1. Fundamentals of the Shear Roll Milling Process
Dilhan M. Kalyon and
Halil Gevgilili
Stevens Institute of Technology
12th Extruder and Continuous Mixer Users Group
Indian Head, MD
October 29, 2002

8. Some Features of the Shear Roll Mill:
The surface of the rolls have spiraling grooves which allow conveying of the material forward
The Material wraps around one roll (feed roll) and detaches from the other one (conveying roll)
The feed roll has rougher surface than the conveying roll.
The speeds of the rolls can be adjusted independently
The gap size between the rolls is adjustable
Both rolls have independent temperature control.
A loss in weight feeder is generally utilized to feed material between the rolls

9. Objectives of the study
To investigate the dynamics of the shear roll mill process and to relate to the rheological behavior of the melt
To specifically focus on the wall interactions and the roll wall slip plays in the sporadic premature detachment of the melt from the feed roll to lead to process failures.

10. Test Material: HDPE, manufactured by Exxon Mobil Corporation
Designation: HDA 601
ethylene hexene copolymer
Density=0.933 g/cc (ASTM D-1505)
Melt Index=0.55 (ASTM D-1238)
General purpose, sheet extrusion grade

11. The process may become unstable under some conditions
Under typical processing conditions, the material sticks to the feed roll with has a roughened surface
Material Sticks to the conveying roll when the conveying roll temperature is is at least 17ºC higher than the feed roll
The process may become unstable under some conditions

12. HAD HDPE

13. HAD HDPE

16. HAD HDPE

17. Sample ejection from the gap
gׂ=70 s-1, t=0.1 s, g=7
Sample ejection from the gap
gׂ=60 s-1
gׂ=50 s-1
gׂ=70 s-1
gׂ=23 s-1
gׂ=10 s-1
gׂ=5 s-1
gׂ=10 s-1, t=1 s, g=10
t=0 s, g=0

18. Critical wall shear stress values at slip in torsional flow
HDPE:
@ 170C tc=0.22 MPa
@ 190C tc= 0.22 MPa
@ 210C tc= 0.23 MPa

19. R, Radius of the roll V1 2h V2 Case-a Case-b Pmax Velocity Extremum y

20. V1>V2 V1>V2 V1<V2 V1<V2 V1 V1 V2 V2
Case-c: No velocity extremum exists in the nip
Case-d: No velocity extremum exists in the nip
V1<V2
V1<V2 V1 V1 V2 V2
Case-e: No velocity extremum exists in the nip
Case-f: No velocity extremum exists in the nip

21. Motion of a particle on the feed roll

22. Conveying Roll surface
Feed Roll surface

24. R, Radius of the roll V1 2h V2 Case-a Case-b Pmax Velocity Extremum y

25. Maximum pressure
Atmospheric pressure

26. White regions are partially detached
Islands of detachments appear when both rolls turn at the same relatively high speed

30. Material detaches from feed roll when the rolls turn at relatively large differential speeds

31. Conveying Roll surface
Feed Roll surface

34. Conveying Roll surface
Feed Roll surface

37. Typical results Run Nr. Material Temperature oC Wall thickness mm
Feed roll
RPM
Conveying roll
Nip shear stress on feed roll, Pa 1
164
2.3 16 29
2.23  105 2
2.2 20 33
2.46  105 3
162
1.65 40
2.47  105 4
1.61
1.9  105

38. Conclusions:
The onset of strong wall slip at a critical shear stress of 0.22 MPa (documented with the steady torsional flow) for the HDPE coincides with the shear stress at which detachment of the melt from the feed roll occurs during shear roll mill process.
The material detaches uniformly everywhere along the rolls if both rolls turn at high speeds with a relatively large speed differential, while only islands of detachment appear if the roll turn at the same high speed.
Temperature and surface roughness are the two factors that determine which roll the melt will stick onto.

39. Conclusions
These findings here can be used to select operating conditions and geometry for the shear roll milling operations and for process control.
However, for the gun propellants the rheological behavior and hence the wall slip behavior is going to change with the moisture content and this important effect needs to be kept track of.

40. We are grateful for the funding of the US Army
TACOM/ARDEC under DAAE30-01-C-1039
and the contributions of:
C. Topolski, S. Rosenberg, E. Krajowski,
and B. Elmasri of US Army
Mr. J. Kowalczyk of Shear Tool and Mr. J. Graybill of MPR
H. Zeigler of ATK Thiokol Propulsion and
A. Wellm of Nitrochemie