Buzz - I had an opportunity to be thinking about injection molding, specifically using 'gas assist'. Anyway I was looking at some scrap and thinking about gassing and voiding in general. What had originally attracted me to the scrap was that there were some cut up sections where the center of the thicker rib areas were almost all void - as though they had been start up or R&D run in as 'gas assisted' parts - where a void is intentionally the outcome in the middle of thick sections. Does this have any additional affect on thinking during the design phase?
Skippy - the experts in the industry say that the overall effect of gas assist is the same as running a thinner wall part - a faster cycle with less shrink and less sink on the part; important to know when working with tooling people. Remember that recommendations concerning raw material shrinkage from the raw materials guys are just that - recommendations; as processors, we have to smarten ourselves up too. Anyway, when you get ready for gas assist, you should set up some trials on known parts from known tools dimensions and should intentionally shoot parts at the same cycle and barrel heats before gas assist and after to observe and measure the changes in SHRINKAGE which should occur reductions in overall shot/part weights - aka the shrinkage should be less. These tests could then be augmented with adjusting barrel temps (stock temp) and cycle time to pull hotter parts in an effort to 'shrink' them some more if too much larger.
Buzz - so if the mold isn't right on the first hit, we're sunk?
Skippy - When there is a question about shrinkage, the typical recommendation is to ask to 'section' molds where possible and put core pins in so that they can be replaced or at least moved around a little bit on an elliptical of some kind. The hotter the material, the thicker the wall, and the shorter the cycle - the more the material is going to shrink under normal circumstances - but you can only makes so much adjustment to these (plus perhaps annealing can be incorporated to 'shrink' an oversize part) processing parameters. The suggestion is that when ready to incorporate gas-assist, do some testing with various materials to see what changes in both 'the direction of flow' and 'cross flow direction' shrinkages that may occur.
finis
Monday, November 26, 2007
Tuesday, November 13, 2007
More 'Cutting Remarks'
Since posting thoughts earlier about ‘Cutting Plastic’ back in September, Skippy and Buzz have had a number of side discussions and have some additional inputs.
Skippy: Hey Buzz – Back on the idea of cutting plastics, someone suggested using a standard or carbide blade for cutting slightly abrasive PVC and Acrylic plastics but installing the blade ‘backwards’; any thoughts?
Buzz: The concept of 'blade in backwards' is a confirmation that a negative rake or tilt to the blade teeth imparts slicing versus gouging action in some plastic saw blade designs. This 'using of a blade improperly' is a bad idea all around – especially with carbide inserted blades – the carbide pieces are joined to the blade body, but are designed to push and cut into the product while cutting, not be pushed against backwards while trying to “exit” a product to be cut. Having the carbide pieces come loose and or be knocked off and slung at the high foot per minute speeds that saw blades run at is a potentially dangerous outcome. These blades just aren’t designed to be used that way. We are agreeing with negative rake in general for plastics along with the right tooth configurations, disagree with using wrong blades 'creatively'. Just buy the right kind of blade to start. Yes, PVC is slightly abrasive, generally due to the loading of talc or calcium carbonate or other fillers - sometimes they are in color and UV packages. While on the subject of abrasiveness, do your production folks a favor - remind them to remove jewelry while handling these plastic articles - particularly gold and silver rings while handling the slightly abrasive PVC - you know those grey marks they leave on the PVC? (come'on you want to test it right? Just rub a ring on the surface . . .) - yup, thats GOLD and SILVER being worn away - puts a new spin on the phrase 'value added' - eh?
Skippy: A few reminders again about safety. The sawn material removed will generally be larger than dust and can be airborne. Inexpensive paper dust masks to filter out the chips (which won't be much if you put together an inexpensive 'catch box' behind the chip path to catch 80% of the chips) and just as importantly, eye protection are always a good idea in a shop environment when using cutting and grinding tools. It may be that you also need a "Lock-Out, Tag-Out" procedure to disconnect all sources of danger when installing blades, doing set-up, and servicing the equipment.
Buzz: eventually someone recommends putting a lubricant on the blades as well. Recommendation - do not put petroleum products on PVC or other plastics in general - depending on the application, the by-products in the can (aerosol propellants etc) can create a variety of problems including UV and color fastness failures, and negative interaction with mating parts (not previously mentioned). If your final installation (what ever this does) needs to be warranted by you, not a good idea to create a future problem.
Skippy: what about ‘Silicone’ spray?
Buzz: Ah yes, good old "silly-cone" spray; next to ‘WD-40’ and Duct Tape, another of the great ‘cure alls’ - falls in line with the 'Bash to fit, Crush to assemble, Paint to hide' axiom- this is generally not a good material to be used in a shop environment as it will get into (and onto) everything eventually (worst is the floors and assembly counter surfaces) - again, if used on and impregnated into PVC can cause other problems - especially if you later want to use any adhesives with gaskets, tapes, labels etc. From a warranty standpoint, it is not a good idea to spray, coat or otherwise inject other stuff into your base compound; bare minimum it is likely to VOID the warranty from your profile supplier as well as their raw material manufacturer.
Skippy: So in general, a user of saw blades to cut plastics is looking to key in on
a) Correct blade design; differs per material; and correct equipment set up and use
b) Correct Cutting speeds (often measured in foot per minute surface speeds)
c) Adequate product support during cutting operations
d) Personal protection correctly applied and used at all times
Buzz: that's right Skip, hopefully you have already used the information to acquire the correct blades and are producing satisfactory results.
Skippy: Hey Buzz – Back on the idea of cutting plastics, someone suggested using a standard or carbide blade for cutting slightly abrasive PVC and Acrylic plastics but installing the blade ‘backwards’; any thoughts?
Buzz: The concept of 'blade in backwards' is a confirmation that a negative rake or tilt to the blade teeth imparts slicing versus gouging action in some plastic saw blade designs. This 'using of a blade improperly' is a bad idea all around – especially with carbide inserted blades – the carbide pieces are joined to the blade body, but are designed to push and cut into the product while cutting, not be pushed against backwards while trying to “exit” a product to be cut. Having the carbide pieces come loose and or be knocked off and slung at the high foot per minute speeds that saw blades run at is a potentially dangerous outcome. These blades just aren’t designed to be used that way. We are agreeing with negative rake in general for plastics along with the right tooth configurations, disagree with using wrong blades 'creatively'. Just buy the right kind of blade to start. Yes, PVC is slightly abrasive, generally due to the loading of talc or calcium carbonate or other fillers - sometimes they are in color and UV packages. While on the subject of abrasiveness, do your production folks a favor - remind them to remove jewelry while handling these plastic articles - particularly gold and silver rings while handling the slightly abrasive PVC - you know those grey marks they leave on the PVC? (come'on you want to test it right? Just rub a ring on the surface . . .) - yup, thats GOLD and SILVER being worn away - puts a new spin on the phrase 'value added' - eh?
