This guide has been compiled to assist you to identify ways to make your life as a Blaster easier and more efficient.
Some of the topics covered may seem common sense to you. In fact, you may have been practicing them for some years. In our country however, most Blasters have never had any specialist training. The following usually applies:.
This is sad but true. No new techniques or improved equipment were ever investigated.
Fortunately this is now changing. By just using a few of the ideas in this guide, you should be able to improve your production and efficiency.
The result of these improvements will flow directly into lower costs and higher profits for you the contractor. There a three major reasons for abrasive blasting. Essentially they all involve using compressed air to propel an abrasive towards a surface to achieve the desired effect.
Widely known as blast cleaning, its primary objective is to remove old coatings, rust and other contaminants from steel. In the case of new steel, its purpose is to remove mill scale which forms during the manufacturing process. Its second major function is to create a surface profile, which is the result of the abrasive particles impacting the blasted surface.
Coating manufacturers generally specify a specific profile to which their particular product would be applied to.
Surface finishing differs from surface preparation in that the desired result of abrasive blasting is to improve the appearance of and utilization of a product rather than condition it for coating. Examples of this application include removal of production contaminants, de-burring of moulds and formed parts, inspection blasting and blasting to enhance a products original features. Hardening or shot-peening of a surface by abrasive blasting is a specialized field that has become essential to the life of high stress components.
In effect, shot-peening stretches and compresses the surface. Increased fatigue strength of metal is achieved by bombarding the surface with a high-velocity stream of pre-selected round balls. Steel shot and glass beads are the most prominent abrasives used for this application. Dust, noise, high pressures and flying debris all contribute to a highly hazardous working environment.
Personal safety is critical and short cuts could prove fatal. In addition to the above, the following are to be worn by all blasters. These suits are rugged in design are reinforced with leather to protect the blaster from abrasive ricochet.
They also feature buckles on the sleeves and pants to keep dust out. An air-fed helmet is designed to protect your life. It prevents you breathing any dust, protects your face from flying particles and offers hard-hat protection. In addition to this, a light-weight helmet reduces fatigue which could lead to a lapse in concentration. An OBE is an air filtration system designed to purify the Blasters breathing air.
It is coupled to the air-fed helmet and removes oil mist, water vapour, odors and debris. It must be noted that it does not remove Carbon Monoxide.
Specialized monitoring equipment is available to detect toxic gasses. It is one thing to have high pressure, but another thing to maintain that pressure with an open end.
So when it comes to abrasive blasting, it is vital to understand that one can only have the correct amount of pressure if one has the volume of air to back it up with. An increase in pressure will increase the volume of air flowing through the nozzle. If the compressor does not produce the volume of air required by the nozzle, it will never achieve the required pressure and result in a lack of production.
What is AIR BLASTER? What does AIR BLASTER mean? AIR BLASTER meaning, definition & explanation
The energy and effective working power of an abrasive particle is proportional to its mass and velocity, i. From this equation, quite obviously, a small increase in particle velocity will have a greater effect than a small increase in particle mass.
Poor efficiency at low air pressure is directly related to operating costs of abrasive, compressor hire, diesel, labour and overheads.
The dramatic effect is shown as follows:. All compressors release moisture as a by-product of compressed air. Some compressors produce moisture and oil. All of the moisture produced in the air receivers, air hose and piping will be driven through the lines into your blast pot where it will saturate stored abrasives. Abrasive blasting equipments biggest enemy is water and oil. The reason is because the water and oil mix with your abrasives and create lumps effectively stopping your abrasives from flowing.
Another problem is if the moisture and oil reaches the surface being cleaned it will provide problems for and coatings that maybe applied later. Moisture could speed up corrosive activity, such as rust. Oil, if it reaches the surface, can cause problems for the future coating to correctly adhere to the surface, such as blistering.
After-Coolers are radiators placed between the compressor and blast pot. They cool the air in order to condense the moisture; they then trap the moisture before it can be carried to the blast machine.
