Hot runner manifold

It is important in this or any other heat stability test to mold the natural resin as a control. Some resins, especially acrylonitrile butadiene styrene (ABS), darken considerably when heated above a particular threshold temperature. In the case of ABS, the butadiene rubber component may begin to go yellow and dark over 450°F. Although the customer may set its machines below 450°F barrel temperatures, shear heating or heating in the hot runner manifold could yield local melt temperatures in excess of 500°F and burn the natural resin. 

One can see from Figure 2.10 that a three-plate mold operation necessitates removal of the ruimer and sprue system, which must be reground, and the material reused. It is possible, however, to eliminate the runner system completely by keeping the material in a fluid state. This mold is called a hot-ruimer mold. The material is kept fluid by the hot-runner manifold, which is heated with electric cartridges. 

Tubular heating elements are extremely durable, resistant to contamination, and quite economical. They can be used on dies, radiant, thermoforming, and hot runner manifold applications. Tubular heaters provide temperatures up to 649°C and offer tremendous design flexibility. 

Direct Flow, Manifold systems, balanced hot runner manifolds, Incoe Corp. 

In the classical IM elastomer processing, a so-called hot runner manifold is used for distributing the mixture from the injection nozzle of the injection unit to the individual cavities. The elastomer, which is located in the hot runner manifolds after the filling cavities, cures and is removed after opening the mold. To make this possible, the molds are designed as three-platen molds. The hot runner is located in the first parting plane, and the products are located in the second parting plane. 

Thus, all the benefits of the system nozzles can be used for single applications without a hot runner manifold, even If not driven with an adjacent machine nozzle. The nozzle bodies are usually made from special hot work steel. This guarantees a high compressive strength, even for continuous temperatures well above 300 °C. With these nozzle concepts, plastics with filler contents of more than 40% and VO-adjusted materials at injection pressures of 2,000 bar or more can be reliably processed. Figure 2.58 shows a typical representative of the manufactured products family with this nozzle series. High processing temperatures, a narrow process window, and the risk of abrasive and chemical wear of the mold components are characteristic of this type of technical components. 

FIGURE 2.64 Hydraulic needle drive, mounted on the hot runner manifold... 

Hot Runner Manifold Systems, Wired Systems, and Hot Halves... 

Fluctuating part quality, incompletely filled parts, and gloss variations indicate defective hot runners. The causes include loose connections or cracks on the hot runner manifold. The mold has to be completely disassembled and any leaked plastic (Figure 5.42) has to be mechanically removed. 

Tooling. Tooling is relatively expensive for injection molds. Production molds are normally machined and burned (electro-discharge machined) from tool steels (P20) and must be sfructured to withstand high pressures. Precision is required to incorporate cooling lines, ejector pins, and cavity pressure transducers or temperature monitoring sensors. The use of hot runner manifolds adds further complexity and cost, but may be justified because cold runners and their associated costs are eliminated in manufacturing. 

Provide adequate heating for the hot runner manifold (1.8 watts/cm or 30 watts/in ) and nozzle (approximately 300 watts)... 

Insulate the hot runner manifold and nozzles from the machine platen or mould cavities by air or compressed temperature resistant sheeting... 

The objective of purging is to clean out the melt in the hot runner manifold in the least amount of time with the minimum amount of material when transitioning from one resin to another or one color to another. This can be accomplished in a number of ways but it always based on the fact that the material near the wall of the manifold is the last to be replaced. 

The injection machine was injecting 15 maximum shot size shots for HIPS. The first shot was injected with mixed mica materials. After injection the first shot, some mica particles still remained in both the barrel and the hot runner manifold. Those particles are assumed to simulate a color or contamination. The second to fifteenth shots used virgin material to purge the previous one and the mica particles. The purged materials were put into a water bath to cool down. Then, they were cut into small pieces and weighed and then put in a crucible for ash testing. 

A low melt temperature in hot runner manifold and barrel is the best condition for purging. The reason is the temperature affects viscosity of the melt. Lower temperature raises the viscosity. When purging was performed, the high viscosity in barrel can remove the previous material in both barrel and hot runner manifold. 

Kumar Aditya. Quantifying Pressure Loss in a Hot Runner Manifold . M.S.Eng. Thesis. University of Massachuseets Lowell, 1997. 

Magda M. Castillo. A Hot Runner Manifold as a Pressure-Volume-Temperature (PvT) Apparatus. Doctoral Dissertation. University of Massachusetts Lowell, 2002. 

Figure 3. Percentage of mica particles in each shot when barrel and hot runner manifold are purged together...

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