Pump design - Plastic injection - Design advice

Gonzalito · Sep 19, 2023

Hello everyone.

My name is Gonzalo, I'm from Argentina, and I have to design a centrifugal pump for a machine of ours.
I've already tested the main geometry by 3d printing the parts and it is all working perfectly. Flow, pressure and current draw are perfect.

Now, the real deal is to move up this design and make it suitable for injection molding.
We mainly pump milk, and water with cleaning agents (alcaline and acid solutions).

The Idea was at first to make the simplest design we could since the annual units we will need are not that high. Around 100 units per year.
In regards tot his my first idea was to make the housing, lid (housing) and impeller out of polypropylene plastic, and that would be mounted on top of the motor through a flange.

The idea was to thermofuse accessories to the body according to our needs.

Picture attached.

Main plastic parts are basically three. The housing, lid and rotor. The original idea I had was to make everything in polyurethane rubber (Sh90 or around that) and everything sandwiched between two steel flanges so I wouldn need to use any seals.

Then my idea migrated to what's printed, and make everything in polypropylene and fuse accesories.

Now, the question comes to this.
I think it is viable to stick to this idea, but I'm not sure if it is adviceable to change to something like this other design.
Picture attached.

What do you think it all comes down to?

I'm open ot any ideas..

Gonza.

1503-44 · Sep 19, 2023

If its works, don't fix it.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

Gonzalito · Sep 19, 2023

Well, this is not a final design.

I need to replace the 3d printed parts for more "industrial" grade materials and so improve durability over time.

EdStainless · Sep 20, 2023

First you have to select materials that are approved for use in food production.
And then you need to make sure that they will hold up to the cleaning chemicals.
And then you need to make sure that your design does not have crevices or corners that could trap material and make them hard to clean.
People typically buy these items and are happy to pay high prices for them to assure that they meet all of the requirements.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

Gonzalito · Sep 20, 2023

Polypropylene would be a good material, at least in the chemical resistance regard.
Solutions are alkaline first followed by acid when cleaning the machine and contact time is also short.

In terms of mechanical resistance and rigidity I think it would also be well suited since the pump has low head and flowrat which in terms I might think that I ternal stresses are low. I'm not an expert in this but it is what intuition tells me.

Polypropylene would also allow me to make.a simpler housing and fuse the accessories needed for each case.

If I'm wrong please advice me.

btrueblood · Sep 21, 2023

PP would likely work ok for awhile. When we (company and crew I once worked with) had a milk delivery system to engineer, we sourced everything from a manufacturer who rated things per NSF sanitary requirements, and/or 3-A standards (ref. USDA grade A for dairy systems). One thing we struggled with is that we had to run very high pH to ensure complete removal of proteins/fats and very low pH for removal of calcium deposits, in order to achieve good clean in place hygiene. Not many polymers can withstand that unless fluorinated.

Gonzalito · Sep 21, 2023

That's really interesting btrueblood..

The machine that uses this pump also receives cleaning treatments as you mention. They are short timed, but specified as you say. Daily an alkaline solution is used for fat deposits removal, an every three days or so, an acid solution. Each cleaning process takes about 7 minutes of recirculation, and also rinsing in between wash cycles.

In this case the machine is used for animal feeding so standards may not be as high grade as for human food processing.

EdStainless · Sep 21, 2023

The advantage of using human food grade products is that they are proven in this service.
Finding polymers that will handle both high and low pH is a very short list.
When a material is attacked it will get rougher, and them material will stick to it more making it harder to clean.
Keep in mind that sometimes it is the filler that is being attacked.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

btrueblood · Sep 22, 2023

"In this case the machine is used for animal feeding so standards may not be as high grade as for human food processing."

Fair enough. We went a bit beyond the standard, since our product was directly customer facing, and a customer seeing chunks of calcium deposit (or worse) dropping into their cup would probably not be happy.

What Ed said applies too, the finish of the parts (and the mold releases and machine lubricants on the surfaces) wear off over time, and the parts get stickier. We tested our system to the equivalent of about 10 years service life time.

Gonzalito · Oct 9, 2023

Thanks everyone.

In regards to this, we have advanced in conversations with an injection molding company and we have agreed that in should advance in the overall design and present it to them so they can give us a better insight regarding the injection capabilities.
In terms o materials they told me we can do pretty much anything. From polypropylene to fiber embedded polyamides. Basically there is no limiting in that regard.

In terms of connections we will go for threaded connections, BSPP.

I'll let you know how everything goes.

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Pump design - Plastic injection - Design advice

Gonzalito

Mechanical

Recommended for you

1503-44

Petroleum

Gonzalito

Mechanical

EdStainless

Materials

Gonzalito

Mechanical

btrueblood

Mechanical

Gonzalito

Mechanical

EdStainless

Materials

btrueblood

Mechanical

Gonzalito

Mechanical

Similar threads

Part and Inventory Search

Sponsor