What is shot blasting?
Shot blasting is a surface treatment process using high velocity abrasive.It is a method through which it is possible to obtain excellent cleaning and surface preparation for secondary finishing operations.
Shot blasting is common used for:
- The cleaning of iron, steel, non-cast parts, forging.
- Mechanical cleaning of sheets, rods, coils, wire.
- Shot peening to alter mechanical properties (incresing resistance to fatigue for springs, gears,…)
- Preapring surfaces to be painted, coated.
In general shot blasting concentrates abrasive particles at high speed (65-110 m/second) in a controlled manner at the material thereby removing surface contaminates due to the abrasive impact.
Types of shot blasting
There are two types of shot blasting: Shot blasting by centrifugal wheel and shot blasting by compressed air.
Shot blast production lines, both manual and automated systems, became possible with the introduction of centrifugal wheel blast machines. The system of shot blasting by centrifugal wheel is more productive than by compressed air and achieves a better more uniform surface finish. The criteria used for selecting the type of shot blasting system depends on the size and shape of the parts, the condition of the surface to be cleaned, final surface finish specification and overall process required.
By compressed air
This system is suitable for lower production applications where maximin flexibility is needed. These systems are very flexible in that the shot can be delivered horizontally through a rubber shose and nozzle assembly. This enables uses in finishing operations of steel frames and weldments thereby replacing hand tools. Because of this, an air blasting machine for a production line is expensive compared to the centrifugal wheel blasting machine. For example, to deliver shot at a rate of 1100 kg per minute a 1650 Hp comressor and 33 workers are needed using 10 mm diameter nozzles delivering 6.5 kg/cm2. On the other hand, between one or a multitude of turbines housed in the same machine. Only one or two operators are needed for such a shotblasting machine.
By centrifugal turbine
Centrifugal wheel blasting is the more common blast cleaning technique as well as the most economical and environmentally friendly method. The turbine delivers abrasive shot by centrifugal force in a specific and controlled direction, speed and quantity. Function of the turbine is similar to that of a fan or centrifugal pump. Shot blasting machines may use one or a multitude of turbines positioned in such a way that the abrasive blast pattern covers the entire surface of the material to be shot cleaned. The shape and size of the parts determine the number of turbines used in a machine. Power of the turbine motor is based on degree of cleaning needed and throughout speed of the material.
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