Skippy: A few reminders again about safety. The sawn material removed will generally be larger than dust and can be airborne. Inexpensive paper dust masks to filter out the chips (which won't be much if you put together an inexpensive 'catch box' behind the chip path to catch 80% of the chips) and just as importantly, eye protection are always a good idea in a shop environment when using cutting and grinding tools. It may be that you also need a "Lock-Out, Tag-Out" procedure to disconnect all sources of danger when installing blades, doing set-up, and servicing the equipment.
Buzz: eventually someone recommends putting a lubricant on the blades as well. Recommendation - do not put petroleum products on PVC or other plastics in general - depending on the application, the by-products in the can (aerosol propellants etc) can create a variety of problems including UV and color fastness failures, and negative interaction with mating parts (not previously mentioned). If your final installation (what ever this does) needs to be warranted by you, not a good idea to create a future problem.
Skippy: what about ‘Silicone’ spray?
Buzz: Ah yes, good old "silly-cone" spray; next to ‘WD-40’ and Duct Tape, another of the great ‘cure alls’ - falls in line with the 'Bash to fit, Crush to assemble, Paint to hide' axiom
Skippy: So in general, a user of saw blades to cut plastics is looking to key in on
a) Correct blade design; differs per material; and correct equipment set up and use
b) Correct Cutting speeds (often measured in foot per minute surface speeds)
c) Adequate product support during cutting operations
d) Personal protection correctly applied and used at all times
Buzz: that's right Skip, hopefully you have already used the information to acquire the correct blades and are producing satisfactory results.
Thursday, November 1, 2007
Working With ‘Air’; Routing and Trimming
Skippy: We seem to get a lot of inquiries about trimming and routing in small job shops. This last month on the road, it felt a lot like that scene from 'The Graduate'; although instead of hearing the word 'plastics' everywhere, it seemed like a lot of folks are thinking that they need to look at 'Robotics'.
Buzz: Well, let's back up a little bit - for plastics and composite materials, air trimming tools are often easy to assemble machines that can be used either by hand or in semi-automatic mode with a little shop engineering to produce good quality parts at a fraction of the cost of robotic trimming.
Skippy: Doesn't that fall into the category of just 'throwing people at a problem'?
Buzz: Easy now, like you, I believe in increasing the productivity of our shop associates using high technology, but not all shops have volumes to justify high dollar investments into Robotics early on. On the other hand, one important item to consider ergonomically about cutting and trimming items with hand operated air tools is that user fatigue can increase when trying to extend cutting tool life and this must be carefully considered during tool selection and implementation (along with labor per unit costs.) Trying to work too fast with 'single fluted' tools can take less time than with 'multi-fluted' tools but quality will suffer. On the flip side, higher quality finishs can be obtained by making multiple passes: one roughing pass and a second finishing pass, but here again you need to consider the additional work for the operator or the semi-automatic machine.
Skippy: What are the critical shop issues?
Buzz: Air Pressure is probably first of the the most two critical items to consider and like a few other essential shop items (electricity?) when the supply drops a ‘little’ the resultant performance and quality drops more precipitously. For instance, these devices often need 90 psi or more at 30 cfm or greater of dry, clean, lubricated air to operate. If in this example with a drop in supply, the tool is receiving less than 70 psi or 20 cfm, then its usable horsepower is cut in half, as well as exhibiting a drop in its rpms. This compounds the quality and time related problems because router bits cutting edge surface speeds are designed for specific feet or inches per minute or second based on their rpms and do not perform as well at the wrong speed; just like the saw blade discussion earlier – time, pressure and surface speed all work together with the tool cutting surface design to yield a ‘sweet spot’. Some times air losses happen during the most innocent of 'plant improvement opportunities'. In the ‘Leaning’ process, shops often add more quick disconnects at multiple work stations to reduce travel time. These changes should be considered carefully as too small a supply line or too many users on a line can cause these pressure problems.
Skippy: You mentioned two critical items -
Buzz: - ah yes, Supply of air as above was the first and the second most important item is a proper maintenance schedule. Air tools are most often hampered or destroyed by particulate damage coming from their operating environments in shops where regular maintenance is not performed often enough. So, with the correct tooling, a well thought out implementation plan and a well executed maintenance program, air routers can be a very cost effective solution in small job shop settings.
Buzz: Well, let's back up a little bit - for plastics and composite materials, air trimming tools are often easy to assemble machines that can be used either by hand or in semi-automatic mode with a little shop engineering to produce good quality parts at a fraction of the cost of robotic trimming.
Skippy: Doesn't that fall into the category of just 'throwing people at a problem'?
Buzz: Easy now, like you, I believe in increasing the productivity of our shop associates using high technology, but not all shops have volumes to justify high dollar investments into Robotics early on. On the other hand, one important item to consider ergonomically about cutting and trimming items with hand operated air tools is that user fatigue can increase when trying to extend cutting tool life and this must be carefully considered during tool selection and implementation (along with labor per unit costs.) Trying to work too fast with 'single fluted' tools can take less time than with 'multi-fluted' tools but quality will suffer. On the flip side, higher quality finishs can be obtained by making multiple passes: one roughing pass and a second finishing pass, but here again you need to consider the additional work for the operator or the semi-automatic machine.
Skippy: What are the critical shop issues?
Buzz: Air Pressure is probably first of the the most two critical items to consider and like a few other essential shop items (electricity?) when the supply drops a ‘little’ the resultant performance and quality drops more precipitously. For instance, these devices often need 90 psi or more at 30 cfm or greater of dry, clean, lubricated air to operate. If in this example with a drop in supply, the tool is receiving less than 70 psi or 20 cfm, then its usable horsepower is cut in half, as well as exhibiting a drop in its rpms. This compounds the quality and time related problems because router bits cutting edge surface speeds are designed for specific feet or inches per minute or second based on their rpms and do not perform as well at the wrong speed; just like the saw blade discussion earlier – time, pressure and surface speed all work together with the tool cutting surface design to yield a ‘sweet spot’. Some times air losses happen during the most innocent of 'plant improvement opportunities'. In the ‘Leaning’ process, shops often add more quick disconnects at multiple work stations to reduce travel time. These changes should be considered carefully as too small a supply line or too many users on a line can cause these pressure problems.
Skippy: You mentioned two critical items -
Buzz: - ah yes, Supply of air as above was the first and the second most important item is a proper maintenance schedule. Air tools are most often hampered or destroyed by particulate damage coming from their operating environments in shops where regular maintenance is not performed often enough. So, with the correct tooling, a well thought out implementation plan and a well executed maintenance program, air routers can be a very cost effective solution in small job shop settings.
There's (often) 'not much new under the sun'
Buzz: This question came up from a application that was using a "Blow Molding" process to produce parts. Instead of de-necking the resultant product, they wanted to end up with a hollow part that was sealed - their thought process included 'gas injection' of course to inflate the hollow section(s):
"I'm trying to find a way to close the hole made by the gas injection needle in a plastic part. This part must come out of the mold without any hole! Can someboby help me with this issue?! Thank you!"
Skippy: Ok, here's an idea, but can I have a piece of the patent?
