Grease

These polymers are more expensive than other plastics such as polyethylene, but in special applications, they fulfill exceptional needs. 

Lithium soap greases with added M0S2 are generally superior to the base lithium greases in wear reduction, lubrication, and mst prevention. In systems where the lithium soap acts as an EP lubricant, the M0S2 has little effect on the grease. The amounts of M0S2 added vary fi-om 0.25% to up to 25%. 

Gas under pressure can act as a lubricant. What factors affect the lubrication qualities of a gas  

What are the advantages and disadvantages of gas lubrication compared to normal liquid lubricants  

The analysis of trace metals in oils can be an indication of excessive wear. Explain. 

Refiners prepare lube base stocks from residual oils by removing asphaltenes, aromatics, and waxes. Lube base stocks are hydrofinished, blended with other distillate streams for viscosity adjustment, and compounded with additives to produce finished lubricants. 

Solvent-based processes for removing asphaltenes, aromatics and waxes were discussed in Section 2.2. The next few paragraphs give a quick overview of catalytic dewaxing. 

Catalytic dewaxing (CDW) was developed by Exxon Mobil in the 1980s. The process employs a shape-selective zeolite called ZSM-5, which selectively converts waxy n-paraffms into lighter hydrocarbons. 

The Isodewaxing Process, commercialized in 1993 by ChevronTexaco, catalytically isomerizes n-paraffms into iso-paraffins. This decreases the wax content and increases the concentration low-viscosity hydrocarbons, both of which are desirable. Isodewaxing also removes sulfur and nitrogen, and it saturates aromatics. Products have a high viscosity index (VI), low pour point, and excellent response to additives. 

Catalytic dewaxing and Isodewaxing are discussed in more detail in the second volume of this book. 

Before immersing the steam delivery tube into the test lube, steam should be passed through the delivery tube until condensation in the tube cea.ses. 

The steaming rale should be so adjusted as to double the volume of the contejits of the lube in 4-6 miiiule.s. 

The end of the delivery lube dipping into tlic oil should be cut at an acute angle and should rest at the bottom of the test tube so that no portion of the oil escapes agitation. 

Nolc Tlie iinporlaiice of these stnlic tests in industry has considerably decreased. Tiiey have been replaced with a Dyn.iniicDeniulsibi lily Test which measures the ability of an oil to separate from water under actual circulating conditions and correlates better with practice 

Name some. specific JubricanLs which must have high water separation 

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Greases may contain soaps of lithium, calcium, sodium, aluminium, etc., or they may be non-soap greases. 

Non-soap greases using finely divided solids as thickeners are useful as lubricants at elevated temperatures. Materials used include organO Clays such as dimethyldioctyl-decyl-ammonium bentonite (Bentone greases) or selected dyestuffs which produce brightly coloured greases. 

M.p. SS C, b.p. 2I0 C. Important fatty alcohol obtained from naturally occurring glycerides. Used in the pharmaceutical and cosmetics industries and as a gel stabilizer for greases. 

During the formulation of an oil, blending of all these components gives an extremely wide variety of products described in the classification. Nevertheless, the lubricating greases make up a special product category among them. 

Using one or another type depends on the desired properties for the grease, in particular the high or low temperature properties. 

The great number of possible associations between the types of liquid lubricants and gelling agents results in many different categories of greases ... 

Within this category, the greases are divided into those based on simple soaps and those based on complex soaps. The latter generally have better high temperature and structural stability properties under high mechanical shear they also have higher resistance to water than their simple soap-based counterparts. 

Lithium hydroxide with 12-hydroxy-stearic acid (or hydrogenated castor oil) they form the family of lithium greases very commonly used for general lubrication and bearing lubrication. 

Lime with tallow-derived fatty acids they are the so-called calcium greases that are often used as subframe greases and water-resistant greases. 

Sodium hydroxide with stearic acid they constitute the sodium greases, used in the lubrication of bearings under dry conditions and gear trains. 

The complex greases are obtained by the reaction of bases with mixtures of organic and/or inorganic acids. The three groups of complex greases are ... 

Calcium complex soap greases, obtained by the reaction of lime and a mixture of fatty acids and acetic acid. These greases offer good high temperature and anti-wear/extreme pressure properties related to the presence, in the soap, of calcium acetate that acts as solid lubricant they have good mechanical stability. 

Aluminum complex greases, obtained by the reaction of aluminum isopropylate with a mixture of benzoic acid and fatty acids. These greases have a remarkable resistance to water, very good adhesion to metallic surfaces, good mechanical stability properties and resistance to temperature. They are less common than the first two types. 

Greases Mechanical and rheological behavior and its persistence Consistency and viscosity Mechanical stability Oxidation resistance... 

There are numerous tests for characterizing the mechanicai properties of iubricants cone penetration of greases, extreme pressure tests (as in the four-ball test), etc. 

Antirust properties (greases) NFT 60-135 Rust spots on bearing after test... 

Apparent viscosity (greases) NFT 60-139 ASTM D 1092 Forced passage of the grease in a capillary tube... 

Cone penetration (greases) NFT 60-132 ISO 2137 ASTM D 217 Penetration of weighted cone... 

Dropping point for greases NFT 60-102 ISO 2176 ASTM D 566 Heating up to the fail of the first droplet... 

Sulfated ash in lubricating oils in greases NF T 60-143 ISO 3987 ASTM D 874 NF T 60-144 ASTM D 128 Weight of residue after treatment of the ash by sulfuric acid and calcination As above... 

Modem UHV chambers are constmcted from stainless steel. The principal seals are metal-on-metal, thus the use of greases is avoided. A combination of pumps is nomially used, including ion pumps, turbomolecular pumps, cryopumps and mechanical (roughing) pumps. The entire system is generally heatable to 500 K. This bakeout for a period of... 

It is often advisable to lubricate ground-glass joint surfaces with an extremely thin film of vaseline. This applies particularly to joints employed in assemblies for distillation under reduced pressure. For distillations under greatly reduced pressures or at very high temperatures it is essential to employ a special lubricant, e.g., silicone grease. 

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