The impact treatment

Evolution
The "impact treatment", modern substitute of traditional sandblasting and shot-blasting is undergoing massive changes and evolutions. Created first with the sole aim of "stripping", today, thanks to the technology of the equipments used and the diversity of the products projected, it became a full technique.

Définition
The impact treatment: this is a surface treatment process by small and numerous projectiles aimed to generate physical, chemical or mechanical modifications of the support.

Technique
The technique used consists in using either a gas vector (usually the compressed air), or a centrifugal force (wheel) to project at high speed grains (projectiles) which will strike on a repeated way the parts (supports). In this process, the results obtained depend on two criteria:
- kinetic energy: E = ½ mv2
At the time of the impact, each grain has an energy depending on its mass and its speed which is immediately converted to work in contact with the area to be treated (aggression, stress, strain).
- the cover: Cn = 1-(1-C1)n
It depends on the number of efficient impacts during the treatment, it means the number of grains projected and the passing number of the projections on the part.
The impact treatment makes use of extremely varied projectiles, different projection methods and various parameters which act upon the result.

Variables
The impact treatment variables are numerous and it is advisable to take it into account according to the application considered.
- projectiles: materials, granulometry, shape, density, projection speed, projection distance, angle of impingement, covering rate, time, etc.. (see details in heading parameters).
- the projection process: hydropneumatic, hydraulic, pneumatic, centrifugal, or gravity (see details in heading comparisons).
- treatment: manual, remote controlled, mechanized, automated, computerized, etc.

Parameters
The parameters which act upon the results and give very various aspects to the parts surfaces are particularly:
- the product: grain shape, granulometry, hardness, voluminal mass, etc.
- its outflow: in kg/ mn actuallly projected on the part.
- its speed: in revs/ min for the blastwheel, in compressed air pressure (bar) for the air blast.
- the action conditions: angle of fire, distance of fire, jet scanning (speed, number of passing), movements of parts and movements of the jet.

The impact treatment became a very advanced process and a tool associated with advanced techniques. It is no more linked to the sole surfaces preparation, but to the cleaning, the finishing and the mechanical treatment of surfaces. The choice of the good parameters is the only guarantee of a good result (see details in heading parameters).