Heating Elements are the heart of a hot runner system. For this reason, when you are looking for replacement heaters, cost should not be as important as quality.
Over the years, injection molding heating elements have changed as rapidly as the injection molds themselves. The term “hot runner casting” itself explains the features of the casting process, in which the mold channels are constantly heated.
If you think of the mold as a body, then the heater is the heart, the controller is the brain, and the thermocouples are the nerves that connect the whole system together. And just like in the case of a real body, if any of the elements do not work correctly, the system will fail completely.
When choosing replacement parts for your heating system, pay more attention to the quality of the heaters than the price. The difference in the price of heaters from a good manufacturer and from a bad one is negligible compared to the total investment. The benefits of a stable heating system, improved heating parameters and finished product quality will be much greater than the savings from buying cheap heaters.
Don’t know which manufacturer to choose? Everything is simple! When ordering heaters from the Be-cu company, you will receive high-quality heating elements not at the lowest, but quite affordable prices.
#1 Cartridge Heaters For Molds
Cartridge heaters are installed around the gating channel to ensure a uniform heating temperature. It is very important to keep the distance between the heating elements and the collector equal to or not less than one diameter of the heating element.
Thermocouples must be placed at equal distances between the heating elements and the gate channel and the probe must be immersed at least 35 mm deep to ensure accurate readings.
If using cartridge heaters with a built-in thermocouple, it is very important to make sure that the thermocouple is correctly installed closer to the center of the heater and at least 5 mm from the leads.
The most common causes of breakdowns are:
- Short circuit of outputs. This can be corrected by changing the connection type of the heaters. If conventional fiberglass insulated wires were installed, this could be the cause. Hot runner systems emit gases during operation, which sometimes impregnate the fiberglass, allowing short circuits between the wires. Depending on the temperature of the environment around the wires, other connection options can be used. For example, wires with Teflon insulation are more resistant to gases, but the temperature cannot exceed 250 degrees, and heat-resistant nickel wires with fiberglass insulation and silicone impregnation can withstand up to 450 C.
- The built-in thermocouple gives incorrect readings. This can happen for two different reasons. One reason is that the thermocouple should be placed in the center of the heating element. If this is not the case, you will never get the correct gating flow temperature. The second reason is that the grounded or ungrounded thermocouple is not taken into account.
- Performance issue. In standard heaters, the coil winding is uniform. But to ensure maximum performance, cartridge heating elements with distributed power are more suitable, in which the density of winding of the heating coil is greater at the ends to compensate for heat loss and provide a more uniform heating temperature.
#2 Tubular Heating Elements
Electric heaters are inserted into special recesses on the mold manifold. This allows the heat to be precisely directed to the desired areas of the mold, such as gate outlets.
Tubular heaters are in most cases the most popular choice. These are universal heating elements, they are affordable, inexpensive and easy to install. And most importantly, they do their job!
TENs, however, have their drawbacks. And the most important thing is accessibility. The molds require specially shaped heating elements that will exactly match the shape of the channels on the manifold. It can take a long time, up to several months, for some manufacturers to manufacture a custom-made tubular heater. Heatl produces tubular heaters in 3 to 7 business days, but if you need a faster and more versatile solution, choose flexible heating elements. Heatl’s flexible moldable heaters can be molded directly on the mold and are easy to bend even by hand.
With flexible heating elements, you do not have to worry about whether the manufacturer made the correct drawing of the heater, because even the slightest discrepancy in the shape of a conventional heating element will not allow you to correctly install the heater on the mold. The thermocouple must be placed in the tubular heater in the same way as in the case of cartridge heating elements.
#3 Nozzle Heaters
One of the first designs of hot runner nozzles was quite simple – a cartridge heater was inserted into a drilled hole in the center between several gating channels. When replacing heating elements in systems of this design, the following should be considered:
- Does the hole have a flat bottom? This is very important for obtaining correct readings from the thermocouple, as air is a strong insulator. In the standard design of cartridge heaters, the end of the heater tube has a slightly concave shape due to the manufacturing process. In order to ensure correct temperature measurement, the contact between the bottom of the hole and the end of the heater must be as tight as possible.
- What is the diameter of the hole in which the cartridge heater is installed? It is very important that the hole exactly matches the diameter of the heater to ensure tight contact. Tolerances of cartridge heating elements are already taken into account by manufacturers in the manufacture of heaters. In Heatl cartridge heaters, the actual diameter of the heater is 0.16 mm smaller, that is, the 10 mm heater has a diameter of 9.84 mm to ideally fit the 10 mm hole. For better heat transfer and easier dismantling of heaters when installing cartridge heating elements, it is recommended to use high-temperature mounting paste.
- Where is the thermocouple located? The end junction of the thermocouple must be placed in the center of the flat end of the heating element tube to ensure correct temperature measurements.
- What are the requirements for connecting the built-in thermocouple? Since modern controllers have different requirements, please consult your control system supplier for exact parameters.
#4 External Heating – Spiral Heating Elements
When spiral heating elements were introduced into the design of molds , this significantly increased the speed of the cycle and the quality of the products produced. Uniform heating of the sprue nozzle ensures less degradation of the material, since there is no strong overheating. When you replace a coil heater, consider the following:
- Heater section . The flat or square cross-section of a spiral heating element has a huge advantage over a round profile. This is because flat sections have better contact with the sprue surface and a faster recovery time. For heaters with a round section, contact will be only at the extreme points of the heating element tubes, and heaters with a flat profile provide tight contact of the entire surface of the heating element.
- Correct helix winding . In order to achieve a uniform distribution of heat around the sprue, the spiral heating element must have a dense winding at the ends of the heater and a thinner one in the middle. This will compensate for heat loss at the ends of the sprue and provide a uniform temperature throughout the channel.
- Position of the internal thermocouple . The built-in thermocouple should be placed as close to the end as possible.
- Diameter of the spiral heater winding . The inner diameter of the coil must match the diameter of the sprue in order to sit very tightly. Ideally, the heater is pressed into the sprue. Brass sheathed or steel crimped helical heaters can also be used.