Deciding on a high temperature grease – what to look for

Once you’re working in a machinery situation the place the temperatures get a little heated, selecting the best grease is a critical choice to get right. How do you make the suitable determination?

The internet has some excellent resources on the market that may help guide you to making the fitting decision.

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

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

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

One such resource is the Machinery Lubrication web site, where we discovered a wonderful primer on all the factors that it’s essential consider in deciding on the best kind of high temperature grease.

deciding on 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 lots of criteria to consider when selecting a high-temperature grease for warm, 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 number of details to resolve, the collection of greases that should accommodate extreme temperature conditions is a difficult resolution, and given potential for incompatibility problems and the high costs for many 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 could also be uncovered to process temperatures of a number of hundreds of degrees, and may expertise sustained temperatures of 250ºF to 300ºF (120ºC to ±150ºC). Automotive assemblers hold painted metal parts on long conveyors and weave them by giant drying ovens to dry painted metal surfaces. Operating temperatures for these gas-fired ovens are maintained around 400ºF (205ºC). You may see that there’s a wide temperature range to consider here.

In these cases, the choice factors differ appreciably. In addition to heat resistance, the grease to be used in a sizzling metal mill application might require distinctive load-carrying capability, oxidation stability, mechanical stability, water wash resistance and good pumpability, and at a price suitable for giant-quantity consumption. With the entire necessary factors to consider, it is beneficial 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 that are inherent to whatever place you’re going to be using it. There is common correlation between a grease’s helpful temperature range and the expected worth per pound. For instance, a fluorinated hydrocarbon-based (type of synthetic oil) grease might work successfully as high as 570ºF (300ºC) in area applications but can also price 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 important: mechanical (shear and stress) stability, oxidative stability and thermal stability. Oxidative and thermal stresses are interrelated. High-temperature applications will usually degrade the grease via thermal stress, in conjunction with oxidative failure occurring if the product is involved with air. This is analogous to what’s to be expected 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 on account 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 sure 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 often begins with the consideration of base oil performance properties. This can also be a very good starting point for grease products. Base oils will be subdivided into mineral and synthetic types. Mineral oils are probably the most widely used base oil component, representing approximately 95 percent of the greases manufactured. Artificial esters and PAO (synthetic hydrocarbons) are next, followed by silicones and some different exotic artificial oils.

The American Petroleum Institute divides base oils into five classes 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 how well they disperse and hold the additives which are added to the grease product. Generaally speaking, the higher Teams are more resistant but cost more.

Mineral and synthetic base oils degrade thermally in conjunction with oxidative degradation if the product is in touch with air. The break level at which the person 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). three,four The grease producer will choose supplies given their acquaintedity, and maybe availability, of the raw materials. If the manufacturer 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 synthetic base will typically be chosen for new product development.

Thickeners

The materials selected as the grease thickeners may be organic, comparable to polyurea; inorganic, such as clay or fumed silica; or a soap/advanced cleaning soap, akin to lithium, aluminum or calcium sulfonate complex. The usefulness of the grease over time is dependent upon 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 extreme example. However, because grease performance relies on a combination of materials, this does not characterize the useful temperature range. Some examples of the kinds of thickeners you could have to select from could possibly be:

Natural polyurea – presents temperature range limits much like the metal cleaning soap-thickened grease, however additionally it has good antioxidation and antiwear properties that come from the thickener itself. Polyurea thickeners would possibly turn into more in style but they are tough to manufacture, requiring the dealing with of several poisonous 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, however in addition has inherent high dropping points and EP/antiwear properties.

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