Dust Control Handbook for Industrial Minerals Mining and Processing

that the material falls before landing on the belt. Longer transfer distances permit fine particlesto separate from the material being transferred, while shorter transfer distances reduce the timeavailable for fine material to separate from the material being transferred, thus reducing dustemissions. Additionally, longer transfer distances also contribute to belt sagging. When beltssag, they allow material to become trapped between the idlers, which in turn allow the materialto release fugitive dust, as well as directly damaging the belt. To address this issue, someoperations use impact cradles (often called impact beds). An impact cradle system may include aslick top cover to allow smooth belt movement as well as underlying rubber layers to absorbimpact (Figure 5.8). In areas of low impact or no-impact, even lighter duty side-support cradlescan be used (Figure 5.9). For effective impact cradle design, refer to Conveyor EquipmentManufacturers Association (CEMA) Standard 575–2000 (Table 5.1 and Figure 5.7) [CEMAStandard 575–2000].Table 5.1. Impact cradle ratings to be used based on impact loading [CEMA Standard 575–2000]Code Rating Impact Force W x h (ref.)Lbflb-ftL Light duty