Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B66—HOISTING; LIFTING; HAULING
  • B66C—CRANES; LOAD-ENGAGING ELEMENTS OR DEVICES FOR CRANES, CAPSTANS, WINCHES, OR TACKLES
  • B66C3/00—Load-engaging elements or devices attached to lifting or lowering gear of cranes or adapted for connection therewith and intended primarily for transmitting lifting forces to loose materials; Grabs
  • B66C3/12—Grabs actuated by two or more ropes

Definitions

• the present invention relates to a rope operated mechanical grab for handling loads, in particular for handling bulk loads.
• the present invention further relates to a grab assembly and to a method for handling bulk loads.
• a first common type of mechanical grabs is the clamshell grab, which is characterized by a relatively low weight and high capacity and which is generally used to handle free-flowing bulk materials.
• the shells of these grabs are pushed downwards into the material by two arms when two pulley blocks are pulled together in a vertical way.
• a second common type of mechanical grabs is the scissors grab, which operates in a different way with horizontal pulley blocks above a main hinge point between lever arms.
• the combination of the horizontal pulley blocks and the central hinge point results in a circular closing path of the shells.
• trimming grabs which comprise two arms, which are pivotally connected to a top block at the tops of the arms.
• the trimming grab comprises shells at the lower ends of the arms and comprises closing sheaves in the middle of the arms.
• a benefit of a trimming grab is that the grab shells travel in a substantially horizontal plane upon movement between an open and closed position, whereas other grabs will come up during closing.
• the flat horizontal closure of the trimming grab is beneficial to obtain a constant, i.e. flat scraping of bulk material upon filling the grab, whereas other grabs would have to dig into the bulk material to obtain a good filling.
• the closing line passes only along multiple closing line guiding sheaves. The passes will result in a relatively large closure force, i.e. the force at which the grab shells can be moved towards each other during closing of the grab.
• this known trimming grab has the drawback that the closure length of the grab, i.e. the length of the closing line that needs to be drawn in by the crane for closing the grab, is relatively large, because the closing line is guided over multiple closing line guiding sheaves. This large closure length results in a relatively low closing speed of the grab, which reduces productivity of the grab during use.
• a rope operated mechanical grab for example a four rope operated mechanical grab that is operated by a crane with two hoisting lines and two closing lines, for handling loads, in particular for handling bulk loads
• the mechanical grab according to the invention comprising: a first lever arm, comprising a first end and an opposed second end, wherein the grab comprises a first grab shell mounted at the first end of the first lever arm, a second lever arm, comprising a first end and an opposed second end, wherein the grab comprises a second grab shell mounted at the first end of the second lever arm, a direct pivot connection between the second end of the first lever arm and the second end of the second lever arm that is free of any sheaves, wherein the first lever arm comprises a closing line attachment point, wherein the second lever arm comprises an initial closing line guiding sheave, and wherein the grab is configured to receive a closing line, which is configured to be attached to the closing line attachment point and configured to extend from the closing line attachment point, via
• the mechanical grab according the present invention thus comprises a first lever arm and a second lever arm, which are pivotally connected to each other at their second, e.g. upper ends.
• the pivotally interconnected lever arms together have a shape that mimics an A in a closed position of the grab.
• the pivot connection between the lever arms is a direct pivot connection, which means that the first lever arm and the second lever arm rotate with respect to each other about a common axis of rotation.
• This pivoting configuration forms a first difference with the known grabs, since the known scissors grabs are pivotally connected at a central section of the arms and since the known trimming grabs are not directly connected to each other at the upper ends of the arms, but instead comprise a top block, to which each of the arms is pivotally connected.
• the construction of the grab according to the present invention is thus less complex than that of existing grabs, thereby allowing the weight of the grab to be less, thus giving rise to an improved productivity.
• a crane can only handle loads up to a certain threshold load, which implies that a larger amount of bulk material can be grabbed when the empty weight of the grab is reduced.
• Each of the lever arms of the present grab comprises a grab shell, wherein a first grab shell is mounted at a first, e.g. lower end of the first lever arm and wherein a second grab shell is mounted at a first, e.g. lower end of the second lever arm.
• the first grab shell and the second grab shell contact each other to define an interior of the grab in between them.
• the lever arms of the grab In an open position of the grab, the lever arms of the grab have moved away from each other and the grab shells are spaced at a distance from each other. In this opened position of the grab, the lever arms preferably become aligned almost antiparallel, i.e. aligned at almost 180° from each other, both substantially extending in a horizontal direction.
• a closing line is connected to the grab for effecting a movement from the open position of the grab to its closed position, or vice versa, by a crane to which the closing line is attached and from which the grab is suspended, for example by means of one or two hoisting lines.
• the closing line is configured to be connected to the closing line attachment point at the first lever arm and is guided towards the crane via the initial closing line guiding sheave at the second lever arm.
• the closing line With the closing line attachment point and the initial closing line guiding sheave provided on opposed lever arms of the grab, the closing line will horizontally cross between the lever arms when installed on the grab.
• the closing line After extending horizontally towards a closing line guiding sheave, e.g. towards the initial closing line guiding sheave, the closing line may directly extend towards the crane in a substantially upward direction, without passing along further deflection sheaves of the grab, in order to minimize contact between sheaves of the grab, thus to minimize wear of the sheaves and the closing line.
