Belt conveyor and crushing unit

A belt conveyor and a crushing unit includes a conveying upper run presenting a feed end and a discharge end, and a return lower run, with the conveying upper end including a curved extension, which is concave and ascending and presents an inlet lower portion and an outlet upper portion of the conveying upper run, where the belt conveyor imparts to the material a path that is substantially coplanar and opposite in relation to that imparted to the material in the inlet portion, and with ascending curved path presenting at a determined belt speed, a centrifugal force sufficient to maintain the material seated against the curved extension of the conveying upper run until reaching the discharge end.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/BR03/00054, filed on Apr. 1, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention refers to an endless belt conveyor for vegetable or mineral bulk products, and more particularly to an endless belt conveyor for the formation of a closed loop in a fixed or movable crushing unit. The invention is further directed to a crushing unit comprising the belt conveyor.

2. Description of the Related Art

Crushing units are well known, particularly those mounted on a vehicle chassis, comprising belt conveyors which are respectively and operatively associated with a crusher and with a classifying screen, for allowing the material, which is rejected by the classifying screen and passed through the crusher, to be reconducted to the screen, in order to be submitted to a new classification. This system of returning the crushed material to the classifying screen is generally denominated closed crushing loop and is schematically illustrated inFIGS. 1 and 2of the enclosed drawings.

In the movable crushing units mounted on a vehicle chassis V, the bulk material to be crushed is directly or indirectly fed to a first belt conveyor10which conducts the material to a classifying screen20, for example a vibrating screen, in which it is separated. The material passing through the classifying screen20is collected, for example in a hopper21and conducted to a discharge conveyor22, which conducts the material passing through the classifying screen20to a storage heap S or any other adequate collecting means.

The large material rejected by the classifying screen20is conducted to a crusher30, so as to be reduced to the desired size of the crushed product. The material released from the crusher30is fed to a second return belt conveyor40arranged beside the first belt conveyor10, but which conducts the crushed material upwardly and in an opposite direction to the conduction direction of the first belt conveyor10, so that it may release the crushed material at a height sufficient to allow the transfer of the material, by means of an inclined chute50, to the first belt conveyor10, which conducts the material back to the classifying screen20, completing the closed crushing loop. It should be noted that the feeding of bulk material to the crushing unit can be made in the first belt conveyor10, for example in the region where the crushed material is received, or in the second belt conveyor40.

In these crushing units, the length of the second belt conveyor should be dimensioned to position its discharge end at a height much higher than that of the feed end of the first belt conveyor10, in order to allow the transfer of the crushed material coming from the crusher30and to be returned to the classifying screen20. In the illustrated construction, in which the first and the second belt conveyors10and40are arranged side-by-side, the transfer is carried out through the inclined chute50.

The above-described closed loop has the function to reduce all the material sent to the crushing unit to a size that is smaller than the mesh of the classifying screen20. This arrangement is applied to both the movable units and to the fixed units and it is particularized in that the return of the material to the classifying screen20is accomplished by means of two belt conveyors disposed side by side and moved in opposite directions.

One of the disadvantages of this solution refers to the height that the discharge end of the second belt conveyor40should present and which should be much higher than the height of the feed end of the first belt conveyor10.

In order to avoid the material being carried by the second belt conveyor40from sliding in a direction opposite to that of the conveying run, the slope angle of the second belt conveyor40must be limited, usually not higher than 20 degrees.

The closed loop, as described above, requires a very long second belt conveyor40, which besides increasing the cost in the case of movable units on wheels, impairs the displacement of these crushing units on highways.

The first and the second belt conveyors10and40on being arranged side by side increase the width of the crushing unit, exceeding the limit dimensions for highway transportation, requiring either the partial disassembly of the unit, or special authorizations to travel on highways.

BRIEF SUMMARY OF THE INVENTION

Considering that the limitations imposed to the slope angle of the belt conveyors often lead to the difficulty in providing these conveyors in installations to be constructed in reduced spaces, it is an object of the present invention to provide a belt conveyor for bulk material, which allows in a determined longitudinal conveying extension, to lift the bulk material being carried at a height that has not been attained before with the known prior art belt conveyors.

