How to choose a cold runner system or hot runner system for medical products? When designing medical molds, the choice of cold runner or hot runner system mainly depends on several factors such as material type, part design, production volume and cost. Selecting the right mold design system in medical molding can bring significant benefits in terms of productivity, quality and cost-effectiveness. However, before deciding to select a system, the specific requirements and potential disadvantages of the project need to be carefully considered.
Hot runner system for medical molds
Hot runner systems are heating component systems used in injection molds. Their main function is to inject melted plastic particles into the mold cavity. Hot runners use heating to keep the plastic in the runner and gate molten, so that the plastic in the runner does not solidify after each injection, and there is no need to remove the water outlet in the runner when the plastic product is demolded. This process is sometimes also called hot manifold system or runnerless molding.
Hot runners are formed by injecting hot liquid into the mold through a hot runner system. Hot liquid can be hot oil, hot water or air. By heating, it has better fluidity, so that it can flow to more delicate and complex parts in the mold. The hot runner, like a warm river winding inside the mold, with its unique heating system, ensures that the plastic melt always maintains a constant temperature during the flow process, just like a hot spring in spring, nourishing every detail. It cleverly avoids the cooling and solidification of the material in the runner, making each injection molding a seamless artistic creation, greatly improving production efficiency and reducing waste generation, as if it is the most fluent water cycle in nature, which is endless and endless.
The hot runner can be heated independently and thermally insulated in the injection mold, so that the heat loss caused by contact with the “cold” mold can be compensated separately. Therefore, the production of medical products using molds designed with hot runner systems can make the plastic parts of higher quality, reduce raw material waste and reduce costs. However, due to the relatively high price of hot runner systems, they are generally suitable for injection molding products with higher requirements and greater difficulty.
At present, hot runner system molds are mainly used in the production of plastic parts with the smallest weight below 0.1 grams and the largest weight above 30 kilograms. Hot runner molds are widely used in electronics, automobiles, medical care, daily necessities, toys, packaging, construction, office equipment and other fields. Very suitable for customized manufacturing of plastic products in medical-related fields.
Working principle of hot runner system
The working principle of hot runner system is mainly to control the heater through the thermostat, generate heat and inject molten plastic from the nozzle into the mold. During the injection molding process, the temperature sensing line will detect the temperature of the molten plastic in real time and transmit the signal to the thermostat. The thermostat controls the heater according to the preset temperature value and adjusts the power output of the heater to ensure the stability of the temperature of the molten plastic. At the same time, the nozzle is used in conjunction with the gate sleeve of the mold to control the flow direction and flow rate of the plastic. When the molten plastic is injected into the mold, the plastic in the mold will cool and solidify according to the preset shape and size, and finally form a product.
In the hot runner system, there are two main ways for the heat of the heater to be transferred to the nozzle: direct heating and indirect heating. Direct heating means that the heat of the heater acts directly on the nozzle and transfers the heat to the nozzle by heat conduction. Indirect heating means that the heat of the heater acts on the hot runner plate and transfers the heat to the nozzle by heat convection. In practical applications, the appropriate heating method is selected according to the specific conditions of the mold and production requirements.
When applying hot runner technology, the correct selection of gate type is crucial. The gate type directly determines the selection of hot runner system components and the manufacture and use of molds. Therefore, according to the different gate types, the hot runner system can be divided into three types: hot tip hot runner system, sprue hot runner system, and valve hot runner system. Each type of hot runner system has its important application characteristics and scope of application.
Medical mold cold runner system
The cold runner is a channel next to the mold cavity to inject dissolved materials into the mold to form plastic parts. The main function is to allow the plastic in the runner to cool and solidify after each injection, and then the solidified plastics such as the gate and runner condensate need to be removed from the mold manually or mechanically for waste treatment.
The cold runner is more like a quiet stream in winter. Although it lacks the warmth and vitality, it shows a different charm in specific occasions with its simple, direct and low-cost characteristics. It does not require complex heating devices, reduces equipment investment and energy consumption, just like a simple and unpretentious philosophy of life, and sees the truth in the ordinary. In the pursuit of economic efficiency and rapid response market demand, the cold runner interprets the perfect balance between efficiency and cost in its unique way.
Since the cold runner system cannot completely control the plastic flow trajectory in the plastic part, it may affect the quality of the plastic part. Therefore, it is more suitable for the production of some medical plastic products that are more cost-sensitive and do not require particularly high precision. However, it will produce more waste, and due to the cooling and solidification of the plastic, it may affect the fluidity and filling effect of the plastic melt during the next injection molding to a certain extent.
Basic principles of cold runner molds
- Plastic heating and melting: First, solid plastic particles are fed into the barrel of the injection molding machine, where they are subjected to high temperature and shear force, gradually heated and melted into flowable liquid plastic.
- Injection pressure establishment: The molten plastic builds up sufficient injection pressure under the push of the screw or piston of the injection molding machine.
- Plastic injection into the mold: Under the action of injection pressure, the molten plastic is injected into the mold cavity through the mold’s gating system (cold runner). Here, the cold runner refers to the plastic flow channel in the mold that connects the injection molding machine nozzle and the mold cavity. These channels are not heated during the injection molding process, so they are called cold runners.
- Plastic cooling and shaping in the mold: The molten plastic injected into the mold cavity gradually cools and solidifies under the action of the mold’s cooling system to form the desired plastic product.
- Product demolding: When the plastic is completely solidified, the mold opens, and the product is ejected from the mold through the ejection mechanism to complete the entire injection molding process.
The first thing to consider when choosing a medical mold design system
The application of hot runners and cold runners in injection molds is significantly different. Hot runners are suitable for high-end, high-difficulty, and high-demand injection molded products. They can improve production efficiency and reduce scrap rates, but the price is relatively high; while cold runners are suitable for simple, low-demand plastic parts. They are cheaper, but may affect the quality of plastic parts. The choice of injection molding method needs to be weighed according to the specific situation. The most important of these are the type of plastic matrix and additives, the weight and dimensional wall thickness of the parts, the quality requirements of the parts, the tool life, and the production requirements of the parts.
Between choosing hot runners and cold runners, injection mold designers need to think carefully and weigh the pros and cons like craftsmen who carefully plan. Consider both the complexity and precision requirements of the product, and the production cost and efficiency improvement. This is a collision of wisdom and experience, and every choice is a profound interpretation of the art of mold design.
Ultimately, whether you choose the warm and delicate care of the hot runner or the simple and practical approach of the cold runner, both are aimed at optimizing the mold design, allowing each drop of plastic melt to accurately shape the ideal product form, and shine with the brilliance of craftsmanship and innovation. Only in this way can the plastic parts required by medical industry customers be perfectly produced.