Although medical product companies are usually not directly involved in hot runner selection, in the mold project, having hot runner system suppliers participate in the early stages of project development can bring many benefits, such as accelerating the verification process of product parts, improving product quality and reducing Product Cost. Therefore, medical product injection molders need to choose the right hot runner technology and suppliers.
Hot runners are melt split systems in multi-cavity injection molds. 4-32 cavity molds are most common in medical product injection molding. The hot runner consists of a manifold, a spout, a hot runner plate, and a thermostat.
The manifold is a component that splits the molten material and transports the molten plastic from the injection molding machine into the mold cavity of the mold. Its function is to transfer the molten raw material to the nozzle, and in the case of friction and shearing force and heating, the state of the molten stream is not changed as much as possible. Most suppliers manufacture manifolds by drilling holes in steel plates that have been previously contoured, and then mounting heaters on the steel plate or in the steel plate. In most applications, the manifold is designed with several heating zones that are individually controlled by the thermostat.
The hot runner nozzle connects the manifold and the cavity, typically shaped like a conduit for precise temperature control over the entire length of the conduit. The design and selection of the nozzle is important for product aesthetics, fill fill and optimum cycle time. The end of the nozzle is the "gate" - the hole in which the plastic melt enters the cavity. The size, design and technology of hot runner nozzles of different configurations vary widely.
The open hot runner hot runner operates on the thermal cycle principle of the molten material injection-nozzle cooling solidification-opening-injection (next cycle) in each injection cycle. After the melt is injected into the cavity, the plastic cools and hardens in the gate area. After that, the injection molded product emerges from the cavity, leaving a small gate mark on the product. Many hot gate nozzle designs use multiple types of steel to cope with the thermodynamics of the injection molding process.
The nozzle of the valve gate is most commonly used in medical equipment molds, using the mechanical movement of the valve needle to open and close the gate. The valve needle is usually driven by a pneumatic piston and cylinder. The opening and closing of the gate is controlled mechanical operation, so the valve gate system has better balance and repeatability.
The gate mark, the material remaining at the gate on the product, is also a common consideration when selecting a valve gate for medical applications. The open hot gate design makes it possible to stick gates on the product to form larger gate marks. The valve-type nozzle of the mechanical switch has little trace on the joint between the valve needle and the product surface and is not easily found.
Hot runner plate
The hot runner plate provides support for the mold and withstands the clamping force during injection molding. Hot runner plates with unreasonable internal support or insufficient flatness will result in shorter die life and lower product quality. If the hot runner plate is deformed under the clamping force load, the key contact surface of the mold clamping may be worn, causing flash and product size problems.
Hot runner suppliers should design pillars in the hot runner plate. These struts are connected to the hot runner plate through the gap of the manifold to withstand cyclically reciprocating clamping force loads. This provides support for the mold at both the center and outer edges of the hot runner plate. The use of structural finite element analysis technology ensures a robust template design. In addition, the cooling water pipe integrated in the hot runner plate prevents irregular thermal expansion and prevents uneven pressure distribution on the mold surface.
The operation of the hot runner is inseparable from the thermostat, and the thermostat can be used to control the heating of the system. Hot runner thermostats must be able to control different types and models of heaters. In a group of hot runner systems, the heat losses vary from place to place, making temperature control more difficult and complex. The high-end thermostat can adjust the algorithm to match each heater. These thermostats allow the temperature difference between the manifold and the nozzle to be less than 1 Â°C. At present, many thermostats are PC-based platforms that can perform other functions while controlling temperature, such as controlling servo motors and production management software.
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