JPS6052368B2 - Glassy coating surface stress measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring surface stress of vitreous coatings.

So-called vitreous coatings include enamel applied to the surface of copper utensils, enamel applied to the surface of cast iron utensils, enamel or cloisonné applied to the surfaces of aluminum, brass, copper, etc., and enamel applied to the surface of ceramics. The glaze applied, etc.
Many things are deeply related to life.

The surface stress of these coatings plays an important role for the following reasons. First, in order for the coating to adhere well to the substrate, to withstand thermal shock and mechanical shock, and to be resistant to attack by chemicals, the coating must have an appropriate amount of compressive stress.

If the surface stress is tension, it will easily crack, peel easily, and have poor chemical durability. Furthermore, if the surface stress is an excessively large compressive force, spontaneous peeling, commonly referred to as "nail skipping", tends to occur. On the other hand, in the case of ceramics, the surface stress of the glaze is sometimes used as tension to cause cracks, and the resulting decorative effect is sometimes utilized.

The pattern produced by a crack and its fineness are determined by the tension, so it is necessary to select an appropriate tension depending on the purpose.
Conventionally, in the case of ceramics, the surface stress of these glassy coatings has been measured by cutting the object to be measured perpendicular to the coating surface to prepare a thin sample, and measuring the photoelastic effect of transmitted light. There are ways to measure stress.

In the case of enamel, a thin plate is made from the same material as the substrate to be coated, one side of the thin plate is coated with enamel, fired, and the degree of warpage of the thin plate is measured when it is cooled to room temperature. Methods for estimating surface stress are known. This method does not directly measure the coating on the object itself, but indirectly estimates the surface stress using a simulated test plate. However, the former method of measuring the photoelastic effect is a destructive test, which is laborious and expensive, and cutting into a thin sample partially relieves stress, so the measured value is not the true value. The problem was that it deviated from the original.

Note that even if this method is applied to enamel, the measurement is generally difficult because the enamel layer is destroyed during the preparation of the thin sample. In addition, the latter method of measuring the degree of warpage of a mock test plate cannot be applied when the substrate is made of a material that is difficult to make into a thin plate, such as cast iron, or when the substrate is made of cast iron, alloy steel, or non-ferrous alloys. If the material is a material whose thermal expansion characteristics change due to heat treatment, there is a high possibility that the measured value will differ from the surface stress value of the actual object to be measured.

In this way, the conventional measurement methods do not directly measure the coating surface stress of the actual object to be measured, but instead involve destructive inspection or measurement using a simulated test plate. Due to its drawbacks, it has not been a satisfactory method for measuring the surface stress of vitreous coatings.

Therefore, the present invention aims to provide a device that can directly measure the surface stress of a vitreous coating of an object to be measured such as an actual instrument by destroying it, and in particular relates to a device for measuring surface stress of a vitreous coating. . The present invention will be explained below from its basic principle.

In a glassy coating layer, the principal stress normal to the surface is generally zero since the surface is a free surface.

Therefore, stress exists only in the direction parallel to the surface. When light travels through such a medium, there is a difference in refractive index due to the photoelastic effect between light that travels while vibrating parallel to the surface and light that travels while vibrating perpendicular to the surface. This refractive index difference Δn is determined by the surface stress p(K9/c!i) and the photoelastic constant C(Kg/d)-1 of the coating.
−ν is determined according to the equation.

Therefore, if the photoelastic constant C is known, the refractive index difference Δn
By determining the surface stress p, the surface stress p can be determined.
The vitreous core of the present invention utilizes the above basic principle. - The surface stress measuring device of the coating has two
Surface stress can be determined simply by knowing the difference in the critical refraction angles of different types of polarized light, allowing for simple and quick measurement.

That is, the device of the present invention includes a light source of coherent light, a light projection mechanism for projecting the coherent light from the light source onto a vitreous coating layer, and a vitreous coating layer that can be installed on one side in close contact with the surface of the vitreous coating layer. An exit prism having a larger refractive index than the coating layer, a telescope for measuring the critical refraction angle at the interface between the coating layer and the exit prism for the exit light, and selecting polarization in an arbitrary vibration direction for the exit light from the exit prism. It is characterized by comprising a polarization mechanism that transmits light and forms interference fringes.

FIG. 1 conceptually shows a part of the apparatus of the present invention.

1 is coherent light projected onto the vitreous coating 2 by a light projection mechanism, and 3 is the coating surface.

4 is an exit prism with one side in close contact with the surface 3, and 5 is an objective lens of the telescope.

Incident light 1 is projected onto the surface 3 of the coating layer 2 and produces scattered light within the enamel layer due to inhomogeneities of the enamel layer, such as emulsion particles, crystallites, small bubbles, etc.

Of the scattered light, light 6 that travels very close to the surface 3 and parallel to the surface 3 becomes a critically refracted light at the interface 3'' between the coating layer 2 and the prism 4, is extracted by the exit prism 4, and is focused at the focal point of the objective lens 5. Converges to a point 8 on surface 7.Surface 3
Other lights, such as 9 and 10, which do not travel parallel to , have an incident angle smaller than the critical refraction light when they reach the interface 3'', so they travel at points 11 and 10 above point 8 on the focal plane 7.
It converges to 12. Therefore, on the focal plane 7, the area above the point 8 is bright because the light reaches it, and the area below the point 8 is dark because the light does not reach it, and the point 8 is the boundary between bright and dark. The technique of determining the refractive index from the position of the boundary between brightness and darkness has already been adopted in Atsube's refractometers and the like. By the way, if surface stress exists in the coating, even if the light 6 travels parallel to the coating surface 3, there will be a difference in refractive index between the light vibrating parallel to the coating surface and the light vibrating perpendicular to the coating surface, as described above. Therefore, the position of the bright and dark boundary 8 is also different.

