Grinding machining is the final process of bearing machining. It has a direct impact on the accuracy, performance and service life of the finished bearing product. During the machining process, the coolant prevents workpiece burns, improves the surface accuracy and roughness of workpieces, and improves the resistance of workpieces and machine tools. The ability to rust, extend the life of tools and machine tools has a very important role. Therefore, the rational use and maintenance of grinding fluid is very important in the bearing processing.
1. Effect of cutting fluid
The use of wet processing in the bearing processing process can greatly increase the cutting capacity and service life of the tool, improve the product accuracy, and reduce the scrap rate. The main advantage of using wet cutting machining fluid is
1) Lubrication: The cutting fluid can lubricate the tool and increase the cutting capacity of the tool;
2) Cooling effect: A certain flow of cutting fluid can cut the heat and reduce the temperature of the tool;
3) Effluent action: The cutting fluid can flush away the chips and fall into the chip sluice. At the same time, the swarf in the groove can also be used to achieve hydraulic chip removal.
4) Raise the surface roughness of the workpiece: The cutting fluid will remove the iron scraps on the processing surface, and the iron scraps will not scratch the processing surface, thereby increasing the roughness;
5) Reducing corrosion: Selecting suitable cutting fluid can prevent workpiece and machine tool rails from rusting.
2. Reasonable use of cutting fluid
The cutting fluid can be divided into two major categories: oil-based cutting fluid and water-based cutting fluid. Oil-based cutting fluids, such as those used in the ultra-precision machining of bearing plants, use kerosene as the cutting fluid to add a small amount of mechanical oil. After the oil-based cutting fluid passes through the processing site, it generally contains only solid impurities such as abrasive grains and chips. In practice, only the solid impurities need to be separated to obtain a clean cutting fluid, so the treatment thereof is relatively simple. The other type is a water-based cutting fluid represented by an emulsion in which fine oil droplets are highly dispersed in water. The emulsion also contains various surfactants and rust inhibitors. After the emulsion passes through the processing site, it contains solid impurities such as abrasive grains and chips, and it is also easy to breed microorganisms. Microorganisms include bacteria, molds, fungi, etc. These are the main factors affecting the quality of the emulsion. The normal emulsion contains no more than 1000 bacteria/mg. When the bacteria content reaches 10,000 to 100,000 particles/mg, the emulsion will It can turn black and stench, and the cooling and lubrication effect drops rapidly, giving off an unpleasant odor, corroding the equipment, and even the bacteria blocking the filter. At this time, all the emulsion must be replaced and the circulation system thoroughly cleaned.
3. The mechanism of bacterial growth in cutting fluid
The bacteria in the emulsion can be divided into two types of anaerobic bacteria and anaerobic bacteria. Among them, anaerobic bacteria are the main culprit causing the black odor of the emulsion. Emulsions always contain a certain amount of insoluble oxygen, so there are always pro-oxidant bacteria breeding and growth in this environment, while the consumption of insoluble oxygen in the emulsion, resulting in the lack of oxygen in the water, then the anaerobic bacteria will take the opportunity to reproduce Hyperplasia and anaerobic bacteria use nutrients and salts in the emulsion as nutrients, and at the same time decompose ammonia, hydrogen sulfide, and other unpleasant and pungent gases. The organic acids decomposed by anaerobes cause the pH of the emulsion to drop and interact with it. The reaction of iron causes the emulsion to appear grayish black. This process is performed quite quickly in a "dead water" environment with a certain temperature and a certain amount of impurities. The purpose of the emulsion treatment system is to try to delay the process.
4. Use and maintenance of cutting fluid
4.1 Configuration (dilution) The configuration of the cutting fluid is diluted with a certain proportion of water. Water-based cutting fluids, especially emulsions, pay attention to the following points when diluting:
1) Water Quality Water should not be used in excess of the recommended hardness under normal circumstances, because calcium and magnesium ions contained in high hardness water will cause anionic surfactants to fail, emulsions decompose, and metal soaps that are insoluble in water appear. Even if the emulsion is made of a non-ionic surfactant, a large amount of metal ions can also cause the micelles to aggregate, thereby affecting the stability of the emulsion. Too soft water should not be used, and emulsions that are configured with too soft water tend to generate large amounts of foam during use.
