Shot blasting is one of the most sought after techniques as an alternative to surface preparation. It has emerged as the winner in creating the cheapest cleaning solution yet strong and invincible in performance that its existence cannot simply be ignored. From wood, aluminium, glass to iron, brass, steel and what not, shot blasting has taken everything in its stride and given good surface cleaning alternatives to every surface preparation pertinent to pre-treatment operations such as galvanising, electroplating, enamelling, glass coating and rubberising.
This method is safe and very viable because of handling different metals efficiently. We have two types of blasting methods known as grit blasting and abrasive blasting. In grit blasting, wherever we cannot apply steel shots, we can go for soft media types like alumina, silicon carbide and walnut shells for non-metal surfaces like walls, wooden threshold, etc.
In shot blasting, steel balls are best to clean up metal surface for cleaning, paint preparation and scraping away contaminants and rust. Because the impact of blasting relies on the size of media and compression for cleaning and profiling, the result must be calculated to assure its efficacy. Thus, it can be a big challenge to achieve the desired outcome if the impact energy of the abrasive from its size and velocity is not calculated before the operation. It can lead to product damage or inaccurate blasting performance.
Treatment on steel structure depends on the thickness and calibre of the metal. While small steel pellets and shots are used to blast the surface, other media type like child iron grit and steel grit do have their own performance values.
Steel Shots :Tiny steel balls that are made of hard steel as small as 1 – 6 mm in diameter are commonly used for blasting of different steel surfaces. Each size has its own degree of impact once it is fired at high speed against the surface being prepared. As the size increases, the impact becomes greater and the surface metal becomes coarse. Similarly small sizes are for a smooth polished surface.
Chilled Iron Grit : Sometimes harsh metal treatment is required for ferrous types and thick metal base which has smaller mill deposits or oxide formation on ferrous castings and carbon steel types. Using angular abrasive media in the blasting, excellent result is achieved. The technique is good to remove paints from such metal but the media may damage aluminium surface due to its highly intense compression on the surface layer as it is not meant for aluminium as Chilled iron grits have a high scraping power on softer metals.
Steel Grit : Unlike steel balls, steel grit is angular metal chips used in blasting and stripping steel and foundry metals. It is best to make the surface ready for painting by hard scraping or etching on hard metals because paints, enamels stick to somewhat rough surface more firmly and strongly. Other industries like railways, bridges, metal parts and forging industry need steel grit blasting more commonly when contaminants are removed from steel or any other metal.
Owing to the perfection and economy of shot blasting in various applications, it has become synonymous with quality and efficiency. With more of environment friendliness, shot blasting eliminates the usage of non-eco friendly and harsh chemicals and provides higher production rates, wider abrasive ranges and good blast pattern accuracy both for foundry metals and metal sheets.
These are some of the main reasons why industries in the manufacturing sector prefers shot blasting over any other methods of treating metal before preparation.
Shot blasting is being the most significant and important method used in cleaning of mill-scaled and rusted surfaces but the type of abrasives used is considered for its effect and impact. Also since wheel blasting method and air blasting both have different impactions; the former is used on larger machineries and equipments. A wheel blaster consists of radial bladed wheels onto which the abrasive is fed. The wheel revolves at high speed giving forceful ejection of the abrasive onto the steel surface, its force being determined by the size of the wheels and their velocity. But this cleaning mechanism is not meant for softer metals or metal sheets. Mill scale and dust is removed by separator screens to remove finer dust particles.
Shot blasting can also use water jet technique to contain dust formation in the environment. A strong force of water near to the media gives the surface a clean makeover. While surface cleaning must adhere to the blast size, velocity and media type, the condition of the steelwork must also be considered prior to performing any blasting.
In the case of high build paint coatings and thermally sprayed metal coatings, rough media like angular grit profiles can perfectly provide the best result. Shot abrasive cannot do justice here as they tend to give shinning rather than scraping but they are good for thin layered paints such as pre-fabrication primers. When we consider surface contaminants having significant impact on the surface present other than mill scale and rust and the most atypical like pitted surface conditions may not be removed by the dry blast cleaning process.
Overall, the type and size of the abrasive used in blast cleaning have a significant effect on the profile and amplitude produced. In addition to the degree of cleanliness the shot blasting machine will exhibit using particular media, surface readiness for steep preparation depends on its specifications that should also consider the degree of roughness or smoothness before the coating can be applied to the area.