Injection molding machines, feeding

Closing the Mold. One half of the mold is attached firmly to the melting/feeding end of the injection molding machine. The other half slides horizontally to open or close the mold. The moving half is driven mechanically or hydraulically. When it closes the mold, it is held firmly by clamping action to withstand the injection pressure. 

Two-Stage" Injection Molding Machine. Instead of using a reciprocating screw to melt the plastic and to push the melt into the mold, the extruder screw may feed the molten plastic into a separate reservoir, and then a separate plunger can feed the melt into the mold. 

Note that the feed mechanism of the injection molding machine is activated by the plunger stroke. The function of the torpedo in the heating zone is to spread the polymer melt into thin film in close contact with the heated cylinder walls. The fins, which keep the torpedo centered, also conduct heat from the cylinder walls to the torpedo, although in some machines the torpedo is heated separately. 

A typical arrangement for a direct screw-transfer injection-molding machine for thermosets is shown in Figure 2.16. The machine has two sections mounted on a common base. One section constitutes the plasticizing and injection unit, which includes the feed hopper, the heated barrel that en closes the screw, the hydraulic cylinder which pushes the screw forward to inject the plasticized material into the mold, and a motor to rotate the screw. The other section clamps and holds the mold halves together under pressure during the injection of the hot plastic melt into the mold. 

An injection molding machine is used. The clamping unit is used as a press and preplasticizing is done in the injection unit. With this technique, much more precise feeding of the preplasticized mixture keeps the molding tolerances down. 

On account of their low viscosity, liquid silicone rubbers are processed chiefly by liquid injection molding (LM), a technique which resembles the injection molding of plastics and is combined with a meter/mix unit developed specifically for the process [7]. Additional homogenization is effected by a static mixer located between the mixing station and the feed screw of the injection molding machine (Fig. 5). 

The main component of the reciprocating screw injection molding machine. It may have various sizes, lengths, and compression ratios. It is used to feed, compress, melt, and meter the resin for injecting into the mold cavity. Basically divided into 3 major sections feed section, deep screw depths to convey the resin into the next screw s section transition section, gradually decreasing screw depths when resin is compressed, forced against the barrel s surface, and melts and... 

Feed hopper An inverted conical or pyramidal vessel mounted over the feed port of an extruder or injection-molding machine that contains a supply of pellets or powder being fed. Feed hoppers typically have a slender window from bottom to top along one side to permit observation of the feedstock level. 

The screw configuration is as follows thread depth ratio, approximately 1 2, and L/D ratio, 17/1 to 23/1 (standard three-zone screws feed, transition or middle, and metering or feed zones). Screws are equipped with a nonreturn valve to prevent backflow. Decompression-controlled injection-molding machines have an open nozzle. A short nozzle with a wide bore (3-mm minimum) is recommended in order to minimize pressure loss and heat due to friction. Residence time should be as short as possible, and this is accomplished with barrel temperatures at the lower limits of recommended settings. ... 

Bulk density (p ,) is the density of the uncompressed polymer particles and interparticle voids, whereas the bulk factor is the ratio of the solid and bulk densities. Low bulk densities and high bulk factors indicate problems with the flow of resin particles. When the bulk density is less than 0.2 g/cm , difficulties arise in conveying particles through the hopper or feed zone of an extruder or injection molding machine. ... 

Injection molding requires an injection molding machine, a mold, and ancillary equipment such as materials feeding and conveying equipment, dryers, mold temperature controllers, chillers, and robotics and conveyors. 

Two standard specifications for extruder and injection molding machines are LID and the helix angle. Length L is the length of the flighted section, which consists of the feed section, transition section, and metering section for metering screws diameter D is the outside diameter. 

This screw is more appropriate for a plasticating unit of an injection molding machine. The zero-meter screw is used to reduce the temperature build-up in the material by deepening the depth of the channel in the melt conveying zone of the extruder. The obvious drawback is that the pressure generating capability of the screw will be adversely affected, but this is not a major concern in injection molding applications. In other applications, however, the approach outlined in Section 8.3 is recommended. An extension of the zero-meter screw is the zero-feed zero-meter screw shown in Fig. 8.34. 

Figure 2 A schematic diagram of a four live-feed arrangement based on twin-barrelled injection molding machine and two double live-feed devices.

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). 

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