Corrosion Resistance Problems
Many mechanical specifications insist on hot-dip galvanizing for steam tunnels or outdoor applications. Is there any side by side comparison between the two methods?
Q1. I stumbled across your forum while Googling. We are manufacturing a line of insulated pipe guides and slides with a B-117 1,000 hr powder coat surface. Many mechanical specifications insist on hot-dip galvanizing for steam tunnels or outdoor applications. Is there any side by side comparison between the two methods? M. R.
Featured Content
Q2. We are a manufacturer located in NW Iowa. We supply heavy truck cab suspensions to OEM customers. One of our customers requires our finishes to pass a 365hr salt spray test on both flat and curved sections. We pass the test on flat parts but fail on the curved. We have been working with our suppliers on this and have tried several different things over the past few months but again failed the latest testing. We would be interested in talking with someone about possible strategies to try to achieve a passing result and improve our process. Thanks. J.W.
A. Following is an answer from my August 2006 column that seems to apply here, as well.
Corrosion resistance is primarily achieved by a combination of substrate selection, pretreatment chemicals, occasionally primers, and a good topcoat. You can obtain the same corrosion resistance by using these attributes in different combinations, or all of them at once, depending upon the particular corrosion requirement.
Since your product substrate is selected for reasons other than corrosion resistance, you must compensate with pretreatment chemicals and primers and topcoats. You may even achieve your corrosion requirements using just the proper pretreatment and a single topcoat. Following is our experience on your substrate (cast ductile iron) with the choices you have available:
No pretreatment and powder coating topcoat | 100+ hours |
No pretreatment; e-coat primer and powder topcoat | 100+ hours |
Iron phosphate and powder coating topcoat | 500+ hours |
Zinc phosphate and powder coating topcoat | 750+ hours |
Iron phosphate and e-coat primer and powder coat topcoat | 1,500+ hours |
Zinc phosphate and ecoat primer and powder coating | 2,000+ hours |
As I always recommend, you should test your particular selection(s) prior to final implementation.
RELATED CONTENT
-
Touch-up Options for Powder Coated Parts
Is it true that powder coating cannot be touched up? Powder coating expert Rodger Talbert offers options for powder coating touch-ups.
-
Improving Transfer Efficiencies in Coating Operations
There are many methods for addressing electrostatic grounding in metal painting processes, and Tim Ulshafer from Mueller Electric says the best method for your process is a simple and worthwhile exercise.
-
Preparation of Stainless Steel for Powder Coating
Should type 316 stainless steel castings be sandblasted before powder coating, or can they be chemically etched? Should the parts be pre-heated in an oven before coating?