Chihiro Hayashi

Application of the theory of plasticity of the cold pilgering of tubes

Abstract This paper deals with the appllication of the theory of plasticity to the cold pilgering of tubes, i.e. the presentation of an analytical model of the cold pilgering process, fundamental equations, some examples of calculations, and limited results of experimental operations. By using this theory, the stresses, strains, and roll-separating forces during the pilgering process are calculated theoretically, and also the characteristics of the cold pilgering process are demonstrated: calculated values are in close agreement with experimental data. In the industrial operation of this process, groove design is very important as the dimensional accuracy of the tubes and the life of the tools is highly dependent on this design: the presented theory can be successfully applied to this topic. By using the theory, the deformation of a tube can be calculated for given dimensions of the groove and mandrel: however, by applying this procedure conversely, it is possible for the appropriate groove dimensions to be determined. A new groove designed using this procedure has been applied to industrial operation of the process, and has brought about a marked improvement in the dimensional accuracy of tubes, and a dramatical increase in yield and productivity. The new groove has been applied successfully to various materials, e.g., stainless,steel, titanium, zirconium alloy, copper, and copper alloy.

A Study on the Direct Applicability of a Set of Grooves of Multi-Roll Wire Mills for Different Materials

Investigations were carried out on the direct applicability of a set of grooves of multi-roll wire mills for different materials having different stress-strain curves. Special evaluation was made on the stability of the geometry among different materials when rolled under the same mill setting conditions. Influence of inter-stand tension generated by the change in roll force due to the difference in stress-strain curve was studied both numerically and experimentally. A group of three-roll and four-roll-type mills is superior to two-roll-type mill in getting rid of the time for mill setting.

Advancements in Cone-type Rotary Piercing Technology

A cone-type piercing mill was developed by the authors for materials with poor hot workability. This piercing mill is called “the super piercer” in Europe. It has a pair of cone-type main rolls supported at both ends with their roll axes inclined and crossed so as to enable piercing at high feed and cross angles. In order to ensure the best performance of the rotary piercing, disc rolls are adopted instead of plate guide shoes. The super piercer was put into practice at the small-diameter seamless tube plant operated in 1983. The recent progress in our research and development on the super piercer has resulted in the concept of “the new super piercer,” which allows expansion piercing. Namely, the development of the skewing technology for disc roll axes and its application to the cone-type piercing technology has realized remarkable increase in the expansion ratio. The new super piercer was adopted as the core technology of the new medium-diameter seamless tube plant operated in 1997. In this paper, studied in detail were the influences of the expansion ratio, feed and cross angles on the rotary forging effects, redundant shear deformations and power consumption.

Heat transfer and pressure loss characteristics of very compact heat sinks with plate fins cooled by jets

High-performance and very compact heat sinks have been developed for effective cooling of VLSIs with high heat-generation densities. Their heat transfer and pressure loss characteristics in air-jet cooling have been experimentally studied. The highly compact heat sinks were plate-fin arrays with a very small fin pitch of 0.4-2.0 mm. The rectangular jet nozzle width that gave the highest cooling performance was 30 to 40% of the streamwise length of the heat sinks. The influence of fin height on heat transfer became weak when the ratio of the height to the thickness of the fin exceeded approximately 35. When the air flow rate was constant, the thermal conductance increased as the fin pitch decreased. For a constant fin pitch, heat sinks with smaller fin thickness showed larger thermal conductance at a given blower power consumption. In our experimental range, the heat dissipation rate per unit heat sink volume increased as the base plate area of the heat sink became small.

Recent Progress of Rolling Technologies in Japan.

After the Plaza Agreement of G5, which was held in September 1985, the Yen was highly appreciated, and the Japanese government changed its policy from the encouragement of exports to the expansion of the domestic market. Fortunately, the government policy has been a success, and the production of hot and cold strip, large wide flange beam, wire and rod has recovered. Investment for equipment is under way and there are plans for renewing mills. However, the steel tube mills are highly dependent on the foreign market, the production of steel tube was drastically cut due to the sharp drop of the dollar and sharp rise of the yen. Nevertheless, research and development has been actively promoted and many marvelous results have been reported in every field. Iron and steel industries in Japan are still confident and innovative.