• the initial closing line guiding sheave may be the sole closing line guiding sheave of the grab, so that the closing line departs from the grab after having passed the initial closing line guiding sheave.
• the grab may comprise further closing line guiding sheaves along which the closing line is to be passed before departing to the crane.
• the closing line is typically guided towards the centre of the grab, in between the respective pivot connections of the top block with each of the lever arms, to depart from the grab at the top block in the upward direction.
• This guiding requires additional sheaves in the top block, which solely serve the purpose of guiding the cable and which have no contribution in increasing the closure force of the grab, thus only result in additional wear and friction.
• no top block is present and the cables depart from the grab at the closing line guiding sheaves at the lever arms, thereby reducing the wear and friction that is present in existing grabs.
• the sheaves in the top block of the existing trimming grabs introduce a reversal in the bending direction of the closing line.
• the guiding along the closure sheaves for example only concerns bending in a clockwise direction, whereas the guiding along the sheaves in the top block of the existing trimming grab concerns bending in the counter clockwise direction.
• This reversal of the bending of the closing lines further deteriorates the wear of the closing lines used in existing trimming grabs.
• the absence of a top block and corresponding sheaves in the present grab may lack such bending reversals, thereby further reducing wear and friction of the closing lines.
• the omission of a top block and lighter construction of the lever arms may lower the centre of gravity of the grab, resulting in more stable positioning on sloped surfaces, fur example on piles of bulk material, thereby reducing the risk of tumbling of the grab.
• the first lever arm has an intermediate section, in between its first end and its second end
• the second lever arm has an intermediate section, in between its first end and its second end
• the closing line attachment point is provided at the intermediate section of the first lever arm
• the initial closing line guiding sheave is provided at the intermediate section of the second lever arm.
• the lever arms In between their first, e.g. upper ends and their second, e.g. lower ends, the lever arms comprise respective intermediate sections, e.g. centrally in between the first and second ends, preferably in the middle of them, and thus centrally between the pivot connection and the grab shells.
• the closing line attachment point is mounted to the first lever arm at the intermediate section thereof, thus in between the pivot connection and the first grab shell.
• the initial closing line guiding sheave is mounted to the second lever arm at the intermediate section thereof, thus in between the pivot connection and the second grab shell.
• the closing line guiding sheave and the closing line attachment point are provided at respective lever arms centrally in between the grab shell and the pivot connection. This placement provides for a useful balance between closure force and the closure length, i.e. reaching a desired closure force whilst having an acceptable closure length.
• the first lever arm comprises a successive closing line guiding sheave at its intermediate section, and the closing line is configured to extend from the closing line attachment point, via the initial closing line guiding sheave and via the successive closing line guiding sheave, directly towards the crane from which the grab is configured to be suspended.
• the grab may contain exactly two closing line guiding sheaves for the closing line, namely the initial closing line guiding sheave and the successive closing line guiding sheave.
• the closing line is configured to span between the lever arms for two passes: once from the successive closing line guiding sheave to the initial closing line guiding sheave and once from the initial closing line guiding sheave to the closing line attachment point, in order to increase the closure force compared to when the closing line were to make a single pass between the lever arms.
• This grab preferably contains no further guiding sheaves for this closing line, to avoid that the closure length will become too large and that the closing speed of the grab will become too low to be practically feasible.
• the closing line attachment point is provided at the first lever arm, the initial closing line guiding sheave is provided at the second lever arm and the successive closing line guiding sheave is provided at the first lever arm again.
• the closing line is thus configured to span from the intermediate section of the first lever arm to the intermediate section of the second lever arm and back to the intermediate section of the first lever arm before extending further upward, e.g. without passing along further closing line guiding sheaves of the grab, towards the crane from which the grab is suspended.
• the second lever arm comprises a second closing line attachment point at its intermediate section
• the first lever arm comprises a second initial closing line guiding sheave at its intermediate section
• the grab is configured to receive a second closing line, which is configured to be attached to the second closing line attachment point and configured to extend from the second closing line attachment point, via the second initial closing line guiding sheave, directly towards the crane.
• the grab is adapted to receive a second closing line from the crane from which it is suspended.
• a second closing line typically acts parallel to the closing line, i.e. the first closing line, to double the closure force of the grab, without increasing the closure length.
• Such a second closing line may either be attached to a second closing winch of the crane or may be connected to the first closing line at a closing line coupling element.
• Such a coupling element may be configured to receive the first closing line and the second closing line, i.e. after they have departed from the grab, and may connect the closing lines to each other so that only a single, e.g. common closing line extends towards the crane.
• the second closing line extends through the grab in a direction opposite to the first closing line and may essentially be mirror symmetric with respect to the first closing line.
• the distal end of the second closing line is configured to be connected to the second closing line connection point on the second lever arm, where the first closing line is connected to the first lever arm.
• the second closing line passes from the second lever arm to the first lever arm to be guided along the second initial closing line guiding sheave, before being guided upwards to the crane from which the grab is suspended.
