Method for measuring the length of straight seam steel pipe

The high-frequency induction coil of the straight seam steel pipe should be as close as possible to the position of the extrusion roller. The internal stress of the steel pipe is small and evenly distributed, which can effectively prevent stress corrosion cracking, high dimensional accuracy, and facilitate on-site welding construction. If the induction coil is far away from the extrusion roller, The effective heating time is longer, the heat-affected zone is wider, and the strength of the weld seam decreases; on the contrary, the edge of the weld seam is insufficiently heated, and when the heat input is insufficient after extrusion, the edge of the weld seam being heated cannot reach the welding temperature, and the metal structure remains. It remains solid and forms incomplete fusion or incomplete penetration; when the input heat is insufficient, the heated weld edge exceeds the welding temperature, resulting in overheating or molten droplets, causing the weld to form a molten hole. The impedance is one or a group of special magnetic rods for welded pipes. The cross-sectional area of the impedance should generally not be less than 70% of the inner diameter of the steel pipe. A proximity effect is generated, and the eddy current heat is concentrated near the edge of the tube blank weld, causing the edge of the tube blank to be heated to the welding temperature. Using the process of pre-welding and then precision welding, the welding process is stable and the weld seam is high. The resistor of the straight seam steel pipe is dragged inside the tube blank with a steel wire, and its center position should be relatively fixed close to the center of the extrusion roller.

1. Grating ruler length measurement.
The basic principle is: that two fixed-length grating rulers are installed outside both ends of the straight-seam steel pipe. A rodless cylinder is used to drive the grating ruler close to both ends of the steel pipe. The interference phenomenon of light is used to measure the length of the straight-seam steel pipe. It is characterized by high accuracy. However, grating scales are expensive and difficult to maintain and are sensitive to the effects of dust and site vibration.

2. Camera length measurement.
Camera length measurement uses image processing to measure the length of steel pipes. The principle is to install a series of equidistant photoelectric switches on a certain section of the straight-seam steel pipe conveying roller and add a light source and camera to another section. When the steel pipe passes through this area, the length of the steel pipe can be determined based on the position of the image captured by the camera on the screen based on a certain photoelectric switch. The characteristic is that it can realize online measurement, and the length data can be obtained when the steel pipe passes through the length measurement area without any interval. The disadvantage is that if a special light source is not used, the steel pipe will be interfered with by external light. When a special light source is used, the brightness of the steel pipe end after chamfering is high and the reflection of light is strong, which can easily cause reading errors.

3. Encoder length measurement.
The principle is to install an encoder at the oil cylinder, use the oil cylinder to push the steel pipe to move on the roller table and install a series of photoelectric switches at equal distances on the other side. When the steel pipe is pushed by the oil cylinder and the end of the pipe touches the photoelectric switch, the recorded encoder reading is, to convert the stroke of the oil cylinder, so that the length of the steel pipe can be calculated. The characteristic is that the steel pipe needs to be raised when measuring length. In addition, there are errors in photoelectric switch detection, which may require adequate measurement.

4. Improved encoder length measurement.
This method is an indirect measurement method. By measuring the distance between the two end faces of the steel pipe and their respective reference points, the length of the steel pipe is indirectly measured. Set up one length-measuring trolley at each end of the steel pipe, with the initial position being zero and the distance L. Then move the length of the editor to the walking distance (L2, L3) of the respective steel pipe ends, L-L2-L3, which is the length of the steel pipe. This measurement method overcomes difficulties such as the large volume of the steel pipe, the complex environment of the production site, and the inability of the measurement mechanism to pass through the lower support platform of the steel pipe. This method is easy to operate, the measurement accuracy is within ±10mm, and the repeatability is ≤5mm.