STEELS

Following is a list of some of the most commonly used materials for mold construction. They include the following:

-- P-20 Pre-hard steel. Rc 29-36. The most common tool steel used, it is a favorite among mold makers for its durability and machining qualities.

-- H-13 Air hard steel. Rc 46-54 Great for high production cavities and cores, slide bodies, lifters, and gibs.

-- S-7 Air hard steel. Rc 54-56 Used for many of the same applications as H-13 however somewhat less stable and more prone to cracking. Great for long wearing gibs and guides.

-- M-2 High speed steel. Rc 60-62 used where tough rigidity is required such as tall thin core pins or blades.

-- 420 SS stainless steel. Rc 49-53 Best for achieving high polish finishes. Also for corrosive polymers such as PVC.

-- Beryllium Copper. Primarily used for inserting small areas in tools that may be prone to over heating. The thermal characteristics of beryllium copper make it the best choice for wicking heat out these areas.

-- 7075 T-6 Aluminum. Generally used for short run or prototype tooling, however the hardness, wear resistance and ability to take a good polish has caused many a short run mold to outlast its projected life.

-- Lamina. "Lamina" is a name brand material that is used for wear plates. This material is a bronze over steel laminate that imparts long life to moving parts with a minimum of lubrication. In addition to wear plates it is commonly used for large locking surfaces.

New materials.

Because of the liability involved in the high stakes molding business mold makers are reticent to change from known materials. For example a new material was introduced a few years back as being the successor to P-20. The great advantage was to be that it was weldable without leaving any flaws to show through textures. Problem was that after a few months of operation it became evident that the texture had begun to wash away with the plastic flow. Many very expensive cavities then had to be replaced. As a result of debacles such as these, mold makers are very skeptical of new materials when the old ones, even with their shortcomings, are known quantities.