2) The dilution of the dilute cutting fluid is related to the stability of the emulsion. Before using the cutting fluid, it is necessary to determine the dilution ratio and the volume of the required emulsion, and then calculate the amount of the used fluid and the amount of water. When diluting, select a clean container, pour all the required water into the container, and then add the original solution under low-speed stirring. During the configuration, the feed rate of the original solution is based on the non-emulsified stock solution. Note that the procedure for adding stock and water cannot be reversed.
4.2 Maintenance
Extending the service life of the emulsion In addition to choosing the proper coolant quality and proper use, the maintenance of the cutting fluid is also a very important factor. The maintenance of cutting fluid mainly includes the following items:
(1) To ensure the smooth circulation of the liquid circulation circuit, remove the metal shavings, metal powder, mold mucus, the decomposition of the cutting fluid, and the grinding wheel ash, etc., in order to avoid clogging.
(2) Bacteriostatic cutting fluids (especially emulsions) are essential for bacteriostatic growth. In the course of the use of cutting fluids, bacteria should be regularly checked and appropriate measures taken promptly.
(3) Purify chips and floating oil such as metal powder in cutting fluid in a timely manner to eliminate bacteria growth environment.
(4) Regularly check the PH value of the cutting fluid, there are major changes, and take corresponding measures in time.
(5) Adding cutting fluid in time, since the cutting fluid will be continuously consumed due to splashing, atomization, evaporation, and the carrying of processing materials and chips during the recycling process, it is necessary to add new fluid in time to meet the total amount of circulating fluid in the system. constant.
5. Purification of cutting fluid
The filtering and purifying of the cutting fluid means the process of removing a certain proportion of relatively large solid particles in the cutting fluid from the cutting fluid. The filtered and purified cutting fluid can be reused for mechanical processing to achieve the purpose of recycling. The advantages of filtration and purification of cutting fluid are mainly manifested in the following aspects:
1) Prolong the replacement period of cutting fluid: According to the practice of our factory, the replacement cycle of the cutting fluid after filtration and purification can be greatly lengthened.
2) Improve the service life of tools and grinding wheels: In recent years, studies have shown that the life of the tool (or grinding wheel) can be extended by reducing the impurities (such as chips, grinding wheel powder, etc.) in the cutting fluid from 40 μm to less than 10 μm. 3 times.
3) Improve the surface roughness of the workpiece and reduce the scrap rate.
4) Extend the service life of pipelines and pump sets. Solids and other chips in the cutting fluid will accelerate the wear of pipes and pumps and other components.
6. Filtration purification of cutting fluid
The filtering and purifying of the cutting fluid can be roughly divided into two major categories of filtration and separation, but they are often combined in practical production.
6.1 Separation device:
1) Sedimentation tank: As shown in Fig. 1, separation baffles and baffle plates are installed in the sedimentation tank to separate and remove suspended dirt and slick oil. The chips and solid dirt are deposited on the bottom of the tank. The clarifiers, which precipitated and isolated the suspensions and slicks, flowed over the partitions and into the clean liquid storage section of the settling tank. This device is suitable for purifying the cuttings and wear debris of various cutting fluids. It is especially suitable for the separation of large and large chips. Figure 2 is another type of sedimentation tank with a scraper chain that can scrape fine chips and solid dirt settled on the bottom of the tank out of the tank and into the dirt box. It is suitable for the centralized cooling system of water-based cutting fluids, and is particularly suitable for the grinding liquid grinding and grinding of the cast iron. The precipitation tank has poor separation effect on fine chips, fine particles and high-viscosity cutting oil.
Figure 1 sedimentation tank
Figure 2 Scraper sedimentation box
2) Magnetic Separator: The magnetic separator has long been used in the grinding process to purify the grinding fluid. It uses the principle of magnetic adsorption to rely on a continuously rotating drum to remove iron chips and other magnetically conductive metal particles. Separation process: When the dirty grinding fluid flows through the slowly rotating drum adsorption area, the magnetic solid particles are magnetized under the magnetic field, adsorbed on the surface of the drum, and taken out of the grinding fluid flow area, after the rubber pressure The roller squeezes and dewaters, and then scrapes off the grinding dust on the drum by means of a squeegee against the drum. This magnetic separator can also remove some of the other non-magnetic impurities while separating the magnetic solid particles. See Figure 3. It is suitable for the purification of emulsions, water-based synthetic fluids and low-viscosity cutting oils.
