A quality hot runner system is critical to the injection molding of consistent, high quality parts. One of the most important performance aspects of a hot runner system is its temperature uniformity. The temperature should be consistent across the hot runner system and should not vary with time. Even slight variations in temperature can have a negative impact on part quality and consistency.

Suppliers of high quality hot runner systems are aware of the importance of temperature uniformity and therefore design towards this goal. However, a well-designed hot runner system does not function without an often overlooked component, the temperature controller. Regardless of how well the hot runner system is designed, its temperature uniformity can suffer if paired with an inadequate controller whether or not the controller’s display shows any indication of a problem.

Properly controlling the temperature of a hot runner system is a dynamic task. During injection, shear heat is generated in varying amounts throughout the hot runner system. How well the temperature controller responds to this sudden non-uniform addition of heat will determine if the various segments of the hot runner are able to consistently return to the same temperature prior to the next shot. Failure to do so will result in shot-to-shot inconsistencies. Although there are many factors that determine how well a temperature controller performs, the most critical factors are the control algorithm, response time, tuning, type of output voltage control and thermocouple resolution.

All temperature controllers use an algorithm to determine how much power to send to the heaters based on the difference between the temperature reading and set-point. Most controllers use a PID algorithm to adjust the power output to maintain set-point while others use the more advanced PIDD control, which allows the controller to stabilize back on set-point more quickly after a temperature disturbance.

A controller’s response time is determined by how often the controller compares the temperature reading to the set-point and makes a power adjustment. The faster the response time, the quicker the controller will be able to respond and the less impact temperature disturbances will have.

The various sections of a hot runner have very different thermal response characteristics. The manifold block, for instance, has a large mass and sees relatively little shear heating. The nozzle tips, on the other hand, have a small mass and are subjected to large heat sinks and a lot of shear heating. The different controller zones must respond very differently depending on which section of the hot runner they are controlling. Tuning of the control zones to properly set the algorithm constants is extremely important. Some controllers have preset constants that can be changed manually if a zone doesn’t appear to be controlling properly. Other controllers will tune themselves when first turned on; and still others continuously tune themselves to better control the hot runner after it has reached set point and is being subjected to the thermal variations caused by the molding process.

There are two basic types of output voltage control. Many controllers use an on/off type of control and constantly turn full voltage on and off, controlling by changing the percentage of the time that full voltage is being applied. This can create temperature oscillations and shorten heater life. Other controllers use a phase angle firing, always sending power but varying the voltage output to the desired value .

The last element to consider is thermocouple resolution, which defines to what increments the temperature reading is measured. Some controllers measure to one degree Fahrenheit while other controllers can measure and respond to differences as small as one tenth of a degree.

Because the temperature controller plays such an important role in the performance of the hot runner it is important to do your homework when selecting the most appropriate one for your application.

Injection moulding and core injection moulding require auxiliary equipment such as mould temperature controllers, chillers, and robots. Mould temperature controllers are essential for achieving consistent part quality and operational efficiency. Their primary function is to regulate the heat exchange between the mould and the heating/cooling medium (usually water or oil) throughout the injection moulding cycle. Precise temperature control ensures uniform material flow, minimizes residual stress, and accelerates cooling without compromising structural integrity.

For example, in producing some high-precision, high-production plastic parts, even small temperature fluctuations (±2°C) can cause warping or surface defects. Therefore, high-precision mould temperature controllers maintain thermal stability to ensure that each part meets strict tolerances. In addition to quality, temperature consistency also directly affects cycle time. Faster cooling can reduce idle time between cycles, but excessive cooling can cause brittleness. Topstar’s mould temperature controllers achieve this balance by using real-time data to adjust the cooling rate based on material properties and mould geometry.

The quality of injection-moulded parts essentially depends on how well the thermal conditions in the machine are controlled. These include the thermal balance of the injection mould as well as the temperature of the cylinder and screw. The temperature control of the mould fulfils two tasks:

heating the mould up to operating temperature
keeping the mould at operating temperature

Thermal balance of the injection mould
The injection mould is cyclically heated by the injected material. The heat is dissipated by the thermal conduction in the material and in the steel of the mould to the surface of the temperature control channel, where the heat is given off via heat transfer to the circulating heat transfer medium (water or oil). The temperature control unit dissipates the heat of the heat transfer medium and returns the cooled medium to the circulation.

Influence of the temperature control on the injection-moulded parts
Good control of the thermal processes is directly discernible from the constant high quality of the injection-moulded parts and an optimised cycle time, because the mould temperature influences the surface quality, shrinkage, warping and fluidity of the material. Here are some examples for illustration:

Sink marks and blowholes are often typical of moulds that are too hot
Gloss differences occur if the mould temperature is too high
Warping can occur in the case of uneven temperature distribution in the mould or high temperature differences between material and mould
Jetting can occur if the mould temperature is too low
The homogeneous and adapted control of the mould temperature restricts such injection errors to a minimum.