For example, by observing these two types of light through a polarizing plate 13 placed behind the focal plane 7, the boundary between bright and dark can be confirmed separately, and the refractive index difference Δn between the two can be determined. Can be done. However, with practical enamel and glaze, the surface is generally not flat and the refractive index within the coating layer is non-uniform, so the boundary between light and dark is not necessarily clear, and it is difficult to determine the refractive index difference with sufficient accuracy. I can't. In this respect, in the device of the present invention, as a result of using a coherent light source, the light that reaches the focal plane 7 forms fine interference fringes, and the prominent ones of these are used as targets instead of the boundaries between bright and dark. By doing so, the refractive index difference can be determined with sufficient accuracy. Examples of coherent light sources include gas laser light, gas discharge lamp light whose coherence is improved by passing through a pinhole, and incandescent light bulb light. This will be explained in more detail with reference to the embodiment shown in FIG.

An opening 22 is bored in the pedestal 21, and an exit prism 23 and an entrance prism 24 are fixed thereto. Also, the rotation fixed shaft 26 of the laser table 25 and the rotation fixed shaft 2 of the telescope 27.
8 is provided. The pedestal 21 has prisms 23 and 24
Legs 30 and 31 are provided so that one side of the test piece can be stably brought into close contact with the surface of the glassy coating 29 of the object to be measured.
On the laser table 25, a laser tube or an oscillation tube 32 including a laser tube and a reflection prism 33 are provided.
As shown in the figure, a laser beam 34 emitted from a laser oscillation tube 32 has its direction changed by a reflection prism 33 and is projected onto a coating layer 29 via an input prism 29. A turnbuckle mechanism 35 is provided between the upper end of the laser table 25 and one end of the pedestal 21, and the inclination angle of the laser table can be changed around the rotating fixed axis 26, thereby projecting the laser beam onto the coating layer. The angle can be changed as appropriate. The telescope 27 is also rotatable around a rotating fixed shaft 28, and can be fixed at an appropriate angle using a handle 36 that can be tightened and fixed with a screw and a grooved plate 38 that can slide the shaft 37 of the handle 36. can. The telescope 27 includes an objective lens 40 that converges the light from the exit prism 23 onto a focal plane 39,
In this case, there is a rotatable polarizing plate 41 between the objective lens 40 and the focal plane 39, and an eyepiece with a micrometer or an eyepiece for observing the interference fringe pattern imaged on the focal plane 39. It is equipped with 42. Prism 23, 24
The shafts 43 and 44 are loosely supported in shaft holes provided in the pedestal 21 to the extent that they can move a little, and the coating 2
The mutual positions can be variably determined according to the surface of 9. For measurement, a prism 2 is placed on the surface of the coating 29.
An immersion liquid having a refractive index close to that of 3 and 24 is dropped to ensure optical contact between the surface of the coating 29 and the prisms 23 and 24. Although the entrance prism 24 in the above embodiment is not essential to the present invention,
If this is used, the amount of light emitted by the exit prism 23 increases, which is advantageous in terms of measurement.

That is, as shown in a partially enlarged view in FIG. 3, if the refractive index of the entrance prism 24 is made larger than the refractive index of the coating layer 29, most of the incident light 1 will pass near the exit prism 23. , more light is extracted by the exit prism 23 and reaches the focal plane 39, making measurement easier. It is also effective when the incident angle of the incident light 1 to the interface 3'' is equal to the critical angle, so it is desirable to adjust the inclination angle of the laser table 25 in this way.On the other hand, the telescope 27 has an optical axis whose optical axis It is necessary to select the angle so that it is parallel to the emitted light.As can be understood from the above explanation, the device of the present invention can quickly and non-destructively measure the surface stress of a vitreous coating. It is extremely useful for process and quality control.

[Brief explanation of the drawing]

L Fig. 1 is a diagram explaining the basic principle of the present invention, Fig. 2 is a diagram showing an embodiment of the device of the present invention, and Fig. 3 is a diagram explaining the basic principle of the present invention.
It is a partially enlarged view of the figure. 23... Injection prism, 24... Input prism, 2
7... Telescope, 29... Glassy coating, 3
2. Loser single oscillator tube.

Claims (1)

[Claims] 1 A light source of coherent light, a light projection mechanism for projecting the coherent light from the light source onto the glassy coating layer, and a light projection mechanism that has a refractive index lower than that of the glassy coating layer, which can be installed in close contact with the surface of the glassy coating. A large exit prism, a telescope that measures the critical refraction angle at the interface between the coating layer and the exit prism for the exit light, and selectively transmits polarized light in any vibration direction for the exit light from the exit prism to form interference fringes. A surface stress measurement device for a glassy coating, characterized in that it is equipped with a polarization mechanism.