A bolt is a most commonly used mechanical component and is used with nut for joining two parts together.
A nut and bolt are used to connect the parts or plate and can undergo large amount of pressure without causing any damage to the parts being tightened.
The joint made by using nut and bolt is temporary joint as it can be unfastened by making use of a suitable tool.
Thread friction at the lower of the bolt is used to keep the parts together which includes a little stretch of bolt and compression of the part.
A washer is a disk shaped thin plate with a hole that is normally used to distribute the load of the threaded fastener.
They are highly used for instance a car has about 1000 bolts and nuts.
Now, let us discuss about the parts of the Bolt:
The various parts of the Bolt are:
- Head: The uppermost portion of the bolt is called head. The head size is used in determining proper selection of wrench or socket used to turn or hold the bolt or nut.
2. Shank: It is the second main part of the bolt. It is the cylindrical portion as you can see in the above pic. The tail portion of the shank is threaded to accommodate the bolt.
It can be further subdivided as:
- Grip Length: This part accommodates the parts to be assembled. Grip length should be equal to the combined thickness of parts to be joined.
- Thread Length: It is the part of the bolt that accommodates the nut.
- Nominal Length: It is the sum of the thread length and grip length.
Another important thing to consider in bolt and nut is the threading.
As already discussed the the external helical ribs on the lower portion of the shank is called as threading. Usually a bot mate with the internal threads of the nut.
- The top of the rib or the threaded portion is called the crest or thread tip
- The end portion of the groove is called the thread root.
Measurement of the Thread
- Threads are measured by threads per inch for Us fasteners commonly called as thread count.
For example 10 would represent 10 threads per inch.
- Metric fasteners specifies the distance between the thread in terms of thread pitch. For example: 1.1 pitch would have 1.1 mm between each thread.
- Thread Gauges are available that matches the thread against those on the gauge.
Application of threading
- The b type of thread used for most of the application are coarse with deep groove.
- Some threads are finer, with shallower groves.
- Bolts with fine thread are used only under special condition such as when the parts being fastened have thin walls.
- Right hand Thread: Bolts and screw normally have right hand threads i.e turned to right when tightened.
- Left Hand Threads: Occasionally bolt, screw and nuts with left handed threads are used i.e turned to left counterclockwise when tightened.Manufacturing of the bolts :Carbon and steel alloy are used for nut and bolt manufacturing.
Nut- manufactured by blanking and threading.
Bolt- Manufactured by forging and threading.
Type of bolt
The various type of bolts are:
- Rock bolt
- Anchor bolt
- Shoulder bolt or Stripper bolt
- T-head bolt
- Square head bolt
- Elevator bolt
- Sex bolt or Chicago Bolt
- Flange bolt
- Lag bolt
- Hex bolt
- Hanger bolt
- Carriage bolt
- Arbor bolt
- Machine bolt
- Plow bolt
- Stud bolt
- Timber bolt
- Toggle bolt
Advantages of Bolted connection:
The various advantages of bolted joints are:
- Less man power required compared to the rivet connection.
- Time taken for fastening is less
- It is a cold process so no risk of fire.
- Bolts can be easily be replaced or retightened easily in the case of faulty bolting or damaged bolts due to accidents/hazards.
- High strength bolts are much stronger than rivets. Hence number of fastener required for bolts are lesser when compared with rivet.
- Tightening of the bolt is a much silent process as compared with rivets where a lot of hammering has to be done.
Disadvantages of Bolting connection
- In axial tension bolted connection have lesser strength as the net area at the root of the thread is less.
- Increased vibration can reduce the strength of the bolts.
- Unfinished bolts have less strength due to non-uniform diameter.