A machine or a structure is made of a large number of parts and they need to be joined suitably for the machine to operate satisfactorily. Parts are joined by fasteners and they are classified as permanent or detachable (temporary) fasteners. Welded and riveted joints are examples of permanent fasteners. Threaded fasteners like screws, nuts, bolts, studs, cotter, and knuckle are examples of detachable (temporary) fasteners.
A fastener can, thus, be said to be a device that mechanically joins or affixes two or more objects together.
Need for Fastening:Â
Metals need to be joined for various reasons, for example
- In certain mechanisms, components have to be joined to restrict their motion to some degree.
- Â It may be impossible or very costly to manufacture certain complex-shaped components. They are made in several parts and then joined together.
- It is better for some products to be made as assemblies so that it is easier to disassemble them for maintenance purposes.
- Transporting a disassembled product is sometimes easier as compared to transporting the entire product. A good example is a bridge. Individual sections are fabricated, taken to the correct position, and then joined by welding or riveting to construct the complete structure.
Mechanical Fastening:Â
Mechanical fastening refers to the use of a part or parts that physically limit some or all of the degrees of freedom of a part with respect to another.Â
Below is a list of common fastening methods, and some examples.
Screws:Â
Joining pieces of wood in furniture.
Nuts and bolts:Â
Machine components, almost all mechanical products.
Rivets:Â
structural beams in buildings, and airplane bodies. bridges;
Staples:Â
Holding together sheets of metal, or plastic.
Seams:Â
Sheet metal joints (e.g. trash cans).
Clips:Â
spring clips, o-clips (commonly used in electrical motors to hold shafts in place with respect to housing).
Snap-fasteners:Â
camera body, electronic toys, caps of containers, etc.