There are many instances where a circular sectioned member must be held firmly, but able to be released. For example in the field of butt welding of plastics pipes, the pipe ends must be firmly clamped to allow them to be urged towards and away from, successively a trimmer plat and a heater plate, and the pipe ends forced against each other to allow butt welding to take place.

Hitherto, pipe clamps on automatic butt fusion machines have involved a total of eight screws, that whilst providing a most effective clamping of pipe ends have the disadvantage of it being a time consuming operation, requiring considerable effort by an operative.

The screwthreads of the screws work under extreme loads, and any shortage of lubricant at the interface of the threads of the screw and the associated threads in a bore on a clamp member creates increased torque that can lead to premature failure.

The object of the present invention is to provide a clamp that avoids those disadvantages mentioned above.

According to the present invention, a clamp for circular section members, comprises a bottom clamp part with a semi-circular recess, a top clamp part with a mating semi-circular recess, a means of detachably attaching one side of the top part to the bottom part with provision for adjustment, and there being a disconnectable toggle clamp connection between the top part and the bottom part to the opposite side.

By having a top part removable from the bottom part, an advantage of the previous screw arrangement is retained. In such as automatic butt fusion machines where it is the ends of relatively long pipe iengths that are being held, the absence of a top clamp part makes easier the manoeuvring of the pipe end onto the bottom clamp part.

Preferably, and to one side of the clamp, the bottom clamp part has a threaded rod pivotally attached to the bottom clamp member, to receive a threaded stem on the lower end of which is a rounded thrust block. Thus, the top clamp part at its corresponding end may have an upwardly facing recess to receive the thrust block. At the opposite side, the lower clamp part may have

pivotal links located thereon, the outer ends of which are connected by a pivot for attachment of a toggle lever. The top clamp part may have an upwardly facing recess, and the toggle member may have a roller to locate in the recess.

Thus, with the top clamp part removed, a pipe end can be positioned in the bottom clamp part. One side of the top clamp part is hooked under the thrust block of the stem, and pivoted to lay on the pipe. If it is apparent that the opposite end of the top part cannot engage the toggle clamp, the screwed stem can be adjusted on the threaded rod, to allow the top clamp part to be raised or lowered, to enable the opposite end to connect properly to the toggle clamp. When the top clamp part is laid over the pipe, the pivotal links can be pivoted to bring the roller on the lever into register with the recess on the top clamp part, and the lever swing to overlay the top clamp part, and put the line of action between the roller and the top clamp member to beyond the pivotal connection of the lever to the links and when the upward force on the roller serves to maintain the clamp in a closed or locked condition.

An essential advantage of the invention is the relative speed at which such as pipe ends can be clamped, with reduced physical effort on behalf of the operative. Another advantage is that a screw threaded adjustment between the rod and stem is not required under load, but the threaded engagement do permit small adjustments if, e. g., vibration or agitation causes a marginal loosening of the clamp. The top clamp part can be identically formed at both ends, simplifying the fitting of the top clamp part to the bottom clamp part. The presence of a roller at the end of toggle lever has the advantage of substantially alleviating loads on the toggle system as the clamp is activated and deactivated, that are known to be harmful in conventional toggle systems.

One embodiment of the invention will now be described with reference to the accompanying drawings, in which:- Figure 1 is a perspective view of a clamp in accordance with the invention, in the closed or locked condition; and Figure 2 corresponds to Figure 1 but shows the clamp in the open or unlocked condition.

In the drawings, a clamp 1 has a bottom clamp part 2 with a semi-circular recess 3 and a

top clamp part 4 with a mating and co-operating semi-circular recess 5.

To one side of the clamp, the bottom clamp part 2 has a threaded rod 6 pivotally attached to the bottom clamp member, to receive a threaded stem 7 on the lower end of which is a rounded thrust block 8, and the top clamp part at its corresponding end has an upwardly facing recess 9 to receive the thrust block 8. At the opposite side, the lower clamp part 2 has pivotal links 10 located thereon, the outer ends of which are connected by a pivot 11 for attachment of a toggle lever 12, the top clamp part 4 has an upwardly facing recess 13, and the toggle member has a roller 14 to locate in the recess.

Thus, with the top clamp part 4 removed, a pipe end can be positioned in the bottom clamp part 2. The recesses 9 of the top clamp part 4 are hooked under the thrust block 8 of the stem 7, and the top clamp part pivoted to lay on the pipe. If it is apparent that the opposite end of the top part cannot engage the toggle clamp, the screwed stem 7 can be adjusted on the threaded rod 6, to allow the top clamp part to be raised or lowered, to enable the opposite end to connect properly to the toggle clamp. When the top clamp part 4 is laid over the pipe, the pivotal links 10 can be pivoted to bring the roller 14 on the lever 12 into register with the recess 13 on the top clamp part, and the lever 12 swung to overlay the top clamp part 4, and put the line of action between the roller 14 and the top clamp part to beyond the pivotal connection of the lever to the links and when the upward force on the roller serves to maintain the clamp in a closed or locked condition.