In the November 2016 issue of Production Machining, pages 38-41, highlights the many problems of integrating the more expensive No-Lead Brass production with traditional “leaded” brass production. Metal finishing shops face new challenges in fabrication and segregation of a unique product.
Since No-Lead Brass wears differently than traditional brass, changes in cycle times, coolants, and cutting tools are required. Stone Chemical Company CU400L will clean, brighten, and remove leachable lead from brass, copper, and bronze parts and allow them to be used in the same applications as No-Lead applications without the headaches.
Lead has been a lubricant for brass, bronze, and copper processing since ancient times. Brass can contain several hundred ppm to 2 % residual surface lead. Lead is hard to remove because the alloy metals in brass (primary Zinc) and bronze (primarily Tin) can also be plucked out with lead by conventional means and ruin the alloy. Current strategies for removing lead require harsh conditions, produce low yields and have waste problems.
The purpose of this letter is outline the Stone Chemical Company passivation process using the proprietary product CU400L for the removal of leachable lead from brass, bronze, and copper parts down to near 1 ppb. The obstacles to removal of leachable lead from the surface of the brass, bronze, and copper are:
- The coating of processing oils on the surface that physically prevent water containing the lead removal solution from contacting lead.
- The presence of some lead metal in crystal “holes” rather than all of it sitting on the surface of the metal crystal structure.
- The presence of lead metal just below the surface of the part that might “pop up” later during use.
The removal of lead occurs in two stages:
- The surface conditions on the metal parts are adjusted by using a CU400L to:
- Remove surface oils and other debris blocking access to surface lead
- “Prime” the exposed lead for removal by making it more reactive.
- CU400L allows the lead removal to proceed smoothly.
- The surface lead is dissolved out of the holes by the mildly acidic CU400L, which alters the oxidation state of the lead while minimizing the loss of Copper and Zinc from Brass; and Copper and Tin from Bronze.
- The mildly acidic CU400L gently rearranges the metal crystal structures to “fill in” the empty lead “hole”. This will have a brightening effect on the brass.
- The phosphate component of CU400L passivates the surface by combining with some of the Brass (primarily Zinc) or Bronze (primary Tin). Lead just below the surface of the brass is now sealed in.
Stone Chemical Company has obtained two United States Patents (US Patents Nos. 7,771,542 and 8,618,038) for the invention to safely remove surface lead from metals including brass and copper which are used in potable water systems. The removal of lead from the environment is currently an EPA goal for health and wellness as reflected in the 1991 National Primary Drinking Water Regulations and the 1996 Safe Water Drinking Act amendments.
For mildly oily parts, CU400L has adequate cleaning ability. However, for heavily soiled parts, the parts can be pre-cleaned by either SW100L (a neutral dispersing cleaner) or SW150L (an alkaline non-dispersing cleaner).