Investigating the impact properties of rubber as a material for shredder hammer tips

A preliminary study into the feasibility of using rubber-tipped shredder hammers has been conducted by testing the impact properties of rubber against cane and non-cane objects, which typically accompany cane billets into the shredder. Rubber layers were fixed to a projectile and fired at cane samples, 'tramp iron' objects and dirt particles. The damage to the cane was assessed using POC analysis. The rubber layers trialled were 6, 10 and 20 mm thick; two rubber compounds were trialled, one at 90 SDH which is the hardest commercial rubber available, and 70 SDH (slightly softer). The cane damage tests showed that the rubber-tipped projectiles could prepare the cane in a . similar manner to the standard projectile (no rubber attached). The thicker 70 SDH rubber layers were found to produce lower levels of damage than the rest of the rubbers and standard projectile. This decrease in damage was a result of the impact energy being absorbed by the viscoelastic rubber, which reduced the preparation efficiency of the impact event. The rubber compounds were found to withstand considerable impact against metallic materials as long as the impact load was widely distributed, but fractured or failed when the impact loading was concentrated due to sharp edges or comers on the metallic objects. Sand, soil and gravel caused no apparent damage to the rubber, except where the rubber had been previously fractured; the small 'dirt' particles embedded in the fractures and further reduced the serviceability of the rubber.