This invention relates to plate rolling and particularly to method and apparatus for rolling steel plate of small diameter. The invention also relates to the formation of uniform tapered pipe sections suitable for various applications e.g. for use as a tapered pole having street lighting applications.

The inventor has devised apparatus and methods for plate bending and forming pipes of cylindrical construction such as those disclosed in U.S. Patent Specification No. 3,879,994 to the same inventor and European Patent Specification No. 0029345; There is disclosed a method of plate rolling to form substantially cylindrical pipes simply by bending a plate about a rotatable mandrel.

Steel plate is rolled by engaging an edge of a plate under a flange of a gripper rib extending axially along the cylindrical surface of the mandrel. The mandrel is turned to advance and curve the plate about the surface of the mandrel.

Complete pipes may be formed by this method by curving plate about the mandrel through approximately 180° then engaging the opposite edge of the plate with the mandrel and curving the remaining 180° to form a complete cylinder.

The present invention is specifically concerned with the production of tapered pipes that can be formed on a tapered mandrel having a gripper somewhat similar to that described in my earlier patent. It has been found to be possible to simply form a tapered mandrel and to then curve the plate about the mandrel resulting in the formation of a tapered pipe, however there are difficulties with providing different diameters for a given taper with any given mandrel.

This invention relates to improvements in and relating to tapered mandrels and in particular to mandrels used in connection with the forming of tapered steel poles and the like by the forming process as described in US

Patent Specification No. 5,245,849.

There is disclosed therein, a plate rolling apparatus, for rolling a plate to

form a pipe which is tapered, a gripper rib on the mandrel for receiving the edge of a flat plate. The mandrel is mounted between support frame ends and a pressure roller mounted beneath the mandrel and adapted to contact the surface of the plate and apply a squeezing force against the plate and the mandrel during a rolling operation, the pressure roll being laterally moveable relative to the centre line of the mandrel depending upon the location of the gripper rib in the region of the roller so as not to foul the gripper rib, yet applying said squeezing force to said plate as required. A mandrel having an adjustable taper angle is disclosed as an adjustable mandrel support member and mandrel journal to accommodate variable mandrel diameters and angles of taper, the mandrel including a series of disc like laminations mounted in serial formation each lamination having a diameter of slightly less than an adjacent one on one side and slightly more than one on the other side so that the formation of laminations taken together form a frusto conical body for forming a flat plate into a tapered curved section upon rotation of the mandrel and the plate held in the gripper.

The specific arrangement disclosed provides for a wide range of plate diameters and taper angle to be accommodated. However, in practice, it is commonly found that taper angle variations are not required for various sizes of poles and pipes. It is more likely that variations in minimum and maximum pole diameters will be required for a given length workpiece.

Thus, in the forming of tapered tubular articles by the mandrel process, it has been found that a given tapered article requires a mandrel of practically constant taper over its full length and the mandrel taper can be set to suit a range of tapered pipes of various sizes and lengths either side of that standard size article from which the mandrel has been specifically designed.

In some cases the article has a series of components each tapered substantially the same such that the components can be either welded or "slip jointed" together to make a long finished product. In other cases, the diameter of the pipe at the small and large end can vary substantially as can the thickness and grade of material being used to form the pipe.

A difficulty arises as to how the mandrel might be constructed to provide a set tapered angle and provide a pipe having differing diameters at a given reference point. For example, at the small or large end of the mandrel to form tapered pipes having the same taper angle but having a range of small and large diameters at its respective ends.

It is an objective of the present invention to provide a plate rolling apparatus for rolling a plate to form a tapered pipe in which set up time is minimised and a range of pipe sizes can be easily accommodated on the same plate bending machinery with segmented mandrels. There is provided, according to the present invention, a plate rolling apparatus for rolling plate into a tapered pipe comprising a rotatable mandrel mounted between support frame ends, said mandrel including a gripper for holding a plate therein and pressure means mounted beneath the mandrel for maintaining the plate in contact with the mandrel so that upon rotation of the mandrel the plate is formed to follow the curvature of the mandrel, wherein the mandrel includes a plurality of interconnected tapered frusto conical segments of short length relative to the overall length of the mandrel, each having the same taper angle and a large diameter end matching the small diameter end of an adjoining segment and a small diameter end matching the larger diameter end of an adjoining segment, the thus formed segments forming a tapered mandrel of a length to suit said plate bending apparatus, the mandrel having a small and large diameter to suit the size of pipe to be formed.

