(1) High Wear Resistance
Glass fibers and inorganic fillers are widely used in plastic formulations to enhance rigidity and mechanical properties. When these additives are introduced, they enter the mold cavity at high speeds along with the molten plastic, causing significant friction against the cavity walls. If the mold material lacks wear resistance, the cavity is prone to excessive wear; therefore, materials used for such molds must possess excellent wear resistance.
(2) High Corrosion Resistance
Many plastic additives-such as flame retardants-and the chemical action of the molten plastic itself can corrode the mold cavity. Damage is further exacerbated when the plastic raw materials contain abrasive fillers or reinforcing agents. To mitigate this, it is advisable to use corrosion-resistant steel or apply surface plating (such as chrome or nickel plating) to the mold.
(3) Good Thermal Conductivity
Effective mold temperature control significantly impacts the quality of plastic parts during injection molding, a factor that is particularly critical when processing semi-crystalline thermoplastics. While copper alloys generally offer far superior thermal conductivity compared to alloy steels, they have lower elastic moduli, hardness, and durability. The lower thermal conductivity of steel can be compensated for by using an efficient cooling system.
(4) Good Dimensional Stability
During injection molding operations, mold cavity temperatures can exceed 300°C. Such significant temperature fluctuations can induce microscopic structural changes in the cavity, leading to dimensional instability in the mold and, consequently, the plastic parts. To address this, tool steels (heat-treatable steels) that have undergone appropriate tempering are often selected. While heat treatment is typically employed to enhance hardness and wear resistance, it must be managed to minimize dimensional changes in the mold; alternatively, machinable pre-hardened steels-which require no further heat treatment after machining-can be used. (5) Good polishing performance
The inner walls of mold cavities require a very low surface roughness to ensure the plastic parts achieve a high-gloss finish; consequently, these surfaces generally undergo polishing. Since a smoother, more lustrous surface is preferred, the mold material must be easy to polish and free from defects such as impurities or porosity.
