WO2009130395A1

WO2009130395A1 - Grab

Info

Publication number: WO2009130395A1
Application number: PCT/FI2009/050327
Authority: WO
Inventors: Kalle Pohjola
Original assignee: Rannikon Konetekniikka Oy
Priority date: 2008-04-24
Filing date: 2009-04-24
Publication date: 2009-10-29
Also published as: EP2274224A4; FI20085362A; RU2010146263A; FI120680B; EP2274224A1; FI20085362A0

Abstract

The grab has an upper table (10), a lower table (20) and a suspension mechanism, which connects the tables and the length of which is adjustable, with the aid of which mechanism the distance between the upper and lower table can be altered. The scoop of the grab is made up of two jaws (16a, 16b), which can be opened and closed, and which are attached to the lower table in a pivoted manner (26). The crane beams (30) are attached at their first end to the jaws and at their second end to the upper table. When closing, the jaws rotate around the rotation axis passing through the first ends of the crane beams into a closed position. The grab further has support chains (48), which are attached to the jaws for supporting them during the opening movement of the jaws. In the opening movement the jaws rotate around the imaginary rotation axis passing through the attaching rings (50) of the support means to the opened position. The opening and the closing thus happen in different ways in the grab, whereby making a compromise between the expansion and the closing speed/force is avoided. The attaching rings of the support chains are attached to the jaws so that they are situated substantially further from the central line of the grab than the attaching pins (28) of the crane beams. The grab can be a rope grab, whereby said suspension mechanism connecting the upper jaw and lower jaw is a rope gear.

Description

Grab

The invention relates to a grab, which has an upper table, a lower table, a suspension mechanism, connecting the upper and lower table and having adjustable length, two openable jaws, which jaws are attached to the lower table in a pivoted manner, and crane beams, which are attached at their first end to the jaws and at their second end to the upper table.

Rope driven grabs are loading means, which are suspended to an arm of a loading device with the aid of support ropes. The grab has an upper table and a lower table, which are connected to each other with a rope gear. The support ropes of the grab are attached to the upper table. The scoop part of the grab is made up of two jaws, which are attached at their front edge to the lower table in a pivoted manner. The jaws are further connected at their rear edge to the upper table with crane beams. The grab is opened and closed by loosening or tightening closing ropes, whereby the distance between the upper and lower table is altered. When the closing ropes are loosened, the lower table and the jaws drop downwards due to their own weight, whereby the jaws rotate away from each other, i.e. the grab opens. Sometimes it is necessary to use additional weights in the lower table in order to ensure the opening of the jaws. Correspondingly, when the closing ropes are tightened, the lower table rises toward the upper table and the jaws rotate toward each other, i.e. the grab closes. When the grab is closed both the closing ropes and the support ropes support the grab.

In a traditional rope driven grab, the aim is to optimize the closing force, the expansion of the jaws of the scoop and the speed of the opening and closing movements. A sufficient closing force is needed, in order for the jaws of the grab to bite well into the material to be handled, and especially for the jaws to be pressed tightly against each other at the end of the closing stage. In order to ensure sufficient expansion of the grab, the crane beams are most often attached at their first end close to the outer rim of the scoop in the vicinity of the bottom edge of the scoop. An operation geometry for a grab which strives towards as large an expansion as possible however leads to the closing force of the jaws in the beginning of the closing movement being very great and the closing movement being unnecessarily slow. The closing movement gets faster as the jaws get closer to each other at the end stage of the closing movement, but at the same time the closing force is reduced. In order to achieve a sufficient closing force, choices need to be made in the structure of the grab and especially in the placement of the pivot attaching points of the jaws of the scoop, which choices make the opening and closing movements of the jaws slower. The movement speed of the jaws however has a substantial effect on the pace of the use of the grab and thus on its efficiency. The overall efficiency is often a main selection criterion when purchasing a grab.

It is an object of the invention to provide a structurally new grab, with which the disadvantages and flaws associated with known grabs can be reduced. It is especially an object to provide a grab, where the jaws of the scoop close and open quickly and reliably.

The objects of the invention are obtained with a grab, which is characterized by what is presented in the independent claims. Some advantageous embodiments of the invention are presented in the dependent claims.

