I have so many stories about grease over the years that if I posted them all here it would probably double the size of this thread ..........
I'm not going to read the whole thread again so my apologies in advance if some points have already been made. Here's my thoughts. I'll say here and now it is awfully hard to select one grease that will fill all your needs, unless you're lubricating just a couple of machines. In my present job we use 4 different greases for different applications but then again we are looking after about 100 pieces of equipment on one job site.
1. What is the application..?
Slow moving, heavily loaded pins & bushes that don't rotate 360 degrees (Loader pins, ripper pins, etc) are better lubricated with a moly-based grease. 3% moly as a minimum, 5% is even better.
Low speed rolling element bearings would be better using an EP lithium complex grease.
High speed rolling element bearings (such as fan drives) are better using a specific high-speed bearing grease. These greases are often (but not always) synthetics.
2. How is the grease applied..? Hand grease gun..? Power grease gun..? Automatic lube system..?
Each of these forms of applications needs potentially a different fluidity of grease - the NLGI Number, so that you can pump it into the bearing and for it to stay there until the next time you grease. NLGI 000 would be for super Arctic temperatures up to a NLGI 3 for desert application around 50 DegC. A hand-applied grease would normally be an NLGI #2, an autolube would often be a #0 or a #1, but it's very much dependent on ambient temperature. Of course if you hand apply the grease it needs to be less fluid (more "sticky" or "tacky") because it might be 4-8 hours before you grease again, where an autolube system might be greasing every 15 minutes.
As a comment here a lot of people find it totally amazing that a manufacturer can produce 6 different grease viscosities from NLGI 00 to NLGI #3 all
using the exact same ISO VG 220 base stock. The difference in fluidity all comes from the additive package.
3. Mineral-oil based grease versus synthetic..?
The
high quality mineral oil based greases I've worked with from companies like Exxon-Mobil & Shell are every bit as good performance-wise as synthetics such as Molub-Alloy in my opinion, and usually 30-50% cheaper. I went away from synthetic grease a number of years ago except for some very specific applications (fan bearings are one) and am more than happy with the results.
4. Water wash-out and corrosion resistance. If you're in an area where there is a lot of rain or your equipment works in lots of mud you need to consider the resistance of the grease to being washed out of the joint, and also the resistance to corrosion.
5. Heavily-loaded pins. These would be pins on machines like large front-end loaders, big excavators, shovels, etc. A high-performance grease is essential for these pin/bush joints. A lot of my experience is on Cat 994's and similar wheel loaders. We found early on that 5% moly grease wasn't cutting it on its own. We soon came to the conclusion that what was required was a grease that could maintain a lubricant film under extreme loads in 24/7 operating conditions. Here's where the "4-ball weld & scar test" comes in. I won't bore you with how it's done. See ...
http://www.luboron.com/pdf/4BallTestDescription.pdf if you want details. Basically the test gives a result in kilogrammes, the higher the number the better the grease film will resist shearing in the joint and keep the pin and the bush apart, even if it's only by a couple of thousandths of an inch. The length of the scar before the balls weld themselves togehter is also a sign of how well the grease keeps the metal surfaces apart.
Now most typical NLGI # multi-purposes greases will have a 4-ball test load of around 315kg. High performance greases will often give 5-600kg, extra-high-performance greases will be around 800kg.
We found that greases with 5-600kg 4-ball numbers were not doing the job on big loaders and went to an 800kg 4-ball grease. When you might be talking of $3-5000 per pin, plus bushes, plus downtime, plus machining, etc, you can't afford to make mistakes with grease.
The relevant numbers for everything listed above should be on the spec sheet for the grease. If I couldn't find ALL of them I wouldn't even consider buying that particular grease.
I will tell one story here. I visited a mine site where they were having lots of pin troubles on big wheel loaders. They looked well-greased on the face of it, plenty of fresh grease visible, and all the diagnostics on the autolube systems showed that the pumps and injectors were all performing as they should. Head scratching time .......
I asked them " What grease are you using"
"A special grease from Mobil" was the answer
It turned out that the grease they were using was one called "Mobilgrease Special" (well it was special, it said so right there on the barrel...!)
When I looked at the tech spec for it. NO moly additive and a 4-ball weld load of 315kg ....!! Reading the spec sheet it was designed for automotive lubrication on things like a pickup truck. In fact that's how Mobil marketed it but because the customer had gone out to tender for greases accountants not maintenance pros had made the decision what lubricants to buy.
At least we found what was wrong and why they were having so many pin problems. It must have cost them close to $100,000 in parts alone before the problem was sorted.