Plastics & Rubber World - September/October 2019 - 36

extrusion

➡ Continued from page 35

New equipment has helped to make
profile dimension validation less time
consuming

grinder, used to process waste PVC. "The
machine delivers material fragments into
oversized storage bags," says Coxill. "That
can be delivered to third party customers, or directed to our silos to support inhouse production."
In addition, there is an emergency
generator which can power the machines for 30 minutes if the plant loses
its electricity supply. This is important,
as it gives us time to shut the machines
down, purging material from the barrel.
As Coxill says: "You don't want PVC hardening in there."
At any one time, Epwin has over 100
tools for use across the extrusion lines.
Each machine will use four or five examples on rotation. A tool will be used for up
to six days, after which it is switched out.
The tools are then inspected for wear and
other damage, in a course of actual and
preventative maintenance.
"PVC degrades steel," says Steve Coxill, who works primarily in tooling maintenance and design. "It leaves waxy deposits on the metal. Anything over seven
days in the machine and that build up
can really have a negative effect on product quality."
Epwin has a fully-equipped toolroom
with laser welders and wire eroders to
help maintain and rebuild the tooling.
Each part has a lifetime of about two million metres of profile production, but with

expert care this can be further extended.
Continuous monitoring of dimensional accuracy is essential. "We use a series
of tools, including a shadowgraph," says
Coxill. "We put a template on the machine
and then compare that with the actual
product, based on a magnified view and
the X and Y axes measurements. There's a
minimum and maximum line, but as long
as it's within tolerance, that's OK."
The latest piece of kit in the metrology
room is an automated digital camera system. This is used to photograph a product
sample and that data is used to check variance from nominal dimensions. Precision
is the name of the game, with measurements made to four decimal places.
That data is entered into the QC-Calc
system, which delivers statistical process
control by analysing historical data. If a
dimension is getting larger or smaller, it
could highlight an issue with the tooling,
which is then checked for any issues. Before the addition of this new hardware,
dimensional tests on each sample could
take up to 25 minutes. With the automated system, that has been reduced to just
50 seconds.
In the end, maintaining consistency of
the finished products is essential. Variations in the profiles can have costly consequences, so investment in technology
helps to ensure customers get the highest
quality.

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Plastics & Rubber World - September/October 2019

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