Pubdate：05-16-2022 Views：3311
Cover compounds come in many varieties, and are selected to be compatible with the service they are going to perform and the atmosphere in which they are going to be working. A list of common cover compounds is shown in the Cover Compound Properties list.
In addition to selecting the correct cover compound, we must determine proper thickness. Accordingly, a consideration of "frequency factor" is in order.
Belt cycle frequency increases with the increased belt speed and decreases as the conveyor length increases. The more often a given section of the belt carries a load, the faster the wear rate will be. The cover of a 50 ft. belt carries twice as much material at 400 ft. per minute as it does at 200 ft. per minute. By the same token, at the same speed, the 50 ft. belt carries a load twice as often as does a 100 ft. belt. "Frequency Factor" can be calculated as follows:
Frequency Factor = Belt length in feet, divided by the Belt speed in Ft/Minute The chart on the next page will help in selecting the amount of carry cover needed based on frequency factor, cover grade, lump size and product properties.
In the case of single-ply, straight-warp rubber belt constructions, it is wise to use balanced covers. Further, at no time should one cover be more than twice the thickness of the other. Belts where this ratio is exceeded are subject to cupping.
Textures applied to the belt surface can overcome natural limitations of the elastomers involved and provide for appropriate gripping action. Currently, there are many textures and cleat patterns available which do an exceptional job of handling freely flowing materials, such as wood chips, grain, sand, aggregate and fertilizer. They will enable you to handle inclines, limited only by the system and the surcharge angle of the material itself.
If a "freely flowing" material (think of crystals of salt) is dribbled onto a stationary, horizontal surface, the top of the surface of this freely formed pile forms a unique angle to the horizontal. This angle is called the angle of repose.
If we now jiggle or vibrate this pile, as on a conveyor belt, the pile tends to flatten out. Depending on the characteristics of the material and the type and amount of movement and vibration (that is, the individual conveyor system), this angle will decrease, anywhere from 5° to as much as 20°. The resultant angle is known as the angle of surcharge. (It is important to note that the angle of surcharge will vary from conveyor to conveyor).
The inclinability of a given material is obviously limited by the angle of surcharge of that material on that specific conveyor.
At conveyor angles that are less than the angle of surcharge, an appropriate textured surface will "lock" the material to the belt enabling the conveyor system to operate at that incline.SKE provides many such surfaces:
For angles of incline greater than the angle of surcharge, special means must be provided to handle the material such as:
Incline requirements may force you to select a belt elastomer with different release characteristics, depending upon the materials' surcharge angle. Rubber can handle "freely flowing materials" at inclines up to 18 degrees, under most weather conditions. PVC, on the other hand, would be limited to approximately 12 degrees.
Abuse resistance may be an important factor in selecting your belt. For instance, concern over excessive impact or rip-resistance could suggest an UsFlex straight warp construction might be preferable to the standard plied belt constructions. Cover stock concerns can be handled by cover elastomers that are specifically formulated for the materials being handled.
For instance if cutting and gouging of the carry cover is a concern, Matchless and Matchless Plus compounds will help alleviate the problem. Granite cover compounds are designed to handle the general run materials and are compounded to provide good cut and gouge resistance as well as good abrasion resistance. However, if the belt is seeing high abrasion cover loss, a Titanium cover stock would be recommended.
Slider belt conveyor systems generally require a bottom conveyor belt surface with a lower coefficient of friction than troughed conveyor systems. Normally a bare fabric or frictioned bottom surface would be used. Or if a rubber cover surface is desired, SKE offers the Duroslide low coefficient of friction slider bed compound.
Loading conditions – Favorable - Ideally, the materials should be moving in the direction of belt travel and approximate belt speed when it is deposited on the belt. - Unfavorable –Material being loaded at a ninety degree angle to the belt direction or in the opposite direction as belt travel, as well as skirtboards and trippers, should be considered in your conveyor belt selection decision.
Flame retardance* is a highly desirable property in conveyor belts which are going to be used in systems where combustion or explosions are a concern, such as grain, underground mining, etc. In certain applications, flame retardant belting is mandatory. Be aware of such standards and advise your belt supplier of your requirement.
It is important to note that: *AII fire retardant belting will burn under some set conditions. If the defenses built into the belt are overwhelmed, the belt will burn. You can help protect your installation by being aware of and practicing, those safety standards that are currently in your industry, whether mandated by law or not.
Zero slip controls, side motion sensors, fire detection, and fire suppression equipment, such as required by MSHA, should be included in any appropriate approach to fire hazard control in addition to the use of the fire retardant belting. The temperature range for the installation must be considered. Do consult your SKE Representative or refer to the Cover Compound printouts available from the web site.
Chemical reaction from oils, acids, bleaches, vegetable and animal fats, ozone, ultraviolet, etc. needs to be considered when selecting the elastomer for your conveyor belt. In wood products applications, elastomers with at least a moderately oil-resistant characteristic do well particularly on pine and similar products.
Static control is a consideration in some conveyor applications (usually, grain and mining) due to
the atmosphere in which the belt must operate. Rubber compounds are available which are static-conductive, and which will safely dissipate a static charge on a properly and contiguously grounded conveyor system.
It is the conveyor operator's responsibility to be aware of all safety standards and governmental regulations (example - Grain elevator standards) applicable to his or her specific system. Sources of such information include:
