Breaker plate

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. 

When the head is assembled, the breaker plate acts as a melt seal in the parting line between the barrel and the head assembly. For this reason, it is important to ensure proper alignment of the breaker plate when it is installed and correct torque on the head bolts during re-assembly and warm-up. Also, the recess in which the breaker plate is held must be cleaned very carefully to avoid any scratches. Any misalignment or damage to the breaker plate or flange recess will lead to polymer leakage. 

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. 

As the polymer flows off of the screw, it tends to retain the helical motion that it obtained traveling down the screw channel. This twisting flow could lead to aesthetic as well as structural defects in the extrudate. However, a breaker plate effectively hinders this motion, causing the flow downstream to be predominantly axial. 

One more use of a breaker plate is as a static mixer. Mixing is necessary to produce the homogeneity required in the melt. Several designs allow the breaker plate to serve its conventional functions while also creating flow dynamics that improve the level of mixing in the melt. These devices can be stacked in a series to create various flow fields for different mixing applications. 

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The screw consists of a feed section, a rapid transition section, and a metering section a rounded forward end prevents stagnation. The breaker plate that converts the rotary motion of the melt into smooth, straight flow should have as many holes as possible both ends of each hole should be countersunk for streamlined flow. 

The temperature of the melt downstream from the breaker plate may exceed the front barrel temperature, because of the mechanical work transmitted to the resin by the screw it varies with screw speed and flow rate. The melt temperature is measured by a thermocouple inserted into the melt downstream from the breaker plate. A hooded exhaust placed over the extmder die and feed hopper removes decomposition products when the extmdate is heated. 

Fig. 4. Pipe or tubing die for in-line extmsion A, die body B, mandrel, pin, and male die part C, die, die bushing, and female part D, die-retaining ring E, die-retaining bolt F, die-centered bolt G, spider leg H, air hole I, seat for breaker plate J, ring for attachment to extmder and K, die land (15).

Hammer Crusher (Fig. 20-27) Pivoted hammers are mounted on a horizontal shaft, and crushing takes place by impact between the hammers and breaker plates. Heavy-duty hammer crushers are frequently used in the quarrying industiy, for processing municipal solid waste, and scrap automobiles. 

In the second type of mill (Fig. 20-28), a cyhndrical grating is provided beneath the rotor for product discharge. Some hammer crushers are symmetrically designed so that the direction of rotation can be reversed to distribute wear evenly on the hammer and breaker plates. When such a Pennsylvania nonreversible hammermill is used for reduction, material is broken first by impacl against hammers and then by rubbing action (attrition) against screen bars. Performance data of Pennsylvania reversible hammer mills are shown in Table 20-14. 

Rotor Impactors The rotor of these machines is a cylinder to which is affixed a tough steel bar. Breakage can occur against this bar or on rebound from the walls of the device. Free impact breaking is the principle of the rotor breaker, and it does not rely on pinch crushing or attrition grinding between rotor hammers and breaker plates. 

It should also be noted that although it is not their primary function, the breaker plate and filter also assist the build-up of back pressure which improves... 

Example S3 The output of polythene from an extruder is 30 x 10 m /s. If the breaker plate in this extruder has 80 holes, each being 4 mm diameter and 12 mm long, estimate the pressure drop across the plate assuming the material temperature is 170°C at this point. The flow curves in Fig. 5.3 should be used. 

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. 

A manufacturer of extruded plastic sheeting had been experiencing problems with small contaminants appearing in their polypropylene-polyethylene (PP-PE) extruded sheets. The source of this contamination needed to be determined in order to overcome the problem. Several sheets containing particles were submitted for investigation, as well as some isolated particles taken from an extruder breaker plate. 

Figure 39 ATR spectrum of a particle from the extruder breaker plate (top) along with the...

In conclusion, the particles from the extruder breaker plate were identified as being polyetherimide. The particles in the polymeric matrix, however, appear to be inorganic in nature, containing aluminum and oxygen, as aluminum oxide, with traces of copper. 

Significant heat generation during the breakdown also means that cooling must be efficient if the mill is in constant use. Stronger than normal breaker plates commensurate with the overall strength of the mill body will also need to be fitted, otherwise production will be frequently interrupted due to rupture of weaker breaker plate units. 

The single roll crusher shown in Figure 2.13 consists of a toothed crushing roll which rotates close to a breaker plate. Figure 2.14 is an illustration of an industrial model. The material is crushed by compression and shearing between the two surfaces. It is used extensively for crushing coal. 

The pressure change across a breaker plate can also limit a process. The pressure change across the plate can be estimated by using simple equations for flow through a tube [5]. The calculation ignores end effects and is shown in Eq. 11.6 ... 

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]...

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. 

Consider purging the extruder plasticator when it contains plastic that can be detrimental to startup and/or producing unacceptable products (Chapter 3). If a plastic was left in the barrel for a while, with heat off, the processor must determine if the material is subject to shrink. It could have caused moisture entrapment from the surrounding area, producing contamination that would require cleanup (this situation could also be a source of corrosion in/on the barrel/screw). Even with the same plastic in the machine from a previous run, the entire machine should be cleaned and/or purged, including the hopper, barrel, breaker plate, die, and downstream equipment. 

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). 

Seat (or breaker plate Ring for attachment extruder Die lend... 

A reactor containing acrylic acid (305 g), 37.3wt % aqueous sodium acrylate (3204 g), and water (1465g) was treated with ethoxylated (15 EO) trimethylolpropane triacrylate (12.2g), 2,2 -azobisamidinopropane dihydrochloride (0.61 g), and sodium persulfate (3.05 g). The mixture was purged for 30 minutes and further treated with hydrogen peroxide (0.244 g) dissolved in water (5g) and ascorbic acid (0.244 g) also dissolved in water (5g). The mixture was then heated in a thermally insulated mb for about 30 minutes the temperature at the start of the reaction was 113 C. The reaction started after a few minutes and proceeded under adiabatic conditions until the product was isolated and comminuted through a meat grinder equipped with a 6 mm breaker plate. The residue was dried at 80°C under reduced pressure and the produce, was isolated having a sieve fraction of 300 to 600 pm. 

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