Technical Field of the Invention

The present invention relates to a feeder apparatus for feeding material to be crushed or ground to a roller crusher. The invention also relates to a method for feeding material to be crushed or ground to a roller crusher.

Background Art

When crushing or grinding rock, ore, cement clinker and other hard materials roller crushers may be used having two generally parallel rolls which rotate in opposite directions, towards each other, and which are sepa- rated by a gap. The material to be crushed is fed by gravity or choke-fed into the gap. One type of roller crusher is called high pressure grinding rollers or high pressure roller crushers. This type of roller crusher uses a crushing technique called interparticle crushing. Here, the material to be crushed or pulverised is crushed not only by the crushing surface of the rolls, but also by particles in the material to be crushed, hence the name interparticle crushing.

One example of a high pressure grinding roller is described in

EP-516 952. High pressure grinding rollers of this kind use autogenous protection, i.e. a layer of the material to be crushed is retained on the surface of the rolls. Thus, the material to be crushed will not wear only on the surface of the roll, but mainly on the autogenous protection layer.

A general problem associated with high pressure grinding rollers is the difficulty to quickly and securely establish the autogenous protection layer. It is necessary to have a proper composition of the material fed into the gap of the high pressure grinding roller or else the material will not adhere properly to the outer surface of the rolls, thereby increasing the wear on the actual surface of the rolls.

Summary of the Invention

It is an object of the present invention to provide an improvement of the above technique and prior art. More particularly, it is an object of the present invention to provide a feeder apparatus for feeding material to be crushed or ground to a roller crusher such that an autogenous protection layer quickly and securely is established on the roller crusher. Further, it is an object of the present invention to provide a method for feeding material to be crushed or ground to a roller crusher.

These and other objects as well as advantages that will be apparent from the following description of the present invention are achieved by a feeder apparatus and a method according to the independent claims.

A feeder apparatus for feeding material to be crushed or ground to a roller crusher is provided. The roller crusher has two generally parallel rolls arranged to rotate in opposite directions, towards each other, and separated by a gap. The feeder apparatus comprises a main feeder for feeding a first portion of said material to the gap of the roller crusher. The feeder apparatus is characterised in that it further comprises an auxiliary feeder for feeding a second portion of said material to the roller crusher. The auxiliary feeder is arranged to feed said second portion of material to at least one of the rolls at a speed which is adjustable in relation to a surface speed of said at least one roll. This is advantageous in that an autogenous protection layer quickly and securely can be established on the outer surface of the rolls of the roller crusher. Normally, material fed into the gap of the roller crusher will have trouble to adhere properly to the outer surface of the rolls. This depends on several factors, such as for example, that the material is fed at an unsuitable speed, in an unsuitable direction, or has an unsuitable composition. When material, however, is fed to the rolls of the roller crusher by the auxiliary feeder, in addition to the material fed into the gap of the roller crusher by the main feeder, both the speed, composition and direction of that second portion of material can be determined in order to quickly and securely achieve the desired autogenous protection of the rolls. In a preferred embodiment of the present invention, the auxiliary feeder is arranged to feed said second portion of material to at least one of the rolls at a speed essentially corresponding to a surface speed of said at least one roll.

The auxiliary feeder may be arranged to feed said second portion of material to said at least one roll in a direction essentially tangential to an outer surface of said at least one roll, which is advantageous in that the providing of the autogenous protection of the rolls will be further facilitated.

The auxiliary feeder may comprise at least one belt conveyor, and preferably two belt conveyors, each belt conveyor being arranged to feed said second portion of material to a respective roll of the roller crusher. This is advantageous in that both rolls of the roller crusher may be provided with the same autogenous protection in a controlled and simple way. Naturally, if desired, the autogenous protection of the two rolls could be varied by operating the two belt conveyors at different speed or direction and by using different compositions of the fed material . The auxil iary feeder may alternatively comprise at least one screw conveyor.

The second portion of the material may comprise new material, recirculated screen material, adhesive, any other suitable material or a combination thereof. Thus, the material composition may be varied in order to achieve the best possible result under the existing circumstances.

The feeding apparatus may further comprise a recirculation device arranged to collect a recirculation portion of material that has been crushed or ground by said roller crusher and to transfer said recirculation portion to said auxiliary feeder. This is advantageous in that the feeding apparatus will thus be totally automatic. There will be no manual requirements to provide the auxiliary feeder with material to be fed to the rolls.

The feeding apparatus may further comprise a conditioning device for conditioning said second portion of material, said conditioning device may comprise a water supplying device. This is advantageous in that the composi- tion of the material easily can be controlled.

The main feeder may be arranged to choke feed said first portion of said material to the gap of the roller crusher, which is advantageous in that improved crushing performance can be achieved.

According to a second aspect of the invention, the invention relates to a method for feeding material to be crushed or ground to a roller crusher. The roller crusher has two generally parallel rolls arranged to rotate in opposite directions, towards each other, and separated by a gap, wherein a first portion of said material is fed to the gap of the roller crusher by a main feeder. The method is characterised in that a second portion of said material is fed to at least one roll of the roller crusher by an auxiliary feeder at a speed which is adjustable in relation to a surface speed of said at least one roll.

The second portion of material may be fed to said at least one roll in a direction essentially tangential to an outer surface of said at least one roll.

