Page 427 - Industrial Power Engineering and Applications Handbook

Switchgear and controlgear assemblies 13/401
metals. These cleaners emulsify faster than other types Remove 10 ml of this solution and add a few (three to
and are more suitable for heavy production lines. five) drops of phenol phthalein and shake.
Emulsion cleaners These are emulsified chlorinated Titrate this against N/lO-HCl solution until the colour
solvents and are kerosene based, suitable for mineral changes to pink.
oils (petroleum and heavy petroleum greases) and A burette reading will indicate the actual pointage of
deep-drawn components, using lead compounds as the bath compared to the standard (approximately
lubricants. They are also suitable for non-ferrous 3-6) for a concentration of 3-5%. Obtain the
metals. standard pointage from the chemical manufacturer.
Solvent cleaners These are tri-chloro ethylene (TCE)
and are highly evaporating cleaners, possessing toxic For each one point of lower strength, add 1 litre of chemical
properties. Their application is the same as for neutral per 100 litre of bath.
cleaners.
Note
Concentration, bath temperature and dipping time N/lO-ready-made laboratory chemicals are easily available.
These are indicated in Table A13.2.
Precautions to be observed
Tank material
A mild-steel (MS) tank with wall thickness of 4-6 mm, 1 When making a fresh bath, stir the chemical well in
with a heating arrangement and a thermostat temperature a separate container, preferably in hot water, before
control, will be ideal for this purpose. Even when a cold mixing it into the tank.
process is adopted, heating will be imperative during 2 Skim off oil and grease scum from the surface of the
winter or in cold climates, where the bath temperature bath every day or more frequently, depending upon
would be less than 40°C. A protective lining inside the the amount of work being handled.
tank is generally not essential, as the chemical does not 3 When using alkali base cleaners, protect the eyes and
attack the metal. An anti-corrosive paint, such as epoxy skin from direct contact with the chemical.
or polyurethane may, however, be provided to enhance
the life of the tank. The thermostat and heater may be of Water rinsing
stainless steel or ordinary water heaters could be used.
The tank may be made slanting ( *inch in an 8-feet length To rinse, wash the surface in clear, continuous running
is adequate) to have an overflow system to remove the water to remove all traces of degreasing agent from the
oil and grease scum during the degreasing process. surface. Tko/three dips at room temperature are sufficient.
An MS tank with a wall thickness of 3-4 mm is
Checking the bath concentration adequate, otherwise the thickness can be similar to that
The concentration of bath solution in caustic-based for the degreasing tank but without the heating
cleaners can be checked by a simple titration method as arrangement. It may also be coated with an anti-corrosive
noted below, while for the remaining types of cleaners, paint to enhance its life.
a visual check of the degreased surfaces will be sufficient. Carry out the rinsing before the chemical dries on the
The titration method is as follows: surface.

e Pipette out 10 ml of bath solution and add 90 ml of Descaling or acid pickling
distilled water (total 100 ml). This is a process to remove heavy black scale and rust
from the surface. Hot-rolled sheets that may have such
scale formation need only be acid pickled. Cold-rolled
Table A13.2 Concentration, bath temperature and dipping time
sheets, which may carry no such scales, need not be acid
pickled. Depending upon the type of surface, one of the
Type of Concentration Bath temperature Dipping time following methods may be adopted.
cleaner
Alkaline 3-5% by weight 90-95°C 10-15 min For heavily scaled and heavily rusted surj5aces
cleaners or volume of bath
Neutral 3-5% by (i) 50-70°C 3-5 min Acid pickling This can be done under the following
cleaners weight or (ii) Also possible 10-15 min operating conditions, either with sulphuric acid
volume of bath at room temp. (H2S04), or hydrochloric acid (HC1). H2S04 releases
(4045°C) a lot of fumes and is ineffective under cold conditions.
Emulsion No dilution 5040°C 3-5 min It forms iron sulphate, which forms a hard deposit at
cleaners the bottom of the tank and is difficult to remove (see
table on next page).
Solvent No dilution 80°C 3-5 min Tank material A mild-steel (MS) tank, with a wall
cleaners
thickness of 4-6 mm, and having an acid-proof lining
Note The exact values will depend upon the surface condition of of FRP (fibre-reinforced plastic), rubber or PVC will
the material and the field experience and skill of the operator. For be suitable for this purpose. A heating arrangement,
more accurate details consult the chemical manufacturer. even if a cold process is adopted, will be ideal for