Today's markets are increasingly using hot runner systems. As with many technologies, hot runner systems have emerged to make things better and faster at less cost. The cold runner system wastes every time the mold is opened. When injection molding the parts, the multi-cavity cold runner system will cause a lot of raw material waste, which makes the profit margin of the molders seriously damaged.
Savings in raw material costs are the main driving force behind the switch to hot runner systems; another factor is the shortened delivery time. The molders and mold makers have become increasingly sophisticated with regard to process and process technology, making their interest in hot runners increasingly strong.
Although hot runner systems have a number of significant advantages, in order to ensure that the right and most effective injection molding process is obtained, it is also necessary to consider the specific application situation and consider the issues of part size, aesthetic requirements, yield, raw materials, and additives. .
The analysis of various hot and cold runner systems and their advantages and disadvantages is as follows:
Cold runner
The advantages of a cold runner are its ease of use and its ability to meet certain aesthetic requirements. Cold runners can reduce injections to transparent acrylates or polycarbonates that transmit light, preventing injections from causing visible banding effects in some areas.
As for the shortcomings of the cold runner, in addition to the waste of raw materials, the defects of the cold runner include adding steps to the entire automated or manual process. Removing the cold runner from the part of the mold requires robots or workers to separate these parts from the runner. Depending on the size of the flow path, the value of the waste may reach hundreds of thousands of dollars, especially for expensive materials such as polycarbonate. In order to maximize the profitability of the modeler, hot runners are usually a good way to save money.
For more cavity systems, cold runners may not be satisfactory. In the case of multiple cavities, the gate plastic will exceed the total amount of injection molded parts. At this time, the gate cooling time will exceed the cooling time of the injection molding part, so that the cycle time of the mold user is controlled by the gate cooling time, and this processing condition is difficult to satisfy. The hot runner can solve this problem, it can effectively increase the total number of individual cavities, because the gate is in the molten state throughout the processing.
In summary, the use of cold runners has the following characteristics:
1, the most suitable for complete sets of products with nozzles die;
2, fast delivery time;
3, for injection molding of symmetrical parts;
4, low production costs;
5, more sensitive to semi-crystalline materials;
6, the maintenance cost is relatively low;
7, flexible nozzle position;
8, to meet the needs of large outlets;
9. There is a limit to the maximum number of cavities;
10, easy to understand and easy to operate.
Hot runner
In simplifying the injection molding process and reducing part waste, it is important to eliminate the need to inject a large secondary cold runner. The key is to ensure that the melt stays molten throughout the flow path system so that it does not solidify until it reaches the cooled cavity wall.
Internally heated hot runner
The internally heated hot runner system was the first hot runner system to be put on the market, and their appearance has gone through many steps. In order to solve the various problems of the cold runner, the first solution developed is to heat the nozzle, thereby creating maximum benefits for the production of parts and components. The second method studied was a tubular hot runner system. In this technique, the main channel is heated, the molten resin flows from there to the unheated vertical sprue, and then flows through the nozzle into the cavity. Another group of molders, which emerged at about the same time as the tubular hot runner system, began placing heated probes in each vertical runner, leading to an unheated insulated runner. Since the insulated runner is cooled at the nozzle and it is difficult to maintain the "cycle" operation, the key is to ensure that the resin remains molten as it passes through the nozzle. These three technologies were later combined to form an "internally heated" hot runner system.
Internally heated hot runner
The internally heated hot runner system may be more complex than the cold runner system, but it makes the processing of difficult-to-process resins more flexible and reduces resin waste. Because the flow path is in an annular geometry, the internally heated hot runner can handle resins that are not excessively sensitive to shear, and amorphous materials, etc., are also well suited for this technique (except for those on residence time. Sensitive materials, such as polycarbonate.)
Until today, because of the high cost of externally heated hot runner systems and the required experience, some molders still insist on using internally heated hot runner systems, even cold runners.
Externally heated hot runner
The externally-heated hot runner begins with a steel block that houses a passage for molten resin. A heater fixed around the outside of the steel block heats the flow plate from the outside to make it uniformly heated inside. The melt is then dispersed throughout the heated manifold plate, into the heated nozzle, then to the final nozzle, and into the various cavities.
Externally heated hot runner
The advantages of the hot runner system are obvious. With reasonable design, this system can effectively eliminate the waste of materials during each injection cycle while achieving maximum injection molding capability and achieve “win-winâ€. D-ME, as a supplier of mold technology, will recommend hot runners to customers as much as possible because it not only saves a lot of raw materials, but also brings other conveniences to the process of the molders.
It is worth noting that it is difficult to create a completely smooth, heated trace from the entrance of a hot runner system to each hot tip. Some hot runner systems may achieve this effect, but there are times when the resin needs to cool down just at the nozzle in order to prevent wire drawing or run-out. Moreover, the flow rate and the injection speed have a great influence on the resin processing and the color change. The hot runner system design is well-suited to a certain type of resin, and it is not uncommon for a resin to be unsuitable. Traces of heated traces can usually correct these problems. Regardless of which hot runner the designer uses, consideration should be given to the resin used and the injection molded part application.
In summary, the use of hot runners has the following characteristics:
1, can be very effective in saving raw material costs;
2, support lean manufacturing;
3, to meet the demand for high output;
4, well adapted to use multiple identical cavity injection molding;
5, reduce labor and automation costs;
6, increase production speed;
7, improve processing efficiency;
8, reduce raw material recycling costs;
9. Some modelers still do not know enough about it;
10, very suitable for multi-cavity mold.
Each runner system has its own unique advantages and disadvantages, from the unheated "cold" flow path to the externally heated "hot" flow path. Hot runners require large up-front investment, but they also produce higher benefits. The increase in processing and speed can earn the cost of the entire system in just a few months, which is very attractive to mold users.
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