In the conventional method of flash-butt welding, a master cam having a prescribed master pattern is employed. We have devised a voltage feedback control system which catches flash effect from flashing voltage and converts it into signal to control the speed of approach to work, and we have succeeded in applying industrially our method to manufacture the landing gear of aircrafts. In our welding tests using material 4330 Si Mod. or 4340 Si Mod. for the landing gear of aircraft, this method has been proved to be excellent. In addition, it has been proved that the flash-butt welding machine using the voltage feedback control system has the following advantages: 1. Flashing voltage can be reduced by 30-50%. 2. Flashing is stable and quiet, and flashing dust is small in size. 3. Welding conditions can be chosen in a wide range, and, moreover, they are stable and less affected by external factors such as power source voltage, dimension and shape of work, etc. 4. Owing to self-controlling ability, preheating is performed automatically. Hence there is no need to use preheater or to choose preheating conditions. 5. Flashing metal loss can be cut down by about 50% than usual flash welding method. (Welding time can be also shortened.) 6. Input power is reduced to 1/3-1/5, therefore power source can be simplified. 7. Welding process are stable, quality of weld is excellent. Moreover, even those materials that were difficult to weld by the conventional methods can be welded by this method. 8. There is no need of preliminary front end preparation to facilitate flash start on butt faces. 9. No freezing takes place, and no great skill is required for welding.
In previous report (the 1st report), it was made clear that nickel and monel welding electrodes had to contain a little Al and Ti in their weld metals for prevention of porosity in weld metals, improvement of their mechamical propertis and prevention of micro cracking with decreasing ductility. Increased Al and Ti in the welding electrodes, however, promote the occurrence of hot cracking in nickel weld metals, because the content of Si in weld metals is increased by reducing reaction of Al and Ti with the silicates (SiO2) of the coating flux. In this paper, the authors investigate the relations between SiO2 content in the coating flux and Si content in weld metals, effect of Si content on weld crackings of nickel and monel weld metals. The results are summarized as follows: 1) Si content in nickel and monel weld metals increases owing to the increase of SiO2 content in coating flux of the welding electrodes. 2) Hot cracking of nickel weld metals aggravates remarkably due to the increase of Si content in the weld metals. 3) Effect of Si content on hot cracking of monel weld metals was less than that of nickel weld metals. In overlaying monel on carbon steels, however, hot cracking of monel weld metals is remarkable owing to the increase of Fe in the weld metals caused by the penetration of Fe in the steels. 4) In case of increased Si content in nickel weld metals, it is possible to prevent micro cracking of nickel weld metals when Al and Ti contents in the weld metals are more than three times Si content in the weld metals. 5) It is clear that micro cracking of monel weld metals is not influenced by Si content in the weld metals.
This paper discribes an experimental study on the characteristics at low temperature of welded polyacetal (Duracon). The results of some measurements on the mechanical properties, fracture surfaces and X-ray diffraction pattern are reported and discussed. This study intends to clarify the low temperature characteristics of weld comparing with those of base material, and to discuss the change in mechanical properties from room temperature down to the neighborhood of -70°C and fracture in low temperature experiment from a microscopic view point. Notch and load velocity effects on the brittle fracture tendency are also discussed. Testing materials were polyacetal board of 2 mm in thickness, and tests were carried out at low temperature of methylalchohol and dry ice. A heat plate welding apparatus, with which specimens could be secured under fixed contact force, was made in order to carry out the experiment of welding. The following summary can be made of the experimental results. Tendency of low temperature characteristics of the welded material is generally similar to that of the base material, except that a change of elongation occurs at each temperature. Effect of load velocity is observed both on the basic and the welded materials, and brittleness becomes great when the temperature is low and load velocity is high. Notch effect is also observed both on the base and the welded materials, and this effect appears great with the welded material and the base material. Correlations are observed between fractured surface and mechanical testing results, as well as between X-ray differaction pattern and mechanical testing results.
The three-point bending strength for HT-80 of bainitic structure obtained by isothermal heat treatment with hydrogen and hydrogen free were investigated in relation to the prior austenite grain size and ferrite lath size. The fracture surface and unit facet size were observed by two stage replica method and Electron Scanning Microscope. The fracture stress of specimen with hydrogen depended on prior austenite grain size and was lower than that of hydrogen free specimen. Those fracture surfaces were observed remarkably secondary cracks along the boundary of ferrite lath and interface between matrix and carbide. The unit fracture facet for hydrogen embrittlement, therefore, was defined the zone between secondary cracks. The unit facet size for hydrogen embrittlement was smaller 1/2-1/3 than unit facet size for cleavage fracture of hydrogen free specimen at-196°C tested. The fracture morphologies of hydrogen embrittlement at 25°C tested were different from hydrogen free specimen at -196°C tested. The fracture morphologies of specimen with hydrogen were observed the QCHE, not observed the intergranular fracture. The fracture morphology of hydrogen embrittlement was influenced by hydrogen diffusion and accumulation in ferrite lath boundary.
