2021-09-02
| There are many varieties and brands of lubricating grease, and the brands are often confused. Therefore, it is very important to learn to correctly identify the varieties of lubricating grease and the quality of lubricating oil for strengthening the lubrication management of field equipment. The varieties and brands of lubricating oil can only be determined after chemical inspection and analysis. Some commonly used greases can also roughly judge the type and quality change of grease through simple methods and appearance color. 1. Simple identification method for types of lubricating grease (1) Appearance and color can be used as the basis for preliminary judgment. Calcium base grease and lithium base grease are creamy, and sodium base grease is fibrous. (2) All kinds of fatty acid soap base fats have a certain degree of oil smell and fragrance. Various hydrocarbon fats do not have this smell. They usually have the smell of mineral oil and wax. (3) Identify whether a lubricating grease is sodium based grease or calcium based grease. Take a small amount of grease sample with your finger, dip it in a little water and twist it slightly. If it emulsifies rapidly, it is sodium based grease, and if it cannot emulsify, it is calcium based grease. The same method can be used to identify whether a long fiber grease is calcium sodium grease or barium grease, because barium grease is also a grease with strong water resistance. Calcium sodium base grease can also be emulsified, but it is only slightly emulsified, not completely emulsified. (4) Fill a beaker with some grease, then heat it up and measure the temperature change with a thermometer. When the temperature reaches 90 ~ 100 ℃, if it is calcium based grease, it will dissolve and separate the soap oil, that is, the soap mass floats in the oil. If it is a sodium base grease or calcium sodium base grease, it cannot dissolve at 100 ℃, and the time is prolonged, the calcium sodium base grease will also have oil soap separation. If it is alkyl grease (Vaseline), it will completely dissolve at 60 ~ 70 ℃, and it will be a uniform liquid after dissolution. 2. Simple identification method of lubricating oil quality
Whether the lubricating quality of lubricating oil is good or not must be tested and analyzed whether various technical indexes meet the standards before a correct conclusion can be drawn. However, the quality change of lubricating oil can also be generally judged by the following simple methods.
(1) The appearance inspection shows that the new mineral oil has fluorescence reaction. The so-called fluorescence reaction is to use a glass bottle to contain lubricating oil. In the outdoor sun, a layer of oil surface has a slight blue reflection. The fluorescence reaction of used old oil disappears. The oil with good quality shall be clear when viewed with the naked eye from the glass test tube, while the light oil shall be transparent or translucent without turbidity. There shall be no suspended particles in the oil, and there shall be no precipitated impurities at the bottom of the glass bottle. (2) Smell: if the used lubricating oil is seriously aged, it often has an acidic and irritating smell. This should be separated from extreme pressure gear oil. Extreme pressure gear oil contains chemical elements such as sulfur, phosphorus and chlorine. It also has a certain odor, but there is no irritating odor. (3) Fill the lubricating oil into the water test tube or beaker and heat it on the alcohol lamp. If there is a sound, it indicates that the oil contains water.
(4) Take 100ml oil sample for mechanical impurities and filter the oil with l00 mesh copper wire mesh. If the viscosity of the oil sample is too high, some gasoline can be added appropriately for dilution and then filtered. Check the impurities on the filter screen to roughly judge the condition of impurities in the oil. If there are impurities such as iron dust and sand particles, they can be detected.
3. Quality change and discrimination of lubricating grease in storage and use
Due to the influence of the external environment (such as air, water, dust or other harmful gases) and the mechanical force (such as stamping, shearing, etc.) generated by the relative movement of the working parts, the lubricating grease will change in two aspects. One is chemical change: the components of the lubricating grease (base oil, thickener) are affected by light, heat and air, Oxidative deterioration may occur. After the base oil is oxidized, a trace of organic acids, aldehydes, ketones, lactones and other components will be generated. The fatty acids and organic metal salts in the thickener may decompose to form a trace of organic acids. Therefore, acidic substances (increased acid value of lubricating grease) will be generated, resulting in corrosion of lubricated parts, even corrosion, and loss of lubrication and protection. Second, physical changes make the grease structure worse or even damaged due to mechanical action, the consistency of grease decreases, and the lubrication efficiency becomes worse; Or the poor sealing conditions of mechanical lubricating parts lead to the mixing of dust, impurities and moisture in the grease, resulting in the deterioration of the quality of the grease. Whether the lubricating grease is deteriorated needs to be judged by laboratory analysis. In the absence of laboratory equipment and laboratory personnel, experienced personnel can check and make preliminary judgment.
