Español
Pусский
If the flatness of a certain mechanical seal is 0.0009, the value cannot be tested by the ordinary gauges, and the interference effect of light wave is usually used to conduct such testing.
What is the interference effect of light wave？According to the principle of wave theory,the conditions for two waves to interfere are: ① the two waves have the same vibration direction at the meeting point;②the two waves have the same frequency;③ two waves have a fixed phase difference at the meeting point (two identical sodium lamps will not work, only the light emitted by the same light source can be divided into two beams to meet the coherence condition).
What is the interference effect of light wave？According to the principle of wave theory,the conditions for two waves to interfere are: ① the two waves have the same vibration direction at the meeting point;②the two waves have the same frequency;③ two waves have a fixed phase difference at the meeting point (two identical sodium lamps will not work, only the light emitted by the same light source can be divided into two beams to meet the coherence condition).
The superposition effect of two beams of light satisfying the coherent condition is: where the wave path difference is an integer multiple of the wavelength, the light intensity is strengthened; where the wave path difference is an odd multiple of half a wavelength, the light intensity is reduced to zero (darkening) . This is the principle of light interference. see picture below：
Then how to use the light wave interference effect to test the flatness of the sealing faces of the mechanical seal? The principle of flatness test is as follows:
Let the incident angle i=0, e is the thickness of the gas film (that is, the distance from the point on the surface to be detected to the flat crystal), λ is the wavelength of the light wave, and δ is the wave path difference of the light, then δ=2e+λ/2. when δ=kλ , the points on the detected surface become darker; δ=(2k+1)λ/2, the points on the detected surface become brighter; (where k=0,1,2,3,4,...,k is an integer)
Let the incident angle i=0, e is the thickness of the gas film (that is, the distance from the point on the surface to be detected to the flat crystal), λ is the wavelength of the light wave, and δ is the wave path difference of the light, then δ=2e+λ/2. when δ=kλ , the points on the detected surface become darker; δ=(2k+1)λ/2, the points on the detected surface become brighter; (where k=0,1,2,3,4,...,k is an integer)
The following conclusions can be drawn from the above formula: (i) The gas film thickness difference (height difference) between two points corresponding to two adjacent light bands is λ/2, (for sodium lamp λ=0.589µm, λ/2≈ 0.3µm) (ii) two adjacent light bandwidths b=λ/2Sinθ, (θ is the air film inclination angle) (iii) when e=0, δ=λ/2 (half-wave loss), dark fringes appear.
According to this principle, the obtained qualified light band (this means the flatness test of the mechanical seal is qualified) is as follows:
