Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
  • B23K20/14—Preventing or minimising gas access, or using protective gases or vacuum during welding

Definitions

• the present invention relates to a method for joining parts of metal by means of diffusion welding, comprising the following steps: establishing a joint between opposed bounding surfaces on the respective parts to be joined, heating of the parts to a predetermined temperature in at least those areas bordering on the joint, joining the parts by pressing the parts together, and cooling the parts.
• joints can be formed having properties and iicrostructures which are very similar to those of the base material and joining is possibl where the form of the work pieces makes it difficult to use other methods. Furthermore, joints can be made having minim deformations and without consecutive machining or forming.
• the cost of the equipment is usually very high, a fact that limit the size of the parts that may be diffusion welded in an economi manner.
• the necessity of supplying heat and a high compressive force in an environment such as vacuum or protective atmosphere will give rise to grave problems as regards the necessary equipment and therefore constitute a substantial limitation in the applicability of the method.
• the method requires very careful and thorough surface preparation and, besides, that it requires more time than conventional methods.
• a certain tension is maintained in the laid pipeline, and for this purpose the laying vessel must have anchors by means of which it is pulling itself forward during the laying of the pipeline. These anchors must from time to time be moved forward in front of the vessel and for this purpose it is necessary to use auxiliary vessels.
• the joint at the outset is given the form of a cavity which has a generally increasing height from the periphery towards the middle and is provided with at least one connecting conduit, in that the cavity of the joint during the heating first is supplied with an inert or reducing flushing gas until the
• OM joint is tightly closed along its periphery, in that the " cavity of the joint thereafter may be put under vacuum via the connecting conduit, and in that the joint thereafter is pressed together with a predetermined speed for the further diffusion welding.
• At least one of the bounding surfaces of the joint i ' s provided with serrations along the periphery. This will ensure sufficient escape of flushing gas during the early phases of the joining.
• a further advantageous form of the joint is obtained if at least one, preferably both bounding surfaces are given conic form.
• the conical form is easier to machine in a sufficient exact manner, and if both surfaces are conical, one convex and the other concave, one will obtain a self-aligning effec between the parts when they are pressed together. Such a form will also provide good assurance of complete fusion.
• helium is preferred because during its manufacture it is cooled down to such a temperature that it is virtually guaranteed to be oxygen free.
• commercially available and reliable helium detectors can be used to contr that the periphery of the joint is absolutely closed before the vacuum is applied.
• an activating alloy i.a. 60/40 Palladium/Nickel.
• This alloy may be introduced as a thin strip or possibly be applied on one or both bounding surfaces by means of electro plating. This will i.a. result in reduced diffusion time.
• the connecting conduit for supplying flushing gas or removin gas for pulling a vacuum may advantageously be arranged in one of the parts to be joined, preferably near its periphery
• conduit may be plugged immediately after the ⁇ diffusion welding by means of a deep welding electrode or c Plasma-TIG while the temperature of the parts still is sufficiently high, for instance 400 - 600 C.
• Figures 1 and 2 show a first embodiment of two parts at beginning and completed diffusion welding, respectively.
• Figures 3 and 4 show a second embodiment of the two parts at beginning and completed diffusion welding, respectively.
• Figures 5 and 6 show a further exemplifying embodiment of two parts at beginning and completed diffusion welding, respectively.
• Figure 7 shows the parts of Figure 6 upon further compressic
• Figure 1 shows a section through a portion of two parts 1 an . • 2, which may be bolts of structural steel such as ST 52-3.
• Figure 1 may also be visualized as showing an axial section through a thick-walled pipe, the axis of the pipe being at th left of the figure.
• a joint 3 is formed, which is bounded by a concavely curved bounding surface 4 on the part 1 and a plane bounding surface 5 on the part 2.
• a connecting conduit 6 is arranged in the part 1, said conduit opening into the cavity 3 of the joint and with its other end being connectably alternately with a source of flushing gas and a vacuum source (not shown) .
• the arrows F indicate a variable compressing force, while the bell- shaped curve to the left of the parts 1 and 2 indicates the axial temperature distribution in the parts.
• a suitable c pressing force F This force may be created by means of a simple jack system (not shown) , which for instance may comprise a clamping ring on each of the parts 1, 2, the clamping rings being interconnected by means of hydraulic cylinders.
• a simple jack system (not shown)
• the heating is started, for instance by means of an inductio coil (not shown) .
• flushing gas is supplied ' through the connecting conduit 6. The flushing gas will fir leak out along the periphery 7 of the joint due to minor irregularities or serrating on the bounding surfaces of the joint.
• the purpose of the flushing is to keep oxygen away from the joint surfaces in order to prevent oxidation of the during the heating, possibly also to remove oxides that may already be present. Regardless of how well the bounding surfaces 4, 5 have been cleaned before the welding, even a short exposure to the oxygen of the air will cause an oxide layer of a thickness in the order of 350 - 1000 A, depending on the air temperature and humidity.
• the connecting conduit 6 When the joint thus is closed along its periphery 7, the connecting conduit 6 is connected to a vacuum source, which thereupon reduces the pressure in the cavity 3 to about 10 torr. Concurrently, the temperature of the parts 1, . is increased as suggested schematicly by the curve to the left in Figure 2 , to a maximum temperature of about 1350 C. With a suitable compressing force F the joint 3 will be closed in a matter of seconds. This result is schematicly shown in Figure 2. Complete diffusion welding will take place in the course of 15 - 30 minutes. (However, one has obtained complete welding in diffusion times as short as 8 minutes at. about 1350 C.) Thereafter the parts are coole in calm air down to about 600 C, which will take about 4 minutes for a material thickness of 40 mm. At this tempera the connecting conduit may be plugged, i.a. by means of a deep welding electrode or Plasma-TIG welding.
• Figure 3 shows two parts 1 and 2 with generally the same outer form as in Figure 1.
• the welding joint 3 he has a different form, its bounding surfaces 4 and 5 both being conical, one concave and the other convex.
• the top angles are different so that the joint will have increasing thickness towards the middle.
• the distance between the apic of the joint surfaces can amount to about 10% of the thickne o the parts 1, 2.
• the conical form of the bounding surface 4, 5 makes the parts 1, 2 self-aligning when they are presse together.
• the conical form also helps to avoid insufficient diffusion in the middle of the joint, as easily could happen if the lower bounding surface 5 was plane and the upper bounding surface 4 conically concave.
• the pressure during the diffusion welding is a very importan parameter which is difficult to control. According to the Welding Handbook previously mentioned it is supposed that the pressure cannot be brought higher than the uniaxial creep stress of the material at the temperature prevailing at any time without using forms to prevent floating. The us of such forms is cumbersome and entails increased cost, and in some applications such forms cannot be used due to lack of access. Since the diffusion speed generally increas with the square of the pressure, by increasing the pressure to the double or triple of the creep stress, one could bring the diffusion time down to about one fourth or one ninth, respectively, of the corresponding diffusion time for uniaxi pressure. Alternatively one could permit considerably more of oxides on the joint surfaces and thereby possibly delete flushing of the joint with a reducing gas.
• the invention aims a establishing a triaxial stress condition in the joint area. It will be known that in tensile testing of thicker test rods a contraction will occur by shear deformation, a cleava fracture finally taking place in the middle zone. This cleavage fracture is caused by the axial tension in the midd being very much higher than the yield stress of the material the material on both sides of the contraction holding back by means of radial stresses. For this reason the axial stre increases, the yielding subsiding when the difference betwee the axial stress and the radial stress becomes. less than the yield stress (Trescas principle) .
• one aims at utilizing the triaxia phenomenon by providing the parts 1, 2 with a substantial constriction in the joint area as compared to the adjacent material.
• An example is shown in Figure 5.
• hydrogen is used as flushing gas, as is evidenced by the flames indicated along the periphery of the joint.
• the compressive force may be removed and the diffusion time and temperature be held until the residual pores have been closed by re ⁇ crystallization. If a much quicker joining is desired, this can be obtained by electroplating the joint surfaces or introducing in the joint a strip of activating alloy, for instance of the type Pd/Ni 60/40.
• Tests performed with the method according to the invention by using bolts of structural steel ST 52-3 having 40 mm diameter have given excellent results with respect to for instance ductility and tensile strength. More than 60% elongation has been measured in the heat effected zone for bolts which have been bent to hair needle shape. The rupture surface showed essentially shear fracture.
• the invention may also be advantageously utilized for other purposes than fabrication of large pipelines. For instance, it may be used in welding joints in trusses for bridges and offshore structures.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Pressure Welding/Diffusion-Bonding (AREA)

