Slurry pump impeller casting

[arunmrao]

This question is about manufacture of high chrome dredger pump impeller casting.

I have received a customer's casting with no drawing for reengineering.

The casing is a simple job, but with the impeller I have a challenge.

Normally, the internal threads for engaging the shaft, is machined on a in situ cast mild steel insert or a cast thread using ceramic cores.

In this case, there is a mild steel insert used with a cap/flange on top.

Normally, there exists a vertical split in the insert during casting ( a "C" section), so that while the casting cools, this insert also closes, like a spring, thus avoiding cracking.

But, I am seeing an insert, without this slot, I am stumped.

Look for some insights or tips about manufacturing such castings.

The casting weighs about 1160 kilos and the material is high chrome iron.

Thanks in anticipation.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[arunmrao]

I have a sketch of the impeller, now available. Please view and offer your comments or tips to cast the impeller with insert.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1500039989/tips/Impeller_Model_1_w86mwx.pdf[/url]

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[Artisi]

Just a random thought, if the shaft / impeller is threaded right hand, think about cutting a coarse thread left hand on the outside of the insert with the insert cast into the impeller.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[EdStainless]

We used to machine flutes into the OD of the inserts, and made sure that there were no square corners.
We also made sure that the inserts were hot (usually by making sure that molten metal flowed over them.

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P.E. Metallurgy, Plymouth Tube

 

[arunmrao]

Is the insert cryo fit (liquid Nitrogen)? I am leaning towards that idea?

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[EdStainless]

I hesitate to shrink fit the steel, Ni-Hard does not like being under tensile stress.
This is a large casting, you could almost make the steal insert in two pieces.
Cast in a fairly thin wall part, then mechanically insert the thicker threaded one.

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P.E. Metallurgy, Plymouth Tube

 

[arunmrao]

EdStainless,

Thanks, and that is how I have been manufacturing impellers. Though a few have moved away from cast inserts, by having ceramic cores with threads. Thus the bore would have cast threads and they are just cleaned on a lathe.

I pursued this technology, but failed , and then gave up as business moved away.

Now, once again after 20 years, I see an impeller that has a whole insert!!. I was stumped.

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[Artisi]

arunmrao, I should have added "and machine the impeller hub internal thread after casting"

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)