Buzz: Sure if it already hasn't been invented before -
Skippy: Design the needle injection/retraction point through essentially a hot runner area - sequence the activity so that the needle is retracted through hot plastic after the gas injection then freeze the aperature -
Buzz: Good answer; now for the bad news, based on your small amount of feedback, a quick search of the internet based hot runner folks yielded a quick note back from the questioner - "Thank you for your cooperation!"
It seems that the quick and easy answer was to use a Gunther System (these folks already have a huge knowledge base assembled on hot runner components and applications) - information can be found at:
http://www.guenther-hotrunner.com/php/start.php?lang=us
http://www.guenther-hotrunner.com/Download/Katalog/englisch/KAP-01-02-()-EN-NEEDLE-VALVE-TECHNOLOGY.pdf
Skippy: glad to be of help - sometimes just a nudge is as good as a push -
"I'm trying to find a way to close the hole made by the gas injection needle in a plastic part. This part must come out of the mold without any hole! Can someboby help me with this issue?! Thank you!"
Skippy: Ok, here's an idea, but can I have a piece of the patent?
Buzz: Sure if it already hasn't been invented before -
Skippy: Design the needle injection/retraction point through essentially a hot runner area - sequence the activity so that the needle is retracted through hot plastic after the gas injection then freeze the aperature -
Buzz: Good answer; now for the bad news, based on your small amount of feedback, a quick search of the internet based hot runner folks yielded a quick note back from the questioner - "Thank you for your cooperation!"
It seems that the quick and easy answer was to use a Gunther System (these folks already have a huge knowledge base assembled on hot runner components and applications) - information can be found at:
http://www.guenther-hotrunner.com/php/start.php?lang=us
http://www.guenther-hotrunner.com/Download/Katalog/englisch/KAP-01-02-()-EN-NEEDLE-VALVE-TECHNOLOGY.pdf
Skippy: glad to be of help - sometimes just a nudge is as good as a push -
Thursday, October 4, 2007
Portable water-cooled chillers
Skippy: Hey Buzz - had this question come up concerning 'chilling' capacity - "Can anyone tell me what difference a more powerful process pump makes in a portable water-cooled chiller (25 or 30 ton) for injection molding processing? I have two competing quotes for a machine - one new with a 5 hp process pump and one used (much cheaper) with a 3 hp process pump. Otherwise, they appear to be approximately similar in specs. Can anyone help?"
Buzz: Hmm, depending on the sizing of the pump head, and the tubing connections, it may be that one pump is moving more gpm (Flow) or one was sized to make more efficient use of power. The short course is that the differences are probably in net cooling capacity and the more 'correct' unit more closely matches either your current cooling needs or perhaps your future needs (hopefully someone ran the analysis.)
Skippy: So that’s it?
Buzz: Unfortunately, no. Since these units are likely to work on one or more machines, and or one or more molds, the real answer might also be that what is really needed is two smaller units with them working in tandem on different areas of molds. Or they may need to be 'lag loaded' together to match the demand needs in the plant environment with the various size molds and cooling requirements one might encounter depending on production rates and the temperature of the plant process water (depends on whether is recirculated or not).
Skippy: What’s the difference in flow got to do with cooling – if the water available is the same temperature?
Buzz: To show a rough idea on the change in cooling capacity based on 'flow', try this simple experiment at your local gas station (assuming you are allowed to pump your own gasoline):
On a typical warm day, dispense the gasoline at a steady, slow to moderate rate into your tank, paying attention to the temperature of the gas nozzle assembly in the palm of your hand. Assuming the gas is stored in the ground it is likely that it is cooler than the ambient air (at around 56 degrees or so in the tank in the ground) the nozzle in your hand should feel 'cooler' in short order. This is because the cooler gasoline coming up from the ground as it flows by that point is pulling heat from the metal nozzle. Stop the process. After waiting a few seconds for the nozzle temperature to normalize again, dispense the gasoline at a much higher rate - and the nozzle should get colder quicker than in the first instance. The temperature of the gas from underground didn't change (still 56 degrees), but the amount of gasoline flowing by the point is pulling heat from the nozzle at the higher rate.
Skippy: ok, here are some typical sites for some clarification on 'flow' versus cooling capacity and the importance of 'right sizing'; along with some pros and cons in general to keep in mind about portable chillers:
http://www.temperaturecorporation.com/loadsizing.htm
http://www.process-cooling.com/CDA/Archives/b306d426847b9010VgnVCM100000f932a8c0____
http://www.engineersedge.com/industrial-equipment/portable-chillers.htm
Buzz: Now you're 'cookin with gas' . . . er uh, no; different topic. Remember, in the system, the questioner is looking for someone to clarify the inferred 'cooling capacity' as a function of this pump size business. Hopefully, the system as a whole has been analyzed rather than get caught up in just one generic item aka 'process pumps'.
Another topic to keep in mind is the fact that 'turbulent flow' is desirable (think and inquire about cooling channel design and layout.) And since we're starting to dig a little deeper, if you are thinking about cooling on injection molds versus part weight distribution in general, another interesting topic to look into is 'melt flipping' which will create a more balanced mold to be 'cooled' in the first place -
http://www.immnet.com/articles?article=406
Of course these topics would be good for a later session -
Have a good day -
Buzz: Hmm, depending on the sizing of the pump head, and the tubing connections, it may be that one pump is moving more gpm (Flow) or one was sized to make more efficient use of power. The short course is that the differences are probably in net cooling capacity and the more 'correct' unit more closely matches either your current cooling needs or perhaps your future needs (hopefully someone ran the analysis.)
Skippy: So that’s it?
Buzz: Unfortunately, no. Since these units are likely to work on one or more machines, and or one or more molds, the real answer might also be that what is really needed is two smaller units with them working in tandem on different areas of molds. Or they may need to be 'lag loaded' together to match the demand needs in the plant environment with the various size molds and cooling requirements one might encounter depending on production rates and the temperature of the plant process water (depends on whether is recirculated or not).
Skippy: What’s the difference in flow got to do with cooling – if the water available is the same temperature?
Buzz: To show a rough idea on the change in cooling capacity based on 'flow', try this simple experiment at your local gas station (assuming you are allowed to pump your own gasoline):
On a typical warm day, dispense the gasoline at a steady, slow to moderate rate into your tank, paying attention to the temperature of the gas nozzle assembly in the palm of your hand. Assuming the gas is stored in the ground it is likely that it is cooler than the ambient air (at around 56 degrees or so in the tank in the ground) the nozzle in your hand should feel 'cooler' in short order. This is because the cooler gasoline coming up from the ground as it flows by that point is pulling heat from the metal nozzle. Stop the process. After waiting a few seconds for the nozzle temperature to normalize again, dispense the gasoline at a much higher rate - and the nozzle should get colder quicker than in the first instance. The temperature of the gas from underground didn't change (still 56 degrees), but the amount of gasoline flowing by the point is pulling heat from the nozzle at the higher rate.
