Replacing cast iron with 4140
Replacing cast iron with 4140
(OP)
We buy a helical pinion gear to our customers drawing which we assemble into our product. The customer material spec is for an alloy gray cast iron, 3.1 to 3.6% carbon, 2.1 to 2.8% silicon & 1.15 to 1.50% chromium. There are other elemental requirements as well but they are all lower concentrations.
I don't know the loads but it runs at 300 to 3000 RPM & is splash lubricated by motor oil.
A gear supplier has suggested using 4140 instead of gray cast iron. It would be heat treated to the same hardness. I am not a gear engineer and obviously the customer would have to approve any change. I would just like some opinions on this proposed change. How would the two materials compare in strength, wear, etc. I don't want to take this to the customer if it is obviously a bad idea.
I don't know the loads but it runs at 300 to 3000 RPM & is splash lubricated by motor oil.
A gear supplier has suggested using 4140 instead of gray cast iron. It would be heat treated to the same hardness. I am not a gear engineer and obviously the customer would have to approve any change. I would just like some opinions on this proposed change. How would the two materials compare in strength, wear, etc. I don't want to take this to the customer if it is obviously a bad idea.





RE: Replacing cast iron with 4140
RE: Replacing cast iron with 4140
Our current supplier has gone out of business, trying to find a new source.
RE: Replacing cast iron with 4140
You did not give many details of your gears. In general, a higher strength material is beneficial when the pinion gear is a smaller diameter than its mate. This helps to equalize the tooth bending capabilities of the two gears.
The only benefits to using gray iron for gears are cost and wear properties under marginal lubrication conditions. As CoryPad noted, the carbon in gray iron is in the form of graphite flakes, which makes it wear (and machine) very nicely. But those graphite flakes also make gray iron very prone to fracture. So its fatigue properties suck.
However, if the existing gear material was giving adequate performance, I don't see why you would want to change material. High quality gray iron stock is available in continuous cast bar form, from many suppliers. It would be less expensive and would machine much nicer than 4140. So you might want to suggest that material to your vendor.
Hope that helps.
Terry
RE: Replacing cast iron with 4140
RE: Replacing cast iron with 4140
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: Replacing cast iron with 4140
Dan T
RE: Replacing cast iron with 4140