When to Use Hot Runner in Injection Mold

Plastic Injection Molding Overmolding Cold runner refers to the part between the mold entrance and the product gate. Plastics in the runner are kept flowing by injection pressure and its own heat. The runner is part of the molding material, but it does not belong to the product. Therefore, when we design the mold, we must consider both the filling effect and how to save materials by shortening and reducing the runner. This is the ideal situation, but it is difficult to achieve the best of both worlds in practical applications.

Hot runner, also known as non-runner, means that the plastic in the runner does not solidify after each injection, and the water outlet in the runner does not need to be removed when the plastic product is demolded. Since the plastic in the runner is not solidified, the runner is still unobstructed during the next injection.

In short, the hot runner is an extension of the injection molding machine nozzle.

Hot runner molds are widely used in industrially developed countries and regions in the world today. This is mainly because hot runner molds have the following significant features:

Shorten the molding cycle of parts

Because there is no cooling time limit for the runner system, the parts can be ejected in time after molding and curing. The molding cycle of many thin-walled parts produced by hot runner molds can be less than 5 seconds.

Save plastic raw materials

In pure hot runner molds, there is no production cost because there is no cold runner. This is particularly important for applications where plastics are expensive. In fact, major international hot runner manufacturers have developed rapidly in the era when oil and plastic raw materials are expensive in the world. Because hot runner technology is an effective way to reduce material costs and reduce material costs.

Reduce waste and improve product quality

During the hot runner mold molding process, the temperature of the plastic melt is accurately controlled in the runner system.

Plastics can flow into each mold cavity in a more uniform state, resulting in parts of consistent quality. The gate quality of hot runner molded parts is good, the residual stress is low after demolding, and the deformation of the parts is small. Therefore, many high-quality products on the market are produced by hot runner molds.

Eliminating subsequent processes is conducive to production automation.

After the hot runner mold is formed, the product is the finished product, and there is no need to trim the gate and recycle the cold runner. It is conducive to production automation. Many foreign product manufacturers combine hot runners with automation to greatly improve production efficiency.

Expand the application scope of injection molding process

Many advanced plastic molding processes are developed on the basis of hot runner technology. Such as PET pre-molding, multi-color co-injection in the mold, and multi-material co-injection process.

Although hot runner molds have many significant advantages compared with cold runner molds, mold users also need to understand the disadvantages of hot runner molds. In summary, there are the following points:

Rising mold costs

Hot runner components are relatively expensive, and the cost of hot runner molds may increase significantly. If the part output is small, the mold tool cost ratio is high, and it is not economically worthwhile. For mold users in many developing countries, the high price of hot runner systems is one of the main problems that affect the widespread use of hot runner molds.

High requirements for hot runner mold manufacturing process equipment

Hot runner molds require precision processing machinery to ensure. The integration and matching requirements between the hot runner system and the mold are extremely strict, otherwise the mold will have many serious problems during the production process. For example, poor plastic sealing leads to plastic overflow and damage to the hot runner components, interrupting production, and poor relative position between the nozzle insert and the gate leads to a serious decline in product quality.

Complex operation and maintenance

Compared with cold runner molds, hot runner molds are complex to operate and maintain. If improper operation is used, it is very easy to damage the hot runner parts, making production impossible and causing huge economic losses. For new users of hot runner molds, it takes a long time to accumulate usage experience.