The British patent specification No. 725,739 describes a machine for manufacturing chains, particularly heavy chains, by flash welding, in which the manufacture of each link takes place in several succeeding working steps at different operating stations arranged along a substantially circular course. A pillar at the centre of said circular course supports at its upper end radial arms equal in number to the operating stations, said arms being rigidly connected to form a unit in which the angles between adjacent arm are equal and equal to the angular intervals between the operating stations. The arm unit is rotatable about a vertical axis through the centre of the course. Each of the arms is provided with a conveyor for advancing the chain inwards (that is, towards the vertical axis). A drive mechanism serves to rotate the arm unit step by step in one and the same direction, the angular displacement imparted to the arm unit during each step being equal to the angular spacing of the operating stations. The angular displacements referred to serve successively to present the ends of the chains hanging down from the receiving ends of the conveyors to the operating stations along the course. In a first operating station, a piece of bar stock is heated and bent into a C-shaped lug hooked on to the last link of the piece of chain hanging down from the receiving end of the conveyor; in the next operating station, the flash welding operation is carried out; in the next operating station, a trimming operation is carried out to remove welding burrs and welding spray; and in the last operating station, a stud is added to the link. During the next angular displacement, the chain is advanced by the conveyor a distance equal to the pitch of the chain, in order to place the finished link at the proper height for receiving another C-shaped lug in the first operating station. The chains leaving the discharge ends of the conveyors are received by an open bin which is divided into four compartments and arranged to share the rotary motion of the arm unit about the vertical axis. The necessarily limited capacity of the bin renders the apparatus described unsuitable for the manufacture of long continuous lengths of heavy chain, for instance anchoring chains of the size and length required for floating oil-boring platforms.
A chain making apparatus not subject to the above limitation is proposed in the U.S. Pat. No. 3,701,251. In the apparatus described therein, a radial arm provided with a conveyor for advancing the chain inwards is rotatably supported by a tubular pillar at the centre of the circular course around which the operating stations are distributed. The discharge end of the conveyor is located above the upper end of the hollow pillar. The chain moves through the vertical passage provided by the tubular pillar into a chamber arranged below the shop floor and connected to a horizontal channel allowing the successive withdrawal of the chain towards a delivery point, for instance a lighter. This arrangement requires a mode of operation of the arm which is different from the one described in the British patent specification No. 725,739. Let it be assumed that there are N operating stations evenly distributed along the course. The successive angular displacements required to move the arm from the first to the last of N successive stations are carried out in one and the same direction, resulting in a total angular displacement of (N-1).multidot.360/N degrees, while the angular displacement required to restore the arm to the first of the N successive operating stations is carried out by rotating the arm by an angle of (N-1).multidot.360/N degrees in the opposite direction. In the example described in the U.S. Pat. No. 3,701,251, there are four operating stations; the arm is moved from the first to the last of the four stations by three counter-clockwise rotation steps of a quarter-turn each, and returned to the first station by a clockwise rotation step of three-quarters of a turn.
The U.S. Pat. No. 3,701,251 also proposes to supply the apparatus with at least one additional arm supported by individual bearing means on said tubular pillar, in order to allow the simultaneous manufacture of at least two chains. This arrangement has, however, not proved successful, as the periodical twisting action to which the chains hanging down into the tubular pillar and the adjoining chamber are subjected is apt to entangle them with each other, whereby the required orderly advancement of the chains is rendered impossible.
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