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Bentonite grease abrasive properties? #5214432 09/16/19 02:19 PM
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berlyn Offline OP
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Hello fellow Bitogers,

is there any info regarding this point? if the grease thickener is abrasive, will it affect bearing tolerances? I could not find any metrics about the magnitude of such properties.
Any input is welcome,

Regards,

Re: Bentonite grease abrasive properties? [Re: berlyn] #5214499 09/16/19 04:08 PM
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nthach Offline
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AFAIK, bentonite grease isn't used all that much anymore - unless it's a "food-safe" grease such as that used in a KitchenAid stand mixer in the gearbox. It's also specified by some brands of power equipment as a gearbox grease.

Bentonite is the same stuff used in clumping cat litter as well. It does get slippery when wet. I would imagine as a grease, when the bentonite is added, it serves as a sponge and it's micronized to a point where it won't harm a bearing.

Re: Bentonite grease abrasive properties? [Re: berlyn] #5214656 09/16/19 07:49 PM
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RDMgr Offline
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Excellent question, the answer is that clay grease can be abrasive. Clay is a mined product. The particles are extremely fine and in an oil carrier can act like a mild lapping compound or polish. I once ran a 25-pound Timken EP test on a 35-pound OK Load clay grease for ten minutes and then ran the same test on the same grease and test specimens for ten minutes at 70 pounds. The test passed. The 25-pound run polished the contact area improving the contact profile creating closely mated surfaces. This was abrasive wear running in the contact surfaces.

Clays are not used as much as they used to be. They can perform well at high temperatures if the base fluid meets the temperature requirements of the application. However, complex soap greases can also perform well at temperature. A problem with clay grease at elevated temperature is that they can become very abrasive if the operating temperature exceeds the capacity of the base oil leaving a significant accumulation of clay in a bearing. This is sometimes seen in applications like kiln car wheels.

Clay grease is extremely sensitive to cross contamination with other greases with degelling being the primary result.

Re: Bentonite grease abrasive properties? [Re: RDMgr] #5217058 09/19/19 12:40 PM
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berlyn Offline OP
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Hello nthach,
Hello RDMgr,

thank you both for your feedback.

@nthach,

could you please provide some extra info about the brands that specify the bentonite thickener as a gearbox grease? (I imagine it should be NLGI 000 or 00)

@ RDMgr,

thanks for your valuable feedback. Based on your answer, I would assume a good practice to use a clay grease as a priming, run-in and contact pattern check grease in the beginning of the life of an element, then switch to a silicate grease after degreasing. What are your thoughts on this?

Regards,

Re: Bentonite grease abrasive properties? [Re: berlyn] #5219180 09/21/19 08:07 PM
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RDMgr Offline
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Berlyn,

What is your application? You are using terms normally used with large open gears like "priming, run-in and contact pattern". Terms like this are normally used in reference a grinding mill or kiln that you would find at a cement plant. FYI-Greece has a fairly large cement industry.

Re: Bentonite grease abrasive properties? [Re: berlyn] #5219189 09/21/19 08:21 PM
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4WD Online Confused
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Much in the US is mined in Wyoming … being a natural clay no doubt small amounts of silica, volcanic ash, etc could be present. Don’t have a need for it myself …

Re: Bentonite grease abrasive properties? [Re: RDMgr] #5220656 09/23/19 04:08 PM
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berlyn Offline OP
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RDMgr,

Actually not a specific application so far. I stumbled upon this characteristic of the specific grease type while trying to enrich my knowledge of the subject. Based on your input I will avoid the use of the specific type of grease in very small bearings with very tight tolerances.
Yes cement and lignite mining in Greece are big sectors of the industrial production and high melt point lubricants are easy to find. Who would also thought that after USA and China, Greece comes in 3rd place of bentonite export (Milos isl.).

4WD,
I agree that the specific thickener type is not so common as Li, Ca or Ba ones, but there are applications for everything since the pros and cons of the grease are always a function of the application.

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