Coefficient of friction stainless steel on bronze 1

[solidman25]

I am developing a worm gear assembly that uses a stainless steel worm and a bronze worm gear in combination. The closest thing I can find in my books or online is steel and bronze which only lists a lubricated value of 0.16.

1. Would you suggest using the steel and bronze value
2. Do you have a good source for a coefficient of friction values that do list a stainless steel and bronze coefficient of friction.
2. Do you know why there is no dry/ clean coefficient of friction value listed for bronze and steel?

 

[gruntguru]

Do you want a static or dynamic friction coefficient? (The one you quoted is probably static). Why dry? Are you going to operate the gears dry? If so, the materials you have chosen would seem to be sub-optimal.

Link
Gives Aluminium Bronze on steel 0.45, Phosphor Bronze on Steel 0.35

je suis charlie

 

[tbuelna]

The un-lubricated material combination you describe for your worm gear set is probably not a good choice. If there is anything more than even a very small load transmitted by the gear set, then you should apply some form of lube - dry film, grease or oil. And if the transmitted load is very small, consider using some type of self-lubricating plastic for the worm gear.

For design purposes, you'll need both the static and dynamic friction values for clean/dry bronze on stainless. The specific bronze/stainless alloy composition can also make a difference. Some free machining alloys contain materials that might reduce friction. The relative surface roughness at the contact interface will also have an effect on friction characteristics. With smooth/clean/dry stainless steel on bronze I don't think you'll get a static friction below 0.30. A static friction of 0.16 for this combination with grease lube sounds like a reasonable number to use for design purposes.

 

[romke]

friction between bronze and stainless steel might be somewhat higher then bronze on steel, both static and dynamic - although i have no real figures.

generally speaking stainless steel would not be the preferred choice to obtain low friction, both in dry and lubricated conditions. one of the prerequisites for lubrication is that the lubricant adheres well to the mating materials involved. adherence to stainless steel is less then with steel. in a wormgear due to the very high sliding between the gears adherence is even more important.

i would not consider stainless steel unless the environment really requires it - it will make lubrication, obtaining a acceptable lifespan and low friction a lot more difficult.

 

[Tmoose]

Is the worm bronze or stainless?

As others said, running oil free will likely be a challenge.
Some machine design handbooks go so far as to say stuff like this -

" Why Not to Use Worm Gears -
There is one particularly glaring reason why one would not choose a worm gear over a standard gear: lubrication. The movement between the worm and the wheel gear faces is entirely sliding. There is no rolling component to the tooth contact or interaction. This makes them relatively difficult to lubricate. The lubricants required are usually very high viscosity (ISO 320 and greater) and thus are difficult to filter, and the lubricants required are typically specialized in what they do, requiring a product to be on-site specifically for that type of equipment. "

If the loads are low enough to consider running oil-free, maybe a self lubricating plastic would be an option.
There are lubricants designed for "open gearing" that stay put pretty well.​

 

[tbuelna]

Tmoose- From the OP, "...that uses a stainless steel worm and a bronze worm gear in combination."