How effective are materials for good wear in a dry-running air motor?

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In summary: The author is considering whether a gear pump arrangement would do the job - it only needs to output 6 shaft watts, but they are concerned about wear. There are standard gears avalable in steel and delrin, and with a bit of searching, in ceramic.
  • #1
Mike_In_Plano
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Hello,

I'm puzzling over the likelihood of building a dry-running air motor for 25khrs @5-20kRPM.

I'm considering whether a small gear pump arrangement would doe the job - it only needs to output 6 shaft watts, but I'm concerned about wear.

Standard gears are avalable in steel and delrin, and with a bit of searching, in ceramic. I'm wondering what would be a good combination of materials between the endplates and gear. It seems that the endplates would have to be under a bit of compression to ensure that the air leakage doesn't become excessive over time.

Does this seem a reasonable conjecture?

It also seems the endplates would be a complimentary material:
Steel vs teflon loaded delrin plate
Ceramic vs teflon loaded delrin plate
Delrin vs Hard steel

Finally, how would one go about accelerating wear testing?

Well, I guess that wraps it up (and then some :)

Best Regards,

Mike
 
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  • #2
The bearing material makers often have data sheets showing wear rates. Tho it can depend on speed as well as pressure and countersurface material. They may just show a few data points and leave you to guess the rest.

I see Dupont has a lot of leaflets online about Delrin's wear characteristics.

I'm kind of amazed at running a gear pump so fast. You can't use a centrifugal pump? You'd avoid a lot of the sliding sealing surfaces.
 
  • #3
You have no single chance with a dry plastic bearing at 25,000/min. It would melt.

In case this is a matter of vapour pressure, some lubricants have an extremely low one. Use with plain bearings of sintered metal.

You may try with unlubricated ceramic ball bearings.

An other direction is magnetic bearings.

Or could you maybe use the pressurized air in a set of "aerostatic" bearings? Similar to hydrostatic ones, with big leaks, connected in series with your engine?
 
  • #4
Thinking again at the aerostatic bearing...

Let's imagine your engine can be a centripetal turbine (you didn't mention that). Then you might inject the air at the periphery, use some of its energy contents to rotate the turbine, and let the air exit through the shaft at the bearings, where the remnant pressure gives lifting and centring force.

Maybe it doesn't fit your needs, but it's puzzling.
 

1. What are the most important properties to consider when choosing materials for good wear?

The most important properties to consider are hardness, toughness, ductility, and resistance to wear and corrosion. Hardness is important because it determines a material's ability to resist scratches and wear. Toughness is important because it measures a material's ability to withstand impact and shock. Ductility is important because it measures a material's ability to deform without breaking. Resistance to wear and corrosion is important because it determines a material's ability to withstand environmental factors that can cause it to degrade.

2. How are materials tested for their wear resistance?

Materials are tested for their wear resistance through various methods such as abrasion testing, impact testing, and corrosion testing. Abrasion testing measures a material's ability to resist being worn down by constant rubbing or scraping. Impact testing measures a material's ability to withstand sudden impacts or shock. Corrosion testing measures a material's ability to resist degradation from exposure to chemicals or other environmental factors.

3. What are some examples of materials with good wear resistance?

Some examples of materials with good wear resistance include metals such as steel, titanium, and aluminum, as well as ceramics, composites, and certain types of plastics. These materials have high hardness, toughness, and resistance to wear and corrosion, making them suitable for applications that require good wear resistance.

4. How can the wear resistance of a material be improved?

The wear resistance of a material can be improved through various methods such as heat treatment, surface treatments, and alloying. Heat treatment involves heating and cooling a material to alter its microstructure and improve its properties. Surface treatments, such as coatings and plating, can also improve wear resistance by adding a protective layer to the surface of the material. Alloying is the process of adding different elements to a material to improve its properties, including wear resistance.

5. What factors should be considered when selecting materials for good wear?

When selecting materials for good wear, factors such as cost, availability, and intended use should be considered. Some materials may be more expensive or difficult to obtain, but may offer superior wear resistance. Additionally, the specific application and environmental conditions in which the material will be used should also be taken into account to ensure that the material will perform well under those conditions.

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