• the symmetric closing lines i.e. the second closing line extending in the grab in a direction opposite to the first closing line, have the advantage that the closure force can be spread symmetrically between the lever arms, and therefore also between the grab shells, resulting in a more uniform closure movement. Furthermore, as indicated above, the presence of two closing lines provides that the closure force can be two times higher than with a single closing line or, alternatively, that the tensile force in the two closing lines can be half the tensile force that would occur in a single closing line, whilst still obtaining the same closure force between the grab shells.
• the second lever arm comprises a second successive closing line guiding sheave at its intermediate section, and the second closing line is configured to extend from the second closing line attachment point, via the second initial closing line guiding sheave and via the secondary successive line guiding sheave, directly towards the crane from which the grab is configured to be suspended.
• the grab may also contain exactly two closing line guiding sheaves for the second closing line, namely the second initial closing line guiding sheave and the second successive closing line guiding sheave.
• This grab preferably contains no further guiding sheaves for the second closing line either, to avoid that the closure length will become too large and that the closing speed of the grab will become too low to be practically feasible.
• the second closing line attachment point is provided at the second lever arm, the second initial closing line guiding sheave is provided at the first lever arm and the second successive closing line guiding sheave is provided at the second lever arm again.
• the second closing line is thus configured to span from the intermediate section of the second lever arm to the intermediate section of the first lever arm and back to the intermediate section of the second lever arm before extending further upward, e.g. without passing along further closing line guiding sheaves of the grab, towards the crane from which the grab is suspended.
• the grab further comprises: a lifting frame, with which the grab is configured to be suspended from the crane, e.g. from at least one hoisting line of the crane, at least one first lifting line, which extends between the lifting frame and one of the first grab shell and the first lever arm, and at least one second lifting line, which extends between the lifting frame and one of the second grab shell and the second lever arm.
• the grab according to this embodiment is configured to be suspended from the crane by means of the lifting frame, which is adapted to be suspended from the hoisting line of the crane, or a plurality of hoisting lines, for example two hoisting lines in the case of a four rope operated mechanical grab.
• the lifting frame is typically suspended above the grab, i.e. the grab shells and the lever arms, and allows the hoisting line from the crane above it to extend in a substantially vertical direction, whereas the lifting lines towards the lever arms or the grab shells typically not extend entirely vertical, but also have a component extending sideways, because the lever arms and the grab shells are typically wider than the lifting frame.
• the at least one first lifting line preferably two first lifting lines, is connected to the lifting frame and to the first lever arm or the first grab shell. With two first lifting lines, a respective first lifting line may extend to each of the sides of the first lever arm or the first grab shell, to support the first grab shell in a stable manner.
• the at least one second lifting line preferably two second lifting lines, is connected to the lifting frame and to the second lever arm or the second grab shell. With two second lifting lines, a respective second lifting line may extend to each of the sides of the second lever arm or the second grab shell, to support the second grab shell in a stable manner.
• the first and second lifting lines preferably comprise lifting chains, which enable reliable support of the grab, without having substantial wear during their lifespan.
• the lifting lines may extend from the lifting frame to either the lever arms or to the grab shells, depending on the construction of the grab.
• the grab shells are mounted fixedly to the lever arms, for example by means of a welded connection, as in conventional grabs, the both options for the lifting lines are possible.
• the present invention also provides a grab in which the grab shells are releasably connected to the first ends of the lever arms.
• the lifting lines are preferably connected to the lever arms, for example to the first ends of the lever arms, to ensure that the grab can also be suspended from the lifting lines when the grab shells are disconnected from the lever arms.
• the first grab shell and the second grab shell each comprise at least one respective lifting eye
• the at least one first lifting line is connected to the at least one lifting eye of the first grab shell
• the at least one second lifting line is connected to the at least one lifting eye of the second grab shell.
• the lifting lines are attached directly to the grab shells via the lifting eyes.
• This embodiment may be beneficial where the grab shells are mounted fixedly to the lever arms, for example to obtain a high degree of stability of the grab.
• grab comprises a closing line coupling element, configured to receive the first closing line and the second closing line and configured to connect the closing lines to each other.
• the closing line coupling element is thus configured to recombine the closing lines so that only a single, e.g. common closing line eventually extends towards the crane.
• the direct pivot connection comprises a pivot pin, extending at least partially through one or more bearing seats in the first lever arm and through one or more bearing seats in the second lever arm.
• top block has several advantages mentioned above. Furthermore, the absence of such a top block, and the provision of a direct pivot connection, takes away a degree of freedom of the grab. Accordingly, the direct connection between the lever arms provides that the grab can stand upright in its open position more stable on a ground plane, when not in use, without having the risk that either one of the lever arms tumbles down.
• the grab shells are mounted to the lever arms by means of a releasable connection.
• the grab according to this embodiment differs from the known grabs, such as trimming grabs and scissor grabs, which generally comprise grab shells that are fixedly attached to the lever arms.
• the releasable connection allows exchange of grab shells, so that the type of grab shells can be adapted to the specific type of bulk material for which the grab is to be used, without requiring replacement of the entire grab.
• grab shells with a large volume may be installed, whereas small grab shells may be installed when the grab were to be used to handle heavy materials like pig iron or iron ore.