Skippy: ok, here are some typical sites for some clarification on 'flow' versus cooling capacity and the importance of 'right sizing'; along with some pros and cons in general to keep in mind about portable chillers:
http://www.temperaturecorporation.com/loadsizing.htm
http://www.process-cooling.com/CDA/Archives/b306d426847b9010VgnVCM100000f932a8c0____
http://www.engineersedge.com/industrial-equipment/portable-chillers.htm
Buzz: Now you're 'cookin with gas' . . . er uh, no; different topic. Remember, in the system, the questioner is looking for someone to clarify the inferred 'cooling capacity' as a function of this pump size business. Hopefully, the system as a whole has been analyzed rather than get caught up in just one generic item aka 'process pumps'.
Another topic to keep in mind is the fact that 'turbulent flow' is desirable (think and inquire about cooling channel design and layout.) And since we're starting to dig a little deeper, if you are thinking about cooling on injection molds versus part weight distribution in general, another interesting topic to look into is 'melt flipping' which will create a more balanced mold to be 'cooled' in the first place -
http://www.immnet.com/articles?article=406
Of course these topics would be good for a later session -
Have a good day -
Tuesday, September 25, 2007
Bathtubs and Truck Bed Liners
Buzz: a question came in from someone wanting to explore the following: “What is the best technology to fabricate the large scale molds from aluminum alloys for making bathtubs & liners for small truck boxes, by vacuum thermoforming plastic sheet?”
Skippy: this person appears to be inquiring about several different types of products in general –
a) Bathtubs – are generally started using a thinner gage, often acrylic capped vacuum or ‘thermoformable’ sheet that is dual or tri extruded - the back side will generally accept (be adhered to) a post formed added rigid backing material - often fiberglas (less expensive) or urethane (more expensive) - a few larger players dominate most of this 'commodity' market - quite a few regulations and certifications that you should make yourself aware of before offering these products to the construction industry.
b) truck bed liners - usually made from Polyethylene, again for high rate, usually formed on Aluminum water cooled molds - few new people enter this highly competitive market since the big players command so much volume in the market, the product is 'mature' and the cost to enter with a better product would be relatively prohibitive - good luck here.
Buzz: What about the similarity processing questions on the forming?
Skippy: For high(er) volume production and accurate shrinkages on construction related products, you would probably want to use a water cooled aluminum mold where cooling lines would be molded or embedded into a sand cast aluminum (or drilled through a machined aluminum mold.) Best place to start would be with someone with plastics expertise who can help you design the part in 3D to produce a pattern to be used with the casting house. Note - shrinkages on the materials in a) and b) are quite different, and it is important to work with your designer and sheet extruder on the ‘orientation’ of the sheet.
c) Truck boxes - could be made more rigid with fiberglas like a tub if constructed from the right materials, but are also often made from Polyethylene. When designed into the mold, these are easy to machine apart to get mating boxes and lids. They are often ‘rotationally molded’- totally different process.
Skippy: this person appears to be inquiring about several different types of products in general –
a) Bathtubs – are generally started using a thinner gage, often acrylic capped vacuum or ‘thermoformable’ sheet that is dual or tri extruded - the back side will generally accept (be adhered to) a post formed added rigid backing material - often fiberglas (less expensive) or urethane (more expensive) - a few larger players dominate most of this 'commodity' market - quite a few regulations and certifications that you should make yourself aware of before offering these products to the construction industry.
b) truck bed liners - usually made from Polyethylene, again for high rate, usually formed on Aluminum water cooled molds - few new people enter this highly competitive market since the big players command so much volume in the market, the product is 'mature' and the cost to enter with a better product would be relatively prohibitive - good luck here.
Buzz: What about the similarity processing questions on the forming?
Skippy: For high(er) volume production and accurate shrinkages on construction related products, you would probably want to use a water cooled aluminum mold where cooling lines would be molded or embedded into a sand cast aluminum (or drilled through a machined aluminum mold.) Best place to start would be with someone with plastics expertise who can help you design the part in 3D to produce a pattern to be used with the casting house. Note - shrinkages on the materials in a) and b) are quite different, and it is important to work with your designer and sheet extruder on the ‘orientation’ of the sheet.
c) Truck boxes - could be made more rigid with fiberglas like a tub if constructed from the right materials, but are also often made from Polyethylene. When designed into the mold, these are easy to machine apart to get mating boxes and lids. They are often ‘rotationally molded’- totally different process.
Thursday, September 20, 2007
Cutting plastic -
Buzz: - Hey Skippy - this one sounds pretty easy:
"We are currently cutting a (approx. .040 wall) PVC profile extrusion with a diamond saw blade. (Very messy) Has anyone got any suggestions how we can make an accurate and clean cut with a minimum of dust? We only do about 500 cuts per day."
Skippy: Fortunately, cutting PVC stock materials is a rather common activity in the plastic business, and a good number of saw blade manufacturers have already solved this problem. Your results will improve if you have access to several pieces of information and or tools - how you approach may well be dictated by the arbor size and speed of the motor (and speed reduction?) available to you.
a) the saw blade design - several saw blade manufacturers produce a 'bi or triple tooth' style design - the saw blades have carbide inserted teeth that are welded on to the blade body - some are 'spade like - more pointed' and some are 'clean-out like' more blunted by slightly wider - in this way, the blade progressively nibbles into the material and then cleans out the sides of the cut. Blades having teeth slightly wider than the blade body are preferable.
b) the foot per minute (fpm) of the teeth moving through the material is important versus the size of your part, the wall thickness of any unsupported walls and the support given to the part while the cut is going on - saws with variable speed motors are best - often with multiple pulleys and belt reductions etc to be able to change the final arbor rotation speed - simple calculations in combination with different saw blade diameters should enable you to get into the right ranges -
c) just going from memory for rigid pvc, 4500-9000 fpm saw blade speed (sweet spot might be around 6000-9000 fpm if the product has about a .040-.050 wall typical) with a 80-100 tooth bi or triple tooth design blade with a slight NEGATIVE RAKE (5 degrees) angle on the teeth in a 10-14" diameter blade will suffice - so depending on the arbor speed(s) available, the arbor size dictating the build of the blade, the diameter to put you into the right speed range, you should have good success. Additionally, these blades will cut many thousands of cuts before needing resharpening, and can be resharpened generally a couple times. I don't sell for any saw people, but an example catalog can be found at
http://www.generalsaw.com/resource/plastic.html
which contains a general catalog – “friends in the business" use blades similar to those described on pages 10 and 11 –
Buzz: Thanks for the 'quick answer' but aren’t their any other cutting methods that are less messy – like ni-chrome hot wire or spinning knives etc?
Skippy: Well, the best solution was one I saw was published almost 30 years ago and had to do with the spinning knife (which I'll get to in a minute) - if you do in fact feel compelled to move away from currently inexpensive sawing methods -
a) First, the 'ni-chrome wire solution' - unless you buy an off the shelf product (source included), you are going to have to mess around a bit with the ni-chrome and a variable DC power source - amperage/heat/tensioning will be an issue - requires the wire or heated knife to be hot enough to part the part but cool enough not to get the sides gooey for the wall thickness - be prepared for some trial and error - and by all means provide some ventilation for the hcl gas that comes from PVC as it burns and degrades - there are heated knives that fabricators use for cutting sheet - not too wild about them myself - examples here:
http://www.ppe.com/ - look under "Heated Knives"
b) if you decide to go with a spinning knife style cold blade 'cutter', some info -
You'll need some 'bushings' that approximate the shape of the extrusion to keep it from deforming during the impact/torque of the cutting and shearing action. As the knife is rotated about an axis (like any single tooth on a saw blade or the shearing action not unlike a paper cutter) you are looking for either two support surfaces - one on either side of the rotating knife path, or one to shear against with the cutting action not unlike a desktop slicing paper cutter style movement. We always accomplished making cutter bushings with a wire EDM machine to burn a hole the shape of the extrusion through the center axis of a 2 1/2" to 3" steel rod 6-8" in length, then part the rod in two making to pancake shaped disks and ground the faces that the knife would pass between perpendicular to the outside diameter (except for turning a slight chamfer on the circumferences for a 'entry' for the knife.)
An inexpensive way to do this is to take a couple of 2-3" long 'rings' of steel or other round metal material and convert it to bushings with a cental hole shaped like the extrusion in the following manner:
Turn the ring on it's side so that when you stand the profile up in the center of the ring, there is space between the part and the inside ring diameter - it is this air space that needs to be filled -
Do a little analysis to find one of the LARGEST parts in terms of overall size and thickness, and then add a layer of masking tape to all surfaces which approximates a part just a little bit bigger. You might want to then spray a little silicone spray on the outside of the tape to increase it's release characteristics. Suspend or stand the part (say 2 1/2 times the length of the ring) up in the center of the ring with a portion of the taped part held parallel in the inside central axis of the ring and fill the void with ordinary automotive body filler and hardener. Hold every thing square until the body filler sets and hardens. If this is a SET of bushings, align another ring on top of the first ring by aligning their outside diameters, and fill the second ring with body filler and hardener. Once all is set, pull out the taped profile and then use a grinder or sander etc to dress the 'face' perpendicular to the central axis and outside diameter (if you did one bushing) or the two opposing 'faces' of the bushing pair that a knife can now pass between. If you have done this, you will end up with a bushing pair that once held in alignment (line up as you set up with a part or two on the inside to align) will give you very nice support faces for a knife to pass between and good support on the part. You also will find that if you heat the part slightly (say to about 120-130 degrees F, the part will cut with much less torque requirements and still be under the approximately 160 degree heat deformation temperature of the material.
Now of course, all you need is a hot enough knife or a cold one moving with enough inertia or slicing torque to "cut" the part while it is at rest - and that's a whole different discussion.
"We are currently cutting a (approx. .040 wall) PVC profile extrusion with a diamond saw blade. (Very messy) Has anyone got any suggestions how we can make an accurate and clean cut with a minimum of dust? We only do about 500 cuts per day."
Skippy: Fortunately, cutting PVC stock materials is a rather common activity in the plastic business, and a good number of saw blade manufacturers have already solved this problem. Your results will improve if you have access to several pieces of information and or tools - how you approach may well be dictated by the arbor size and speed of the motor (and speed reduction?) available to you.
a) the saw blade design - several saw blade manufacturers produce a 'bi or triple tooth' style design - the saw blades have carbide inserted teeth that are welded on to the blade body - some are 'spade like - more pointed' and some are 'clean-out like' more blunted by slightly wider - in this way, the blade progressively nibbles into the material and then cleans out the sides of the cut. Blades having teeth slightly wider than the blade body are preferable.
b) the foot per minute (fpm) of the teeth moving through the material is important versus the size of your part, the wall thickness of any unsupported walls and the support given to the part while the cut is going on - saws with variable speed motors are best - often with multiple pulleys and belt reductions etc to be able to change the final arbor rotation speed - simple calculations in combination with different saw blade diameters should enable you to get into the right ranges -
c) just going from memory for rigid pvc, 4500-9000 fpm saw blade speed (sweet spot might be around 6000-9000 fpm if the product has about a .040-.050 wall typical) with a 80-100 tooth bi or triple tooth design blade with a slight NEGATIVE RAKE (5 degrees) angle on the teeth in a 10-14" diameter blade will suffice - so depending on the arbor speed(s) available, the arbor size dictating the build of the blade, the diameter to put you into the right speed range, you should have good success. Additionally, these blades will cut many thousands of cuts before needing resharpening, and can be resharpened generally a couple times. I don't sell for any saw people, but an example catalog can be found at
http://www.generalsaw.com/resource/plastic.html
which contains a general catalog – “friends in the business" use blades similar to those described on pages 10 and 11 –
Buzz: Thanks for the 'quick answer' but aren’t their any other cutting methods that are less messy – like ni-chrome hot wire or spinning knives etc?
Skippy: Well, the best solution was one I saw was published almost 30 years ago and had to do with the spinning knife (which I'll get to in a minute) - if you do in fact feel compelled to move away from currently inexpensive sawing methods -
a) First, the 'ni-chrome wire solution' - unless you buy an off the shelf product (source included), you are going to have to mess around a bit with the ni-chrome and a variable DC power source - amperage/heat/tensioning will be an issue - requires the wire or heated knife to be hot enough to part the part but cool enough not to get the sides gooey for the wall thickness - be prepared for some trial and error - and by all means provide some ventilation for the hcl gas that comes from PVC as it burns and degrades - there are heated knives that fabricators use for cutting sheet - not too wild about them myself - examples here:
http://www.ppe.com/ - look under "Heated Knives"
b) if you decide to go with a spinning knife style cold blade 'cutter', some info -
You'll need some 'bushings' that approximate the shape of the extrusion to keep it from deforming during the impact/torque of the cutting and shearing action. As the knife is rotated about an axis (like any single tooth on a saw blade or the shearing action not unlike a paper cutter) you are looking for either two support surfaces - one on either side of the rotating knife path, or one to shear against with the cutting action not unlike a desktop slicing paper cutter style movement. We always accomplished making cutter bushings with a wire EDM machine to burn a hole the shape of the extrusion through the center axis of a 2 1/2" to 3" steel rod 6-8" in length, then part the rod in two making to pancake shaped disks and ground the faces that the knife would pass between perpendicular to the outside diameter (except for turning a slight chamfer on the circumferences for a 'entry' for the knife.)