(1) The color turns black, indicating oxidative deterioration. If only one layer of the surface changes color, one layer of the surface can be scraped off and can still be used as usual. It is best to check the change of pH, that is, drop phenolphthalein indicator on a small amount of grease, mix it evenly, twist it with your fingers, if it is red, it means that the grease remains alkaline; If it does not change color, it indicates that the fat has become acidic. Generally speaking, the lubricating grease that becomes acidic cannot be used on valuable instruments to avoid corrosion, but it can be used in rough equipment that is not afraid of corrosion.
(2) The formation of adhesive film on the surface also belongs to oxidation, especially the grease made of dry vegetable oil, which is easy to occur. The treatment method is the same as above.
(3) Oil evolution indicates that colloidal stability has been destroyed. In case of slight oil separation, the surface oil can be removed, and most of the rest can still be used, but try not to use it in high temperature and high load parts. Products with severe oil separation cannot be used.
(4) Due to the absorption of water or leakage of rainwater, the oil is easy to produce surface emulsification. If the emulsified metamorphic part is completely removed, the remaining part can still be used. In case of serious emulsification, the water content of the remaining part may exceed the standard. This can be judged from the color. The more water, the lighter the grease color, the darker and opaque the luster.
(5) One of the reasons for the thinning of lubricating grease is that the storage temperature is too high. It needs to be immediately transferred to a cool environment for storage to restore its original consistency. If the temperature is not too high or the consistency cannot be restored, another reason is the change of pH (check with phenolphthalein indicator).
(6) One of the reasons for the hardening of grease is caused by long-term freezing. In this way, it can be stored at a slightly higher room temperature (e.g. 30 ~ 40 ℃) for a period of time to restore it to its original state. In this case, excessive temperature heating cannot be used. The hardening of some lipids is due to the characteristics of lipids. For example, synthetic calcium based lipids tend to harden in winter. As long as it does not affect the use, the above thermal insulation treatment is not necessary, but only mixing properly.
(7) In use, there are many indicators to judge the failure of bearing grease. The performance requirements of bearing grease are mainly colloidal stability (oil separation), mechanical stability (100000 shear tests to prolong the working cone penetration value) and oxidation stability. The comprehensive result of these three indicators is the bearing life.
The lubricating grease running in the bearing is damaged by mechanical force, which breaks and shortens the fiber of the thickener and reduces the ability to maintain the grease structure, that is, the consistency becomes low. If the consistency changes, it will be lost from the working surface; At the same time, during operation, the grease will be affected by the temperature rise, and the base oil will evaporate and reduce, or the oil separation loss of some base oil due to the colloid damage of grease will reduce the oil content of grease, and there is also the possibility of oxidation and deterioration.
Therefore, for bearing grease, if the content of base oil in the grease after operation is less than 60% ~ 70% (i.e. 30% ~ 40% loss of base oil due to evaporation or oil separation), the lubricating capacity will be reduced or even lost, resulting in bearing damage and shutdown accident. At the same time, the consistency of grease decreases and deteriorates due to oxidation, which will affect the working of bearing in operation.
（2） Management of lubricating oil and grease in equipment use
During the use of lubricating oil and grease, it is inevitable that they will continue to age and deteriorate, or even be completely scrapped. If the quality management and monitoring of oil products are strengthened during use, the abnormal deterioration of oil products can be prevented, the aging speed can be reduced, the service life can be prolonged, and the equipment can achieve the best lubrication, so as to make the production unit run for a long period of time.
1. Quality management of lubricating oil in equipment use
(1) Causes of lubricating oil aging and deterioration:
① Water and air can oxidize oil products. In the process of use, the oxidation speed is accelerated by the influence of temperature and pressure. After the oil products are oxidized, organic acids and sediments are produced. The presence of active metals can accelerate oxidation.
