/ep_edm/en/contect_799.html SHINI PLASTICS TECHNOLOGIES, INC.

Special Reports

2013 Quarter 4 Issue 17

Temperature Control of Hot Runner System

Share to:
The hot runner system must be in heat balance state where the heat loss is compensated by heating. The temperature control is very important for hot runner system, especially for the pouring gate of hot runner mold and hot nozzle which are really sensitive to changes of temperature. Even temperature change of several degrees may lead to defective product. Therefore, precise temperature control is really important for well-functioning hot runner system. So far, most temperature controller adopts P.I.D. structure which can limit the temperature change within 1℃. 

Placement of thermocouple is another key point for temperature control. There are two key places in hot runner: one is pouring gate whose temperature condition is very important for both melt’s mobility and continuous pressure; the other one is the place where the output of heat is the most and the plastics is at risk of thermal decomposition. Therefore, the thermocouple should be installed in the place where the expected temperature is the highest, but not the place where heat loss occurs, like place near press ring, seal ring or the outside area of hot runner. Now the heat balance can be analyzed via computer, which can basically locate the points of high temperature on hot nozzle and flow distribution plate. 

The hot nozzle of hot runner usually adopts external heating which sets a spiral pipe heater outside the hot nozzle. Sometimes it may adopt internal heating which set a heating bar inside the hot nozzle. As for runner plate, it usually use pipe heating bar to heat. The pipe heating bar is set on both upper and lower surfaces after curving along with the runner plate.

Reasons for the temperature displayed on PV screen of temperature controller can’t reach to the set temperature on SV screen: 
1. The power of hot runner’s heating system is small. 
2. The heat dissipation of hot runner system is too fast. 

Solutions are as following: 
1. Increase the power of hot runner’s heating system.
2. Check the heat insulation of hot runner system.

Reasons for the great difference between the displayed temperature on temperature controller and the actual temperature :
1. Setting of thermocouple type of hot runner temperature controller doesn’t agree with the thermocouple model. 
2. The thermocouple of hot runner is short circuit. 
3. Has set the process deviation.

Solutions: 
1. Set hot runner thermocouple model correctly. 
2. Check lines and connect them correctly. 
3. Eliminate the process deviation to set the P.D. to be 0. 

Severe fluctuation of temperature of the hot runner temperature controller is caused by the following reasons: 
1. Have no self-adjustment. 
2. Is self-adjusting, but set the inappropriate parameters. 

Solutions:
1. Self-adjust. 
2. Modify the self-adjusting parameters. 

Notes: 
①P.I.D. percentage values, time of integration and differential time.
②P.D. percentage values plus differential time