Selection and application of high performance phenolic resin for abrasive cutting disc manufacturing(2)
2.Application of phenolic resin in abrasive cutting disc
The binder used in the abrasive cutting disc is mainly a phenolic resin, and its function is to solidify the loose abrasive to form a tool having a certain shape, a certain hardness and strength, and a certain grinding performance. Both the powder separation resin and the liquid phenolic resin are used as the grinding wheel binder, but their effects are different.
Liquid phenolic resins are abrasive wetting agents, while powdered phenolic resins are the primary binder.
The powdery phenolic resin is a white or pale yellow translucent solid powder at normal temperature. It is easy to absorb moisture and dissolve into organic solvents such as alcohol and acetone. The specific gravity is 1.18-1.22, the softening point is 95°C-115°C, and the free phenol content is 0.5%-3.5%. The liquid phenolic resin has a brownish red viscous appearance and can directly undergo a condensation reaction under heating to become a solid which does not dissolve or melt. The viscosity of the resin liquid is 300 - 2500 mPa.s (centipoise) / 25 ℃ (rotational viscosity method), the solid content is 65 - 80%, and the free phenol content is ≤ 18%. The total amount of resin added in the grinding wheel ranges from 15 to 36%.
In addition to the binder, the resin abrasive also needs to be added with a filler. Fillers can alter the properties of the bond and improve the performance of the wheel while reducing costs. Commonly used fillers are hemihydrate gypsum powder, fine-grained corundum or silicon carbide powder, cryolite, pyrite, iron sulfide and the like. The colorant is generally iron red powder, carbon black or the like.
The production process of abrasive cutting disc mainly includes two kinds of cold pressing process and hot pressing process:
The most basic mixing principle of the cold pressing process is to first wet the coating with the resin liquid, and then add the resin powder, additives and other materials. The resin liquid wets the surface of the abrasive to form a thin resin film, so that when the surface-impregnated abrasive is mixed with the resin powder and the filler, the powdery substance is effectively bonded to the abrasive surface of the impregnated resin. Usually the weight ratio of the powder is from 1.8:1 to 3.5:1.
The production technology of high-density hot-pressed grinding wheels is very high, and the mixing requirements are different from those of cold-pressing processes. Generally, the dry mixing method is used, or the abrasive is wetted with furfural less than 1% by weight of the abrasive as a wetting agent, and then uniformly mixed with the resin powder.
The resin powder generally has a fluidity of 15-20 mm, or even smaller, and cannot use liquid phenolic. Resin and powdery resin with high fluidity.