I know that your materials should be fractional melt, but since they are "fractional" even a small change can affect the apparent "stiffness" of the melt at any given temperature.
In the materials that you mention, it is not uncommon for the OD and ID of the tubing tooling to be larger (in some cases up to 60% or more) than the final size of the tubing so that the material can be drawn down prior to entering the calibration. Are you using common tooling for all of the materials, or do you have different pins and shells for different sizes of tubing from different materials?
Also the die gap is established by making sure that the calibration and extrusion centerlines in both planes (side view and top down) are straight in line with one another. Vacuum tanks, takeoffs and cutting devices are notorious for vibration and will "creep" along the floor if able - is the line "in Line?" if not, you are perhaps not applying cooling evenly down line.
Buzz: yes sir, and doen't forget
3) Lubrication - two of the materials - PP and PE have an affinity to move from being cohesive to adhesive as they get hotter - generally, most custom extruders use a lubricant (water or other proprietary) systems to lubricate the material as it enters the calibration. Is this system working correctly? Nylon is VERY sensitive to moisture - is your drying system capable, is the (lack of) moisture level very well maintained? It goes without saying that PP, PE and Nylon all require different pins and shells and draw downs to make the "same" size tubing. Anyone that tries to run all three from the same tooling perhaps can by sacrificing rate or quality. Best to optimize for each material and go clean to clean between materials on machines.
Skippy: yup, and this is key -
4) Calibration cooling - is it dependable and repeatable? Is it actually working? Your vacuum tank calibration cooling might be hooked up to
a) well water; coming up out of the ground, it is likely to be around 55 degrees all year round - good system if dependable in terms of gallons per minute
b) city water; likely to change temperature with the seasons - 55 or so in the winter to possibly 75 degrees of more in the summer. Again, are you sure that your supply in gallons per minute is known and repeatable?
c) some sort of internal water recovery system (cooling tower, chiller); do you do preventative maintenance on the system, again do you know day to day what the temperature and actual gallons per minute availability is
Once the supply of water is maintained, then it has to be APPLIED to the calibration in a known manner. I like to put gallons per minute meters in line supplying my calibration - for a couple of reasons -
a) once we know for instance that 7 gals per minute at 55 degrees on a part running 150# per hour at "X" feet per second through the calibration at 300# per thousand feet is running WELL, I note that as being critical to being repeated in the future.
Buzz: ok, all together now, b) are we ready for "silly?"
We often encounter plants with a problem like this, where everything is running well as in a) above, and then the process "goes south". I always ask what is "new at the line" - "Nothing" is generally the reply. Then I ask "what else is new in the plant?" and we find out that three other lines were being started at the same time, and the SUPPLY of water which was capable of giving me 7 gal per minute with valve open 1/4 is now being diverted into filling three more lines. A quick check on my gal per minute meter shows that at my line, we've dropped to 3 gals per minute and the parts are "folding" (too hot). I open the supply valve at my line from 1/4 to say 1/2, bringing my supply back up to 7 gal per minute and line settles out. Don't forget that when the other three lines eventually settle into production and turn their valves from FULL to fill to 1/4 to run that we will suddenly have TOO much water (check the gage) and have to make an adjustment again. One of these gages on every line allows each operator to know what effect others are having on his line, and what to do to get back in control rather than just "trying zone three for 5 degrees" etc.
Skippy: wow, just goes to show you that laying down the foundations is really important. Other simple thoughts include making sure that the water application in the tank is even - water rings get plugged up with rust, shavings, dirt etc, and make sure water is cooling all sides evenly.
Buzz: We haven't really talked much about how to set up the calibration, the materials of construction to seal around the tube after the calibration and from compartment to compartment etc, but have been focused on the "fold" probably happening with either uneven flow out of tools or uneven cooling in the Calibration.
Once again, we can be called upon for additional help, training etc in your plant as required.
Just our "two cents" -
"We just got a vacuum tank and have had several jobs tool really well on it. On the past few jobs, we are getting a fold in the wall of the tubing that we cannot seem to work out. Materials are PP, PE and Nylon. I know that we are probably missing something simple. Any suggestions or resources that can help me trouble shoot?"
