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InductIve heatIng tube bendIng machInes
on RussIan shIpbuIldIng enteRpRIses
The advertorial is based on the article by
V.A.Nikitin,
V.I.Chervinsky
Maximum diameter of pipes applied in ship systems and in ship propulsion systems is 273 mm, in specific cases it runs up to 325 mm. In spite of development of cold bend- ing machines, Russian shipbuilding enter- prises traditionally use machines with in- ductive heating for bending of pipes, which diameter exceeds 159 mm. The reason is not only in major diameter of bended pipes and high efforts of bending accordingly, but also in other advantages of machines with inductive heating, such as: • Capability of achieving of steep bends with radius up to 1.5 dt
(where dt is exter-
nal diameter of pipe) with permitted values of ellipse and thinning of outer wall. • Capability of achieving 2 closely–spaced bends (straight section between 2 bends up to 1.0 dt
), because it is impossible to
achieve the same space on cold bending machines.
First pipe–bending machines with induc- tive heating were installed on Russian enterprises in 1960s. Many of them are used to the present day, thus proving their high reliability. At the same time, their service life expired long time ago, and they are morally outdated. In recent decades, outdated machines are gradually replaced by their newer analogues, based on recent developments in power driven equipment and inductive heating equipment. As known, the essence of bending with inductive heating is kept in continuous and sequent pipe bending with use of induc- tor for local heating of strained cut. At that they receive an elementary deflection in the
When pipe moves through inductor, heating zone moves along the pipe, and elementary deflections sum up consequently, forming shaped section of certain radius. As practice shows, the width of heating zone must be narrow and run up to (1.5–2.5)s where s is the width of pipe wall. At that neighboring cold sections prevent the tube from elonga- tion. Due to the fact, that the temperature of strained pipe cut varies from 800°C to 1200°C, bending efforts are in 5–8 times lower in comparison with cold bending. This allows producing equipment of lower weight and size, in comparison with cold bending. They use two manufacturing schemes for pipe bending, distinct from each other by method of bending effort application: bending with use of pressure roller and bending with use of carriage. When bending with use of pressure roller, pipe moves along its center–line over guid- ing rollers affected by effort P and heated with inductor. Line feed and cross feed drive of pressure roller switch on simulta- neously.
Bending with use of pressure roller pro- vides achievement of any value of bending radius (unlimitedly high) without apply- ing of any special bending tools. Also, this machine can produce both left and right bending.
Pipe bending with use of carriage is also performed by longitudinal motion of pipe over driving rollers affected by effort P. Bending is achieved because of easy rota- tion of carriage relatively to its axis. The
adjustment of machine on defined bend- ing radius is performed by setting required distance between axis of carriage and axis of pipe.
Shipbuilding enterprises perform both bending schemes, but scheme with use of carriage is more popular because it pro- vides higher quality of bending. There are machines, capable to perform bending by both schemes. At that, bending with radius, which doesn’t exceed (3–4)dt
is performed
by carriage, and if the radius exceeds this value, then pressure roller is applied. 3D–model of pipe bending machine with use of carriage of UTG-IN–type (УТГ–ИН) machines is depicted on Fig. 1. This ma- chine possesses electro carriages for main and secondary motions. Machines of this type possess the following design feature: presence of lengthener on short foundation slab which allows bending tubes of up to 6 and above meters length. The standard length of bended pipes is 9 meters. These machines possess three driving rollers to perform pipe motion. Universal type ma- chine, capable of bending either by carriage or by pressure roller in range from 1,5dt
to
heating zone affected by effort imposed on pipe.
Fig.1
∞, has some insignificant functional differ- ences. First of all, one of these differences is the capability to move carriage of driving rollers along the housing of machine in order to set up required distance between pressure roller and inductor l. Machines are equipped with optical motion detectors by x–y–z coordinates, what allows to perform bending, based on analysis information. Most enterprises use thyristor converters as frequency converters (generators). Also, insignificant amount of old–type electric machine converters is still in use. They plan to implement new type of electric machine transistor–based converters. The power of converters is 125–160 kW, frequency is 2.4 kHz (thickness of pipe walls usually does not exceed 12 mm). Cooling systems design significantly af-
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