|When shrinking FEP roll covers it is
important to insure that the roll cover will fit the roller.
Cover must slip easily over full roll lengths insuring that the
cover will shrink to the roller diameter. Also, a lint-free towel
will help you provide additional protection and you will need a
sharp knife for trimming.
Hot air guns, capable of delivering air
temperature from 500°F/260°C to 750°F/398°C
are recommended for shrinking the FEP roll cover. It
may be desirable to partially close the inlet air control on the
guns to reduce air flow.
To insure a smooth, uniform covering without
wrinkles, the use of two guns is recommended, particularly
for roll cover diameters above 3 1/2 inches. The two guns
are used on opposite sides of the roll horizontally opposing each
other with one slightly ahead of the other.
Small diameter roll covers can be applied
with one gun, but care may be needed to prevent wrinkles and to
heat the cover sufficiently to get the desired grip on the
roll. Experience has shown that oven or steam heating is
During shrinkage, heat must be applied
evenly around the circumference to insure a finished surface free
of wrinkles or blisters. To insure even heating when
localized heat sources are used (such as hot air guns), some
method is required for rotating the roller at a fairly uniform
speed. A speed ranging from 10 to 30 revolutions per minute
Experience in shrinking has shown that the
the roller should be rotated by its axle. Rotational forces
applied through the unshrunk cover to the roll may tend to cause
twists and wrinkles.
Hand rotation of a roller supported on
journals is often all that is necessary. However, a lathe or
similar device is ideal. A machine lathe has a further
advantage of providing a power driven carriage for supporting and
advancing the guns along the roller.
Never leave the shrinkage operation
unattended. An operator must be available to "work
out" wrinkles or other problems that may develop.
The shrinking operation can be stopped at
any time. Upon restarting, ample time should be allowed for
the roller temperature to come back up before the traverse motion
As your technique is developed, it may be
desirable to begin shrinkage in the center of the roller and work
to each end. This method has proven helpful for long
covers. However, be very careful during initial shrinkage to
avoid wrinkling, and to start with the cover projecting equally
over each end of the roller.
If a roll cover becomes damaged or for some
other reason must be removed, it may be cut at one end and peeled
off in a diagonal fashion.
Multiple coverings can be made (one on top
of another) so that new surfaces of material can be exposed
without removing the roller from the machine. By peeling off
one layer, a new surface is ready for use.
- Read all instructions first.
- First, insure that the roll cover will fit the
roller. Cover must slip easily over full roll lengths insuring that
the cover will shrink to the roller diameter. The roll cover should be
longer than the surface to be covered because it may change length slightly
during installation. Select a standard length that allows at least 3
inches of extra roll cover per 100 inches of roll face to allow for possible
shortening and an additional 2 or 3 inches for end
- Cover shaft ends, bearing, or other sharp projections
that may cause scratches or deposit dirt on the inside of the roll
cover. A lint-free towel placed over a the shaft provides good
protection. Slip the cover onto the roller carefully to avoid necks,
creases or scratches. (It may be easier to stand the roller on end
during the assembly)
- Position the roll cover so that it projects about one
inch past the roller shoulder at the starting end. Most of the excess
cover will therefore project beyond the opposite roll end.
- Inspect the assembly and remove all foreign
particles between the cover and the roller.
- Begin shrinkage by pointing the guns (or gun) at the
rotating roller about 2 inches from the starting end. The gun muzzles
should be held two or three inches away from the work and be pointed slight
towards the roller end
See Detail B -I llustration B) Heat
this area until the cover shrinks down smoothly onto the roller. As
the cover shrinks tightly, the guns should be brought closer to the work and
positioned about one inch away.
- Shrink the cover which extends beyond the roller
shoulder to its smallest diameter. This contraction may tend to pull
cover over the roll shoulder. therefore, be sure to maintain the
cover extension at the opposite end of the roller. The end
of the cover is now attached and the unshrunk portion should stand out at a
relatively uniform distance from the roller surface. (See Detail A)
- At this point, stop the rotation on the long rollers
and line up the roll cover along its length. It should be straight
with a minimum of twist.
- Resume rotation. Position gun muzzles about one
inch from the roll cover for a metal roller or about two inches for a
nonmetallic roller (example: rubber, wood, etc.) Move the heat
guns slowly and symmetrically along the roller toward the unshrunk
end. The guns should always point towards the starting end with the
angle between the roller axis and each gun muzzle from a 60 to 75 degree
angle. Never aim the guns at the unshrunk area ahead of where
you are working. The muzzle should point about 1/2 inch behind the
transition slope between the shrunk and unshrunk roll cover (see Detail B
- Illustration A)
- Advance the guns slowly to heat the roll cover and the
roller to insure a good shrink fit. The exact traversing speed is
difficult to predict as it is influenced by the heat capacity of the roller,
its diameter, and the amount of shrinkage required. As a starting
point, a traversing speed of about 1 inch per minute is suggested for metal
rollers and from 1 to 3 inches per minute for nonmetallic rollers. Let
the job dictate your speed. When you have found a speed which seems
to be acceptable, slow down a little more. Under no circumstances
should two areas of the roll cover be shrunk so that there is an unshrunk
portion between them. If the cover lengthens as it shrinks,
one end must be free or wrinkles and bubbles may appear.
- If a wrinkle or other surface distortion develops
during the shrinking process, stop forward movement of the guns and avoid
heating the problem area directly. Move back down the roll a little
and approach the problem area slowly. Watch out for overheating on
rubber rollers. It may also be helpful to stroke the distorted area
lightly with the lint-free towel. The strokes should be made from
the area being heated toward the unshrunk portion. After the cover
straightens out, the guns can be put back in normal shrinking position and
the traversing motion resumed. (On a nonmetallic roller small wrinkles can
be caused by overheating. They will usually disappear after cooling)
- Application is complete when the last end is shrunk
down over the roller shoulder.
- Roll covers should be trimmed at each end after
shrinkage is complete. A sharp knife will suffice. There are
advantages to leaving a cuff (a necked down portion) on the cover past each
roller shoulder. This excess helps anchor the roll cover and reduces
the possibility of liquids getting between the roller and the cover.
Tubing ends can be cut flush with roller shoulders if necessary. When
trimming, keep the cut edge of the cover smooth and free from nicks that may
develop into tears during roller use.