When the grinding wheel surface temperature, if the cooling measures is not good, it's easy on the workpiece surface (from tens to hundreds of um um) occur secondary quenching and tempering. If the grinding wheel surface layer of the instant temperature exceeds steels AC1 point, the role of the secondary coolant quenched martensite, while in the subsurface due to temperature gradients, short time, only the formation of high-temperature tempering organization This makes the surface and subsurface between the tensile stress and the surface of a thin brittle secondary hardening martensitic, when can not afford, it will crack.
Heat treatment of
A) residual austenite retained austenite grinding wheel grinding wheel grinding wheel because heat and pressure generated changes occur at the same time may be accompanied by tempering and grinding wheelsurface cracks. Amount of residual austenite should be controlled within 30%.
2) carbon concentration diffusion layer nitrided layer carbon concentration is too high, easy to form a nitrided layer tissue or excessive free mesh carbide carbide. Because this substance extremely hard, the wheel grinding process may lead to local overheating tendencies and incidence surface tempering. Nitrided layer carbon concentration is too high, the surface will produce excessive residual austenite. Resulting in burns and cracks. Therefore, the surface carbon concentration increases, reducing the performance of the grinding wheel, the general surface carbon concentration should be controlled within the range of 0.75% -0.95%.
3) carbide distribution should be uniform carbide distribution and morphology, particle size not greater than the average diameter lμm; carbide morphology should be spherical, powdered or finely punctate distribution along the net, mesh or angular carbides are not allowed.
4) decarburization heat treatment. Surface or environmental cause improper surface oxidation, so that the workpiece will produce a thin carbon layer, this layer will cause decarburization soft wheel overload or overheating, resulting in surface tempering.
5) tempering the premise of ensuring the hardness, the tempering temperature is as high as possible a number, as long as some of the annealing time. This can improve the surface carburized hardened plastic, and the residual stresses are balanced or lower. Improving the distribution of surface stress. This can reduce the probability of cracks occur workpiece, thereby improving the efficiency of the grinding wheel grinds the workpiece.
6) deformation should minimize heat deformation. This reduces the grinding wheel margin. If the heat deformation is too large, if the operation is not in the workpiece grinding wheel radial runout maximum at the beginning of the grinding wheel, grinding wheel each time point at which the grinding wheel is removed margin would not be normal, resulting in burns and cracks.
Grinding wheel burns inspection methods:
1 view color method
2 pickling
3 microstructure France
4 microhardness France
5 magnetic bomb method
Grinding wheel burns classification:
Grinding wheel burns a variety of different classification methods. According to Burns look different, can be divided into full burn (whole surface burns), patchy burns (burns on the surface appear scattered spots), uniform lines like burns, burns periodic striation; according to changes in the surface microstructure can be divided back Fire burns, quenching and tempering burns; also according to burn depth into shallow burns (burn thickness <0.05mm), moderate burns (burn layer thickness between 0.005 ~ 0.01mm), deep burns (burn layer thickness> 0.01mm) . In production, the most common is uniform shaped lines are periodic burns.
As the grinding wheel surface burn occurs often accompanied by oxidation, and in parts of the surface oxide film. And because the thickness of the oxide film to the different interference of reflected light different states; thus showing a variety of colors. So usually grinding wheel to determine the color of the surface extent of the burn, which is "the concept of color Law" on the steel, it burns with the strengthening of the general color rendering white, yellow (400-500 ℃), brown, purple ( 800 ~ 900 ℃), blue (blue) changes. Different depths grinding wheel, the machining surface oxide film thickness burns and different color.
Color Burn reflects only serious burn-in phenomenon, and when the parts of the surface color change, the surface tissue burns could have occurred changes often difficult to identify this type of burn, so the performance parts greater harm. Currently, people in order to better control the degree of burn, has been changes in the organization of the surface of the burn were classified, generally divided into nine from 0-8, wherein 0 lightest and 8 the most severe burns.
Grinding wheel burn prevention measures
1 to minimize the heat generated by the grinding wheel.
2 Try to accelerate heat distribution.
3 to avoid the impact before the procedure.
Grinding wheel burns affecting factors and solutions
(A). Grinding wheel grinding wheel conditions affecting manner:
1 grinding wheel I excessive.
