When quenching and cooling plastic mold steel, attention should be paid to four aspects. They are cooling medium problems, cooling equipment problems, clear mold surface covering problems, and manual operation technical problems. So what are the more practical mold steel quenching cooling techniques?
1. Plastic mold steel spray quenching method Large and complex, especially thick and thin workpieces and die steel, in order to avoid excessive quenching stress in cooling, control the cooling speed of different parts of different stages of the cooling process. There are spray (water or aqueous solution), spray (compressed air and water sprayed to different parts of the part by atomization), gas quenching and other methods, which have the advantage of controlling different media or different flow rates, pressure to control and adjust each temperature The cooling rate of the area; or changing the number and position of different nozzles; cooling evenly. Vacuum high pressure gas quenching which is currently popular in mold heat treatment is.
2, plastic mold steel grade quenching method
The mold steel or workpiece heated to the austenitizing temperature is quenched into a cooling medium (usually a salt bath) whose temperature is near the martensite transformation temperature, and is left for a period of time, so that the surface of the workpiece and the center temperature gradually become uniform. The air cooling is taken out and the martensite transformation is completed at a lower cooling rate. This method can significantly reduce the deformation and improve the toughness of the mold steel, and is one of the commonly used quenching methods for the mold parts. There are two types of temperature selection for mold steel quenching. One is to take 10~30 °C above the Markov transformation starting temperature (Ms point) of the steel of the workpiece to be processed; the other is to select 80~100 °C below the Ms point. The residence time of the classification should also be well mastered. If the temperature is too short, the temperature is not uniform enough to achieve the purpose of classification quenching; if it is too long, non-martensitic transformation may occur to reduce the hardness.
3, plastic mold steel isothermal quenching method
The mold steel workpiece heated to the austenitizing temperature is quenched into a hot bath at a temperature slightly higher than the Ms point of the quenched steel grade, and the phase change is completed to obtain the lower bainite structure or the lower bainite and Markov. Body mixed tissue. The purpose of this method is to relieve deformation and cracking, and to have small quenching stress. Has similar strength and toughness to tempered martensite.
4, plastic mold steel single liquid quenching method
The mold steel or parts are heated to austenitizing and then quenched into water, oil or other cooling medium, and cooled for a certain period of time (cooled to a region below the pearlite type transition temperature or martensite transformation temperature) to take out the mold steel air cooling. Since the mold steel cooling process is completed in a single cooling medium, it is called a single liquid quenching method.
5, plastic mold steel two-liquid quenching method
As the name implies, the quenching and cooling process of the die steel is done in two cooling media (usually water, oil). The cooling process is ideal, which is rapidly cooled in the pearlite transformation region and slowly cooled in the martensite transformation region. The specific method is to first quench the mold steel or parts heated to the austenitizing temperature into the high temperature region. A medium (usually water or a brine solution) to inhibit pearlite transformation of supercooled austenite when cooled to 00 °C. When it is left and right, quickly remove the second medium (usually oil) that is transferred to the low temperature zone and slowly cooled. Since the martensite transformation is carried out under milder cooling conditions, it can effectively alleviate or prevent deformation and cracking, which is commonly referred to as water quenching and oil cooling. This method requires a high level of skill. Sometimes understood as three kinds of media, namely the first water, the last oil, and finally the air.
Avoiding the deformation and cracking of the mold steel during use, it is also necessary for the cooling of the mold steel after the quenching process, so that the mold steel is not easily deformed, has suitable viscosity under the use conditions, is not flammable, explosive, Non-toxic and so on.