There is also provided a tapered segment as defined for use in the formation of a tapered mandrel. The invention also provides a method of constructing a tapered mandrel for a late rolling apparatus comprising the steps of constructing a series of mandrel components each having a similar taper angle and matching diameters at each end to form an elongate fabricated tapered mandrel wherein a plurality of said segments are aligned end to end. Finally there is provided a mandrel for a plate rolling apparatus in which a plate is rolled to form a tapered pipe wherein the mandrel includes a plurality of aligned interconnected frusto conical segments each having a constant

predetermined taper angle, the segment being of short length relative to the overall length of the mandrel, the mandrel having a large diameter end and a small diameter end, the large diameter end and the small diameter end matching the diameter end of adjourning frusto conical segments to form a mandrel having a uniform taper angle.

Thus, the present invention sets out to solve the problem of providing tapered pipes of differing diameters but utilising as few mandrel components as is necessary with a minimum of set up time. The problem is solved by the invention by constructing the mandrel in short segments such that the mandrel can be built up by assembling appropriate segments in correct order to give a uniformly tapered mandrel of the length to suit the forming machine being used at a diameter to suit the product to be formed at a given reference point such as at the small end of the pipe to be formed.

The invention will now be described in greater detail with reference to the accompanying sketches in which :

Figure 1 is a schematic view of a typical mandrel construction with a family of segments made according to the invention.

Figure 2 shows in greater detail the construction of the mandrel segments. It is to be understood that the mandrel of the present invention is adapted for use with machinery as disclosed in earlier filed applications discussed earlier in this specification and hereby incorporated herein by cross-reference.

The mandrel segments 10 are designed as shown in Figure 1 to form a family of mandrels each family having a given taper angle. A typical taper angle would be 10 mm per metre and a typical segment length is 1 mm. A typical mandrel diameter at the small end would be 60 mm for products such as out reach arms on lighting poles or 150 mm to 200 mm for power transmission poles. The typical mandrel diameter at the large end would be 200 mm for lighting poles up to 900 mm and above on power transmission or high mast light poles.

With reference to Figure 2, each mandrel segment has a hole bored through its axis to accommodate a axially fitted tie rod which is used to

compress the segments together in groups of say ten which means that assuming that each segment is one metre long, the group of ten would provide a mandrel of ten metre lengths and suit a plate forming machine having a ten metre spacing between the mandrel gripping and driving means, not shown, but which has been described in greater detail in previous specifications now open to public inspection, for example, US Patent No 5,245,849.

The mandrel is built of solid construction such that segments of over 200 mm in diameter are fabricated from steel plate and steel plate ends or from solid steel when the diameter is below 200 mm. Torque is transmitted from the plate bending machine to the mandrel from segment to segment by drive keys 12, 13 which intermesh as illustrated. Gripper 15 is fabricated separately and secured, for example by bolts, onto the segments as shown in exploded Figure 2. The operation of the gripper has been described in detail in my previous specification as mentioned above. Upon assembly of the segments, it is necessary that the gripper sections are aligned accurately segment by segment and this is achieved by accurate machining of the drive keys.

When the segmented mandrel is mounted into the bending machine, mounted on centrally located tie rod 16, drive torque is transmitted to the drive keys 12, 13 from one segment to the other. Drive may be transmitted to the mandrel from each end of the segmented mandrel via the drive keys from the machine drive ball race turntable 17 driven through spur gear 18.

The turntable 17 includes a radial key recess 19 engageable with key 13 at the end of the segment to provide the drive connection between the turntable and the mandrel segments 10.

In use, the required mandrel taper and the diameter is determined for a given pipe or pole to be formed on the mandrel and the mandrel is then assembled with the appropriate segment with the correct diameter at the small end and the mandrel diameter required at the large end can also be determined mathematically and thus it is predictable as to whether or not the products will be correctly formed over its length from the mandrel segments nominated and used in the makeup of the segmented mandrel. If necessary, a trial run on one

plate can be used to verify the mandrel segment selection and minor changes as to the position of the reference end can be used to ensure correct forming of the product. Even if there is slight variation in the diameters of the segments, it is possible in practice to achieve a perfect fit up of the two edges of the curved pipe along its length since gaps of up to 25% of diameter can be tolerated and still give correct size for welding of the gap.

Thus, in practice, an inventory or family of segments manufactured each having the same taper say, a 10% taper, with varying diameters from say a minimum diameter of 100 mm up to a maximum of 700 mm is possible which means that the number of mandrel segments required in that given family is 60 each being a metre long. Those 60 segments can be used as a "segment bank" for forming tapered pipes in 10 metre lengths and having minimum and maximum diameters in the range between 100 mm and 700 mm. In addition, the tapered pipes of mandrel length thus formed can be interconnected after manufacture to form an elongated pole of great length as required. The invention is characterised by the fact that the mandrel segments are relatively simple to manufacture and are easy to assemble into the plate forming machine.