I am seeking information about the possibility of converting a standard cast iron impeller drawing to a NiHard on a one to one basis. The central bore is a reverse taper with a key way. No MS inserts permitted as per the drawing. A minimum of 75% blue contact in the bore with the shaft is specified. Please advise the possibilty of manufacturing an impeller under such constraints.
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NiHard pump impellers
- Thread starter arunmrao
- Start date
you are asking a tough one. It would depend on how much you want to spend. Typical hard iron impellers (NiHard, High Chrome etc) are manufactured with a thread such as Acme. Machining a bore, especially tapered, and cutting a keyway are really difficult in hard iron, and more so if the hole is 'blind' i.e. not completely thru the hub. With the accuracy you are looking for, you would probably require finish machining in the hardened state (there is always some distortion during heat treatment).
If you have to move to a different material for the impeller, you may want to review the attachment to the shaft in the interest of practicality and economy.
good luck
mac
If you have to move to a different material for the impeller, you may want to review the attachment to the shaft in the interest of practicality and economy.
good luck
mac
Ni-Hard (which was the Canadian version of Chrome Iron- a hardened alloy within 600-700 BHN)is about 2.5-3 times as expensive as cast iron.
It can be cut, machined, ground, etc. as long as it is annealed before it is machined. It must be reduced to approx. 300-400 BHN in order for it to be machined with "everyday" carbide cutters. We use Acme as well as standard UNC threads (both blind and through taps)in our High Chrome, but after the part is hardened, the threads need to be chased (which can be a pain during assembly). Tapers are also somewhat manageable in the annealed state, but a good machinist can do it.
On occasions, such as a sealing face, a skim (finish) cut may be required, especially when teflon or other harder gaskets are required.
Costwise.....if you are replacing your cast iron part 4 or 5 times a year, the high chrome (or Ni-hard) may be beneficial. The cost may be higher at first, but after looking at it in a labor and shut-down state, the extra $$$ may be worth it. Jack
It can be cut, machined, ground, etc. as long as it is annealed before it is machined. It must be reduced to approx. 300-400 BHN in order for it to be machined with "everyday" carbide cutters. We use Acme as well as standard UNC threads (both blind and through taps)in our High Chrome, but after the part is hardened, the threads need to be chased (which can be a pain during assembly). Tapers are also somewhat manageable in the annealed state, but a good machinist can do it.
On occasions, such as a sealing face, a skim (finish) cut may be required, especially when teflon or other harder gaskets are required.
Costwise.....if you are replacing your cast iron part 4 or 5 times a year, the high chrome (or Ni-hard) may be beneficial. The cost may be higher at first, but after looking at it in a labor and shut-down state, the extra $$$ may be worth it. Jack
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