② The consumption and decomposition of additives in lubricating oil reduce the quality of oil. The use temperature and mixed medium (such as water, fuel oil, emulsion, etc.) can promote the consumption of additives and accelerate the decomposition speed. Mixing water, impurities and other harmful components is the direct cause of oil deterioration. It not only decomposes additives, but also destroys lubrication and causes wear.
③ Improper oil mixing can also deteriorate the oil.
④ Electric field can also accelerate oil aging.
(2) Lubricating oil quality management:
① Control the oil temperature. In order to prevent the oil temperature from being too high, the oil temperature should be controlled at the lowest point of the working temperature. For systems with lubricating oil coolers, attention should be paid to regulating the cooling water. For systems without coolers, attention should also be paid to the heat dissipation of the oil tank.
② Prevent water, gas, dust and other harmful substances from mixing into the lubrication system. The lubrication system shall prevent the leakage of water, gas, dust and other harmful substances. Try to prevent the leakage of emulsion, fuel oil, dust, etc. If the oil has been mixed with air and water, pay attention to timely discharge. When mixed with dust, pay attention to filtering in time.
(3) Strengthen lubrication management and take anti deterioration measures. Special personnel shall be responsible for the management of lubricating oil. The oil shall not be mixed without the approval of the Engineer in charge or the mixing test. The lubrication system shall be kept clean and sealed. The inner wall of the oil tank shall not be painted, and oil soluble substances such as lead, copper or red lead shall not be used as sealing materials. When replacing new oil, the oil tank, pipeline and lubricating parts must be washed to prevent the deteriorated components remaining in the old oil from polluting the new oil. The lubrication system shall be equipped with oil purification equipment. Pay attention to quality tracking during the use of oil products, and take measures in time if problems are found.
2. Management of lubricating grease in equipment use
(1) Grease type and service temperature range: the service temperature range of grease made of different types of base oil is as follows:
Base oil category service temperature range / ℃
Petroleum Lubricating oil-60 ~ 150
Diester-60 ~ 150
Neopentyl polyol ester-50 ~ 180
Silicone oil-70 ~ 150 (200250)
Polyolefin oil-70 ~ 250
Fluorooil fluoroether-40 ~ 200 (250350)
(2) The filling amount of grease in the bearing is appropriate: the filling amount of grease has a great impact on the bearing operation and grease consumption. Excessive grease filling in the bearing will increase the bearing friction torque, cause excessive bearing temperature rise and lead to grease leakage; On the contrary, insufficient or too little filling may cause dry friction of the bearing and damage the bearing.
The schematic diagram of grease filling amount and bearing temperature rise is shown in Figure 3-1.
Filling excess grease will also cause excess grease to leak from the lubricating parts, which will have an adverse impact on the mechanical operation. There are many different empirical formulas to calculate the appropriate filling amount of lubricating grease.
Generally speaking, for sealed bearings, the filling amount of grease should be 1 / 3 ~ 2 / 3 of the internal cavity of the bearing. When the bearing is filled with grease, the temperature increases.
Fig. 3-1 schematic diagram of grease filling amount and bearing temperature rise
1 - proper filling; 2 - overfilling; 3 - insufficient or poor greasing
(3) Relevant provisions on supplement and replacement of lubricating grease in use: the lubricating grease will be oxidized and deteriorated in use, the base oil will be reduced, and sometimes it will lose its lubricating effect due to mixing with external impurities, or it will be gradually consumed in the working process. Therefore, the lubricating grease must be supplemented and replaced regularly to meet the lubrication requirements of components.
The relubrication cycle of bearing varies according to the size of bearing, relative motion speed, load, operating temperature and sealing effect of bearing. Most bearing manufacturers take DN value as the calculation standard. For convenience, there is also a list of relubrication cycles.
For single row ball bearings, the relubrication cycle of 8 hours per day under medium radial load and temperature below 65 ℃ is shown in table 3-1.
It can be seen from table 3-1 that the higher the speed, the shorter the relubrication cycle.
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