Screen-pack breaker plate

Fig. 11 Foamed sheet extrusion line. 1 Primary extruder, 2 blowing agent metering and flow control, 3 screen pack/breaker plate, 4 secondary extruder, 5 annular die, 6 cooling mandrel, 7 guide rolls, 8 winders. [38]...

The build up of pressure is aided by the use of a breaker plate, which is a thick disk of perforated metal positioned just downstream of the tip of the screw. A screen pack, comprising layers of woven metal mesh, is placed on the upstream side of the breaker plate. The screen pack increases back pressure within the metering zone and acts as a filter to catch any extraneous material that may have entered the extruder. 

Against the forces exerted by the melt flow, the screen packs are backed by a thick, densely perforated steel disk called a breaker plate. The outer rims of the breaker plate and of the screen pack fit into a round recess in the end of the extruder barrel and are clamped in place by the adapter flange of the adjoining piece of equipment, usually that of the extrusion die. To change a clogged screen pack, the die adapter flange has to be removed, the old pack taken out and replaced with a new one, and the equipment reassembled. 

If a screen pack with breaker plate is used, disconnect the crosshead (or die) from the extruder and remove the breaker plate and screen. If necessary, appropriate action is taken to clean them (Chapter 17). 

Extrusion of tubes, hose, and profiles is done on standard extruders for rubber. The usual temperature pattern is a gradual increase of temperature from the feed zone to the die. The die temperature is typically 100°C (212°F), and the screw temperature is approximately the same as the temperature of the feed zone [44]. Processing aids are almost always required to improve the surface appearance and to increase the extrusion rate. Extrusion represents only a small proportion (about 10%) of the total consumption of fluorocarbon elastomers [52].Cold feed extruders typically used for extrusion of rubber stocks are also suitable for the extrusion of fluorocarbon elastomers. Extrusion should be carried out at temperatures below 120°C (250°F) to avoid scorch. In most cases a breaker plate and screen pack are used to generate backpressure on the screw and to remove foreign particles from the stock. A straight head is used for the extrusion of profiles or tubing, whereas a cross-head die is used for... 

Figure 7.1 Design of an extruder plasticating barrel (a) feed hopper (b) heaters (c) screw (d) thermocouples (e) backpressure regulating valve (f) pressure gauges (g) breaker plate and screen pack...

The spin pump (metering pump) delivers the molten polymer to a spin pack, which consists of a top cap and a breaker plate to distribute polymer evenly, then into a filtration media and out of the spinneret. The filtration media contains either different layers of special sand, layers of different size of stainless steel screens, or sintered metals. In addition to removing the foreign particles, gel particles and undesirable conglomerate additives, filtration may also improve the polymer melt homogeneity due to its torturous path and high shear of the filtration media. 

Melt from the screw usually is forced through a breaker plate with a screen pack. Extra heat develops when melt goes through the screens, so some... 

The breaker plate is a metal disk located perpendicular to the melt flow at the barrel exit. Containing several holes through which the melt passes, it is generally a little larger in diameter than the screw and mounts in a recession in the barrel exit flange. The breaker plate has three main purposes 1) to seal the end of the barrel, 2) to hold the screen pack, and 3) to straighten out the flow. 

The most common form of melt filtering is the use of screen packs. The screen pack is held in the breaker plate by melt pressure as the polymer exits the barrel. The breaker plate often contains a pocket to hold screens that are nominally the same diameter as the screw. 

When it is time to change a screen pack, the condition may be indicated by an increase in head pressure, an increase in pressure drop across the breaker plate, a decrease in output, or a defect in the extrudate. Changing a screen pack involves extruder downtime. The extruder must be shut down and the head disassembled. The breaker plate is removed and the old screens are extracted and discarded. At this point, the breaker plate... 

Head n. (1) In any extrusion operation, the delivery end of the extruder, usually fitted with a hinged gate that may contain a breaker plate and screen pack, to which the adapter and die are attached. (2) In blow molding, the entire apparatus by which the molten plastic is shaped into a tubular parison. This may include an adapter, a parison die, and a melt accumulator. 

View port Breaker plate, screen packs and adapter ring... 

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