Barrel heater bands

Electrical problems related to barrel heaters, band heaters, and instruments occur constantly in most production lines. In most cases, the problem is easily identified and fixed. For example, most barrel heaters are configured with a current meter on the control panel. If the controller is calling for heat on the zone and the meter... 

Table 5.2 Selection guide for barrel heater bands (courtesy of Spirex)...

A term applied to a variety of vessels used in vulcanising mbber articles. See Autoclave and Dry Heat Cure. Also refers to heater bands used on extruder barrels and similar machines. 

Fig. 14.23 Typical blow molding die A, choke adjusting nut B, mandrel adjustment C, feed throat D, choke screw E, die head F, plastic melt G, die barrel H, heater band /, choke ring J, centering screw K, clamp ring L, die heater M, die N, mandrel. [Reprinted by permission from J. D. Frankland, A High Speed Blow Molding Process, Trans. Soc. Rheol., 19, 371 (1975).]...

Melting the Plastic Material. The plastic pellets are fed through a hopper into an extruder screw, typically with an L/D ratio of 20/1. The first half of the screw compresses the pellets and squeezes out air. The third quarter of the screw melts the pellets, 70 percent by friction, 30 percent by conduction from heater bands on the extruder barrel. This is called preplastica-tion. The fourth quarter of the screw pumps the melt forward to the front of the extruder, where it goes through a one-way valve to prevent backflow. As the molten plastic accumulates at... 

Alternatively, for vessels up to 101, an electric heating band (barrel heater) may be used, having a power of approximately 30 W of reactor volume. In no case should heating rods or tubes inside the reactor be used, because localized high temperatures, aggravated by the low stirring rate, will cause unfavourable medium alterations and cell damage. 

Heat is usually applied in various amounts and in different locations, whether in a metal plasticating barrel (extrusion, injection molding, etc.) or in a metal mold/die (compression, injection, thermoforming, extrusion, etc.). With barrels a thermocouple is usually embedded in the metal to send a signal to a temperature controller. In turn, it controls the electric power output device regulating the power to the heater bands in different zones of the barrel. The placement of the thermocouple temperature sensor is extremely important. The heat flow in any medium sets up a temperature gradient in that medium, just as the flow of water in a pipe sets up a pressure drop, and the flow of electricity in a wire causes a voltage drop. 

Held in place by the head assembly is an adapter, which guides the melt stream from the barrel exit into the die entrance. There may be a fixed nozzle in the head, which can be fitted with a custom adapter for each die employed. For the best temperature control, the nozzle and adapter should each have their own heater band. Usually a single temperature control circuit is used for the nozzle/adapter zone, but for a long transfer pipe to the die, multiple circuits maybe necessary. 

Rubber extruders used to be heated quite frequently with steam because of the relatively low extrusion temperatures. Today, many rubber extruders are heated like thermoplastic extruders with electrical heater bands clamped around the barrel. Oil heating is also used on rubber extruders and the circulating oil system can be used to cool the rubber. Many rubber extruders use water cooling because it allows effective heat transfer. 

Are the heater bands rotated so there is not an area on the barrel or head tooling that could have a cold area due to all the heater band endings aligned ... 

Viscosity curve is shifted. There are a number of items that can cause the viscosity curve to shift up or down. Cheek to see that the proper calibration values have been entered for the pressure/force transducer. Check the die to ensure that it is not partially bloeked, eausing greater than normal pressure drops. Lastly, eheek for a shift in either the barrel or die temperature. Burned-out heater bands or maladjusted temperature eontrollers will eause large shifts in experimental results. 

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