Thermal plastic process for reducing a diameter of metal pipe by heating an annular limited section of the pipe while cooling adjacent sections has been developed. This report is concerned with the method of the process, its principle and the effect of parameters for shrinkage of pipe. The principle of shrinkage of pipe is explained that the limited section of pipe heated by an annular induction coil tends to radially expand outwardly. However, due to the self-restriction against thermal expansion and reducing the yielding strength because of high temperature condition, the heated section's diameter is not increased so much as that of free expansion. As a result, a diameter of thermal plastic processed part is reduced in comparison with initial one after cooling. As for the parameters, maximum temperature, coil length, diameter, wall-thickness and number of repetition are given. Effects of parameters for shrinkage of pipe are as follows. As maximum temperature becomes higher and coil length becomes shorter, the shrinkage of pipe is increased. And as diameter and wall-thickness of the pipe become bigger respectively, the shrinkage is increased slightly. Furthermore, if this process is repeated for the same pipe, the shrinkage is increased.
In order to make clear the mechanism of wetting and to treat it quantitatively, we tried to reveal the interface structure at advancing edge of Sn-Pb alloy droplet on Cu plate. Liquid droplet of alloy on a Cu plate was blown off by high speed Ar gas heated to a temperature of about 475 K, and concentrations of elements along the vertical cross section of interface were measured using AES analyser scraping by Ar sputtering. The results showed that Sn enrichment was formed at the interface immediately after melted down of alloy and the most outside edge of halo was Sn only. The experiment method used proved to be a useful method for the analyse of interface between liquid and solid.
In wetting phenomena, interfacial energy between liquid and solid is of importance. We investigated the structure of Cu/Pb-Sn interface and estimated interfacial energy on the bases of the experimental results, and discussed the wetting mechanism. The followings were inferred from the results. The spreading of halo depends on the amount of intermetallic compound formed at the solid/liquid interface which varies interfacial energy. The supplied liquid from droplet into a halo lowers the concentration of intermetallic compound and promotes spreading of halo. The spreading of drop let depends on the spreading of halo which lowers surface energy of solid for the spreading of drop let. At an equilibrium state of intermetallic compound formation and liquid supply from droplet, the spreading stops by means of that work of spread becomes zero. The tendency of spreading of Pb-Sn alloys on Cu plate estimated from the phenomena above mentioned showed good agreement with the well known spreading phenomena.
Electrode life tests were conducted in resistance spot welding of organic composite coated steel sheets. The electrode lives obtained were almost equivalent to those of ordinal coated steels despite the fact that electrodes during the tests rapidly wore out. The long electrode lives can be attributed to a high contact resistance between the material coated with an organic film and an electrode. That is to say, although the high contact resistance leads to the rapid wear of electrodes caused by a frequent surface flash, this in turn effectively restricts a current path into a specific contact area between the material surface and the electrode and maintains a high current density sufficient to form a nugget even when the electrode wears out.
Investigation was conducted to evaluate potential factors in production lines which might influence resistance spot weldability of organic composite coated steel sheets. Those factors including electrode hardness, electrode downward speed (impact force), water flow rate, spot welding current and a relative location of an organic film to an electrode were selected and examined. The results showed that the sensitivity of this material to these factors is not very much different from that of conventional coated steels and thus this material can be used in established production lines without any special modifications.
In the present paper, a new type GTA welding system using a hollow tungsten electorode is proposed to ignite and sustain a welding arc in a vacuum like the open space. In the developed system, Ar gas for discharge is supplied to arc space through the hollow tungsten electrode. The results of the present work are summarized as follows, (1) Even in a low pressure condition, a small quantity of Ar gas flow can ignite and sustain an arc discharge and the arc can melt the base metal. (2) In a low pressure condition, a stationary arc follows a transient arc. The period of the transient arc discharge increases with the decrease of Ar gas flow rate. (3) With the decrease of Ar gas flow rate, the arc voltage increases and the penetration of base metal (stainless steel) increases in size.
