Do you understand all the grease standards for construction machinery?

2024-03-14

Do you understand all the grease standards for construction machinery?

First, the physical and chemical indexes of engineering machinery grease

The physical and chemical indexes of grease mainly refer to the appearance, consistency, metal corrosion and rubber compatibility. The type and quality of grease can be preliminarily judged by its appearance. Consistency is the soft and hard consistency of grease, which initially reflects the thixotropy of grease, that is, the difficulty of deformation of grease under external force; Corrosion is whether the grease corrodes the metal and inhibits the corrosion of the metal index; In some lubrication areas, compatibility with rubber is very important. NB/SH/T0985-2019 standard does not require the color of the product, but specifies the consistency, corrosiveness and compatibility of the rubber.

1. Consistency

Consistency is the basic index of grease, indicating the soft and hard consistency of grease, and has an important relationship with the retention ability of grease in the lubrication part, sealing property, and the way of pumping and filling of grease. At present, the consistency grade commonly used in the world is according to the consistency grade of the American Grease Association (NLGI), which divides the consistency of grease into nine grades, as shown in the following table.

Classification of grease consistency

The consistency of grease is usually measured by the size of the coning degree, and the larger the coning degree value indicates that the grease is softer, and the opposite is harder. Cone penetration is an important basis for dividing grease grades and selecting grease, and is also an important index for controlling product quality in the process of research, production, storage and use.

The coning degree of grease usually includes working coning degree, non-working coning degree, extended working coning degree and block coning degree. NB/SH/T0985 -- 2019 standard requires the determination of working cone penetration, non-working cone penetration and extended working cone penetration, and the detection method is GB/T269.

Indicators are as follows:

(1) The index of non-working cone penetration is required to be "report";

(2)60 working cone penetration index requirements: No. 1 is 310 ~ 340, No. 2 is 265 ~ 295, and No. 3 is 220 ~ 250;

(3) 100,000 times extension cone penetration index requirements: No. l is not more than 380, No. 2 is not more than 350, No. 3 is not more than 320.

2. Corrosiveness

Protecting metal parts from corrosion is one of the important characteristics of greases. The thickening agent of grease and the Base Oil itself are not corroding metals, and the reason for the corrosion of grease is mostly due to the acidic substances produced by the oxidation of grease, which are related to its water resistance, oxidation stability, colloidal stability and adhesion. Corrosion test is to check whether the grease itself has a corrosive effect on the metal, in order to prevent the corrosion of non-ferrous metals by the grease itself with construction machinery. NB/SH/T0985-2019 standard requires that the corrosion of grease used in construction machinery be determined according to GB/T7326 grease copper corrosion test method (B method), the test conditions are T2 copper, 100℃, 24h, and the index requirements are that the copper sheet has no green or black change.

3. Rubber compatibility

The compatibility of grease and rubber refers to the performance that the volume, hardness and strength of rubber do not change too much when the grease is in contact with the rubber. Grease in use, in many occasions and parts will be in contact with the rubber sealing element, and sometimes the grease will lubricate and seal between the metal and the rubber. In the condition of lubricating grease and auxiliary sealing, adapting the rubber to a small amount of expansion is advantageous for sealing. However, if it is too swollen, soft and sticky, or too contracted and hardened, it will affect the working performance of the rubber seal. In these cases, if the rubber material has been selected, it is necessary to select another suitable grease to adapt to it; If the grease has been selected, a suitable rubber part must be selected to match it.

Various shaft pins on the working arms of construction machinery such as excavators and loaders and the walking tracks of excavators and pushers are lubricated by grease. In order to prevent the intrusion of external impurities or the leakage of grease, rubber sealing rings are equipped at both ends of the shaft pin. How the compatibility of rubber sealing ring and grease is very key to the sealing effect, so the grease for construction machinery needs good rubber compatibility.