The grab according to the invention has an upper table, a lower table and a suspension mechanism, which connects the upper and lower table. The length of the suspension mechanism is adjustable, so the distance between the upper and lower table can be altered with its aid. The grab has two jaws, which can be opened, which are attached to the lower table in a pivoted manner and which make up the scoop part of the grab, The jaws can be rotated into an opened position, whereby a downwards open opening is formed in the grab, and into a closed position, where the jaws settle tightly against each other, forming a scoop which is closed at the bottom edge. The grab is lowered onto the material to be loaded in the opened position, whereafter the jaws are moved to the closed position, whereby the material to be loaded is left inside the scoop part. The grab further has crane beams, which are connected at their first end to the jaws and at their second end to the upper table. When closing the jaws they rotate around an imaginary rotation axis passing through the attaching points in the first ends of the crane beams to the closed position. The basic idea of the grab according to the invention is that it further comprises support means, such as support chains, which are attached to said jaws for supporting the jaws of the grab during the opening movement of the jaws. During the opening movement the jaws rotate around the imaginary rotation axis passing through the attaching points of the support means to the opened position. The opening and the closing of the jaws thus happen in different ways in the grab, whereby making a compromise between the expansion and the closing speed/force is avoided. In an advantageous embodiment of the invention the support means have been attached at their first end to attaching rings on the outer surface of the jaws and said crane beams have been attached at their first end with second joint pins to the jaws, so that the attaching rings are substantially further from the face edge of the jaws and from the central line of the grab than the second joint pins. The attaching rings have preferably been placed in a location on the outer edge of the jaw, which is as far away as possible from the face edge of the jaw. By placing the attaching rings as far away as possible from the central line of the grab, a good expansion of the jaws is obtained. By placing the attaching pins of the crane beams closer to the central line of the grab, a great closing speed in on the other hand obtained.

In a second advantageous embodiment of the invention the attaching rings of the support means are situated approximately halfway in the height of the jaws when examined in the vertical direction, i.e. substantially at a lower level that the second joint pins. By placing the attaching rings of the support means remarkably lower in relation to the jaw, the leverage effect is made effective also at the end stage of the opening of the jaws.

In a third advantageous embodiment of the invention the crane beams are attached at their first end with second joint pins to a support frame, which is in the top edge of the jaws. Since the attaching points of the crane beams, i.e. the second joint pins, have been placed remarkably high in relation to the_. jaw, the closing movement of the jaws is due to the leverage effect quick in the beginning stage and slower in the end stage.

In a fourth advantageous embodiment of the invention there are two support means, such as support chains, for each jaw. The grab preferably further has an auxiliary framework, whereto the second ends of the support means are attached.

In a fifth advantageous embodiment of the invention the grab is a rope grab, whereby said suspension mechanism connecting the upper jaw and lower jaw is a rope gear, which comprises a first rope pulley group attached to the upper table, a second rope pulley group attached to the lower table and a closing rope connecting the rope pulley groups.

It is an advantage of the grab according to the invention that its closing time and opening time are very short. At best the closing and opening time of the grab is only about half of the corresponding times of traditional grabs, which remarkably increases the overall efficiency of the grab.

It is further an advantage of the invention that the weight of the upper table and the beams of the grab function therein as the weight, which opens the grab. The opening of the grab thereby becomes reliable without a need for additional weights.

It is a further advantage of the invention that substantially shorter crane beams and closing ropes can be used therein than in traditional grabs, which gives rise to savings in material costs. An advantage of the shorter crane beams is further their lower weight and better resistance against buckling.

In the following, the invention will be described in detail. In the description, reference is made to the appended drawings, in which figure 1a shows as an example a rope grab according to the invention seen from a first side and figure 1b shows the rope grab of figure 1 a seen from a second side.

Figures 1a and 1b show as an example a rope grab according to the invention seen from two different sides. The grab has a plate-like upper table 10, to the underside of which is attached a first rope pulley group 12a, and a lower table 20, to the top side of which is attached a second rope pulley group 12b. The rope pulleys are connected to each other with closing ropes 14, by tightening and loosening which the upper and lower table can be moved towards each other or away from each other The first and second rope pulley and the dosing ropes thus make up a rope gear, through which the upper table and the lower table are in direct connection with each other. Support ropes are attached to the upper table of the grab, by which ropes the grab is suspended to the arm of a lifting device (the support ropes are not shown in the figure).

The grab has two tray-like jaws, a first jaw 16a and a second jaw 16b, which make up the scoop of the grab. The jaws have two face sides 17 and a curved bottom 19, which connects them. The face edges 18 of the jaws are compatible to their shape, so that the face edges can settle substantially tightly against each other when the scoop closes. In the top edge of the jaws there is a support frame 24 made up of two parallel plate-like parts for supporting the jaws. The support frame is attached at its edge, which is closer to the face edge 18 of the jaw, to the lower table 20 with first joint pins 26. The jaws 16a, 16b of the grab are connected to the upper table 10 with two parallel, rod-like crane beams 30, which are connected to each other with a perforated connecting plate 31. The crane beams are attached at their first end with second joint pins 28 to the edge of the support frame, which is farthest from the face edge 18. The second joint pins are situated essentially above the jaw when examined in the vertical direction of the grab, only slightly lower than the level of the first attaching pins. In the opposite edges of the upper table there are edge plates 32, which extend downwards from the level of the upper table. The second ends of the crane beam are attached with third joint pins 34 to the ends of the edge plates.

Above the upper table 10 there is a frame-like auxiliary framework 40, which has two essentially parallel side plates 42 and two essentially parallel connecting rods 44, which connect the ends of the side plates. Both of the jaws 16a, 16b of the grab are attached to the auxiliary framework 40 with two support chains 48. The support chains are attached at their first end to an attaching ring 50, which is situated on the outer edge of the jaw, near the face side 17 of the jaw, in a location, which is farthest away from the face edge 18. The attaching ring 50 of the support chain is thus situated clearly further away from the face edge 18 of the jaws and from the centra! line of the grab than the second joint pins 28, wherewith the crane beams 30 are attached to the support frame. When examined in the vertical direction the attaching rings are situated approximately halfway in the height of the jaws, i.e. substantially lower than the second joint pins 28. The second ends of the support chains are attached to the ends of the side plates 42 of the auxiliary framework. In the middle of the side plates there are attaching apertures 46 for attaching opening ropes (the opening ropes are not shown in the figure). In the embodiment shown in figures 1a and 1b the auxiliary framework is connected to the jaws with support chains. For a person skilled in the art it is clear that also other support means, which can withstand extension stress, such as ropes, cable wires or rods, can be used instead of the chains. The grab according to the invention is opened by lowering the entity made up by the upper and lower table, the rope gear and the jaws downwards, while at the same time keeping the auxiliary framework 40 in its place, whereby the jaws of the grab rotate around the imaginary first rotation axis passing through the attaching rings 50 into an open position. The opening can also be done by lifting the auxiliary framework and holding the other parts of the grab in place. In order to make possible the opening of the jaws, the closing ropes 14 are loosened simultaneously with the relative movement of the auxiliary framework and the other parts of the grab. During the opening stage, in addition to the own weight of the jaws, the weight of the upper and lower table and the rope gear helps to open the jaws. By moving the auxiliary framework sufficiently away from the jaws, the jaws are made to open to their widest position possible, i,e, to a position, where the face surfaces of the jaws are substantially horizontal. In this position the grab can be lowered onto the materia! to be grabbed.

When it is desirable to close the grab, the upper table 10 and the lower table 20 are moved towards each other by tightening the closing ropes, whereby the jaws of the grab rotate around the imaginary second rotation axis passing through the second joint pins 28 into a dosed position. Simultaneously with the tightening of the closing ropes the auxiliary framework 40 is lowered downwards, so that the support chains do not prevent the closing of the jaws, Since the distance from the outer edge of the jaw to the second rotation axis is relatively large, the closing speed of the jaws is also high.

In the rope grab according to the invention the closing and opening mechanisms are thus partly separated from each other, whereby making a compromise between the expansion and the closing speed/force is avoided.

Some advantageous embodiments of the grab according to the invention have been described above. The invention is not limited to the solutions described above, but the inventive idea can be applied in numerous ways within the scope of the claims.

Claims

1. A grab, which has an upper table (10), a lower table (20), a suspension mechanism, connecting the upper and lower table and having adjustable length, two openable jaws (16a, 16b), which are attached to the lower table in a pivoted manner (26), and crane beams (30), which are connected at their first end to the jaws and at their second end to the upper table, characterized in that it further comprises support means, such as support chains (48), which are attached to said jaws (16a, 16b) for supporting them during the opening movement of the jaws.

2, The grab according to claim 1, characterized in that said support means are attached at their first end to attaching rings (50) on the outer surface of the jaws

(16a, 16b) and said crane beams (30) are attached at their first end with second joint pins (28) to the jaws, so that the attaching rings are substantially further from the face edge (18) of the jaws and from the central line of the grab than the second joint pins.

3. The grab according to claim 2, characterized in that the attaching rings (50) are placed in a location on the outer edge of the jaw (16a, 16b), which is as far away as possible from the face edge (18) of the jaw.

4. The grab according to claim 2 or 3, characterized in that the attaching rings (50) are situated substantially on a lower level than the second joint pins (28) when examined in the vertical direction.

5. The grab according to any of claims 2—4, characterized in that the attaching rings (50) are situated approximately halfway in the height of the jaws (16a, 16b) when examined in the vertical direction.

6. The grab according to any of claims 2-5, characterized in that the crane beams (30) are attached at their first end with the second joint pins (28) to a support frame (24), which is in the upper edge of the jaws (16a, 16b).

7. The grab according to any of claims 1-6, characterized in that it has two support means, such as a support chain (48), for each jaw (16a, 16b),

8. The grab according to any of claims 1-7, characterized in that it further comprises an auxiliary framework (40), whereto the second ends of the support means, such as the support chains (48), are attached.

9. The grab according to any of claims 1-8, characterized in that it is a rope grab, whereby said suspension mechanism connecting the upper jaw and the lower jaw is a rope gear, which comprises a first rope pulley group (12a) attached to the upper table (10), a second rope pulley group (12b) attached to the lower table (20) and a closing rope (14) connecting the rope pulley groups.