Patent GB-190428301-A (GB)
Title: Improvements in and relating to the Electric Welding of Turbine Blades and Apparatus therefor
Inventor: FERRANTI SEBASTIAN ZIANI DE
Filed: 1904-12-23
Granted: 1906-03-23
Abstract: 28,301. Ferranti, S. Z. de. Dec. 23. Welding; working by electricity; making turbines. -The inventions described in Specifications Nos. 11,921 and 15,186, A..D. 1903, which relate to the electric welding of turbine blades on to the wheels, rings, or drums which carry them and to apparatus used in the process, are modified in order to obtain a stronger weld with less disturbance of the neighbouring metal and to leave a smooth passage between the blades. According to one method, the wheel is composed of two discs a, Fig. 1, with fine slits c milled across the meeting edges as shown in Fig. 2. The end of the blade b is cut with a shank f, Fig. 4. The blade is held in the welding-jaws with only the shank projecting, and the current traverses the partly-cut teeth d, which are isolated from the body of the wheel by the slits and are so proportioned that they heat more rapidly than the blade shanks. Considerable pressure is applied during welding, resulting in the actual welding surface being forced into the wheel, the displaced metal filling up the slits and leaving a smooth and clean rim surface. In a modification, a centre disc with slits cut straight across the face may be interposed, and in further modifications any number of discs may be used ; all the slits may be cut straight across and the width of the teeth graded and the discs staggered to form resulting teeth of approximately the blade section, the outer discs in this case being left plain; discs of graded thicknesses may be used. For low-speed turbines where thin discs may be used, the wheel is formed of two discs w, Fig. 12, flanged at x, the corner of the flange being slitted as shown in Figs. 1 and 2. In a modification, a central disc is interposed. When multiple wheels of this type are built to a common shaft, the spaces between the rims may be filled up by circumferential rings of channel or like section, into which the shrouded ends of the fixed blades project. According to another method, the welding surface of the wheels &c. is cut up into rings by circumferential grooves of such a width and spacing that the surface presented under each part of the blade is approximately of the same width as the thickness of the blades at that part. This method is also applicable to multi-stage turbines with cylindrical or conical drums. Any surface disturbance due to the weld is flattened by the welding-jaws, which are flush with the end of the blade proper, and which come into contact with the surface of the wheel &c. after the current has been automatically cut off. When a still smoother rim surface is required, the surface is rolled, after the grooves have been cut, to close the grooves over as shown in Fig. 18. The grooves may be made of V-section to facilitate this operation. After the rolling, the surface may be machined or ground. In another method, the grooved surface is covered by a plain thin strip having holes punched to the blade pitch and shaped similar to but larger than the blade section. In this process, the shank f, Fig. 4, is made rather longer, and the edges of the blades come down on to the side portions of the strip and secure it in position apart from any attachment due to the welding. When a very thin strip is employed, the punched holes may be omitted. In a modification of the circumferential-grooving method, the wheels may be built of a number of discs 14, Fig. 21, separated by rings 17 or by some of the discs being dished. The discs may be graded and spaced according to any of the foregoing methods. According to another method, the surface may be grooved by a semi-rotating cutter or by a bnttended rotating cutter to form projecting teeth of approximately the blade section, as shown for example in Fig. 27. This method leaves an irregular surface after welding, which may be covered by the insertion of stampings 23, Fig. 29, between each pair of blades b, the ends being turned over and pressed into grooves 24 .cut round the sides of the rim. In another method, the blades are formed with long shanks which are welded to circumferential rings formed at the bottom of grooves the full width of the shank, running round the drum in positions corresponding to the rings of blades. In this case the welding- jaws also contain the greater part of the blade shank. After welding, the spaces between the blades are filled by packing-pieces caulked in position. When the blades require to be shrouded, the outer ends are formed with long narrow shanks for the reception of the shrouding-strip, which is in short lengths with square holes correctly pitched and larger at the outside than at the inside surface. The strips may be single or double, with scarfed or half-checked ends arranged to break joint. The strips may be cut from flat plate and to a curved form when a conical path through them is required, or they may be cut from a strip