NB/SH/T0985 -- 2019 standard requires the determination of compatibility with nitrile rubber and polyurethane rubber, the index requirements are that the hardness change of nitrile rubber is not less than -30IRHD, the tensile strength change rate is not less than -70%, the elongation at break change rate is not less than -80%, and the volume change rate is between 0 and 40%. The hardness change of polyurethane rubber is -5IRHD +5IRHD, the tensile strength change rate is not less than -70%, the elongation at break change rate is not less than -60%, and the volume change rate is between -5% and + 15%. The test methods were GB/T1690, GB/T531 and GB/T528, respectively.

Second, the component index of engineering machinery grease

1. Kinematic viscosity of base oil

The content of base oil in grease is as high as 70% to 98%, which plays a decisive role in the lubrication performance of grease. The viscosity of the base oil is closely related to the evaporability, high and low temperature performance, oil film thickness and so on of the grease, but also affects the adhesion and sealing of the grease, therefore, in order to meet the harsh lubrication conditions of construction machinery, it is very important to choose the right viscosity of the base oil. The technical requirements of the NB/SH/T0985-2019 standard for the kinematic viscosity of base oil (100 ° C) are only "reported".

2. Type of thickener

In grease, the thickening agent content is about 2% to 30%. The thickener can disperse in the base oil and form a spatial network structure, which plays an effective adsorption and fixation role on the base oil, determining the basic properties of the grease such as mechanical stability, colloidal stability, high temperature resistance and water resistance, and is used to distinguish various different types of greases.

For the type of thickener, the standard does not make clear provisions, the requirement is only "report". Therefore, in addition to fatty acid lithium soap thickener, other thickeners such as bentonite, lithium calcium soap, complex calcium, etc., can also be used to prepare grease for construction machinery.

3. Performance test of lubricating grease for construction machinery

Grease is a kind of lubricating material with structural characteristics. The type and basic properties of grease can be judged by the physical and chemical indexes of grease, but the actual use effect of grease with the same physical and chemical indexes is often very different due to the different structure, so it is necessary to further verify and judge by performance simulation test or actual application test.

(1) High temperature performance

The high temperature performance of grease is to maintain the stability of its structure and performance and long service life when the grease is applied to high temperatures. When the grease is heated, the properties may change, such as changing from a non-flowing state to a flowing state, changes in consistency, evaporation, oil separation and oxidation, etc., which will affect the performance of the grease at high temperatures. The factors affecting the high temperature performance of greases include drop point, evaporation loss and so on.

Drop dots. The drop point is one of the important quality indicators in the grease standard, and it is also an indicator closely related to the maximum use temperature of the grease, and the maximum use temperature of the general grease should be more than 15℃ lower than the drop point temperature. The drop point of the grease has a great relationship with the composition of the thickener, the drop point of the general calcium-based grease is 75 ~ 95℃, the drop point of the lithium grease is greater than 170℃, and the compound lithium grease is greater than 250℃. Therefore, the determination of the drop point of the grease helps to identify the type of grease and roughly determine the maximum use temperature of the grease. The drop point index of lubricating grease for construction machinery is required to be No. 1 not less than 170℃, No. 2 not less than 175℃, No. 3 not less than 180oC, and the test method is GB/T4929.

Evaporation loss. The evaporation loss of grease refers to the degree of evaporation loss of base oil when the grease is used under high temperature (or vacuum) conditions or for a long time, which mainly depends on the type of base oil, fraction composition and molecular weight. The smaller the evaporation loss of grease is, the better the high temperature property of grease is. If the evaporation loss of the grease is too large, it will increase the consistency of the grease, increase the friction, shorten the service life and deteriorate the protection performance. The evaporation loss index of lubricating grease used in construction machinery is not more than 2.0%, and the test method is GB/T7325.