The method may further comprise recirculating material that has been crushed or ground by said roller crusher by collecting a recirculation portion of the crushed material and transferring said recirculation portion to said auxiliary feeder.

The method may further comprise conditioning said second portion of material before it is fed to said at least one roll, said conditioning may comprise supplying water to said second portion of material.

The first portion of said material may be choke fed by the main feeder to the gap of the roller crusher.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, etc]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, etc., unless explicitly stated otherwise. Further, by the term "comprising" it is meant "comprising but not limited to" throughout the application.

Brief description of the drawings

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

Fig. 1 is a perspective view of a roller crusher without a feeding ar- rangement, and

Fig. 2 is a perspective view of a roller crusher having a feeder apparatus according to one exemplary embodiment of the present invention. Detailed description of preferred embodiments of the invention

Fig. 1 illustrates a conventional roller crusher 1 without a feeding arrangement.. The roller crusher 1 has two crushing rollers 2, which are parallel to one another and rotate in opposite directions, towards each other. Each one of the crushing rollers 2 has a shaft 3 with end portions 4 mounted in respective roller bearings 5. The roller crusher 1 has a feeding arrangement 6 for feeding material to be crushed to a crushing zone of the roller crusher 1 . After the material has been crushed in the crushing zone, it is transported away from the roller crusher 1 .

In Fig. 2, a roller crusher 6 having a feeder apparatus 7 according to one embodiment of the present invention is illustrated. The feeder apparatus 7 is adapted to feed material to be crushed or ground to the roller crusher 6. The roller crusher 6 has two generally parallel rolls 8 arranged to rotate in opposite directions, towards each other, and are separated by a gap. The feeder apparatus 7 comprises a main feeder 9 for feeding a first portion of the material to the gap of the roller crusher 6, and two auxiliary feeders 10 for feeding a second portion of the material to the roller crusher 6. The auxiliary feeders 10 feed the second portion of material to the two rolls 8 at a speed which is adjustable in relation to a surface speed of the two rolls 8. Each one of the auxiliary feeders 10 comprises a belt conveyor which is arranged to feed the second portion of material to the rolls 8 in a direction essentially tangential to the outer surface of the rolls 8. The feeder apparatus has two recirculation devices 1 1 , one for each roll 8, arranged to collect a recirculation portion of material that has been crushed or ground by said roller crusher 6 and to transfer the recirculation portion to the auxiliary feeder 10. Thus, the second portion of material fed to the rolls 8 can be either new material, recirculated screen material, adhesive, any other suitable material or a combination thereof. The feeder apparatus 7 has four conditioning devices 12 for conditioning the second portion of material. The conditioning devices 12 are merely constituted by a water supplying device. Naturally, other types of conditioning devices 12 can also be used for the feeder apparatus, e.g. for heating, cooling, or mixing the second portion of material, or adding a chemical conditioning agent to the second portion of material. During the crushing operation of the roller crusher 1 , the first portion of the material to be crushed is transported by the main feeder 9 of the feeder apparatus 7 and introduced in the funnel of the roller crusher 6. The material then travels by gravity from the funnel to the crushing zone. When the materi- al has been crushed by means of the two parallel and rotating crushing rolls 8, it travels by gravity out of the crushing zone in order to be transported from the plant. Simultaneously, a second portion of the material is transported by the two auxiliary feeders 10 to be introduced directly on the rotating crushing rolls 8. The second portion of the material is generally more fine-grained than the first portion of the material and is feed to the rolls 8 at a speed which is adjustable in relation to a surface speed of the rolls 8. By adjusting the feeding speed of the auxiliary feeders 10, some characteristics of the autogenous protection layers of the rolls 8, such as for example their thickness, can be controlled to a certain extent. When material is fed to the rolls 8 of the roller crusher 6 by the auxiliary feeder 10, in addition to the material fed into the gap of the roller crusher 6 by the main feeder 9, both the speed, composition and direction of that material can be determined in order to achieve the desired autogenous protection of the rolls 8. The recirculation devices then collect a recirculation portion of material that has been crushed or ground by said roller crusher 6 and transfer the recirculation portion back to the auxiliary feeder 10.

According to a second aspect of the invention, a method for feeding material to be crushed or ground to a roller crusher 6 is provided. The roller crusher 6 has two generally parallel rolls 8 arranged to rotate in opposite di- rections, towards each other, and separated by a gap, wherein a first portion of said material is fed to the gap of the roller crusher 6 by a main feeder 9. The method is characterised in that a second portion of said material is fed to at least one roll 8 of the roller crusher 6 by an auxiliary feeder 10 at a speed which is adjustable in relation to a surface speed of said at least one roll 8.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended claims. For instance, the number and type of main feeders and auxiliary feeders can be varied. The feeders may, for example, be belt conveyors, screw conveyers, or be feeding by gravity.

The recirculation device may be varied in different ways and can be of any suitable sort. The same applies to the conditioning devices and the amount thereof.

By new material is meant material that not yet has passed through the gap between the rolls of the roller crusher. The new material that is fed to the rolls of the roller crusher by means of the auxiliary feeder may comprise ad- hesive or any other suitable material in order to achieve the desired autogenous protection layer on the rolls.