Hydrochloric acid stripping of chromium deposits is an effective way to process a variety of base metals. A strip bath of this type will prove to be a valuable asset to the chrome plating shop. Besides being an effective strip, for certain parts, it will also be useful to remove build-up on burner caps, thieves and related articles. Following is advisory information for use of such a stripper.
|Hydrochloric 20° Acid||25% Volume (10-40% range)|
|Process Time||As required for deposit thickness|
Inhib-All is a liquid organic additive for hydrochloric acid solutions. It is a unique blend of inhibitors and surfactants that greatly improves the action of the stripping bath. The use of Inhib-All will allow for improved stripping of the chromium layer while also providing protection of the base substrate. Inhib-All also produces a thin foam blanket on the tank surface that reduces fuming, as well as a thin film on the part that prevents oxidation during transfer.
|Stops over-stripping & protects the base metal.|
|Conserves acid, by as much as 40-50 %.|
|Provides faster stripping rates.|
|Reduces drag-out and waste treatment.|
|Promotes better & safer stripping of chrome.|
While alkaline solutions, such as Polystrip-26, are used for the electrolytic stripping of steel, hydrochloric acid is used for a wide variety of other substrates. For several reasons, including the non-dissolution of the base metal, the following base metals should be stripped in this acid type bath, by simple immersion:
Aluminum and zinc substrates must not be stripped in the acid bath, as they will dissolve. Aluminum is best stripped by reversing in a chromium solution, such as a reverse etch or directly in a non-fluoride plating bath. Zinc cannot be stripped in either acid or alkaline solutions. The only way to remove chromium from a zinc substrate is to grind and/or polish the part.
Adequate rinsing is mandatory following the stripping bath. This rinse will stop the action of the acid on the substrate as well as remove the chloride from the drag-out film, which would otherwise severely contaminate the plating bath. Special care should be used to thoroughly rinse all parts, racks, hooks, etc. and especially those that tend to trap solution. It is also good practice to process parts through an alkaline solution, following stripping and rinsing, in order to neutralize all residual acid films. A bath, such a Polystrip-26, can be used for such neutralization.
The exact stripping rate will depend upon the concentration of the hydrochloric acid, the temperature and the amount of chromium already present in the bath. However, 0.15 mil per hour of stripping is usually expected. Under optimal conditions, removing up to 0.3 mil per hour is possible.
Being an acid solution, all equipment must be designed properly and of corrosion resistant materials. Tanks are normally fabricated of steel and lined with ChemLock #100 or PVC. PVC ventilation equipment must be used in order to remove acid fumes from the tank area. The tank should be covered when not in use, so as to reduce plant corrosion and conserve energy by allowing the ventilation system to be turned off. Hydrochloric acid is very aggressive and will easily corrode steel items, such as roof trusses and superstructures. These items, as well as adjacent walls and floors, should be covered with a suitable protective coating.
Regular and routine additions should be made so as to maintain the bath at its optimum concentration. Hydrochloric 20° Acid is added based upon chemical analysis of the solution. Inhib-All should be added, based upon visual inspection of the foam blanket during stripping. Inhib-All should be added in increments of 0.5% by volume.
This process uses industrial strength chemicals which must be handled carefully and in accordance with the directives provided in the individual MSDS forms. Read and understand the MSDS on all of these chemicals before handling or using. Ensure that all regulatory standards are followed and limit personal exposure as required for Cr(VI) and other chemicals by OSHA.
Avoid personal contact with these chemicals, avoid splashing and avoid breathing any fumes released during operation. Do not inhale any dust, mist or vapors from these chemicals. Do not allow these products to contact the skin or eyes. In case of contact, flush immediately with large amounts of fresh water and seek immediate medical attention. Wear protective clothing such as aprons, gloves, face masks and respirators. Be sure that adequate eyewashes and emergency showers are available nearby before handling or using any of these chemicals. Designated work clothing should be worn while using these chemicals and the worker(s) should thoroughly shower and change into fresh-clean street clothing before going home. Decontaminate all work clothing before reuse. The user is responsible for providing adequate work clothing, personal protection, limiting personal exposure and providing any required clean-up, decontamination as well as any needed medical attention.