• the releasable connection allows for replacement of grab shells, for example in case the grab shells have worn out.
• the grab shells suffer from wear during the grabbing of bulk material, having an influence on their lifespan, whereas other components, like the lever arms, do not suffer from such wear, thereby having a longer lifespan.
• first lever arm and the second lever arm each comprise at least one respective lifting eye at their first ends, the at least one first lifting line is connected to the at least one lifting eye of the first lever arm, and the at least one second lifting line is connected to the at least one lifting eye of the second lever arm.
• the lifting lines are attached directly to the lever arms via the lifting eyes.
• This embodiment may be beneficial where the grab shells are mounted to the lever arms releasably, for example to ensure that the grab can also be suspended from the lifting lines when the grab shells are disconnected from the lever arms.
• the releasable connection between the lever arms and the grab shell comprises a pen connection and/or a bolted connection.
• the grab shells each comprise a bent bottom, a respective side wall on opposed sides of the bent bottom and stiffening ribs in between the side walls and extending parallel to the side walls.
• the bent bottoms of the grab shells together define the interior of the grab, configured to hold the bulk material in the closed position of the grab.
• the stiffening ribs of each of the grab shells may be flush with the respective lever arm to which the grab shell is attached.
• the lever arms may for example be integral with the stiffening ribs to allow for an optimal rigidity of the grab and to optimize the transfer of forces between the lever arms and the grab shells, in particular during the closing of the grab, during which relatively large forces may act onto the lever arms and the grab shells.
• each of the grab shells further comprises at least one cover, which each extends between a side wall and a stiffening rib, to at least partially close off an interior of the respective grab shell.
• the first grab shell may comprise a first cover between a first side wall and a first stiffening rib and a second cover between a second side wall and a second stiffening rib.
• the second grab shell may comprise a first cover between a first side wall and a first stiffening rib and a second cover between a second side wall and a second stiffening rib.
• the covers between the side walls and the stiffening ribs may contribute to the stiffness of the grab shells, which may in particular be beneficial where the grab shells are releasable from the lever arms. In the absence of a connection with the lever arms, the grab shells would otherwise be relatively weak and easy to deform, whereas the covers may contribute in preventing deformations of the grab shells.
• covers in the grab according to the present embodiment also provides a further difference in view of the known grabs, which lack such covers.
• the absence of covers is essential in trimming grabs, because trimming grabs rely on spilling of bulk material over the edges of the bottom, to prevent overloading of the grab.
• trimming grabs are used to grab heavy materials and rely on scraping over the top surface of the bulk material to become filled.
• covers were to be provided on such trimming grabs, the bulk material could not be spilled, resulting in the risk that the grab could not be closed due to a too large amount of bulk material being present in the grab shells.
• scissors grabs which have sheaves moving into grab shells of the opposed lever arm in an opened position. In case covers would be provided in such scissors grabs, the grabs could not be opened fully, because the sheaves would collide with the covers.
• each of the covers further extends between the side walls and over the stiffening ribs to substantially close off the interior of the respective grab shell.
• the covers may cover the entire grab shells between their respective side walls.
• the covers in the present embodiment can be used to cover the top sides of each of the grab shells, to be able to substantially close off the interior of the grab in its closed position.
• the covers prevent the bulk material from escaping from the grab, for example under influence of wind, which provides for more environmentally-friendly handling of bulk materials.
• the first lever arm and the second lever arm are rotatable relative to each other about the direct pivot connection to move the grab between a fully closed position and a fully opened position of the grab, and the lever arms are, upon movement between the fully closed position and the fully opened position, configured to rotate over an opening angle in a range between 100° and 170°, preferably in a range between 120° and 150°, for example over 150°.
• the grab according to this embodiment enables a relatively large opening angle, and thus a relatively large spread between the grab shells in the fully opened position.
• the opening angle will remain lower than 170°. In this way, it may be prevented that the closing cable, which spans between the lever arms, will contact the bulk material that is to be grabbed.
• a maximum opening angle of less than 170° ensures that the closure force exerted by the grab is already sufficient at the onset of closing.
• An opening angle larger than 170° would yield the risk that the grab cannot be closed by pulling the closing line.
• the first grab shell and the second grab shell each comprise a planar cutting edge, wherein, in the fully closed position of the grab, the planar cutting edges are aligned non-parallel relative to each other, and wherein, in the fully opened position of the grab, the planar cutting edges are aligned in a substantially vertical plane.
• the grab shells have cutting edges aligned horizontally and parallel to each other in the closed position of the grab.
• This trimming grab will not be opened as much as 180°, which implies that the cutting edges of these trimming grabs will be set at an angle relative to the vertical direction in the fully opened position of the grab.
• the present embodiment of the grab differs from the known grabs in that, in the closed position of the grab, the grab shells contact each other with the cutting edges, which define a discrete angle in between them and which are aligned non-parallel. In the fully opened position, the planar cutting edges are spaced apart, but are aligned parallel to each other and parallel to a vertical direction.
• the planar cutting edges Upon lowering the opened grab onto the bulk material that is to be grabbed, the planar cutting edges will encounter less resistance upon penetrating the bulk material. As a result, the grab will be lowered further into the bulk material under influence of its own weight compared to an existing grab of similar weight but with non-vertical cutting edges.
