Bowl mill

A ball mill with a housing (1) that accommodates three stationary rollers (2) rolling along a rotating track (3). The rollers are held against the track by means of an upper and lower frame (9 & 10). The frames have springs (11) between them. Rods (8), each connected to a hydraulic cylinder (24) and extending out of the housing, engage the upper frame (9). To allow the rollers to be lifted off the track, a piston associated with the hydraulic cylinder can be charged at either end, the rollers are attached to the lower frame with hinges 25 and an angle-setting device, and the frames are connected by tension structures that limit the expansion of the springs.

The invention concerns a bowl mill with the characteristics in the preamble 
to claim 1. 
A bowl mill of this type is known from Aufbereitungs-Technik 12 (1971), 
pages 537 to 549. The milling force is applied with tension structures 
like cables or rods that engage an upper frame and are secured to the base 
of the mill. The force is transmitted from the upper frame to a lower 
frame through springs and hence to the rollers. The springs, which are 
helical, are simple and reliable. 
The way the rollers are accommodated in the housing, however, prevents them 
from being lifted off of the milling track over the frames and lowered 
again. Lifting them can be desirable for example when a malfunction in the 
combustion chamber of the boiler served by the mill suddenly interrupts 
the supply of hot air to the mill, leaving a supply of coal in the mill 
reservoir. If the rollers could be lifted in such a situation, the 
material being milled could be removed from the mill while the bowl 
continued to rotate. 
A bowl mill in which the rods that transmit the milling force can be 
shifted back and forth with hydraulic cylinders is known from Grman OS No. 
2 839 815. The rods engage a one-part frame through the intermediary of 
hinged joints. The rollers are mounted on holders on the frame in such a 
way that they can be lifted off the track along with the frame, returning 
to their original position on the track when lowered again. Still, the 
rollers in this mill must be held against the track resiliently by the 
hydraulic cylinders, which is very expensive from an engineering aspect. 
The object of the invention is to provide a mill in which the rollers can 
be held against the track resiliently by simple means and lifted off the 
track. 
This object is attained in a mill of the overall type by means of the 
characteristics in the body of claim 1. Practical embodiments of the 
invention will be evident from the subsidiary claims. 
The springs between two frames can be retained in this mill because they 
are not completely released when the tensioning structures lift the 
frames, and their position between the frames will remain secure.

A bowl mill has a housing 1 that accommodates the milling mechanisms. The 
milling mechanisms consists of three stationary rollers 2 that roll over 
the track 3 of a rotating bowl 4. Bowl 4 is vertically oriented and 
mounted on a drive mechanism 5 that powers it from a motor 6. Drive 
mechanism 5 rests on a base 7. 
The milling force is transmitted through rods 8 secured in base 7. Rods 8 
engage a resilient structure consisting of an upper and lower frame 9 and 
10. Between frames 9 and 10 are springs 11, preferably helical. Rollers 2 
are attached to lower frame 10 with roller mounts 12 at an angle to the 
vertical. The milling force transmitted to upper frame 9 through rods 8 is 
forwarded to rollers 2 through springs 11, lower frame 10, and roller 
mounts 12 in such a way that the rollers are held against track 3 at a 
prescribed level of resiliency. 
Rods 8 are articulated to upper frame 9 with a hinged joint. A head 13 that 
accommodates an eye 14 is fastened to the top of rod 8. A clamp 15 passes 
through eye 14 and is secured in upper frame 9 with screws 16. Clamp 15 is 
accommodated in the recess in a fork 17 positioned along with a lining 18 
in the eye 14 in head 13. Between the lining 18 resting against head 13 
and the clamp 15 secured to upper frame 9 is a ball 19. The bottom of head 
13 has a concave contact surface 20 that faces a matching convex contact 
surface 21 on upper frame 9. 
Rod 8 extends out of housing 1 at a point that is sealed off with a dynamic 
seal. The dynamic seal consists of a sealing-air chamber 22 that has a 
sealing-air supply connection. Between sealing-air chamber 22 and rod 8 is 
a bellows 23. 
The bottom of rod 8 is attached to a piston accommodated in a hydraulic 
cylinder 24 in such a way that it can be charged at either end. The piston 
can be constantly pressurized while the mill is in operation or can be 
mechanically blocked. 
The mounts 12 that hold rollers 2 are attached to lower frame 10 with 
hinges 25. The angle of inclination of rollers 2 is secured by means of an 
angle-setting device that consists as illustrated in FIG. 4 of a bolt 26 
articulated to roller mounts 12 and of a holder 27 fastened to lower frame 
10. Bolt 26 is secured in holder 27 and rests against springs 28. A 
bushing can be employed instead of springs 28 if a rigid angle-setting 
device is employed instead of a resilient device. As will be evident from 
FIG. 1, there are two angle-setting devices for each roller 2. Bolt 26 is 
threaded. Displacing a nut along bolt 26 will vary the length of the bolt 
between holder 27 and roller mount 12. Each length represents in 
conjunction with hinges 25 a particular inclination of a roller 2 to the 
vertical. The angle of inclination can also be adjusted by employing 
bushings of different length. 
Upper and lower frames 9 and 10 are connected by tension structures that 
limit the extension of springs 11 when frames 9 and 10 are forced apart. 
The tension structures preferably consist of threaded bolts 29 that extend 
through both frames 9 and 10. When the mill is in operation the contact 
surface of the head 30 of each threaded bolt 29 rests against upper frame 
9, whereas a nut 31, which functions as a lower contact surface and is 
mounted on threaded bolt 29, is at a certain distance from the bottom of 
lower frame 10. Cables connected to frames 9 and 10 or hooks that engage 
the frames can be employed as tension structures instead of the threaded 
bolts. What is essential is the cables or hooks also only come into action 
and accordingly limit the expansion of springs 11 when frames 9 and 10 are 
forced apart. 
When the mill is in operation, rods 8 are tensioned and the milling force 
is activated by charging hydraulic cylinder 24. Varying the pressure in 
hydraulic cylinders 24 will vary the milling force whether the mill is in 
or out of operation. When rollers 2 have to be lifted off of track 3, 
hydraulic cylinder 24 is shifted in such a way as to apply pressure to 
rods 8. The concave contact surface 20 on the head 13 of rod 8 thrusts 
against the matching convex contact surface 21 on upper frame 9 and lifts 
the frame. Once a stroke of a certain length has been completed, threaded 
bolts 29 will begin to entrain lower frame 10. Since springs 11 cannot 
expand completely, they will remain in place between frames 9 and 10. When 
rollers 2 are returned to track 3, they will assume their original 
position.