3) Centrifugal separator: Centrifugal separator is based on the difference in the specific gravity of the cooling lubricant and the chip, and the separation of the chip by centrifugal force generated by the high-speed rotation of the separator. The separation of oil and water is also based on the difference in the specific gravity of the different liquids. The purification process is that the cooling lubricating liquid with fine particles enters the inside of the rotor through the sewer pipe, rotates with the rotor at a high speed, and the centrifugal force generated by the rotation causes the fine particles to throw toward the wall, and the net liquid overflows from the top. When too much debris accumulates inside the separator rotor, stop the filtration and clean the rotor. See Figure 4. The performance of the separator is determined by its number of revolutions and radius of gyration. Manual unloading and semi-automatic unloading centrifugal separators can be used for the purification of emulsions, synthetic fluids and low viscosity cutting oils. Centrifugal separators have high separation accuracy, but high-speed rotation is prone to air bubbles, so they are not suitable for large-capacity separation.
4) Vortex separator: It can separate fine chips and fine particles, but it cannot separate light dirt and oil. The vortex separator principle is shown in Fig. 5. The purification process is as follows: the cooling lubricant with fine particles is pressed tangentially along the inner wall of the cylinder section, and fully rotates in the cylinder section, and spirals down the inner wall and enters into the conical section separation zone. The circling intensity in the separation zone is further increased. The faster the next time, the centrifugal force generated by the hovering force causes the fine particles to throw toward the wall, and then the fine particles fall along the inner wall and flow out from the bottom flow mouth. The centrifugal force acting on the fine particles is often several to several tens of times larger than the weight of the fine particles, so the fine particles are easy to throw. The center of the cone forms an air column due to the spiral, and a low-pressure zone appears at this adjacent place, causing the purified cutting fluid to rise and flow out from the top overflow port. This separator is generally supplied with a pressure of 0.25 to 0.4 MPa and an outlet pressure of 0.04 to 0.06 MPa. When separating a cutting fluid containing a large amount of chips or containing large chips, in order to prevent the underflow opening of the cone from being blocked, the cutting fluid must be gravity-precipitated or magnetically separated beforehand. This separator is suitable for high-speed grinding, high-force grinding, and general refining of synthetic liquids, emulsions, and low-viscosity oil-based cutting fluids.
Various types of sedimentation tanks and separators can be combined when selected to increase the purification rate and the degree of purification. For example, a sedimentation tank can be used in combination with a magnetic separator to remove slicks, abrasions, chips and grinding wheels, magnetic separators, sedimentation tanks and The vortex separator is used in series to obtain an accuracy of about 10 μm. However, this method is only suitable for single-machine small-flow conditions, and the processing volume is generally not large.
6.2 Filtering device
1) Gravity tape filter: As shown in Fig. 6, a single-cycle system for the purification treatment of grinding fluid in bearing grinding. The system uses a magnetic separator and a gravity paper tape filter. The filter media of the filter is non-woven and has a filtration accuracy of 20 μm. The dirt from the machine is naturally returned to the magnetic separator. After the primary filter of the magnetic separator, most of the magnetic particles are adsorbed. Then the magnetic separator outlet flows into the drain pan of the filter belt and flows into the drain pan. On the filter paper, the filter paper is laid on the transport network, and the transport network automatically transports the stained paper according to the switch signal of the level switch. The emulsion passes through the filter paper into the clean water tank in the lower part of the filter, and the impurities and dirt oil are trapped on the surface of the filter paper. When the filter paper is blocked, the floating switch of the liquid level switch rises, turns on the liquid level switch, drives the transmission chain net to output the dirty paper, and enters the new paper at the same time, the liquid level above the filter paper drops quickly, the float ball resets, and walks At the end of the paper, the filter paper and filter residue fall into the dirt carton. The system can automatically and independently control, the operation is simple and easy, the most widely used, the filter accuracy is determined according to the choice of filter paper, the specifications of the series of filter produced by our company are 25L/min~2000L/min.
