Discover the process of crafting high temperature grease – from ingredients to production methods. Learn more about this essential industrial lubricant.
Grease is used to reduce the friction and wear between the moving parts of machinery. When the operating temperatures are high and to lubricate a piece of hot equipment you need grease that can function under extreme temperature conditions.
For example, in a steel mill, the bearings are exposed to temperatures of several hundred degrees like 120° C – 150° C. In such a situation, the grease will need exceptional mechanical stability, oxidation stability, load-carrying capabilities and water resistance. The price also has to be suitable as the grease will be used in large volumes.
When used in high-temperature applications grease will degrade through thermal stress and oxidation failure if it is in contact with air. In such a situation, you need a high-temperature grease.
Various applications require different types of grease with different properties and compositions. Grease is made up of 85% of base oil, 10% of thickener and 0% – 5% of additives.
The important point to consider in base oils is their performance properties. Base oil is divided into synthetic and mineral oils. Mineral oils are the most widely used to make grease. Nearly 95% of greases are manufactured using mineral oils, followed by synthetic esters and synthetic hydrocarbons (PAO) followed by silicon and other synthetic oils.
Some of the base oils are polyesters, diesters, fluorinated silicones, chlorinated silicones, perfluoroalkyl ethers, phosphate esters and polyglycols.
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Thickeners can be organic, inorganic or soaps/metal soaps and the selection of a thickener depends on the application. Organic thickeners can be polyurea, calcium sulphonates and more. Inorganic thickeners can be fumed silica, clay and more. Soaps can be calcium stearate, sodium stearate, lithium stearate, aluminium or calcium sulphonate complex and more.
Tungsten Disulphide (WS2) particles are used because they are inert, non-toxic, non-magnetic and have high resistance to thermal and oxidation degradation.
The additive should be able to work with the thickener and the base oil to get a balanced and stable mixture. The additives impart properties like corrosion resistance, oxidation stability, wear resistance, water resistance and low-temperature flow characteristics.
The different manufacturing processes used to make grease are open kettles, pressure kettles, contactor vessels and continuous processes.
This is the simplest but not the most efficient process for manufacturing grease. The kettles have a flat unsealed lid with the inside of the kettle being at ambient pressure. The processes like saponification, dehydration and finishing take place in the kettle.
The fatty acids, base oils, alkali metal hydroxides and water are charged into the kettle. Partially blended grease is removed from the bottom of the kettle and again added to it from the top. Once the components are well blended the grease is sent to a mill. In the mill, soap thickener is dispersed throughout the mixture. It is then sent to the kettle to be packed and stored.
This process takes advantage of the faster saponification process that takes place at higher pressure. The pressure kettle has a sealed lid and is designed to contain higher pressure. The high pressure is due to the steam given off during the reaction.
The pressure kettle is used for the saponification process and then the mixture is sent to an open kettle. The open kettle process is followed to make grease.
In this, a specially designed contactor vessel is used for the saponification process. The vessel is charged with a base oil, a small amount of water, fatty acid and alkali. The steam from the reaction is used to pressurise the vessel.
Once the reaction is completed the grease is sent to the finishing kettle where the rest of the base oil and additives are added. The output is then packed.
This process offers many advantages over batch processes. The equipment used to make grease of the same amount is smaller. It offers better control over the process and helps to produce a consistent output.
In this process, the base oil, the heated fatty acid or ester and the alkali solution are charged into a reactor. The materials are circulated at high temperatures and high pressure till the reaction is completed. The mixture is sent to a flash chamber where the grease is dehydrated.
Additives and additional base oils are added to it. The mixture is moved to the finishing section and packed.
Grease manufacturing is considered to be an art and the better control you get over the raw materials, reactions and processing conditions the more consistent the output from batch to batch.