"Key Plastic Extrusion Indicators"

Skippy – hey Buzz – the hot summer months are finally here. We were involved in a question having to do with “extrusion performance indicators”:

What are your Key Performance Indicators for your plastics production process?

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Buzz – well, here are a few thoughts from a profile extruder's point of view -

First, consider the intended outcome in an environment bounded by these four statements:

a) The extruder is responsible for continuously pumping plastic at a prescribed temperature and pressure
b) The cooling station (water, air, vacuum, etc) is responsible for continuously holding the plastic in the intended shape until cool
c) The take off unit is responsible for continuously pulling the extrudate down line through the "magic foot" represented by the interaction of the extruder and the cooling station
d) The cut off device is responsible for intermittently cutting good parts to length

Skippy – sounds like a pretty simple explanation of “extrusion” –

Buzz – well it is; and for a complex set of interactions, it is often best to “categorize” information in a way that reduces the over all complexity. When it comes time to troubleshoot a problem, for every production related symptom, ask yourself two questions and answer them;

1) which piece(s) of equipment is the one responsible for this condition?
2) What minimum change or correction must be made to achieve maximum desired improvement result?

Buzz - Here’s an example – based on one of our tenets – the greatest good an operator will ever do is to be a great OBSERVER -

The operator reports that he has been making boxes of product for some time now. In the last couple of boxes he has observed the following –

a) the part is still in spec, although he has made some “minor” adjustments to the take off speed
b) the boxes of product all contain the right amount of product and weigh the same as they have been for some time for full cartons – again because the parts are all in spec
c) a box normally takes about 55 minutes to run off –
d) the last box took 65 minutes to complete without a break or any casual loss

What is happening at the line?

Skippy – hmm – well you didn’t mention a cut off device, so we can eliminate that –

Buzz – right

Skippy – the parts are continually in spec, so the “magic foot relationship” is being maintained – it is therefore unlikely that the cooling station is the culprit -

Buzz – right

Skippy – once again, all we sell is time; and it took 10 minutes more to make a box of product

Buzz – yes . . .

Skippy – well the take off is responsible for that line speed and the direct measure of what gets done in a given amount of time in terms of product, so we must have been SLOWING the take off over time –

Buzz – yes right. So what ELSE is going on?

Skippy – well the parts are the right size, and a full box still weighs the same, as we drop the take off speed, therefore the extrusion output must have been dropping over time as well –

Buzz – bingo – and what could be causing that?

Skippy – well a couple of things, but upon a closer inspection at the extruder, it appeared that the pressure was up, the melt was hotter etc, so it was concluded that the screens might be being blocked over time by debris – which was verified during a screen change. After the screen change, the line was brought back up and the proper speed on the takeoff was yielding good boxes again at 55 minutes . . .

Buzz – perfect –

Skippy – but that was so EASY –

Buzz – yes you are correct. Once you categorize your information and step through it logically, things “fall into place pretty easily”. Good work.

This has been working for us for nearly 30 years - the measure of "how well" we are doing (since in the end, all we all sell is TIME) is the number of good units at the correct/reasonable cost produced in that time; insuring both we and our customer profit and continue to exist.

Just our two cents
Skippy and Buzz