Material to slide on Stainless Steel 3

[christianstehle]

I have the following problem:

A slab gate (in a dam outlet) is guided by bronze guide plates sliding on stainless steel guides. The gate jerks when it is operated, and I suspect this is caused by galling between the two materials.

Does anyone have any suggestions on what material to use in stead of bronze. The contact pressure is about 20 MPa and the relative movement is slow.

Thanks
Christian

 

[insideman]

I would think that UHMWPE would be a good choice.

 

[TVP]

If the temperature is low (as room temperature, ~ 25 C) then UHMWPE sounds like a good option. Elevated temperatures would probably require PTFE.

 

[insideman]

I disagree. PTFE is too soft and cold flows too much.

 

[christianstehle]

Thanks for the suggestions guys. I will investigate the material properties before making any decisions.

 

[joro]

You may want to look at acetals such as Delrin.

cheers
joro

 

[Hush]

Providing the cost isn't prohibitive you may be better off changing the gate guide material. Low hardness 300 series stainless will gall easily.

 

[Lakeshore]

Are you confident that the actuator you are using to move the slab gate isn't causing the "jerking"?

 

[gentcho]

The jerking is self-exited oscilations in the elastic system of the gate and actuator caused by the falling characteristic of the friction in relation of the velocity between plates and guides. To avoid the oscilation you need to minimize the diference between friction at rest and friction at motion. If is possible first try MoS2 grease or change the sliding with rolling. The increasing of the stiffness of the actuator increases the frequency of oscilations above the free vibrations frequency of the system.
cheers
G

 

[diamondjim]

They have some anti galling coatings.
Would this be too simple a reply?

 

I think the issue you are having is due to copper precipitation. If you run Stainless on Ally/Bronze in an un-lubricated condition you get the copper being drawn out the Ally Bronze and deposited on the stainless steel. This causes a similar material galling problem. the only way to overcome this is to separate the materials by lubrication or by a bearing. If you cannot lubricate (the easiest option) then physical separation is the best option. PTFE as suggested by some does not have the best properties in water, most of the PTFE's that are OK in water, are not the best for bearing. Other plastics such the Ultra High Weight polymers are much better in water, and could be considered. Acetals do not have the best wear factor around, and most unmodified Nylons will not be great. One branded material I found you may want to try is Ertalyte TX

 

[flamby]

The bronze plate and Stainless steel combo is not there by any bad design. These are tested materials and you will also find them on a lot of hydraulic gates.

What is causing the problem, I dont know for sure but I want to bet my few cents on lack of lubrication system spelled "bad maintenance". The guys are probably not following any maintenance schedule specified by the designer. The another possibility is poor construction where the contracter has not adhered to the specified tolerances. So I urge you, not to blame the material, but to do a little bit of investigation on what the real cause of the problem is.

 

[christianstehle]

Thank you very much for all the valuable input!!

Just to add a little information on the design of the system. There is no lubrication between the materials, the bronze strips on the stainless steel actually form the liquid seal.

The observation that the actuator could cause the problem is possible, but there are definite signs of galling (visual). The friction was such that the bolts holding the bronze strips sheared off.

Anti galling coatings could be a solution. To change the design of the system will be very expensive (the gate is situated 80m down an intake tower).

As a matter of interest, the dam is Sterkfontein Dam in South Africa.

Cheers
Christian

 

[Mandrake22]

Christian,

You might try Nitronic 60 for the stainless elements. Here is some data:

NITRONIC 60 Wear and Corrosion Resistant (UNS S21800) Registered trademark of ARMCO ADVANCED MATERIALS CORPORATION

This alloy provides a significant lower cost way to fight wear and galling compared to Nickel or Cobalt based alloys. Its uniform corrosion resistance is better than 304 stainless in most environments. The yield strength of Nitronic 60 is nearly twice that of 304 and 316 stainless steels. Chloride pitting resistance is superior to that of type 316 stainless; Nitronic 60 provides excellent high temperature, oxidation resistance and low temperature impact.

