The inspection method for cast iron rulers according to the latest national standards
1. Check the straightness of the working surface of the cast iron ruler
Use equal height blocks to support the Type I and Type II straightedge at the standard support marks 2L/9 from both ends of the straightedge, and select the appropriate bridge deck according to the length of the working surface of the straightedge (usually 8-10 steps, with a span between 50 and 500mm); Then place the bridge deck at one end of the ruler and fix the reflector or level on the bridge deck; The bridge deck is gradually moved from one end of the flat ruler to the other end according to the span, and the reading at that position is taken from an autocollimator with a division value of 1 "(or 0.005mm/m) or an electronic level with a division straight of 0.001mm/m (a composite level with a division value of 0.01mm/m can be used for a first level flat ruler with a working face length greater than 500mm, and a frame level with a division value of 0.02mm/m can be used for a second level flat ruler) for each span moved; The difference between its maximum and minimum values is the straightness error of the straightedge working surface. The straightness error of any 200mm on the working surface can be determined by selecting 50mm or 100mm bridge slabs and inspecting them within any 200mm using the above method.
For flat rulers with a working face width greater than 60mm, they should be inspected according to the flatness requirements, and the flatness tolerance value should not exceed the straightness tolerance value specified in Table 2.
2. Check the contact point area ratio of cast iron ruler
Apply display agent to the working surface of the inspected ruler, grind it onto a flat plate or ruler with an accuracy not lower than its precision, and display obvious contact points on the working surface of the inspected ruler. Then use a transparent thin plate (such as an organic glass plate) with 200 small squares of 25.mm × 2.5mm engraved within a range of 50mm × 25mm, and place it at any position on the working surface of the inspected ruler. Observe the proportion of the area containing contact points in each square in sequence (in units of 1/10). Calculate the sum of the above ratios and divide by 2 to obtain the ratio of the contact point area of the detected area.
3. Verify the perpendicularity of the side of the cast iron ruler to the working surface
Place the ruler on a flat surface and align the gauge holder with a dial indicator with a division value of 0.001mm to zero on a standard square ruler using a standard round rod. Then, in the same way, the dial indicator is placed against one side of the ruler, and the reading of the dial indicator is the perpendicularity error of that side. Similarly, detect the perpendicularity error of the other side and take the maximum error value.
4. Check the parallelism between the upper and lower working surfaces of the cast iron ruler
Place the ruler on a precision flat plate with the working surface as the base, and use a micrometer with a division value of 0.001mm mounted on the gauge holder to measure the height difference at no less than three points on its working surface, which is the parallelism error.
When a suitable flat plate is not available, it is allowed to place the side of the ruler on a supporting surface and measure the height difference of the ruler using a lever micrometer with a division value of 0.002mm or a gauge with a division value of 0.002mm.
5. Check the natural deflection of cast iron ruler
Support the ruler with equal height blocks at the standard support marks 2L/9 from both ends of the ruler and place it on the reference plane. Use an indicator or comparator with a scale of 0.001mm to measure the reading in the middle of the working face length; Then move the height block to the maximum support distance position (at both ends of the ruler), stabilize for 10 minutes, and read it with an indicator or comparator; The difference Y between two readings is the natural deflection of the ruler.