thicker at one side than the other and bent between plates, so as to have the correct cone internally and to form part of a plain cylinder externally. The machine employed for blade welding is of the same nature as that described in Specification No. 15,186, A.D. 1903, but has no provision for cutting either slots or grooves. A base 32, Fig. 35, carries a main slide 33 on which a welding - slide 34 is mounted. As shown in the Figure the slide is at the end of its out or welding stroke ; it is reciprocated by an adjustable crank and link 101. A cam may be substituted for the crank, especially where parts of the travel are to be performed more quickly than others. As the slide 33 moves in, a blade is ejected from a magazine 52 on the slide by a fixed adjustable r o d 50 through a hole in a plate 44 and at the end of the stroke is located in the welding- jaws in the correct position for gripping. The permanent jaws 37, 38, Fig. 38, are mounted on the slide 34, and the jaw 37 is pivoted at 40 for clamping by a wedge 41 formed in one with a screwed pin 48. Detachable jaws 35, 36 are fixed to the permanent jaws and are shaped to pass between consecutive blades as shown in Fig. 39. The jaw 35 is resiliently mounted to facilitate insertion of the blade, and the jaw ends are formed to swage the wheel surface in the neighbourhood of the weld. The welding-slide has a small motion relatively to the main slide as limited by a screw 43. The slides are yieldingly connected by a spring 47 adjustably compressed by nuts 49 on the pin 48. At the termination of the welding stroke, the spring is compressed and the wedge 41 causes the blade to be firmly clamped. The action of the spring permits a moderate pressure of the parts to be welded during heating up. The welding-slide lags behind the main slide on the instroke under the control of a rod and friction bearing-pieces. This lag further facilitates the insertion of a blade between the jaws. A spring 54 acting against a lug on the magazine depresses the plate 44 under the control of a stud and slot 68, to bring the hole into the clear position when not prevented by a detent 57 on a spring-controlled lever 56, operated by a spring member 59 mounted on a slide 61 adjustable with respect to the stroke of the main slide by a screw 62. An adjustable bracket on the slide 61 carries a spring and lever 64 for operating a replacing- lever 53 forked on to the plate 44. When a hammer blow is to be given after welding, a bracket 69, Fig. 40, is substituted for the bracket 39, Fig. 35, and the pusher-rod is extended and clamped in the outer arm. A tubular extension of the pin 48 slides in a bearing 70 and carries an adjustable trip 72, a buffer 76, and a spring-pressed weight 74. On the in-stroke, the spring is compressed and the weight is held by a detent 73, and at the end of the welding-stroke the trip 72 releases the weight, which during its travel operates a switch to cut off the welding-current. The switch may be operated by the travel of the slide. The crank shaft 103 is preferably driven by gearing, such as that described in Specification No. 15,186, A.D. 1903, arranged to give a slow speed during welding and knocking-up and a high speed during the remainder of the cycle. In some cases the controlling-cam may be arranged to give a second slow motion during the registration of the blade in the jaws. In some cases also, a single slide may be substituted for the double slide 33, 34. In the preferred arrangement for current control, two switches are connected in series. One switch is actuated by a cam on the shaft 103, and closes the circuit when the parts to be welded are in contact. The other switch 110, Fig. 37<b>, is closed at the end of the in stroke by a stop 111 and lever 112, and is held closed by a resiliently-mounted trip-finger 116 connected to a lever 82 preferably mounted on knife edges. The shortening of the blade during welding causes relative motion of the slides 33, 34, aud a contact-arm 81 on the slide 34, adjusted according to the duration of the welding operation required, releases the finger and allows the spring 113 to open the switch. The cam-actuated switch is afterwards opened. In a modified form of machine, continuous rod may be used, and, where plain blade ends only are required, the blade as welded may be cut off by a circular saw. When shanks and shrouding-tags are required, punches and dies are fitted at the back of the welding-slide and are operated by levers and eccentrics in synchronism with the other motions of the machine. The finished blade is registered in the welding-jaws by the end of the rod, which is then withdrawn to the correct position for punching. For this feed motion, two sets of oppositely-disposed clamping-devices are used, one of which is shown in Fig. 46. The turbine wheel or drum is mounted on a horizontal shaft in a headstock traversable on ways by a screw. Welding-machines as described are mounted on compound slides, one on each side of the drum, and operate either on separate rings of blades or on opposite halves of the same