The different plastics and processing properties of the plastics lead to different loads, which must be taken into consideration not only in the design but also in the selection of the material required for molds. Steel has the ideal qualifications, because its properties can be modified by alloying elements, special production processes, and heat treatment, and it can be adjusted to various requirements. Moreover, the possibility exists of using surface treatment to add to the already advantageous properties of the steels and thereby suits the requirements for long Plastic Pail Mould life and economical manufacture.

  The most important requirements for the injection mold steels are:

  1) High compressive strength expected even at high temperatures.

  2) Wear resistance

  3) Great toughness

  4) Corrosion resistance and good thermal conductivity.

  Also, the mold maker experts the following properties:

  1) Good machineability

  2) Good hobbing capabilities (where required).

  3) Dimensional stability during heat treatment.

  4) Good polishing properties.

  5) Surface texturing without difficulties (where required).

  Finally, the mold steel should be readily available, a requirement that demands a standardization of sizes and universally suitable types of steel.

  Considering the various stresses to which the 18L Pail Mould material is subjected,it is understandable that not all conditions can be met with one grade of steel. The experiences of many years and the close cooperation between steel producers and consumers have led to the development of mold steels that can be divided into the following groups: nitriding steels; casehardened steels; prehardened steels; fully hardened steels; corrosion-resistant steels; merging steels;hard material alloys.