It is common practice for roller builders across the Globe to use either Nylon or Polyester
film to wrap around the newly rubber covered roller prior to curing.
Some use a combination of both whilst others have a preference to use exclusively either
Nylon or Polyester film?
Why do we see variables, and what are the reasonings behind the choices we make?
How is the roller built?
1. Strip Extrusion or Crosshead extrusion?
2. Sheet built (calander) using traditional table or simple spin station.
3. Three roll-builder?
4. How is the roller cured, steam or electric?
5. If electric, what pressure is used within the autoclave?
Answers and further deliberations?
Strip Extrusion or Crosshead extrusion?
1. This method is a widely accepted by most of the larger roll producers, the rubber
is forced through a screw, normally screened through a die block to get rid of any
contaminations. The compound gets heated making it more elastic and workable.
The extruded ribbon is free from air entrapment. The only air entrapment
possible is between the layers when applying the compound to the roll, however
pressure is being applied whilst the compound is being extruded onto the roll
surface by applicator rollers, these rollers should displace any air entrapment.
This method is well proven; however, operator error can occur where applicator
pressures are not consistent, mostly this can be isolated to the ends of the rolls.
Skilled operators know this and soon learn why rolls get rejected. Overbuild is
normally high on extruded rolls and can be in the region of anywhere from 8mm
to 15mm overbuild dependent on final thickness of coating, shore hardness,
experience and wrapping techniques employed.
2. Sheet built (calander) using a traditional table or a simple spin station.
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These rolls are the most traditional way of covering rolls, we still see companies
today using this method with great success. They employ people who are skilled
and have a real feeling of how to do the job, they know how to eliminate air
whilst building by overlaying or but jointing the sheets and know how to wrap to
give them air free rolls. Predominantly they use Nylon wrap either wet or dry but
more and more use Polyester. Harder compounds ranging from 50 – 99 shore
tend to be wrapped in Nylon where the softer compounds tend to be wrapped in
polyester film, in either 23 or 36 microns of thickness. There is a significant
increase in air entrapment when applying compound by simply wrapping around
the steel core, there is usually many pieces of rubber applied increasing the
possibility of air entrapment. In these cases wrapping becomes a major and often
crucial part of the covering operation, much effort goes into getting rid of
supposed air entrapments or at least attempting to. We also see tissue papers
wrapped around rolls prior to wrapping with nylon, this allows the operators to
quickly take the nylon from the roll once cured, also extending the life cycle of
the nylon. It’s also common place for larger rolls that have been covered in this
way to be held from the autoclave for 24 hours then being re-wrapped prior to
3. Three roll building.
This method is widely accepted throughout the World.
Pressure is applied to the compound onto the roll surface thus eliminating air
entrapment. The rolls are built tight and therefore overbuild is significantly
reduced, allowing wrapping without significant pressure. Polyester film is the
preferred method for all rolls that have been built using this technique, we see
clients use both 23 and 36 microns.
4. Curing method steam or electric.
When curing in steam, Polyester films are more susceptible to breaking down,
especially when you have long cure cycles and higher temperatures, the thinner
23 microns film may break up. This has no detriment to the roll whilst curing, but
can create a build-up of small particles within the autoclave that needs clearing.
These particles, if not cleared, may cause water trap issues which will lead to
poor cure cycles i.e. cold spots etc.
Nylon maybe the preferred method for curing rolls in Steam autoclaves, however
the 36 microns polyester is also widely used.
5. Electric autoclave
When using electric autoclave, the roll coverer has another advantage, he can
load the autoclave with more pressure, providing the vessel has the appropriate
rating and certification. This extra pressure is additional to the already wrapped
roller. It squeezes the roll yet again and if any air entrapment is there it is
hopeful this could be released whilst in post-cure. Electric autoclaves are
becoming more popular, the industry recognised the beauty of increasing
pressure and not temperature. Ramping up slowly allowing the rubber to have a
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It is widely accepted to use either Nylon cloth or Polyester film. Nylon cloth can be used
either wet or dry, what the company uses is down to their experiences and almost
tradition, they are almost condemned to do it that way because it’s how they were
shown and what they have always used more or less successfully! The techniques and
materials used are generally either passed down or taken from a competitor’s methods,
once in place seldom get looked at again!
This is my mind is a failure, stop, look and assess.
When using Nylon some coverers like to apply Wet Nylon, this will shrink more than dry
nylon within the cure cycle, unfortunately, more compound is therefore required to
ensure final diameters can be met.
So, this begs the question did I really need to wet the bandage or not? Maybe he could
have used dry Nylon? Maybe we could have used Polyester film? 23 Microns? 36
So many variables, and unfortunately, normally not considered!
Imagine to really look deeper into the whole covering cycle?
“Example” We applied pressure to a thin extruded ribbon, the rubber was warmed and
was very elastic and masticated, it worked for the operator beautifully! Then imagine we
now wrap it merely to form a cylindrical shape whilst in the autoclave? Do we need to
see the operator swinging on the bandage, or take the nylon through a series of wheels
to increase pressures?
“I have asked many people why they apply so much pressure to a roll whilst wrapping
and always in advance I have their answer, “to get rid of any air that’s in the roll”. My
answer “why not build a roll with no air, or even believe you can build it with no air, its
Once we believe this we can address wrapping in an organised professional manner
rather than, old tradition handed down. If the wrap is merely for protection to the final
shape why not wrap without excessive pressure, reduce the required overbuild, reduce
the labour cost of taking the nylon off the roll after curing, recoiling it ready for the next
roll. Yes, the nylon will last a long time, dependent on length of cure cycle etc.
Polyester does give other advantages, it’s easy to apply, affordable, can be simply
ground or tuned off once the roll is vulcanized. The two types normally used for roll
coverings are 23 and 36 microns, again these gauges signify individual preference born
from tradition and experience. But seldom are they questioned, for instance 23 microns
will easily break whilst being applied to the roll when excessive pressure is applied, so
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I believe more focus could be placed into the building technique employed, research how
it`s built, how much overbuild is used, is there a better way? Do this for every hardness
of compound and grade. Make evaluations to wrapping in Nylon/ polyester. If built
correctly less focus COULD be placed on the wrapping, if you now use Nylon try 36
microns, if 36 microns works then evaluate 23 microns!
Don’t be afraid to use an alternative, pull away from what you’ve always done but make
sure it`s evaluated professionally.
You never know you may just save some money and have a greener credential for your
If you would like further information on the NYLON & POLYESTER films please send us an
enquiry we will be happy to assist.
Thank you for taking the time to read this article we hope it has created questions that
force deliberations within your business.