• a cutting edge angle is defined between the cutting edge of the first grab shell and the cutting edge of the second grab shell in the fully closed position of the grab, and the cutting edge angle is defined in a range between 100° and 170°, preferably in a range between 120° and 150°, for example at 135°.
• planar cutting edges may be aligned vertically in the fully opened position of the grab, in order to obtain the beneficial penetration effect of the grab that is described above.
• the present invention provides a rope operated mechanical grab, comprising: a first lever arm, comprising a first grab shell mounted at an end thereof, a second lever arm, comprising a second grab shell mounted at an end thereof, a pivot connection between the first lever arm and the second lever arm, wherein the first lever arm comprises a closing line attachment point, wherein the second lever arm comprises an initial closing line guiding sheave, and wherein the grab is configured to receive a closing line, which is configured to be attached to the closing line attachment point and configured to extend from the closing line attachment point, via the initial closing line guiding sheave towards a crane from which the grab is configured to be suspended, wherein the first grab shell and the second grab shell each comprise a planar cutting edge, wherein, in a fully closed position of the grab, the planar cutting edges are aligned nonparallel relative to each other, and wherein, in a fully opened position of the grab, the planar cutting edges are aligned in a substantially vertical plane.
• the grab according to the second aspect of the invention differs from the known grabs in that, in the closed position of the grab, the grab shells contact each other with the cutting edges, which define a discrete angle in between them and which are aligned non-parallel. In the fully opened position, the planar cutting edges are spaced apart, but are aligned parallel to each other and parallel to a vertical direction. Upon lowering the opened grab onto the bulk material that is to be grabbed, the planar cutting edges will encounter less resistance upon penetrating the bulk material. As a result, the grab will be lowered further into the bulk material under influence of its own weight compared to an existing grab of similar weight but with non-vertical cutting edges.
• a cutting edge angle is defined between the cutting edge of the first grab shell and the cutting edge of the second grab shell in the fully closed position of the grab, and the cutting edge angle is defined in a range between 100° and 170°, preferably in a range between 120° and 150°, for example at 135°.
• planar cutting edges may be aligned vertically in the fully opened position of the grab, in order to obtain the beneficial penetration effect of the grab that is described above.
• the grab according to the second aspect of the invention may be embodied with details as described herein with reference to the first aspect of the invention, including one or more of the optional and/or preferred details thereof, e.g. as stated in the appended claimset.
• the present invention provides a rope operated mechanical grab, comprising: a first lever arm, comprising a first grab shell mounted at an end thereof, a second lever arm, comprising a second grab shell mounted at an end thereof, a pivot connection between the first lever arm and the second lever arm, wherein the first lever arm comprises a closing line attachment point, wherein the second lever arm comprises an initial closing line guiding sheave, and wherein the grab is configured to receive a closing line, which is configured to be attached to the closing line attachment point and configured to extend from the closing line attachment point, via the initial closing line guiding sheave towards a crane from which the grab is configured to be suspended, wherein the grab shells are mounted to the lever arms by means of a releasable connection.
• the grab according to the third aspect of the invention differs from the known grabs, such as trimming grabs and scissor grabs, which generally comprise grab shells that are fixedly attached to the lever arms.
• the releasable connection allows exchange of grab shells, so that the type of grab shells can be adapted to the specific type of bulk material for which the grab is to be used, without requiring replacement of the entire grab.
• grab shells with a large volume may be installed, whereas small grab shells may be installed when the grab were to be used to handle heavy materials like pig iron or iron ore.
• the releasable connection allows for replacement of grab shells, for example in case the grab shells have worn out.
• the grab shells suffer from wear during the grabbing of bulk material, having an influence on their lifespan, whereas other components, like the lever arms, do not suffer from such wear, thereby having a longer lifespan.
• the releasable connection between the lever arms and the grab shell comprises a pen connection and/or a bolted connection.
• a pen connection or bolted connected maybe released relatively easily to enable rapid exchange of grab shells, whilst still offering a reliable support for the grab shells.
• the grab according to the third aspect of the invention may be embodied with details as described herein with reference to the first aspect and/or second aspect of the invention, including one or more of the optional and/or preferred details thereof, e.g. as stated in the appended claimset.
• the present invention further provides a grab assembly for handling loads, in particular for handling bulk loads, comprising: the rope operated mechanical grab as disclosed herein, preferably as recited in the claims, at least one closing line, configured to bring the grab from an opened position, e.g. a position in which the grab shells are spaced at a distance from each other, into a closed position, e.g.
• the closing line comprises a proximal end that is adapted to be connected to a crane, in particular to a closing winch of the crane, and an opposed distal end that is attached to the closing line attachment point of the first lever arm, and wherein the closing line is, from its distal end, guided towards the crane directly via the initial closing line guiding sheave on the second lever arm.
• the closing line in the grab assembly is connected to the grab for effecting a movement from the open position of the grab to its closed position, or vice versa, by a crane to which the closing line is attached and from which the grab is suspended, for example by means of one or two hoisting lines.
• the closing line is connected to the closing line attachment point at the first lever arm and is guided towards the crane via the initial closing line guiding sheave at the second lever arm.
