(1) Measuring the inner diameter of small O-ring with cone rod. The measuring range is below 50mm of QQ section 2070619135434.jpg, and the measuring error is not more than (+0.02mm). The O-ring of the same inner diameter specification can use the same cone rod, without considering the cross-sectional diameter of the ring. As shown in Fig. 1, it is a set of steel rods with 1:100 taper. There is a diameter groove on the cone rod at every distance of 10 mm. The accuracy of each diameter groove is 0.1 mm, which can be estimated to be 0.01 mm. When measuring, the O-ring slides down along the cone rod and reads out the diameter scale at the stop. In order to make the O-ring coaxial along the cone rod, the guide sleeve is designed. In order to make the O-ring stop without space between the cone rod and the cone rod, the size of the compression code should be appropriate. The inner diameter of the compression code is 0.1 mm larger than the thick end of the cone rod, and the wall thickness is 6 mm. The height varies with the hardness of the rubber ring. Within the range of low, medium and high hardness, the pressure code height is 3, 6 and 15 mm, respectively. For conical rods above 40mm in QQ section 20170619135434.jpg, the compression height should be 1.5 mm, 3 mm and 6 mm, respectively. When the weight of the compression code is doubled or decreased, the measurement error is only 0.01-0.02 mm, so the weight selection of the compression code is not very strict.
(2) SM flexible ruler can be used to measure the inner diameter of rubber O-ring in QQ section 20170619135434.jpg55-380mm. Flexible ruler is made of translucent film (macromolecule material). The principle of reading is basically the same as that of vernier calipers. The method is simple, easy to master, and can directly roll the flexible ruler from the tail into a circle close to the measured object. The flexible ruler is opened or tightened by two fingers with rubber finger sleeve. Before using, the flexible ruler contacts the tested sealing ring circle, and reads the value shown by the double coincidence lines of the main ruler and the sub ruler of the flexible ruler, that is, the inner diameter of the tested sealing ring. When measuring, attention should be paid to placing the O-ring on a smooth and flat glass or plastic plate. In the measurement, the flexible ruler should not be stretched (or tightened) to avoid the error caused by the deformation of the sealing ring. The force level of flexible ruler is similar to that of caliper.
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