How long should a rubber belt last?
Most rubber belts are not taken out of service because they no
longer perform. Many rubber belts are removed from machines because they
have reached a certain thickness such as 50 mm or 45 mm, but are often
capable of continued performance if rubber belt tension is simply increased.
Most rubber belts are removed from service because of damage to
the rubber belt resulting from accidents, poor machine operator
practices, poor maintenance, etc.
Good quality rubber belts used to pre-shrink 14-3/4 oz. (500 gr/m2)
denim, if properly maintained by well trained shrinking machine
operators, should last between 11 and 14 million yards (10 and 13
million meters). Some users have even reported greater useful
life.
Rubber belts used for lightweight goods or cotton blends, as well
as belts used to improve cloth hand only, may last between 20 and 25
million yards (18.3 and 22.9 million meters).
Unfortunately, many users of good quality rubber belts who shrink
heavy weight denim fabric regularly obtain only 7 to 9 million yards
(6.4 to 8.2 million meters) of useful life. This may be due to poor
operator skills, poor preparation of cloth to be pre-shrunk, and
poor rubber belt and shrinking machine maintenance.
Why am I experiencing wavy selvages?
Wavy selvages normally appear only after the cloth has conditioned
for several hours or even days after having been pre-shrunk.
In most cases, the problem is caused by moisture differential
between the cloth edges and the body of the cloth. A typical reason
for this differential moisture is excessive moisture pick up by the
cloth edges due to over spray during dampening of the goods prior to
entry into the rubber belt. The cloth edges may pick up extra
moisture from skyer rolls if spray pattern is too wide for the
cloth.
Under spray can also cause this problem if cloth edges are dryer,
relative to the body of the cloth when it enters the rubber belt
unit.
Sometimes, when belt tension has not been increased during belt
grinding, excessive curl of the belt edges will result in the edges
being ground thinner than the body of the rubber belt. Thin belt
edges will carry more rubber belt cooling water, which will be
absorbed by the cloth edges.
Improperly adjusted, or poorly operating water removal rolls may
also allow more cooling water to remain on the belt edges and can
result in wavy selvages.
Rubber belts that are too narrow for the cloth being processed
may develop wavy selvages. The rubber belt ideally should be 8
inches (200 mm) wider than the widest cloth to be processed.
Using insufficient temperature of the steam heated rubber belt
cylinder can sometimes result in wavy selvages.
Insufficient palmer cylinder temperature can result in cloth
edges leaving the palmer with more moisture than the body of the
cloth. Occasionally a wavy selvage on only one side or on both sides
of the cloth can sometimes be traced to a worn, or improperly
operating pad used prior to dry cans in the process prior to
compressive pre-shrinking.
There is occasionally a tendency for liquid squeezed from the
cloth at the pad to follow a diagonal twill pattern to one side of
the goods resulting in that side of the goods retaining greater
moisture. Even after partial drying on heated cans, moisture on the
one side may be higher.
Rolls of heavyweight denim taken from the pad/dry can finishing
range with 7% or more residual moisture, if not passed through the
compressive shrinking machine within 4 hours or less may sometimes
have dryer edges at the time the goods is being pre-shrunk and this
can result in wavy selvages.
Standing rolls of pre-shrunk goods on end will often result in wavy selvages.
Why do I have roughness throughout the interior of my rubber belt?
Most rubber belt shrinking machines have the internal water spray installed in the wrong location. The internal water spray is used to lubricate the belt interior. Lubrication is important so that, as the rubber belt elongates and becomes wider as it is squeezed at the nip point, it
can slip easily against the surface of the pressure roll. Otherwise, elongation of the belt will be restrained and the capacity of the rubber belt to recoil,
elongate and compact the cloth will be reduced. Severe abrasion to the rubber belt interior may also occur.
Therefore, the internal water spray should be located just below the pressure roll and after the water removal roll. Water sprays located at the back side of the rubber belt are very much less effective, since most water applied to the belt inner surface at this location, will be removed by the wiping action of the belt idler roll and the water removal roll (s), by the time it arrives at the pressure roll.
When my rubber belts get reduced to 2 inches (50 mm) or less, why can I no longer obtain the required warp shrinkage and the cloth is corrugated?
When rubber belts reach a thickness of 2 inches (51 mm) or for rubber belts ordered at 2 inches (51 mm) thick, the amount of lengthwise tension required to insure best performance is ½ inch (13 mm) of stretch of the 12 inch (305 mm) marks placed on the belt edge. Failure to apply sufficient lengthwise tension to a rubber belt will often greatly reduce the capacity of the belt to shrink, cause generalized light corrugations in some shrunk fabrics and may result in the occurrence of cracks on the belt interior.
