Two-roll press for pressure treatment of granular material

In two-roll machines for high-pressure disintegration of granular material, in which typically only one of the two rolls is motor driven, while the other roll is driven by means of friction via the granular material pressed in the roll gap, and thus operates as a drag roll, it is proposed to equip the drag roll with a separate, smaller drive mechanism including a separate smaller drive motor. This drive is thereby dimensioned in such a way that the startup of the drag roll is ensured and a drop in revolutions per minute of the drag roll is avoided. Alternatively, this separate drive is enlarged in such a way that it can transmit 10% to 40%, preferably 20%, of the total required drive power.

BACKGROUND OF THE INVENTION 
The invention is directed to a two-roll machine, in particular a roll 
press, as well as to a method for operating the two-roll machine for the 
pressure treatment of granular goods, with two rolls that are rotatably 
mounted in a machine frame so as to be able to be rotated in directions 
opposed to one another, separated from one another by a roll gap, between 
which the granular material is drawn and is subjected to interparticle 
pressure treatment and is thereby disintegrated. One of the two rolls can 
be a fixed roll whose bearings are supported on the machine frame, and the 
other roll can be a loose roll, supported on the machine frame by a force 
acting from the outside. 
High-pressure roll presses or, roll presses, are known for what is called 
the interparticle crushing of granular material, such as for example 
cement klinkers, which granular materials are pressed in the roll gap at 
high pressure to form plate-like agglomerates, which agglomerates are 
subsequently disagglomerated, whereby the material, pressed once, already 
comprises a high portion of the desired fineness. 
In known high-pressure roll presses, one of the two rolls is fashioned as a 
fixed roll, supported against the machine frame via its bearings, while 
the other roll, as a loose roll, is supported via its bearings against an 
external force, for example against the hydraulic cylinder of a 
hydropneumatic system, with which the roll pressure force is applied and 
the adjustment of the width of the roll gap is carried out. 
In known roll presses, normally both rolls are driven in opposite 
directions at the same RPM, by means of separate, equally large, drive 
motors with the necessary components of gearing, coupling, and torque 
bearings. 
Due to the forcible coupling of the two rolls via the granular material 
located in the roll gap during the pressing, a differential loading of the 
individual drives cannot be excluded, particularly when the two rolls 
differ in diameter from one another. 
In addition, the coupling of the two rolls via the pressed material, with 
simultaneous separate driving of the two rolls, results in increased wear 
on the roll surfaces because the driving of the rolls forces a slippage of 
the speed of the pressed material in relation to the speed of the 
circumference of the rolls. 
In order to avoid these disadvantages, in DE-38 34 425 A1 it is proposed to 
provide only one of the two rolls with a rotational drive, while the other 
roll is frictionally driven as a drag roll via the material located in the 
roll gap. By means of this measure, in addition to a savings of energy, 
significant improvements are also achieved with respect to the wearing of 
the roll surfaces, since the speed of the circumference of the drag roll 
can adapt itself completely to the pressed material. A different diameter 
of the two rolls is also no longer significant in this case, since an 
approximately equal circumferential speed arises for both rolls due to the 
frictional force. However, in certain operational situations there may be 
difficulties in starting the dragged roll, whereby disturbances in the 
operation are caused, in particular during the final grinding in the 
circulation with further systems parts (ball mill, sifter). 
SUMMARY OF THE INVENTION 
The aim of the invention is to further develop the known two-roll machine 
from DE-38 34 425 A1 in such a way that the described disadvantages are 
avoided while the achieved advantages can be exploited. 
This aim is solved with respect to the apparatus by means of providing each 
of the rolls with a drive motor, one drive motor being smaller in size 
with respect to its power relative to the other, such that the roll that 
the smaller motor drives will operate at least partially as a drag roller. 
By means of the inventive measure of driving the rolls of the two-roll 
machine with rotational drive motors of different sizes, different 
operational states of the two-roll machine can be set, with full enjoyment 
of the advantages known from DE-38 34 425 A1. Thus, according to the 
invention it is for example possible for one of the rolls, advantageously 
the fixed roll, to stand in connection with a rotational drive motor, 
which applies 100% of the drive power required for the operation of the 
two-roll machine, so that during operation of the two-roll machine, when 
the roll gap is filled with granular material, the other roll, preferably 
the loose roll in this case, operates as a drag roll, driven by the fixed 
roll via the frictional force. According to the invention, this roll 
operating as a drag roll is connected with a rotational drive motor that 
is very much smaller in relation to the other roll, which smaller motor is 
intended only to ensure the starting of this drag roll, and otherwise is 
drivingly reactivated only in case of a drop in the revolutions per 
minute. 
