Grease is a complex of 4 items...
base complex..
tackifier...
base oil....
additives...
When looking at any grease all parts are equally important.
Unfortunatly a lot of consumers are told by sales people that the tac of a grease as the main component that makes grease better than others.
Some demos to show how tac holds up is by putting a dab of grease on a surface, then smacking it with a hammer to show how the tac hold's the grease in place (and hoping the grease being tested doesn't splatter all over you). Another way, is to take a dab between your fingers and pulling them apart. This too will show how much tac is used. In that little test, you can actually count the amount of "strings" or "fibers" that stay attached. This too would prove the same basic point as smacking it with a hammer.
Tac is there to hold the grease in the bearing.
The complex also plays a role in a good grease.
There is many complex's available and used by grease manufactures.
1. Lithium
2. Lithium 12-Hydroxysterate
3. Lithium Complex
4. Calcium
5. Calcium 12-Hydroxysterate
7. Calcium Complex
8. Barium
9. Barium Complex
10. Aluminum Complex
11. Bentone
12. Polyurea
Now the most popular complex that you will see used is the lithium complex. Almost everyone has a tube of lithium in their shop.
So what does that do? It holds the base oil used as the lubrication for the bearings. Oil cannot just be poured over a bearing as it would simply run out of the bearing, therefore the complex holds it in place until it is needed. As the complex heats up it allows the oil to dispurse and lubricate. As the complex cools back down it is suppose to absorb the oil back into the complex. Here is where it starts to get sticky.. This is called reversability. This is a measurement of how well the complex can take the oil back into the complex. If the complex cannot take back in to oil, then the oil will seep out and leave nothing but the complex and tac. Example of this is when you pulled the cap off the front wheels of your car or boat trailer and see the wax buildup in the little cap. So this is a very important part of a grease as it is what maintains the grease together.
More on the complex, Why so many different types?, There is certain applications needing certain types. Extreme high temps like 900degs would use a bentone(clay base) grease.
Here is one of the biggest problems that a grease has and many have experienced this..
Ever see a grease turn milky looking? Alot of people have, especially the ones sitting on the side of the road with wheel bearings wiped out.
The cause, water mixing with the complex. The most popular complex (lithium) tends to do this more than some others. Lithium complex is a soap base and will emulsify with water or retain water in the complex thus the milky color. Of course water has what kind of effect on metal parts? Another thing water does is thin out the complex and then the oil will milk up and then the complex cannot retain the oil.
To see what I'm talking about try this.. Take a dab of grease in the palm of one hand and put some water on it. Now with your index finger, mix the water into the grease and see how it turns milky and if enough water milks in, it will start to actually thin out or breakdown.
Consider that most equipment sitting outside, or expose to high levels of cold and heat will be affected by moisture.
These are some of the reasons I will not use this complex myself. Unfortunatly most bearing manufactures tell you that lithium is what they recommend and of course it is easier to obtain at just about any parts house.
Now alot of people think that if it is a synth grease as many are now adays, that it will perform better. Well, just like motor oils, if extended drains are needed or extreme temps are met, then a synth will be a good option but in most cases where grease is used, I find, your application is more frequent due to the water washout and such and that if the complex washes out so does your synth oil. There fore, alot of wasted money in that case. No, I'm not saying that synth is worthless but with a high moisture application such as a boat trailer or in cooling systems where high moisture is present, using a lithium grease it is.
Ep additives is another part of a good grease. There is extreme pressures present in all bearings as all the weight of your equipment is riding on the bottom of that bearing thus it will squeeze out the hydrodynamic properties of any oil thus relying on the barrier additive properties of the grease. Most use a zddp or zinc type of additive and then some of the more expensive use moly. Now again, both work well, moly seems to provide a better barrier than zinc under really extreme pressures as well as moly has a higher resistance to heat. Again though, If your complex washes out, the barrier additive does as well.
Are you starting to see where the complex can dictate a better grease than just tac? I have seen some greases with dang near pure tac and it looks like bubble gum. Problem though is when the complex washes out taking the oil out, you have bubble gum in your bearings with no lubrication.
The more tac needed, the less lubrication(or oil) is usually the case, so depending on your bearing speed, determines the tac. the higher speed bearings tend to use less tac whereas the slower ones can have more.
If you want to avoid water wash out use an aluminum complex grease with moly and it will not mix with water thus lasting longer and you ultimatly don't have to grease as much and end up using much less over the period of a year and end up saving you money in the long run. Also aluminum complex will mix with any other base complex with exception to a bentone which wont mix with anything.
Well, that is grease 101.
[ May 31, 2002, 08:44 AM: Message edited by: BOBISTHEOILGUY ]
