The exact characteristics of the surface texture have become remarkably important. On the one hand, surface texture is a key effective and reliable factor on a component, and on the other hand, its measurement and analysis can be used as an excellent diagnostic tool to know how to produce the desired surface.
The surface profile requires a better method than the old nail drawing test on a surface, which includes accurate measurements and special analysis. By moving the nail on a surface, the smooth surface can certainly be distinguished from the rough surface. A good machinist may be able to create a comparable level by using an example of an accurate level for comparison. In The Industrial Inspection Method, the author states that if the fingertip moves along the surface or at a speed of approximately 2.5 cm / s, the irregularity and roughness of the surface can be felt up to 22 micrometers. However, the real problem with the finger-contact method, and most traditional and older methods, is that they try to reveal only the roughness of the surface, while the surface texture contains many complex and interdependent internal properties. Although it has long been recognized the importance of the role of the surface in the scientific treatment of a component, the main interest in the texture of the surface has been further developed due to the need to control the manufacturing process.
The surface texture is very sensitive to changes in production method, a change even in the composition of the raw material or the surface hardness of the part will be reflected as a change in the texture of the machined surface. Tool erosion, strain on materials and improper machining conditions and environmental conditions can all have traces and effects on the surface.
In order to indicate the unevenness of the surface in general, the symbol √ is used. The surfaces that belong to mechanical operations without chipping and the surfaces that belong to mechanical operations with chipping are used with the symbols √0 and., Respectively. The table below shows the comparison between surface quality marks in different standards.
The position of the surface quality indicator marks is shown as follows:
a: means the same Ra with roughness height
b: Surface production method: such as heat treatment, chemical, stone making and other operations related to the surface.
c: Test sample length
d: For fibers
e: Depth of cut
Roughness measurement methods
The following methods can be used to measure the roughness of surfaces:
1- Comparative method:
The simplest means of measuring surface roughness is to compare the surface roughness of the workpiece with the surface of the inventory samples, which have a certain roughness height. They determine the comparison and the size of the roughness.
Ra roughness determination table
The ISO standard has 12 steps or classes for shaping and classifying levels in terms of payment, such as the following table:
2. Digital roughness gauge
Electromechanical gauges are commonly used to measure surface roughness in series work. In this machine, a touch bar with a very fine diamond tip is pulled on the work surface about 6 to 10 mm, the end of this rod is located inside the bucket. Due to the unevenness of the work surface, the touch bar moves up and down inside the bucket, breaking the lines of force in the coil, creating a weak magnetic current. Current changes are transmitted to the hand by amplifiers and are readable on a calibrated screen in units of surface roughness. In some of them, surface roughness changes are printed on the tape simultaneously. On these devices, a key is usually installed, which is used to select different rows of roughness.
The important points in choosing a digital roughness meter are as follows:
• Measurement accuracy
• Ability to measure various parameters (roughness RA, RZ, RY, Rq, Rp, RT, RMAX, RV, R3Z, RS, RSM, RSK, RMR)
• Type of measurement (METRIC um, Imperial, inch)
Ability to connect to a computer or printer
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