• the initial closing line guiding sheave may be the sole closing line guiding sheave of the grab, so that the closing line departs from the grab after having passed the initial closing line guiding sheave.
• the grab may comprise further closing line guiding sheaves along which the closing line is to be passed before departing to the crane.
• the closing line With the closing line attachment point and the initial closing line guiding sheave provided on opposed lever arms of the grab, the closing line horizontally crosses between the lever arms when installed on the grab. After extending horizontally towards a closing line guiding sheave, e.g. towards the initial closing line guiding sheave, the closing line may directly extend towards the crane in a substantially upward direction, without passing along further deflection sheaves of the grab, in order to minimize contact between sheaves of the grab, thus to minimize wear of the sheaves and the closing line.
• the closing line is, from its distal end, guided towards the crane directly via the initial closing line guiding sheave on the second lever arm and via the successive closing line guiding sheave on the first lever arm.
• the grab may contain exactly two closing line guiding sheaves for the closing line, namely the initial closing line guiding sheave and the successive closing line guiding sheave.
• This grab preferably contains no further guiding sheaves for the closing line, to avoid that the closure length will become too large and that the closing speed of the grab will become too low to be practically feasible.
• the closing line attachment point is provided at the first lever arm, the initial closing line guiding sheave is provided at the second lever arm and the successive closing line guiding sheave is provided at the first lever arm again.
• the closing line thus spans from the intermediate section of the first lever arm to the intermediate section of the second lever arm and back to the intermediate section of the first lever arm before extending further upward, e.g. without passing along further closing line guiding sheaves of the grab, towards the crane from which the grab is suspended.
• the grab assembly further comprises a second closing line, comprising a proximal end that is adapted to be attached to the crane, in particular to the closing winch of the crane, wherein a distal end of the second closing line is attached to the second closing line attachment point of the second lever arm, and wherein the second closing line is, from its distal end, guided towards the crane directly via the second initial closing line guiding sheave on the first lever arm.
• a second closing line comprising a proximal end that is adapted to be attached to the crane, in particular to the closing winch of the crane, wherein a distal end of the second closing line is attached to the second closing line attachment point of the second lever arm, and wherein the second closing line is, from its distal end, guided towards the crane directly via the second initial closing line guiding sheave on the first lever arm.
• the grab receives a second closing line from the crane from which it is suspended.
• a second closing line typically acts parallel to the closing line, e.g. the first closing line, to double the closure force of the grab, without in increasing the closure length.
• Such a second closing line may either be attached to a second closing winch of the crane or may be connected to the first closing line after having departed from the grab, so that only a single, e.g. common closing line extends towards the crane.
• the second closing line extends through the grab in a direction opposite to the first closing line and may essentially be mirror symmetric with respect to the first closing line.
• the distal end of the second closing line is configured to be connected to the second closing line connection point on the second lever arm, where the first closing line is connected to the first lever arm.
• the second closing line passes from the second lever arm to the first lever arm to be guided along the second initial closing line guiding sheave, before being guided upwards to the crane from which the grab is suspended.
• the symmetric closing lines i.e. the second closing line extending in the grab in a direction opposite to the first closing line, have the advantage that the closure force can be spread symmetrically between the lever arms, and therefore also between the grab shells, resulting in a more uniform closure movement. Furthermore, as indicated above, the presence of two closing lines provides that the closure force can be two times higher than with a single closing line or, alternatively, that the tensile force in the two closing lines can be half the tensile force that would occur in a single closing line, whilst still obtaining the same closure force between the grab shells.
• the second closing line is, from its distal end, guided towards the crane directly via the second initial closing line guiding sheave on the first lever arm and via the second successive closing line guiding sheave on the second lever arm.
• the grab may also contain exactly two closing line guiding sheaves for the second closing line, namely the second initial closing line guiding sheave and the second successive closing line guiding sheave.
• This grab preferably contains no further guiding sheaves for the second closing line either, to avoid that the closure length will become too large and that the closing speed of the grab will become too low to be practically feasible.
• the second closing line attachment point is provided at the second lever arm, the second initial closing line guiding sheave is provided at the first lever arm and the second successive closing line guiding sheave is provided at the second lever arm again.
• the second closing line thus spans from the intermediate section of the second lever arm to the intermediate section of the first lever arm and back to the intermediate section of the second lever arm before extending further upward, e.g. without passing along further closing line guiding sheaves of the grab, towards the crane from which the grab is suspended.
• the grab assembly further comprises at least one hoisting line, configured to suspend the grab from the crane, wherein the at least one hoisting line comprises a proximal end that is adapted to be connected to the crane, in particular to a hoisting winch of the crane, and an opposed distal end that is attached to the grab, and wherein the distal end of the at least one hoisting line is preferably indirectly connected to the grab shells, for example via the lifting frame, via the at least one first lifting line and via the at least one second lifting line.
• the present invention also provides a method of handling bulk loads by means of a grab assembly as disclosed herein, e.g. comprising the grab as disclosed herein, comprising the steps of: moving the grab towards a loading location in its opened position; pulling at least one closing line, i.e. pulling the first closing line and the second closing line, if present, to bring the grab into its closed position, in order to grab bulk material within the grab shells; moving the grab towards a discharge location; and releasing the at least one closing line, i.e. releasing the first closing line and the second closing line, if present, to bring the grab into its opened position, in order to discharge the bulk material from the grab shells.