(2) a reasonable parameter setting of the grinding wheel, grinding wheel usage reasonable choice. In the grinding wheel burns appear dosage is low, you should increase the longitudinal feed speed: grinding wheel when large burns, should reduce the amount of feed, increasing the number of grinding wheel.
3 reasonable workpiece speed setting is too high or too low is not good.
4 Magnetic insufficient workpiece stops adjustment magnetism.
5 wheel spindle spindle runout overhaul.
6 wheel drive system and the strict control of the grinding wheel spindle clearance, wheel belt tension adjustment appropriate.
7. Workpiece and the grinding wheel motor torque selection is adequate.
(Two), wheel choice questions: (see Wheel selected articles)
1 Wheel improper material selection, selection of the most basic wheel grinding wheel abrasive grinding wheel to the workpiece with the skin with the rationale.
(2) partial small wheel size, wheel size to meet the conditions required selection roughness rough number.
3 wheel rigid hardness, softening point selection wheel, improve self-sharpening wheel.
4 Wheel organization is too small (tight), choose too large, loose wheel; to facilitate chip, reducing the incidence of burns. In some cases, large pores can be considered wheel.
5 of the grinding wheel for special treatment.
6 wheel diameter is too large, and the grinding wheel size increases will cause burns; condition of the workpiece can be selected smaller diameter grinding wheel, especially for the grinding wheel inner circle.
7 slotted surface of the grinding wheel to use, this grinding wheel is called "intermittent grinding wheel" can reduce the heat and increase the cooling effect; also conducive to the full chip.
8 Grinding Wheel, timely wheel dressing.
9 good balance wheel, the grinding wheel must be finely balanced so that the grinding wheel work in good balance.
10 sustained wheel sharpness.
(Three), cooling issues:
Normal cooling method
A grinding wheel grinding fluid improper selection, reasonable choice of grinding wheel grinding fluid. Grinding wheel generally choose oily liquid, reducing wheel grinding zone temperature, it will be appropriate to reduce the incidence of burns. In the case of a conditional choice brand wheel grinding fluid.
(2) can be taken in case certainly not wet the dry grinding.
3 wheel grinding fluid supply fully effective, not only to supply sufficient grinding wheel area, and the pressure to be large; just can lower the temperature and the full chip.
4 maintain the purity of the coolant.
5 Keep the temperature of the coolant is low, which can reduce the temperature of the grinding wheel area, if necessary, can be used when the radiator.
6 wheel grinding fluid nozzle placement is wrong, should be as close to the grinding wheel so that the nozzle area.
7 Coolant nozzles installed air baffle.
8 Use the internal cooling wheel: internal cooling method is rigorously filtered coolant through the hollow cavity of the hollow spindle wheel introduced. Due to centrifugal force, the cutting wheel along the pore fluid thrown around to direct the cooling wheel grinding zone.
Structure within the cooling wheel
Attachment: centerless grinding burn some of the reasons and solutions:
1 guide wheel speed is too low; increase the guide wheel speed.
(2) improper selection wheel grinding wheel: size too small, wheel too hard, tight organization; let put coarse grinding grain, hardness put soft, loose tissue.
3 longitudinal feed excessive; decreases guide wheel tilt angle.
4 At the entrance worn too much, the front piece appeared burns; rotating guide wheel frame.
5 at the exit worn too much, so that the workpiece into a spiral burn all traces; rotating guide wheel frame.

  With: high efficiency, suitable diameter, length range:
1, the feeding mechanism used alone CVT (imported frequency converter, gear motors) according sharpened pieces of wire size, feeding speed can be adjusted (sharpened speed) to achieve optimum grinding  results.
2, the feed with clutch device, convenient manual feed mill trial, if fault can be promptly stopped feeding.
3, the bevel gear wheel transmission mechanism to adjust the level, simple operation, easy to adjust.
4, compact structure, adjustment mechanism design is reasonable, easy to adjust the cone angle changes, simple operation.
5, the use of imported special wide-type sharpened dedicated wheel, its wear resistance, high hardness, long life, HY-D2-D4 type with wide-type wheel widths up to 155mm, increasing sharpened pieces of grinding (grinding ) time, diameter φ5 less, can be a sharpened, and the surface finish, good brightness.