The most popular choice of the best hot runner for

2022-08-06
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Selecting the best hot runner for injection molding of medical products

although OEM companies manufacturing final medical products usually do not directly participate in the selection of hot runner, in mold projects, involving hot runner system suppliers at the early stage of project development can bring many benefits, such as accelerating the verification process of product components, improving product quality and reducing product costs. Therefore, injection molding processors of medical products need to correctly select hot runner technology and suppliers

hot runner

hot runner refers to the melt shunting system in multi cavity injection mold. The mold with cavity is the most common in the injection molding of medical products. The hot runner consists of a splitter plate, a nozzle, a hot runner plate and a temperature controller

diverter plate

the diverter plate is a component for diverting molten materials, which can transfer molten plastics from the injection molding machine to the mold cavity of the mold. Its function is to transfer the molten raw material to the injection port, and do not change the state of the molten material flow as much as possible under the conditions of friction, shear force and heating. Most suppliers process the flow channel by drilling holes in the steel plate with preliminary machined profile to produce a splitter plate, and then install a heater on the steel plate surface or in the steel plate. In most applications, the splitter plate is designed with a number of heating zones that are individually controlled by the thermostat

in order to obtain the best effect, the flow divider design process should include detailed application analysis of injection molded products, such as product quality, raw material type and process expectation. The design of splitter plate will affect the quality and function of injection molded products. In the design of unqualified splitter plate, if the length of molten material flowing from the splitter plate to each injection port is different, it will lead to the imbalance between the mold cavities, resulting in different sizes of each product. Without proper treatment, the heat and shear process in the splitter plate will lead to polymer degradation, resulting in product performance defects and discoloration

important components of hot runner: injection port, splitter plate (upper and lower left) and temperature controller (right)

more complex splitter plate design can realize special applications such as multi-component/multi-color mold, stacked mold injection and matched product injection. Multi component injection molding can produce a single product composed of multiple materials. For example, a handle assembly having a soft touch feature. Laminated injection molding can double the output of existing machines. The stacking system of small machines can also achieve the same output as that of single-sided molds on large equipment. The laminated hot runner supports two or four layers of laminated die, doubling or quadrupling the output per cycle. Paired molds enable each injection to produce two or more components of a combined product. For the hot runner suppliers, in-depth analysis is required to achieve the cavity balance of the matching die, and the splitter plate needs to be designed by mechanical balance method

nozzle

the hot runner nozzle connects the splitter plate and the mold cavity. The typical shape is like a catheter, which can accurately control the temperature within the entire catheter length. The design and selection of injection port is very important for product aesthetics, injection filling and optimal cycle time. The end point of the gate is the "gate" - the hole where the plastic melt enters the mold cavity. The size, design and technology of hot runner nozzle with different structures are very different

the open hot sprue hot runner works on the thermal cycle principle of molten material injection - sprue cooling solidification - mold opening - injection (the next cycle) in each injection cycle. After the melt is injected into the mold cavity, the plastic cools and hardens in the gate area. After that, the injection product is ejected from the mold cavity, leaving a small gate trace on the product. Many hot gate designs use a variety of types of steel to cope with the Thermokinetics of the injection molding process

the nozzle of valve needle gate is most commonly used in medical equipment molds. The mechanical movement of valve needle is used to open and close the gate. The valve needle is usually driven by a pneumatic piston and cylinder. The gate opening and closing are controlled mechanical operations, so the valve needle gate system has better balance and repeatability

gate mark, that is, the material remaining at the gate on the product, is also a common consideration when selecting needle gate for medical applications. The open hot gate design may cause large gate marks by sticking the gate on the product. The valve needle injection port of the mechanical switch has a small trace at the joint between the valve needle and the product surface, which is not easy to be found

hot runner plate

hot runner plate provides support for the mold and bears the clamping force during injection molding. The hot runner plate with unreasonable internal support or insufficient flatness will shorten the service life of the die and reduce the product quality. If the hot runner plate deforms under the clamping force load, the key contact surface of the mold locking may be worn, resulting in flash and product size problems

