Moly Grease vs. Lithium: What’s the Big Deal?

Molybdenum disulfide (Moly) is a solid additive, most commonly used in extreme pressure applications. The Moly particles are intended to fill in tiny imperfections in the machined surfaces and protect against “welding” during shock loading and heavy loads; however, the material is also known to stick to surfaces and cause a coating to build up. There are a few different explanations for why Moly is used in greases. Some say this is to coat the moving parts in a bearing and protect them when they run out of grease, which would prevent wear. Others say that the Moly actually coats abrasive contaminants to prevent them from scoring the moving surfaces inside of the bearing. Whatever the application-specific reason is, Moly is used because it sticks to other materials and helps protect bearings that are not lubricated consistently.

Automatic lubrication solves the problem of inconsistent lubrication by reducing the human element. Automation allows the lubrication events to be scheduled and monitored so that consistent lubrication is virtually guaranteed. The automatic systems apply a small replenishing volume of grease, keeping a constant film of lubricant between the contact surfaces of the bearing. No more missed grease points, no more lost time and no more dirty grease guns on the floor. With automatic lubrication, there may not be the same need for Moly because every bearing will receive the grease it requires to keep it lubricated and purged of contaminants.

At Graco, we recommend that any grease used in our automatic lubrication systems be limited to 5% solid content or less. Moly is a solid. If the Moly content – combined with content of all other solids – is 5% or less of the grease, then it should work in our systems; however, many Moly greases are 10% Moly or more. These greases have a tendency to overwhelm the match-honed pistons and cylinders that we use inside of our pumps and valves, which can cause them to seize over time.

Graco is a product- and solution-oriented company, not a grease company, but we do offer a grease for the convenience of our customers. This is a solid-free lithium complex grease, and there is a reason for this. Grease compatibility is an issue because of what can happen when two incompatible greases are introduced to each other. This is important to consider when refilling a reservoir that already contains grease. Lubrication grease is a mixture of oil and soap or another thickener. The portion of the grease that determines the compatibility is the thickener. Lithium complex is the thickener that is most compatible with other thickeners. There are only a few other thickeners that are not compatible with lithium complex, when using one of the Graco greases.

Ultimately, Graco does not make recommendations for the grease used in a given application because choosing the right grease is really up to the equipment manufacturer and the customer. But where our pumps and valves are concerned, Graco recommends keeping the total solid content at 5% or less, including Moly content. This will help to ensure a long, dependable life from Graco industrial lubrication products.

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