Buffers / Bumpers

The hardness of a rubber buffer is measured in Shore A. The lower the hardness index number, e.g. 50 Shore A, the softer the buffer. Example reference values for shore hardness would be: 40 Shore A (soft – gummy bear), 60-70 Shore A (middle – car tire), 90 Shore A (hard – softwood). 

Simplified hardness classification of buffers: 

40-50 Shore A = medium soft buffer 
70 Shore A = normal hardness 
80-90 Shore A = hard rubber parts 

Shore hardness is specified with very high tolerances of at least +/-5 Shore A, corresponding to deviations occuring during production. Lower tolerances are only possible to a limited extent, making stricter specifications of buffers uneconomical.

Contrary to rubber buffers, cellular buffers do not receive a hardness grading. Due to their cell structure a measurement of hardness is not possible. To determine the characteristics, volume weight is used. High cell number/low density = low volume weight. Low cell number/high density = high volume weight.

The stated value for maximum energy absorption refers to a standardized room temperature of +20 °C. This value decreases with rising temperatures. For a single thrust, e.g. 1 x per hour, this only needs to be taken into account when higher temperatures ( > 50 °C ambient temperature) occur. However, if the buffer is impacted repeatedly in shorter intervals, this has to be taken into account, as well as the fact that the buffer might not have enough time to disperse the thermal energy. Also, the buffer will settle and will not take his original shape in time. This lowers the possible energy absorption value for the next thrust. If energy input and energy disposal are not balanced, the buffer will be destroyed. The resulting heat in conjunction with the pressure forces make the buffer lose its characteristics and it will eventually crystallize.

To ensure sufficient safety, buffers are often ordered larger than necessary. However, when compressed, a buffer will build up a counter-force directly proportional to the buffer size. The larger the buffer, the higher the reset force and the corresponding deceleration. Therefore, buffers should not be dimensioned too large, “just to be on the safe side”. Maximum permissible deceleration and end forces on the structure must be observed.

The minimum details required are: effective mass, velocity, maximum permissible deceleration, and information about framework conditions/particular application.

For this kind of arrangement, the distance between the outer planes of the buffers must be at least 40% of the buffers’ diameter (e.g. if the buffer diameter is 100 mm, the distance between buffers must be 40 mm). Furthermore, buffers arranged next to each other must be struck simultaneously.

During standard operational and environmental conditions, rubber and cellular buffers are maintenance-free, with a long lifespan. We recommend regular visual checks concerning cracks, embrittlement, or other damages. If such damages are detected, the buffers must be replaced. Buffers should be replaced at least every 5 years when used as a safety component. Buffers showing damage or traces of weathering must be replaced immediately, if necessary, measures to avert possible hazards must be taken – please consult maintenance instruction WV0180-0170-E (PDF on www.conductix.de/en).

No permanent loads must be applied to the buffers, and therefore they must not be used as bearing points (in compressed state) for repair or maintenance work. Only perpendicular (to the base plate) application of force is permissible. Furthermore, buffers must not be climbed on or be exposed to other extreme lateral forces.