Factors influencing belt durability

  • Number of belts in one set

Belt gearing is designed for optimal number of used belts. If the number of belts in one set decrease, lifetime of remain belts lowers disproportionately. If for example: according to calculations drive requires usage of 10 belts, and if one belt will be removed, lifetime of remain belts decreases not by 10% but by 30%.

  • Belts tension

Do doskonałego przenoszenia mocy i osiągFor excellent drive transferring and for reaching required belts durability a very important factor is to ensure correct belts tension. Belts should be tensioned as appearing slippage at the pulley not exceed 1%.  Too small tension causes excessive belts slippage at belt pulley; too big tension – decrease belt lifetime as well as quicker bearings wear in propulsion machinery and driven machinery.  During machines transportation and during storage is required to lower belts tension.  As the tension was correct it is recommended its calculation, performing and controlling according to methods described in Designer Handbook

  • Correct belt pulley selection

Important factor of reliability and equal operation of V-belts is exact fulfilling of conditions specified for belt pulleys:

 belts should work at grooved pulleys of dimensions fitted to belt section, as only side (working) walls of belt were in contact with walls of pulley grooves

  pulley grooves should be smooth, without deformations, snagging and contaminations, particularly grease and oils. Surface coincides of groove pulleys should not be painted

  all grooves edges of belt pulleys should be rounded of radius   r>1 mm

  minimal recommended diameter of pulley for given belt section should be observed unless compactness of gear is going to be reached at all costs, even at the expense of reduced efficiency and lowering of belt lifetime

  all wheel belts should be balanced statically (degree of quality Q in accordance to VDI 2060); additionally for wheel belts which peripheral speed exceed 30 m/s, or if a ratio of diameter to width of pulley rim dp/s<4 while v>20 m/s, should be balanced dynamically (degree of quality Q 6.3)

  with respect to belt lifetime is recommended to use pulleys of big diameters, for which belt speed should be between 25-30 m/s

  grooved pulleys should be made according to recommendations included in Designer Handbook, fifth edition – 2012, chapter 4


  • Belts coupling in belt units

W celu In order to transfer a power which increase a power transferred by one belt, special units are used which consist of a few single belts of the same section and the same length, completed in one unit or power bands belts are used. In determining number of belts in a gearing it is necessary to remember, that in most favorable conditions works single belt. In multibelt gearing all dimension differences particular belts and grooves at pulleys create parasitic circulating power and increase belts slippages what negatively affect gearing efficiency and belts lifetime. In comparison with belt units better conditions of power transferring possess power bands belt. In multibelt drives, to ensure comparable tension of each single belt is necessary to use selected belts with respect to length tolerance. Tolerance of length in belt unit is considerably lower in relation to tolerance of belts which do not work in the same set. “Stomil Sanok” SA produce also belts of small length tolerance (with marking L=L), which do not require complementing in belt units. I case of damage of one belt is necessary to exchange whole belt unit. Belts of different producers should not be joined in one belt unit. Power bands belts must not be used at pulleys of belt units.


  • Usage of tension rollers

In a gearing, where is not possible to strain a belt by changing a distance between driving machine and driven machine, a tension roller can be used for belt tension. Other phenomenon, which require usage of tension roller are vibration of long belt tie rod of small tension or short tie rod during rapid load changes. Each usage of rollers increase frequency of belt inflection and introduce additional bending stresses, what shorten its lifetime. Tension rollers can be placed outside and inside of belt. Tension rollers placed outside of a belt cause belt deflection in the opposite direction then during normal operation, what seriously shorten belt lifetime. So is decisively recommended to use tension rollers from inside of belt. Dimensions of grooves of internal rollers should be the same as dimensions of grooves for work pulleys. For power bands and normal profile belts is allowed to use flat internal rollers. Diameter of internal roller should be bigger or equal minimal diameter recommended for given belt section. Internal roller decrease angle of wrap, so is necessary to place it as close as possible to a big pulley. External rollers must be flat and must possess diameter bigger or equal 1,5 of minimal diameter, recommended for given belt section. External roller increases wrap angle, so it must be placed as close as possible to small pulley. External and internal tension rollers should be placed from the passive tie rod side (loose); this exclude change of gearing rotation.


  • Cleanliness

Belt gearing is sensitive for chemical influence of environment, its temperature and humidity, as well as lubricants and pollutions. In case a gearing operate in an environment of increased pollution, then it should be protected by special covers. Power bands belts require special protection from environmental pollution. Oils and lubricants cause decreasing of coupling between belt and pulley as well chemically affect at belt causing its quick destruction. Minor pollutions like dust and sand cause quicker grinding of side walls of belt and pulley. Big pollutions like stones can cause destruction (snagging) of belt pulley or belt rapture. Belt gearing should be screened and protected from direct influence of environmental conditions.


  • Storage of belts

Properly stored V-belts do not lose their properties rods for years. Rubber products stored in adverse conditions together with bad handling change physical properties. These changes are caused by influence of oxygen, ozone, extremely unfavorable temperatures, light, humidity or solvents. Storehouse should be dry and free of dust. Belts should not be stored together with such materials like: solvents, fuel, lubricants, acids and other chemicals. Low temperatures of storage are not usually harmful for V-belts, but because they are getting rigid in low temperatures, is necessary to heat them until +20oC. Belts should be protected from direct influence of heat sources. V-belts should be protected from light, mainly from direct solar radiation as well as strong artificial light with large share of ultraviolet as for example not covered fluorescent lamps (ozone is created). To protect from harmful ozone influence, storage compartments can’t possess appliances which create ozone, for example: fluorescent light sources, mercury lamps, electrical high voltage devices, etc. Compartments of big humidity are not good for storage of V-belts. Relative humidity of air is best for V-belts if is lower 65%. Pay attention to store belts in not-tensioned state as well as not distorted state. If there are stored in a hanging position, then the mandrel the belts are hanged should have diameter at least 10 times bigger than belt thickness.

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