An inexpensive way to do this is to take a couple of 2-3" long 'rings' of steel or other round metal material and convert it to bushings with a cental hole shaped like the extrusion in the following manner:
Turn the ring on it's side so that when you stand the profile up in the center of the ring, there is space between the part and the inside ring diameter - it is this air space that needs to be filled -
Do a little analysis to find one of the LARGEST parts in terms of overall size and thickness, and then add a layer of masking tape to all surfaces which approximates a part just a little bit bigger. You might want to then spray a little silicone spray on the outside of the tape to increase it's release characteristics. Suspend or stand the part (say 2 1/2 times the length of the ring) up in the center of the ring with a portion of the taped part held parallel in the inside central axis of the ring and fill the void with ordinary automotive body filler and hardener. Hold every thing square until the body filler sets and hardens. If this is a SET of bushings, align another ring on top of the first ring by aligning their outside diameters, and fill the second ring with body filler and hardener. Once all is set, pull out the taped profile and then use a grinder or sander etc to dress the 'face' perpendicular to the central axis and outside diameter (if you did one bushing) or the two opposing 'faces' of the bushing pair that a knife can now pass between. If you have done this, you will end up with a bushing pair that once held in alignment (line up as you set up with a part or two on the inside to align) will give you very nice support faces for a knife to pass between and good support on the part. You also will find that if you heat the part slightly (say to about 120-130 degrees F, the part will cut with much less torque requirements and still be under the approximately 160 degree heat deformation temperature of the material.
Now of course, all you need is a hot enough knife or a cold one moving with enough inertia or slicing torque to "cut" the part while it is at rest - and that's a whole different discussion.
Tuesday, September 18, 2007
Trouble with Extruded and Injection Molded Parts
Skippy: Hey Buzz - here was someone who needed help – “I have developed a new product for the construction industry. All was good while in u.s. except tooling costs. We decided to outsource to china to try to resolve this problem but in doing so we set ourselves back (over a year now) from taking this to market. ... (Product includes) both extrusion and injection molding ... with tight tolerances as profile extrusion marries to injection components. Also seeking advice on injection molds as currently mold maker claims to be doing "adjustments" to molds for about three weeks now. I am leery as to the quality of molds loss of temper etc. What should I look for in pics before final payment is made to ensure I am receiving a quality mold?”
Buzz: Any serious plastics professional will tell you that there are three major considerations in assemblies of injection molded and extruded parts - particularly when they are going to be used together with other mating parts, and sold anonymously through distribution into a vague category like 'Construction' - especially with warranty related questions in the background. The inquiry didn't mention number of cavities and general mold design criteria so without specifics it would be difficult to 'direct' them on the injection molding portion at this early point.
Skippy: What is needed?
Buzz: Consistent, clear and written communication should be the watchwords. Depending on which of these following items you NEED, it will change the way one would think about design and tool up of either plastic process, and the resulting 'tweaks' needed on tooling -
1) Dimensions (critical, control, reference)
2) Aesthetics (critical, control, reference surfaces)
3) Physicals (flammability, electrical, impact, UV, reactivity with other parts etc)
Skippy: So what thinking should be included in the ' big picture '?
Buzz: Here are a few general thoughts to consider (assuming the DESIGN issues are taken care of:)
a) Photostereolithography - for $1500 or so you can have sample parts made to dimension for critical assembly fits, including undercuts, blind holes etc. Bet on the final injection molded parts being closer to print than the extrusions (caveat - a poorly or improperly packed, voided, or stress-molded-in part can 'hit the numbers' and still be a poorly performing part in application - see Aesthetics and Physicals) and then have some examples of the extrusion produced with high and low critical tolerances produced by p- as above and submitted by your extruder. In many years, we've not found more than about a half dozen with more than 3-4 CRITICAL dimensions for assembly between parts. On the other hand - a major item to think about during the contract review process would be what OTHER mating parts does your system need to match up with? It may be that one of the parts is not yet fully developed in how it relates to them . . .
b) Understand what you NEED in terms of the big three stated above - one of the three is always easy to produce at 'rate and weight'; two of three is more difficult and probably will affect production rates, all three will nearly always affect production and discard rates and therefore your final delivered price.
c) Insist that your sample parts be produced from the actual production tooling at PRODUCTION rates from PRODUCTION material - nothing creates more ' availability to market headaches ' than to submit your sample assemblies for further consideration (aka engineering evaluations - electrical, UV, or smoke/flame) only to find out that the sample parts were made from a general purpose or utility grade of material that does not include any additives addressing your special needs - self extinguishing characteristics, dielectric properties, impact or notched IZOD capability, UV characteristics, static dissipative qualities, biocides, fungicides etc.
d) Work with a house that has their own in-house wire capability for the extrusion tooling. It is much less costly to open up or remake the extrusion tooling than the injection molding tooling - probably on the order of 6-10 to one. Ask to see examples of their tooling and their tool storage area. Notice how they keep the unused tooling on the shelf - cleaned and measured, shiny and production ready or rusty, filled with plastic and unkempt against the day someone might reorder? A number of houses will quote inexpensive flat plate tooling, but be wary of the how these tools work over multiple lots of raw materials which can and do change - particularly if your spec a 'utility grade' of material.
e) Be at least a little paranoid; Trust, but Verify. For every one of the good plastic outfits out there, there are some who won't measure up beyond the sample parts. Look for a house that has some sort of quality system/policy (with or without the ISO moniker), with sample retains on less than perfect quality parts used year to year to maintain quality checks on output, and written records of past production runs including retained information back to incoming raw materials and supplier raw materials certifications if possible etc.
f) While working with your Product Manager, get it in writing; material specs, quality and production records - ask to attend and help fill out a 'Contract Review' - answering the couple dozen critical questions that a good processor needs answers to to ' help them help you ' is a critical path to success. Some sales people can actually act in this ' Product Management ' role; and unfortunately many can't.
g) Ask for and be prepared to get enough samples to have engineering testing done on the resulting samples - and do it.
A well run product development process has additional nuances of course, but these should give you a good grounding.
Buzz: Any serious plastics professional will tell you that there are three major considerations in assemblies of injection molded and extruded parts - particularly when they are going to be used together with other mating parts, and sold anonymously through distribution into a vague category like 'Construction' - especially with warranty related questions in the background. The inquiry didn't mention number of cavities and general mold design criteria so without specifics it would be difficult to 'direct' them on the injection molding portion at this early point.
Skippy: What is needed?
Buzz: Consistent, clear and written communication should be the watchwords. Depending on which of these following items you NEED, it will change the way one would think about design and tool up of either plastic process, and the resulting 'tweaks' needed on tooling -
1) Dimensions (critical, control, reference)
2) Aesthetics (critical, control, reference surfaces)
3) Physicals (flammability, electrical, impact, UV, reactivity with other parts etc)
Skippy: So what thinking should be included in the ' big picture '?
