đĩa phễu và các tấm bên, nên được san phẳng để ngăn chặn sự tắc nghẽn của vật liệu trong phễu ở các góc sắc nét. Đó là khuyến khích mạnh mẽ để xây dựng một mạng lưới mạnh mẽ trong đầu phễu đệm các cú sốc khi vật liệu bị rơi vào phễu bằng cách lấy. Nó cũng bắt cục u, gỗ, và tất cả các vật liệu khác lừa đảo và ngăn ngừa tắc nghẽn trong máng của hệ thống băng chuyền trong unloader . | Miscellaneous 295 plate of the hopper and the side plates should be flattened out in order to prevent the clogging of the material in the hopper in sharp corners. It is strongly advisable to build a sturdy grid in the top of the hopper as it cushions the shocks when the material is dropped into the hopper by the grab. It also catches lumps wood and all other rogue material and prevents clogging in the chutes of the conveyor-belt system in the unloader and behind the unloader. The walls of the hopper can wear out rather quickly through the abrasion particularly by wet material. Abrasion resistant plates can be built-in to prevent this wear as far as possible. If required a dust-suppression system can be built-in as well as vibrators to prevent clogging of the material. Apron feeders conveyors To unload the hopper a number of mechanisms can be used for example - apron feeders for ore and similar materials - heavy duty belt conveyors for coal - vibrating feeders. Each mechanism has its own advantages and disadvantages. Apron feeders and conveyors in an unloader can only offer a very limited distance for transportation. The heavy load from the material in the fully-loaded hopper resting on the feeder or belt and the extra force which is needed to draw the material out of the hopper require considerable power. Problems with hoppers and conveyors can be overcome as follows - A wide feeder with enough body to take up the impact of the material in the hopper should be used. - A grid in the top of the hopper should be fitted to cushion the shocks of the material dropping out of the grab opened above the hopper. - Construction of skirts between the hopper and the conveyor must be very carefully engineered in order to prevent damage to the conveyor or apron feeder. - Enough power must be available to drive the conveyor and apron feeder. The brake-out-force from the material out of the hopper can be considerable. 296 Cranes-Design Practice and Maintenance Fig. .
