Tape surface roughness: what is it and why it matters

Surface roughness — a combination of irregularities and microdefects in the material that occur during its processing. These irregularities can be visible or hidden and vary in size, shape, and distribution. Even minor defects can significantly affect the performance of steel or alloy. Roughness has a negative effect on the mechanical and physical properties of the material, and in some cases determines the success or failure of the entire technological operation.

The value of roughness is important for many industries:

• Mechanical engineering: roughness affects friction between parts, which can lead to their rapid wear or a decrease in the efficiency of the mechanisms. It is especially important to take this factor into account for products operating under high loads and extreme temperatures.
• Electronics manufacturing: roughness affects the quality of soldering and assembly of components, as well as the reliability of electrical connections. Excessive irregularities can damage the tightness of the contacts.
• Construction: roughness affects the adhesion (adhesion) of building materials such as concrete, paint and other coatings.

In general, the control and management of roughness is an important aspect of the production of cold-rolled strip, which ensures the high quality of the final product and the efficiency of technological processes.

The main parameters of roughness

Several key parameters are used to assess the roughness of the tape. Each of them allows us to accurately describe various aspects of irregularities and their impact on the functionality of the material:

• Ra — arithmetic mean deviation of the profile — the parameter shows the average deviation of the profile from the midline at the base length. Ra gives a general idea of the height of irregularities and their uniformity. This is one of the most commonly used indicators for assessing roughness.
• Rz — the height of the irregularities at ten points — calculated as the sum of the arithmetic deviations of the heights of the five highest protrusions and the depths of the five deepest depressions relative to the midline at the base length. The parameter helps to estimate the maximum height of irregularities that affect performance.
• Rmax — maximum profile height — reflects the difference between the highest point and the deepest depression of the profile at the base length. Allows you to determine the maximum height of profile irregularities. It is used in design and quality control.
• Sm — the average pitch of irregularities — the average distance between irregularities on the surface. It is defined as the length of a section of the profile containing at least five irregularities. It allows you to estimate the average pitch of irregularities, as well as the effect of roughness on friction and wear. This parameter is especially important for products subject to dynamic loads.
• S — the middle pitch of local ledges — characteristics the average distance between local protrusions. The indicator makes it possible to estimate the average size of microgeometry elements that affect the physical and mechanical properties of the surface, such as adhesion to other materials and wear resistance.

Roughness measurement methods

For controls Contact and non-contact methods are used for surface roughness. Each has its own advantages and limitations.

Contact methods for measuring roughness

• Profilometers: devices that scan the surface with a diamond needle. Data on the movement of the needle are recorded by sensors, after which the roughness parameters (Ra, Rz, etc.) are displayed on the screen. This method is suitable for measuring both macro- and micronoughness.
• Contourographs: advanced devices that measure not only the profile, but also the contours of the surface. They are used for detailed analysis of microgeometry and provide accurate and complete information about surface roughness.

Optical methods for measuring roughness

They are based on the use of light to visualize and analyze the surface. They allow you to get images of the surface with high resolution and accuracy.

• Interferometers: devices that use light interference to obtain high-precision images of a surface — redistributing the intensity of the light flux due to the superposition of several light waves. The interferometric method makes it possible to measure macro- and micronoughnesses, which is important for high-tech industries.

Contact methods provide quick and accurate measurements of macronoroughness, but they can miss microdefects. Optical methods provide a more detailed view of surface microgeometry, but require more time to process the data.

Factors affecting the surface roughness of the tape

Roughness cold rolled strip depends on many factors, ranging from the quality of the source material to the operating conditions.

• The quality of the source material: irregularities on the surface of the raw material can lead to similar defects on the finished tape. For example, cracks and chips on the source material often cause high roughness.
• Tape production process: The technologies used and the configuration of the equipment greatly affect the surface quality. For example, improper adjustment of the rolling mill will lead to uneven belt tension, which will cause microroughness and other defects on the material surface.
• Operating and storage conditions: exposure to moisture, dust, dirt and other external factors lead to premature wear and surface damage — scratches, cracks and other irregularities. Also, improper storage of the tape, for example, in conditions of high humidity or in direct sunlight, adversely affects its quality and leads to a change in roughness.

Roughness control and management

To ensure high product quality, roughness control should be carried out at all stages of production:

1. Raw material control: checking the source material for cracks, chips, corrosion and other defects.
2. Setting up equipment: proper adjustment of rolling mills and other process equipment helps to avoid uneven belt tension and defects.
3. Using high quality rollers: rollers made of wear-resistant materials with a low coefficient of friction minimize the risk of burrs and irregularities on the surface of the cold-rolled strip.
4. Polishing: to reduce roughness after rolling, the tape is polished, including using special pastes and tools.
5. Testing and quality control: regular quality analysis surfaces (visual inspection, use of measuring instruments and other methods of control) at all stages of production make it possible to identify and eliminate defects in a timely manner.
6. Process optimization: test results make it possible to effectively optimize production processes. Based on the data obtained, it is possible to change the rolling speed, pressure, temperature and other process parameters.

Production of tape with specified roughness parameters on PZPS

Surface roughness is particularly important for tapes made from the following materials:

• Electrotechnical steels: 20895, 20880, 20860, 20832, 21895, 21880, 21860, 21832.
• Corrosion resistant steels 12X18N9, 12X18H10T, 10X17N13M3T, heat-resistant and heat-resistant steel 20X13 and alloy HN78T.
• Precision alloys: 29NK, 36N, 42N.

At PZPS, you can buy cold-rolled strip in accordance with GOST 503-81 with a low level of roughness. Thanks to modern equipment and advanced inspection methods, our specialists can accurately assess macro- and micro-surface defects and ensure the high quality of the finished product. For supplies, please contact our sales department or leave application on the site. We will get back to you as soon as possible.

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