GB2116877A

GB2116877A - A rollermill

Info

Publication number: GB2116877A
Application number: GB08306081A
Authority: GB
Inventors: Richard Fullalove
Original assignee: Henry Simon Ltd
Current assignee: Henry Simon Ltd
Priority date: 1982-03-20
Filing date: 1983-03-04
Publication date: 1983-10-05
Also published as: GB2116877B; GB8306081D0

Abstract

A rollermill has a pair of grinding rolls (12, 15) forming a nip through which stock is passed from feed rolls (30) the grinding roll (15) being mounted on a cradle (14) for movement on a pivot (13) relative to a subframe (11) operation of a cylinder 17 separating the rolls in the absence of stock. The pivot (13) is just above the common plane of the two rotational axes of rolls (12, 15) so that as roll (15) approaches roll (12) it converges at an acute angle with a tangent to roll (12) at the nip thus providing a substantial mechanical advantage with only low power exerted by cylinder (17). This tangential approach is thus advantageous when compared with the radial approach of the movable roll in existing systems. <IMAGE>

Description

SPECIFICATION A rollermill This invention concerns rollermills of the kind having a pair of grinding rolls forming a nip through which stock is passed to be ground, and wherein one of said rolls is movable with respect to the other so that they may be separated when no stock is flowing and brought into close grinding relationship in the presence of stock to be milled. Conventionally, the rolls are mounted side-by-side with their axes in a common horizontal or inclined plane. Usually, one roll is fixed to the machine frame and the movable roll is manoeuvred along a straight line which is substantially perpendicular to a tangent to the fixed roll at its point of closest proximity with the movable roll. A level and/or spring system is included to provide a mechanical advantage giving a ratio of the grinding load to the force applied as something in the region of 6:1.Nevertheless, considerable force is required to move the roll and any roll separating force applied by foreign bodies passing through the nip must necessarily be large to overcome the force applied by the lever system, thus damage to the roll surfaces can occur.

An object of the present invention is to provide a rollermill of the kind generally described above, wherein the prime force applied to the movable roll is considerably reduced whilst ensuring adequate grinding force at the nip.

According to the present invention, there is provided a rollermill having a pair of grinding rolls forming a nip through which stock is passed to be ground, one of said grinding rolls being movable with respect to the other thus to enable the rolls to be separated in the absence of the stock and placed in close working relationship in the presence thereof, characterised in that movement of the movable roll is such that as it approaches the fixed roll, its surface converges at an acute angle with a tangent to the fixed roll at the position of closest proximity of the two rolls.

The invention will be further apparent from the following description, given by way of example only, with reference to the accompanying drawing which is a fragmentary end elevation showing one half of a rollermill made in accordance with the invention.

Referring now to the drawing, the rollermill comprises a main frame 10 carrying a subframe 11 on which is mounted for rotation a fixed grinding roll 12. Pivotally mounted at 13 on the subframe 11 is a cradle 14 which carries the movable grinding roll 15.

The cradle 14 is pivotally attached at 16 to the ram of a pneumatic or hydraulic cylinder 17. Thus, as will be described, the cradle 14 carrying the movable roll 15 is pivotable by operation of the cylinder 17 to separate the rolls 12 and 15.

A pre-set dead stop 18 is provided to ensure that the rolls do not come into contact at the lowermost position of the cradle 14, and a roll gap adjustment device 19 is provided to set the closest position of the rolls above that dictated by the dead stop 18. The adjustment device 19 includes a hand wheel 20 at each end of the rollermill which can beset by the operator before and during a grinding operation.

The rollermill also includes a feeding mechanism including a pair of feed rolls 30 together with all those other essential features of a rollermill, not forming part of the present invention, which are not shown or described herein.

In the drawing, the grinding rolls are shown to be in contactthough in practice the nip is in the region of 0.3mm in the case of fluted rolls. This will be referred to as a grinding position. When no stock is flowing to the nip of the grinding rolls the cylinder is extended to raise the cradle 14 and thus separate the rolls.

