A unique, rotating axis grab solved a challenging problem faced by a manufacturer of special refractory products. The application required a device that could safely pick up and gently rotate 2,500 lb refractory blocks that are 6 – 20 inches thick and 40 – 72 inches long.
These refractory blocks are very brittle and slippery to hold, similar to chalk. The dilemma for Bushman engineers was to apply the right combination of gripping pad material and gripping force. If the block were to slip, the dust would fill in the pad crevices and the grab would lose its grip. If the block was gripped too tightly, it would crumble and fall to the floor. Additionally, the sides of the blocks were not parallel, and had low spots making the application even more complex.
Bushman’s solution was a group of five gripping pads, one center rectangular pad and four round “satellite” pads (lower picture at right). This combination applies the right amount of pressure. Each of the satellite pads is in a “ball and socket” pivot joint attached to a spring backed movable arm. The satellite pads compensate for the uneven surface of the blocks, and maintain enough gripping area to adequately distribute the required gripping force. The pad material was made from special conveyor belting and glued to the plate. The block is rotated about its horizontal axis by the grab rotation drive system. Bushman selected an AC variable frequency drive to achieve smooth starting and stopping, thus preventing the block from slipping out of the grab’s grip.
This design effectively provided a solution to handle heavy, yet delicate loads with uneven, slippery surfaces, and simplified a difficult and time-consuming material handling process for the customer.