Depending on the type of overload, the appropriate protection systems are chosen and employed is design of machines. For instance, relays, overload release and circuit breakers are used to protect systems against mechanical overload (Bhalja & Maheshwari, 2011). The most common overload protection systems are mechanical and hydraulic overload protection systems. Mechanical overload protection systems are used in mechanical presses; the working principle is based on a delicate shear plate that requires approximately 130% capacity to be broken. When the shear plate is broken, a slide in position has some space of free distance that allows the press to go through a complete stroke. The shear plate is replaced after each case of overload. Hydraulic overload protection systems are more common because the force of the press can be restricted by controlling the hydraulic pressure, and the press can be restarted after an incidence of overload without having to change the plates. Overload protection systems (a) mechanical (b) hydraulic (Altan & Tekkaya, 2012). The system consists of an oil pad placed between the slide and the connecting rod to which pressure is applied when force is developing. The pressure from the oil is used to move another piston, which acts to intensify the pressurized air. In case the oil pressure (air pressure) exceeds a threshold value, the oil is sapped back into a tank. Therefore, the force applied is restricted and some space is created for free movement. (Altan & Tekkaya, 2012). a) Torque guard Torque guards are overload protection devices used in power transmission applications. A spring with a load cam follower placed in a core and detent causes the core and load to rotate jointly. Thus the load always resets in one position and stays in phase when tripped. The system automatically resets when it goes back into the set position after tripping, normally by moving the machine after the overload is cleared. Torque guards assist to protect mechanical systems from damage that may result from extreme torque produced by jamming and overloads. The automatic reset and instant reaction capacity offers consummate guard and reduces down-time. The system disengages at the stipulated torque limit (Grote & Antonsson, 2009). b) Torque limiter A Torque Limiter is a torque overload system consisting of a spring loaded friction style. The load connected to the friction pads is regulated in order to transmit the process torque is transmitted. An overload torque that exceeds the set torque makes the system to slip, preventing overloads from passing through the system. The torque limiter stops slipping when the load drops below the set level, transmitting the torque. In a torque limiter, the phase between input and output is not kept constant. This system can be used in a chain drive with a machined sprocket placed between the friction pads to act as the slip interface so that shutdown and restart is not necessary (Grote & Antonsson, 2009). Torque limiters are regularly used in applications such as conveyor systems, machine tools, and off-highway mobile equipment. c) Axial guard Axial guards are used in systems where the load acts in the linear rather than revolving direction. This overload protection device provides greatly accurate and repeatable trip point. The point of load set is simply adjusted by rotating a screw. The Axial Guard instantly trips when overload occurs and the tie between the load side and drive side is disengaged. The Axial Guard is reset by a slight push or pull in the reverse direction, allowing production to be revived swiftly and downtime to be reduced (Grote &
In industrial applications, overload occurs when machines are loaded beyond their capacity leading to breakdown of the machine. For this reasons, machines must be protected against mechanical overloading using overload protection systems…
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