the hot runner supplier shall design the struts in the hot runner plate. These struts are connected to the hot runner plate through the gap of the splitter plate and bear the cyclic clamping force load. In this way, the mold can be supported at the center and the outer edge of the hot runner plate. The application of structural finite element analysis technology can ensure the realization of solid and durable formwork design. In addition, the cooling water pipe integrated in the hot runner plate can prevent irregular thermal expansion and uneven pressure distribution on the die surface

temperature controller

the operation of hot runner is inseparable from the temperature controller, which can be used to control the heating of the system. The hot runner thermostat must be able to control different types and models of heaters. In a group of hot runner systems, the heat losses are different from each other, which makes the temperature control more difficult and complex to avoid the impact on the experiment. The high-grade thermostat can adjust the algorithm to match each heater. These thermostats can make the temperature difference between the distributor and the injection port lower than 1 ℃. At present, many temperature controllers are based on PC platform, which can perform other functions while controlling temperature, such as controlling servo motor and production management software

experimental mold and process development

the design of hot runner has a crucial impact on the performance of injection mold. Although hot runner can be used in most injection product applications, the early involvement of hot runner suppliers in the project can save a lot of time and resources

computer aided engineering tools are used to perform melt flow analysis, heat distribution, and structural analysis. The goal of the analysis is to understand what happens when the polymer melt flows through the splitter plate, so as to design the best hot runner system solution

practice and utilization of medical industry 4.0 equipment manufacturers often use test molds to determine product performance and develop injection molding processes. When considering the overall system performance, many forming test molds fail to take the influence of hot runner into account. The forming process that works well in the single cavity test mold may not be suitable for the 32 cavity hot runner mold, and the products produced by the same process are different. During the forming test phase of the project, the hot runner supplier can use prediction tools and experience to determine the applicability of the hot runner in the high cavity mold, so as to make the design more reasonable and speed up the certification of the production mold. The initial review of the application of injection molding products can make the optimization of injection molding process and the later injection molding production more reliable

future technology

the demand of medical equipment molding companies promotes the continuous development of hot runner technology. Smaller and smaller products and thinner wall thickness will prompt researchers of hot runner to look for new manufacturing technologies and materials. When the product becomes smaller and thinner, the injection pressure required for material injection will be greatly increased, requiring smaller hot runner, melting path and injection port. At present, the injection molding machine can produce an injection pressure of more than 50000 pounds per square inch (3000 bar), which can meet the production needs of thin-walled products. Only the optimized hot runner system can withstand these pressures in thousands of cycles without failure

the injection molding process requires complex and accurate heating and cooling control, and advanced temperature control technology is also essential. Optimize heat control, reduce the need for cooling, and improve efficiency and quality; Heating and materials will also cause harmful phenomena caused by metal fatigue. The new technology will optimize the heat distribution; A new algorithm of temperature controller is developed to manage the heating, cooling and temperature change of the whole system more efficiently and strictly

case analysis

a medical product injection molding company sought a hot runner solution from husky: small product size, use of engineering plastics, laminated mold and multi-mode cavity at the same time

according to the properties of resin, Heskey recommends using four cavity test mold and hot runner to evaluate the whole process. Through the audit, it was found that due to the fact that plastic raw materials are shunted in the hot runner, "murielginollin, global marketing manager of solvit polymers, said that the retention time in the plate is long, so it is not recommended to use the lamination scheme in this case. The stack design will cause the molten plastic to remain in the splitter plate for approximately eight minutes before reaching the mold cavity. Husky's test of plastic raw materials showed that as long as the retention time exceeded four minutes, the raw materials would fade

the customer finally decided to replace the laminated die with the high cavity single-sided die. With the test data of the test mold, Heskey can use the mold flow analysis results that have been verified in practice to carry out accurate analysis and optimize the splitter plate design of the high mold cavity system. The product size and shrinkage value shall be directly communicated with the mold manufacturing company to reduce the number of mold modifications. The final production mold system passed the certification soon

the above is a typical example of the success of OEM product manufacturers, mold manufacturers and hot runner suppliers through close cooperation. (end)

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