Pump Impeller Casting

You need a molding model to make a casting, so you need to piece your impeller back together or make a replica...

https://www.custompartnet.com/wu/SandCasting

I'm not a mechanical engineer. To me it seems your proffered information is insufficient to provide advice. For instance:

• How many days, years, or decades did the failed impeller succeed in moving your unknown fluid?
• What is this unknown fluid?
• How much larger is the impeller clearances than the largest anticipated particulate in this fluid?
• Did a larger than anticipated particulate reach the impeller?
• How corrosive is the fluid?
• How damaged is the impeller housing?
• Is there any shock absorbing coupling between the impeller and the prime mover (motor)?
• Did this absorbing coupler seize or break when the impeller failed?

It was only in service for 90 years.

A complete redesign might be necessary.

The primary consideration is the compatibility between the wetted materials and the wetting agent. However, the forum has yet to discover why the pump manufacturer is unable to ship a replacement impeller so as to save the trouble of making one.

"Time is money" _{- Anonymous Poster #0}

Three "Howdies" to you!

How much time do you have?

How much experience with impeller casting do you have?

How much does a replacement pump cost?

42, 42, and 42, respectively.

"Excuse me sir!Can you tell me when the next train leaves! How much are those bananas? And how deep is that mud puddle?"

The next train leaves in 15 min....those banana's are $.39 apiece.....that mud puddle is about 3" deep....

5 minutes

.49 per pound

2"

I don't understand how difference could be so dramatic?

Here is a link for making a propeller.Since you give no specifics, this may be exactly what you want.Impeller/Propeller technologies are similar.

https://www.popularmechanics.com/technology/infrastructure/a24153/ship-propeller-manufacturing/

On the other end of the size/skill area,try this:

https://ibuildit.ca/projects/wooden-blower-fans/

Casting is such a specialist process that it would requires us to type books of detail for you and then you only have the words and not the experience. Sorry to hear that your pump failed.

If everything else (Motor, volute, bearings etc) is OK, then this may be an opportunity to get a better impeller than the original.

There have been significant advances in design and fabrication of those in recent years. Your pump manufacturer (In Australia) will be helpful. You will essentially need to tell them the details already mentioned earlier but also some other things like inlet static pressure, head to be pushed and so on. Probably best to fill in a request for quotation form from the supplier and nominate that you already have the housing and prime mover available.

What sort of capacity are you talking about? Some here hinted at "off the shelf" and that's usual for less than 20 L/sec but if you're talking about 200L/sec then the power savings to be achieved by having a specific designed impeller will recover costs often within 12 months or less and most of those pumps will run for years/decades.

What's the duty cycle? Are you starting the pump against closed valve or just a full pipe.

There's more to getting a good solution than just casting another impeller.

To make a casting you need a pattern of the finished impeller. This pattern needs to have allowance for shrinkage as the metal cools and also draft so it can be removed once the sand is rammed up. It isn't good to have a lovely pattern firmly wedged in the box after the sand has been rammed, and you can just bet that when that happens some smarty will come along and see your mess up.

Next you need a drag and cope the name for the two boxes that will hold the molding sand and retain their shape when the sand is rammed up.

Then there is the molding sand itself which is not just any old sand but one that will hold its shape when compressed but allow gasses to escape. For the molding sand you require a bonding agent, can be clay or many and various other resins or oils.

You need to allow risers for the metal to fill so as to provide a resevoir for the shrinkage and to allow the air in the mould to escape when the metal is poured in else you will make a miniature Mount Etna, not a good look.

There needs to be vent tubes almost reaching to the mould to allow gasses to escape from the sand mix as it heats.

You need weights and pins to hold the cope and the drag together for there is nothing worse than the two parting company and spilling molten metal all over the floor or you.

When all this is done you need the metal which has the correct properties for the task and somewhere to melt said metal like in a furnace. Then there is the ladle protected by a suitable refractory to move the molten metal from the furnace to the mould.

But before the metal is poured it needs to be degassed so the finished article does not contain small or microscopic gas chambers which will create cavitation. Degassing also prevents embrittlement from the furnace gasses, oh and then there is the flux to float any impurities to the surface so they can be skimmed off before you pour.

Sound too hard, your right, would be better to take the impeller to a small foundry and let them do all the work and know that they should guarantee their work.

I have cast pistons and wheels and other items out of Aluminium in sand moulds and in metal moulds. Sure it is great for the self esteem to have made a specialist article for something for which no part is available but in my case my time is cheap if not a little nasty at times so a few failures don't matter a tad it is just experience.

Have I turned you off?

Thanks, very informative!!

Might as well buy a 3d printer since based on the information provided, trial and error is your methodology so rapid prototyping is your friend, as is a very high dollar value liability insurance policy.

Thanks all for the comments and ideas. As discussed with the Boss, we will proceed to cast the impeller and at the same time to buy a new one. Lead time to receive new impeller is almost a year whilst to cast one it only takes about 2 months. Material has been decided, we are going to use ALUMINUM BRONZE (AB2) for the sea water application vacuum pump. Will share the photos later..

One might also look into:

• gas-welding the <...ALUMINUM BRONZE...> original to effect repairs, and
• fitting a suitable strainer/filter upstream to remove the damaging solid species, and
• ordering 2 from the supplier and keeping one as a strategic spare, given the <...almost a year...> lead time needed to bring this equipment back into service - "Time is money" _{- Anonymous Poster #0}
• coating the repaired impeller with a suitable material, such as a plastic, in an effort to keep the wetting fluid away from the impeller materials, and
• 3-D printing a plastic impeller as a replacement, using the original as a pattern for the printing process