Metal working – Method of mechanical manufacture – Shaping by direct application of fluent pressure
Patent
1987-02-26
1989-02-07
Larson, Lowell A.
Metal working
Method of mechanical manufacture
Shaping by direct application of fluent pressure
29727, 72 56, B23P 1100, B21D 2602
Patent
active
048022730
DESCRIPTION:
BRIEF SUMMARY
In the manufacture of numerous industrial apparatus (heat exchangers, steam generators, self-bound tubes, for example), it is necessary to expand tubular elements in order to assemble and fix these tubular elements. The diameters and thicknesses of these tubular elements may vary considerably. As a guide, the tubes of steam generators for use in nuclear power stations have diameters of the order of 20 mm and a wall thickness of the order of 1 mm whereas certain self-bound tubes used in defence equipment have diameters of the order of 100 to 200 mm and a wall thickness of the order of 40 to 80 mm.
A method currently used to expand tubular elements is hydraulic expansion. Conventionally, hydraulic expansion is carried out using a mandrel or expander which is introduced into the tube which is to be expanded and supplied with pressurised fluid. The expander is provided with annular seals of very small cross-section which close off, in leaktight manner, the ends of the annular hydraulic expansion chamber formed between the internal surface of a tube which is to be expanded and the external surface of the expander when the latter is in position inside the tube. Seals of this kind having a constant diameter and cross section do not guarantee satisfactory contact with the inner surface of the tube if the diameter of the tube varies in accordance with normal manufacturing tolerances. Consequently, it is frequently necessary to use several expanders and seals of different diameters in order to follow the variations in the internal diameter of the tubes. Moreover, if the minimum diameter of a tube corresponds to the maximum diameter of the hole which is intended to receive the tube, there may also be leakage at the seal and, furthermore, the tube may not be adequately expanded against the wall of the hole.
Finally, in view of the small diameter of the seals (generally of the order of 1 to 2 mm), the deformation of the tube between the expanded part and the non-expanded part is considerable. This results in substantial stresses in this zone and, during the service life of the apparatus, cracking may develop which threatens the reliability of the equipment, requiring shutdown of the installations and sealing of the defective tubes.
The aim of this invention is to remedy the disadvantages of the prior art by means of an hydraulic tube expansion tool, comprising a body which carries at least one pair of seals, each seal comprising a head fixed on the surface of the elongate body and a skirt forming a crown which surrounds a portion of the elongate body at a small distance from the outer surface thereof, the skirt being made of a material having of sufficient flexibility to be slightly reduced in diameter when the tool is introduced into a tubular element.
In an embodiment by way of example, the skirts of the seals which constitute a pair are connected to each other in order to outwardly delimite an inner annular chamber intended to receive an expansion fluid. Rings are advantageously clamped against the heads of the seals and may, if necessary, envelop the flexible skirts partially or totally. These rings consist, for example, of a plurality of abutting sectors and a cylindrical cover may be slid around these rings in order to act as a stress distributor between the sectors and the tubular element which is to be expanded.
In order to carry out expansion over considerable lengths, the seal according to the invention may be mounted on an elongate body comprising an internal expansion chamber which extends between two pressure compartments, the first pressure compartment communicating solely with the internal expansion chamber, whilst the second pressure compartment communicates with the internal expansion chamber and with an intake channel for a pressurised fluid intended to create pressure in the pressure compartments in order to maintain constant elongation of the body of the tool all the time that there is pressure in the annular expansion chamber.
The invention also relates to a process for hydraulically expanding a lo
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patent: 2691418 (1954-10-01), Connolly
patent: 2799348 (1957-07-01), Page
patent: 3220235 (1965-11-01), Peccerill
patent: 4210991 (1980-07-01), Cooper
patent: 4467630 (1984-08-01), Kelly
patent: 4608738 (1986-09-01), Miller
patent: 4616392 (1986-10-01), Snyder
Cockerill Mechanical Industries
Larson Lowell A.
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