September 2019

HOW INFRARED TEMPERATURE SENSORS OF EXERGEN CAN REDUCE WASTE WHILST MANUFACTURING PLASTICS?

APPLICATION NOTE: VACUUM THERMOFORMING

Thermoforming is one of the oldest and most common methods of processing plastic materials. Vacuum formed products are all around us and play a major part in our daily lives.

The process involves heating a plastic sheet until it is soft and then draping it over a mould. A vacuum is then applied, pulling the sheet into the mould. After cooling down the sheet is ejected from the mould. In its advanced form, the vacuum forming process utilizes sophisticated pneumatic, hydraulic and heat controls, thus enabling higher production speeds and more detailed vacuum formed applications.

The heaters used in vacuum forming are generally infrared elements mounted within a reflector plate. In order to obtain the best vacuum forming results, it is essential that the plastic sheet is heated uniformly over its entire surface area and throughout its thickness. In order to achieve this, it is necessary to have a series of heating zones that are controlled by energy regulators.

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APPLICATION NOTE: BLOW MOULDING

In the process of making PET bottles (polyethylene terephthalate) there is a fine line where the high output per bottle blowing machinery and the requested quality of the bottle come together. Taking into account that such machines must be able to produce a broad range of sizes and shapes and produce various quality bottles, it’s obvious that many variables must be kept under control during the process. One of the key parameters to control is the temperature.

How does this work?
The bottle blowing station machine’s infeed starwheel picks up the preforms and transfers them to the preform conveyor belt. Then, while rotating continually, they run through a system intended to uniformly heat up the preform. When a set temperature is reached, the preform is moved to the blow molding section of the machine, where it is molded in the desired shape by applying pressurized air. If the temperature of the preform is not uniform, or has not reached or has exceeded the desired value, the end product will have defects: holes in the bottle if the temperature was too high, not completely extended bottles if the temperature was too low, or variances in the thickness of the bottle if the temperature was not uniform (or combinations of these three). These bottles have to be discarded and this reduces the yield of the machine and increases the waste.

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RELEVANT TECH NOTE #9: IRT/C MONITORS PLASTIC INJECTION MOLD CLEARING

In high volume plastic injection molding machinery, a molded part that does not clear the mold can cause serious problems, including a long down time to clean up or make repairs.

A particularly useful property of the mold is its shininess, which means low emissivity. Accordingly, the infrared radiation from an open mold is primarily reflected from the room, and thus an IRt/c pointed at the mold would not read much higher than room temperature. However, if a part is still in the mold, the IR radiation is far higher since the high emissivity of the plastic part is easily seen by the IRt/c as the temperature of the hot part. By mounting an IRt/c so that it can view the part as the mold opens, a reliable and inexpensive part detection system can be installed. Simply connect the IRt/c to a simple thermocouple controller with alarms interfaced to the mold position. For efficient coverage of the mold, two IRt/c’s can be wired in parallel and connected to a single controller, so that a part viewed by either sensor will alarm.

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RELEVANT TECH NOTE #22: CONTROLLING VACUUM FORMING AND THERMOFORMING PROCESSES

For forming plastics, radiant heat with an IRt/c is an excellent combination of heating method and control. They work extraordinarily well together, since both the heating and measuring occur right at the surface, where the plastic is located. The IRt/c reading is unaffected by reflections from the heater, since the spectral response of the 6 to 14 micron IRt/c lens filters out the shorter wavelengths of the radiant heater energy.

The IRt/c may be mounted in between ceramic heaters, or in the shroud or reflector of the radiant

heater, such that it can see in between the elements. Select any of the IRt/c models, depending on the field-of-view required to see past the elements to the painted surface. Care should be taken in mounting the IRt/c in such a way as to keep its temperature below 200°F (93°C) and to keep the lens clean. The IRt/c.3x is the preferred model for this application because of its small physical size and builtin air purge. It can be used in temperatures up to 250°F (121°C) when the air purge system is used. For still narrower fields of view, the IRt/c.5 and IRt/c.10 with 5:1 and 10:1 FOV respectively are very popular.

Read the full Tech Note here