It is a further more specific object of the present invention to provide a belt conveyor such as defined above, which presents a discharge end that is sufficiently lifted to discharge the bulk material in another belt conveyor, which is at least partially aligned above the first conveyor and which is driven in an opposite direction to the direction of the first conveyor, in order to avoid the side by side arrangement of the conveyors to provide the return of the bulk material to a processing equipment through which it has already passed.

It is a further object of the present invention to provide a crushing unit, particularly a crushing unit on a vehicle chassis, comprising the belt conveyor mentioned above and a conventional belt conveyor operatively associated thereto, in order to define a closed crushing loop having substantially reduced longitudinal extension and width, and according to which the bulk material is returned to a classifying screen after passing through a crusher fed with the material rejected by the classifying screen.

These objects are attained through a belt conveyor comprising a conveying upper run presenting a feed end disposed vertically spaced from and above a discharge end, and a return lower run. The conveying upper run comprises a curved extension, which is concave and ascending and presents an inlet lower portion and an outlet upper portion, the latter ending at the discharge end of the conveying upper run, where the belt conveyor imparts to the material a path that is substantially coplanar and opposite in relation to that imparted to the material in the inlet lower portion, the curved extension presenting a curvature so as to produce, on the material conveyed at a determined belt speed, a centrifugal force sufficient to maintain the material seated against the ascending curved extension of the conveying upper run, until reaching the discharge end.

The belt conveyor defined above may be utilized, for example to form the closed loop of a crushing unit in which the conveyor receives the material from a crusher, conducting the material at a height sufficient to transfer it to another belt conveyor vertically disposed above the first one and conducting the crushed material to a classifying screen.

DETAILED DESCRIPTION OF THE INVENTION

As already described in relation to the known construction of the movable crushing unit illustrated inFIGS. 1-2, in order to make the crushed material return to the classifying screen20after it has passed through the crusher30, two belt conveyors10,40have been used arranged side-by-side, one of them being the second belt conveyor40responsible for conducting the material received from the crusher30, until reaching a height which is sufficient to transfer, by means of the inclined chute50, the material to the first belt conveyor10which conducts the crushed material back to the classifying screen20.

In the installations where there is no limitation of space, the full width of the two belt conveyors10,40arranged side-by-side is not a problem, the same occurring with the longitudinal extension of the second belt conveyor40, which must reach a height at its discharge end so as to allow the crushed material to be adequately transferred to a feed end10aof the first belt conveyor10, maintaining an inclination within the acceptable limits for the correct upward conveyance of the material.

However, in determined cases, as it occurs with the movable crushing units on wheels, the problem of the dimensions in terms of width and longitudinal extension of the crushing unit is of great importance, which makes desirable to obtain the lift of the crushed material and its return to the classifying screen20on a vehicle chassis V with acceptable length and width to circulate on a highway and at an acceptable or compatible cost in relation to the usual solutions.

Considering the specific application exemplified in the drawings, the second belt conveyor40comprises a conveying upper run41and a return lower run42. The conveying upper run41presents a feed end41adisposed so as to receive the bulk material to be conveyed, and a discharge end41bdisposed at a height above the feed end41a, so as to allow the bulk material to be transferred to another belt conveyor or another bulk material processing equipment. In the present exemplary construction, the other conveyor is the first belt conveyor10, which is responsible for conducting the material to the classifying screen20, whereas the feed end41aof the conveying upper run41receives the material from the crusher30. It should be understood that the second belt conveyor40could be assembled in different installations, in which an intense lift of the bulk product in relation to the longitudinal extension available to the lift is desired.

According to the invention, the conveying upper run41comprises a curved extension43, which is concave and ascending and presents an inlet portion43aand an outlet portion43b, the latter ending at the discharge end41bof the conveying upper run41, where the second belt conveyor imparts to the material a path that is substantially coplanar and opposite in relation to that imparted to the material in the inlet portion43a.

In order that this material M to be conveyed remains seated on the material support face of the conveying upper run41throughout the whole curved extension43in which the material has its path progressively altered upwardly and backwardly, until it presents an opposite direction to that of the inlet in the curved extension43, the second belt conveyor40is driven at a determined velocity to produce, in the curved extension, a centrifugal force which is sufficient to maintain the material M in the second belt conveyor40until reaching the discharge end41b, when the material M is allowed to fall onto any collecting means. Thus, the radius of curvature of the curved extension43is dimensioned as a function of the conveying height to be achieved, and also of the speed allowed for the second belt conveyor40.

The radius of curvature of the curved extension43can be constant or it can vary decreasingly upwardly, so as to allow a higher centrifugal force in the upper region of the curved extension43to be achieved, from a given displacement velocity of the second belt conveyor40.

In order to allow the conveying upper run41to present the curved extension43concave and ascending, the latter has its material support face marginally seated on support rollers44that are arranged to maintain the desired curvature for the curved extension43, preventing the conveying upper run41from collapsing to the inside of the contour of the curved extension43.

According to the present invention, the sustaining face of the curved extension43presents a pair of opposite marginal portions43c, each being seated on at least one support roller44, as illustrated inFIGS. 7-14, or also on a plurality of support rollers44, such as illustrated inFIGS. 3-5.

As illustrated inFIG. 3, the conveying upper run41of the second belt conveyor40may further comprise a linear extension45arranged immediately downstream of the feed end41aand ending in the inlet portion43aof the curved extension43, with which it matches. This linear extension45is conventionally supported by rollers46which are disposed so as to impart to this linear extension45a slope that is at maximum equal to a limit slope value of a belt conveyor.

The conveying upper run41has its ends seated on respective end rolls47and48, between which is defined the return lower run42medianly arranged around at least one compensating roll49.

With the above-mentioned construction, it is possible to provide a belt conveyor that is capable, in a given longitudinal extension of its travel, to lift the material M being transported at a height much higher than the one that would be attained with the conventional constructions of linear belt conveyors.

In the exemplary construction illustrated inFIGS. 5-6and directed to the crushing unit of the closed loop type illustrated inFIGS. 1-2, the second belt conveyor40is constructed with its conveying upper run41presenting a linear extension45followed by a curved extension43in which the material M is intensely lifted and backwardly conducted in a direction that is opposite to the conveying direction in the linear extension45and in the inlet portion43aof the curved extension43.

The height of the gap existing between the inlet portion43aand the outlet portion43bof the curved extension43is sufficient for the discharge end41bof the conveying upper run41to transfer the material M to the feed end10aof the first belt conveyor10, which is herein vertically disposed above the second belt conveyor40and generally in a substantially parallel and vertically aligned mode in relation to the conveying upper run41of the second belt conveyor40, as illustrated inFIGS. 5-6. In this case, the feed end10aof the first belt conveyor10is positioned within the curved extension43, below the discharge end41aof the conveying upper run41of the second belt conveyor40.

The constructions of the present invention thus allow achieving, not only a substantial reduction in the longitudinal extension of the crushing unit, but also a considerable width reduction, due to the fact that the two belt conveyors are disposed one over the other and no more side by side, whereby it is also possible to suppress the inclined chute50for transferring the material from the second to the first belt conveyor10.

As already mentioned, the new belt conveyor40can be entirely formed by a curved extension43with a single radius or with different radii of curvature, which can be progressively reduced to increase the centrifugal force on the material M, as the angle of inclination increases, until the total inversion of the conveying direction in the discharge end41bhas been achieved.

In the embodiments illustrated inFIGS. 7-14, the curved extension43has its material support face in each marginal portion43cseated on a support roller44, whose radius of curvature defines the radius of curvature of the curved extension43, each of the support rollers44which define the radius of curvature of the curved extension43being mounted to a respective shaft externally journalled to the adjacent side of the second belt conveyor40.

In a constructive variation illustrated inFIGS. 9-10, the first belt conveyor10has its feed end10amounted around a roll R, which is disposed internally and eccentrically to the support rollers44.

In this constructive option, each of the support rollers44defining the radius of curvature of the curved extension43is mounted to the respective shaft externally journalled to the adjacent side of the second belt conveyor40.

In another constructive variation illustrated inFIGS. 11-14, the first belt conveyor10has its feed end10amounted around a roll R, which is provided internally and coaxially in relation to the support rollers44. In the constructive option illustrated inFIGS. 11 and 12, the roll R of the feed end10ais incorporated, in a single piece, to the two support rollers44. In the constructive option illustrated inFIGS. 13 and 14, the roll R of the feed end10ais supported on a common end of the two support rollers44, internally to the latter.