Temperature Control in Plastics Processing Applications

Thermocouples are needed in the plastics processing industry at different places for temperature monitoring. Whether for temperature measurement on surfaces, at injection and diecasting moulds, or for measuring the melting temperature in injection nozzles. With us, you will find the right thermocouples adapted for your application.

With over 30 years of experience, we’ve become a leading supplier of temperature sensors, and temperature controls for plastics processing equipment. Our extensive knowledge has helped us design products that offer you higher productivity and minimize your downtime.

We design, engineer and manufacture thermocouples and RTD’s. Whatever the process, whether it is new or existing, we can supply the appropriate temperature sensor. If you are unable identify the specification of thermocouple or resistance thermometer you require, we can also help identify your requirements. We can manufacture any design of thermocouple so you get the correct sensor for your process.

Plastics Manufacturing Processes

Injection-Molding Machines

Most thermoplastic materials are molded by the injection-molding process: the polymer is preheated in a cylindrical chamber, to a temperature at which it will flow, before it is forced into a relatively cold, closed mold cavity. High pressures are required to feed the molten polymer into the mold, and these typically are achieved by a reciprocating screw. After the polymer melt has solidified in the cool mold, the screw rotates backward to ready the next charge of polymer for the next cycle. In the meantime, the mold opens, and the finished product is removed.

Temperature sensors are located throughout the injection-molding equipment: from the heated barrel to the mold itself as well as in the mold-cooling medium. Typically, the sensors are Type J thermocouples. The controller type varies with the barrel size, but most plastics machinery requires PID control.

Extruders

In much the same way that injection-molding machinery uses a heated screw feed, extruders use the same principle to melt plastic and force it through a die that give the material its final shape. Many continuous shapes can be achieved. Some systems consist of a screw enclosed in barrels, around which are mounted multiple band heaters. Large extruders use cast-in heaters that include two halves that bolt together; these usually include both a heater and a cooling water or oil channel.

Temperature sensors — usually Type J thermocouples — are mounted against the outside of the barrel using a spring assembly. Controller type varies as the size of the barrel increases. This is primarily due to the large amount of friction generated in larger machines, which require cooling.

Thermoforming Machinery

In the thermoforming process, sheets of plastic, foam or any other heat-sensitive material are heated until pliable in a preheating rack and then conveyed into one of two types of presses to form the final plastic shape. The first type is a mold composed of two heated halves. They close, forming a package such as an egg carton. The second type is a vacuum-forming operation. In these systems, the one-piece mold is positioned under the preheater. Small holes in the face of the mold are connected to a vacuum pump. Once the sheet is pliable, the mold is moved into position. A vacuum is drawn that pulls the pliable material into the desired form.

In both types of thermoforming machinery, thermocouples typically are located in the molds. The controllers are usually proportional only.

Pellet Dryers

Moisture creates problems during plastics processing. It can cause poor or inconsistent quality in the final product. For this reason, dryers are used to remove moisture from the plastic pellets before they are melted. These systems typically consist of an air heater, a blower and a proportional-only controller with a Type J thermocouple in the airflow.

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