Buzz: Here are a few general thoughts to consider (assuming the DESIGN issues are taken care of:)
a) Photostereolithography - for $1500 or so you can have sample parts made to dimension for critical assembly fits, including undercuts, blind holes etc. Bet on the final injection molded parts being closer to print than the extrusions (caveat - a poorly or improperly packed, voided, or stress-molded-in part can 'hit the numbers' and still be a poorly performing part in application - see Aesthetics and Physicals) and then have some examples of the extrusion produced with high and low critical tolerances produced by p- as above and submitted by your extruder. In many years, we've not found more than about a half dozen with more than 3-4 CRITICAL dimensions for assembly between parts. On the other hand - a major item to think about during the contract review process would be what OTHER mating parts does your system need to match up with? It may be that one of the parts is not yet fully developed in how it relates to them . . .
b) Understand what you NEED in terms of the big three stated above - one of the three is always easy to produce at 'rate and weight'; two of three is more difficult and probably will affect production rates, all three will nearly always affect production and discard rates and therefore your final delivered price.
c) Insist that your sample parts be produced from the actual production tooling at PRODUCTION rates from PRODUCTION material - nothing creates more ' availability to market headaches ' than to submit your sample assemblies for further consideration (aka engineering evaluations - electrical, UV, or smoke/flame) only to find out that the sample parts were made from a general purpose or utility grade of material that does not include any additives addressing your special needs - self extinguishing characteristics, dielectric properties, impact or notched IZOD capability, UV characteristics, static dissipative qualities, biocides, fungicides etc.
d) Work with a house that has their own in-house wire capability for the extrusion tooling. It is much less costly to open up or remake the extrusion tooling than the injection molding tooling - probably on the order of 6-10 to one. Ask to see examples of their tooling and their tool storage area. Notice how they keep the unused tooling on the shelf - cleaned and measured, shiny and production ready or rusty, filled with plastic and unkempt against the day someone might reorder? A number of houses will quote inexpensive flat plate tooling, but be wary of the how these tools work over multiple lots of raw materials which can and do change - particularly if your spec a 'utility grade' of material.
e) Be at least a little paranoid; Trust, but Verify. For every one of the good plastic outfits out there, there are some who won't measure up beyond the sample parts. Look for a house that has some sort of quality system/policy (with or without the ISO moniker), with sample retains on less than perfect quality parts used year to year to maintain quality checks on output, and written records of past production runs including retained information back to incoming raw materials and supplier raw materials certifications if possible etc.
f) While working with your Product Manager, get it in writing; material specs, quality and production records - ask to attend and help fill out a 'Contract Review' - answering the couple dozen critical questions that a good processor needs answers to to ' help them help you ' is a critical path to success. Some sales people can actually act in this ' Product Management ' role; and unfortunately many can't.
g) Ask for and be prepared to get enough samples to have engineering testing done on the resulting samples - and do it.
A well run product development process has additional nuances of course, but these should give you a good grounding.
Thursday, September 13, 2007
Surface Preparation for Painting
Buzz: Ran into a question concerning surface preparation for plastic being decorated: “I need help to design a flame unit to treat a flat plastic product. I am building a machine to accurately align an applique on the part. It is a low volume application and has a shoestring budget. It can be a Rube Goldberg type machine so any help would be appreciated.”
Skippy: Flame annealing the surface of PP and PE products will definitely improve the adhesion properties of many adhesive systems and inks - you can prove this in short order just playing the flame from an off the shelf 'sweated copper tubing' burner using a 'paint removal spreader tip' quickly over the area to be 'stuck to'.
The easiest way to accomplish what you want to do uses gravity for the application motion - the parts are 'dropped down an incline', and the surface to be treated is hit with one or more gas burners - you need a hot flame on and off the surface in a very short time span so as not to release the other residual 'stress' in the product as extruded or molded. LP versus Natural gas burners are much better suited and commonly available for this process. Best results will be with a tunable flame that is in the blue color range starting at approximately 1100 degrees F (and could be hotter - check with the burner manufacturer to see optimum and working temperatures) – yellow flame is too cold. Applying the flame UNDER the part is easiest to control although ring type burners for 360 degree application are available.
Buzz – what about safety?
Skippy – Good observation - Be sure to build in the necessary safety devices used to SHUT the unit down immediately if your process goes out of temperature range or allows product to catch fire (which inevitably happens), use Personal Protection Equipment (heat gloves, eye protection, keeping extra skin covered etc). Another hint, stay away from highly flammable clothing as the operator - rayon, polyester, etc are NOT GOOD CHOICES. Use protective clothing/handling gloves tailored to the task and be sure to keep an appropriately rated fire extinguisher handy -
Again, the 'blue flame' concept mentioned is in approximately the 1100 degree F or more range; depends on time and temperature - it does oxidize the surface. The burner at the action point is only one part of the system - you need to use a thermocouple in the flame stream (in the right temperature range,) and a temperature reading and gas control device to get an idea of where you are at temperature wise for repeatability each production cycle. If you need more exposures, the product can be run through successive rings, or passed successively through a single ring or burner. You might need to put a cooling cycle or water source between rings or passes.
Do not scavenge rings from your stove at home - you need to consider the burners, any cooling required, the distribution of flame versus part size and time, etc. take a peek at this or similar sites -
http://www.flametreatingsystems.com/stanhead.htm
I'm sure these or other people can help you get started.
Monday, September 10, 2007
Wherefor consultants?
Skippy: Hey, Buzz, I've been hearing an awful lot about these guys called consultants ... why does anyone use or need them?
Buzz: Well, depending upon who you talk to, you can get a whole bunch of different answers. You see, there's been quite a bit of change that's crept into the manufacturing socioeconomic structure over the past thirty five or so years. Back in the mid 1970's, a person would enter into a segment of the manufacturing workforce that they had been either trained in or educated to pursue and they hoped their contributions would lead to continued growth and success for an organization and a lifetime of advancement opportunities.
Skippy: Makes sense to me - so what's changed?
Buzz: Well, the measurement of growth and success began to become so competitive that a lot of companies came to believe that if the entire skilled workforce was not actively and aggressively upwardly mobile, then they must not be doing their jobs.
Skippy: But we need "worker bees", you can't continue to sustain growth without having a layer of middle management core disciplines in place to tactically exercise all of the upper management strategic objectives.
Buzz: Exactly. And what began to happen was these middle management personnel began to use their entry level positions to gain experience and move on to another opportunity until the timing was right for some organization to recognize them as either a valued asset or, better yet, ready to move up when an opportunity became available. When this scenario began to accelerate nationwide, there were more than just a few companies that quickly discovered that when they had the good fortune to meet some of their strategic goals, they had neither the experienced staffing or systems maturity to satisfy the increasing customer demands.
Skippy: So is this how the consultants became involved?
Buzz: Well, I'll just say that thirty five years later, there are a lot of manufacturing professionals who have either sustained the environments of job changes, corporate downsizing's or the expected attrition due to retirements that have an abundant amount of knowledge and experience to offer in their fields of expertise.
Skippy: Any way to know how and when to select the right ones?
Buzz: Absolutely, but let's save that for another chat . . .
Buzz: Well, depending upon who you talk to, you can get a whole bunch of different answers. You see, there's been quite a bit of change that's crept into the manufacturing socioeconomic structure over the past thirty five or so years. Back in the mid 1970's, a person would enter into a segment of the manufacturing workforce that they had been either trained in or educated to pursue and they hoped their contributions would lead to continued growth and success for an organization and a lifetime of advancement opportunities.
Skippy: Makes sense to me - so what's changed?
Buzz: Well, the measurement of growth and success began to become so competitive that a lot of companies came to believe that if the entire skilled workforce was not actively and aggressively upwardly mobile, then they must not be doing their jobs.
