How to measure the length of welded steel pipe

The blanks used for welded steel pipes are steel plates or strips. With the rapid development of continuous rolling production of high-quality strip steel and the advancement of welding and inspection technology, the quality of welds has been continuously improved, and the varieties and specifications of welded steel pipes have increased day by day, and seamless steel pipes have been replaced in more and more fields. Welded steel pipes have lower cost and higher production efficiency than seamless steel pipes. Welded steel pipes are divided into straight seam welded pipe (LSAW steel pipe) and spiral welded pipe (SSAW steel pipe) according to the form of weld seam. Classification by production method: process classification - arc welded pipe, electric resistance welded pipe, (high frequency, low frequency) gas welded pipe, furnace welded pipe.

According to the different technical requirements of the manufacturer, according to the different technical requirements of the manufacturer, the length measurement system has a variety of length measurement methods.

1. Camera length measurement. Camera length measurement uses image processing to measure the length of welded steel pipes. The principle is to install a series of equidistant photoelectric switches on one section of the welded steel pipe conveying roller table, and add a light source and a camera to the other section. When the welded steel pipe passes through this area, the length of the welded steel pipe can be determined according to the position on the screen of the image captured by the camera at a certain photoelectric switch. It is characterized in that online measurement can be realized, and length data can be obtained when the welded steel pipe passes through the length measurement area without intervals. The disadvantage is that if the special light source is not used for lighting, the welded steel pipe will be disturbed by the external light. After using the special light source, the welded steel pipe will reflect strong light due to the high brightness of the pipe end after chamfering, which will easily cause reading errors.

2. The basic principle of measuring the length of the grating ruler. Two fixed-length grating rulers are respectively installed on the outside of the two ends of the welded steel pipe. The grating ruler is driven by a rodless cylinder close to the two ends of the welded steel pipe, and the length of the welded steel pipe is measured by using the optical interference phenomenon. It is characterized by high precision. However, encoders are expensive and difficult to maintain, and are sensitive to dust and field vibrations.

3. The principle of encoder length measurement is to install an encoder on the oil cylinder, use the oil cylinder to push the welded steel pipe to move on the roller table, and install a series of equidistant photoelectric switches on the other side. When the welded steel pipe is pushed by the oil cylinder and the end of the pipe touches the photoelectric switch, the stroke of the oil cylinder is converted from the recorded encoder reading, so that the length of the welded steel pipe can be calculated. It is characterized in that the welded steel pipe needs to be lifted when measuring the length. In addition, photoelectric switch detection also has certain errors, which may require comprehensive measurement.

4. The improved encoder length measurement method is an indirect measurement method. The length of the welded steel pipe is measured indirectly by measuring the distance between the two end faces of the welded steel pipe and their respective reference points. A length measuring trolley is set at each end of the welded steel pipe, the initial position is 0, and the interval is 1. Then move the editor length to the travel distance (L2, L3) at both ends of the welded steel pipe, where L-L2-L3 is the length of the welded steel pipe. This measurement method overcomes the difficulties of the large volume of the welded steel pipe, the complex environment of the production site, and the inability of the measurement mechanism to pass through the lower support frame of the welded steel pipe. The method is simple to operate, the measurement accuracy is within 10≤5 mm, and the repeatability is ≤5 mm.

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