Introduction to knowledge of metallographic microscopes
There are many types and types of metallographic microscopes, the most common ones are desktop, vertical and horizontal. The structure of a metallographic microscope usually consists of three major parts: an optical system, an illumination system, and a mechanical system. Some microscopes also come with a variety of functions and photography devices. At present, microscopes have been connected to computers and related analysis systems, making metallographic analysis and research work more convenient and faster.
1. Optical system
Its main components are the objective lens and eyepiece, which mainly play a magnifying role. and get clear images. The quality of the objective lens directly affects the quality of the image. The eyepiece magnifies the image magnified by the objective lens again.
2. Lighting system
Mainly includes light sources and illuminators as well as other major accessories
(1) Type of light source
Including incandescent lamps (tungsten lamps), tungsten halogen lamps, carbon arc lamps, xenon lamps and mercury lamps, etc. Commonly used are incandescent lamps and xenon lamps. Generally, incandescent lamps are suitable for use as light sources on medium and small microscopes, with a voltage of 6-12 volts and a power of 15-30 watts. The xenon lamp is ignited by instantaneous pulse high voltage. Generally, the normal operating voltage is 18 volts and the power is 150 watts. It is suitable for observation and photography of special functions. Generally, large metallographic microscopes are often equipped with two illumination sources at the same time to adapt to ordinary observation and special observation and photography.
(2) Lighting method of light source
There are mainly critical lighting and Kohler lighting. Astigmatism lighting and parallel light lighting are suitable for use in special situations.
1) Critical illumination: The image of the light source is focused on the surface of the sample. Although high brightness can be obtained, the uniformity of the brightness of the light source itself is very high. Currently rarely used.
2) Kohler illumination: The characteristic is that the primary image of the light source is focused on the aperture diaphragm, and the field diaphragm and the primary image of the light source are focused on the sample surface at the same time, providing a very uniform illumination field, which is currently widely used.
3) Astigmatism lighting: It is characterized by low lighting efficiency and is only suitable for projection tungsten lighting.
4) Parallel light: The lighting effect is poor. It is mainly used for dark field lighting and is suitable for various light sources.
(3) Light path form
According to the form of optical path design, there are two types of microscopes: upright and inverted. The one with the ground surface of the sample facing upward and the objective lens pointing downward is the upright type, while the one with the ground surface of the sample facing downward and the objective lens pointing upward is the inverted type.
(4) Aperture diaphragm and field diaphragm
The aperture diaphragm is located near the light source and is used to adjust the thickness of the incident light beam to change the quality of the image. Reducing the aperture diaphragm can reduce spherical aberration and off-axis aberration, increase contrast, and make the image clear, but it will reduce the resolution of the objective lens. The field diaphragm is located on another bracket. Adjusting the size of the field diaphragm can change the size of the field of view. The smaller the field diaphragm, the better the image contrast. Adjust it to the same size as the eyepiece field of view during observation.
(5) Color filter
It is used to absorb the unnecessary part of white light and only let light of a certain wavelength pass through to obtain excellent images. Generally there are yellow, green and blue.
3. computer system
It mainly includes the stage, lens barrel, adjustment screws and base.
(1) Stage: used to place metallographic samples.
(2) Lens barrel: used to connect objective lenses, eyepieces and other components.
(3) Adjustment screws: There are coarse adjustment screws and fine adjustment screws for image focus adjustment.
(4) Base: plays the role of supporting the mirror body.
