Heated-manifold mold

Hot-manifold mold n. An injection mold equipped with an internal heater located in the center of the melt stream in the manifold and nozzle system. This type of mold was developed for thermally sensitive resins to provide gentler heating and avoid the decomposition problems experienced with external heating techniques because of excessive temperature differences. 

Hot Runners The hot-runner system of an injection mold is characterized by a heated manifold, inside the framework of the mold, which carries melted plastic from the machine nozzle to the gates of the cavity without heat loss. Hot runners are also viewed to save material volume, as... 

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. 

A thermoplastic injection mold in which the mold that contains the runner system has its own heating elements to keep the molding material in a plastic state ready for injection into the cavities, from which the manifold is insulated. 

Injection molds are machined from a variety of tool steels and then hardened or in some cases plated with chromium, nickel, or proprietary materials. Large molds use prehardened tool steels because they cannot be hardened after machining. 124 Stainless steel is employed for some smaller molds, particularly those used for optical and medical parts and for corrosion resistance. Since they provide better heat transfer and, thus, shorter molding cycles, materials such as beryllium copper are used as inserts in critical areas. Injection molds are usually cooled or heated with water, although oil or electric heater cartridges are employed for high-mold temperatures. Mold-temperature controllers pump water into the manifolds and then into cooling fine machine into the molds. 

Consequently, many injection molding machines monitor and/or control oil temperature. Typically, hydraulics are run prior to molding to heat the oil to an acceptable temperature, and an oil temperature setting or window is often an interlock on the molding cycle. Oil is also cooled by water that is forced through a cooling manifold. This prevents degradation of the oil. Oil is also filtered to prevent wear in the hydraulic cylinders and lines. 

Injection molds are usually cooled or heated with water, although oil or electric heater cartridges are used for high mold temperatures. Mold temperature controllers pump water into the manifolds and then into cooling Unes machined into the mold. 

The basis of this approach goes back to the early days of composite manufacturing and is widely used in a broad range of applications. In most cases, matched metal tooling was used to build the geometry on both sides of the part containing a manifold system or pipe construction inside each mold where the liquid was pumped through to heat the tool itself. 

In a hot runner mold, the runner is contained in a manifold which has electrical heating cartridges. The heated runner keeps the GRTP in a fluid condition (Fig. 7-4). 

Typical molded parts for this technology are intake manifolds made from fiber reinforced PA (Figure 1.20). Remarkabie is the fact that the processing temperature of the polymer is around 300 °C where the metal alloy of the core (tin-bismuth) has a meit temperature of 140 °C. But the contact surface will only get a contact temperature of 120 °C caused by the high heat conductivity of the metal. However the high manufacturing costs will limit the application field of the process. 

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