What is the effect of water resistance in lubricating grease?


Release time:

2023-04-12

Lubricating grease with good water resistance ensures that it can still provide good lubrication in the presence of water, while lubricating grease with poor water resistance is not suitable for areas in contact with water. For example, the continuous casting operation process in the steel rolling industry is characterized by a large amount of cooling water directly spraying on the hot steel billet. At this time, not only does a large amount of water enter the bearings, but also a large amount of water vapor is generated and exists on the surface of the bearings. Lubricating grease is always in a high temperature and high humidity state. If the water resistance of the grease is not good, it is easy to be washed and lost, losing its lubricity.

1. The Important Use Significance of Water Resistance of Lubricating Greases

Lubricating grease with good water resistance ensures that it can still provide good lubrication in the presence of water, while lubricating grease with poor water resistance is not suitable for areas in contact with water. For example, the continuous casting operation process in the steel rolling industry is characterized by a large amount of cooling water directly spraying on the hot steel billet. At this time, not only does a large amount of water enter the bearings, but also a large amount of water vapor is generated and exists on the surface of the bearings. Lubricating grease is always in a high temperature and high humidity state. If the water resistance of the grease is not good, it is easy to be washed and lost, losing its lubricity.

For the vast majority of parts used, lubricating grease is required to have good water resistance. But there are some parts that require the opposite, such as the lubricating grease used on knitting machines and sewing machines, which are often expected to be water-soluble; When grease splashes onto the fabric, it can be easily removed through a rinsing process, while lubricating grease with good water resistance is not easy to remove oil stains. Therefore, it is important to be flexible when selecting lubricants.


2. Moisture and water resistance of lubricating grease

Lubricating grease itself contains water, which can be divided into two types. One is structural water, and water is the stabilizer in the grease, which has an important impact on the formation and properties of the grease structure. The other type is free water, which is not expected in lubricating grease and must be restricted. But the water resistance of lubricating grease refers to the object, and water comes from the outside. Water resistance refers to the ability of lubricating grease to be insoluble, non emulsifiable, difficult to absorb water from surrounding media, not washed away by water, and not significantly change its own performance when in contact with water.

The water resistance of lubricating grease mainly depends on the thickener, followed by the base oil. Generally speaking, lubricating greases based on silicone oil have better water resistance, followed by mineral oils and ester oils. Polyether based oils have poor water resistance. For thickeners, urea based grease and hydrocarbon based grease have good water resistance, followed by aluminum based grease, barium based grease, calcium based grease, composite aluminum, composite barium, and composite calcium based grease, followed by lithium based grease, while sodium based grease and composite sodium based grease have poor water resistance.


3. Summary of evaluation methods for water resistance of lubricating greases

Measurement method for water resistance of lubricating grease: SH/T0109. This standard refers to the ASTM D1264 method for measuring the water resistance of lubricating grease. The plan of the water resistance testing machine is shown in Figure 1.

During the experiment, 4g ± 0.5g of the sample was loaded into the 204 type ball bearing and rotated at a speed of 600r/min ± 30r/min. The water temperature was controlled at 38 ℃± 2 ℃, and a flow rate of 5ml/s ± 0.5ml was sprayed on the protective plate of the bearing sleeve. The amount of lubricating grease washed away by water within 1 hour was used to measure the water resistance of the lubricating grease.


4. Other evaluation methods for water resistance of lubricating greases

Simple judgment method. Method regulation: Apply lubricating grease thinly on a 1mm thick glass sheet, and then immerse it in distilled water at 25 ℃, 50 ℃, and 90 ℃ for 5 hours. Observe the changes in the lubricating grease film and distilled water for judgment.