Introduction
Selection of correct high temperature grease is a very crucial task. There are certain criteria that should be kept in mind while selecting a high temperature grease. Various factors such as oil type, viscosity, additives, properties, operating temperatures, atmosphere, speed, etc. should be considered in the selection process. It becomes essential to select a high-quality grease to meet the requirements of high temperature and effective operations.
Properties of High Temperature Grease
Following are the properties to be considered while selecting the high temperature grease:
- Base Oils: The selection process often begins with considering the base oil performance properties for oil lubricated appliances. Furthermore, base oils can be categorized into 2 types- mineral oils and synthetic oils. Mineral oils are most commonly used base oil with 95% of grease manufacturing. The list is followed by synthetic oils such as PAO, then silicones and then other exotic oils.
- Thickeners: Thickeners can be of two types- organic such as polyurea and inorganic such as clay, fumed silica or soap made of complex combinations like lithium, aluminium or calcium. The usefulness of grease can be determined by its package and not solely on the basis of its thickening or base oil. The most used grease is the organic polyurea grease as it has a melting point of 2,732ºF (1,500ºC). However, it is difficult to manufacture as it consists of dealing with few harmful substances.
- Additives: The selection of additives should be done wisely after considering it as the part of the whole process rather than just seeing it as a discrete part. Additives play a huge role for grease by providing oxidation stability, resistance to corrosion, water and wear, low temperature, etc. The additives should be chosen correctly to make it work in synergy with thickeners and base oils.
Five Categories of Base Oils
As mentioned earlier, base oils are one of important properties to be considered for high temperature grease. The American Petroleum Institute has divided base oils in 5 different categories which are as follows:
- Group 1: Products such as naphthenic and paraffinic petroleum are included in this group. These are made up of a high percentage of various unsaturated molecules and have properties of oxidation. Moreover, polar products are also included in this group and are often known as heterocycles.
- Group 2 & 3: Both group 2 and 3 consist of minerals oils that require extensive properties and are saturated with hydrogen molecules. These base oils have oxidative and thermal properties which reduces the use of heterocyclic molecules and are really effective.
- Group 4: Group 4 consists of synthetic hydrocarbons better known as SHC fluids. They are a combination of two or more smaller hydrocarbons and larger synthesized molecules. Though these base oils offer more and better stability, they are quite expensive.
- Group 5: The base oils under group 5 usually have a defined path but their degradation properties are different from the rest of the groups. They are neither thermal nor oxidative.
Compatibility of High Temperature Grease
Compatibility is an essential part while choosing the high temperature grease because greases are made up of different complex balanced chemicals. Potential issues can arise if different greases are mixed together at high temperatures. If the issues increase, the only possible solution remains to dismantle the whole equipment and clean it thoroughly. The best way to avoid those issues is to test every grease used in the operation. It is also generally advised to use the same family of thickeners such as lithium to lithium, aluminium complex to aluminium complex, etc. Another important aspect to remember is the moisture sensitivity. If the grease is sensitive to moisture, it can generate the risk for the product due to moisture degradation even if it can bear the heat and high temperatures. For example, water soluble glycol oil cannot be used in applications which are sensitive to moisture. This is because even if the fluid can resist the thermal breakdown from the heat, the moisture keeps the performance of operation at risk.
How to Select Correct High Temperature Grease
Here are some of the steps to follow while selecting the high temperature grease:
- Temperature Range: It is important to know the temperature range of the operations. There are high chances of operational range being less than what it always seems. The best way to determine the operating temperature range of grease is to use contact or non-contact sensors for its measurement.
- Continuity: Another important thing to know is whether the operation is continuous or intermittent. It is advisable to use top-tier grease if the operation is continuous.
- Heating and Cooling Cycles: It is important to know whether both heating and cooling cycles are in sync with operating and non-operating intervals of the machinery. During those intervals, there are high chances of moisture being induced through atmosphere or impingement.
- Relubrication: Another important aspect to be considered is what is the reasonable interval of relubrication. It is advisable to use a top- tier product if the relubrication process is difficult. Though those top-tiers products are expensive, they reduce the cost of repetitive relubrication process.
- Cosmetic Issue: The last important aspect to be considered are possibility of any cosmetic issues. It is essential to balance the relubrication frequency and volume to prevent the product from contamination issues.
Take Away
This is the brief explanation about what aspects should be considered while selecting the correct high temperature grease. We hope those tips will be effective for you. Please let us know through your valuable feedback and the suggestion in the drop box.