文献翻译—注塑模具简介

附录

THE INTRODUCTION OF MOLDING The mode is at the core of a plastic manufacturing process because its cavity gives a part its shape. This makes the mold at least as critical-and many cases more so-for the quality of the end product as, for example, the plastic unit or other components of the processing equipment.

1.1 MOLD COMPONENTS

Molds used in injection molding consist of two halves; one stationary and one movable. The stationary half is fastened directly to the stationary plate and is in direct contact with the nozzle of the injection unit during operation. The movable half of the mold is secured to the movable platen and usually contains the ejector mechanism. There are many possible mold designs, including multiple piece molds for complicated parts. On production injection molding equipment many articles may be shot at the same time by the use of multiple cavity molds. The use of a balanced runner system carries the plastic from the sprue to each individual cavity. At this point the material passes through a gate into the cavity. The gate is a restriction, smaller than the runner, to provide for even filling of the mold cavity and to allow the products to be easily removed from the runner system. With most injection molding systems, the articles can be snapped away from the runner or sprue without additional trimming. Products that have been injection molded can usually be identified by finding where the gate was broken off. The gate will usually be located at the edge or parting line of an object or in the center of cylindrical product.

Molds are expensive, as are the machines. Yet, once the product has been designed, molds made, and production started, articles can be produced in quantity at low cost. Virtually all thermoplastics can be injection molded through variations in mold and machine design.

Mold (and die) parts that are mass-produced and standardized in shape and dimension are referred to as “standards”(or, “standard parts”). Specialized operators of milling machines, lathes, electronic discharge machining (EDM) equipment and grinders produce mold components, independently of each other, following detailed mold part drawings. Finally, all these items come together with the standard mold base and hardware and are assembled by the mold maker. Today, standard components for the moldmaking industry are marketed by a number of companies.

1.2 HOT RUNNER SYSTEMS

Hot runners are classified according to the ways they are heated: insulated-runner systems (it is not described in this article) and genuine hot-runner systems.

The latter can be further sub-classified according to the types of heating: internal heating and external heating.

Heating is basically performed electrically by cartridge heaters, heating rods, band heaters, heating pipes and coils, etc. to ensure uniform flow and distribution of the melt, usually a relatively elaborate control system comprising several heating circuits and an appropriate number of sensors is needed. The operating voltage is usually 220 v to 240 v, but small nozzles frequently have a low voltage of 5 v , and also 15 v and 25 v operating voltage.

Runner systems in conventional molds have the same temperature level as the rest of the mold because they are in the same mold block. If, however, the runner system is located in a special manifold that is heated to the temperature of the melt, all the advantages listed below accrue. Runner manifolds heated to melt temperature have the task of distributing the melt as far as the gates without damage. They are used for all injection molded thermoplastics as well as for cross linking plastics, such as elastomers and thermosets.

In the case of thermoplastics, these manifolds are usually referred to as the hot-runner system, the hot manifold, or simply as hot runners. For crosslinking