Introduction to the measurement method of the inner diameter and aperture of precision steel pipes

First, direct measurement (the most commonly used measurement method, which is often used in the production and inspection process of our precision steel pipes)

The method of directly measuring the aperture using two or three-point positioning is also the most commonly used aperture measurement method. According to the accuracy level, size and quantity of the aperture to be measured, general length measuring tools that can measure the aperture can be used, such as vernier calipers (see calipers), tool microscopes, universal length comparators, horizontal length gauges (see length measuring machines), horizontal optical meters (see comparators) and pneumatic measuring instruments, etc.; special aperture measurement tools can also be used, such as internal diameter micrometers, internal diameter dial indicators and dial indicators, internal diameter micrometers, electronic plug gauges and aperture measuring instruments based on pneumatic, optical, electrical and other principles.

① Use a lever mechanism to measure the hole: commonly used in hand-held aperture measurement tools, such as internal diameter dial indicators, mechanical or electrical internal diameter micrometers, etc. The difference between the measured aperture size and the calibration ring gauge aperture is read from a dial indicator, or mechanical or electrical micrometer through a lever mechanism. The measuring aperture range of this type of hole measuring tool is generally 10 to 800 mm, among which the measurement accuracy of the internal diameter micrometer can reach 3 to 5 microns.
② Using the wedge principle to measure the aperture: It is also commonly used in hand-held aperture measuring tools. Among them, the internal diameter dial indicator used to measure small holes can measure holes as small as 0.5 mm in diameter. When the measured aperture compression probe moves the measuring rod with a cone, the aperture error can be read from the dial indicator or micrometer. The three-point positioning method is suitable for measuring holes with a diameter of more than 3 mm. When the measuring rod rotates, the measuring rod moves forward by the fixed nut, and the three measuring heads move outward through the cone with a spiral boss at the top of the measuring rod to contact the measured hole. Read the measured aperture size from the scales on the fixed sleeve and the differential cylinder. This type of aperture measurement tool includes a three-jaw internal diameter micrometer.
③ The seat-type aperture gauge made of pneumatic, optical, electric, and other principles must be used to measure high-precision apertures at a constant temperature close to 20°C. The range of aperture measurement of the light wave interference aperture gauge is 1 to 50 mm, with an accuracy of ±0.5 microns.

Second, indirect measurement (when there is a dispute between the supply and demand sides of the steel pipe size, we will consider using this method to verify the accuracy of the measurement data)

First measure the function related to the aperture, and then convert the aperture size. There are mainly two methods: ① Using the principle of three points to determine a circle, measure the coordinate values of any three points on the circumference of the measured hole, and then calculate the coefficients D, E, and F in the equation x2＋y2＋Dx＋Ey＋F＝0, and then calculate according to the calculation formula
② Use a roller with a known diameter to roll against the wall of the measured hole, measure the circumference of the measured hole, and then calculate the aperture. This method is suitable for measuring holes with a diameter greater than 500 mm and a continuous surface. The measuring tool that applies this method is called a large-diameter measuring instrument, which is also often used to measure the outer diameter of large workpieces. (However, this measurement method is not very accurate. Some scholars have also studied methods such as multi-roller measurement and computer simulation calculation to improve accuracy, but I think it has little practical value.)

Third, comprehensive measurement
It mainly uses a smooth plug gauge to check whether the inner hole of the steel pipe or the mechanical workpiece is qualified by the pass-stop method. I will not explain it here.