Lubricating Greases: Composition, Types, and Applications, Diapositivas de Mecánica de Materiales

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ING. ELECTROMECANICA

TOPICOS SELECTOS DE INGENIERIA

RAFAEL ALEJANDRO

GRASAS DE ESPESANTE ORGÁNICO, SIMPLE, COMPLEJO Y

GRASAS ESPECIALES

Introduction A lubricating grease is a semi-fluid material consisting of a thickening agent, a base oil, and usually a series of additives. The nature and percentages of the components of the fat depend a lot on the applications for which it is intended.  (^) Base oil: 75-96%

• Mineral oil
• Synthetic oil
• Vegetable oil  (^) Thickener: 3-25%
• Simple metallic soaps
• Complex metal soaps
• Thickeners with non-soap base
• Inorganic thickeners  (^) Additives: 0-10%

Base oil Represents 80% of the average of the total fat mass, gives this large part of its properties Base oils can be:

• minerals
• synthetics

Additives They are included in the composition of fats in order to improve their properties Adherence Corrosion and oxidation resistance Improves the viscosity index

Thickeners

The thickener is a material that in combination with the selected lubricant, this will produce the solid to semi-fluid structure.  (^) Grease consistency (amount of thickener)

• Consistency based on the viscosity of the base oil Depending on the viscosity of the base oil, we will need more or less thickener. A slightly viscous oil will need a higher consistency, that is, a thicker network, so that the oil does not escape. On the other hand, the more viscous oils will need a lower consistency to allow a good release of it.
• Consistency depending on the use of grease (equality of base oil viscosity) Within the same type of greases (with the same viscosity and type of base oil), the grease with the least consistency will be selected for centralized lubrication cases, and the most consistent grease for those cases in which you want to seal or avoid contamination by foreign elements, water, dust, process products.

 Simple soaps  Lithium soaps  (^) Lithium soaps are used as lubricating grease thickeners in high temperature applications.  (^) They have higher melting points than conventional sodium or potassium soaps (drop point of 180ºC, and maximum service temperature of 140ºC).  (^) Greases with such thickeners are resistant to loss of consistency and leakage.  (^) They have excellent anti-rust and corrosion properties.  (^) They have a moderate resistance to water.  (^) The additives in these fats work better than in other media.  (^) It has excellent sealing properties.

• (^) Calcium soaps They are usually accompanied by water because they are added to give them greater stability. They are formed by reacting a fatty acid with calcium hydroxide in a mineral oil medium. The appearance is packed fibers with a smooth texture. They are the cheapest and do not emulsify with water (they do not undergo phase transitions and can be pumped well).
• (^) They have a low thermal stability (low drop point) and good mechanical stability.
• (^) They have very good resistance to water.
• (^) They are used to lubricate water pumps, machines that operate in mild conditions. There are two types:

1. Stabilized with water whose maximum working temperature is 90ºC.
2. Hydrostearic derivatives that are more thermally stable than those of hydrated calcium (Maximum working temperature: 120-130ºC).

• (^) Complex soaps Complex soaps have been developed to meet the most rigorous temperature conditions of modern machines. The structure of the thickener is formed when a fatty acid derivative is reacted simultaneously with other polar compounds, called complexing agents, together with a basic component. These complexing agents usually have a molecular weight than that derived from fatty acid.
• (^) Lithium complex soaps
• (^) They have extraordinary resistance to water washing and excellent structural and thermal stability.
• (^) They have a high drop point (260ºC), which makes them tolerate high working temperatures (175ºC).

• (^) Aluminum complex soaps
• (^) They have high drop points of around 260ºC.
• (^) They have excellent resistance to water.
• (^) The fibrous structure of fat is smaller than that of other fats, which gives it a series of advantages: 1- For its manufacture it requires less thickeners. 2- Better pumpability 3- Retention in equal measure (high or low I.V. or synthetic oils). By modifying this type of grease with montmorillonite, other properties are improved, such as its performance at high temperatures, mechanical stability, oil separation and very good starting torque properties at low temperatures.

When to use grease? Oils are the first choice for lubrication, but greases are used when:  (^) The parts to be lubricated are difficult to access or require infrequent lubrication  (^) When it is crucial to maintain a seal to prevent contaminants from entering the system  (^) The system is unable to retain oil  (^) The most common applications are bearings, gears and gaskets.

METHODS FOR THE APPLICATION OF GREASE  (^) Manual method

• (^) Grease gun (risk of excessive grease / grease mix)
• (^) Spatula (High risk of contamination)
• (^) Brush (for open gears, high risk of contamination)  (^) Automatic method
• (^) Spot lubricator
• (^) Centralized lubrication systems
• (^) Single line (single point non-progressive injection)
• (^) Multiple lines with a single injection point
• (^) System with two progressive distribution lines

Special organic grease

THE GREASES MAINTAIN THEIR LUBRICATING PROPERTIES AND

VISCOSITY TO REDUCE MAINTENANCE COSTS, COMPONENT FAILURE

AND DOWNTIME IN DEMANDING APPLICATIONS. THEY ARE SOLID TO

SEMI-SOLID MATERIALS CONSISTING OF A LUBRICATING FLUID, A

THICKENER AND ADDITIVES. THEY ARE USED IN MANY INDUSTRIAL

APPLICATIONS SUCH AS BEARINGS, BEARINGS, AND OTHER MOVING

PARTS.