2) Flat bed tape filter (positive pressure tape filter)
The positive pressure flat bed filter body consists of a movable upper case and a fixed lower case. The name of each part of the flat bed tape filter produced by our company is shown in Figure 7. The upper box is connected with two cylinders and can be vertically raised and lowered. When working, it is clamped by oil cylinder or air cylinder. There are filter paper and metal strips between the upper and lower boxes, and the steel has the function of supporting and conveying filter paper. The rubber packing is installed at the joint of the upper box and the lower box of the filter. During work, the scum and scums enter the upper tank through a pipe at a certain pressure. The particulate impurities in the scum and water are trapped by the filter paper, and the filtered net liquid is collected into the net tank. When the filter paper is used for a period of time, the throughput of the float decreases, and when the internal pressure rises to a certain degree, the system will automatically cut off the input of the emulsion and drive the emulsion out of the tank by the compressed air. After a set period of time, the cylinder The upper box is raised, the filter belt is moved horizontally, new paper is input, and then the upper box is pressed down to start the next cycle. The entire control process is controlled by the PLC to complete the predetermined action. The control method includes pressure control and time control for selection, continuous filtering, adjustable preset values ​​and automatic paper change.
Figure 7 Flat bed tape filter
1 Sluicant inlet 2 Inlet automatic control valve 3 Flexible hose 4 Filter belt 5 Air bag 6 Upper housing 7 Lower housing 8 Net fluid outlet 9 Pressure control valve 10 Contaminating vehicle 11 Compressed air inlet 12 Four-position valve 13 Contaminated fluid Dispenser 14 Cleaning nozzle 15 Cleaning fluid return pipe 16 Cleaning fluid collection tank 17 Purge tank
3) Negative pressure filter
Negative pressure filter is currently the most widely used form of filtration, negative pressure filter in many forms. Negative pressure filters mainly include paper negative pressure filter and Hoffmann negative pressure filter.
3.1) Paper Negative Pressure Filter
Figure 8 shows the tape negative pressure filter produced by our company. The tape negative pressure filter is a large box body. There is a negative pressure chamber at the bottom of the box. The stainless steel filter paper bracket is used to separate the upper part of the negative pressure chamber from the dirty fluid box. After the filthy fluid enters the slop tank, the cutting fluid enters the negative pressure chamber through the filter medium, and the pump evacuates the negative fluid from the negative pressure chamber to the machine tool. Under the suction of the pump, the negative pressure chamber will form a negative pressure to accelerate the filtration speed of the medium. When the impurities accumulate on the filter paper to form a “filter cake†and reach a certain thickness, the vacuum relay in the negative pressure chamber will initiate the sewage discharge. The squeegee drives the filter paper to run for a distance, allowing the dirty paper to exit the filter area, while entering a new piece of paper and continuing to filter. The paper belt negative pressure filter has a fast filtration speed, high filtration accuracy, and no requirement for cutting fluid.
3.2) Huffman filter
The filth fluid enters the upper part of the filter medium. The filter medium uses the metal chain as a bracket, and the fan is used to suck air in the negative pressure chamber to form a negative pressure, forcing the cutting fluid to pass through the filter medium and enter the negative pressure chamber. Impurities such as slicks on the surface of the cutting fluid can be blown to the end of the filter cake and exit the filter zone along with the filter cake. When the filter cake thickens, the resistance increases, and the negative pressure reaches the set value, the chain drags the filter cloth out of the filter area, and at the same time walks into the new paper and continues filtering. The whole machine is automatically controlled by a PLC programmable controller and has a fault self-diagnosis function, which is suitable for the requirements of a modern unmanned processing environment. As shown in Figure 9.