• Figure 1 schematically depicts an embodiment of the grab according to the present invention in a fully opened position
• Figure 2 depicts the grab of figure 1 in a closed position
• Figure 3 depicts a frontal view on an embodiment of the grab assembly according to the present invention
• Figure 4 schematically depicts a detailed view on the grab of figure 2, showing the planar cutting edges
• Figure 5 depicts a side view on the grab assembly of figure 3
• Figure 6 depicts a cross-sectional view along plane E - E in figure 5.
• Figures 1 and 2 depicts an embodiment of the grab according to the present invention, to which is referred with reference numeral 1.
• the grab 1 is shown in its fully opened position and in figure 2, the grab 1 is shown in its closed position.
• the grab 1 is a four rope operated mechanical grab 1, which is configured to be operated by a crane by two closing lines 101 and two hoisting lines 102, as is shown in figures 3 - 6.
• the grab 1 is intended to handle bulk loads like bauxite, pig iron or stones.
• the grab 1 comprises a first lever arm 11 and a second lever arm 21, which each comprise a first end and an opposed second end.
• the grab 1 comprises a first grab shell 12 mounted at the first end of the first lever arm 11 and a second grab shell 22 mounted at the first end of the second lever arm 21.
• the lever arms 11 , 21 of the grab 1 have moved away from each other and the grab shells 12, 22 are spaced at a distance from each other.
• the first grab shell 21 and the second grab shell 22 contact each other to define an interior 2 of the grab 1 in between them.
• the interconnected lever arms 11, 21 together have a shape that mimics an A.
• the grab 1 comprises a direct pivot connection 31 between the second end of the first lever arm 11 and the second end of the second lever arm 21.
• the pivot connection 31 comprises a pivot pin, extending through bearing seats in the first lever arm 11 and through bearing seats in the second lever arm 21.
• the pivot connection 31 is free of any sheaves and does, opposed to existing trimming grabs, not comprise a top block.
• the grab shells 12, 22 are mounted to the lever arms 11, 21 by means of a bolted releasable connection 32.
• the releasable connection 32 allows exchange of grab shells 12, 22, so that the type of grab shells 12, 22 can be adapted to the specific type of bulk material for which the grab 1 is to be used, i.e. using the same lever arms 11, 21 without requiring replacement of the entire grab 1.
• the grab shells 12, 22 each comprise a respective bent bottom 13, 23 and respective side walls 14, 24 on opposed sides of the bent bottom 13, 23.
• each of the grab shells 12, 22 comprises a frontal side wall 14, 24 and a rear side wall 14’, 24’.
• the bent bottoms 13, 23 and side walls 14, 24 of the grab shells 11 , 21 together define the interior 2 of the grab 1 , configured to hold the bulk material in the closed position of the grab 1.
• the grab shells 12, 22 further comprise stiffening ribs 15, 25 in between the side walls 14, 24 and extending parallel to the side walls 14, 24.
• the stiffening ribs 15, 25 of each of the grab shells 12, 22 are substantially flush with the respective lever arm 11, 21 to which the grab shell 12, 22 is attached.
• the lever arms may be integral with the stiffening ribs to allow for an optimal rigidity of the grab and to optimize the transfer of forces between the lever arms and the grab shells, in particular during the closing of the grab.
• Each of the grab shells 12, 22 further comprises two covers 16, 26, which each extend between a side wall 14, 24 and a stiffening rib 15, 25, to at least partially close off an interior of the respective grab shell 12, 22.
• the first grab shell 12 comprises a first cover 16 between a first, i.e. the frontal side wall 14 and a first stiffening rib 15, and a second cover 16’ between a second, i.e. the rear side wall 14’ and a second stiffening rib 15’.
• the second grab shell 22 comprises a first cover 26 between a first, i.e. the frontal side wall 24 and a first stiffening rib 25 and a second cover 26’ between a second, i.e.
• the covers 16, 26 between the side walls 14, 24 and the stiffening ribs 15, 25 contribute to the stiffness of the grab shells 12, 22, which is beneficial in the present embodiment, with the grab shells 12, 22 being releasable from the lever arms 11, 21.
• covers may be provided to extend between the side walls and over the stiffening ribs to substantially close off the interior of the respective grab shell. In such embodiments, the covers cover the entire grab shells between their respective side walls.
• the grab assembly 100 comprises the grab 1, of which the second lever arm 21 comprises a closing line attachment point 33 and of which the first lever arm 11 comprises an initial closing line guiding sheave 34.
• the closing line attachment point 33 is provided at an intermediate section of the second lever arm 21, i.e. in between the second lever arm’s 21 first end and second end.
• the initial closing line guiding sheave 34 is provided at an intermediate section of the first lever arm 11 , i.e. in between the first lever arm’s 11 first end and second end.
• the grab assembly 100 comprises a closing line 101 , configured to bring the grab 1 from the opened position into the closed position and vice versa.
