Grease performance and its evaluation index

Greases are used in a wide range of applications and work conditions vary widely. Different mechanical equipment requires very different grease properties. Grease performance is a combination of grease composition and preparation process. The evaluation of grease performance is not only decisive in production and research work, but also essential in the selection and inspection of grease in the use department. According to the specific conditions of the grease parts of automobiles and engineering machinery, the basic requirements for grease are: proper consistency, good high and low temperature performance, good extreme pressure, abrasion resistance, good resistance to water, corrosion, rust and stability. Sex and so on.

l. Consistency

At the specified shear force or shear rate, the degree of deformation of the grease structural system is measured to express the structurality of the system, which is the concept of consistency. It is an important performance indicator related to the retention and sealing properties of the grease on the lubricated parts, as well as the pumping and filling methods of the grease. Some lubrication points use grease because they have a certain consistency, which gives them a certain resistance to loss. Greases of different consistency are suitable for different working conditions such as mechanical speed, load and ambient temperature. Therefore, consistency is an important indicator of grease.

The consistency level of the grease can be expressed as the degree of penetration. The penetration of the grease refers to the depth of the standard cone of the specified weight penetrating the grease sample under the specified time and temperature conditions, expressed as (l/10) mm. The measurement of the penetration of the grease can be carried out according to the method specified in the "Measurement method of grease penetration" (GB/T269-91). Grease penetration usually includes four types: no work, work, extended work, and block penetration. The non-working cone is generally not as effective as the working cone, and it usually represents the consistency of the grease in use. It is best to use the working cone. Extended working penetration is suitable for taper measurements measured over 60 times. Summary of the method for measuring the penetration of grease: The cone assembly is released from the cone meter at 25 ° C, and the cone is sunk into the depth of the sample for 5 s to determine the above four degrees of penetration of the grease.

Cone penetration reflects the deformation and flow properties of the grease at low shear rates. The higher the cone penetration value, the softer the fat, that is, the smaller the consistency, the easier it is to deform and flow; the lower the cone penetration value, the harder the fat, that is, the greater the consistency, the less likely to deform and flow. It can be seen that the degree of penetration can effectively represent the consistency of the grease and is an important basis for the selection of grease. In China, the range of the degree of penetration is used to divide the consistency of the grease. GB7631.1-87 is consistent with the consistency number of the American Grease Association (NLGI), which is widely used internationally.

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How to clean and judge whether to replace SKF cylindrical roller bearing

When disassembling the lower bearing inspection, first record the appearance of the SKF cylindrical roller bearing, confirm the residual amount of the lubricant, and wash the bearing after sampling the lubricant for inspection. As a cleaning agent, gasoline and kerosene are commonly used.

The cleaning of the removed bearing is divided into coarse cleaning and fine fine washing. In the container, the metal mesh bottom is placed first, so that the bearing does not directly contact the container. In rough cleaning, if the bearing is rotated with dirt, it will damage the moving surface of the SKF cylindrical roller bearing, so you should pay attention to it. In the rough cleaning oil, use a brush to remove the grease and the adhesive. After it is almost clean, it is transferred to the fine wash.

Fine washing is to carefully clean the bearing while rotating it in the cleaning oil. In addition, the cleaning oil should always be kept clean.

2. Inspection and determination of SKF cylindrical roller bearings

In order to determine whether the removed SKF cylindrical roller bearing can be reused, check the SKF cylindrical roller bearing after cleaning. Carefully check the raceway surface, the dynamic spring surface, the state of the mating surface, the wear of the cage, and the bearing clearance. The increase and the presence or absence of damage and abnormality regarding the decrease in dimensional accuracy. For non-separable ball bearings, use one hand to support the inner ring and rotate the outer ring to check if it is smooth.

Separate SKF cylindrical roller bearings such as tapered roller bearings can be inspected separately for the raceway surface of the moving body and the outer ring.

Because large bearings cannot be rotated by hand, pay attention to checking the appearance of moving bodies, raceways, cages, ribs, etc. The higher the importance of bearings, the more careful inspection is required.

The determination of whether it can be reused is determined by considering the damage degree, mechanical function, importance, operation premise of the German SKF cylindrical roller bearing, and the period until the next inspection. However, if there are the following defects, they can no longer be used, and new bearings must be replaced:

(a) cracks or gaps in any of the inner ring, the outer ring, the moving body and the cage;

(b) There is a break in any of the ferrule and the moving body;

(c) obvious jamming on the raceway surface, ribs and moving body;

(d) The cage is significantly worn or the rivet is significantly slack;

(e) There is rust and injury on the raceway surface and the moving body;

(f) There are severe indentations and marks on the raceway surface and the moving body;

(g) There is significant creep in the inner diameter surface of the inner ring or the outer diameter surface of the outer ring;

(h) significant discoloration due to heat;

(i) SKF cylindrical roller bearings sealed with grease, and the seal or dust cover is damaged.

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