Low Concentration Baths
The Low Concentration Dura hard chrome bath offers several distinct advantages over conventional baths. Bath additives are used with generic chromic acid, so there are no proprietary chrome blends to buy. This bath is used for all hard chrome applications including flash plating and heavy build-ups on either OD or ID work. Its user friendly, easy to control and inexpensive.
The savings in electricity and chromic acid are very significant.
This bath is much less costly to operate than an older contaminated bath is.
Following are the benefits of using this process over conventional 30-40 oz./gal. baths.
- 70% faster plating speeds than older contaminated baths.
- Improved rinsing and reduced staining.
- Slower build-up of bath impurities.
- Less chrome spray on bussing, tank rims and equipment.
- Better deposit color, hardness and corrosion resistance.
- Lower electrical costs and reduced chromic acid consumption.
- 40 % less chrome misting for better OSHA & EPA numbers.
This Dura bath operates with a chromic acid range anywhere from 15 up to 25 oz/gal. In general, most shops select 20 oz/gal. as the optimum control point. There are pros and cons to levels below 20 oz/gal. Concentrations of 15 oz/gal. are less tolerant to impurities, have less throwing power and require a higher voltage.
The process uses the liquid Dura-3000 Additive as a catalyst to enhance the deposit properties. The Dura-3500 Booster (used only for the initial bath make-up) increases the plating speed. The Dura-76 Additive is used to buffer the bath, chelate bath contaminants and increase the throwing power. Following are the typical control points:
|Chromic Acid||20.0 oz/gal.||15 – 25|
|Ratio||120:1||100 – 150|
|Dura-3000 Liquid||3 % Vol.||2 – 5%|
|Dura-3500 Booster||1.0 oz./gal.||0.75 – 1.25|
|Dura-76||2.5 oz/gal.||2.0 – 5.0|
|Trivalent Cr||1 % of Hex.||0.70 – 2.0|
|Metallic Contaminants||< 5.0 g/l (Fe & Cu combined)|
|Chloride||< 20 ppm|
|Insolubles||< 0.04 g/l|
|Temperature – F||140||120 – 150|
|Current Density||2 ASI||1 – 8 ASI|
Do not add the Dura-3500 Booster to baths that plate parts with highly stressed base metals or those with surface hardness exceeding 45 RC, without first stress relieving the parts by baking and then shot peening prior to plating, see QQ-C-320. This is especially important for deposits thicker than 0.001” because the base metal stress can transfer to the chrome deposit causing macro-cracking, and in severe cases a loss of adhesion, especially after grinding.
The only downside for not using Dura-3500 in these baths is a slightly slower plating speed. You should, however, still use the Dura-3000 Additive.
The optimum concentration of Dura-3000 is 3 %; the Dura-3500 Booster is 1 oz/gal. and the Dura-76 is 2.5 oz/gallon. Regular maintenance additions should be made to maintain these levels, as follows:
|Item||Per 100,000 Ampere Hours||Approx. Per 100 lbs. of Chrome|
|Dura 3000||0.25 gals||1 gallon|
|Dura 76||2.5 lbs.||10 pounds|
Also, send a bath sample to Plating Resources, Inc. on a monthly basis for a complete analysis.
The Dura-3000 low concentration bath allows operation at High Efficiency and at high current densities (if needed) for even faster plating speeds. Typical plating speeds (per side/hour) are:
2 ASI: 0.00125″ 4 ASI: 0.00250″ 6 ASI: 0.00375″
Bath Conversions & Operation:
Most baths can be converted to the Dura-3000 Low Concentration process, assuming that the contaminants are not excessive. Of particular concern are the trivalent, iron and copper levels. These contaminants degrade the plating quality which is more profound at low chrome levels. Existing baths (with high chrome levels) are converted by diluting with water until the desired chromic acid concentration is obtained. This dilution also reduces the contaminant levels, which works in your favor. The portion of the bath that is removed can be used as a feed stock, if desired, to replace the chromic acid that is plated out.
Submit a bath sample to Plating Resources, Inc. for a detailed analysis and conversion procedure.
Bath control becomes somewhat more important when low chrome levels are used. Routine bath analysis should, therefore, be performed on a more frequent basis. Plating Resources, Inc. also provides this service.
There is one concern that should be reviewed when looking to adopt a low concentration bath. Low levels of chromic acid increase the baths resistance which means that a slightly higher voltage will be needed to maintain the same current density. The lower the chrome level selected the more important this issue becomes. Reduced bath conductivity also provides slightly less covering power and the bath is more intolerant to high impurity levels. Shops with sufficient rectifier voltage capacity will be able to easily overcome this concern. The use of the Dura-3000 and Dura-76 Additives will greatly assist with conductivity and improved bath operation.
The Dura-3000 bath contains chromic acid, sulfuric acid Dura-3000, Dura-3500 Booster and the Dura-76 additives. These are all industrial strength chemicals and must be handled carefully and in accordance with the directives provided in the individual SDS forms.
Read and understand the SDS 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) 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.