Page 31 - Plastics News June 2021

FeAtures

as it must be equal in both chains. If tension is too loose, side, and watch the clearance between the chain
there may be ripples and alignment issues; if it is too rail’s chain adjuster bolt head and the side of the
tight, there can be excess wear on sprockets and wear form tool. Some thicker materials are forgiving and
bars. Mechanical tensioners are inconsistent compared can tolerate wider tolerances, but especially with
to pneumatic ones, but even pneumatic tensioners can high shrink value material or a lot of cavities, the
result in uneven tension if not checked appropriately. narrow gap is imperative.
Chains should be replaced as needed when stretching ● Parallel Chain Rails: Be sure to start with the chain
or wear occurs, and if one chain needs replacement, rails parallel to the form tool. Each side should have
both should be replaced at the same time to maintain 3/8 in.-½ in. clearance on the outside of the form
consistent tension.
tool to the chain on the rail. Chain rails need to be
Common Issues to Troubleshoot set up parallel from the form station stabilizer to the
exit end of the machine. If a “V” formation is needed,
it should not exceed 2 in., and should be done from
the infeed of the machine to the infeed form station
stabilizer rod only. From the mold to the exit end of
the machine, parallel chain rails are imperative.
● Chain Stretch: Chains can stretch and wear over
time. To check this, first measure a certain number
of links (say, 60) at the same spot on each chain. If
there is a difference, even a slight one, it’s likely that
stretch has occurred. Next, remove both chains from
the rails, lay the chain on the floor, and place the
pins on the chain facing each other, making sure the
chains are pulled tight equally. Measure the chains,
and if one is longer than the other or the pins don’t
align, replace both.
Some shot-to-shot misalignment may occur even if the ● Stripper Plate Location: The stripper plate should
above adjustments to the rail are made. When issue arises not extend below the sheet line when stroked, and it
especially, now when experts from OEM’s can’t travel should stroke as the platen is retracting. The stripper
to service and maintain equipment in person, it can be plate should hold sheet in place and almost appear to
helpful to have a checklist for troubleshooting. stay still as the sheet evacuates the cavities. If the
sheet bows upwards, making it hard to strip parts out
Here are 10 of the most important steps for troubleshooting
misalignment and other common issues in thermoforming of the mold, the stripper plate may need adjustment.
applications. ● Exit Pan Location: The exit pan between the rails and
after the tool should be set at the sheet line. The
● Cooling Tubes: Make sure cooling tube heights are set
to twice material thickness, or, for thicker materials, pan should set so the sheet is not able to sag when
at a maximum of 0.020-0.030 in. above the material indexing out of the mold. Problems occur frequently,
height. This can be accomplished with a gauge especially with thinner materials, if the exit pan is
between the top of the chain and the cooling tube. lowered and the sheet doesn’t catch the pan and is
bound instead.
● Pierce Wheels: Set the pierce wheels at the infeed of
the chain rail so the sheet is being pushed all the way ● Sheet Orientation: Sheet orientation can cause
down onto the pin. This ensures that the sheet is set issues. To check it, submerge a 6-in. square piece of
in correctly, thus eliminating unnecessary stress to material into 400 F hot cooking oil or place in a 400
the chain, saddle, or guidebar and premature wear. F oven. Once heated, measure the difference from
the cold to the heated materials both in the index
● Clearances: Keep the distance from the edge of the and across index directions, A sheet orientation of
tool to the chain down to a maximum of ½-in. per greater than 10% may cause problems.

31 June 2021 Plastics News