(2) Colloidal stability

Grease is a colloidal structure dispersion system formed by base oil and thickener, and the base oil has a tendency to separate out under pressure or heat, that is, oil separation. Oil separation is a characteristic of grease, any kind of grease has the phenomenon of oil separation. The amount of oil is determined by the colloidal stability of the grease, which is one of the indicators to measure the quality of the grease, and has an important impact on the storage and use of the grease. If the colloidal stability of the grease is good, the tendency of oil separation is small; If the colloidal stability of the grease is poor, it is easy to have more serious oil separation under the action of heat, pressure, centrifugal force, etc., resulting in a rapid decline in service life, and make the grease thicken and dry, and lose lubrication. The general grease loses 50% of the base oil will affect the lubrication effect, and the grease should be replaced and scrapped.

At present, the test methods for determining the stability of grease colloid in China include pressure oil separation, steel mesh oil separation, storage oil separation and centrifugal oil separation. Construction machinery grease standards require the use of steel mesh oil separation method to assess its colloidal stability, the index requirements for No. 1 is not more than 10.0%, No. 2 and No. 3 is not more than 5.0%, the test method is NB/SH/T0324.

(3) Oxidation stability

The oxidative stability (chemical stability) of grease refers to the ability of grease to resist oxidation during storage and during use. The oxidation stability of grease has an important impact on its service life, and affects the corrosion resistance, structure and other properties of the grease, so the grease should have good oxidation stability. The oxidation of grease depends on the nature of its composition, related to thickeners, base oils and additives, etc., and is also affected by the conditions of storage and use such as temperature, moisture, etc.

The thickening agent and base oil in the grease are easily oxidized in long-term storage or at high temperatures, resulting in corrosive oxides, colloids and substances that destroy the lubrication structure, which are easy to cause corrosion of metal parts and reduce the service life of the grease. In addition to selecting the base oil and thickener with good oxidation stability, adding appropriate antioxidants or antioxidant preservatives can improve the oxidation stability of the grease to improve the service life of the grease.

NB/SH/T0985-2019 standard requires SH/T0325 to evaluate the oxidation stability of lubricating grease used in construction machinery, which is also an internationally common method to determine the oxidation stability of lubricating grease. The test conditions are 99cc temperature, 100h time, 758kPa pressure. The index requirements are that the pressure drop is not greater than 80kPa.

(4) Low temperature performance

The low temperature performance of grease refers to whether the grease is easy to flow and pump at low temperatures, which can be expressed by low temperature similar viscosity or low temperature rotational moment, and can also be expressed by the consistency of the grease at low temperatures. The similar viscosity of grease indicates the rheological property of grease at a certain temperature. The size of the viscosity will have a greater impact on the use of grease, the greater the viscosity, the greater the friction resistance, especially at low temperature conditions, the impact is more significant. Measuring the similar viscosity of the grease can predict whether the grease is easily moved or pumped through the pipe to the site of use. NB/SH/T0985-2019 standard requires the use of low temperature similar viscosity to evaluate the low temperature performance of construction machinery grease, the index requirements are no higher than 600Pa·S l, no higher than 950Pa·S 2, no higher than 1350Pa·S 3, and the test method is SH/T0048.

(5) Rust prevention

Rust resistance mainly refers to the ability of grease to protect metal from rust temporarily. Wet heat test is an index to evaluate the protection performance of grease against metal. Due to its own characteristics, grease can maintain a sufficient grease layer on the metal surface, prevent corrosive substances from eroding the metal surface, and resist water vapor, oxygen, acid and other corrosive gases or liquids through the grease layer to erode the metal. In order to meet the protection performance of construction machinery under rain, wet and other environments, construction machinery grease needs to have excellent rust prevention. NB/SH/T0985-2019 standard requires that the protective performance of lubricating grease used in construction machinery is evaluated according to the wet heat test method of GB/T2361 anti-rust grease, and the index requirements are class A.

Previous: How to choose hydraulic oil to prevent pipe explosion? Next: Liquid nitrogen instead of cutting fluid