The impacts treatment

Place of the process among the other
There are several processes to clean a part. Some like sanding down, brushing or degreasing have a very partial effect only; on the contrary, others allow reaching a high degree of cleanness such as the chemical sanding down and the cleaning by abrasive projection.
The choice of the process will be done according to the kind of parts to treat and the cleanness or aspect degree to be obtained, knowing if the structure surface must or not be attacked.
If the comparison between the different processes stops with the aggression, one can consider that the only abrasive projection makes it possible to obtain such a result. On the contrary, if one seeks a means of cleaning, other processes exist which do not have the use flexibility of the "impact treatment".

Its advantages
Flexibility
There is a large variety of equipments. They depend on the application, the output and the use required. There are heavy, mechanized or automated installations on site, as well as light and mobile equipments for the interventions on building sites.
Adaptability
Regarding the parts to be treated, there is no size limit either structure limit in so far as the substratum is harder than the surface. This process is suitable as well for new work as for maintenance or renovation. It makes it possible to treat partially some areas while sparing non concerned areas.
Safety
With the control of the operations linked to a good selection of the abrasives, one can obtain good conditions of reproducibility and achievement of the recommended results.
Efficiency
One uses the principle of the "intensive bombardment" of a part by abrasives grains which each works at the same time "like a tool". As a consequence, several grains act in little time on the surface to be treated. The output of such a process is exceptional.
Economy
The possibility to reprocess some abrasives which have been thrown to re-use them after generates a reduction in the operating cost and in the cost price. The recycled abrasive is then sorted, sifted and the dust is removed before it goes back in the blasting machine.
Cleanness
The projectiles, acting as cleaning agents, generate only inert pollutions. They are therefore easy to catch and evacuate. Contrary to the generally accepted ideas, the abrasives projection is considered as "cleaner" and "less polluting" than the chemical stripping.

Its limits
The technical limits
They are of two types:
1) Those due to the support.
- the support is too fragile and can be bent or deteriorated under the action of the impacts.
- the initial state of the surface is too degraded or irregular to obtain a good result.
- the shape of the support prevents the jet from reaching the areas to be treated with the conventional means.
2) Those due to the projectiles.
- the projectile can leave traces on the surface. These traces are harmful to the good durability of the future coating.
- the badly adapted projectile can become embedded and leave inclusions on a too soft support.
The economic limits
They are also of two kinds:
1) bad ratio results/ cost in comparison with the other competitive methods.
2) bad integration of the process in the production line (i.e.: in galvanoplasty).

The others cleaning processes

Manual cleaning
Grinding, sanding down, brushing, burning or spalling with a needles hammer are some processes which are dependent on man's hand and therefore its fluctuations. Regularity and repetitivity are impossible, as well as the control of work efficiency (removal or not of matter).
Lack of quality, precision, output (except in the case of automated machines).

Cleaning by friction or shock
The parts are loaded in bulk in a tumble barrel and rub the ones against the other. This method with barrel originated the "Tribofinition". This technique is almost used to treat small parts with some fragility, or a manufacture precision which have to be respected.
Used for the small parts polishing (generally on non ferrous materials).

Chemical cleaning
Special cases of stripping called "acid bath" where the parts are soaked in the acid and then rinsed. It is appropriated for small parts because of the bath volume and it is very restricting on the level of rejections.
Limited in sizes, without surface aggression (subjected to a rigorous legislation).

Hydraulic cleaning
Water projection
Use of a kind of fire hose which projects water at high pressure reaching several hundreds of bars. This process is used generally only on huge parts of several tons for which handling is difficult or even impossible (work on site)
Generally no surface aggression (except in the case of a very high pressure)
Water + sand projection
This is the same principle but with the projection of a mixture made of 80% water and 20% sand. The sand can be recovered by decantation in a hopper and be re-used after filtering.
This process is called "Hydro-blast".
The kind of parts is very varied and the treatment is soft, without any violent aggression or dusts.

Hydro-pneumatic cleaning
Abrasive + water + air projection
The principle is the same as Hydro-blast but the vector is not the high pressure water anymore but the compressed air which projects and pulverizes on the parts the water/ abrasive mixture, brought at the level of the nozzle by a low water pressure. The water plays a role of shocks absorber and then the surface undergoes little aggression. This process is called "Wet process" (see heading wet way). It is used in cabins with an external operator and adapts well to the automated machines for a continuous work. The applications are very varied for parts of quality and precision.
The treatment is very soft and without any dusts.

Conclusion
If the technical requirements do not impose a specific process, it will be always judicious to choose a process as various as possible. The investment is made for a long time and at the time of the decision, one is unaware of the manufacture evolution. It will be necessary to avoid the badly adapted installations or the ones which require a constant surveillance otherwise the operating and maintenance cost will increase consequently.