fracture of the D~qT specimens was 95-I00%. Tests of the DWTT specimens established that the base metal of the pipe has a high resistance to fracture in the range 20-15~ (Fig. i),

Long-term tests showed that splral-welded gas pipe performs well and is reliable enough to be used in gas lines in the Far North and Siberia.

IMPROVEMENT IN THE QUALITY OF WELDS ON BUTT-JOINED STRIP

V. G. Mokeichev, S. G. Molchadskli, and V. Ya. Kulvas

UDC 621.771.237:621.791,7.03.015

The domestic production of KSO-80.01 strip butt-welding units has now been mastered. These units are designed for joining hot-rolled strips together in order to permit continuous operation of metallurgical equipment, as well as to increase the productivity of cold-rolling mills by permitting the use of large coils. The units, designed by the All-Union Scientific- Research and Planning-Design Institute of Metallurgical IMchlne Construction (VNIImetmash) and serially produced by the Pskovsk Heavy Electrlc-Welding Equipment Plant, provide for com- plete automation of welding and auxiliary operations. The unit is distinguished by its flex- ibility and reliability and is equal to the best foreign models. In recent years the units have been installed on two high-capacity pickling lines and a continuous tinplate rolling mill at the Karaganda Metallurgical Combine, as well as at certain plants abroad,

During startup and introduction of the units at the Karaganda combine, problems were en- countered with the flash welding technology which led to a reduction in the quality of the welds and an increase in the number of weld failures during subsequent rolling.

The first of these problems was connected with premature short-circuiting of the ends be- fore upsetting due to a reduction in the welding voltage, insufficient power in the welding circuit, excessively high rates of approach, or irregular motion of the frame of the unit. The quality of the joints is also adversely affected by current interruptions or by reductions in current intensity due to slowing of the frame or its stopping as a result of late connec- tion of the upsetting drive.

Such malfunctions in machine operation usually occur with a reduction in pressure in the hydraulic system, discharge of the storage battery, sticking of the upsetting valve, or for other reasons. These problems are usually encountered in the transition from flashing to up- setting and, due to the rapidity of these processes, cannot be observed by operating personnel with constant oscillographic monitoring of the welding process. At the same time, analysis of the quality of welds provides evidence of the unavoidable appearance of oxides in the butt Joints both in the case of short-circulting of the ends over 2-4 half-periods prior to upset- ting and in the case of a current interruption of the same duration.

To detect deviations/in the welding cycle in time and permit the rejection of defective joints, the control circuit for the welding operation was augmented by a special upsetting control block (UCB). The block operates on the principle of analysis of the sequence of ar- rival of signals and the command to connect the upsetting drive, completion of flashing pro- gram, and the actual beginning of upsetting or short-clrcuIzing of the ends during flashing. The last two phenomena are fixed from the passage of a short-clrcult current in the welding power circuit, this current alternating sinusoidally and recorded with a special current sen- sor.

Figure 1 shows a graphof the displacement of the movable frame of the unit during flash- ing and upsetting and the change in the weldlng current in a single time scale, The final part of the frame-travel program $, with allowance for the response time of the hydraulic sys- tem T, is shown by the dashed llne. The figure also shows the KOS-model track sensor, which generates the command to begin upsetting.

During normal operation of the unit, the current sensor generates a signal after genera- tion of the command to begin upsetting -- with allowance for the respone time of the hydraulic system -- but before completion of the entire frame-travel program during flashing (event 2

All-Unlon Scientific-Research and Plannln~-Deslgn Institute of Metallurgical Machine Construction. Translated from Metallurg, No. 5, pp. 36-37, May, 1987.

0026-0894/87/0506-0135512.50 �9 1988 Plenum Publishing Corporation 135

S. lwc

I Kos

Fig. I. Graph of the change in the welding current i: and the displacement of the movable frame S during flashing and upset- ting: i) moment of generation of command to begin upsetting; 21 moment the welding current reaches the short-circuit value; 3) moment of completion of the frame-travel program during flash- Ing.

Fig. 2. Diagram of upsetting control block,

occurs in the time interval between events 1 and 3). The appearance of a current signal be- fore connection of the upsetting drive (the occurrence.Of event 2 before event i~ is evidence of premature short-clrcuiting of the ends. Conversely, the complete absence of the signal or its arrival after completion of the flashing cycle (the nonoccurrence of event 2 or its occurrence after event 3) is indicative of a problem in the operation of the hydraulic drive for upsetting.

The block diagram of the UCB in Fig. 2 reflects the design features of the KSO-80.OI,V butt-weldlng units, The flashing schedule is linearly approximated by segments of the path traveled by the frame of the unit. The frame travels over each of these segments at a con- stant velocity. The different steps in the welding operation are made to occur in the proper sequence by a programming unit provided wlth the necessary set of programs and linked with a stepper motor. The motor acts on the control valve of the hydraulic system, which has a feed- back coupling with the movable frame.