Skippy: Oh boy, I hope that our 30 years of extrusion experience can be of some benefit. We do this for a living, and would be glad to come in and help - Note these comments are not meant to criticize, but we will assume nothing -
Mentioned in your post:
"We just got a vacuum tank and have had several jobs tool really well on it. On the past few jobs, we are getting a fold in the wall of the tubing that we cannot seem to work out. Materials are PP, PE and Nylon. I know that we are probably missing something simple"
Buzz: Let's talk about a couple of these elements to see if you are in fact "missing something".
Skippy, ok, A) You got a new vacuum tank. Was this the only addition to the line, or did you get some new tooling with it to make particular parts as well? You mention the first few jobs ran "well" - were they in the same materials? Using the same tooling? Do you have a program in place to tear down the machine from job to job and a set up sheet that has been gone over to be sure that all processing conditions are "correct"? Are you running more or less lines now that in the past (see calibration - aka water)
Buzz: right, then B) Suddenly, you are having problems with the extrudate folding over in the wall of the extrudate - is it in one area only, or all around the tube - A fold usually indicates one of several things -
1) The wall balance versus the "draw down" is not correct.
When you shear off some material coming out of the die at rate, the parison (tube shape) pushed out should flow out roughly horizontally for a small way (until gravity kicks in).
Question? Do you clean the machine up totally from material to material (clean means all plastic out of the tooling to bare metal, pull the screens, pull the screw and clean all down to the metal?) If not, you might have material hung up in the barrel or at the tip of the screw, in the screens or breaker plate that isn't moving. Since the screw is imparting ribbon flow that must be converted into plug flow through the breaker plate, if you interrupt this plug, erratic and generally uneven flow through the balance of the tooling may occur. You might also have material caught up in one or more spider legs - causing whacked out flow that an operator is trying to correct with pin/shell relationships -
Once the material flows through the gate adapter in plug flow, through the spider and pin/shell in even distribution and assuming that your tooling is approximately 5 degrees above the correct melt temperature, then you should be delivering a "tube" out of the tooling that is ready for draw down and calibration -
Skippy: Good point, but it also might be
2) Die Gap - this is the distance between the Die Face and calibration. Assuming that the wall is even, then we would want the Die Gap to be even from every point on the die to every point on the calibration. Since the tooling is larger than the calibration, you need to back the tank AWAY from the die so that "draw down" can occur. The correct distance away will be somewhat variable based on
a) the melt temperature and "stiffness" of the melt"
b) the wall thickness versus the cross sectional area
c) the lot of material - yes I know that your materials should be fractional melt, but since they are "fractional" even a small change can affect the apparent "stiffness" of the melt at any given temperature.
In the materials that you mention, it is not uncommon for the OD and ID of the tubing tooling to be larger (in some cases up to 60% or more) than the final size of the tubing so that the material can be drawn down prior to entering the calibration. Are you using common tooling for all of the materials, or do you have different pins and shells for different sizes of tubing from different materials?
Also the die gap is established by making sure that the calibration and extrusion centerlines in both planes (side view and top down) are straight in line with one another. Vacuum tanks, takeoffs and cutting devices are notorious for vibration and will "creep" along the floor if able - is the line "in Line?" if not, you are perhaps not applying cooling evenly down line.
Buzz: yes sir, and doen't forget
3) Lubrication - two of the materials - PP and PE have an affinity to move from being cohesive to adhesive as they get hotter - generally, most custom extruders use a lubricant (water or other proprietary) systems to lubricate the material as it enters the calibration. Is this system working correctly? Nylon is VERY sensitive to moisture - is your drying system capable, is the (lack of) moisture level very well maintained? It goes without saying that PP, PE and Nylon all require different pins and shells and draw downs to make the "same" size tubing. Anyone that tries to run all three from the same tooling perhaps can by sacrificing rate or quality. Best to optimize for each material and go clean to clean between materials on machines.
