Extrusion Surging - potential trouble areas

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