This paper deals with reduction of manufacturing time for various types and low volume of products in the process of arc-welding assembly. As an example of "weld-assembly" process, we examined the case of assembling dump-bodies where 23 kinds of bodies are assembled through 26 stages of weld-assembly jigs. The jigs are instantaneously moved to a new configuration by servo motors or pneumatic cylinders, eliminating waiting time to change the arrangement for new products. In order to minimize a total weld-assembly time, a simulation-method was developed for determining the most suitable sequence of works. A result of simulation shows that a difference of total time between the most suitable and the worst cases is as great as 9%. To maintain a good process efficiency with the help of the simulation, data-aquisition system was established to get the weld-assembly time for each work at each stage, and the weld-assembly line was designed to centrally computer-controlled. At the early stage of the development simulation time was too long to use the method practically, therefor we examined the way of reducing simulation-time by the characteristics of specific combination of work-sequences and so on.
Aluminum test pieces with thermally-sprayed surface layers of Si, Fe, Cu and Ni in a thickness range of 30-200, um were remelted by CO2 laser radiation at varying power densities of 3.8×103-4.2×104 w/cm2. The metallurgical structure of the alloyed surface layers was examined by optical microscopy. It was found that the melting and alloying behavior of the surface layers was governed by the relationship between the power density and the thickness and properties of the sprayed materials. Macrosegregation due to power density differences was also observed in the alloyed layers. In view of metallurgical structure, the following hypothesis was made about the alloying process. It is assumed that the aluminum base metal began to melt at the interface with the sprayed layer due to the heat conducted through the latter. The sprayed element still in solid phase then dissolved into the molten pool of Al due to diffusion to produce the alloyed layer. Convection induced by the density difference worked to promote alloying. The alloying process was simulated using ABAQUS version 4.7, a general purpose Finite Element Method (FEM) code for unsteady state thermal diffusivity analysis. Good agreement was seen between the simulation results and experimental data.
In this study, the influence of brazing process conditions on the Ni brazed joint (Ni-Cr-B) strength of stainless steel (SUS304) was investigated by creep rupture test. The effects of the brazing clearance were discussed based on the experimental analysis using EPMA and SEM. The results obtained are as follows ; (1) The effect of brazing clearance on the creep rupture strength is not observed though it had the biggest effect on the static tensile test. (2) When the brazing clearance exceeds 20 μm, the brazing layer is separated into two layers. The central line zone of the brazing layer 2 (embrittlement layer) has the composition close to the original brazing alloy, and the other layer is solid solution of Ni-Cr (brazing layer 1). The embrittlement layer gradually disappears through diffusion into the neighboring brazing layer 1 area over a long period of high temperature (1073 K) creep testing.
The influence of vanadium on the reheat cracking sensitivity was examined on various Cr-Mo steels and the experimental results were discussed from the view point of the combined influence of chromium, molybdenum and vanadium. Steel specimens were prepared in the laboratory ; the chemical composition ranges of them were 0 to 2.0%Cr, 0.28 to 0.8%Mo and 0 to 0.4%V. The cracking test was performed by using an implant test machine of the constant-strain type. The cracking sensitivity of each steel was compared by the term of critical restraint stress to produce reheat cracking. The contour lines of the critical restraint stress were drawn in the Cr-Mo contents diagram and the shift of these lines brought by the addition of vanadium was indicated. The influence of vanadium differs largely depending on each set of Cr-Mo contents. The groups of 0%Cr-Mo steels and Cr-0.28%Mo steels are originally insensitive to cracking. They become very sensitive by vanadium of a small quantity as 0.1%. On the contrary, the groups of Cr-0.5%Mo and Cr-0.8%Mo steels, which are originally sensitive to cracking, are affected a little by vanadium. The critical restraint stress is the function of two factors, the stress-relaxation characteristic and the fracture strength. The decrease of critical restraint stress (the increase of cracking sensitivity) is mainly brought by the decrease of stress relaxation. Vanadium affects little the original value of fracture strength of Cr-Mo steels.
