Shot Blasting Advantages -Low Cost Surface Preparation Process
Mechanical shot blasting has many proved advantages over other contemporary process for the following reasons:
- The blast surface is ideally suited for subsequent
- The finished surface is completely free of scale,
dust content and chemical deposit.
- A uniform silver matt finish without blemish is
- Shot blasting although removing scale
completely, does not remove any virgin metal.
- Operation is simple, requiring the minimum of
labor and control is by push button.
- The machine is entirely suitable for installation
in continuous process lines.
- The floor area taken up by a shot blast
installation is mush less than that normally required
for acid pickling.
- There are no attendant problems, such as effluent disposal.
- he whole
cleaning costs are
very much less
approx Rs. 250 to
Rs. 300 per ton
Fig. A while pickling
which is costing Rs. 500 to Rs. 1100 pre ton for
stainless steel strips, wire etc. Fig. 5A
Office & Factory
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|| Shot Blasting is the Cheapest and most effective method for Surface Preparation Above image shows shot blasted steel sections like angles, channels, beams, tee, Pipes & Coils. Shot
Blasting provides a uniform and consistent fine matt or rough surface. The surface becomes perfectly suitable for painting, galvanizing and metal spraying.
|Shot blasting can form permanent bond between shot blasted surface and protective coating like paint, zinc and epoxy powder coating etc. It also reveals surface defects in the metal. It increases the life of protective coating adheres tenaciously to the scale-free, blast cleaned surface. Thus maintenance cost for repainting can be considerably reduced.
The relationship of abrasive size to both impact power and coverage is as under : Doubling the shot size increases the mass or impact power per grain eight times. Conversely, doubling the shot size reduces the number of shots per lbs to one-eighth.
Shot blasting is essential for longer paint life. Various experiments have proved that the length of paint life depends mainly on the strength of bond
between the paint and the basic surface. The quality of this bond depends on the complete and through
|Effect of Shot Size on impact & Coverage
||Approx. impact Value
||Approx. Nos. Shots/lb
||Equiv. Size of
l n Grit
|Shot Impact Value varies as the cube of the diameter (2:1 Size = 8:1 Impact Value and 1:8 number of shots / lb). Considering Impact value of 70 size shot as 1.
removal of mill scale, rust and other contaminants prior to painting and on obtaining an uniformly etched surface.
When paint is applied to sealing, rusty and contaminated surface life of paint is poor.
||There will be uneven expansion resulting in cracks in the scale and other contaminants. Those cracks extend to the paint film and to the base metal. Slowly patches of these scale loosen themselves from the base metal and fall off taking the paint film along with them.
While doing so, they expose the base metal, rust and the scale to the direct action of the atmosphere or the process conditions. Thus the damage is self multiplying, resulting in total plant failure and even reduction in size of the member. Therefore, it is evident that the member should be thoroughly clean of all foreign matters right to the virgin metal.
|oday shot blasting is the cheapest and most effective method of surface preparation. PF&FPL has supplied shot blasting machines for surface preparation of stainless steel plates, wire rods, angles, channels, flats, round bars, machines having 6 to 16 throwing wheels capable to shot blast both sides simultaneously.