Problems Encountered in Seamless Steel Tube Rolling and Solutions

For many years, on-line inspection of the diameter of round products has been standard practice in production processes such as extrusion, galvanizing, and wire drawing. In most cases, a caliper or a camera with a computer-controlled display is used with a typical measurement tolerance of a few microns. These instruments are increasingly being used in finishing operations such as centerless polishing of bars, trimming, and the like.

However, in the production of hot rolled tubes, these instruments are used relatively rarely because of the harsh environment and large diameter. The purpose of this paper is to illustrate the detection of the outer diameter of the steel pipe under the above-mentioned environment and through the online communication function with the host computer, to input the measurement data in real time for the control system to achieve control, and the caliper is used in the seamless steel pipe production plant. And used very successfully.

A steel pipe made of a single piece of metal with no seams on its surface is called a seamless steel pipe. According to the production method, the seamless pipe is divided into a hot rolled pipe, a cold rolled pipe, a cold drawn pipe, an extruded pipe, a top pipe, and the like. The maximum diameter is 650mm and the minimum diameter is 0.3mm.

Obviously, if a system can measure the outer diameter and wall thickness simultaneously, this would be an ideal system. However, from the working principle of the current generation of instruments, it is not feasible to measure products with tight tolerances. Therefore, this paper mainly introduces the on-line measurement of the outer diameter and the off-line detection of wall thickness, outer diameter and inner diameter.

1. Problems encountered in seamless steel pipes

Accurate measurement of the outer diameter of the steel pipe under actual production conditions is not an easy task. Production conditions are:

– high temperature, typical temperature is 700 ° C ~ 1100 ° C or higher;

–high speed;

– have radial displacement and vibration;

– the pipe end is deformed;

– have iron oxide skin;

– steam and smoke;

– There are splashes;

– The measuring instrument is subjected to shock and vibration.

Therefore, the problem faced by the in-line measurement system is that the measurement is performed reliably, accurately, and stably within a tolerance of a few hundredths of a millimeter (0.01 mm). The most important thing is to maintain this performance in continuous production year after month, year after year.

2, caliper

For the detection of the outer diameter of the seamless steel pipe, it is necessary to overcome the problems of high temperature, high speed, iron oxide scale, steam smoke, vibration, large diameter and the like. To this end, we have adopted a solution.

Firstly, the optical measuring principle is adopted for the detection of the seamless steel pipe to realize the non-destructive measurement. The photoelectric measuring head adopts the spacing double barrel tube probe mode, and the measuring head distance can be automatically adjusted, so that the outer diameter detection of various specifications can be realized. The detection of a variety of seamless steel tubes in production is also achievable. The optical measuring device can realize high-precision online non-destructive testing, and the measurement can achieve real-time measurement. The measuring frequency can reach 500Hz~1000Hz, achieving high-speed measurement.

Secondly, the caliper adopts positive pressure shunt cooling and dustproof technology, and uses high pressure blower to achieve sweeping and dustproof, clearing the iron oxide scale, water mist dust and other interference near the probe, and has a steel guide groove to guide the seamless steel pipe. Through the caliper, the whole cast iron structure is adopted, and the device adopts industrial devices to ensure accurate measurement in a vicious environment. At the same time, the probe part is equipped with a cooling and dustproof system, so that it can measure the seamless steel pipe under high temperature conditions. , 700 ° C ~ llOO ° C detection can be.

After many experiments, we found that there are two main reasons for the jitter error: First, the image of the CCD chip has a ghost phenomenon when the object is shaken, resulting in a decrease in the voltage difference between the output of the CCD chip and an increase in the width; Acquisition and communication transmissions are not synchronized, and signals at different times combine to cause data confusion. By using an imported LED light source with a brightness above 50,000mcd, we reduced the exposure time of the probe to 100 microseconds, which is equivalent to a sampling frequency of 10000 Hz. Eliminates the ghost phenomenon when the measured object shakes. At the same time, multiple synchronization technologies such as light source-signal acquisition unit pulse synchronization, multi-channel acquisition synchronization, signal acquisition-communication transmission synchronization, etc. are adopted in the circuit system, and the jitter error is completely eliminated. Therefore, the vibration in the seamless steel pipe rolling does not affect the accuracy of the measurement.

The caliper solves the problems encountered in rolling, and there are not many vulnerable parts inside the caliper. It has a long service life and can be used for a long time. It only needs to be cleaned and maintained regularly, with simple maintenance and short time. It brings great convenience to the uninterrupted measurement of seamless pipe. The caliper measurement can obtain a variety of information such as maximum diameter, minimum diameter, average diameter, and ellipticity.

3, pipe end defects

The pipe end of the seamless steel pipe is very easy to produce defects. To solve this problem, after the seamless steel pipe is produced, the pipe end defect laser thickness gauge can be used for measurement.

3.1, tube end defect detection

End-of-pipe defect detection uses industrial camera capture and image processing techniques to detect tube end defects and to issue a “cut” or “release” signal to the dicing saw and conveyor equipment based on the test results. The image processing method is to identify whether there is a section of the collapsed pipe wall and the amount of collapse in the inner hole of the steel pipe under the statistical model, and then determine whether the pipe end needs to be sawed.

3.2, tube end laser thickness gauge

The seamless steel pipe will have defects such as uneven wall thickness at both ends of the pipe after rolling, so each steel pipe will be cut off at both ends. Since the length of the tube end where each tube has defects is not equal, it is difficult to determine the specific cut length at the time of excision. The pipe end wall thickness detecting device determines the length of the pipe end with defects by continuously detecting the wall thickness, and marks the defect and the qualified part boundary line by the marking machine, thereby providing a dimensional basis for the pipe cutting process. In addition to measuring the wall thickness, the tube end laser thickness gauge can also detect the inner diameter and outer diameter of the part.

Conclusion

The application of measuring equipment in the production of seamless steel tubes ensures the inspection of different sizes of steel pipes, displays a variety of data in production, and tests various information required for the process. By monitoring the relevant diameters, early detection of roll wear or Other problems in production, increase productivity (monitoring quality trends). It brings great convenience to the production of seamless steel pipes and enhances their quality.

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