Endless Bar Rolling System

Susumu Ohkawa, Plant Engineering Division, NKK Corporation, Makoto Doi, Tsu Research Labs., Hiromasa Hayashi, Applied Technology Research Center, NKK Corporation, Yoshihiro Hirase, Materials & Processing Research Center, NKK Corporation and Yuki Sugawara, Engineering Division, NKK Corporation     

1. Outline
"ENDLESS BAR ROLLING SYSYTEM" enables welding of billets that come from a re-heating furnace at the upstream side of a rolling mill train and realize the endless rolling operation for long products.
Although a test facility has been reported, no endless rolling had previously been used in commercial production in a mini-mill. The main reasons for this are the development of the following two technologies was difficult:@(1) Welding of hot billets of a large cross-section area in a short time and the high joint quality that is required to improve yield, and (2) completely and smoothly deburring in a short time to avoid any surface defects and for deformation of the billets.
In order to achieve these subjects,  "High Performance Flash Welding Machine" and original "Free Rotation Disk Cutters Deburring Machine" have been developed. Furthermore, the reliable control system in which high precision and high-speed processing are possible has been developed.

2. Contents of Technology
The main component of Endless Rolling System consists of a flying welder moving synchronously with the traveling billets, and a fixed type deburring machine,  as shown in Fig. 1.
In the welding system, the new welder has developed by using DC power supply system and new hydraulic system. It is shown in Fig. 2.
Compared with the conventional AC power supply system, by the new DC power supply system, continuous flashing and the high output power of the welder were realized, and very short welding time was enabled.
In high quality welding of billets with a large cross-section area, reduction of the reactance of a secondary circuit and the high-speed response of upsetting cylinders are required.
It was very difficult to reduce reactance in mechanical restrictions of large welders. Minimization of reactance was realized by the optimal arrangement of secondary conductors which designed by the reactance calculation of magnetic field analysis and multiple welding transformers.
The hydraulic system of upsetting cylinders succeeded in very compact, and high efficiency and equal-speed response compared with the conventional large hydraulic system with the electro-hydraulic servo-valves, as using the multi-hydraulic system which directly connected the hydraulic pump with the cylinder.

Fig.3 shows the welding joint part of 150@mm square cross section billet. The height of weld burr has 15mm or more and 30mm or more of width. It is necessary to deburring flat and smooth in several seconds on-line.
In this case, since burr and a billet are the high temperature which is about 1000, if the conventional deburring machine is used, the residual cutting edges will occur at corners of the billet.
Then, two free rotation disk cutters have been stationed as shown in fig.4, and the method of carrying out deburring by passing the billet between the two cutters was devised using the rolling power of the rolling mill. By this method, the residual cutting edges were not occurred at the corner of the billet (fig.5).

3. Conclusion
This endless rolling system is called "EBROSTM."  We received three orders of this system from overseas in 2000. It is under starting one by one now. Among these, the EBROS of  Shiu Wing Steel Ltd. (Hong Kong) started operation in July 2001 and is operating in commercial production now.
This technology bringing great progress and profits was not the wild dream of many rolling mill engineers, it came true. We will strive for the spread of this technology.



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