Modern machinery is a marvel of engineering. Internal combustion engines of generators, for example, have controlled explosions taking place in the engine cylinders with rates up to 3600 rpm. That translates to 60 explosions per second in a two-stroke engine or 30 explosions per second in a four-stroke engine. And diesel generators usually work 24×7. As such, the machine must be capable of handling extreme forces for long periods.
Another thing to keep in mind during the product design phase is the ease of maintenance. Any machinery requires certain maintenance routines after specified running hours. The design must be such that engineers and technicians can access and dismantle as many parts as necessary to service, repair, or replace them. As a result, it is necessary to secure machinery components using non-permanent means.
The sometimes extreme forces combined with the necessary flexibility means that a high degree of variability is required from the different types of fasteners. Their sole purpose is holding machine parts in place against excess vibration, force and pressures while maintaining the possibility of easy disassembly in case of non-permanent fasteners.
Bolts are the most common type of fasteners. These machine elements are usually used to hold two unthreaded components together. A bolt has external male threads on one end and a hexagonal head on the other.
The bolt is normally fastened with a nut on the other end. Sometimes, one of the parts has a threaded hole to replace the bolt and minimise the number of components.
There are many different types of bolts to choose from. Each type provides some trade-offs. Let`s take a look at some popular bolts types.
Hex head bolts have the bolt head in the shape of a hexagon and can be tightened easily using a wrench. The six sides offer a good granularity of angles to approach the bolt from. This is especially important for bolts fastened in difficult to reach spots.
Hex head bolts have machine threads extending halfway or all the way up to the bolt head. Partially threaded bolts deliver a higher shearing capacity. Hex head bolts are extensively used in machinery as they are easy to assemble and disassemble.
The tools needed are also quite commonly available. Regular spanners are affordable and easy to use. Socket set may be used to reach bolts in difficult to reach areas. A single adjustable wrench is all one needs to fasten or unfasten many different sizes of hex head bolts and nuts but this should not be made common practice.
This type of bolt resembles a simple Threaded Rod. The main difference between the two is that a double end bolt has a thread in both ends instead of having it for the whole length of the piece.
They can be used with a nut at one or both ends, with the other end mating with a hole that has a respective thread size.
Eye bolts have a thread at one end and a loop at the other end. The loop`s purpose depends on machine design and size.
For example, a few eye bolts can be used together to support the weight of the structure during lifting. Another possibility is using a series of eye bolts to direct wires or cables through them all.
Basically the same as a hex-head bolt with one distinctive difference – the head of the bolt has 5 sides. This means that the most common tools can not be used for fastening or unfastening these bolts.
That adds an extra layer of precautionary dimension, as anyone with a wrench cannot disassemble a structure.
Carriage (or coach) bolts have a convex metal head followed by a square neck and thread. This type is mostly used to fasten wood elements. It is designed to fit its square neck into a wood piece through pressure. This feature gives carriage bolts the self-locking element.
The bolt is hammered gradually while securing the other side with a nut. This creates a pocket for the square neck in the wood, holding the bolt firmly in place.
Also called Allen bolts, these types of fasteners typically have a cylindrical head with a hexagonal hole inside them. An Allen wrench or a hex socket tool can be used for tightening.
Other designs come with a domed button or a flat head countersunk head.
They require less space the method of tightening allows to have the head level with or below the surface of the material in case there are pre-drilled holes in the material.
These bolts come in the shape of a horseshoe. While there is no thread on the bent section, the straight ends are usually threaded all the way.
U-bolts are excellent for securing the position of tubes and pipes or the position of other parts relative to tubes without making any holes in the tube itself.
There are many other variations of bolts available in the market. Some of them are:
Screws have a structure similar to bolts. They have a male thread starting from the tip and the head can be of various shapes. However, there are some key differences between a bolt and a screw. While bolts can easily hold unthreaded objects together with a nut, a screw usually needs internal threads to maintain a grip.
Commonly, screws are self-threading (self-tapping), meaning that they create the thread into the material during installation. So no previous tapping is necessary.
Many different screw designs are in use. They all have specific pros and cons and the application will decide which one to select. Following is a list of the types of screws:
We shall discuss some important screws that we need to be aware of as it is important to choose the right kind depending on the use.
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