The authors have confirmed in the previous paper that vanadium increased the reheat cracking sensitivity of Cr-Mo steels by the role of decreasing the stress relaxation. This role of vanadium may be related to the precipitation hardening induced by vanadium carbide. In this paper, the cracking sensitivity of Cr-Mo-V steels was discussed from the view point of the precipitation of various carbide phases. X-ray analysis was carried out on the carbide phases extracted electrolytically from the simulated-HAZ specimen tempered at 973 K. Following experimental results were obtained on the steels of the chemical composition ranges of 0 to 2%Cr, 0.28 to 0.8%Mo and 0 to 0.4%V. (1) The increase of cracking sensitivity brought by the addition of vanadium corresponds closely to the increse of hardness induced by the secondary-hardening. (2) The steels of lower molybdenum content are originally less sensitive to cracking. With the addition of vanadium, vanadium carbide precipitates and it converts the steels secondary-hardenable, and hence, cracking-sensitive. (3) Steels of higher molybdenum content are originally secondary-hardenable ; this is brought by molybdenum carbide. In the vanadium-bearing steel, vanadium carbide precipitates replacing molybdenum carbide. However, the original cracking sensitivity is varied little by vanadium, because those two carbides induce the secondary hardening of the same magnitude.
The use of CTOD bend specimen with a deep notch whose length is equal to the plate thickness is not always appropriate to obtain the toughness data applicable to fracture performance evaluation of weld joints. In this paper, HAZ-notched bend test and tension test have been conducted using specimens with different notch depth, which were extracted from a multipass weld joint of 30 mm thick high strength steel (TMCP type) with 460 MPa class yield point. The critical CTOD value at unstable fracture initiation obtained by the deep notch bend test was apparently smaller than that for the tension specimen. Fracture mode was also affected by the specimen type : Perfect cleavage fracture was dominant in the deep notch bend specimen, whereas unstable fracture preceded by a large amount of stable crack growth was observed in the tension specimen. Difference between CTOD results for the deep notch bend specimen and the tension specimen can be attributed to the crack tip constraint effect. The deep notch bend specimen exhibits significantly elevated crack tip stress and higher stress triaxiality compared to the tension specimen. By contrast, a shallow notch bend specimen showed a similar fracture behavior and critical CTOD value as the tension specimen. For the assessment of fracture resistance of welds by the CTOD bend test, the notch depth should be designed to simulate the plastic constraint expected in weldments.
Electrical discharge machines (EDM) have conventionally been used for cutting the nozzle blade holes in steam turbine diaphragm spacer rings due to high precision requrements. Problems assosiated with this method are slow cutting speed and a potential for fire resulting from the usage of oil. The abrasive water jet (AWJ) machine avoids these problems makes it possible to cut three-dimensional curved work pieces in the horizontal position. This is performed by utilizing two heads with each head featuring simultaneous control in five axes. AWJ technology makes relatively high speed cutting possible while maintaining high precision requirements. The results obtained are summarized as follows; (1) Abrasive water jet cutting technology and equipment have been established to perform precision cutting of three-dimensional curved surfaces while obtaining higher productivity than the conventional EDM method. The use of two cutting heads with individual simultaneous cotrol in five axes makes this technology possible. (2) A significant man hour reduction has been achieved as a result of increased productivity by utilizing high speed cutting (10 to 50 mm/min) along the nozzle blade profiles. (3) AWJ cut surfaces exhibit approximately 1/5 the surface roughness of conventional EDM cut surfaces. The accuracy of the cut hole geometry satisfies specification requirements for maximum allowable gap between the nozzle and hole profile. (4) Because no oil is used with AWJ cutting, the danger of fire has been eliminated and environmental compatability is improved.