Skippy: yup, and this is key -
4) Calibration cooling - is it dependable and repeatable? Is it actually working? Your vacuum tank calibration cooling might be hooked up to
a) well water; coming up out of the ground, it is likely to be around 55 degrees all year round - good system if dependable in terms of gallons per minute
b) city water; likely to change temperature with the seasons - 55 or so in the winter to possibly 75 degrees of more in the summer. Again, are you sure that your supply in gallons per minute is known and repeatable?
c) some sort of internal water recovery system (cooling tower, chiller); do you do preventative maintenance on the system, again do you know day to day what the temperature and actual gallons per minute availability is
Once the supply of water is maintained, then it has to be APPLIED to the calibration in a known manner. I like to put gallons per minute meters in line supplying my calibration - for a couple of reasons -
a) once we know for instance that 7 gals per minute at 55 degrees on a part running 150# per hour at "X" feet per second through the calibration at 300# per thousand feet is running WELL, I note that as being critical to being repeated in the future.
Buzz: ok, all together now, b) are we ready for "silly?"
We often encounter plants with a problem like this, where everything is running well as in a) above, and then the process "goes south". I always ask what is "new at the line" - "Nothing" is generally the reply. Then I ask "what else is new in the plant?" and we find out that three other lines were being started at the same time, and the SUPPLY of water which was capable of giving me 7 gal per minute with valve open 1/4 is now being diverted into filling three more lines. A quick check on my gal per minute meter shows that at my line, we've dropped to 3 gals per minute and the parts are "folding" (too hot). I open the supply valve at my line from 1/4 to say 1/2, bringing my supply back up to 7 gal per minute and line settles out. Don't forget that when the other three lines eventually settle into production and turn their valves from FULL to fill to 1/4 to run that we will suddenly have TOO much water (check the gage) and have to make an adjustment again. One of these gages on every line allows each operator to know what effect others are having on his line, and what to do to get back in control rather than just "trying zone three for 5 degrees" etc.
Skippy: wow, just goes to show you that laying down the foundations is really important. Other simple thoughts include making sure that the water application in the tank is even - water rings get plugged up with rust, shavings, dirt etc, and make sure water is cooling all sides evenly.
Buzz: We haven't really talked much about how to set up the calibration, the materials of construction to seal around the tube after the calibration and from compartment to compartment etc, but have been focused on the "fold" probably happening with either uneven flow out of tools or uneven cooling in the Calibration.
Once again, we can be called upon for additional help, training etc in your plant as required.
Just our "two cents" -
Wednesday, July 29, 2009
- Bigger in your customer's eyes on a small budget -
Skippy: How do you act bigger with critical customer follow up without breaking the budget?
Buzz: As a small to medium size business (or even a small consultant group) you probably realize that in addition to the discipline of an active Customer Relationship Management program spitting out follow up activity, you have actionable follow up as well.
Skippy: Of course, plenty; from having meetings and teleconferences transcribed to keeping on top of customers critical time sensitive contacts to ordering supplies remotely, etc.
Buzz: Check out www.microtasking.net For a nominal charge, just about any customer or vendor follow up activity can be handled once or on a recurring basis on your behalf - think and be big on a small budget -
Buzz: As a small to medium size business (or even a small consultant group) you probably realize that in addition to the discipline of an active Customer Relationship Management program spitting out follow up activity, you have actionable follow up as well.
Skippy: Of course, plenty; from having meetings and teleconferences transcribed to keeping on top of customers critical time sensitive contacts to ordering supplies remotely, etc.
Buzz: Check out www.microtasking.net For a nominal charge, just about any customer or vendor follow up activity can be handled once or on a recurring basis on your behalf - think and be big on a small budget -
Wednesday, July 1, 2009
Profile extrusion info from NPE 2009
Skippy: Hi all - just back from a productive outing at NPE in Chicago -
Buzz: - I heard the show numbers were really down -
Skippy: Well yes, it did seem that the number of plastics personnel there were highly diminished from what we had observed the last 10 shows in a row back to 1979, but on the other hand, the folks that were there appeared to have a real reason to be there.
Buzz: and so the quality of the contacts was likely to be good?
Skippy: Right. I have a bag full of materials that are coming back from the variety of disciplines we are constantly going through - profile extrusion, thermoforming, injection molding both conventional and low pressure structural foam, and fiberglass composites.
There seemed to be a bigger focus on this show from the vendors on pooling the products (training, controls, common sense shop info etc) into more system wide solutions rather than just selling the newest loader, calibration, etc.
I will be assembling some of the materials regarding the profile extusion elements first and posting soon -
Buzz: - I heard the show numbers were really down -
Skippy: Well yes, it did seem that the number of plastics personnel there were highly diminished from what we had observed the last 10 shows in a row back to 1979, but on the other hand, the folks that were there appeared to have a real reason to be there.