Signals corresponding to completion of the penultimate (n -- I) and last (n~ flashing stages are sent from the welding control circuit to three memory input elements Yl, M2, and M3. Another signal, corresponding to the presence of a short circuit in the power circuit of the welding transformer, is sent from the current sensor CS. The coincidence elements Cl, C2, and C3 generate logic signals which indicate the character of the welding process as it takes place. These signals pass through the gate GTI and the memory elements M4 and M5 and enter the inputs of amplifiers AI, A2, and A3, which light the indicating lights LI, L2, and L3. Illumination of the lights indicates either normal occurrence of the welding operation (LI) or malfunctions in the operation of the welding unit. These malfunctions correspond either to short-circuiting of the ends before upsetting (L2) or late connection of the upset- ting drive (L3).

The UCB was originally added to the control system as an "adviser" to the operator (light signallng). It was later incorporated into the automatic control circuit of the welding unit to generate signals preventing the further movement of defective welds and permitting their prompt rejection.

136

The introduction of the UCB has stabilized the quality of the welds, improved working conditions for operating personnel, and ensured timely detection of problems and malfunctions in the welding unit. In particular, the rollability of welds made on one unit installed on a continuous rolling mill has long stood at 99.0-99~8%, which is significantly higher than the indicesattained in previous domestic and foreign practice.

Due to the relative simplicity of the UCB and the efficiency of the monitoring operation, the UCB may find wide use on units for flash butt welding, operating in different types of me- tallurgical facilities and in other sectors of the economy.

IMPROVING THE ACCURACY OF CASING ON A TUBE-PRODUCTION UNIT WITH PILGER MILLS

D. S. Fridman, I. F. Khaidukov, UDC 621.774.36.014 N. I. Zelenyi, A. S. Ivakhnenko, and Yu. A. Starostin

During the XI Five-Year Plan, the Ural Scientific-Research Institute of the Tube Indus- try collaborated with the Severskii Pipe Plant to develop a set of control and measurement procedures designed to increase the accuracy of casing made on model 168-325 tube-production units with Pilger mills. The work proceeded in two directions: increase the accuracy of tube wall thickness and increase the straightness of the generatrix.

The problem of increasing tube accuracy on the 168-325 tube-production units (TPU) was solved by optimizing the deformation regimes and by developing and introducing new roll pas- ses and methods of pass adjustment on the Pilger mill, sizing mill, and straightening machine.

To increase wall-thickness and tube-diameter accuracy on the Pilger mill, we introduced a new pass system which reduces the longitudinal variation of wall thickness. We also intro- duced stiffer rolls with a wider body to reduce transverse variation of same.

Besides permitting an increase in rolling speed without intensifying the operation of the feed mechanism, large-diameter rolls make it possible to deepen the groove in the neutral section (without a reduction in roll stiffness) and on the free-running section for rolling large-diameter shells. This in turn makes it possible to roll a large volume of metal with one revolution of the rolls. Another positive factor is the possibility of increasing the diameter of the rolls in the sections corresponding to the maximum roll-separating force. This results in less deflection of the roll and, thus, alleviates the factors which contribute to variation of wall thickness on the Pilger mill.

One of the main problems in the production of casing is satisfying the GOST with respect to the straightness of the generatrix, particularly on the end sections (the allowable curva- ture is 1.3 mm per linear meter of tubing).

If we consider that about 90% of the tubes produced on the TPU 168-325 is casing, then the importance of eliminating or significantly reducing end curvature becomes evident. It was proposed that this problem be solved by redistributing the strains so as to reduce the total reduction of the tube radially on the sizing mill and correspondingly increase strain on the Pilger mill and reducing mill. However, it is known that such a change in deformation gen- erally results in lower productivity on the Pilger mill.

Using a mathematical model fo@ optimization, we studied different variants of strain distribution and their effect on the performance indices of the tube-production unit. We also determined the optimum strain on the Pilger mill and we optimized the dimensions of the semifinished product and rolls, tube cutting, and mill operating regimes. The results ob- tainedon a computer were checked under production conditions. We studied factors affecting the accuracy of the rolled tubes (especially the amount of end curvature), metal consumption, and mill productivity. As a result, we developed a rollingschedule which not only alleviates end curvature on the tubes but maintains the present productivity of the mills.

Ural Scientific-Research Institute of the Tube Industry (UralNITI). Severskii Pipe Plant, Translated from Metallurg, No. 5, pp. 38-39, Nay, 1987.

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