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Surface evaluation
General technical evaluation of surface and its quality
Speaking of surface cleanness in the branch of blast cleaning, we mean a numerical value given by the parameter Sa – the degree of surface adjustment that is described in detail in the norm ČSN ISO 8501 This norm also specifies types of surface, or the grade of corrosion. The standard norm used for blasting is numerical value Sa = 2.5; for other values see Tab. 1.
| Table 1 Degrees of surface adjustment by blasting | |
|---|---|
| Sa | Characteristic |
| Sa 1 | Soft blasting |
| Sa 2 | Proper blasting |
| Sa 2 1 | Very good blasting |
| Sa 3 | Visually clean steel surface |
The second important parameter is numerical value Rz (middle value of highest highs).
Building on experience, value Rz = 40 (in μm), is the most used, which depends mainly on the choice of a suitable abrasive.
Note:
Some company websites show values (tables) of abrasive consumption in relation to the nozzle size, performance (blasted surface in m2 at a time unit) and so on. However, at first it is always necessary to evaluate surface parameters according to Sa and Rz and just then to derive other values. It is very difficult to count the abrasive consumption or blasting efficiency as there are too many operational and technical conditions which will have influence on the result.
We have tested the surface blasting speed with different kinds of pollution and adjustment.
