外文资料翻译资料来源：书籍文章名：Compression and Transfer Molds书刊名：English for Die & Mould Design and Manufacturing作 者：JianXiong Liu 出版社：北京大学出版社，2006章 节：2.4 Compression and Transfer Molds页 码：P43P49Compression and Transfer Molds外文原文：Compression Molding Compression molding is the basic forming process where an appropriate amount of material is introduced into a heated mold, which is subsequently closed under pressure. The molding material, softened by heat, is formed into a continuous mass having the geometrical configuration of the mold cavity. Further heating (thermosetting plastics) results in hardening of the molding material. If thermoplastics are the molding material, hardening is accomplished by cooling the mold. Fig. 2-6 illustrates types of compression molding. Here the molding compound is placed in the heated mold. After the plastic compound softens and becomes plastic, the punch moves down and compresses the material to the required density by a pressure. Some excess material will flow (vertical flash) from the mold as the mold closes to its final position. Continued heat and pressure produce the chemical reaction which hardens the compound. The time required for polymerization or curing depends principally upon the largest cross section of the product and the type of molding compound. The time may be less than a minute, or it may take several minutes before the part is ejected from the cavity. Since the plastic material is placed directly into the mold cavity, the mold itself can be simpler than those used for other molding processes. Gates and sprues are unnecessary. This also results in a saving in material, because trimmed-off gates and sprues would be a complete loss of the thermosetting plastic. The press used for compression molding is usually a vertical hydraulic press. Large presses may require the full attention of one operator. However, several smaller presses can be operated by one operator. The presses are conveniently located so the operator can easily move from one to the next. By the time he gets around to a particular press again, that mold will be ready to open. The thermosetting plastics which harden under heat and pressure are suitable for compression molding and transfer molding. It is not practical to mold thermoplastic materials by these methods, since the molds would have to be alternately heated and cooled. In order to harden and eject thermoplastic parts from the mold, cooling would be necessary.Transfer Molding The transfer molding process consists of placing a charge of material (extrudate or preheated preform) into the chamber, referred to as the pot. The press is activated and travels upward making contact with the floating plate, which closes the two halves of the mold. Further travel of both plates causes contact of the plunger with the material in the pot. Material is then forced through a sprue or sprues directly into the closed cavity. When the cavity is completely filled, the excess material forms a cull in the pot (excess waste material). After the part is cured, the press is opened and the floating plate and bottom plate separate from the top plate, exposing the plunger and cull. As the press travel continues, the floating plate motion is stopped by straps fastened to the top plate. This separates the two halves of the mold, and the part remains in the lower half until knockout pins extract it. Since the process requires that the single charge (shot) of material be transferred from the pot to the cavities, it is known as pot-type transfer (Fig. 2-7). An operator is needed to remove the cull from the pot plunger, remove the part or parts, clean the mold, charge a single shot of preheated material into the pot area, and activate the press. A relatively short time after the patenting of the transfer mold; transfer presses were developed. These consist of a main clamping ram located at either the top or the bottom of the press, with one or more auxiliary rams mounted opposite the clamping ram. The clamping rams activate the movable platen. The auxiliary rams are fastened to the stationary platen and are used to activate a plunger, which moves within a transfer sleeve or cylinder. For the plunger in the bottom half of the mold, the process consists of placing preheated preforms or extrudates in the transfer sleeve or cylinder, closing the two halves of the mold, and activating the plunger, which forces material out through channels, known as runners, and through the restricted gate area into the mold halves. When the cavities are completely filled, the excess material remains as a cull at the face of the plunger. After the material is cured, the press is opened at the parting line, parts are removed and the gate, runner and cull. This molding process is commonly called the plun- ger-transfer method. A typical mold construction is shown in Fig. 2-8. If the bottom plunger- transfer