Summary for hot rolled vs cold rolled steel Discussion
hot rolled vs cold rolled steel comes up here in two coating contexts: chrome plating and powder coating. Brian Fletcher asked whether steel quality or chemistry could be causing rough chrome finish variation on hot rolled pickled-and-oiled A-36, noting the parts are pickled, polished, and plated. Tom Pullizzi said anything is possible, but the more likely cause is a change or loss of control in the electroplating process, and he pointed first to polishing and alkaline cleaning, then to copper cyanide bath behavior, anode dissolution, nickel bath contamination, filtration, and iron buildup. He stressed that unacceptable variation usually means the process is not under adequate control. Later, Larry Smith asked whether cold/hot rolled steel can be specified for powder coat, and Troy Hartwig reported that hot rolled pickled and oiled blanks often outperform cold rolled in ASTM B117 salt spray testing, asking why. The thread does not give a final technical explanation for the powder-coat result.
Q. Being a captive manufacturer, we receive close to 1 million a year of plated product but I see our chrome products finish vary throughout the year. Recently we have run into a roughness problem, our plater claims material is the cause. We use a hot rolled pickled in oil product A-36 steel, the material is double skin passed, stress free, surface quality is superior to a standard a-36 sheet produced in USA; we buy from mills in Japan and France. Steel is pickled to remove laser oxide, polished to remove imperfections, and plated (copper, nickel, chrome). Is there any truth to steel quality creating this type of problem? What’s the difference between cold/hot rolled … they both go through same polishing process prior to plate? Does chemical make-up of the steel (i.e., more or less carbon) affect surface finish? Thanks for any information.
Brian Fletcher
– Gresham, Oregon
1999
A. Anything is possible, but it is most likely that something changed in the electroplating process.
I would first look for:
1. Changes in the polishing step and the alkaline cleaning step for changes in the buffing compounds versus the ability of the alkaline cleaner to remove the compounds. (example: Do some parts get run in an alkaline cleaner before the cleaner is up to temperature?)
2. Copper cyanide baths can cause a lot of roughness if the copper anodes are not dissolving correctly. (example: Bath runs in and out of balance as the day wears on.)
3. Shelf roughness in nickel plating solutions could come from precipitated iron, inadequate filtration etc. (example: iron builds up in nickel plating tank and drops out when pH gets too high.)
It may be too obvious for words, but unacceptable variations in a process are the result of processes that are out of adequate control. Someone must make a decision that your plating process is under control so that you can take your investigations elsewhere.
Tom Pullizzi
Falls Township, Pennsylvania
1999
Q. WITH REGARD TO MATERIAL SELECTION CAN “COLD/HOT ROLLED STEEL” BE SPECIFIED? IF IT IS TO HAVE A POWDER COAT FINISH?
THANKS.
Larry Smith
– Winston-Salem, North Carolina
2004
Q. We test the performance of our powder coat line by spraying blanks and then salt spray per ASTM B117. I have noticed the Hot rolled pickled and oiled blanks typically outperform the cold rolled blanks. Can somebody explain why I am seeing this?
Troy Hartwig
– Schofield WI USA
October 6, 2017