I. The history, present and future of hot runner
Hot runner systems (hot runner systems) originated in the injection molding industry without runner system, as an advanced plastic injection molding processing technology, the popular use in Western developed countries can be traced back to the middle of the last century or even earlier. Hot runner has many advantages, therefore, the development in foreign countries is relatively fast, many plastic mold factory produced by more than 50% of the mold using hot runner technology, some mold factory even reached 80% or more. In China, this technology in the last decade to really be fully promoted and applied, with the continuous development of the mold industry, hot runner in plastic molds used in the proportion also gradually increased, but on the whole has not reached the proportion of foreign hot runner mold.
In recent years, the gradual promotion of hot runner technology in China, which is largely due to the rapid development of China’s mold exports to European and American companies brought about by the volume. In Europe and the United States, injection molding production has relied on hot runner technology. It can be said that the mold without the use of hot runner technology is now difficult to export, which also caused a lot of mold manufacturers for hot runner technology awareness on the change.
2.the principle of hot runner
Cold runner is the part between the mold inlet and the product gate. The plastic is kept flowing in the runner by the injection pressure and its own heat. The runner is used as a part of the molded material, but it does not belong to the product. Therefore, when we design the mold, we have to consider both the filling effect and how to save material by shortening and narrowing the runner, which is the ideal situation, but in practice it is difficult to achieve the best of both worlds.
Hot runner, also known as no runner, means that the plastic in the runner does not solidify after each injection, and it is not necessary to remove the spout from the runner when the plastic product is demolded. Since the plastic in the runner does not solidify, the runner is still open for the next injection. In short, the hot runner is an extension of the injection molding machine nozzle.
3.the characteristics of hot runner mold
Why there is this hot runner technology appear? And what benefits can hot runner technology bring us? Engineers who are familiar with the injection molding process know that conventional injection molding often has the following disadvantages
a. difficulty in filling; b. easy deformation of thin-walled large parts; c. waste of raw materials in the sprue; d. poor quality of injection molded parts in multi-cavity molds.
2.Disadvantages of hot runner molds
Although hot runner molds have many significant advantages compared to cold runner molds, mold users also need to understand the disadvantages of hot runner molds. To summarize, there are the following points:
▲ Rising mold cost
Hot runner components are more expensive, and hot runner tooling costs can increase significantly. If part production is small, the high percentage of mold tooling costs is not economically viable. For many mold users in developing countries, the expensive price of hot runner systems is one of the main issues affecting the widespread use of hot runner molds.
▲ Hot runner mold making process equipment requirements are high
Hot runner molds require precision processing machinery as a guarantee. The integration and cooperation requirements of hot runner system and mold are extremely strict, otherwise the mold will have many serious problems during the production process.
▲Complex operation and maintenance
Compared with cold runner molds, hot runner molds are complicated to operate and maintain. If the use of improper operation is very easy to damage the hot runner parts, so that production can not be carried out, resulting in huge economic losses. For new users of hot runner molds, it takes a long time to accumulate experience in using them.
4.Components of a Hot Runner System
Although there are many hot runner manufacturers and many hot runner product lines in the world, a typical hot runner system consists of the following major components: hot runner plate, nozzle, temperature controller, and auxiliary parts.
A successful hot runner mold application project requires several components to ensure. Two of the most important technical factors are the control of plastic temperature and the control of plastic flow characteristics.
★Plastic temperature control
In the hot runner mold application plastic temperature control is extremely important. Many of the processing and product quality problems that occur during the production process come directly from poor temperature control of the hot runner system. For example, poor product gate quality when using torpedo type hot nozzle gates for injection molding, difficulty in fully closing the valve pin when molding with valve type hot nozzles, and inconsistent part filling time and quality in multi-cavity molds. If possible, hot runner systems with multi-zone sectional temperature control should be selected to increase flexibility and strain in use.
★ Control of plastic flow
The plastic should flow in a balanced manner in the hot runner system. The gates should be opened at the same time so that the plastic fills the cavities simultaneously. For parts with a large difference in weight, the sprue size should be designed to be balanced. Otherwise, there will be some parts not enough mold pressure, but some parts are overfilled and over-pressurized, poor quality and other problems. Hot runner sprue size design should be reasonable. Size is too small mold filling pressure loss is too large. Size is too large, the hot runner volume is too large, plastic in the hot runner system in the residence time is too long, destroy the material properties and lead to parts can not meet the requirements after molding.