Why do I frequently get large deep cracks on the inside of rubber belts?
Large deep cracks on the belt interior with no signs of general surface roughness on the belt interior, are usually the result of insufficient belt tension. When adjusting belt tension, always start by relaxing all tension on the rubber belt. Always place new marks 12 inches (305 mm) apart on the edge of the relaxed belt. For belts thicker than 2 inches (51 mm) stretch the belt until the marks are 12-1/4 inches (311 mm) apart. For belts less than 2 inches (51 mm) thick, stretch the belt until the marks are 12-1/2 (318 mm) apart. After stretching the belt always rotate the belt several revolutions and again measure the distance between marks again. Re-adjust the tension to the correct amount and again rotate the belt several revolutions
followed by re-measuring the marks. Continue to repeat these operations until the marks remain
stable at the desired distance apart.
Why do I frequently get wrinkles on the cloth edges which look like crows feet?
To eliminate these edge pleats, which are the result of overfeed of the cloth edges into the rubber belt nip, increase tension on the cloth entering the rubber belt. Most machines are equipped with a variable speed control roll. Slowing down the speed of this roll will apply greater tension on the cloth. It is not recommended to increase compression of the rubber belt to eliminate selvage creases, although this will often serve to eliminate the selvage creases, it will also reduce rubber belt useful life.
When I process certain dark colored fabrics why do I get an annoying loud whistling sound from my rubber belt?
It is not always possible to eliminate this high pitched sound. In some cases increasing the temperature of the steam heated cylinder or pre-heating the cloth using the hated can located between the fabric skyer and the rubber belt unit will reduce or eliminate the noise. Increasing rubber belt heated cylinder temperature
may also reduce rubber belt useful life.
Some success has been reported in eliminating the noise by hanging a heavy cotton cloth over the emergency cooling water spray pipe and allowing the cloth to just drape onto the top of the steam heated cylinder. Water from the emergency cooling spray is allowed to lightly drip onto the cloth so that very light moisture wicks down the cloth and onto the heated cylinder. This reportedly sometimes solves the problem.
Cloth shrinkage coming off the shrinking machine appears to be perfect based on shrinkage measurement marks measured at the machine exit, but when the cloth is re-checked before shipment to the customer, warp shrinkage is as great as 4% or 5%.
This is usually a problem of cloth elongation after shrinking. The cause may be insufficient moisture in the cloth being pre-shrunk or too much or too little moisture in the cloth coming from the palmer. Cotton fabrics usually require about 1% of moisture for each one ounce per square yard of cloth weight
prior to entering the rubber belt. Too little moisture in the cloth being pre-shrunk does not permit the cloth to take on a stable new dimensional memory. Yarns may tend to push out or elongate and the cloth will again shrink when washed.
Too much or too little moisture in pre-shrunk cloth coming from the palmer will also result in elongation of the cloth during relaxation. Ideally cloth coming from the palmer should have 4% residual moisture content. Less than 4% moisture content will usually result in relax elongation of the cloth, while more than 4% residual moisture content will result in less stable cloth which can be stretched with slight tension such as is normal during inspection and rolling of the cloth.
Cloth between the rubber belt unit and the palmer is often slack on one side and causes wrinkles going into the palmer.
Parallel of the pressure roll and the steam heated rubber belt cylinder is extremely important. If this adjustment is not made precisely, fabric shrinkage will vary from side to side causing a slack selvage on one side of the cloth coming out of the rubber belt. This may also cause the rubber belt to track forcibly to one side, resulting in belt edge cracks.
Why do we frequently get cracks along the outer edge of our rubber belts?
Cracks forming on the side edge of a rubber belt may be the result of several conditions. Failure to grind a radius on the rubber belt outer edge, as the original radius disappears with repeated surface grinding of the rubber belt, is a common cause of cracks on the outer belt edge. A sharp angle on the belt outer edge causes a focus of mechanical stress which promotes the formation of cracks in this area.
Poor rubber belt tracking adjustment can result in belt edge cracks caused by the excessive force of the belt edge working against the limit roller.
Limit rollers set tight up against both belt edges or rollers set at an improper angle are a leading cause of belt edge cracks. Limit rollers which do not turn due to defective bearings or peeling chrome plating on roller surfaces can lead to belt edge cracking.
Rubber belt edge cracks often are the result of damage to the belt edge by lifting straps etc, during installation of the rubber belt on the shrinking machine.
