If a repair is preferable, what techniques should be used? In most cases belt repairs will be one of three types: vulcanized, metal fasteners or cold cure. Each of these are covered below with their application methods
TYPES OF BELT REPAIR
Vulcanized Repairs are the closest match to the original belt manufacturing procedures employed at the factory. Using the vulcanization process, damaged or missing sections of cover or carcass can be replaced with little sacrifice of belt strength. The key to vulcanized repairs is restoration of damaged cover or carcass areas in a carefully trimmed, cleaned, and rematched fashion. Figures 9-1 and 9-2 illustrate the removal of cover damage. After cleaning and cementing, new uncured cover rubber is inserted per Figure 9-3. The repair is then cured by means of heat and pressure producing a result (Figure 9-4) that is nearly imperceptible after the belt is returned to service.
Figures 9-5 through 9-10 show the essentials of carcass puncture or fracture repair. Figures 9-11 through 9-14 illustrate edge repairs. Figures 8-26 and 8-27 cover the repair of broken cables in a steel cord belt.
In all cases, the new uncured rubber, whether cover stock or inside gum, adheres to both the virgin belt and the repair elements with adhesion values nearly equal to the original factory specifications. Thus, the strength and durability of vulcanized repairs.
Where belt damage is extensive or occupies more than about 25% of the overall belt width, vulcanized splicing or insert of a repair section (saddle) by means of two vulcanized splices is often preferable. Figures 4-14, 4-15,4-20, 4-29, and 5-A highlight some of the fundamental steps in vulcanized splicing.
As is evident in the illustrations, vulcanized splices and repairs require special craftsmanship and equipment for best results. Vulcanized work is therefore done mostly by contractor specialists although a limited number of plants have equipped and trained their own personnel.
Metal Fastener Repairs represent a completely different principle in handling the problem of restoring damaged belting.
To begin with, metal fasteners are often the only splicing method used in a wide variety of belt applications.
Therefore, their suitability for repairs is well established. Metal fasteners used strictly for splicing can have many attachment formats including hooks, bolts, staples, and rivets. For most bulk materials handling belt repairs, however, the bolted plate type fastener is selected.
The advantages of the bolt type fasteners are that they’re fundamentally simple to apply, they have good gripping and durability, and they can be installed relatively quickly. (Metal fasteners are not applicable to cover-only repairs.)
To obtain best repair results with bolted plate fasteners, they must be selected in the appropriate size for the belt in question and must be seated so as to grip the remaining strength area of the belt carcass adequately.
Illustrations BFG and FSL show some of the possible applications of metal fastener repairs. The window repair would ordinarily be considered a temporary repair for use only until a vulcanized repair or full resplice can be made. As noted previously regarding steel cord belting, metal fasteners can only be used for longitudinal breaks or splits–they will not grip properly for transverse or diagonal repairs.
Cold Cure Repairs are similar to hot vulcanized repairs in that the damaged belt components, cover or carcass, or both, are restored by inserting new materials. Instead of heat and pressure to accomplish vulcanization, the cold cure material depends on a chemical cure to achieve adhesion to the virgin belt.
Cold cure (or self-cure or chemical-cure) materials can include cover repair patches and strips, fabric ply materials and cements, and various putties and urethane fillers.
Illustrations 1 through 9 show cover patch-type repairs. As with hot vulcanized work, successful cold cure repairs require good craftsmanship. Cleanliness and dryness of the belt work area, as well as ambient temperature control, will affect results.
After the actual making of cold cure repairs, a time element is necessary for the chemical action to reach minimum useful strength, often four hours or more.
From: Technical Notes from the Technical Committee, NIBA- The Belting Association