Buzz: and so the quality of the contacts was likely to be good?
Skippy: Right. I have a bag full of materials that are coming back from the variety of disciplines we are constantly going through - profile extrusion, thermoforming, injection molding both conventional and low pressure structural foam, and fiberglass composites.
There seemed to be a bigger focus on this show from the vendors on pooling the products (training, controls, common sense shop info etc) into more system wide solutions rather than just selling the newest loader, calibration, etc.
I will be assembling some of the materials regarding the profile extusion elements first and posting soon -
Tuesday, February 10, 2009
Are you maintaining a “Three Legged Stool”?
Buzz - Hey Skippy - seat backs and tray tables up and locked please -
Skippy - say what?
Buzz - Well the travel in today's market is so bumpy and most of us don't have the luxury of having a 'Captain Sully' in the cockpit that it seems prudent to have seating that is firmly grounded.
Skippy - It goes without saying that we have a difficult marketplace at present.
Buzz - Yup, most companies (unfortunately) are in full blown ‘survival mode’; the mode consists mainly of gouging out ‘costs’ so as to live to fight another day.
Skippy - It is important to keep in mind though that doing this without enough introspection is akin to sawing legs off the stool you’re sitting on. You’ll want to maintain at least a ‘three legged stool’ with the three pillars necessary to provide stability over unknown terrain -
Buzz - which are?
Skippy -
A) [quality] sales - to existing and potential customers;
it’s easier to keep a customer than get one;
B) cash flow - you can be making sales and losing money etc.;
it never works out on ‘volume’ and lastly
C) human capital – are the right team members in place?
Buzz - Any suggestions?
Skippy - Rather than focus only on cost cutting, an honest internal assessment should be part of the operations mode at this most important time – does your team have a good handle on:
1. The existing problems that are currently facing your company?
2. The quality of key managers you presently employ?
3. The strengths and weaknesses of your company as seen through the eyes of your customers and employees?
4. The current climate of the company, such as morale and its status?
5. The planning that has occurred up to this point?
6. The attitudes of key managers toward the turn around and growth?
7. The story board material that presently exists(brochures, literature, selling aids, etc.)?
Buzz - Sounds like an assessment of these key factors prior to the coming rebuild is critical to take advantage of better company re-positioning and perhaps re-branding.
Skippy - right; and consider an independent audit. An outside consultant’s report can sometimes be not only revealing but also thought provoking. It may open the eyes of the most astute leadership. You must be prepared for real hidden problems that you might have missed. Moving forward before conducting an independent assessment can be deadly to your rebound and future growth.
Skippy - say what?
Buzz - Well the travel in today's market is so bumpy and most of us don't have the luxury of having a 'Captain Sully' in the cockpit that it seems prudent to have seating that is firmly grounded.
Skippy - It goes without saying that we have a difficult marketplace at present.
Buzz - Yup, most companies (unfortunately) are in full blown ‘survival mode’; the mode consists mainly of gouging out ‘costs’ so as to live to fight another day.
Skippy - It is important to keep in mind though that doing this without enough introspection is akin to sawing legs off the stool you’re sitting on. You’ll want to maintain at least a ‘three legged stool’ with the three pillars necessary to provide stability over unknown terrain -
Buzz - which are?
Skippy -
A) [quality] sales - to existing and potential customers;
it’s easier to keep a customer than get one;
B) cash flow - you can be making sales and losing money etc.;
it never works out on ‘volume’ and lastly
C) human capital – are the right team members in place?
Buzz - Any suggestions?
Skippy - Rather than focus only on cost cutting, an honest internal assessment should be part of the operations mode at this most important time – does your team have a good handle on:
1. The existing problems that are currently facing your company?
2. The quality of key managers you presently employ?
3. The strengths and weaknesses of your company as seen through the eyes of your customers and employees?
4. The current climate of the company, such as morale and its status?
5. The planning that has occurred up to this point?
6. The attitudes of key managers toward the turn around and growth?
7. The story board material that presently exists(brochures, literature, selling aids, etc.)?
Buzz - Sounds like an assessment of these key factors prior to the coming rebuild is critical to take advantage of better company re-positioning and perhaps re-branding.
