GB2047658A - Grab for bulk materials - Google Patents

Abstract

The grab comprises grab jaws or arms (1) articulated for (a) rotary movement directly on a cross-member bridging the jaws or arms (1) and articulated (b) for rotary movement on a grab head by means of grab-closing rods (4) linking the head with a respective jaw or arm (1), wherein at least the joints providing the rotary movement (b) are sliding bearings in the form of permanently lubricated joint bearings (13) sealed by slide rings supported by elastic ring seals (21-24) engaging conical surfaces (17-20) of the respective bearing parts. <IMAGE>

Description

SPECIFICATION Grab for bulk materials The invention relates to a grab, suitable for bulk materials, in which grab jaws or arms are articulated for (a) rotary movement directly on a cross-member bridging the grab jaws or arms and articulated for (b) rotary movement on a grab head by means of grab-closing rods linking the grab head with a respective grab joint or grab arm.

In grabs for bulk materials movability in the pivot joints at right angles to the axis of rotation is required in order to prevent the parts articulated to one another from jamming in the event of the grab jaws or arms being laid obliquely on the bulk material, or in the event of the grab striking against the hull of a ship or the like. In order to obtain this movability, in known grabs sufficient play was left between the bearing bush and the bearing pin of the sliding bearings employed. Grabs of this kind are subject to considerable wear, even if the sliding bearings are regularly lubricated. In addition, in the course of time the lubricant ducts become clogged with dust. It is then either impossible to introduce new lubricant at all, or dirt is forced into the bearings together with the lubricant. In any case the bearings are damaged or even destroyed in this way.Repair of the destroyed bearings entails extensive work, such as fitting and welding new bushes or boring out the bushes.

The problem underlying the invention is that of providing a grab which entails less repair work than grabs previously employed and does not normally require regular servicing, and the invention aims to solve the problem by providing a grab, suitable for bulk materials, comprising grab jaws or grab arms articulated for (a) rotary movement directly on a cross-member bridging the grab jaws or arms and articulated for (b) rotary movement on a grab head by means of grab-closing rods linking the grab head with a respective grab jaw or grab arm, wherein at least the joints providing the rotary movement (b) are sliding bearings in the form of permanently lubricated radial joint bearings which have been installed dust-tightly and water-tightly.It is desirable that the joints providing the rotary movements (a) and (b) are sliding bearings in the form of permanently lubricated radial joint bearings which have been installed dust-tightly and water-tightly.

The grab of the invention ensures on the one hand the required movability in at least the joints providing the rotary movement (b), which prevents or minimises jamming even if the grab jaws are laid obliquely on the bulk material, and on the other hand greater loadability of the joints, even for continuous loading, without at least the joints providing the rotary movement (b) having to be serviced at short intervals.

Slide ring seals are preferably provided for the dust-tight and water-tight sealing of at least the radial joint bearings providing the rotary movement (b). The slide rings of these slide ring seals are preferably supported by means of elastic ring seals against mutually facing conical surfaces in two respective bearing parts. Seals of this kind ensure substantially complete sealing against dust and water without restricting the movability of the radial joint bearings.

The radial joint bearing mentioned in the previous paragraph preferably has a central lubricant duct, and closable vent ducts are preferably provided in opposite peripheral regions of the sliding bearing. This kind of lubricant supply ensures that the lubricant is not distributed on one side only, but is distributed in the entire space sealed by the ring seals. At least the said sliding bearings provided the rotary movement (b) include hollow bearing pins whose axis is coincident with the pivot axis of the bearing. Mainly for reasons of weight saving, the bearing pins of all the radial joint bearings may be in the form of hollow pins.

By way of example a preferred form of the invention is described in detail with reference to the accompaying drawings, in which: Figure 1 shows a rope grab in side view, and Figure 2 shows in axial section a radial joint bearing at the articulation between a grab jaw and a grab rod.

In the grab shown two grab jaws 1 are pivotally connected to a cross-member 3 at articulation points 2. The grab jaws 1 are pivotally connected to a grab head 5 by means of grab-closing rods 4 at articulation points 6 and 7. A set of rope pulleys, over which ropes are guided, is provided in the cross-member 3 and also in the grab head 5.

The construction of a radial joint bearing for the articulation point 6 is shown in detail in Fig. 2. The grab jaw 1 is connected to the grab-closing rod 4 by means of a bearing pin 8, the head 9 of which is secured against rotation on the grab jaw 1 by means of a screw bolt 10. The bearing pin 8 is in the form of a hollow pin. On the opposite end to the head 9 the bearing pin 8 carries a ring 11, which is held by a cap 1 2 screwed onto the bearing pin 8.

The grab-closing rod 4 is mounted on the bearing pin 8 by means of a radial joint bearing 1 3. The bearing part seated on the bearing pin 8 is clamped between the head 9 of the bearing pin 8 and the ring 11. The outer part of the bearing is held axially immovably in the grab-closing rod 4 by spring rings 1 4. The head 9 and the ring 11 are provided in their end faces facing the radial joint bearing 1 3 with annular recesses 15, 16, whose outer edges form mutually facing conical support surfaces 1 7, 1 8. Corresponding conical support surfaces 19, 20 are also formed in the grab-closing rod 4.Against these conical support surfaces 17-20 are supported elastic ring seals 21, 22, 23, 24 of slide ring seals which seal the radial joint bearing 1 3 against the outside at their sealing surfaces 25, 26 which lie against and slide on one another.

For the supply of lubricant a radial duct 27 is provided in the grab-closing rod 4 and also passes through the outer half of the bearing.

In order to enable the lubricant to be distributed to both sides, a closable vent duct 28, 29 leads to the outside from each of the two lateral spaces sealed by the slide ring seals.

Although not specifically illustrated the joints at articulation points 2 are preferably also sliding bearings in the form of permanently lubricated radial joint bearings which have been installed dust-tightly and watertightly.

The particular advantages of the grab described and illustrated by the accompanying drawings consist in that, without impairing the operationally necessary movability in the articulation points, the grab is less subject to wear and requires practically no servicing.

Moreover, the use of dust-tightly and watertightly installed radial joint bearings provides the advantage that the grab can be more heavily loaded at the articulation points.

Claims (8)

1. A grab, suitable for bulk materials, comprising grab jaws or grab arms articulated for (a) rotary movement directly on a crossmember bridging the grab jaws or arms and articulated for (b) rotary movement on a grab head by means of grab-closing rods linking the grab head with a respective grab jaw or grab arm, wherein at least the joints providing the rotary movement (b) are sliding bearings in the form of permanently lubricated radial joint bearings which have been installed dusttightly and water-tightly.

2. A grab according to Claim 1, wherein the said sliding bearings have been sealed with the aid of slide ring seals.

3. A grab according to Claim 2, wherein the slide ring seals are provided by slide rings supported by means of elastic ring seals against mutually facing conical surfaces in two respective bearing parts.

4. A grab according to any preceding claim, wherein the said sliding bearing has a central lubricant duct.

5. A grab according to Claim 4, wherein closable vent ducts are provided in oppposite peripheral regions of the sliding bearing.

6. A grab according to any preceding claim, wherein the said sliding bearings include hollow bearing pins whose axis is coincident with the pivot axis of the bearing.

7. A grab according to any preceding claim, wherein the joint providing the rotary movements (a) and (b) are sliding bearings in the form of permanently lubricated radial joint bearings which have been installed dusttightly and water-tightly.

8. A grab substantially as herein described with reference to Figs. 1 and 2 of the accompanying drawings.