GB2094263A - Securing arrangement for the main block of a crane - Google Patents

Abstract

A jib or tower crane has a jib or boom (3), a main block (1) and a light block (not shown). In order to secure the main block (1) to the boom (3) when the main block (1) is not in use, the main block (1) is provided with pulley wheels (2), two on each side of the main block (1), which wheels (2) engage in guide rails (4) provided on the boom (3). Angled brackets (5) are provided in the end of each guide rail (4) to direct the pulley wheels (2) into engagement with the guide rails (4) the boom (3) being nearly vertical. Oscillation of the main block (1) with consequential possible damage is thus prevented when the light block is in use, the main block (1) sliding up and down in the guide rails (4) when the boom (3) is lowered or raised. When the main block (1) is to be used again the boom (3) is raised nearly to the vertical position and the main block (1) lowered out of the guide rails (4), when it is ready for use. <IMAGE>

Description

SPECIFICATION Securing arrangement for the main block of a crane The present invention relates to a device for securing the main block of large cranes.

In large jib or tower cranes, use is generally made of two lifting arrangements, firstly a main block for loads of from 1 5 to 50 tonnes, and secondly a so-called light block for loads of up to 1 5 tonnes.

The light block is generally located either at the extreme end of the jib or boom of the crane or on an extension thereof. On the other hand, the main block is generally located somewhat further in along the boom. The boom of the crane is continually being raised and lowered, depending upon where the load is to be placed. This is when problems arise, particularly in cases where the crane is not permanently anchored to the ground.

When the crane is mounted on a floating drilling rig, movements occur which cause the crane block to oscillate to and fro. When the light block is used, and the main block is hanging down unused, it sometimes happens that the main block swings so violently that it may break the boom of the crane or damage the cable on the light block. This involves expensive repairs to the crane boom, which, in turn, means that the crane is unusable while repairs are being carried out.

Another serious disadvantage if the light block cable is damaged, is that the load and the equipment associated therewith fails down, often causing injury to personnel. In the event of the main block being detached, causing it to fall down, very serious damage may result.

A main block of this kind usually weighs from one to several tonnes. The height of a crane of this kind may be about one hundred metres or more.

The reason why the main block is allowed to oscillate in this way is that the boom of the crane must be capable of being raised and lowered constantly. With the crane boom lowered to its maximum amount, i.e. almost down to the horizontal, the main block is winched right up the crane boom when not being used and only the light block is operating. Irrespective of whether the crane is lurching, there will be no oscillation of significance on the part of the main block.

However, as soon as the crane-driver raises the boom of the crane, problems will arise.

Most blocks used to raise loads of up to fifty tonnes are at least of the threefoidd purchase type. When the crane boom is raised the cable of the main block is free, the more so the higher the crane boom is raised. The effect of this is that there may be violent oscillations of the main block. In practice the main block cannot be attached to the crane boom, as the block must constantly be ready for action and be operated by the crane-driver from the crane control cabin.

It is accordingly an object of the present invention to provide a device for securing the main block of a jib or tower crane when it is not in use, and which allows the block to be used whenever the crane-driver so requires.

According to the present invention there is provided a jib or tower crane having a jib or boom, a main block and a light block, said main block being provided with locating means, said jib or boom being provided with guide means for engaging the locating means of said main block, whereby the main block may be secured when not in use.

Preferably, the locating means is in the form of pulley wheels, desirably two on either side of the main block.

The guide means is preferably in the form of a pair of guide rails, each of which desirably has an angled bracket at one end for directing the pulley wheels into the guide rails.

The present invention will be further illustrated, by way of example, with reference to the accompanying drawings, Figs. 1 and 2 being in accordance with the invention and Figs. 3, 4 and 5 showing cranes not fitted with a device in accordance with the invention.

Figure 9 schematically shows a portion of a crane boom and a main block including a securing device of the present invention; Figure 2 schematically shows the main block of Fig. 1 secured to the crane boom; Figure 3 schematically shows a crane structure which does not include the securing device of the invention with the crane boom in the substantially horizontal position; Figure 4 shows the crane structure of Fig. 3 with the crane boom raised substantially vertically; and Figure 5 schematically shows a crane structure mounted on an offshore drilling platform, such structure not including the securing device of the invention.

As illustrated in Fig. 1, the main block 1 is shown in position ready for securing to the crane boom 3. The main block 1 is provided with pulley wheels 2, two on either side of the block. The crane boom 3 is provided with guide rails 4 to engage the pulley wheels 2 of the main block 1. The guide rails 4 are fitted with angled brackets 5 for directing the pulley wheels 2 into the guide rails 4.

Fig. 2 shows the main block 1 secured to the crane boom 3, the light block 7 in use.

Fig. 3 illustrates the case in which the main block 1 is not secured while the light block 7 is being used. The crane boom 3 has been raised slightly above its lowest position. Even in this position the main block 1 is subject to considerable oscillation.

Fig. 4 shows the same structure as in Fig.

3, but with the crane boom 3 raised substantially vertically. The main block 1 is now liable to swing to and fro to an even greater extent, and the danger of serious damage is greatly increased.

Fig. 5 shows a crane mounted on an offshore drilling platform, and the situation that would arise at operational height.

As illustrated in Figs. 1 and 2, the main block 1 is fitted with pulley wheels 2, two on either side of the block 1. The crane boom 3 is provided with guide rails 4 for engaging the pulley wheels 2. The guide rails are fitted with angled brackets 5 to facilitate engaging the pulley wheels 2 of the main block 1 in the guide rails 4. The crane boom 3 is provided with an extension 6, through which the cable 8 for the light block 7 runs.

The securing device of the invention functions as follows: when the crane-driver wishes to use the light block 7, the crane booms 3 is firstly raised substantially to the vertical position. The main block 1 is winched right up.

Once it has reached the requisite height, as shown in Fig. 1, the main block 1 is lowered.

The pulley wheels 2 then slide down into the guide rails 4. The main block 1 passes between the guide rails 4. The main block 1 is now lowered right down to the lowest ends of the guide rails 4, and the winch for the block 1 is locked in the crane control cabin. The length of the guide rails 4 is adjusted to the maximum oscillation to which the main block 1 is liable whenever the crane boom 3 is raised or lowered. The main block 1 is now secured to the crane boom 3. Thus, when the crane boom 3 is lowered, the main block 1 slides up in the guide rails 4. When the boom 3 is raised, the block 1 slides down in the guide rails 4. The main block 1 is secured, and cannot start oscillating, and cannot now damage either the crane boom 3, the light block 7 or the associated cables 8.

Whenever the main block 1 is to be used again, for an extra heavy load, the crane boom 3 is raised substantially to the vertical position. The winch of the main block 1 is started, and the block 1 is lowered down and out of the guide rails 4. This means that the main block 1 is immediately ready for use.

Claims (6)

1. A jib or tower crane having a jib or boom, a main block and a light block, said main block being provided with locating means, said jib or boom being provided with guide means for engaging the locating means of said main block, whereby the main block may be secured when not in use.

2. A crane as claimed in claim 1, in which the locating means is in the form of one or more pulley wheels.

3. A crane as claimed in claim 2, in which two pulley wheels are provided one above the other, on either side of the main block.

4. A crane as claimed in any preceding claim, in which the guide means is in the form of one or more guide rails.

5. A crane as claimed in claim 4, in which each guide rail has an angled bracket at one end for directing the locating means into the guide means,

6. A crane, substantially as hereinbefore described with reference to-and as illustrated in Figs. 1 and 2 of the accompanying drawings.