Quality notions and care degrees

Definitions
(according to French and Swedish standards)
It is stated according to two criteria for the steel surfaces laminated under heat:

- a criterion of initial state in 4 degrees of contamination: (see states plates)
A steel surface entirely covered with stuck rolling calamine and practically without any rust.
B steel surface which has begun to rust with the beginning of the calamine unsticking.
C steel surface with an important presence of rust and whose calamine disappeared or can be removed through scraping but which presents only little number of cavities visible to the naked eye.
D steel surface whose rolling calamine disappeared under the action of rust, and which presents numerous cavities visible to the naked eye.
- a criterion of final state in 4 care degrees after treatment:
Ds 1 light stripping.
Removing of the particles easily detachable, rolling calamine, rust and other foreign particles. About 50% of the surface has been reached by the shot (covering rate). The surface remains coloured if there was rust at the beginning (Ds 1 or Sa 1)
Ds 2 careful stripping.
The rolling calamine, the rust and other foreign particles are almost completely eliminated. About 80% of the surface has been reached by the shot (covering rate). The surface colouring marks are strongly softened at this stage. Greyish aspect (Ds or Sa 2).
Ds 2.5 very careful stripping.
The result is identical to the previous one except that the only marks of impurity remaining visually detectable are limited to an extremely thin veil under the form of shadows or bands. About 96% of the surface has been reached by the shot. Bright grey aspect (Ds or Sa 2.5).

Ds 3 stripping with blanks.
Complete removing of the rolling calamine, the rust and the foreign bodies whatever their nature is. 99% of the surface has been reached by the abrasive. The support colouring is uniformly in very bright grey and should have the metallic aspect (Ds or Sa 3).

Important
Both criteria above have always to be associated in order to define a treatment. Examples: A Sa 2.5 or B Sa 3 or C Sa 2 (see care plates).

Choise of the quality

Choice of the care degree
It will depend on the future conditions of use of the treated part as well as the nature and the life of the coating applied later.
- Ds 3 is the quality reserved for long lasting protections for coatings which do not support any stain.
- Ds 2.5 is the most common quality also called "Industrial" and reserved for medium lasting protection.
- Ds 2 is the quality realized for the preparations before a short lasting coating such as storage.

Cost of property
Property is directly linked to the number of useful impacts during the treatment called "cover" and to the passing number of the bombarding on the part which sum up in the formula:
Cn = 1 - (1 - C1)n
- C1 is the covering rate obtained after "1" passage for 1 unit of time.
- Cn is the covering rate obtained after "n" passages for n unit of time.
During the successive passages, the number of grains which reach some areas already clean increases and decreases thus the useful covering rate in relation to the impacts number.
The result is that, in practice:
- in order to obtain a Ds 2 property, the treatment has to last 2 minutes,
- in order to obtain a Ds 2.5 property, the treatment has to last 4 minutes,
- in order to obtain a Ds 3 property, the treatment has to last 6 minutes.
Or in the case of an authentic machine with a continuous scrolling:
- in order to obtain a Ds 2 property, the speed has to be 6 m/min,
- in order to obtain a Ds 2.5 property, the speed has to be 4 m/min,
- in order to obtain a Ds 3 property, the speed has to be 2 m/min.

Consequence
The cost price being partly proportional to the time used, the choice of the care degree will be determining in the final cost of the treatment (see some application examples).