You may have heard the term ‘shot blasting’ in relation to metal fabrication, but what exactly does it mean? The simplest way to explain shot blasting in layperson’s terms is as a deep clean for metal. Sometimes, simply wiping down a piece of metal might not be enough to make it sufficiently clean. Although brand new sheet metal might appear to be completely smooth and even shiny on its surface, debris can often be lurking on a microscopic level. Mill scale, rust and other impurities can all prevent metal from being as clean and clear as it might look. There may also be invisible nicks or burrs in the surface of newly-milled metal; these can be sharp and potentially cause injury to those handling it. Shot blasting is an abrasive process that removes impurities and leaves behind a clean and completely level surface.
What is shot blasting for?
If these impurities on the surface of a metal aren’t visible to the naked eye, why might they need to be removed? The answer is that when a metal (or in some cases, other material) needs to be painted or coated, it’s essential that it is completely flawless. A smooth, clean surface ensures complete adhesion of a coating or paint, and can help add many years of life to the metal. But shot blasting isn’t just used for freshly-manufactured sheet metal; it can also be used to revive components that need a really good cleanse. It’s often used, for example, to get rid of baked-on pollution on the surface of vehicles.
How does shot blasting work?
In principle, shot blasting is a bit like scrubbing or exfoliating skin. It offers cleansing on a deep level by blasting the area with abrasive particles. The shot blasting process uses a piece of machinery with a centrifugal ‘blast wheel’. This powerful wheel blasts ‘steel shot’, the abrasive medium, on to the surface at very high velocity, ridding the metal of debris and dirt and balancing out every element within. Steel shot (sometimes called steel beads or steel grit) can have round edges and look similar in appearance to ball bearings, or it can be more jagged and look a bit like gravel. Different sizes and shapes of steel shot are used, depending on the material being processed. In dedicated metalworking facilities and factories, large machines like the one in the image below are used for shot blasting. Smaller pieces of equipment called shot blasting cabinets tend to be used in workshops and for smaller scale projects. Once the steel shot has been fired at the metal, a vacuum mechanism known as the shot blast recovery system sucks the used medium back into the wheel, ready to be propelled out again. On a microscopic level, the surface of the shot blasted metal is left totally uniformly textured. This absolute smoothness is sometimes called ‘surface profile’. In industry, it is often known as ‘anchor pattern’ – because it enables paint and other coatings to stick firmly to the surface.
What is the difference between shot blasting and sandblasting?
You may have also heard of sandblasting, a technique that uses grains of sand or other media like nutshells, plastics or minerals as an abrasive to smooth the surface of metals. The sand used in sandblasting is usually fired at the metal using compressed air, as opposed to the centrifugal wheel used in shot blasting.
What metals are shot blasted?
Cast iron, stainless steel, carbon steel, copper and titanium are all commonly shot blasted materials. Shot blasting is also used to treat other materials, such as concrete and even some kinds of ceramics. The process is especially useful where a very deep clean is needed, or where the material being blasted is particularly dense. This is because it is more abrasive and effective than the more traditional method of sandblasting.
What is steel shot made of?
Despite its name, the ‘steel shot’ medium used to smooth metals in the shot blasting process isn’t always made of steel. Other metals such as zinc, aluminium and even copper are sometimes used. It all depends on the material being shot blasted. In the image below you can see images of shot blast and shot grit, as well as some of the other abrasive media used in sandblasting, such as garnet and ceramic.
Is shot blasting dangerous?
Generally speaking, shot blasting is considered to be less dangerous than sandblasting. This is because the amount of dust produced by sandblasting, and the fact it can be inhaled by those working close to the process. Shot blasting still comes with many risks, however, because it involves the fast propulsion of hard particles from specialist machinery. Shot blasting should therefore only be carried out in a safe, professional environment by knowledgeable experts who are using the correct safety equipment.
To summarise
Shot blasting is an abrasive process ideal for deep-cleaning or stripping sheet metal.