A cathode plasma ball which is formed at the cathode tip end is very interesting from the view point of electric discharge physics. In previous papers, the aathors estimated that this plasma ball would be a cathode-ionization-region which had expanded under the low pressure conditions, but they could not come to the conclusion because the internal construction was not clear. A fine tungsten probe which was insulated with refractory silica was prepared and it was moved across the arc at high speed in order to avoid both the heat damage of the probe and the arc perturbation by probe insertion. Probe measurements in a low pressure arc were quite successfully carried out by this method, and the axial and radial potentials as well as electron temperature distributions were determined with good reliability both in accuracy and reproducibility. Inside the cathode plasma ball, a distinct electron beam current is observed. The beam intensity decreases rapidly as the distance from the cathode tip increases and it disappears at the ball end. The electron temperature, on the other hand, increases greatly as the beam is damped. The above indicates that the emitted electrons from the cathode collide with the neutral or ionic particles, resulting in ther-malization of accelerated electrons. Therefore, the authors concluded that the cathode plasma ball is the cathode-ionization-region in the electric discharge as was proposed by Slepian.
The sources of some characteristics of torque that the lower rotational speed leads to the higher torque in the third (steady) friction phase and the torque rises in the fourth (decelerating) phase are investigated by using transparent acryl resin base material in place of metal. Main results are as follows: (1) The friction interface between the two base materials consists of the two regions, that is, a circular junction region at the centre part and an annular region in which joining and separating repeat violently. (2) The area of the circular junction region depends upon the rotational speed. The higher the rotational speed is, the smaller the area becomes. (3) The phenomenon, that the torque in the third phase becomes lower in the case where the higher rotational speed is selected, is connected to the smaller area of the junction region. (4) As the rotational speed lowers in the fourth (decelerating) phase, the area of the junction region spreads gradually over the interface. Thus the spreading junction region enhances the friction torque and it has a leading effect to characterize the history of torque in friction welding.
In this investigation, the authors aimed to make clear the weldability of electron-beam welds for some commercial constructional high tension steels. Then, the influences of weld heat input on the. weld defects, hardness distributions and impact properties of the electron-beam welds were investigated in this report. The meterials used were three grades of high tension steel as HT-50, HT-60 and HT-80 with 25 mm thick-ness. The conventional low voltage type-electron-beam welder, 30 KV-500 mA (15 KW) in maximum was employed in this experiment. All of the weld bead were performed with bead-on-plate type welding. The active beam parameter, ab adopted was 1.0. The remarkable conclusions are as follows: (1)All of the welds except unstable beads have had no defect according to dye penetrant and X-ray inspections. (2)The hardness in weld metal was generally reduced with an increase of the weld heat input. In Vickers hardness distributions of HT:50 and 60 steels, the hardness in the HAZ near fusion boundary was harder than that in the weld metal. This is considered due to the vaporization of Mn element in weld metal. (3)The value of impact strength for the weld metal usually showed the two levels even at the same testing temperature due to the difference in the form of the fracture path in impact test specimen. Namely, when the fracture occurred straightly along the notched direction, the absorbed energy showed the low value, however, when the fracture occurred out of the notched direction, it showed the high value. (4)The testing temperature, at which the form of fracture path differs, tended to be raised with an increase of the weld heat input. This seemed to be related with the bead width or the hardness difference between base and weld metal. (5)As far as the fracture propagates along the notched direction, there is little variation in the absorbed energies of weld metal for respective material within a limit changed for the weld heat input from 10 KJ/cm through 40 KJ/cm. (6)In case of the welds of HT-50 and 80 steels, the absorbed energies of the weld metal, which show lower value than that of the base metal are usually exceeding the minimum absorbed energy required in.JIS or WES specification, even though the fracture occurs within weld metal. In case of HT-60, however, they are not always satisfied with the criteria of JIS specification. (7)Furthermore, the impact strength of electron-beam welds showed higher value than that of submerged arc welds for HT-50 and 80 steels.