Large acme nut material selection help

I’ve been asked to make some parts for a lift that includes a brass nut. The shaft it lifts is stainless steel 2.5 inch acme thread. The costumer wears these out in about 5 to 6 years. They would like me to make something that will last longer.
The original nut looks like yellow brass and I think it was cast, then machined. They don’t want to wear out the shaft because that is even more problems and cost. This is an outdoor application on an irrigation gate. They have been smearing grease on the shaft for lubrication , but dirt and sand blow into the grease and make an abrasive.
I’m looking for advice on what material to make the nut out of, and what kind of dry lube might work in this application.
I was thinking aluminum bronze from a cost vs strength view.
Any advice would be appreciated.
RT

I think that Aluminum Bronze would be a good choice.
Is there any way to cover it with a Bellows to keep dirt out?

You might be on to something with the idea of covering the shaft.

mc3608 said:

I think that Aluminum Bronze would be a good choice.
Is there any way to cover it with a Bellows to keep dirt out?

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We do big internal acme threads for valve actuators. Customer supplied material. They are made out of aluminum bronze.

A customer of mine asked me to make some 2 1/4"-4 acme nut blocks of acetal. I'll be interested in learning how long those last. Same deal, 2 1/4-4 acme stainless rod.

If you can't manage to cover the shaft maybe you can use a wiper.

Yep, a wiper is what I am thinking as well. Make sure to use a two-way wiper to keep the grease IN on your nut side as it moves along the rod. Additional grease will still need to be applied occasionally but it will reduce the need for that.

Try the shaft bellows. 5-6 years is a pretty good life, nothing is going to last for ever

Vesconite? Will work better wet, dunno about strength.

Brass is certainty not the right material. Bronze, C932 or similar, is the traditional choice. And yes, wipers and a grease nipple in the nut. Best if one can install rubber boots or bellows around the screw, one below and one above the nut.
The life time means very little as it depends on the load, the environment and the duty cycle. Six years can be very good or very bad.