What to do if high-viscosity gear oil is difficult to filter?
author: Leila
2024-09-11
Q: When filtering high-viscosity gear oil, we found that the oil pressure was too high and it could not be filtered. The viscosity grades of gear oil are ISO460 and ISO680. Currently, only filters with a filtration accuracy of 25 microns can be used. If the filter element accuracy is higher, it will not work. The oil pressure is too high and cannot be filtered. We think it is because the viscosity of the oil is too high. How should high-viscosity gear oil be filtered? How to solve this problem?
A: Compared with low-viscosity lubricants, high-viscosity lubricants are indeed more difficult to filter. However, the difficulty in filtering oil is not necessarily caused by high viscosity, but may be due to other reasons.
A: Compared with low-viscosity lubricants, high-viscosity lubricants are indeed more difficult to filter. However, the difficulty in filtering oil is not necessarily caused by high viscosity, but may be due to other reasons.
1. Poor filterability of lubricating oil:
The filterability of lubricating oil, also known as filterability and filterability in some places, refers to whether the lubricating oil can flow smoothly through the filter. Therefore, first of all, you should test whether the gear oil you use has good filterability. The oil has high viscosity, is relatively viscous, and has lower fluidity than low-viscosity oil. However, in some cases, high-viscosity oil is difficult to filter not because of high viscosity, but other reasons. The filterability of lubricating oil is closely related to three factors: the type of lubricating oil additives, the presence of insoluble substances in the lubricating oil, and the hydrolytic stability of the hydraulic oil. Some additives in the oil will affect the filterability, including solid additives and viscosity index improvers. If the lubricating oil contains some sediments, oxidation byproducts, insoluble substances, precipitated paraffin, and poor oil blending technology, it will cause the oil to contain impurities that are difficult to filter. In addition, the poor hydrolytic stability of the oil will also affect the filterability.
The lubricating oil is not stirred evenly during the production process, the additives are not fully dissolved, or the lubricating oil contains certain solid additives, which are easily filtered out by the high-precision filter element, which not only blocks the filter element, but also affects the performance of the lubricating oil. Although most lubricating oil additives are liquid, they are easily soluble in base oil and can pass through high-precision filter elements smoothly. However, some additives are exceptions. Some polymer additives, such as viscosity index improvers, will condense into agglomerates at low temperatures (below 30°C) and are easily filtered out. In some cases, even filter elements with low filtration accuracy will have this problem. When the oil temperature rises, this problem disappears because the molecules of the viscosity index improver stretch out at high temperatures, do not clump, and easily pass through the filter element.
The filterability of lubricating oil, also known as filterability and filterability in some places, refers to whether the lubricating oil can flow smoothly through the filter. Therefore, first of all, you should test whether the gear oil you use has good filterability. The oil has high viscosity, is relatively viscous, and has lower fluidity than low-viscosity oil. However, in some cases, high-viscosity oil is difficult to filter not because of high viscosity, but other reasons. The filterability of lubricating oil is closely related to three factors: the type of lubricating oil additives, the presence of insoluble substances in the lubricating oil, and the hydrolytic stability of the hydraulic oil. Some additives in the oil will affect the filterability, including solid additives and viscosity index improvers. If the lubricating oil contains some sediments, oxidation byproducts, insoluble substances, precipitated paraffin, and poor oil blending technology, it will cause the oil to contain impurities that are difficult to filter. In addition, the poor hydrolytic stability of the oil will also affect the filterability.
The lubricating oil is not stirred evenly during the production process, the additives are not fully dissolved, or the lubricating oil contains certain solid additives, which are easily filtered out by the high-precision filter element, which not only blocks the filter element, but also affects the performance of the lubricating oil. Although most lubricating oil additives are liquid, they are easily soluble in base oil and can pass through high-precision filter elements smoothly. However, some additives are exceptions. Some polymer additives, such as viscosity index improvers, will condense into agglomerates at low temperatures (below 30°C) and are easily filtered out. In some cases, even filter elements with low filtration accuracy will have this problem. When the oil temperature rises, this problem disappears because the molecules of the viscosity index improver stretch out at high temperatures, do not clump, and easily pass through the filter element.
