Loose-plate molds

Figure 10.17 illustrates a semiautomatic floating-plate (loose-plate) mold. The floating plate is a permanent component of the press. It has an opening at its center that will accommodate different size pots and plungers that are needed to fabricate different parts. The floating plate moves either by hydraulic or pneumatic force or by bolts/latches that are built into the mold. An important advantage of these molds is their low cost. 

Figure 10.16 Design of manual loose-plate mold.

There are three popular designs of transfer molds loose-plate, integral, and auxiliary molds. The loose-type molds can be classified into manual and semiautomatic types based on the manner of mounting and mold operation. 

Figure 10.16 illustrates one of the simpler manual transfer molds, which is particularly helpful when the molded piece contains a group of fragile inserts that traverse across the part. The mold is comprised of a plunger, a loose plate with bored through holes in its perimeter, and the cavity. The chamber above the loose plate forms the pot. 

It is important that the mold be dynamically balanced and securely locked in place on the spinning plate. The safety guards around the equipment must be capable of retaining the mold if it comes loose from the spinning plate. The polyurethane mixture must be carefully added to the center of the mold. If it hits the edge of the inlet, strands of "fairy floss-like" polyurethane may be formed. 

There are two disc flow tests. Disc Flow I is a very simple test in which a measured amount of room-temperature loose compound is compressed between two heated die plates at a specific pressure and temperature. The resultant molded disc is measured for thickness to determine the flow the thicker the disc, the stiffer the flow. The Disc Flow II procedure is similar to I except that the mold cavity has five concentric rings. The diameter of the molded disc is measured the larger the disc, the softer the flow. 

---