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Mallable Iron

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John Purdy16/07/2019 17:45:57
183 forum posts
59 photos

I have a set of original Stuart Turner (not the current Stuart Models) castings for the reversing gear for the #1 engine. The eccentric rods are supplied as mallable iron castings and they are both warped to the extent that they won't clean up to the desired 5/32" thickness as required, as there is minimum machining allowance on them. My question for any one who has worked with mallable iron is, are they ductile enough to hammer strait or are they going to snap like normal cast iron would.

These two appear to be identical castings to the one I have just finished machining for my #1 (castings of the the same vintage). It was only slightly warped and machined beautifully, much like mild steel except that the chips came off as little chunks, much like cast iron or hard brass.dscn3207.jpgdscn3211.jpg

pgk pgk16/07/2019 17:53:16
1486 forum posts
285 photos

Not being knowledgeable on the subject I went and looked it up wikipedia

Apparently malleable cast iron requires annealing after casting and thereafter can be stamped, bent or striaghtened so I suppose that depends on whether what was sold as malleable cast iron did go through that process or can be annealed again to be sure?

JohnF16/07/2019 18:15:47
891 forum posts
114 photos

John, the clue is in the name "malleable " I believe you should be able to straighten the part sufficiently to machine it to size. If you have a muffle furnace to re-heat-treat the casting you could heat up and bend it straight then heat treat to restore the properties but I believe you can manage without this for such a small adjustment.

Have a look t this link -- very informative particularly look at "Malleable Cast Iron properties" about 1/2 way down **LINK**


John Purdy16/07/2019 19:02:56
183 forum posts
59 photos


Thanks for the link, it basically confirms what I thought I knew about mallable iron, and why it is more ductile than cast. I was thinking someone here might have had worked with forming mallable iron and could tell me their experience. I will try and straighten them and if not successful can always carve them out of solid!


Brian Oldford16/07/2019 19:03:58
586 forum posts
4 photos

Assuming they are what they claim to be, the clue is in the word "malleable". The swarf from malleable iron will usually appear somewhere between mild steel and regular grey iron.

John Purdy16/07/2019 19:37:54
183 forum posts
59 photos


As I said the when I machined the current one the swarf came off as small little cures more like hard brass and there was none of the black graphite dust you get from normal cast iron. The castings are listed on the Stuart parts list sheet as "mallable iron" as were the con rod, crankshaft, and the piston rod/cross head. The reverse gear parts list lists the eccentric rods, expansion link, drag link, connecting link and reversing lever all in "mallable iron".


John Purdy17/07/2019 18:47:57
183 forum posts
59 photos

Well I attempted to straighten them with a hammer on the anvil and it worked OK but it took a lot harder hits than I thought it would, they definitely weren't soft, the hammer left no marks on them.. They are not perfectly straight but close enough so that they will clean up. Just hope there are no unseen fatigue cracks that will cause them to break when it machine them.  Probably might have been better to put them in the kiln and heat them to red heat and then hammer them straight. Hindsight is great!


Edited By John Purdy on 17/07/2019 18:51:00

vintage engineer17/07/2019 21:08:31
199 forum posts
1 photos

I would heat them up red hot and clamp to a large section of steel and allow to cool.

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