Saturday, September 27, 2008

Alkaline Soak Cleaning

The parts are immersed in tanks of hot alkaline cleaning solution. The concentration of the cleaning solution and the temperature should be maintained as high as is safe for the metal being cleaned in order that the time for complete cleaning may be reduced to the minimum. Agitation of the cleaning solution is desirable, because the cleaning action in soak cleaners depends on the wetting and gradual emulsification of oils and greases. Sometimes saponification of the soil plays a role. Dirt and other solid particles are bound to the metal surface by oils and grease and are removed when the binding material is dislodged from the surface. Heat and agitation speed up the wetting, emulsification, and saponification. The mechanical force of the moving solution is helpful in dislodging the soil; the newly formed emulsions and metal soaps are washed away from the surface which is thus constantly exposed to fresh cleaning agents.

The design of cleaning tanks is described by lux and linford and Myers. The principal points of design are as follows:

  1. To improve agitation of the solution, a sheet metal shield should be installed I front of the steam heating coils to make use of convection currents. In addition, either motor driven propellers or movement of the work should be provided to ensure adequate agitation.
  2. In order that there may be a quiescent layer of solution at the bottom of the tank to provide for settling of sludge, the bottom of the lowest heating coils should be at least 75 mm from the bottom of the tank.
  3. An overflow dam should be provided so that oils and greases floating on the surface will be removed each time a load of work causes some of the solution to overflow into the drain. This is necessary to ensure that the cleaned work is removed through a clean surface.
  4. A mesh grid false bottom is desirable to make it easy to recover parts that drop into the tank.
  5. A means should be provided to control and either indicate or record the temperature.