Selecting a high temperature grease – what to look for

Once you’re working in a machinery situation where the temperatures get a little heated, choosing the right grease is a critical decision to get right. How do you make the proper determination?

The internet has some wonderful resources on the market that can help guide you to making the proper decision.

One such resource is the Machinery Lubrication web site, the place we found a superb primer on all of the factors that you have to consider in deciding on the precise kind of high temperature grease.

Whenever you’re working in a machinery situation the place the temperatures get a little heated, choosing the proper grease is a critical decision to get right. How do you make the correct resolution?

The internet has some glorious resources on the market that may assist guide you to making the right decision.

One such resource is the Machinery Lubrication web site, where we discovered an excellent primer on all of the factors that it’s good to consider in selecting the right kind of high temperature grease.

selecting a high temperature greaseWe’ve referenced much of that information here.

For the total article, check out Machinery Lubrication’s web site here.
What To Consider?
There are a lot of criteria to consider when deciding on a high-temperature grease for decent, grease-lubricated equipment – oil type and viscosity, oil viscosity index, thickener type, stability of the composition formed by the oil and the thickener, additive composition and properties, ambient temperature, working temperature, atmospheric contamination, loading, speed, relubrication intervals, etc. With the variety of details to resolve, the number of greases that should accommodate excessive temperature conditions is a difficult choice, and given potential for incompatibility problems and the high costs for a lot of high-temperature grease, you really have to be selective and discriminating when making the decision of which grease to use.

‘High temperature’ is relative when characterizing temperature conditions. Bearings running in a steel mill roll-out table application could also be uncovered to process temperatures of a number of hundreds of degrees, and will experience sustained temperatures of 250ºF to 300ºF (120ºC to ±150ºC). Automotive assemblers cling painted metal parts on long conveyors and weave them through giant drying ovens to dry painted metal surfaces. Operating temperatures for these gas-fired ovens are maintained around 400ºF (205ºC). You’ll be able to see that there is a wide temperature range to consider here.

In these two cases, the selection factors differ appreciably. In addition to heat resistance, the grease for use in a scorching metal mill application may require exceptional load-carrying capability, oxidation stability, mechanical stability, water wash resistance and good pumpability, and at a value suitable for large-quantity consumption. With the entire vital factors to consider, it is useful to have a grease selection strategy.

Where To Start?
A reasonable starting level for selecting a high-temperature grease is to consider the character of the temperatures and the causes of product degradation which can be inherent to no matter place you are going to be utilizing it. There’s basic correlation between a grease’s helpful temperature range and the expected worth per pound. For example, a fluorinated hydrocarbon-based (type of synthetic oil) grease may work successfully as high as 570ºF (300ºC) in space applications however can also value hundreds of dollars per pound. How well the grease holds up long-term is influenced by the causes of degradation, three of which are particularly vital: mechanical (shear and stress) stability, oxidative stability and thermal stability. Oxidative and thermal stresses are interrelated. High-temperature applications will typically degrade the grease by thermal stress, in conjunction with oxidative failure occurring if the product is in contact with air. This is analogous to what’s to be anticipated with most industrial oil-lubricated applications. Bell Performance’s X-tra Lube Grease provides some advantages in these types of situations because of the residual lubricating power of its additive package, that continues providing lubricating protection after different parts of the grease may have broken down because of these factors in regular use.

What’s In A Grease?
high temperature greaseFor the uninitiated, grease consists of a base oil with a thickener added, plus additional additives thrown in to bulk up certain essential properties of the grease. Think of the whole thing like a sponge – the thickener is the spongy materials that holds the bottom oil together like a sponger holds liquid.

Base Oils
When deciding on lubricants for oil-lubricated applications, one typically begins with the consideration of base oil performance properties. This can be a great starting point for grease products. Base oils could be subdivided into mineral and synthetic types. Mineral oils are essentially the most widely used base oil part, representing approximately ninety five p.c of the greases manufactured. Synthetic esters and PAO (artificial hydrocarbons) are next, followed by silicones and some other exotic synthetic oils.

The American Petroleum Institute divides base oils into five categories based on their performance limits (Groups I-V). They have an inclination to vary by how well they resist thermal or oxidative break down, and the way well they disperse and hold the additives which can be added to the grease product. Generaally speaking, the higher Groups are more resistant but price more.

Mineral and synthetic base oils degrade thermally in conjunction with oxidative degradation if the product is in touch with air. The break point at which the individual oil molecules in a highly refined (Group II+, Group III) mineral oil and synthetic hydrocarbons will begin to unravel, releasing carbon atoms from the molecular chain, is about 536ºF to 608ºF (280ºC to 320ºC). 3,4 The grease manufacturer will choose materials given their familiarity, and perhaps availability, of the raw materials. If the producer makes a particular type of synthetic base fluid and is intimately familiar with the various destruction mechanisms of that fluid, then it is likely that this type of artificial base will often be selected for new product development.

The supplies selected as the grease thickeners could also be organic, such as polyurea; inorganic, similar to clay or fumed silica; or a soap/complicated cleaning soap, resembling lithium, aluminum or calcium sulfonate complex. The usefulness of the grease over time depends upon the whole package together, not just one thing like the thickening system or the type of base oil. As an illustration, a silica grease thickener has a dropping level of two,732ºF (1,500ºC) as one extreme example. Nevertheless, because grease performance relies on a combination of supplies, this doesn’t characterize the helpful temperature range. Some examples of the kinds of thickeners you may have to choose from could possibly be:

Organic polyurea – gives temperature range limits just like the metal cleaning soap-thickened grease, however additionally it has good antioxidation and antiwear properties that come from the thickener itself. Polyurea thickeners may become more common but they’re tough to manufacture, requiring the handling of a number of toxic materials. While the thickener has a high dropping level, the composition begins to thermally degrade at temperatures which limit its usefulness over time at high temperatures.

Calcium sulfonate – much like the polyurea, it possesses inherent antioxidant, rust-inhibiting properties, however in addition has inherent high dropping factors and EP/antiwear properties.

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