Breaker Plate & Screen Pack :

Breaker Plate -
1. This is performed metal disk,  with a multitude of small diameter holes.
2. The breaker plate is placed in between the screw and the die assembly.
3. It's principal function is to provide support for the screen pack.
4. The breaker plate helps also to convert the spiral flow of the polymer melts leaving the screw into a linear, axial one.

Screen Pack -
1. Screen Pack is usually a multilayered,  nearly symmetrical sandwich of metallic wire screens. 

2. It is placed between the screw and the breaker plate,  using the latter for physical support. It's  role is to eliminate the particulate contaminants. 

3. The screen pack composition is always based on trade-offs, there is need to eliminate particulates using screens with high mesh,  but at the same time this create flow restriction,  it reduced the throughput, thus low mesh would be preferred. 

4. Decision should be made as for as the maximum tolerable size of the particulate contaminants.

5. The screen pack must be periodically change. 

6. The change can be done either automatically or manually in both cases it is necessary to detect the critical amount of screen blockage by the filtered-out particles.

 
7. The detection is based on the pressure drop across the screen pack and the breaker plate assembly. 

8. Thus imperative to have pressure transducer on both sides on the assembly.

Example :
• Eliminate gross solid particles from PP melt,  20/60/20 mesh screen pack may be sufficient,
While to eliminate gel particles in film -grade EVAs , 60/180/400/180/60/20 has been used.

      *Breaker plate short notes -
  √ Perforated circular metallic disc of about 4-5 mm thick.

*Functions -
• Support for screen pack .
• Converts the Spiral flow of melt in to stream lined laminar flow.
• Holds back contamination and unmelted particles.

  *Screen pack short notes -
• Wire mesh 40,60,80
• Arrests the unmelted particles and contamination
• Helps in developing back pressure