Deciding on a high temperature grease – what to look for

If you’re working in a machinery situation where the temperatures get a little heated, choosing the right grease is a critical choice to get right. How do you make the suitable choice?

The internet has some wonderful resources out there that may help guide you to making the best decision.

One such resource is the Machinery Lubrication web site, where we found a superb primer on all of the factors that you might want to consider in choosing the fitting kind of high temperature grease.

Whenever you’re working in a machinery situation where the temperatures get a little heated, selecting the best grease is a critical resolution to get right. How do you make the proper resolution?

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

One such resource is the Machinery Lubrication web site, the place we discovered a superb primer on all of the factors that it’s good to consider in deciding on the suitable kind of high temperature grease.

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

For the full 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, operating temperature, atmospheric contamination, loading, speed, relubrication intervals, etc. With the variety of details to resolve, the number of greases that must accommodate excessive temperature conditions is a difficult determination, and given potential for incompatibility problems and the high prices for a lot of high-temperature grease, you really must 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 metal mill roll-out table application may be exposed to process temperatures of several hundreds of degrees, and may expertise sustained temperatures of 250ºF to 300ºF (120ºC to ±150ºC). Automotive assemblers dangle painted metal parts on lengthy conveyors and weave them by way of massive drying ovens to dry painted metal surfaces. Working temperatures for these gas-fired ovens are maintained round 400ºF (205ºC). You possibly can see that there is a wide temperature range to consider here.

In these cases, the choice factors differ appreciably. In addition to heat resistance, the grease for use in a sizzling metal mill application might require exceptional load-carrying capability, oxidation stability, mechanical stability, water wash resistance and good pumpability, and at a worth suitable for large-volume consumption. With the entire necessary factors to consider, it is helpful to have a grease choice strategy.

Where To Start?

A reasonable starting level for selecting a high-temperature grease is to consider the nature of the temperatures and the causes of product degradation which are inherent to no matter place you are going to be using it. There may be common correlation between a grease’s helpful temperature range and the anticipated price per pound. For example, a fluorinated hydrocarbon-primarily based (type of synthetic oil) grease might work successfully as high as 570ºF (300ºC) in area applications however may also cost hundreds of dollars per pound. How well the grease holds up long-time period is influenced by the causes of degradation, three of which are particularly necessary: mechanical (shear and stress) stability, oxidative stability and thermal stability. Oxidative and thermal stresses are interrelated. High-temperature applications will generally degrade the grease by means of thermal stress, in conjunction with oxidative failure occurring if the product is in touch with air. This is similar 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 energy of its additive package, that continues providing lubricating protection after different parts of the grease could have broken down as a result 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 supplies that holds the bottom oil collectively like a sponger holds liquid.

Base Oils

When deciding on lubricants for oil-lubricated applications, one often begins with the consideration of base oil performance properties. This can also be a good starting level for grease products. Base oils might be subdivided into mineral and synthetic types. Mineral oils are the most widely used base oil component, representing approximately ninety five % of the greases manufactured. Artificial esters and PAO (synthetic hydrocarbons) are next, adopted by silicones and a few different unique synthetic oils.

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

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

Thickeners

The supplies chosen as the grease thickeners could also be organic, corresponding to polyurea; inorganic, such as clay or fumed silica; or a soap/advanced soap, equivalent to lithium, aluminum or calcium sulfonate complex. The usefulness of the grease over time is determined by the entire package collectively, not just one thing like the thickening system or the type of base oil. For example, a silica grease thickener has a dropping point of 2,732ºF (1,500ºC) as one excessive example. However, 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 could have to choose from might be:

Natural polyurea – offers 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 might become more standard however they are difficult to fabricate, requiring the dealing with of a number of 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.

Calcium sulfonate – similar to the polyurea, it possesses inherent antioxidant, rust-inhibiting properties, but in addition has inherent high dropping points and EP/antiwear properties.

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