How to detect the flatness of the sealed end face
Thread Content
Flatness (also known as straightness) is an important quality parameter for sealing rings, with a requirement of within 0.0009 mm; such a precision level cannot be measured using ordinary measuring tools. The accurate and rapid method is light interference. It requires an optical plate and a monochromatic light source, usually a sodium lamp. During testing, the flat plate is placed on the sealed surface to be inspected, and an sodium vapor lamp is used to shine light obliquely from above (Figure 15) to count the number of interference fringes. The wavelength of sodium light is 0.6 μm; each interference fringe corresponds to half of this wavelength, meaning that one interference fringe is 0.3 μm long. The flatness of the sealed surface can be determined by the number of interference fringes.
Light interference method is a very accurate way to detect the flatness of sealed end faces. When using the optical interference method to detect the flatness of a sealed end face, the general procedure is as follows: 1. Prepare tools: prepare an optical flat (optical flat plate) and a monochromatic light source (such as a sodium lamp). The quality of the optical flat must be extremely high, with a flatness higher than that of the sealing surface being inspected, so that it can serve as a reference. 2. Clean the surface to be tested: Ensure that the sealing surface is clean, free of dust or other contaminants. Any contamination can affect the clarity and accuracy of the interference pattern. 3. Place the optical flat: Position the optical flat on the sealed surface to be inspected, ensuring as perfect a contact as possible between the two. 4. Irradiation with monochromatic light: Shine a sodium lamp from an oblique upward direction; the light must pass through an optical birefringent plate and be reflected back to the sealed end face. Sodium vapor lamps emit yellow light of almost a single wavelength, approximately 0.6 μm. 5. Observe the interference fringes: Observe the interference fringes formed at the contact point between the two planes. When two planes are nearly perfectly parallel, a set of uniform, parallel interference fringes is formed. 6. Calculate flatness: Measure the number and distribution of interference fringes. Since each interference fringe represents a height difference of half a wavelength (i.e., 0.3 μm), the flatness of the sealed surface can be evaluated by counting the number of fringes. If the stripes are evenly distributed and in small numbers, it indicates good flatness ； If the stripes are messy or numerous, it indicates a significant deviation in flatness. 7. Analysis results: Based on the pattern analysis of the interference fringes, it is determined whether the flatness of the sealed surface meets the specified requirement (within 0.0009 mm). Please note that interferometric testing requires a relatively stable and controlled environment, as environmental factors such as temperature and air flow can also affect the formation of interference fringes. Furthermore, the operator requires certain technical knowledge and experience to perform such measurements. .
I’ve learned about it; I’ve seen it at the pump factory. I’ll operate it next time I go there