7) Centralized filtration of cutting fluid
There are two types of cutting fluid: stand-alone filtration and centralized filtration. Single-cycle filtration means that each machine's filtration system is independent. The single-cycle filtration system is generally equipped with the bearing processing machine, which is generally relatively simple and has relatively low filtration accuracy. It can only meet the requirements for low-precision bearing production and can not meet the needs of high-precision, low-noise bearings. This kind of independent filtration cycle method is generally suitable for working conditions with a small number of machine tools or using different cutting fluids. For large-scale mechanical processing plants that use wet processing, centralized filtration is recommended. The centralized filtration system is a trend of modern wet processing and filtration. Compared with the single-cycle system, the advantages of centralized filtration are as follows:
1) Small footprint: Large centralized filtration systems have a much smaller footprint than stand-alone filtration.
2) Easy to manage: When the cutting fluid is added, the number of points can be reduced, the cutting fluid management personnel can be reduced, the waste cutting fluid can be concentratedly treated, and the environmental pollution is small; the discharged iron scraps are concentrated and the transportation process is convenient; the usage condition of the cutting fluid can be detected centrally.
3) The filter accuracy is easy to control;
4) Easy to implement automatic control.
Figure 10 is a schematic diagram of a typical centralized filtration system. The system consists of an automatic dosing system, a liquid supply pipe, a coarse scraper filter, a paper negative pressure filter fine filter, an aerobic sterilizer, an oil scavenge cleaner, a liquid supply pump set, and an electrical automatic control system.
The cutting fluid is sent from the pipeline to the machine tool or automatic line through the supply pipe in the workshop, and the chips are flushed to the liquid return system. Under the action of the pressure nozzle, the chips and emulsion are returned to the filtration system through the overhead pipeline or the underground pipeline system. The emulsion in the filtration system is first coarsely filtered by the screed sedimentation tank, the larger swarf is sent by the squeegee conveyor to the culvert, and the emulsion is then finely filtered by the negative pressure filter. The liquid is sent back to the workshop by the pump set. The system liquid supply pump group adopts variable frequency constant pressure liquid supply technology to ensure the stability of the pressure and flow of the entire filtration system. When the quantity of equipment used in the workshop changes, the pressure in the pipeline also changes, and the pressure sensor will issue The signal, the pump group will automatically adjust the flow, so that the pressure inside the workshop piping system is constant. The dosing system consists of a dosing tank and a dosing pump, as well as corresponding pipes and regulating valves, which can be automatically dosed according to the set values. Oxygen-increasing devices regularly increase oxygen in the tank, inhibit the growth of anaerobic bacteria, and effectively extend the service life of the cutting fluid. The oil removal device automatically clears the liquid float to avoid corrosion of the cutting oil by the oil. The system has a liquid level detection system that automatically detects the liquid level and outputs a signal. With automatic replenishment function, automatic replenishment of the system. There are manual/automatic/semi-automatic/holiday cycle four modes for electrical control to meet the requirements of different working conditions. During the holidays and holidays, in order to prevent long-term standing and corruption of the cutting fluid, a recirculation pump is added to the system. After the system stops operating, the holiday cycle mode is selected at the control panel, and the system automatically starts the recirculation pump to keep the cutting fluid flowing. Effectively curb the growth of bacteria, greatly prolong the service life of cutting fluids, and achieve cost savings.
The concentrated cooling fluid filtration system provides centralized fluid supply and centralized treatment for the grinding fluid in the production workshop. The coolant can be subjected to centralized filtration, degreasing, oxygenation, and sterilization to achieve control over its concentration, pH, and colony count. Ensure that the coolant does not deteriorate and extend the service life of the coolant. The concentrated filtration and recycling of the cooling fluid can reduce the production cost, reduce the labor intensity of the workers, improve the working environment of the workshop, and reduce the environmental pollution. At the same time, the centralized treatment of the waste coolant can also be realized, thereby further reducing the environmental pollution. It is important that the coolant concentration filtering system makes the coolant quality stable over a long period of time, which ensures the need for bearing ring grinding.
The centralized supply and filtration system of grinding fluid has great promotion value. The one-time investment is not large, but the resource conservation effect is obvious, the social effect is good, and the requirement for the transformation of the workshop is not high.
17-4 PH Stainless Steel Pin & Shaft
Electrical Fan Shaft,Stainless Steel Shaft,Stainless Steel Pin,High Precision Shaft
Yihua Precision Machining Co, Ltd. , https://www.yhmachining.com