The TexLoc Library
How To Shrink Guide-FEP Roll Covers
 
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 500F/260C to 750F/398C 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 not suitable.

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 is adequate. 

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 is resumed.  

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.

 
 

FEP ROLL COVERS (Fluorinated Ethylene Propylene) - 
Heat Gun Temperature:  500F/260C to 750F/398C

Installation
  1. Read all instructions first. 
  2. 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 "cuffs".  
  3. 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)
  4. 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.
  5. Inspect the assembly and remove all foreign particles between the cover and the roller. 
  6. 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.
  7. 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)
  8. 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. 
  9. 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)
  10. 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.  
  11. 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)
  12. Application is complete when the last end is shrunk down over the roller shoulder.
  13. 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.

Summary - Roll Cover Shrinkage

Installation 
Sequence
Gun Position
Along Roller
Gun Distance
From Work
Gun Slope To
Roller Axis
Remarks
1 2" from roller end 2" - 3" 60 to 75 Begin Shrinkage
2 2" from end 1" 60 to 75 Anchor end of cover
3 At roller end 1" 90 Shrink to smallest diameter
4 1"
min. traverse
1" 60 to 75 Metal roller
5 1"-3"
min. traverse
2" 60 to 75 Non metallic roller
6 At roller end 1" 90 Shrink to smallest diameter

**Note...shrink temperature listed above is ONLY for  FEP Roll Covers**

 
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