A moisture separator or trap is installed as close to the blast pot as possible is also useful, it will remove water and oil that has already condensed in the airlines. Air flows best through straight, hard lines. All directional changes and protrusions will interfere with airflow. Properly sized metal piping or plastic tubing can convey air with minimal friction loss, which tends to be common to rubber airlines.
Try to keep your hoses or piping as short as possible, use only as much airline as needed, and avoid erratic bends.
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Even correctly sized hoses will lose pressure every 15 meters and just a degree bend will increase the friction slowing your air down causing it to drop pressure at the nozzle. When bends are unavoidable, make them as gradual as possible.
Using the correctly sized airline is critical in order to get the most from your compressor and blast pot. The inner diameter of the airline should be consistent with the inner diameter of all fittings to allow for smooth airflow.
Airline inner diameter should also be at least four times the nozzle orifice size. If choosing between long air hoses and long blast hoses — keep the blast hoses as short as possible. The blast pot is a coded pressure vessel that must have a stamp and a certificate that states on it its code and date of manufacture as well as the date of its last pressure test. The blast pot is designed to use pressure to deliver abrasives at a high-speed to a given surface creating as much of an impact as possible.
Air enters the blast pot instantly sealing the pot with a pop-up valve; at the same time as air is entering the blast pot air is also sent via a short bit of hose to the tee underneath the pot.
The air in the pot and the air in the hose should be equal, allowing the abrasive to flow with gravity into the stream of air travelling to the blast hose. The size of your blast pot has little to do with the volume of air required to blast; it is simply a grit vessel. For safety reasons inspection bodies approved by the Government should test PBP on a regular basis.
It provides a means to stop the blasting of abrasives from the nozzle when a safety hazard arises. The control valve must also have an override switch that allows a non-blaster to depressurize the pot at any time.
SUCTION-BLAST BASICS: OPTIMIZING MEDIA FLOW
This removes the need of a dedicated pot minder, instead the pot minder could be utilized elsewhere. This ensures a nozzle can continue to provide good service even after it is slightly worn. Remember, though, excessive wear should not be allowed or productivity decreases dramatically. Keep in mind, too, the nozzle entry throat must match the inside diameter of your air supply hose.
The wrong size combination can lead to wear points, pressure drop, and excessive internal turbulence. For maximum productivity, select the nozzle bore size based on the desired blast pressure and the available air pressure and flow.
In addition to the blast-cleaning nozzle, the compressor is supplying air to an air helmet and other components such as air motors and pneumatic controls, leaving cfm available for the nozzle.
This extra flow requirement will either overwork your compressor or decrease productivity. Abrasives are the materials in blasting that actually do the work. Abrasives can be grouped into three general categories:. Can be re-used many times before breaking down and are known as recyclable abrasives. It is necessary to recover and screen metallic abrasives for reuse.
Steel grit and steel shot are commonly used metallic abrasives. Steel grit particles have irregular shapes which make them effective for removing rust and mill scale and for roughening the steel. Steel shot particles are rounded, and are good for removing heavy brittle deposits. This abrasive produces a more rounded profile. Blasting with steel shot can cause elongation of light metals, and can drive mill scale and other impurities into the surface.
These abrasives are normally used once and discarded because they break down after blast cleaning. Other mineral abrasives used in industrial painting are staurolite and garnet. Some abrasives fulfill special blasting needs. Corncobs and walnut shells are soft abrasives used to remove light deposits or partially remove a paint layer.
Baking soda can also remove soft materials or grease.
Basic Principles of Abrasive Blasting
Other specialty abrasives are glass beads, silicon carbide, frozen carbon dioxide dry ice and aluminium oxide. Your coating supplier will always designate the degree of surface preparation required for his materials. Basically their definitions are:. SP 7 Brush-off Blast Cleaning Sa1 4 Blast cleaning of all except tightly adhered residues of mill scale, rust and coatings.
SP T Power Tool Cleaning to Bare Metal Removal of all visible rust, mill scale paint and foreign matter using power tools and producing a minimum profile of 1mm2. The distance from blast nozzle to work piece.