What factors affect the blockage of grinding wheel?
Here let’s talk about some important factors which affect the blockage of grinding wheel. Generally we consider the following aspects:the Influence of Grinding Wheel Itself, the Influence of Machining Parameters, Grinding Fluid and Grinding Way.
▲The Influence of Grinding Wheel Itself
The degree of blockage of different grinding wheels varies greatly. From the point of view of reducing the degree of blockage and improving grinding effect, different kinds of abrasive materials should be used for different workpiece materials. If the selected abrasives can not adapt to the grinding performance of the workpiece material, it is easy to produce a sharp blockage, so that the processing can not be carried out normally
Abrasive grit has a certain effect on grinding wheel blockage. Generally speaking, fine grit is more prone to clogging than coarse grit. When the grinding wheel of #60 is compared with the grinding wheel of #100, the latter has a large amount of plugging under the same conditions. However, with the increase of cutting times, coarse grit grinding wheels have a larger cutting depth than fine grit grinding wheels, so the abrasive cutting edge wears more, and the grinding temperature rises, and the chip melt in the pores increases.After a certain number of times, the plugging amount of coarse grit grinding wheel will exceed that of fine grit grinding wheel.
The hardness of grinding wheel has a great influence on the amount of blockage. Generally speaking, the harder the grinding wheel is, the greater the amount of blockage will be.
The denser the structure of the grinding wheel is , the more the number of working grinding grains have, the shorter the distance between cutting edges occurs, and the easier the blockage happens. The average plugging amount of a grinding wheel containing 45% grinding grains is half that of a grinding wheel containing 49.2% grinding grains.The average plugging amount of a grinding wheel containing 53% of abrasive particles is twice as high as that of a grinding wheel containing 49.2% of abrasive particles.The grinding effect of large pore wheel is better when grinding difficult material which is easy to clog.
The functions of the pores of the grinding wheel are mainly for chip holding and cooling.Generally speaking, grinding wheels with more and larger pores are less likely to be blocked than those with fewer and smaller pores.
▲ The Influence of Machining Parameters
- Linear Speed of Grinding Wheel
The influence of the linear speed is complicated. When the grinding wheel increases from 28.8m/s to 33.6m/s, the speed increases by 16% while the amount of blockage increases by three times. Because the increase of linear velocity reduces the maximum cutting depth of the grinding grain, reduces the chip section area, and increases the cutting times and grinding heat, both of which can increase the plugging amount. However, when the grinding wheel's linear velocity is up to a certain degree (up to 50m/s or more), the plugging amount of the grinding wheel will greatly decrease.
Practice shows that when grinding stainless steel and super-alloy, the speed of grinding wheel at 55m/s is 30%~100% less than that of grinding wheel at 30m/s. Therefore, when grinding hard grinding materials, either a speed lower than 20m/s or a speed higher than 50m/s is adopted. The grinding speed selected between them is very unfavorable for blockage of the grinding wheel.Of course, for all kinds of workpiece materials, each has a certain critical grinding wheel speed value with the minimum amount of plugging.
- Radial Cutting Amount
Radial cutting amount influence on grinding wheel blockage showed a trend of hump, when the radial cutting amount is small, (ap < 0.01 mm) produce jam phenomenon, with the increase of cutting depth, average jam quantity will increase, when the cutting amount increases to a certain extent (ap = 0.03 mm), blocking amount and showed a trend of decrease, increase as the amount of cut after (ap = 0.04 mm), blocked amount is rising sharply.
When grinding hard grinding materials, controlling and mastering the last radial cut is very important to improve the surface quality and precision of the workpiece. Field grinding often encounter such a problem, when the use of 0.005mm cut for the last grinding of stainless steel, often is the grinding wheel in the workpiece surface slip and always do not meet the requirements, continue grinding will cause "gnawing" the workpiece, even cause scrap.The last grinding adopts the radial feed of 0.02mm, and the roughness and precision of the workpiece surface can often meet the requirements. The main reason is that the radial cut volume has great influence on the grinding wheel.
- Axial feed velocity
Generally, under the same total grinding amount, the slower the axial feed speed is, the more times the abrasive will grind the workpiece, thus the higher the surface temperature will be, and the more clog will be increased.For example, when the axial feed speed decreases from 1.2m/min to 0.5m/min, the blockage of grinding wheel increases by 5 times. Under the condition of 0.5m/min, fine chips were produced and most of them were embedded in the pores.When the axial velocity was 1.2m/min, long chips were generated and only embedded in the pores.
- Dressing Speed of Grinding Wheel
When the dressing speed of the grinding wheel is low, the working face of the grinding wheel will be flat and the number of effective grinding edges per unit area will increase. As a result, the cross section area of the grinding wheel will become smaller and the number of cutting chips will increase, which will easily lead to blockage. When the dressing speed of the grinding wheel is high, the working face of the grinding wheel will thicken, the effective grinding particle number will decrease, and a concave part will appear on the surface of the grinding wheel, which will play a role of pore, chip will be easily washed away, and molten objects will fall off easily.Therefore, all kinds of grinding wheel dressing have an optimal speed range.
- Rotating Speed of Workpiece
The influence of workpiece speed on the blockage of grinding wheel is closely related to other factors in cutting conditions. Under the given experimental conditions, the workpiece speed increases by one time, and the grinding wheel blockage increases by three times. This is because the higher the workpiece speed is, the shallowing depth of abrasive particles will be shallow, and the chip section area will be smaller, which is equivalent to the hardening of the grinding wheel, thus easily causing blockage of the grinding wheel.
Different grinding fluids on grinding effects is very big, generally water-based grinding fluid, containing a large amount of mineral oil and oil additives, diluted the oil-in-water milky liquid, and its specific heat capacity and thermal conductivity is small, it is easy to cause in the process of friction between wheel and workpiece adhesive abrasion and wear of diffusivity of the grinding wheel blockage, grinding force increases, eventually cause particle premature breakage and loss, lower the grinding ratio.Therefore, it is generally difficult to process the material should choose better lubricity grinding fluid or grinding oil cooling will better reduce the blockage phenomenon.
In general, crush grinding is more clogging than longitudinal grinding. Due to the large contact area between the grinding wheel and the workpiece during grinding, the cutting edge of the grinding grain has to be rubbed several times on the same grinding mark, and it is difficult for the coolant to enter the grinding area, so the grinding heat is high and it is easy to cause clogging. When grinding longitudinally, the first contact of the workpiece material is one edge of the grinding wheel. The contact area is small, and the coolant is easy to enter the grinding zone. Abrasive wear occurs only at one edge of the first contact.When the wear surface increases to a certain extent, the abrasive grains break and break under the action of grinding force, realizing self-sharpening.Most of the grinding particles can be kept in a sharp state, making the grinding force and heat relatively low.At the same time, a considerable part of the area affected by grinding force and grinding heat can be discharged out of the workpiece in the direction of longitudinal grinding, thus reducing the possibility of chemical adhesion.As a result of the above factors, the longitudinal grinding wheel has a lower degree of blockage than the cutting wheel.