Applications using Nitronic 60 are valve stems, seats, and trim, fastening systems, screening, pins, bushings and roller bearings, pump shafts and rings. Other uses include wear plates, rails guides, and bridge pins. Call High Performance Alloys for an Armco brochure on either of these Nitronic high performance stainless steel alloys.

NITRONIC 60 TYPICAL CHEMISTRY

C Cr Fe Mn N Ni Si
.005 17 63 8.0 .13 8.5 4.0

NITRONIC 60 TYPICAL ANNEALED AND COLD REDUCED MECHANICAL PROPERTIES

(1"annealed bar and 1.75" 50% cold reduced bar, smaller bar can be produced to even higher strengths)

UTS KSI YS KSI ELONGATION R/A HARDNESS
103-195 60-153 64-20% 74-57% B95-C38

Here is a Ryerson link:

http://www.ryersontull.com/stocklist/RedbookServlet?COM=GetTable&ID=1587

 

[ArtFabrication]

You might consider a glass saturated composite like Vespel, almost all wear parts for dairy processes use Vespel due to the low friction and wear properties. It also can take a tremendous load without fracture.

 

[Artty]

You may want to look into wear-comp a material that can be made into what ever size liners that you desire. It is a lubrication free and pretty much dust free material. The name of the company is Hycomp Inc. out of Cleveland Ohio 216-234-2002

 

[butelja]

Vespel is the Cadillac (No, make that the Mercedes (not Daimler-Chrysler)!!) of non-metallic bearing materials. Where nothing else will work, it probably will. Its PV values under lack of lubrication and at high temperature are pretty much unmatched. It is priced accordingly, even making PEEK look inexpensive! If you need it, then it will work well as long as you stay within DuPont's comfort zone for its application.

 

[GRPatel]

How about trying PEEK. It is a substitute of PTFE and better in many ways! You can visit:

http://www.ghardapolymers.com

 

[Traveller]

In the marine industry, there are two non-metallic products that I know of that may be right for your application:

1. Thordon is marketed by Thordon bearings, Inc. 3225 Mainway, Burlington, Ontario, L7M 1A6. It's claimed by the maker to be the best material for service in highly abrasive environments with minimal boundary lubrication. This material is a monolithic polymer of proprietary formulation, and I don't think it's available as a reinforced polymer, but check with them if you want a reinforced material. Thordon is used as a bearing shell liner in water-lubricated propeller shaft bearings (known in the maritime trade as "cutless" bearings). Another application is in water-turbine shaft bearings, where the operating conditions are similar to propeller shaft bearing conditions.

Thordon has a website at:

http://www.thordon.com/

2. Another material is called "Orkot", sold by the Orkot Corporation, 2535 Prairie road, Unit D, Eugene OR 97402. It consists of a woven-glass fiber reinforcement that's embedded in a graphite-filled polymer matrix. The operating conditions and applications are similar to those in 1. above.

Here is an excerpt from an Orkot ad:

"Orkot is a thermoset composite material reinforced by impregnating fabric with thermosetting resins. The result is a material with excellent strength, impact resistance and dimensional stability. The precise formulation of Orkot can be varied to suit specific applications, but all grades have outstanding chemical and mechanical properties. An extremely low coefficient of friction, high PV limit, and superior wear performance makes Orkot a supreme bearing material, particularly when working with heavy loads. With virtually no water absorption or swelling in water, Orkot is a perfect material choice for wet applications. Orkot is commonly used for Offshore Marine bearings, bushings, thrust washers, wear pads and wear rings."

Orkot is marketed by San Diego Plastics who have a comprehensive website at:

http://www.sdplastics.com/orkot.html

This site has all you need to evaluate the material for your application.

These materials are used in applications very similar to yours (water-immersed, high-pressure, boundary lubrication, slow speed) and I believe they're both very good candidates.

 

[busakshamban]

Orkot is marketed by Orkot, which has a manufacturing plant in the US and in the UK (Orkot Marine). Orkot is a superior material for marine bearing applications. San Diego Plastics is merely a distributor of the material, one of many. For the most comprehensive and up to date information visit the Orkot website directly.