1. The particle size and hardness of the resinoid grinding wheel material do not match.
Method: Strictly calculate the ingredients according to the ingredient list and review the key procedures;
2. Cracks in the molded blank. The hot pressing temperature is too high, the resinoid grinding wheel is cooled and heated rapidly, the temperature is too low when the core is removed, the core should be removed in time, the raw materials are damp and deteriorated, or the mixed materials are wrong;
a. End face cracks. The plasticity of the molding material is poor, and the method of unloading the mold is improper. The bottom plate of the molding mold is uneven or the parallelism of the pad is too large.
b. Peripheral cracks. The mold sleeve is severely worn, and the mold sleeve is too tilted when unloading.
c. Aperture cracks. The blank strength is low, the vibration is too large during unloading, the core rod is too worn or the taper is too small, and the unloading sequence does not meet the technical specifications.
d. Diagonal cracks. The spring pad iron used has inconsistent elasticity, which causes the mold to be tilted and compressed to produce diagonal lines. The fine material mold speed is too fast, the pressure is maintained for a short time, and the mold cooperation gap is too large.
e. Prevention of cracks on resinoid grinding wheels: adjust the plasticity of the mixture, the molding die shall not exceed the specified wear standard, the template and the shim shall maintain good flatness, the thickness of the shim shall be consistent, the elasticity of the spring shim shall be consistent, and the mold shall be unloaded according to the technical regulations;
3. Mixing. Before and during mixing, clean up the tooling. Before batching, check whether the raw materials have impurities;
4. Uneven mixing. Mix according to the mixing time required by the technology. Replace the mixer parts that are too worn at any time. The powdered resin material should be sieved according to the mesh number and frequency specified in the technical regulations;
5. The molding hardness does not meet the requirements. The first piece must be inspected, and no less than 30% of the blanks in each batch should be sampled. Check the weighing weight frequently and observe whether the pressure changes frequently;
6. Uneven bridge. Cooling needs to be uniform; the "warping" of the surface of the workpiece without a flat surface is called bridge. This is caused by uneven cooling, which causes the workpiece to shrink unevenly or the uneven pad for loading the furnace. It is mostly caused by thin-film grinding wheels and fine-grained thin products. Thin-film grinding wheels are prone to bridge defects when the cooling speed is too fast;
7. Uneven arrangement and uneven hardness. Adjust the dryness and humidity of the mixture to make it have good moldability. Perform material spreading and scraping operations according to technical requirements. Use pads first according to technical requirements to maintain the accuracy of the press; when feeding, the material spreading and scraping are uneven, the mixed material is too wet, or the material is agglomerated, the feeding is uneven, the mold is worn, and the leakage is serious, and the mold needs to be replaced;
8. The two end surfaces are not parallel. Maintain the accuracy of the press limit table and operate according to technical regulations;
9. The surface is uneven. The tooling equipment is maintained within the required accuracy range;
10. Blistering. Control the temperature hardening according to the hardening curve of the resinoid grinding wheel standard, and strictly control the quality of the mixing process; the molding temperature is too high or too low, and the temperature needs to be adjusted. The curing temperature is too high, and the temperature of the curing furnace is out of control. The binder is wrong; the surface of the superhard abrasive part is convex and deformed or the entire surface is swollen, and it has a resin luster, and some have turtle-shaped cracks.
Causes:
a. The heating rate is too fast or the temperature fluctuates greatly, which easily causes the fine-grained, high-hardness, and tightly arranged parts to bubble and swell. Because resinoid grinding wheel contains a large amount of binder or small pores, if the temperature control is not accurate and the heating rate is too fast, it will cause the binder to react violently, the amount of volatiles will increase sharply, and the internal gas pressure of the blank will be high, causing the product to bubble and swell.
b. The molding material is not mixed evenly, there are binder lumps in the material or it is rich in solvents with lower boiling points (such as ethanol, acetone).
c. Caused by errors in the mixing and molding process, the amount of binder in the part is increased, the unit weight is increased, and the pressure is increased.
