There are various fields of application in Abrasive Blasting Technology:

    - cleaning
    - roughening
    - hardening
    - surface finishing

- Cleaning
Cleaning generally means to blast oxidized, coated or otherwise contaminated surfaces. It aims at uncovering the base material.

- Roughening
Blasting for the purpose of roughening is applied in order to achieve an enlargement of the surface. An enlargement of the surface leads to better sticking of adhesive and coating materials on the base material. In addition, roughening of the surface results in a higher friction coefficient with other surfaces (the surfaces are becoming more slip-resistant).

- Hardening
Blasting to harden surfaces is applied at highly stressed components at which an induction of plastic surface deformation generates internal stress. This internal compression stress shall improve the fatigue limit properties of the component.

- Surface finishing
Here the workpiece is treated to reach a better visual feeling. Certain patterns are applied (glass areas, shower cabinets, etc.) and spurious reflecting spaces are tarnished. The used abrasive is decisive for reaching a respective result.

The oldest patent on surface treatment by using abrasives was developed by the chemist Chew Tilghmann from Philadelphia/USA in 1870.
It is possible to shade, tarnish, engrave, etc. iron, metal, glass, wood and many other materials with the help of a sandblaster.

At that time, the shot-blasting wheel was mentioned as well. In Germany, Hans Weber and Karl Grodol from Kronach in Bavaria applied for a patent on the shot-blasting wheel in 1930 which is still used nowadays.

The blasting technology has been used in industry for decades and we cannot image life today without it.

In principal, the blasting technologies differ from each other as regards type and acceleration of the blasting medium.

- Airless blast cleaning
During the process of airless blast cleaning the abrasive is accelerated by shot-blasting wheels which are equipped with rocker shovels or respective devices.

- Injection blasting
During the process of injection blasting the abrasive is conveyed or accelerated with the help of nozzles through fluid or gaseous carriers. The carrier medium can also lead to cleaning effects.

During the process of airless blast cleaning the abrasive is introduced through the hub of the shot-blasting wheel into a turning rocker shovel and it is expelled within a widely spread blast to the surface of the workpiece to be treated at a high speed and thus also at a high peripheral speed. The accelerating energy is obtained by:

- the speed of the wheel
- the diameter and the width of the wheel.

The highest inflow of abrasive into the wheel is reached when using a wheel with only two shovels. Ejection efficiency, however, is very bad because there is a high degree of spreading.

As regards smaller shot-blasting wheels only 2 shovels are taken due to cost reasons, 4 shovels are taken for medium-sized wheels; and 6 or 8 shovels are used for those units having a big diameter.

Centrifuges are mainly used in steel industry, in foundries and in the field of steel and apparatus construction as well as in ship building. Those are mainly machines which can be rarely designed in such a way that they can be used universally for the treatment of work pieces of different kinds.

It is their task to remove scale, rolling skin and rust from materials made of iron and steel. They run in such a way that profiles, plates, but also quite ordinary structural components as well as pipes are moved past the shot-blasting wheels on a roller table and then they are hit by the leaving abrasive flow.

By applying air blast cleaning in mobile plants it is also possible to perform surface cleaning of concrete and asphalt areas as well as steel floors. The complete machine is moved over the surface by an adjustable transport feeding device. The abrasive impinging on the surface is sucked back with a vacuum airstream via a channel to a storage device being installed above the shot-blasting wheel; then it will be dedusted and fed again back to circulation.

Shot-blasting wheel with indirect feeding and mechanical pre-acceleration

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Airless blast cleaning

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2.2 Injection blasting

The pressure blasting technology can just be divided into sub-classes:

In this regard, the sub-classes divide according to the type of the abrasive, the carrier medium and the kind of the admixing of the abrasive to the carrier medium.

2.2.1 Compressed air blasting (also air blast cleaning or sand blasting)

The abrasive is accelerated by an airstream discharging at a high speed.

During this process the abrasive is in a pressure pot. Compressed air is led to it via ducts or hoses; this air is introduced into the pot and it is pressed on the fed abrasive; then it is moved past the pot and connected with a mixing valve.

Model of compressed-air blasting

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The abrasive enters the mixing valve vertically via an intake port, or via a flowing angle of about 45°.

After the mixing valve, the actual process of admixing the abrasive and the compressed air starts. This is necessary in order to transport the abrasive from the pressure pot to the object to be blasted.

It is to take care that the speed of the mixture consisting of compressed air/abrasive is not too low so that the heavy parts of the abrasive cannot deposit.

The mixture of abrasive/compressed air leaves the nozzle by a manually led blasting jet at a high speed of up to a maximum of 240 m/s; and afterwards it impinges on the area to be cleaned at this high speed.

The operational pressure necessary to obtain acceleration to the mentioned speed within the nozzle should not be less than 5 b. Nowadays, 10 – 12 b have already been applied at the nozzle.

Compared to the method of airless blast cleaning it is of great advantage that the blasting jet is led and that the object to be blasted can be monitored during derusting.

As regards spaces, the performance is slightly lower. The blasting result is, however, often more favourable for the coating with the applied coating materials, i.e. the surface is getting larger to a greater extent than that one at airless blast cleaning; by this considerably higher sticking can be reached for the coating material. Considerably higher roughness heights can be achieved by high impact energy of each grain caused by the decisively higher discharge speed (240 m/s for pressure blasting, a max. of 80 m/s for airless blast cleaning).

This is even supported by the application of angular blasting grain. In order to obtain the desired levels of purity the nozzle is led faster or more slowly across the surface to be treated. Furthermore, the mixing valve can be changed from 0 to 100% within the inlet cross-section so that different loading factors of the compressed airstream can be obtained by this.

The blasting performance also depends clearly on the following components:

- pressure at the nozzle
- volumetric flow of the abrasive
- flowing out amount of compressed air
- nozzle diameter, nozzle shape.

In order to reach a respectively high volumetric flow of the abrasive a mixing valve is required with high cross-section as well as a respective mixing chamber. Of course, the volumetric flow of the abrasive also depends on the flowing quantity and the speed of the compressed air at the moment of the input of the abrasive into the air flow. The proportion of “quantity of abrasive to the quantity of compressed air” is called the loading factor.

The amount of compressed air depends again on the size of the nozzle inlet and the pressure of the nozzle. Even in recent years, considerable increases in the performance have been reached for the pressure blasting method, and in fact by the application of high-volume blasting pots and appropriate mixing valves as well as by the use of large nozzle diameters, i.e. large amounts of compressed air. The maximum nozzle diameter is 20 mm at present.