Skippy - right; and consider an independent audit. An outside consultant’s report can sometimes be not only revealing but also thought provoking. It may open the eyes of the most astute leadership. You must be prepared for real hidden problems that you might have missed. Moving forward before conducting an independent assessment can be deadly to your rebound and future growth.
Saturday, January 31, 2009
"Pita" Management
Skippy – Hey Buzz – Happy New Year. Had someone inquire about "Pita" Management:
“Hi In the molding process when you allow raw material to flow fluently from the extruder at the beginning or end of work you get what we call here a "Pita" It is a big round and hard melted raw material. This raw material is out of the stock but not handled by the shop order and due to that after a while cause mismatch in stock. I would like to hear how do you handle that in your plants and if you have any suggestions for me. Thanks in advance.”
Buzz – Happy New Year as well. Hmm, this question could be looked at two ways – are we talking about the handling, use or disposal of the “pita” or the raw material allocation and subsequent quote effects side?
Skippy – why not both?
Buzz – Ok, from a material handling only point of view, it depends on the condition of the material as is extruded -
In custom shops running multiple materials, it is often that the barrel was given a light coating of a petroleum based product to seal the pores of the barrel. It is a given that your tooling was likely coated with something as well and that you have de-"greased" it etc as you hung and heated up -
A new run of material will pick this up and it is not in your best interest to have petroleum or silicone based products introduced back into your run mix from internally generated scrap - pitch it.
On the other hand, once you are up and running, with a good melt temp, the material can be handled at nearly the correct make up consistency, cool the material by mass quickly, remove water if present and run through granulator being careful to have the resultant regrind not too gummy/sticky - if you generate enough of this due to jamb ups, string ups, etc you may want to consider a "hot granulator" designed to take excess material at or near melt temp . . .
Skippy – okay, how about from a raw material variance standpoint?
Buzz – well, the amount of shop generated regrinds and virgin is a problem that is easy to overcome in your MRP or ERP process with a little examination of your particular system, some history analysis and a slight 'adjustment percentage' to your allocation table from the BOM..
It sounds like you have two major issues -
The first is COST for quoting, and the second is ACCURACY for material allocations.
Material allocations (probably the more important on a month to month basis):
------------------------------------------------------------------------------------------------------------------
Assuming that you have a costed bill of materials for each product, each would call for "X" pounds or kilos of plastic per some measure - thousand feet, 100 meters etc. Unless you have a VERY sophisticated MRP system, you probably have variances month to month in virgin to regrinds before any losses -
There are several losses that occur that belong in the BOM but generally are excluded until the problem becomes so large that it is hard to miss -
1) "Pita"s or start up scrap or jamb ups etc are all "losses" unless recaptured as I indicated in the original reply. If they are ground up and re-run, no loss exists and no variance is expected. For this exercise, we will assume that they are always losses
2) scrap that is lost in and around the granulator - it is rare that material isn't spilled on the floor and swept up, or vacuumed up when cleaning a granulator and going from one material to another or regular maintenance - what happens to it? Unless you re-wash, dry and reuse, again, loss
3) In extrusion, and vacuum or thermoforming versus injection molding, saw shavings, and tool cut offs end up on the floor as saw dust, trims etc. These can be or are losses as well unless recovered.
The closest MOSTLY correct answer is to do a scrupulous study by product - measure all inputs, all saved product, all by product wastes and losses as above, then calculate the % of loss as a measure of the total amount of material consumed and either
a) Increase the raw material per measure in each BOM by the same percentage or
the NEXT most correct answer is to do a scrupulous monthly study on the weights of all final products (net) by raw materials, and using the following formulas -
Beginning inventory + Purchases - minus ending inventory is Material Consumed. (Gross)
Material Consumed - net weight of all saved parts for shipment is Actual Material Used for Product and what ever is left is what was LOST.
LOST/Material consumed is the percentage that each Bill of Material should be increased by (average) to predict material allocations more closely.
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Quoting:
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This same exercise for a year would probably yield that your losses in aggregate are likely in the 1-3% range in a fairly clean well run shop. In this case, you would want to increase the raw material cost component in your quotes by the same or slightly more (slightly more is more likely to leave a little wiggle room until you find all the losses) than the aggregate loss. In this way, you know you aren't going to automatically get a "SURPRISE" loss in margin of 1-3% at year end.
