Mechanical fasteners provide a clamping force between two pieces of material.There is a wide variety of types of fasteners and a variety of materials used to make them. There are threaded fasteners, non-threaded fasteners and special purpose fasteners. Steel fasteners are the most common material used, although aluminum alloys, brass and nickel are amongst other metals used. Aluminum alloy fasteners have the advantage over steel of being much lighter, non-magnetic and more corrosion resistant fasteners. Nickel has the particular advantage of strength at high temperatures.
The choice of fastener will depend on a number of factors:
-Environmental…For example: high, normal and low temperature; corrosive, abrasive and oxidising conditions.
-Nature of the external loading on the fastener…For example: tension, compression, shear, cyclic, impact.
-Life and service requirements…For example: the need for perhaps frequent assembly and disassembly.
-Design of the components being joined and types https://boltworld.co.uk/ of materials…For example: stress concentrations; the elastic, plastic and thermal properties of the materials.
Quantity of fasteners required and cost
With a threaded fastener, the clamping force holding the two pieces of material together is produced by a torque being applied to the fastener to stretch it and this is maintained during the service life of the fastener. The fastener is in tension and the two pieces of material in compression. Bolts mated with nuts and screws with threads in the material are examples of this type of fastener. Low- or medium-carbon steel bolts will typically have a minimum proof strength of about 225 to 400 Pa, the proof strength being the maximum stress the bolt can withstand without acquiring a permanent set. For quenched and tempered mediumcarbon bolts the minimum proof stress is 600 to 650 MPa and quenched and tempered alloy steel about 970 MPa. Threaded fasteners are particularly useful for joining components that are likely to need to be dismounted during the life of the product.