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:
- Too little
- Stop or Guide Rolls
- Excessive Compression
of the Rubber Belt
- Too much Heat
- Too much Tension
- 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
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
|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
Click Here for a full screen diagram
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
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,
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 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) SHIELDâ Belt - when
new, preferably stretch 1/8" (3.17mm) to a maximum of 1/4"
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) SHIELDâ 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.
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.
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