Joints are used to connect parts of a mechanism or machine. These mechanical joints can be temporary or permanent depending on whether the connection needs to be removed frequently or not removed at all. This determination is made by the designers and engineers of the machinery with the maintenance of the machinery taken into consideration.
A bolted joint is the most common temporary joint used in the design of a system or machine. Like the name of the joint states, the joint uses a bolt and screw to connect the two parts. The size of the bolt is determined by the load required to ensure the connection is not severed during operation of the system. A bolt is inserted through a non-threaded hole drilled to the desired or engineered design and then a nut with washer is screwed on the end of the bolt. This type of joint allows the maintenance department to easily disassemble the joint when necessary.
A screw joint is another temporary joint used to assemble two connections. This type of joint utilises a screw only and is inserted through a drilled hole of one arm of the connection. The other arm or connection point is drilled to the desired size and then tapped with a device that threads the hole to the same size as the screw. The screw is then inserted and tightened down through the drilled arm and into the tapped hole of the other arm of the connection. A screw joint is commonly used in soft metal connections so wear can easily be repaired, such as in aluminium joints.
A welded joint is a permanent joint that connects mechanical parts where disassembling is not necessary. The two arms of the connection are designed to insert into each other and then welded together. The type of weld is determined by the engineering department and is done by a certified welder. The welded joint is used on hard metal or steel joints where heavy loads are expected to put stress on the connection. Welding the connection or mechanical joint does not allow for easy disassembly.