Selection and application of high performance phenolic resin for abrasive cutting disc manufacturing(3)
3.Effect of several important indexes of powdered phenolic resin on the performance of abrasive cutting disc
I mainly analyze the five most important technical indicators of powdered phenolic resin:
1) Fluidity (flow length): The flow length of the resin powder is the most important performance index affecting the structure of the binder. The resin with short fluidity tends to flow less during the press curing phase of the mixture, which lowers the density of the mixture and increases its porosity, which is beneficial to improve the NVH performance of the friction material. The biggest disadvantage of short-flowing resins is that the reproducibility of the production process must be guaranteed. Conversely, a long-flowing resin will better bond the various components of the mixture together, increasing the density of the mixture and reducing its porosity. This makes it relatively easy to produce. However, high density and low porosity also make the mixture easy to foam.
2) Urotropine content: The lower the uropol content of the curing agent used for the resin, the lower the crosslink density of the cured polymer, which lowers the hardness of the product. Improve flexibility and reduce the ammonia generated during the curing process, which is not easy to foam. On the contrary, the content of the curing agent is high, the crosslinking density of the cured polymer is high, the hardness is high, the thermal stability is enhanced, and the generated ammonia gas is increased and easy to foam.
3) Gel time reactivity: Gel fast resin can increase productivity by reducing the pressing cycle. However, it is very difficult to control the high-activity resin in the production process, and it is difficult to ensure the reproducibility of each production process.
4) Free phenol: In the early stage of friction material production, free phenol can be regarded as a reaction solvent. Free phenol can reduce the melting viscosity of the resin and improve the wetting property of the resin, so as to better infiltrate the filler and fiber. As the reaction proceeds, the free phenol reacts with the urotropine and the resin to form a cured polymer. If the content of free phenol in the resin is too large, the working environment will be full of odor. However, the free phenolic odor emitted by most resins with less than 2% free phenol is not as severe as the odor emitted by ammonia and formaldehyde. Typical free phenols range from 0.3 to 05%.
In recent years, many grinding wheel manufacturers have undergone extensive tests. The level of free phenol in the phenolic resin powder has a great influence on the performance degradation of the abrasive cutting disc. The lower the free phenol content in the phenolic resin powder, the slower the performance degradation of the grinding wheel. At the same time, the lower the free phenol content, the self-sharpness of the abrasive cutting disc is improved.
5) Particle size (fineness); the particle size (fineness) distribution of the resin powder has a certain influence on the process conditions of the abrasive cutting disc. Under the design of suitable mixing process conditions, determine the particle size ratio of resin powder to abrasive to obtain the best binder structure. This must be fully considered in selecting the appropriate resin powder particle size (fineness).
In general, the finer the particle size of the resin powder, the more liquid phenolic resin is required for mixing. In any case, the coarser the particle size of the resin powder, the less liquid phenolic resin is required under the same conditions. At the same time, the production of hot-pressed grinding wheels requires a powdery phenolic resin having a suitably coarse particle size.
In addition, the need to cause the grinding wheel manufacturer is that if the particle size of the powdered phenolic resin is too fine, in addition to the difficulty of mixing, the increase of the material head, etc., it will also have a certain impact on the hardening of the grinding wheel.