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• 1983
  • 1983-04-12 NO NO831295A patent/NO152590C/no not_active IP Right Cessation
  • 1983-04-13 DE DE8383901237T patent/DE3369922D1/de not_active Expired
  • 1983-04-13 WO PCT/NO1983/000010 patent/WO1983003565A1/en active IP Right Grant
  • 1983-04-13 US US06/568,195 patent/US4566625A/en not_active Expired - Lifetime
  • 1983-04-13 GB GB08333027A patent/GB2130134B/en not_active Expired
  • 1983-04-13 CH CH6697/83A patent/CH661232A5/de not_active IP Right Cessation
  • 1983-04-13 EP EP83901237A patent/EP0105892B1/en not_active Expired
  • 1983-04-13 JP JP58501277A patent/JPS59500606A/ja active Granted
  • 1983-04-13 AU AU14702/83A patent/AU552578B2/en not_active Ceased
  • 1983-04-13 NL NL8320103A patent/NL8320103A/nl unknown
  • 1983-04-13 DE DE19833340235 patent/DE3340235T1/de not_active Withdrawn
  • 1983-12-08 OA OA58177A patent/OA07605A/xx unknown
  • 1983-12-08 FI FI834498A patent/FI74227C/fi not_active IP Right Cessation
  • 1983-12-12 DK DK570983A patent/DK152532C/da not_active IP Right Cessation
  • 1983-12-12 SE SE8306856A patent/SE446515B/sv not_active IP Right Cessation
  • 1983-12-13 RO RO83112842A patent/RO88735A/ro unknown

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