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Hot runner die has been widely used in developed countries and regions of the world. The hot runner injection molding method was introduced in the 1950s, and after a long period of promotion, its market share increased year by year.
In the mid-1980s, hot runner molds in the United States accounted for 15%~17% of the total number of injection molds, 12%~15% in Europe, and about 10% in Japan.
But in the 1990s, the hot runner mold in the plastic injection mold produced in the United States accounted for more than 40%, in the injection mold of large products accounted for more than 90%.
Because the mold hot runner is shorter than the traditional mold forming cycle and saves more raw materials, mold hot runner refers to the use of the heating device to make them melt in the flow channel always does not solidify mold, so the heat flow props in the world’s industrial developed countries and regions have been very widely used.
What are the advantages of hot runner molds?
1. Save plastic raw materials and reduce costs. In the pure hot runner mold, there is no cold runner molds, so there is no production waste.
2. Shorten the molding cycle, and improve the efficiency of the machine, because there is no limit to the cooling time of the cold runner injection molding system, the parts can be timely top out after solidification.
3. Improve product quality, and improve the surface quality and mechanical properties of products.
4. Point gate can be used without a three-plate mold.
5. Single product can be economically formed with a side gate.
6. Improve automation.
7. Use needle valve gate to control gate freezing.
8. The quality of injection parts of multi-cavity molds is consistent.
9. Improve the surface aesthetics of injection products.
10. Small injection pressure can be used, which can effectively reduce the post-deformation of thin-wall products.
Advantages and application of hot runner mold
Reduce waste
Reduce waste and improve product quality. The melt temperature of plastics is accurately controlled in the runner system during hot runner injection mold forming. Plastic can flow into cavities more uniformly, resulting in parts of uniform quality.
Hot runner forming parts gate quality is good, demoulding residual stress is low, and parts deformation is small. So many high-quality products on the market are produced by mold hot runners. For example, many plastic parts in MOTOROLA mobile phones, HP printers, and DELL laptops are made with hot runner injection molds.
Save plastic
In the pure hot runner injection mold, there is no cold runner, so there is no production cost. This is especially important for applications where plastic is expensive.
The major international hot runner manufacturers have developed rapidly in the era of high prices for petroleum and plastic materials. Because hot runner technology is an effective way to reduce material costs.
Production automation
The elimination of follow-up procedures is conducive to production automation. The products are finished after forming by the hot runner of the mold, without pruning the gate and recycling the cold runner and other processes.
Conducive to production automation. Many foreign injection molding manufacturers combine hot runners with automation to greatly improve production efficiency. Many advanced plastic injection molding processes are developed based on hot runner technology. Such as PET performing production, multi-color co-injection in the MOLD, multi-material co-injection process, STACK MOLD, and so on.
Shorten the cycle
The production molding cycle is shortened, because there is no limit to the cooling time of the runner system, and the production molding solidified can be timely top out. Many thin-wall parts produced by mold hot runners can be formed in less than 5 seconds.
Type of plastic material for hot runner
Hot runner injection molds have been successfully used to process various plastic materials.
Such as PP, PE, PS, ABS, PBT, PA, PSU, PC, POM, LCP, PVC, PET, PMMA, PEI, ABS/PC, and so on.
Any plastic material that can be machined with a cold runner injection mold can be machined with a hot runner mold.
Hot runner and cold runner mold comparison
The runner is hot to maintain the plastic material molten. The molten plastic is injected into the hot runner and flomaintainw from the heated manifold into the cavity through the heated nozzles. Here we list some advantages and disadvantages of hot runner injection mould compare with the cold runner system.
1. The hot runner is heated to ensure that the plastic of the runner and gate is kept in a molten state.
Because the heating rod and heating ring are arranged near or in the center of the runner, the whole runner from the nozzle outlet of the injection molding machine to the gate is in a high-temperature state, so that the plastic in the runner remains molten.
After shutdown, it is generally not necessary to open the runner to take out the condensate, and only need to heat the runner to the required temperature when restarting.
2. Saving raw materials and reducing product costs are the most significant characteristics of hot runner molds.
Ordinary gating systems produce a large number of the handle, in the production of small products, the weight of the gating system may exceed the weight of the product.
Because the plastic in the hot runner mold has been in the molten state, products do not need to clip the gate, basically is no waste processing, so can save a lot of raw materials.
Because there is no need for waste recycling, selection, crushing, dyeing, and other processes, it saves labor, time, energy-saving, and consumption reduction.
3. The injection material is no longer mixed with the gate material after repeated processing, so the product quality can be significantly improved.
At the same time, because the pouring system plastic maintains melting, flow pressure loss is small, so it is easy to achieve low-pressure injection of multi-gate, multi-cavity mold, and large products.
The hot gate is conducive to pressure transfer, to a certain extent, can overcome the plastic parts due to insufficient filling and the formation of depression, shrinkage, deformation, and other defects.
4. Wide range of applicable resin, convenient setting of forming conditions.
Due to the improvement and development of hot runner temperature control system technology, the hot runner can not only be used for melting polyethylene and polypropylene with wide temperatures, but also for processing heat-sensitive plastics with narrow temperature ranges, such as POLYvinyl chloride, polyformaldehyde (POM) and so on.
For polyamide (PA) which is easy to salivate, the hot runner can also be formed by selecting a valve hot nozzle.
5. In addition, simplified operation and shortened molding cycle is also important feature of hot runner mold.
Compared with the ordinary flow channel, shortening the opening and closing die stroke, not only the demoulding and forming of a cycle of the parts is shortened, but also conducive to the realization of automatic production.
According to statistics, compared with an ordinary runner, the molding cycle after switching to a hot runner can be shortened by 30%.
The main technical key of the hot runner application
A successful hot runner injetion mold application project needs multiple links to ensure. The most important of these are two technical factors.
One is the control of plastic temperature, the other is the control of plastic flow.
Plastic temperature control
The control of plastic temperature is very important in the application of hot runner mold.
Many machining and product quality problems in the production process are directly caused by poor temperature control of the hot runner system. In essence, the hot runner system eliminates the runner as a part of a finished product.
For example, the quality of the product gate is poor when the hot needle gate method is used for the injection molding process, the valve needle is difficult to close when the valve gate method is used, and the filling time and quality of the parts in the multi-cavity mold are inconsistent.
If possible, the hot runner systems with multi-zone temperature control should be selected as far as possible to increase the flexibility and strain capacity.
Control of plastic flow
Plastics flow in a hot runner system to balance. The gate should be opened at the same time so that the plastic fills each cavity synchronously. For FAMILY MOLD where the weight of the parts differs greatly, the gate size should be balanced.
Otherwise, there will be some parts filling mold pressure is not enough, some parts are filling mold pressure is excessive, the flying edge is too large quality and other problems. The size of the hot runner-runner should be reasonable. Too small mold filling pressure loss.
Conclusion
The price of hot runner injection mold is more expensive than that of cold runner systems mold, but it has obvious advantages for some large projects. It can save plastic materials, shorten the injection molding cycle, improve the quality of products and save costs.
