Use coolant properly 2
Coolant and grinding
Car manufacturers are willing to spend millions of dollars to buy grinding machines, but reluctant to invest in conveyor pipes and cutting fluids, which is now not uncommon in the grinding industry.
In the grinding process, the coolant plays a special role, which not only plays a decisive role in the quality of the product, but also has a great impact on the processing cost. The power consumed by the grinding wheel spindle motor is mainly distributed in the aspects of grinding wheel drive, grinding processing and coolant transfer. The heat generated by the workpiece in grinding must be cooled immediately to prevent excessive local temperatures and material phase changes caused by further heating. The phase transition often causes the formation of residual stress and white layer, reduces the fatigue life of the material, and causes cracks on the surface and sub-surface of the material.
The use of cooling and lubricating fluid and the selection of appropriate process parameters can reduce the heat generated by the grinding surface to a low degree, and most of the heat generated is taken away by the grinding wheel, chips and coolant, so as to achieve the cooling purpose of the production process.
The conveying pressure, flow rate, temperature and flow direction of the coolant have a great impact on the quality and economy of the production process. The pressure controls the flow rate of the liquid, the flow rate and the temperature control the heat conduction rate of the liquid, and the flow direction allows the liquid to clear the air obstacles moving around the grinding wheel. The liquid sprayed must be aligned with the grinding area in front of the wheel to open a channel for air circulation.
The amount of coolant flow depends on the grinding wheel used, and the heat generated by the spindle power consumed during grinding needs to be cooled. In many cases, the time spent on the coolant nozzle and pump/filter design is often close to the operating time of the machine. In other cases, machine tool manufacturers provide a simple nozzle system based on flexible plastic nozzles or small diameter curved metal tubes, especially for tool grinders and grinding machines for aerospace products. The injection pressure of the coolant should match the speed of the grinding wheel, generally between 0.4 and 0.2 kPa. The plastic nozzle can only be moved or shunt at a much lower pressure, and the open small-diameter pipe will even retreat due to the reaction force of the jet force, so it is not suitable for application. Other problems related to the nozzle include high-pressure jet splitting, high-pressure surge in the tube before the outlet, extreme proximity to the grinding wheel, and trial-and-error approach to the target.
The combination of circular nozzles with a high degree of configurability for continuous injection has been extensively tested. In a recent case study, a customer used mineral oil as a coolant to grind the root shape of a turbine blade and found the following advantages:
· The service life of the grinding wheel is doubled, and the glassy CBN content of the grinding wheel is increased by 25% after each dressing;
· Reduced inference force and further improved machining accuracy;
· Eliminate grinding burns and grinding cracks;
· After using laser aiming, the setting speed is accelerated;
· Reduced energy consumption of liquid pumps and cooling units;
· The adjustable degree of nozzle for different machined parts is improved.
Strategic measures should be taken for the application of coolant, that is, only the coolant is used where it is needed, which should effectively save energy and be economical and practical. A good engineering product should have various degrees of tunability that can reduce setup time.
And the selected coolant should be able to meet the processing needs and costs and production benefits. Direct oil products, such as mineral oil, synthetic oil, etc., generally have high lubrication properties, while water-soluble emulsion type coolants, such as synthetic water-soluble emulsions, semi-synthetic water-soluble emulsions and oil/water mixed emulsions are good coolants.
