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United States Supply Company
International Suppliers to Printing and Textile Finishing

Crack prevention with SHIELD® Rubber Belts

Cracks can occur anywhere on a Rubber Belt, but typically develop on the face outside the cloth line, on an edge, or inside the Belt near an edge. Generally, these cracks are caused by the following conditions:

  1. Too little Water
  2. Stop or Guide Rolls
  3. Excessive Compression of the Rubber Belt
  4. Too much Heat
  5. Too much Tension or Stretch
  6. Improper Grinding

    Too little Water - insufficient water, either on the inside or the outside surfaces, will almost always result in the premature formation of cracks on the Rubber Belt. The purpose of the water is twofold: 1) to help keep the Belt temperature cooler and, 2) to lubricate the Belt.

    Without sufficient water cooling, the surface temperature of the Belt may exceed its generally accepted operating temperature. This means faster degradation of the natural rubber until, eventually, as the durometer drops, the Belt becomes exceedingly tacky. A Belt in this condition has a tendency to "chafe" and then stick to the steam cylinder, particularly on the edges outside the cloth line. Initially, the chafing occurs as the Belt actually "chatters" against the heated cylinder, now compounded by the lack of lubrication, a low durometer and most likely a "build-up" of residue on the steam cylinder in this area. As the Belt chafes and the durometer drops, it becomes increasingly susceptible to crack formation. In addition, as the durometer drops, the rubber becomes susceptible to actually "peeling off" or "picking away" from the Belt, adhering instead to the hot cylinder. At this point, it is imperative to grind immediately to eliminate irreparable damage.

    Without sufficient water to serve as a lubricant either inside or outside the Belt, "chafing" will occur. If left unattended, for even short time periods of 30 minutes, the chafing can develop into minute surface cracks. In time, these cracks will grow until controlled by grinding, patching, etc., or until they render the Belt useless.

    General Rule: WATER SHOULD ALWAYS BE THE FIRST THING TURNED ON AND THE LAST THING TURNED OFF.

    NOTE: The lack of water on a Belts interior and/or exterior surface, for as little as an hour, can permanently damage a Rubber Belt.

    Please check the following areas to make sure that water is being properly applied to the Rubber Belt:

  • Inside water spray pipe.
  • Outside water spray pipe. Also check the felt doctor blade or brush at this location to insure adequate "pooling" of water.
  • Water removal rolls. Generally 30 - 40 lbs. (2 - 3 bars) of Pressure is sufficient. Excessive amounts of pressure or squeeze on these rolls may leave the Rubber Belt too dry.

If possible, we recommend the addition of a third spray pipe as diagrammed below. This third spray adds water back to the inside surface of the Rubber Belt as it leaves the squeeze rolls and prior to its contacting the compression roll.

NOTE: United States Supply endorses the use of "Compressive Shrinkage Wax" (see Product Listing) on the Belt's exterior, outside the cloth-line, to help alleviate cracking. This specially formulated Wax helps diminish the chafing that naturally occurs due to the friction generated when the rubber runs against the steam cylinder. Water Pipe Placement Diagram

Click Here for a full screen diagram

Too little Water Stop or Guide Rolls Excessive Compression of the Rubber Belt
Too much Heat Too much Tension or Stretch Improper Grinding

Stop or Guide Rolls - Cracks may develop on the edge of a Rubber Belt if the Belt is allowed to run forcefully against either or both of these Guide Rolls.

  • Position the Guide Rolls 1" (25mm) from each side of the Rubber Belt to allow for normal tracking of the Belt.
  • Make sure the bearings in the Guide Rolls are working properly.
  • Check the Guide Rolls for nicks or burrs and remove if present.
  • Make sure the Guide Rolls are positioned perpendicular to the edge of the Belt (90 degrees).
  • General Rule: The Rubber Belt may run against one stop roll at a time, so long as the stop roll can be kept from turning when grabbed by hand.

