When discussing plastics, most people are familiar with the general concepts. However, the vertical Bakelite injection molding machine may be less known, even among professionals in the plastics industry. Understanding Bakelite powder is essential, as it differs from other plastic materials. There are two primary methods to distinguish Bakelite from other plastics:
1. Knife Pin Method: Thermosetting plastics, such as Bakelite, can be tested with a knife to determine their powdered state, while thermoplastics will leave a trace of tangible material.
2. Burn Test: Burning can also differentiate them. Thermoplastics (like ABS, PC, POM, PA, PET, PBT, PPO) emit distinct odors and smoke based on their composition. In contrast, thermosets like Bakelite are generally colorless and odorless, and they are difficult to ignite.
Despite the differences in processes, Bakelite molds and plastic molds share similarities, particularly in terms of material hardness, thermal expansion and contraction upon heating, and design features such as the size and configuration of exhaust grooves. Common thermosetting resins include polypropylene, amino resin, epoxy resin, phenolic resin, siloxane resin, unsaturated polyester resin, and polyurethane. All thermosetting resins are characterized by their ability to cure, with each resin system exhibiting unique rheological or gelling properties.
Below is an overview of the vertical Bakelite injection molding machine process outlined in four key points:
1. Preheating the Barrel: The Bakelite powder must be preheated to achieve a molten state with the lowest viscosity for effective molding.
2. Injection Pressure: Due to the high filler content (approximately 40%) in Bakelite powder, the injection resistance is substantial. Therefore, a significant injection pressure is required.
3. Drying Not Required: There is no need to dry Bakelite powder before pre-molding, as this can be detrimental to the process.
4. Exhaust Considerations: During the injection molding process, the curing of Bakelite generates water vapor and chemical gases. Consequently, molds should be designed with exhaust grooves, and the mold opening and exhaust processes may need to be enhanced to accommodate this.