• the closing line 101 comprises a proximal end that is adapted to be connected to a crane and an opposed distal end that is attached to the closing line attachment point 33. From its distal end, the closing line 101 is guided towards the crane via the initial closing line guiding sheave 24.
• the grab 1 comprises a successive closing line guiding sheave 35, which is provided on the second lever arm 21, along which the closing line 101 is passed before departing to the crane.
• the grab 1 thus contains exactly two closing line guiding sheaves 34, 35 for the closing line 101, namely the initial closing line guiding sheave 34 and the successive closing line guiding sheave 35. This grab 1 contains no further guiding sheaves for the closing line 101 , so that it is avoided that the closure length will become too large and that the closing speed of the grab 1 will become too low to be practically feasible.
• the closing line 101 thereby spans from the intermediate section of the second lever arm 21 to the intermediate section of the first lever arm 11 and back to the intermediate section of the second lever arm 21 before extending further upward, e.g. without passing along further closing line guiding sheaves of the grab 1, towards the crane from which the grab 1 is suspended.
• the grab assembly 100 could comprises a second closing line 10T.
• the second closing line 10T is displayed in figure 3 in relation to the grab 1 in its fully opened position, whereas the first closing line 101 is displayed in figure 3 in relation to the grab 1 in its closed position.
• the second closing line 10T acts parallel to the first closing line 101, to double the closure force of the grab 1 , without in increasing the closure length.
• the second closing line 10T extends through the grab 1 in a direction opposite to the first closing line 101 and is essentially mirror symmetric with respect to the first closing line 101.
• the symmetric closing lines 101 , 10T i.e. the second closing line 10T extending in the grab 1 in a direction opposite to the first closing line 101, have the advantage that the closure force can be spread symmetrically between the lever arms 11, 21, and therefore also between the grab shells 12, 22, resulting in a more uniform closure movement.
• the grab 1 further comprises a closing line coupling element 103, connected to the first closing line 101 and to the second closing line 10T.
• the closing line coupling element 103 is configured to be connected to a closing winch of the crane.
• the closing line coupling element 103 is thus configured to recombine the closing lines 101 , 10T so that only a single, e.g. common closing line eventually extends towards the crane.
• the grab 1 of the grab assembly 100 further comprises a lifting frame 104, with which the grab 1 is configured to be suspended from the crane.
• the grab 1 further comprises two lifting lines 102, which each extend between the lifting frame 104 and one of the grab shells 12, 22.
• a lifting line 102 is shown to extend between the lifting frame 104 and a lifting eye 36 attached to the second grab shell 22.
• the lifting lines 102 are attached directly to the grab shells 12, 22 via the lifting eyes 36.
• lifting lines may extend from the lifting frame 104 towards lifting eyes 37 attached to the lever arms 11 , 21.
• These lifting eyes 37 are located at the first, i.e. lower ends of the lever arms 11 , 21 , to be positioned close to the grab shells 12, 22.
• the lifting frame 104 is adapted to be suspended from two hoisting lines of the crane and is typically suspended above the grab 1 , i.e. above the grab shells 12, 22 and the lever arms 11 , 21 .
• the lifting frame 104 allows the hoisting line from the crane above it to extend in a substantially vertical direction V, whereas the lifting lines 102 towards the grab shells 12, 22 do not extend entirely vertical.
• the lever arms 11 , 21 and the grab shells 12, 22 are wider than the lifting frame 104.
• the first lever arm 11 and the second lever arm 21 are rotatable relative to each other about the direct pivot connection 31 to move the grab 1 between the fully closed position and the fully opened position by rotation of the lever arms 11 , 21 over an opening angle ⁇ t> — ⁇ $>.
• the opening angle ⁇ t> — ⁇ t> is defined in a range between 100° and 170°, i.e. at 135°.
• the grab 1 thus enables a relatively large opening angle ⁇ t> — ⁇ $> and thus a relatively large spread between the grab shells 12, 22 in the fully opened position.
• the opening angle ⁇ t> — ⁇ t> will remain lower than 170° to prevent that the closing cable 101 will contact the bulk material that is to be grabbed.
• first grab shell 12 comprises a first planar cutting edge 17 and that the second grab shell 22 comprises a second planar cutting edge 27.
• planar cutting edges 17, 27 are aligned non-parallel relative to each other.
• planar cutting edges 17, 27 are set at an angle relative to the bent bottoms 13, 23 of the grab shells 12, 22.
• the planar cutting edges 17, 27 are aligned parallel to each other and parallel to the vertical direction V.
• the grab shells 12, 22 do not have cutting edges aligned horizontally and parallel to each other in the closed position of the grab 1. Instead, the grab shells 12, 22 contact each other here with the cutting edges 17, 27, which define a discrete cutting edge angle (p in between them, i.e. defined between the cutting edge 17 of the first grab shell 12 and the cutting edge 27 of the second grab shell 22 in the fully closed position of the grab 1.
• the cutting edge angle (p is unequal to 180°.
• the cutting edge angle (p is defined in a range between 100° and 170°, i.e. at 135°.

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Citations (4)

• 2021
  • 2021-12-24 NL NL2030293A patent/NL2030293B1/en active
• 2022
  • 2022-12-23 WO PCT/EP2022/087775 patent/WO2023118584A1/en unknown

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