If the force of the Rubber Belt against the stop roll prevents this, however, the Belt is then considered to be too hard against the stop roll and steps should be taken to alleviate this condition. (NOTE: As always, we recommend extreme caution when placing any body part or clothing near a Belt that is in operation).

    Excessive Compression of the Rubber Belt - the maximum recommended compression of a Rubber Belt is 25% of its current thickness. This is generally sufficient even for heavy weight fabrics like denim that require 14-16% shrinkage. Compression in excess of this recommended amount results in additional stress on the Rubber Belt and may result in premature failure, including cracking.

    Make sure that the compression plate (gauge) is set correctly. This is especially important when installing a new Belt and after each grinding operation. An incorrect and faulty setting can result in too much compression on the Rubber Belt. The Rubber Belt Grinding Instructions explain how to properly set this gauge.

Too little Water Stop or Guide Rolls Excessive Compression of the Rubber Belt
Too much Heat Too much Tension or Stretch Improper Grinding

    Too much Heat - The recommended temperature range for the Steam Cylinder is 270 - 290 F (132 - 143 C). Exceeding this temperature will result in faster degradation of the natural rubber. In general, the higher the temperature, the faster the rubber will degrade which necessitates more frequent grinding.

    Too much Tension or Stretch on the Rubber Belt - Please see our Tensioning Instructions for setting the proper tension.

General Rule: Operate the Rubber Belt with as little tension or stretch as possible. (Excessive tension requires an increase of compression on the Rubber Belt in order to achieve the same amount of shrinkage).

Follow these General Guidelines:

  • 2 5/8" (67mm) SHIELD Belt - when new, preferably stretch 1/8" (3.17mm) to a maximum of 1/4" (6.35mm).

Note: The 12" (305mm) mark located on the side of the Belt* should now preferably read 12 1/8" (308mm) to a maximum of 12 1/4" (311mm). If fabric corrugation exists at this point, increase this stretch very slightly until it disappears. Continual adjustments will be required as the Belt is ground and becomes thinner. See 2" (51mm) rule below.

  • 2" (51mm) SHIELD Belt - stretch preferably 1/4" (6.35mm) to a maximum of 1/2" (12.7mm).

    Note: The 12" (305mm) mark located on the side of the Belt* should now preferably read 12 1/4" (311mm) to 12 1/2" (318mm) maximum. If fabric corrugation exists at this point, increase this stretch very slightly until it disappears. Continual adjustments will be required as the Belt is ground and becomes thinner.

    *Note: United States Supply places these marks on all new Belts shipped. With age, however, these marks will fade and will need to be reapplied. Obviously, the marks should be placed as accurately as possible to help insure the proper tensioning of the Belt.

Too little Water Stop or Guide Rolls Excessive Compression of the Rubber Belt
Too much Heat Too much Tension or Stretch Improper Grinding

    Improper Grinding of the Rubber Belt - failure to properly restore the Rubber Belts surface commonly results in the premature formation of cracks.

Generally, cracks develop on the face of the Rubber Belt outside the cloth line. This area is directly exposed to the heated Steam Cylinder and, therefore, is more susceptible to the effects of abrasion, heat, and compression. It is critical to closely monitor this area of the Rubber Belt. Once cracks develop on the surface, it is imperative that they are ground away fully before they are allowed to worsen. Failure to due this may result in permanent damage to the Belt.

See Rubber Belt Grinding Instructions to re-examine how and when to grind a Rubber Belt.

Remember: PROPER AND FREQUENT GRINDING, WHEN NEEDED, ALWAYS RESULTS IN EXTENDED RUBBER BELT LIFE. Common Fallacy: The less one grinds, the longer the belt will last. This statement is a fallacy as a layer of "dead rubber" will only mean more compression is needed to achieve the desired shrinkage. More compression simply works both the Belt and the machine harder. Ultimately, this means more machine wear, as well as, shortened belt life.


Please direct sales questions to sales@ussupplyinc.com, support questions to support@ussupplyinc.com.