Examining High-Pressure Molding. (Molding Methods & Materiald Silver Anniversary Papers).

For his Silver Anniversary Lecture titled, "Molding Sand Systems for the High-Pressure Molding Process" (03-001), H. Roshan, Intellectual Capital Exchange, L.L.C., reviewed research performed on high-pressure green sand molding for the last 25 years. His review focused on six areas: definition of a sand system, raw materials, preparation of a sand mixture, molding processes and control of sand properties. Then, Roshan provided his interpretation of what this segment of the metalcasting industry must do to excel in the future against mounting costs and offshore competitive pressures.

According to Roshan, "High pressure molding is defined as the method of molding in which major compaction of sand is accomplished by compressive force, which should exceed 100 times the rectilinear mold surface area in square inches."

Following is a look at some of Roshan's comments and suggestions on ways to improve each area of a high pressure molding system.

* Sand: "Additions of two screen sands to the sand system has helped in realizing savings in several areas including reduced sand purchases and reduced waste disposal."

* Binder: "Calcium base bentonites promote faster response to mulling with respect to developing compactability and green strength. Reduced mold wall movement is another desirable benefit."

* Sand preparation: "Strength properties of molding sand mixtures depend not only on bentonite quality and content, but also on the degree of temper and the quality of preparation."

* Molding: "The change from jolt compaction to squeeze compaction and then to impact compaction has fundamentally and detrimentally changed the compaction characteristics of sand molds. Fluid impact compaction in which sand is fluidized utilizing expanding gases before compaction produces more uniformity in the hardness and strength."

* Sand properties: "Modern green sand practice is primarily aimed at controlling the compactability in a range most suitable for molding... (However) mold and casting quality are greatly influenced by the sand formulation even though the sand is controlled in a give compactability range." Roshan also proposed that more emphasis must be focused on clay level, green strength efficiency, system processing efficiency and moisture index.