Cleaner, Alkaline

Cleaning, the removal of unwanted matter, is the beginning of the treatment cycle for metal. The unwanted matter may be carbon smut, welding flux, ink, oxidation products, oil, fingerprints, or other material. Cleaners may be classified as solvent-based or aqueous. Within the aqueous class there are many subclasses, the most important of which are the alkaline cleaners. There are also a variety of ways to apply cleaners. As of the mid-1990s, solvent-based cleaner usage is declining. 

The composition of the builders in an alkaline cleaner is dependent on the metal substrate from which the soil is to be removed. For steel (qv) or stainless steel aggressive, ie, high pH, alkaline salts such as sodium or potassium hydroxide can be used as the main alkaline builder. For aluminum, zinc, brass, or tin plate, less aggressive (lower pH) builders such as sodium or potassium siUcates, mono- and diphosphates, borates, and bicarbonates are used. 

The mechanisms by which an alkaline cleaner removes the soil are saponification, emulsification, and dispersion. These mechanisms can operate independently or in combination. Saponification occurs when alkaline salts react with fatty components of the soil, forming a soluble soap compound. 

Immersion Gleaning. The simplest method for using an alkaline cleaner is by immersion. A part is placed on a hook or rack and immersed ia the cleaner solution so that all of the part is below the Hquid level. A typical concentration, temperature, and process time for an immersion cleaner would be ca 75 g/L at 77°C for 5 min. In addition to being the simplest method, immersion is also among the least expensive in terms of equipment. Only a vessel to contain the cleaning solution and a means of heating the solution are needed. 

Alkaline cleaners (caustic based) These are caustic soda based and are suitable for ferrous metals only. They are more effective in removing greases of vegetable oils, rather than mineral (petroleum) oils, as they do not saponify the mineral oils. 

No dimensional change Proprietary brands of alkaline cleaners may be used provided these do not attack metal Soda ash with washing soda and soap are suitable for preparing alkaline cleaning baths No dimensional change unless much impurity is present For small delicate parts 0 1-0-5% silver chromate may be added to reduce attack caused by impurities such as chloride in corrosion product... 

Pickling acids Molten salts Alkaline cleaners Fuel... 

The major waste sources during normal nickel-chromium plating operations are alkaline cleaners, acid cleaners, plating baths, posttreatment baths, and auxiliary operation units. 

Use alkaline cleaners instead of solvents for degreasing operations they can be treated on site and usually discharged to the sewer with permit authorization. 

Alkaline baths, in tin refining, 24 789 Alkaline batteries, 15 611 Alkaline catalysts, in phenolic resin polymerization, 18 762-765 Alkaline cleaners, for metal surfaces,... 

Maintenance and Production Activities Parts cleaning is a common component of maintenance and production activities. These activities often involve the removal of bulk or gross contamination. In the past, maintenance activities were conducted mainly with petroleum solvents such as mineral spirits while production activities employed the use of alkaline cleaners. The use of halogenated solvents became popular because they exhibited good solvency for organic contaminants evaporated... 

Provide Continuous Heating. For tanks containing alkaline cleaner that are well insulated, properly covered, and located where ambient temperatures are not too low, there are benefits to be gained if the tank is not allowed to cool overnight. Derived benefits include reduced absorption of carbon dioxide (i.e. less reduction of alkalinity) and fewer... 

Alkaline cleaners are available which allow the separation of excess oily soil from the cleaner. These formulations involve the use of surfactants that are good detergents but poor emulsifiers. Agitation of the bath during the work shift causes a temporary emulsification, which keeps the soil in suspension. After a prolonged period of inactivity (usually overnight), the oily soils float to the surface where they are skimmed off. This method is quite effective with mineral oil-type soils but is less so with fatty oils. 

The acid rinse can be further recycled to the alkaline cleaner rinse tank. This conserves water by allowing the fresh water feed to the alkaline rinse to be turned off, and also improves rinsing efficiency by helping to neutralize the dragged in alkaline solution. This will prolong the life of the acid bath because the rinsewater dragged into it will already be partially neutralized. Thus the acid bath will not have to be dumped as often. 

Spent process baths can also be reused for other purposes. A common example is to use spent acid or alkaline cleaners for pH adjustment during industrial waste treatment. Typically, these cleaners are dumped when contaminants exceed an acceptable level. However, these solutions remain acidic or alkaline enough to act as pH adjusters. Alkaline cleaners, for instance, can be used in chrome reduction treatment. Since spent cleaners often contain high concentrations of metals, they should not be used for final pH adjustments, however. 

One strategy for avoiding the sludge problem is to use non-chelate process solutions wherever feasible. Non-chelate alkaline cleaners are available, as are non-chelate etchants... 

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