Shot Blasting – Working, Material Used as Shot Media, Advantages,and Applications

Shot blasting is one of the methods of surface treatment in which irregularities on the metal’s surface are removed by the use of particulate grains propelled at high velocity.
Shot blasting is different from sand blasting because shot blasting uses a centrifugal wheel, whereas in the sand blasting method, compressed air is used to deliver its media.

The shot blasting process is a highly effective solution for removing contamination on metal substrates or changing the coarseness or smoothness of a surface before coating.
The force with which the abrasive is propelled can be generated either centrifugally, using a wheel spinning at a high RPM or pneumatically through the medium of compressed fluid or air.

In the shot blasting process, spherical particles are used, unlike the grit blasting in which angular or sub-angular grains are used.

Debris and undesirable imperfections on the surface may cause problems further down the line in subsequent manufacturing processes. So, it is necessary to remove them beforehand through processes like shot basting.

If not performed correctly, shot blasting can cause some damage and losses. Some of them are:-
1) Damage to the equipment.
2) Damage to the workpiece and its surface.
3) Generates dust, which creates a mess.

Shot blasting is preferred over other abrasive surface penetration methods by some of the industries because this process produces high-quality results while being less expensive and safer.

The process of shot peening is similar to the process of shot blasting, but in the shot blasting process, the strength of the material increases through compressive force from the shot media.

Working of the Shot Blasting Process:-

• Shot blasting uses a centrifugal wheel inside a large machine to clean surfaces.
• In the shot blasting process, the surface of the workpiece is subjected to a barrage of shot media at high velocity.
• During this process, the centrifugal wheel propels the shotmedia in which individual shots act as an abrasive.
• This process is performed inside blast cabinets in which the equipment and workpiece are isolated from the environment.
• The method is efficient as the centrifugal wheel requires very little power to run and is easy to use.
• It’s an aggressive technique, so it thoroughly cleans every surface.
• During the shot blasting process, an eye should be kept on issues such as excessive shot blasting and dust collection.

Material that can be cleaned using shot blasting:-

Shot blasting method is mainly used to clean metalslike cast iron, mild steel, copper, titanium, engineering steel, and some other metals.
Shot blasting is also used on concrete and advanced technical ceramics like silicon carbide, alumina, and boron carbide.
Shot blasting normal ceramics like pottery and porcelain should definitely be avoided due to their lower strength and higher fragility.
Shot blasting should also not be used on some soft metals like aluminium and soft copper, as they can be damaged due to the high impact force of shot blasting.
Also, thin metal sheets should not be shot blasted as they will easily warp or distort.

Shot Media Recycling:-

In modern shot blasting equipment, the shot media is recycled through a vacuum, which collects the used particles.
Broken abrasive media are removed by separators, and feeders replace these shots for operations.

Materials that are used as Shot Media:-

Some of the most common shot media are:-
1) Aluminium Oxide:-
Aluminium oxide is an aggressive medium that is non-corrosive and versatile. It is mainly used for hard surfaces that require fine polishing.
Aluminium oxide shots are cheap and reusable. After usage, they break down into small particles and are hence categorised as angular shot media.
2) Steel shots:-
Small steel balls are also used as shot media. These balls are uniform in size, due to which there is equal impact distribution on the surface.
3) Cut WireShots:-
The shot media is made by cutting wire that is divided into equal lengths relative to its wire diameter. These are cheap, have high strength, and are highly abrasive.
4) Glass Beads:-
This shot media is suitable for soft metals as they are gently abrasive, and it also avoids contamination of the surface.
5) Ceramics:-
This shot media generates less dust than other media and applies a smaller amount of force.

Properties Of Shot Media:-

There are some properties of shot media that significantly influence the surface finish of the metal.
Here are four main properties of shot media:-
1) Shape: Most shot Blasting media comes in the form of a round shape, which is suitable for most of the applications.
Other than that, angular shot media are used for more aggressive cleaning applications. The surface of the workpiece becomes rough, which gives better adhesion to coatings, paint, epoxy, and rubber.

2) Size:-
Smaller media sizes are suitable for polishing and achieving clean surfaces.
A larger media size is suitable for aggressive applications such as profiling pr etching the workpiece or preparing it for coating or welding.

3) Hardness:-
The penetration of shot media depends upon the hardness of the shot media.
The harder the shot media, the better the material penetration will be.
Appropriately hard shot media should be selected for the workpiece to avoid damaging the material, and forthe proper shot blasting process to happen

4) Density:-
The shot media with higher density applies a higher force on the workpiece compared to lower density shot media.

Advantages Of Shot Blasting:-

1) No harsh chemicals.
2) Double surface coating.
3) Quick and easy cleanup.

Applications Of Shot Blasting:-

There are wide range of applications of shot blasting. Here are some applications for which the shot blasting is mainly used:-
1) Rust Removal:- The shot blasting process generates enough force to eliminate rust from the material’s surface.
2) Deburring:- Burrs and other imperfections are removed by concentrated media in shotblasting, which creates a more polished and smoother surface.
3) Scaling:- Shot blasting media can penetrate hard-to-reach areas and remove mill scale and oxidised flaky material on the surface, which improves the durability of the workpiece.
4) Ceramic shell removal:- In the investment casting process, shot blasting is utilised to remove the ceramic shell from the casted metal after its solidification. It creates a clean and accurate final product.

Above, we listed the processes for which shot blasting is used. Below are some industries in which shot blasting is used for some fheir processes:-

1) Automotive:-
Body parts or engine parts that are produced in automotive industries are cleaned, and the surfaces are smoothed using the process of shot blasting.

2) Aerospace:-

Shot Blasting for aerospace components that have strict surface requirements are done at pinpointed areas while working on tight tolerances.
Some applications of shot blasting on Aerospace components include deburring turbine blades and cleaning compressor blades.