The advantages of the manner of operation of the two-roll machine with one 
roll fashioned as a drag roll are thus obtained, while at the same time 
the difficulties that can arise in pure drag roll operation without a 
separate drive are largely avoided by means of the "supporting" smaller 
rotational drive motor. 
In order to run up again to the operating revolutions per minute in case of 
a drop in revolutions per minute of the drag roll, according to the 
invention, the rotational drive motor is a RPM-controlled motor, or else a 
coupling is arranged between the rotational drive motor and the roll drive 
assembly, which coupling engages only in case of a drop in revolutions per 
minute. In order to ensure that the revolutions per minute of the drag 
roll are raised in the short term back up to the required operational 
revolutions per minute in case of a drop in revolutions per minute, at 
least the drag roll is connected with a means for monitoring revolutions 
per minute, with which the necessary intervention for the increase of the 
revolutions per minute can be activated. 
An alternative according to the invention is to couple one of the two 
rolls, preferably here as well the fixed roll, with a rotational drive 
motor, which applies 60% to 90%, preferably 80%, of the total drive power 
required for the operation of the two-roll machine, and to equip the other 
roll, which now no longer operates exclusively as a drag roll, with a 
rotational drive motor, which applies the rest of the required drive 
power, namely 10% to 40%, preferably 20%, of the overall required drive 
power. 
By means of torque monitoring, the rotational drive motor of the drag roll 
is controlled in such a way that it holds a constant predetermined torque, 
which corresponds to the desired drive power of 10% to 40%, preferably 
20%, of the overall drive power to be expended in the operation of the 
two-roll machine. Although in this alternative there is no pure dragged 
operation of a roll, and the advantages of pure drag operation are thereby 
somewhat reduced, this is outweighed here by the advantages of operational 
security, since in case of disturbances in operation the rotational drive 
motor of this roll does not have to be started with a time delay, since it 
remains activated at all times during the entire duration of operation. 
Because the drive mechanism for the pure drag roll or, respectively, for 
the roll operating partially as a drag roll, is considerably smaller in 
relation to the main drive of the other roll, the space requirement for 
this drive, consisting of the rotational drive motor, gearing, coupling, 
and torque bearing, is also considerably reduced, so that in rolls with a 
relatively small diameter, both drive mechanisms can be arranged next to 
one another on one side of the two-roll machine, thus also improving 
accessibility for necessary maintenance work. 
Since, in addition, the roll diameter of the two rolls need no longer 
necessarily comprise the same diameter (the same circumferential speed is 
ensured for both rolls by means of frictional force via the granular 
material in the roll gap), it is possible to exchange the rolls 
individually as needed, whereby the idle time of the two-roll machine 
caused thereby is considerably reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In a machine frame 5, the two rolls 1, 2 are rotatably mounted via their 
bearings 6, 7. One of the two rolls, the roll 2 in the exemplary 
embodiment, is driven via its shaft 10 by a rotational drive motor 
M.sub.2, for which purpose the rotational drive motor M.sub.2 is connected 
with the shaft 10 via a V-belt 9 and gearing 3. 
A smaller drive mechanism for the other roll 1, which in this exemplary 
embodiment comprises the same diameter as the roll 2, but which could be 
of a different diameter, is also located on the same side of the machine 
frame. This drive, which is applied to a shaft 11 of the roll 1 and 
consists of a rotational drive motor M.sub.1, V-belt 8 and gearing 4, is 
considerably smaller in relation to the drive for the roll 2 according to 
the invention, since according to the invention only essentially smaller 
amounts of drive power are to be transmitted with this drive. The 
rotational drive motor M.sub.1 is connected with a means for monitoring 
revolutions per minute (12) for the roll 1, if, apart from startup, this 
drive is to be activated only in case of a drop in revolutions per minute. 
The means for monitoring the revolutions per minute could comprise an RPM 
controlled motor as the smaller motor M.sub.1 or could comprise a coupling 
13 between the motor M.sub.1 and the shaft 11 of the roll 1 which engages 
only in case of a drop in revolutions per minute below a predetermined 
speed. 
As is apparent from the foregoing specification, the invention is 
susceptible of being embodied with various alterations and modifications 
which may differ particularly from those that have been described in the 
preceding specification and description. It should be understood that we 
wish to embody within the scope of the patent warranted hereon all such 
modifications as reasonably and properly come within the scope of our 
contribution to the art.