User guide

D-2 l Appendix
Blade and Bushing Lubrication
Friction and heat during cutting
If the blade has a rough surface where the extrudate rubs against it, material will
accumulate on the blade in a cheese grater fashion. This scratched material will
also be passed from the blade to the next cut and be seen as hairs or flakes.
Some of the more flexible materials, such as silicones, soft urethanes and flexible
PVCs, also exhibit drag against the blade during the cutting cycle. The part will
actually stick to the side of the blade and drag down between the bushings.
Typically a small "C" shaped tail of the tube will accumulate in the bottom of the
cutting chamber. This tail actually tore off the tube rather than cut due to the exces-
sive drag against the blade
The generation of heat during cutting can also lead to parts that stick to each other.
They may appear to be welded together, and an extra operation may be required to
separate them. This can be a real problem in materials such as latex, silicone, PP,
and flexible PVC.
Benefits of using lubricants
The primary benefit of using a cutting lubricant is reducing friction. If the cutting
blade is coated with a film of lubricant, the coefficient of friction between the
blade and the plastic tube or profile is reduced, reducing the generation of friction-
al heat.
Lubricants also minimize the tendency for material to stick to the blade, thus mini-
mizing the potential for material to be wiped on the next cut part. The co-efficient
of friction is reduced with varying degrees, depending on the type of lubricant,
which in turn limits the increase in blade temperature. Over time this can lead to
an increase in blade life because the cutting edge will last longer at cooler operat-
ing temperatures.
While lubricants can also help minimize problems caused by rough or poorly
ground blades and cutter bushings, it is generally better to solve the problem than
mask it with lubricants.
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