1.
Introduction
The purposes
of this specification are to remove impurities
on the
metal surface an well as to allow the rust preventive effects to be fully
displayed so that the quality
of products manufactured at industrial machinery plants is assured, and the
specification prescribes treatment in general when chemical cleaning is carried
out as a means to remove rust.
This
document gives precautions on general acid cleaning procedures and for the type
of solvents, concentration, rate of dilution, time, and other details, standard
specifications or each acid cleaning specialists shall be referred.
2. General Precautions
(1) Chemical
cleaning shall be carried out after all the work processes (including hydraulic
and air tight tests) are completed and after chemical cleaning, any
processing, in particular, accompanied by heating shall not be carried out.
If
hydraulic and air tight tests are needed to be carried out after chemical
cleaning for convenience of manufacturing, rust preventive means such as
application of rust
preventive additives shall be provided to prevent rust formation.
(2) Before
chemical cleaning, spatters by welding, slag, chips at the time of machining,
dust, and other impurities shall be thoroughly removed.
(3) Products
shall be handled carefully, and utmost care must be taken to prevent flaws and
damage to products.
(4) When
chemical cleaning is carried out, treatment liquids and immersion time shall
accurately be controlled and utmost care shall be taken to prevent accidents by
over pickling.
(5) If
immersion cleaning is carried out in the chemical cleaning process, air
bleeding inside products shall be taken into account and the immersion
direction and method shall be determined in such a manner so as to prevent
generation of air pots.
(6) The
metal surface after chemical cleaning shall be free from any residual acid
liquid and shall exhibit pH7.
(7) Products
finished with chemical cleaning shall not be stored near acid cleaning tanks or
in a dusty location, and shall undergo rust-preventive treatment promptly after
drying.
3.
Operation Procedure and precautions
The
acid liquid operation process slightly differs depending on materials but, in
principle, comprises the following procedures:
(1) Degreasing
(2) Water
rinsing
(3) Acid
cleaning
(4) Water
rinsing
(5) Neutralization
(6) Water
rinsing
(7) Drying
3-1 Degreasing
When grease, rust, preventive oil, cutting oil, machine oil,
or oily substance such as grease or oil degradation products are coated or
adheres to the metal surface, the oily substance shall completely be removed by
wiping or immersion
* Reference
Chemicals: sodium hydroxide, (caustic soda), sodium
hydrogen carbonate, sodium tripolyphosphate, sodium metasilicate, surfactant,
etc.
Treatment temperature : 50-60℃
Treatment
time : 3-5 hours
3-2 Water
rinsing
(1)
Water rinsing shall be carried out only when
degreasing is performed.
(2)
Using a water hose, spray-brushing or
immersion-brushing is carried out to completely remove degreasing liquid. It is
effective to spray pressurized water to the work piece treated with liquid.
(3) When immersion
rinsing is carried out, allow water to constantly flow to prevent grease
compounds or treatment liquid from floating up on the water surface.
(4) Wetting
on the metal surface of the work just after water rinsing shall be expansion
wetting.(If breakage of water coverage or water repelling portion is visually
recognized1 re-treatment is required for insufficient degreasing.)
3-3 Rust
removal
(1) In principle, the
work piece shall be immersed in a tank filled with treatment liquid. However,
the excessively large work piece may be treated by filling, brushing, or
coating.
(2) The inhibitor
shall be added to the acid liquid, for a uniform beautiful finish surface, free
from smut, and reduction of metal loss.
* Reference
Hydrochloric acid concentrations of 5 to 15% are, in
general, used at room temperature.
The treatment
time is 2-5 hours.
3-4 Water
rinsing
(1) Using a water
hose, water-rushing or immersion-rushing is thoroughly performed to remove the
acid liquid. It is an effective method
to spray pressurized water to the work piece.
(2) Water must be
allowed to constantly flow during immersion-rinsing -
3-5 Neutralizing
(1) The neutralizing
liquid which neutralizes and simultaneously has a temporary rust preventive
effect (ability to prevent rust formation for about 3-7 days if water is not
splashed) shall be used. However, it shall not have any detrimental effects on
adhesion of coating when the metal surface Is coated after the neutralizing
liquid is dried.
(2) The work piece
shall, in principle, be immersed in a tank filled with the neutralizing liquid.
However, excessively large work pieces may be neutralized by filling or
brushing but care must be taken to allow thorough neutralization to take place.
(3) Heating the neutralizing
liquid is an effective means to promote neutralization and accelerate drying.
3-6 Drying
(1) Drying after
chemical cleaning is carried out to enable perfect and effective subsequent
surface treatment. The work piece must be dried immediately after cleaning.
Heating the neutralizing liquid is an effective method to
achieve quick drying.
(2) The cleaned work
piece shall be dried in a clean location, free from dust, to prevent adhesion
of impurities to the clean metal surface.