When flow commences, the cylinder 17 is retracted to draw the cradle 14 downwardly. The pivot 13 is just above the common horizontal plane of the axes of the two rolls, so that the nearest point on the circumference of the movable roll describes an arc which converges with a tangent to the fixed roll circumference at the nip. If the arc were to be extended beyond the point at which the dead stop prevents further movement of the cradle, it would bisect the circumference of the fixed roll immediately below the nip. The convergence of the two roll circumferences at a shallow acute angle, together with the weight of the movable roll and the cradle 14, serve to create a mechanical advantage which provides a ratio of grinding load to the force applied of something in the region of 7:1, whereas the lever system itself produces a mechanical advantage of only say 1.3:1.This advantage enables the use of a mechanical, electrical, hydraulic or pneumatic force actuator of low power, eg. an air cylinder which operates in the region of .68 Bars.

The radius of the arc of movement of cradle 14 and roll 15 about pivot 13 is chosen such that the arc of movement causes the circumference of roll 15 to converge on the circumference of roll 12 at a point which is dependent upon an angle defined by a line between pivot 13 and the axis of roll 15, and a line between the two axes, with the rolls together. It can be shown that for a given force acting downwardly at the axis roll 15, the resultant grinding load at the nip is given by a ratio of the applied force and the sine of the angle between the two lines just referred to. From this it can be shown that for an angle of 1" the grinding load is approximately ten times greater than for an angle of 10 .

Assuming the cylinder 17 to be of the doubleacting type which is thus capable of lifting the cradle 14 as well as applying a grinding force when the rolls are together, then the force required to lift the assembly will be approximately equal to its weight, i.e. in the region of 350 kilograms, and this force is available when acting downwardly to produce a grinding force of between 2,000 kilograms and 20,000 kilograms with the angle referred to above between 10 and 1" respectively. This angle represents the angle of convergence of the moving roll with respect to a tangent to the fixed roll circumference at the nip, and by selecting this angle at between 5 and 10, it is expected that ample grinding loads will be available for all types of rollermill used for reducing grain.

During operation of the rollermill, the presence of a foreign body at the nip will tend to cause the movable roll to ride up over the fixed roll in the direction dictated by the pivotal mounting of the cradle 14. Such movement is to be applied against the relativeiy light load imposed by the low pressure air cylinder and the weight of the cradle and roll. In conventional systems, such movement must be applied against the higher forces generated by a complex lever system and high pressure cylinder.

It is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible without departing from the scope of the invention.

For example, the movable roll, instead of moving about an arc determined by the pivotal mounting of the cradle 14, can be adapted for linear movement in the same general direction.

Furthermore, if required the rolls may be disposed with their axes on a common inclined plane, though the horizontal disposition of the rolls as illustrated is thought two be advantageous, particularly for removal of the rolls for servicing.

Claims

1. A rollermill having a pair of grinding rolls forming a nip through which stock is passed to be ground, one of said grinding rolls being movable with respect to the other thus to enable the rolls to be separated in the absence of the stock and placed in close working relationship in the presence thereof, characterised in that movement of the movable roll is such that as it approaches the fixed roll, its surface converges at an acute angle with a tangent to the fixed roll at the position of closest proximity of the two rolls.

2. A rollermill according to Claim 1, wherein said movable roll is mounted on a cradle which itself is pivotally mounted on a fixed frame member, the pivotal axis being slightly offset from a common plane of the rotational axes of the two rolls at said position of closest proximity.

3. A rollermill according to Claim 2, wherein said common plane is horizontal and said pivotal axis is just above said plane.

4. A rollermill according to Claim 2, wherein the angle defined by a line extending between the pivotal axis of the cradle and the rotational axis of the movable roll, and by the common plane of the two roll axes at said position of closest proximity of the two rolls, is not more than ten degrees.

5. A roliermill according to any preceding claim, wherein the convergence of the two roll surfaces at a shallow acute angle, together with the weight of the movable roll, provide a mechanical advantage such that the ratio of grinding load to the force applied is at or close to 7:1.

6. A rollermill according to any preceding claim, wherein means for driving said movable roll into its working relationship with said fixed roll operates at low power, for example, an air cylinder operating in the region of 0.68 Bars.

7. A rollermill according to any preceding claim, including means preventing actual contact of the two roll surfaces during operation, and means for adjusting the gap at the position of closest proximity ofthe rolls.

8. A rollermill according to Claim 1 wherein said movable roll is movable linearly with respect to said other roll.

9. A rollermill according to Claim 1 wherein said rolls are disposed with their axes on a common inclined plane at said position of closest proximity of the two rolls.

10. A rollermill, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawing.