This invention relates to hook blocks for lifting equipment. Lifting of heavy loads is well known to contain inherent dangers if equipment or procedures fall short of good practice. Ordinary crane and hoist hooks might or might not be fitted with a safety catch. Where a catch is not fitted, the risk of load detachment is quite obvious. Where the conventional type of spring loaded safety catch across the mouth of the hook is fitted, its effectiveness is dubious since its it easily broken, bent, damaged, twisted, corroded or otherwise rendered ineffective by rough treat¬ ment which can occur only hours after fitment. Also this type of safety catch is sometimes deliberately disabled where the operator desires to speed up lifting operations even though this prejudices safety of the system.

According to the present invention there is provided a lifting hook comprising a mounting body leading to a hook member, a safety catch captive on the mounting body and in the form of an arm which is slidably mounted onto the mounting body and movable from a gravity-biassed lowered position in which the arm closes off the mouth of the hook member and a raised position in which the mouth of the hook member is exposed for attachment thereto of loads to be lifted, and a releasable locking member which holds the safety catch in the lowered position.

With such an arrangement, when the lifting hook is used in a normal manner the arm will automatically slide down to

the lowered position under gravity when the safety catch is released by an operator, so as to close off the mouth of the hook member. The safety catch can be constructed in a very robust manner. In particular the arm of the safety catch could be designed in such a way that it extends about the sliding axis of the safety catch to define a bell-shape or disc-shape over the hook member. This has the added advantage that it can provide protection against damage of the hook member when the whole lifting hook arrangement collides with other objects.

Ideally the arm will extend from a sleeve which is slidably mounted about the mounting body. As an alterna¬ tive, however, a support portion of the arm could be slidably located within a slot in the mounting body extend- ing in the axial direction thereof.

The arm can be constrained to move relative to the mounting body in a path directly away from the hook member or in a spiral track away from the hook member about the axis of the mounting body. If the latter arrangement, employing a spiral track, is utilized a simple form of arm (rather than the disc or bell-shape previously proposed) will then be moved away from the mouth of the hook member both in an upwards and a sideways direction so as to provide good access to that mouth. Once the safety catch is released again gravity will cause the arm to move down into the lowered position in the spiral track.

The locking member can be a toggle, button, ring or the like having a locating portion which is biassed into a

locating recess in or a ledge on the mounting body when the safety catch moves to the lowered position and which can be actuated against the bias to release the locating portion from engagement with the mounting body. If the locking member has two independently operable parts which both engage with the mounting body when the safety catch is in the lowered position, this can provide an added safety feature since the locking member cannot be released if one of the parts only is accidentally disengaged. The mounting body is ideally in the form of a sleeve within which a shaft portion of the hook member is retained on a pivot bearing. This allows for the mounting of an existing conventional hook member on the mounting body of the lifting hook of this invention. It is preferred that the mounting body should extend from a swivel joint enabling the lifting hook to rotate about the end of a support rope, chain or cable to which it is connected.

The safety catch can be formed largely or wholly from metal or a robust plastics material and possibly will be coated with rubber or some other resilient material.

The invention may be performed in various ways and preferred embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of one form of lifting hook of this invention in the closed position;

Figure 2 is a similar view of the same hook in the open position;

Figure 3 is a vertical section through the lifting hook of Figure 1;

Figure 4 is a vertical section through an alternative form of lifting hook of this invention; and Figure 5 is a front view of the lifting hook shown in Figure 4.

The form of lifting hook shown in Figures 1 to 3 of the drawings has a connecting bracket 1 provided with holes 2 through which a pin can be passed to connect to a lifting chain or cable. The bracket 1 is mounted within a mounting body 3 of the lifting hook, so as to be able to swivel therein. The mounting body 3 is cylindrical in form and internally has a mounting pin 4 inserted through the head of a hook member 5. A hook 6 extends from this head 5. Slidably located about the mounting body 3 is a sleeve 7 which opens out into a bell-shaped skirt 8 which covers over the tip 9 of the hook 6. An arm 10 is biassed by a spring 11 about a pin 12 held within a bracket 13 so that it is located below a catch 14. The sleeve 7 can be raised- relative to the mounting body only by pressing the tip 15 of the arm 10 so that the other end can pass over the catch 14 as the sleeve 7 is raised. The full raised condition is illustrated in Figure 2. This exposes the mouth of the hook 6 so that loads can be located over the hook. When pressure on the tip 15 of the arm 10 is released and the operator also lets go of the sleeve 7, the sleeve will automatically fall under gravity to the closed position shown in Figures 1 and 3 where again the arm 10 will locate below the catch

14. The mouth of the hook 6 is then covered by the skirt 8 of the sleeve 7.

A similar assembly comprising the parts 10 to 15 could be provided in the diametrically opposite position on the mounting body 3 so that the sleeve 7 can then only be released by pressing the tips 15 of both arms 10. This reduces the risk that a single locking member might be accidentally released, enabling the sleeve 7 to rise so that the load could slip off the hook 6. The parts 1, 3, 4 and 6 will be constructed from sturdy metallic materials but the sleeve 7 could be moulded from materials such as high-impact nylon or other plastics materials. A rubber covering 16 could be formed over the skirt 8 at least, if desired, to protect operators and other objects from the effects of impact from a swinging lifting hook assembly.

In the alternative arrangement shown in Figures 4 and 5 the hook 6 depends from a solid mounting body 17 and a safety arm 18 is carried by a block 19 which carries an enlarged head 20 which is held within a spiral track 21 in the mounting body 17. When a button 22 is pressed this allows a catch 23 to move out of a recess 24 in the mounting body against the bias of a spring 25. The head 20 can then be moved up the track 21 so as to raise the arm 18 away from the tip 9 of the hook 6 and also to one side. When the button 22 and the block 19 are released the block 19 will drop downwards under gravity to allow the head 20 to slide down the spiral track 21 until the catch 23 again moves into

the recess 24 to cause the tip 9 of the hook 6 to be covered by the safety arm 18.