Originally Posted by lawkd
Pete, I really appreciate all the facts you have dug up on grease. This topic is a passion of mine. Regarding the benefits of polyurea-based grease and how it compares to others, below is an excerpt and a link I found (and posted about) last year when I researched this topic to exhaustion. Based on what I found, namely that calcium sulfonate complex grease compares very favorably to polyurea in every way, I decided to keep using Lubrimatic Marine Wheelbearing grease from Home Depot. Easy to get, very inexpensive. If Park Polylube were as easy to obtain without paying a shipping charge that effectively doubles the cost, I'd probably buy that instead, but for under $3 a tub and available a few blocks away, the Lubrimatic is hard to beat. I also agree with sentiments expressed above, that probably the most important element in maintaining bearings, is keeping the grease uncontaminated. No matter how good a grease is, once it's got grit or moisture in it, it has to be changed.
Here's a small excerpt from one of many links I have regarding greases. This one compares calcium sulfonate complex grease with polyurea-based lubricant.
..."The organic polyurea thickener system offers temperature range limits similar to the metal soap-thickened grease, but additionally it has antioxidation and antiwear properties that come from the thickener itself. Polyurea thickeners might become more popular but they are difficult to manufacture, requiring the handling of several toxic materials. While the thickener has a high dropping point, the composition begins to thermally degrade at temperatures which limit its usefulness over time at high temperatures. However, it does not have the pro-oxidant tendencies of the metal soap-thickened greases. The exception is the calcium sulfonate complex thickener system. Similar to the polyurea, it possesses inherent antioxidant, rust-inhibiting properties, but in addition has inherent high dropping points and EP/antiwear properties." ...
http://tinyurl.com/g9cc2 (scroll down half way to "thickeners")
Thank you. Finding good information on polyurea proved to be difficult.
Since you are going to know more about grease than me, I'd like to ask you a few questions.
Everything I've read states that he most important part of a grease is the viscosity of the oil used to make it, high viscosity oil for high speed applications, low viscisotiy oil for low speed applications. Is it safe to assume that automotive greases are made from high viscosity oils? What would the theoretical problems be if you used a grease made of high viscosity oil in a low speed application and visa versa?
I've also heard that aoutomotive greases are becoming increasingy acceptable for bicycle bearings. Is this a function of adding paraffinic oils after cooking the grease? My understanding is that the paraffinic oils added, to back off the apparent viscosity, aren't "trapped" in the thickener like the nepthanic cooking oils, therefore the paraffinic oils are more readily available to lubricate. Or is this because of EP additives that allow the automotive greases to release the oil at a lower load/temp? Or is it because this calcium sulfonate complex is becoming more widely used?
Edit: Is there any merit to the belief that some types of automotive greases don't perform well at the relatively low teperatures seen in bicycle bearings? If so, what greases would those be?
Thanks.