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2 plates mold,3 plates mold and hot runner mold
When it comes to plastic injection molds, There are many classifications for plastic injection molds. The most common division is between cold runner and hot runner molds. In general, hot runners are more expensive than cold runners, but also offer better performance and durability.
According to the basic injection mold gating system, it can be divided into three types:
- Two-plate mold;
- Three-plate mold;
- Hot runner mold is also called runner-less mold.
Other plastic molds, such as the side core pulling mechanism and core-unscrewing de-molding mechanism, evolved from these three types of molds.
| System Type | Advantage | Disadvantage |
| Cold runner | · Lower tool cost · Easily modified · Enables use of robotics | · Typically governs cycle time · Potential for cold slugs · Potential for sprue sticking · Scrap (though regrindable) |
| Hot Sprue or Extended Nozzle | · Faster cycle · Minimizes scrap · Easily maintained · Better temperature control | · Higher tool cost · Potential heat degradation for SBS compounds |
| Hot Runner | · No runner scrap · Faster cycle time · Precise temperature control | · Highest tool cost · Purging · Material degradation · Maintenance |
Two-plate mold
Two-plate mold or single parting surface mold is the simplest and most widely used mold in injection molding.
The 2 plates mold is divided into two parts: the moving half and the fixed half by P/L.
The core side is in the moving mold half, and the cavity side is in the fixed mold half.
The runner is in the fixed mold, and the main runner is arranged on the parting surface.
After molding, the injection-molded product and runner remain in the moving mold half, the product and the injection system are ejected off from the same parting surface.
And the movable mold half is equipped with ejection systems to push the products away after opening the mold.
Three-plate mold
3 plates mold is also called double parting surface mold.
The mold is divided into three parts, a runner stripper plate is added between the top clamping plate and cavity plate.
This structure is suitable for products are not allowed to have gate marks along sidewall, or item with a large projection area and to need multi-point gates.
This kind of mold adopts a pinpoint gate.
This kind of mold has a more complicated structure and needs an additional distance parting mechanism.
The three-plate mold is divided into normal three-plate molds and the simplified three-plate mold.
Simplified three-plate mold doesn’t have four guide pins between moving and fixed half.
Hot runner mold
Hot runner mold is also called runner-less mold, including insulated hot runner mold and heated runners mold.
The plastic in the gating system is always in a molten state, so there will be no gating system material such as two-plate mold and three-plate mold in the process.
The hot runner mold integrates the advantages of the simple action of the two plate mold and the melt of the three plate mold entering from any point in the cavity.
In addition, the hot runner mold has no loss of pressure, temperature and time in the runner, so it not only improves the injection molding quality but also shortens the molding cycle, which is a major innovation in the gating system technology of the injection mold.
In Japan, the United States, Germany and other countries with highly developed injection molding technology, the hot runner injection molds are very popular, accounting for about 65%.
The hot runner system has been widely used, mainly because it has incomparable advantages over traditional 2-plate and 3-plate molds:
Shorten the cycle time
Because there is no limitation of the cooling time of the runner system, the part can be ejected soon after solidification. Many thin-walled parts produced with hot runner molds can be molded in less than 5 seconds;
Plastic Raw Materials Saving
Because there is no runner material in the hot runner mold, there is no production cost. This is especially significant for reducing the cost of raw materials. The major hot runner manufacturers in the world have developed rapidly, for plastic raw materials are expensive now because hot runner technology is an effective way to reduce the cost of materials.
Reduce the failed parts and improve the product quality
For the hot runner mold production, the plastic melt temperature is accurately controlled in the runner system. Plastic can flow into each mold cavity in a more uniform state, producing parts with consistent quality. In addition, hot runner molding has beautiful gate relics, low residual stress, and smaller part deformation. Therefore, many high-quality products on the market are produced by hot runner molds.
Eliminate the subsequent operation
The finished product is obtained after the finished product is molded by a hot runner mold, and subsequent operations such as trimming a gate and regrinding a cold runner are not required. It is good for production automation.
Difference between Two-plate Mold and Three-plate Mold
The structures of the two-plate mold and the three-plate mold are shown. Their differences are as follows.
Different structures:
- Runner ejection plate;
- Guide pins and guide sleeves on the runner ejection plate;
- Fixed distance parting mechanism. The mechanism that guarantees the mold opening sequence and mold opening distance is called the fixed distance parting mechanism.
Different mold gate systems
- Three-plate injection mold can be gated from any point in the cavity, and pinpoint gates are often used.
- The two-plate mold is mostly fed from the outer side of the cavity, and side gates are often used. When the product is large or a large hole in the middle of the product, it can also be fed from the inner side. In addition, the submerged gate can also be cut on the cavity.
- During the three-plate mold production, the runner system and the product will be automatically cut off and separated, which is convenient for realizing automatic production; However, the runner system and the product of the two-plate mold production usually needs to be removed manually.
The different parting surface
There is only one PL during the 2-plate mold injection molding production. The product and the injection system material are taken out from the same parting surface.
However, three surfaces are opened during the three-plate mold injection molding production, and the product and the injection system are taken out from different parting surfaces.
The different manufacturing costs
The three-plate mold are more expensive, and the manufacturing time is longer. In addition, the three-plate mold are more expensive and require a longer manufacturing time because they require additional processes to be performed. The different surface finish Three-plate molds produce products with a better surface finish than two-plate molds.
The different action principle
The three-plate mold can automatically cut off the gate during the production process. The mold can be fully automated, and the product quality is good. The two-plate mold gate can only be manually trimed, and the product quality is not as good. The different size ranges The three-plate mold have a larger range of sizes than two-plate molds.
However, due to the complex structure, the mold failure chance is also high. The different molding cycle times The three-plate mold has a longer cycle time than two-plate molds.
Final words
Hot runner molds are becoming popular in not only injection molding but also extrusion. But this type of machine requires a lot of matching components and associated machines, which can be costly. They can help companies reduce costs in the long run, but the upfront cost may be worth it for some businesses to avoid. This is where 2 or 3 plates mold design comes into play. 2 or 3 plates molds are less expensive than hot runner molds, saving companies both time and money. These molds can also be used in mass production if they need to be. Regardless of the type of mold you plan to purchase, by making sure it has all of the features you want, you can save both time and money and create a great product.