Note that none of this discussion focuses on Regrind availability or max percentage usable. These discussions are beyond the scope of this simple answer.
I hope this simple explanation works. Good luck.
“Hi In the molding process when you allow raw material to flow fluently from the extruder at the beginning or end of work you get what we call here a "Pita" It is a big round and hard melted raw material. This raw material is out of the stock but not handled by the shop order and due to that after a while cause mismatch in stock. I would like to hear how do you handle that in your plants and if you have any suggestions for me. Thanks in advance.”
Buzz – Happy New Year as well. Hmm, this question could be looked at two ways – are we talking about the handling, use or disposal of the “pita” or the raw material allocation and subsequent quote effects side?
Skippy – why not both?
Buzz – Ok, from a material handling only point of view, it depends on the condition of the material as is extruded -
In custom shops running multiple materials, it is often that the barrel was given a light coating of a petroleum based product to seal the pores of the barrel. It is a given that your tooling was likely coated with something as well and that you have de-"greased" it etc as you hung and heated up -
A new run of material will pick this up and it is not in your best interest to have petroleum or silicone based products introduced back into your run mix from internally generated scrap - pitch it.
On the other hand, once you are up and running, with a good melt temp, the material can be handled at nearly the correct make up consistency, cool the material by mass quickly, remove water if present and run through granulator being careful to have the resultant regrind not too gummy/sticky - if you generate enough of this due to jamb ups, string ups, etc you may want to consider a "hot granulator" designed to take excess material at or near melt temp . . .
Skippy – okay, how about from a raw material variance standpoint?
Buzz – well, the amount of shop generated regrinds and virgin is a problem that is easy to overcome in your MRP or ERP process with a little examination of your particular system, some history analysis and a slight 'adjustment percentage' to your allocation table from the BOM..
It sounds like you have two major issues -
The first is COST for quoting, and the second is ACCURACY for material allocations.
Material allocations (probably the more important on a month to month basis):
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Assuming that you have a costed bill of materials for each product, each would call for "X" pounds or kilos of plastic per some measure - thousand feet, 100 meters etc. Unless you have a VERY sophisticated MRP system, you probably have variances month to month in virgin to regrinds before any losses -
There are several losses that occur that belong in the BOM but generally are excluded until the problem becomes so large that it is hard to miss -
1) "Pita"s or start up scrap or jamb ups etc are all "losses" unless recaptured as I indicated in the original reply. If they are ground up and re-run, no loss exists and no variance is expected. For this exercise, we will assume that they are always losses
2) scrap that is lost in and around the granulator - it is rare that material isn't spilled on the floor and swept up, or vacuumed up when cleaning a granulator and going from one material to another or regular maintenance - what happens to it? Unless you re-wash, dry and reuse, again, loss
3) In extrusion, and vacuum or thermoforming versus injection molding, saw shavings, and tool cut offs end up on the floor as saw dust, trims etc. These can be or are losses as well unless recovered.
The closest MOSTLY correct answer is to do a scrupulous study by product - measure all inputs, all saved product, all by product wastes and losses as above, then calculate the % of loss as a measure of the total amount of material consumed and either
a) Increase the raw material per measure in each BOM by the same percentage or
the NEXT most correct answer is to do a scrupulous monthly study on the weights of all final products (net) by raw materials, and using the following formulas -
Beginning inventory + Purchases - minus ending inventory is Material Consumed. (Gross)
Material Consumed - net weight of all saved parts for shipment is Actual Material Used for Product and what ever is left is what was LOST.
LOST/Material consumed is the percentage that each Bill of Material should be increased by (average) to predict material allocations more closely.
--------------
Quoting:
--------------
This same exercise for a year would probably yield that your losses in aggregate are likely in the 1-3% range in a fairly clean well run shop. In this case, you would want to increase the raw material cost component in your quotes by the same or slightly more (slightly more is more likely to leave a little wiggle room until you find all the losses) than the aggregate loss. In this way, you know you aren't going to automatically get a "SURPRISE" loss in margin of 1-3% at year end.
Note that none of this discussion focuses on Regrind availability or max percentage usable. These discussions are beyond the scope of this simple answer.
I hope this simple explanation works. Good luck.
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