Skippy: But we need "worker bees", you can't continue to sustain growth without having a layer of middle management core disciplines in place to tactically exercise all of the upper management strategic objectives.
Buzz: Exactly. And what began to happen was these middle management personnel began to use their entry level positions to gain experience and move on to another opportunity until the timing was right for some organization to recognize them as either a valued asset or, better yet, ready to move up when an opportunity became available. When this scenario began to accelerate nationwide, there were more than just a few companies that quickly discovered that when they had the good fortune to meet some of their strategic goals, they had neither the experienced staffing or systems maturity to satisfy the increasing customer demands.
Skippy: So is this how the consultants became involved?
Buzz: Well, I'll just say that thirty five years later, there are a lot of manufacturing professionals who have either sustained the environments of job changes, corporate downsizing's or the expected attrition due to retirements that have an abundant amount of knowledge and experience to offer in their fields of expertise.
Skippy: Any way to know how and when to select the right ones?
Buzz: Absolutely, but let's save that for another chat . . .
Saturday, September 1, 2007
Product Contamination
Skippy – ran into someone who was asking about how to deal with Product Contamination:
“I have just been given a project to resolve the problem of separation of Ammonium Nitrate from Polystyrene Beads, this contamination takes place a service truck so my project consist of vacuuming the product out of these trucks , then separating the AN from the Poly , and then lean phase conveying the products to their different silo’s. If anyone out there has had to solve this problem please email any ideas.”
Buzz – the problem sounds like a simple one we in the plastic business deal with frequently; one of using a magnetic flux field to disrupt the electrostatic charge between contaminants and pellets, and a air wash deck to separate and remove the contaminants.
There are several products that can do this, and I would search on the phrase above to find companies that have them on the shelf who would provide a sampling to prove that their product will do the job for you.
Specifically, you could find more info on a product that could do that job at sites similar to http://www.pelletroncorp.com/
------------------------
Buzz – Here was an interesting question - "Why does PVC react with polystyrene? It also reacts with several other plastics. The result can be dangerous. Or just messy. Any one know about this"? We had a subsequent discussion where a buddies son had a small plastic toy firetruck with a flexible ‘hose’ that was shot. They had found some similar looking PVC material at the hardware store to replace it with. A couple weeks later, the new hose basically ‘melted off’ the rigid protrusion it had been pushed on to – What’s Up?
Skippy - it is likely that some residual 'aromatic' plasticizer is leaching out of the FPVC and is reacting with the Polystyrene. If you are trying to construct items where it is important to have these two products in contact with each other, you need to work with material vendors who are familiar with using 'non-migrating' PVC compounds - these are special formulations designed to overcome the difficulties you are experiencing. While being extremely compatible with PVC these special plasticizers have very low affinity for ABS and Polystyrene resins and therefore can be used in applications where plasticized PVC comes in contact with these other resins.
Oh, and by the way – watch out what you ‘clean’ PVC with as well - MEK will attack PVC and ABS - if you don't believe it, take a scrap piece of material you don't care about and observe the gloss level (the glossier at the start the better). Apply a little MEK to it with a rag using the appropriate personal protective equipment and watch the material surface move towards 'dull' - you are attacking the material. Acetone is even more aggressive.
In the surface repair process of ABS and PVC fabrications, it is a common practice to take shavings and slowly disolve them in MEK building up an adhesive paste that can can be spread on and into to repair a surface crack. Once the MEK vapor dissipates, the repair area can be machined.
“I have just been given a project to resolve the problem of separation of Ammonium Nitrate from Polystyrene Beads, this contamination takes place a service truck so my project consist of vacuuming the product out of these trucks , then separating the AN from the Poly , and then lean phase conveying the products to their different silo’s. If anyone out there has had to solve this problem please email any ideas.”
Buzz – the problem sounds like a simple one we in the plastic business deal with frequently; one of using a magnetic flux field to disrupt the electrostatic charge between contaminants and pellets, and a air wash deck to separate and remove the contaminants.
There are several products that can do this, and I would search on the phrase above to find companies that have them on the shelf who would provide a sampling to prove that their product will do the job for you.
Specifically, you could find more info on a product that could do that job at sites similar to http://www.pelletroncorp.com/
------------------------
Buzz – Here was an interesting question - "Why does PVC react with polystyrene? It also reacts with several other plastics. The result can be dangerous. Or just messy. Any one know about this"? We had a subsequent discussion where a buddies son had a small plastic toy firetruck with a flexible ‘hose’ that was shot. They had found some similar looking PVC material at the hardware store to replace it with. A couple weeks later, the new hose basically ‘melted off’ the rigid protrusion it had been pushed on to – What’s Up?
Skippy - it is likely that some residual 'aromatic' plasticizer is leaching out of the FPVC and is reacting with the Polystyrene. If you are trying to construct items where it is important to have these two products in contact with each other, you need to work with material vendors who are familiar with using 'non-migrating' PVC compounds - these are special formulations designed to overcome the difficulties you are experiencing. While being extremely compatible with PVC these special plasticizers have very low affinity for ABS and Polystyrene resins and therefore can be used in applications where plasticized PVC comes in contact with these other resins.
Oh, and by the way – watch out what you ‘clean’ PVC with as well - MEK will attack PVC and ABS - if you don't believe it, take a scrap piece of material you don't care about and observe the gloss level (the glossier at the start the better). Apply a little MEK to it with a rag using the appropriate personal protective equipment and watch the material surface move towards 'dull' - you are attacking the material. Acetone is even more aggressive.
In the surface repair process of ABS and PVC fabrications, it is a common practice to take shavings and slowly disolve them in MEK building up an adhesive paste that can can be spread on and into to repair a surface crack. Once the MEK vapor dissipates, the repair area can be machined.
Friday, August 24, 2007
Prologue
Skippy and Buzz and their ' traveling road show ' always start out by acknowledging that the dinosaurs walked our planet for better than 400 million years and were the ' masters of all they surveyed ' for better than 130 million. Interestingly, when they dig up mass grave sites, they often find most of the ' bigger bones ' in a large circle around the ' smaller bones ' -
Skippy: Why do you suppose this is?
Buzz: My guess is that the dinosaurs would ' circle the wagons ' upon discovery of impending danger or while preparing to move into an unknown territory - with the larger, more experienced adult animals at the perimeter and the less prepared in the center of the circle. Perhaps in this way the more experienced members of the tribe would be able to face adversity coming from any direction with the less experienced members able to observe and be at the same time protected -
Skippy: - hmmm
Welcome to our musings -
Skippy: Why do you suppose this is?
Buzz: My guess is that the dinosaurs would ' circle the wagons ' upon discovery of impending danger or while preparing to move into an unknown territory - with the larger, more experienced adult animals at the perimeter and the less prepared in the center of the circle. Perhaps in this way the more experienced members of the tribe would be able to face adversity coming from any direction with the less experienced members able to observe and be at the same time protected -
Skippy: - hmmm
Welcome to our musings -
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