Extruder pressure-head safety

While the measurement of extruder head pressure is very important for product quality purposes, it is also perhaps the most important measurement from a safety standpoint. Excessive pressure can cause rupture of the barrel, damage to head and die components, and injury to personnel from projected hardware and hot polymer. Therefore, accurate pressure readings, high-pressure motor shut-off capability, and properly rated rupture disks are essential for safe operation. 

Head (melt) pressure is measured at the end of the extruder. One pressure transducer is typically mounted just before the breaker plate while others may be placed in the die adapter or die itself. Pressure is monitored for safety purposes, product quality, research and develop-... 

Head pressure is a key extrusion variable. It is advantageous to know prior to extruding what the pressure will be because it affects safety, rupture disk rating, and vent flow. This paper describes development of a model to determine head pressure. The model is not intended to be highly accurate, but to provide a useful estimate. Therefore, the result is termed a head pressure index (HPI). Head pressure results from three process variables melt viscosity, flow rate, and flow restriction. With the HPI, an operator can make quick decisions about operating conditions, such as acceptable screw speed, melt temperature, and vent location. Experimental data is shown that correlates HPI with measured head pressure. 

Head pressure is a key process variable on all extrusion lines. Its value during operation is a critical indicator of extruder performance and stability as well as, perhaps most importantly, safety conditions. Under many conditions, the head pressure is not known until the system is actually run. This occurs most often when there has been a change such as a new material, new die, or new (or rebuilt) screw. In these cases, it is advantageous to know prior to extruding what the head pressure will be because of the pressure s affect on safety, rupture disk rating, vent flow, and other operational aspects. 

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