Nip, angle

The circular geometi y of the crusher gives a favorably small nip angle in the horizontal direction. The nip angle in the vertical direction is less favorable and limits feed acceptance. The vertical nip angle... 

Dehont et al. assumed that the material in the compaction area remains horizontal and moves at the peripheral speed of the rollers. They also considered that the angle a is independent of the roller diameter size and noted that the flake thickness ei depends on the roller speed, the roller surface, and the compaction pressure. All these parameters influence the density of the flake, d. Dehont et al. concluded that if the same flake thickness was obtained with different roller diameters, the flake density would be greater with larger diameter rollers. This is due to the greater nip angle formed, with the larger rolls allowing more material to be compacted. 

In Fig. 2, Po is the horizontal pressure between rolls, 0, the angular position of roll bite, a, the nip angle, 2d, the roll diameter D, h, the height above the roll center line at which feed pressure P is applied, P, the horizontal pressure at 0 = 0, and S, the roll gap. 

Johanson pointed out that no roller compactor theories at that time determined the angle of the nip and the bulk density at 0 = a, except by actually rolling the granular solid in a roll press. He also provided a method to calculate the nip angle and the pressure distribution between the rolls. His calculations... 

Fig. 3 defines the following Pq—horizontal pressure between rolls B—angular position of roll bite a—nip angle 2d—roll diameter D, h—height above the roll center line at which feed pressure Po is applied ... 

Fig. 3 Front view of compactor rolls in horizontal plane depicting nip angle. (From Ref. , courtesy of Transaction ASME.)...

The density of the material, at the point of the nip angle approaches its tapped density value and the material begins to undergo compression between the rolls. The material is then forced through the region of maximum pressure where it undergoes a rapid increase in the density resulting in the formation of the compacted mass. 

In roller presses and pellet mills, converging space (volume) between two counter-rotating rollers and, respectively, the pressure generating device and the extrusion surface. (See also nip angle.)... 

---