2. Low oil temperature:
Temperature affects the viscosity of the oil, which in turn affects the filterability of the oil. Low temperature increases the viscosity of the oil. Therefore, during cold start, the viscosity of the lubricating oil will become greater. When the equipment is running, the oil temperature will increase and the viscosity of the oil will decrease. If the oil is difficult to filter only during cold start, you can heat the oil appropriately or use gear oil with better low temperature performance. Many filters have bypass valves. During cold start, the high viscosity of the oil causes difficulty in filtering, and the bypass valve will open to allow the oil to pass. After running for a period of time, the oil temperature rises, the viscosity of the oil decreases, and it is filtered normally through the filter element again.
Temperature affects the viscosity of the oil, which in turn affects the filterability of the oil. Low temperature increases the viscosity of the oil. Therefore, during cold start, the viscosity of the lubricating oil will become greater. When the equipment is running, the oil temperature will increase and the viscosity of the oil will decrease. If the oil is difficult to filter only during cold start, you can heat the oil appropriately or use gear oil with better low temperature performance. Many filters have bypass valves. During cold start, the high viscosity of the oil causes difficulty in filtering, and the bypass valve will open to allow the oil to pass. After running for a period of time, the oil temperature rises, the viscosity of the oil decreases, and it is filtered normally through the filter element again.
3. Too high flow rate:
If the oil flow rate is too high, it will cause high oil pressure. Therefore, under the premise of ensuring the flow rate, appropriately reducing the oil flow rate can avoid excessive oil pressure. Most fine filters or off-line filters for gear oil are used at low flow rates. Generally speaking, the flow rate can be as low as 1 gallon per minute.
If the oil flow rate is too high, it will cause high oil pressure. Therefore, under the premise of ensuring the flow rate, appropriately reducing the oil flow rate can avoid excessive oil pressure. Most fine filters or off-line filters for gear oil are used at low flow rates. Generally speaking, the flow rate can be as low as 1 gallon per minute.
4. Filter element size:
Some filter elements have a larger filter area and can adapt to the filtration of high-viscosity lubricating oils and can adapt to higher flow rates. For example, the filter element used for paper machine bearing oil has many folds and a larger filter area, but it is more expensive. However, in the long run, it is worth using.
Some filter elements have a larger filter area and can adapt to the filtration of high-viscosity lubricating oils and can adapt to higher flow rates. For example, the filter element used for paper machine bearing oil has many folds and a larger filter area, but it is more expensive. However, in the long run, it is worth using.
5. Filter element material:
The filter medium suitable for high-viscosity oil should have such characteristics: dense filter holes and fine fibers of the filter material. Many high-quality hydraulic oil filter elements belong to this type. Check the filter element description when purchasing. The PQ curve can check the relationship between oil flow/viscosity and the impact on oil pressure. Depth filters are not suitable for high-viscosity gear oils.
The filter medium suitable for high-viscosity oil should have such characteristics: dense filter holes and fine fibers of the filter material. Many high-quality hydraulic oil filter elements belong to this type. Check the filter element description when purchasing. The PQ curve can check the relationship between oil flow/viscosity and the impact on oil pressure. Depth filters are not suitable for high-viscosity gear oils.
6. Impurities in the oil:
If the oil contains impurities, it is also one of the reasons for the difficulty in filtering. In addition, the oxidation of gear oil will produce some insoluble precipitates or colloids, which will affect the filterability of the oil. If there is water in the gear oil, it will also cause the filter element to clog and affect the filtration. Other substances are mixed into the lubricating oil, such as different types and brands of lubricating oil, or salts, chemicals, etc. These substances enter the lubricating oil, react chemically with the oil to produce sediment, causing the filter element to be blocked.
If the oil contains impurities, it is also one of the reasons for the difficulty in filtering. In addition, the oxidation of gear oil will produce some insoluble precipitates or colloids, which will affect the filterability of the oil. If there is water in the gear oil, it will also cause the filter element to clog and affect the filtration. Other substances are mixed into the lubricating oil, such as different types and brands of lubricating oil, or salts, chemicals, etc. These substances enter the lubricating oil, react chemically with the oil to produce sediment, causing the filter element to be blocked.
There are many reasons for impurities to be mixed into the lubricating oil, such as seal damage, poor seal selection and installation; no anti-pollution measures are taken, resulting in impurities entering the lubricating oil, such as the newly purchased machine is put into use without cleaning, and the anti-rust coating or peeling paint enters the oil; the machine that has been stored for a long time is not cleaned, and the lubricating oil enters impurities during storage, transportation and transfer; the debris produced by wear causes the filter element to be blocked, etc.
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