1. Basic principles of heat treatment process
Heat treatment is a process that changes the structure of metal materials by heating, keeping warm and cooling them to optimize their performance. For Beverage bottle preform mold materials, mold steel is common. During the heating stage, as the temperature rises, the atomic activity inside the material intensifies and the lattice structure changes. For example, when heated above the critical temperature, the ferrite and cementite in the steel begin to dissolve to form a uniform austenite structure. The insulation process is to ensure the homogenization of the structure and allow the alloy elements to diffuse fully.
2. Heat treatment methods to improve hardness
Beverage bottle preform mold requires sufficient hardness to resist the wear and pressure of plastics during the injection molding process. Quenching is a key heat treatment process to improve hardness. During the quenching process, the mold material is heated above the critical temperature, kept warm for a certain period of time, and then cooled rapidly. Rapid cooling transforms austenite into martensite, which has the characteristics of high hardness and high strength. For example, for P20 mold steel, the quenching temperature is generally between 820-870℃, and the hardness can be significantly improved after oil quenching. However, quenching can also easily cause internal stress in the material, which requires subsequent tempering treatment to eliminate.
3. Heat treatment strategy to improve toughness
In addition to the hardness requirements, the mold also needs good toughness to prevent cracking during use. The tempering process plays an important role in improving toughness. Tempering is to heat the quenched mold material to a certain temperature range below the critical temperature, keep it warm and then slowly cool it. During the tempering process, martensite decomposes, internal stress is released, and tempered troostite or tempered troostite structures are generated. These structures greatly improve the toughness of the material while maintaining a certain hardness. For example, for quenched mold steel, tempering treatment at 550-650℃ can make the toughness of the material meet the use requirements of Beverage bottle preform mold.
4. Heat treatment considerations for enhancing wear resistance
Beverage bottle preform mold frequently contacts plastics, and wear resistance is crucial. Nitriding is an effective heat treatment process to improve the wear resistance of mold materials. Nitriding is to make active nitrogen atoms penetrate into the surface of mold materials at a certain temperature to form a nitride layer. This nitride layer has high hardness and good wear resistance and corrosion resistance. For example, by using gas nitriding process, at a temperature of 500-550℃, after dozens of hours of nitriding treatment, a layer of nitride layer with excellent performance can be obtained on the surface of the mold material, which significantly improves the wear resistance of the mold in injection molding production. By reasonably combining heat treatment processes such as quenching, tempering and nitriding, the hardness, toughness and wear resistance of Beverage bottle preform mold materials can be fully optimized, thereby improving the quality and service life of the mold.
