Machining of hot-dip galvanized steel

[Shelley223]

I am looking for information on machining hot-dip galvanized steel. Specifically, what types of environmental and safety issues we need to be concerned with? How does the material react with the heat of cutting, and how will it accumulate in our machines, and coolant sumps.
Although i can find lots of info on the web related to the galvanizing process, i cant find anything on how the material reacts when machining afterwords.
Any ideas, or info would be helpful

 

[cloa]

http://www.ehow.com/list_6742826_dangers-cutting-galvanized-steel.html

"Machining galvanised steel health safety" comes up with some helpful link- I agree that you have to wade through a lot of irrelevant links.

 

[Shelley223]

Thanks much, this has some good information on the health aspect of things. I am thinking, cause there isnt much regarding machining of the stuff (in CNC machines), that maybe not alot of people are doing this. I think we may want to really push the thought of machining the parts before the galvanizing with our customer. It is a new project, so they may be more open to the idea.

 

[hokie66]

Would be interesting to know what type parts and machining you are talking about. Galvanizing after machining covers with zinc and changes the geometry of the machined surface.

 

[Shelley223]

They are really large castings actually, not steel, cast iron. They have some pretty tight flatness/form tolerances and i am not sure if we can accurately enough, compensate pre-galvanize, to assure the final product meets the specs.
I guess i should define "large" as my large may not be the same as yours....the biggest guy in the bunch is about 43" long x 20" wide x 5" thick
Lots of drilling/tapping/milling involved and a few bearing bores, so pretty typical machining.

 

[hokie66]

To me, this doesn't seem like an application for hot dipped galvanizing. If you need to provide corrosion protection for the cast iron parts, I would look at a coating system to be applied after machining, but not to mating surfaces.

 

[unclesyd]

You can not allow for HDG coatings. The closest you can come is with high production parts with a very well controlled HDG line and even then it is problematical. Case in point HDG bolts where you have to chase the threads in the nut after HDG. Off hand can't think of any coating for CI that will allow you to coat prior to machining with any tolerance.

If you do have your rough casting already you might want to look at the Dura Bar material. If you have an interest make sure you call them to inquire..

http://www.dura-bar.com/index.cfm

One of my first jobs was to check the thickness of HDG on pipe fittings after they had passed visual inspection. There was a tremendous variation in sample lot,-50% nominal thickness to +200% over nominal thickness.

 

[hokie66]

Unclesyd is right. The thickness of galvanizing varies with the thickness of the part...heavier sections attract more zinc, so there is no effective means of controlling the coating thickness.

 

[Shelley223]

We have worked with Durabar material before, its actually pretty good stuff, but machining these parts out of any type of flat stock would be extrememly expensive, as there would be alot of material removal. We are not really in a position to suggest different types of material anyways. But thanks to all for the info on the inconsistency of the zinc, this is kind of what i suspected.