Analyzing The Situation (As Time Allows)
The points below regarding a repair decision are interrelated in many situations. A general commentary follows:
How extensive is the damage?
Is replacement of the belt a better option?
How much time is available?
Is temporary repair feasible?
If a repair is preferable, what techniques should be used?
What supplies are available?
What personnel are available?
Are outside contractors available?
Are demurrage or other additional costs a consideration?
What insurance is applicable, if any?
Is there a materials handling bypass available?
How extensive is the damage? A small rip or tear along an edge or a small puncture, say up to 6″ longitudinally, may pose little risk of spillage or snagging or nlargement; such minor damage can usually be left for repair at a scheduled down time. Comparatively widespread injuries, like edge fraying or cover scoring, may occupy hundreds or thousands of feet of belt yet not pose an operations hazard; again this type of injury could be left for repair at a scheduled down time.
Transverse and diagonal rips represent loss of essential strength and the tension forces normally carried by the damaged area are transferred to the adjacent section of the belt. If the width of the injury is great enough, the overstressed balance of the belt will yield producing total failure at that point. A common rule of thumb is that if no more than 25% of the belt width is involved, a repair is practical; when more than 25% of the width is damaged, a full resplice or saddle section insertion is preferable.
In many cases, a rip or tear is ragged or partly hidden under the belt cover. Its extent must be carefully determined when making a repair decision. Relatively localized injuries can be drastically enlarged by snagging of a loose flap or dangling cable in a steel cord belt. Repairing or at least anchoring such damages are imperative before resuming belt operations.
Is replacement of the belt a better option? Belt size is often a determining factor in the repair or replace decision. Replacement obviously means the immediate or near term availability of a spare belt. Changeout time for a smaller (shorter) belt often can be less than needed for a major vulcanized repair. Therefore under such circumstances, the replacement choice is optimum. If a spare belt is not available, the time element in securing one versus the estimated repair time (assuming the present belt can be repaired) must be weighed.
Gross damages to a belt with major areas of ripping and tearing, or fire damage, for example, will obviously demand replacement of the belt or the affected sections.
Another factor when considering replacement of an injured belt is whether the belt is a good candidate for offthe-conveyor repairs. Will pushing the belt to provide a little more production right now reduce its potential repairability? The judgment in such a case is like deciding to drive another mile or two on a flat tire and thereby surely ruining it. Sometimes the age of the belt (or tire) makes the decision easier. If either is nearing the end of its normal useful life, trying to save it in the interest of further repairs just isn’t necessary.
How much time is available? As implied in the foregoing questions, the time factor frequently affects belt repair decisions. Only a few fortunate conveyor operators don’t have this as an acute decision–those with two conveyors. In the majority of cases, however, serious belt damage means taking corrective action as quickly as possible, not just diverting material flow to the adjacent conveyor.
Time constraints can take many forms, a few of which are: the need to fill a bunker, complete a production run or a work shift, or the loading/unloading of a train or a ship. In each instance, the interruption of operations will bring up the same questions: repair or replace the belt? Depending on specific circumstances, a major rescheduling of operations may become the only choice.
Is temporary repair feasible? One of the most unhappy things imaginable is to make a rushed repair in a broken belt, then restart the conveyor only to see the belt pull apart again. There certainly is a place for improvised or temporary belt repairs–many have proved successful in maintaining at least partial material flow until other arrangements can be made. On the other hand, an ill-conceived repair is just a waste of valuable time.
The most vital question in considering temporary belt repairs is usually whether or not the tensile strength of the belt carcass can be restored or bridged sufficiently at the point of injury to withstand the drive and take-up forces.
If the nature of the damage will not permit this with some assurance of success, the belt should be completely respliced or have a repair section (saddle) spliced in at the point of injury.
Temporary repairs of the type referred to above would include some form of mending with metal fasteners or a scab overlay held in place with fasteners or elevator bolts. Such temporary repairs are usually employed in conjunction with a reduction of the belt feed rate to lessen effective belt tension.
Gross carcass damages over extensive areas of the belt would obviously limit the feasibility of temporary repairs and make replacement of all or major sections of the belt a preferable remedy.
Although not an all-inclusive list, two other aspects of temporary belt repairs are commonly encountered:
Longitudinal Rips: Both the carcass and steel cord belt rips are often repaired with metal fasteners.
Set transverse to the belt width and placed on 6″, 12″ or greater spacings, the fasteners will reduce spillage and hold the belt together for days, weeks, or even months of additional service. (One absolute caution regarding metal fasteners is that they simply cannot be used to repair transverse breaks in steel cord belting.)
Cover Repairs: When a significant area of cover loss occurs and the underlying carcass is still intact, temporary coating or sealing of the exposed carcass fabric or cables is usually worthwhile. Even if no later vulcanized repairs are to be carried out, repeated coatings with various sealers will generally provide some additional useful belt life.
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
What supplies are available?
What personnel are available?
Are outside contractors available? These questions come under the general heading of maintenance planning.
Any operator of even the most elemental belt conveyor system should give some advance consideration to the possibility of belt damage occurring, and usually under the most disadvantageous circumstances. Some suggestions under each topic are as follows:
Supplies: The most common and often the most effective supplies for basic belt repairs are metal fasteners and their application tools. Even a single belt conveyor operation should maintain enough fastener inventory to do one or two resplices. This will also be suitable for basic rip or tear repairs. Larger operations with multiple conveyors can scale up quantities proportionately.
Less vital, but certainly worthwhile, is a supply of self-curing liquid sealer. These can provide a good temporary coating of exposed carcass fabric. Several easy to use one-part styles are available and they have good shelf life in unopened cans.
Personnel: The first line of defense for basic belt repairs is the conveyor operator or maintenance person.
He or she should be familiar with the use of metal fasteners and coatings as applicable to their particular types of belting. Only an hour or two training is required for fundamental know-how of the fasteners and coatings.
Contractors: In many areas, contractor specialists in belting repair are available on short notice. If not already established, some communication with such a firm is recommended. In addition to basic belt repair capability, the contractor specialist often can provide equipment for complete belt changeout operations, belt saddle sections, off-premises belt rebuilding facilities, and personnel experienced in coping with all types of belt conveyor breakdowns.
Are demurrage or other additional costs a consideration? This topic is related to the time availability discussed previously. Downtime devoted to belt repair or replacement will usually affect production rates, manpower deployment, and other internal matters. When demurrage or other overriding penalties enter the picture, the repair judgment may change.
One of the more likely changes may be the decision to use outside repair contractors who can reduce the net downtime. This might involve greater expense than doing the repair or replacement with in-house personnel only. There is no fixed formula for such matters and each situation must be evaluated on its particular circumstances.
What insurance is applicable, if any? Certain types of bulk materials handling projects or contracts may have specific insurance provisions that can influence repair or replace decisions. The most common of these incorporate protection for the conveyor operator against major tramp material damage to the belt.
In simplest terms, such a contract may specify size, density, heat level and other characteristics of the material to be delivered to the conveyor system. If an unintended destructive item such as a stump, rail, plate, crowbar,etc. comes through in a manner that damages the belt, the insurance policy may compensate for the belt repair or replacement.
If insurance coverage is a consideration, one of the principal functions during the repair operations is to record the nature and cause of the damage. This would include for example, photographs, witness accounts, tramp material samples, damaged belt section, etc.
Is there a materials handling bypass available? An additional factor in judging a repair or replace situation for a damaged belt concerns alternate means of delivering the materials. If material flow can be at least partially maintained, this will provide extra time for belt changeout if that is necessary, or more extensive belt repairs, as appropriate.
Alternate materials handling methods might consist of truck haulage, train or barge haulage, a portable conveyor set-up, or a combination of these. Alternate haulage methods can also be valuable in handling other non-belt related conveyor problems.
From: Technical Notes from the Technical Committee, NIBA- The Belting Association