Molds feed system

Runner system n. This term is sometimes used for the entire mold feeding system, including sprue, runners, and gates, in injection or transfer molding. 

Injection units are rated in terms of the maximum injection pressure and injection volume available. Injection pressure is the theoretical maximum available at the downstream end of the screw. This is a function of the screw diameter and the foree aeting on it. It should not be confused, as it often is, with the hydraulic line pressure acting on the injection cylinder that supplies the force to the screw, nor should it be taken as the pressure available to fill the mold cavities. This is much less because of pressure losses in the nozzle and mold feed systems. Injection pressures are normally quoted in megapascals (MPa), atmospheric pressures (bar), or pounds per square inch (psi) (Table 7.3). 

Major pressure drops occur in forcing the plastie melt through the injection nozzle and hence through the mold feed system and cavities. These pressure losses cannot be quantified by simple rules. They are a fime-tion of the physical form of the flow path, the condition of the plastic melts, the rate of heat exchange, the type of polymer, and the rate and pressure of injeetion. Specific figures can be calculated with adequate aeeu-racy by computer simulations of the molding process. 

Chemical activities in the field of mass screening are often related to combinatorial chemistry [51,52]. One major goal, especially in the field of solid phase chemistry involving polymers like DNA or peptides, aims at the increase in the number of compounds per reactor volume and time. Commercially available microtiter plates are established as reactors in this case whereby robotic feed systems fit perfectly to their dimensions. A drastic reduction of reaction volume and increase in number of reaction vessels ( wells ) leads to the so-called nanotiter plates (e.g. with 3456 wells). Microfabrication methods such as the LIGA process are ideal means for the cost effective fabrication of nano-titer plates in polymeric materials by embossing or injection molding techniques so that inexpensive one-way tools are realized. 

The principal types are two-plate, three-plate, and stack molds. Others include the family mold that has multiple cavities of different shapes in one mold.3, 324 A further distinction concerns the feed system that can be either the cold or hot type. These classifications overlap. Three-plate molds will usually have a cold runner feed system, and a stack mold will have a hot runner system. Two-plate molds can have either feed system. 

The feed system is the flow melt passage in the mold, between the nozzle of the IMM and the mold cavity (Figure 17.1). This feature has a considerable effect on both the quality and economy of the molding process. The feed system must conduct the plastics melt to the cavity via a sprue, runner and gate at the correct temperature/pressure/time period, must not impose an excessive pressure drop or shear input, and should not result in non-uniform conditions at the cavities of multiimpression molds. 

The feed system is an unwanted by-product of the molding process, so a further requirement is to keep the mass of the feed system at a minimum to reduce the amount of plastic used. This last consideration is a major point of difference between cold and hot runner systems. The cold runner feed system is maintained at the same temperature as the rest of the mold. In other words, it is cold with respect to the melt temperature. The cold runner solidifies along with the molding and is ejected with it as a waste product in every cycle. The hot runner system is maintained at melt temperature as a separate thermal system within the cool mold. Plastic material within the hot runner system remains as a melt throughout the cycle, and is eventually used on the next cycle. Consequently, there is little or no feed system waste with a hot runner system. Effectively, a hot runner system moves the melt between the machine plasticizing system and the mold to a point at or near the cavity(s).3 32> 326-332,490... 

Most molds for injection molding are unique in design, which depends on application, fluoroelastomer compound, and feed system (hot or cold runners). Standard systems are distinguished as two plate, three plate, or stack molds [58],... 

In-the-mold decorating Film or foil inserted in mold is transferred to molten plastics as it enters the mold. Decoration becomes integral part of product. Automatic or manual feed system for the transfers. Static charge may be required to hold foil in mold. Most plastics, especially polyolefins and melamines. For parts where decoration must withstand extremely high wear. Single- or multicolor decoration. 

Automatic or manual feed system for the transfers. Static charge may be required to hold foil in mold. 

The purpose of an injection mold is to give the shape of the part (cavity), distribute the polymer melt to the cavities through a runner system, cool the part, and eject the part. During the injection molding cycle, the polymer flows from the nozzle on the injection unit through the sprue, then to the runners, which distribute the melt to each of the cavities. The entrance to the cavity is called the gate and is usually small so that the runner system can be easily removed from the part. A typical feed system for injection molding is shown... 

When a molding machine is purchased, then the buyer is offered a choice of screw sizes three are usually available and these may be referred to as A, B or C. They have different screw diameters and allow an appropriate match of shot size (the feed system volume plus the molding volume) to barrel capacity. However, because they have different screw diameters, not only will the shot capacity vary but so will other things, for example, injection pressure and plasticizing capacity. Normally t e screws have the lowest shot capacity, and the highest injection pressure, whereas C type screws have the highest shot capacity and lowest injection pressure. 

Many plastics moldings are produced which require little or no finishing with many other molding jobs, the only finishing operation is one of removing the feed system. However, many components are decorated and where appropriate, comments on relevant finishing processes will be included in this section. 

In order for the sprue assembly to be ejected cleanly from the mold use a 3 to 6 degree (inclusive) taper on the sprue and incorporate a T type, sprue puller pin in the cold slug well ensure that the pin is secured or keyed in the correct position so as to enable the feed system to fall away, under its own weight, from the undercut on the pin. 

Regranulation of the feed system of a cold runner type mold may be accomplished by using a work handling device so that the feed system, when removed from the mold, is... 

The polymer melt injected from the nozzle of the injection molding machine flows through the sprue, runner and gate, and finally enters the cavity. The, feed system is a generic term for the sprue, runner and gate. The feed system is usually included in the flow analysis as part of the flow channel upstream to the cavity (Fig. 1.2). 

Liquid Injection Molding. Molding machines with special barrels, screws, and feed systems mix and then inject liquids into a mold cavity. Similar to reaction injection molding the two liquids, often silicone or urethane based, react to form a thermoset part. Baby bottle nipples and keycap return springs are two current silicone type applications. 

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