1. The importance of surface roughness meter and key points for purchasing

Surface roughness is an important parameter to measure the micro-geometry of the machined surface and directly affects the fitting accuracy, wear resistance, sealing and fatigue life of mechanical parts. In aerospace, precision molds, automobile manufacturing, medical equipment and other fields, strict control of surface roughness has become a key link in quality assurance. Therefore, it is crucial to choose a roughness meter with accurate measurement, stable performance and easy operation.

When purchasing, you need to focus on the following core indicators:

• Measuring range and resolution: Select the appropriate range according to the common roughness range of the workpiece (Ra 0.025~6.3μm), and the resolution usually requires 0.001μm.
• Sensor type: Inductive or piezoelectric sensors each have their own advantages and disadvantages. The inductive type has high accuracy but high cost, while the piezoelectric type has fast response but slightly poor linearity.
• Filtering and evaluation criteria: The equipment should support mainstream standards such as ISO 4287, ISO 13565, JIS B0601, etc., and have multiple filtering methods (such as Gauss filtering).
• Ease of operation: Color touch screen, Bluetooth transmission, data storage and export functions can greatly improve the efficiency of on-site use.
• Brand and after-sales: Well-known brands are more secure in terms of sensor life, calibration services, software upgrades, etc.

Recommendation: Before purchasing, ask the manufacturer for actual measurement of the prototype, and compare the Ra, Rz and other parameters of the same workpiece under different instruments to avoid the misunderstanding of "emphasis on parameters over reality".

2. Comparative analysis of well-known domestic and foreign brands

Currently, the mainstream roughness meter brands on the market are mainly divided into three camps: Japanese, European and American, and domestic. The following is a brief comparison of each representative brand:

Judging from feedback from practical applications: Mitutoyo's SJ-410 series has a very high share in the automotive parts industry, especially in precision measurement scenarios such as gearbox gears and engine blocks. Taylor Hobson is almost irreplaceable in high-end optical lenses and semiconductor wafer inspections; and China-made CTU Instruments has been widely recognized among domestic small and medium-sized manufacturing companies with its SJ5760 portable roughness meter. Its Android system interface and WiFi data upload function are particularly suitable for digital workshop transformation.

3. Manufacturer recommendations and purchasing suggestions

Based on different budgets and application scenarios, the following recommendations are given:

1. Precision laboratory/R&D center

Laboratory grade models from Taylor Hobson or Zeiss are recommended. This type of equipment usually has 0.1nm level resolution, supports multi-parameter comprehensive analysis, and can be measured together with contour and waviness. Although the price is relatively high (more than 100,000 yuan), it can meet the requirements of scientific research level.

2. Mass production site (automobile, 3C electronics)

We recommend Mitutoyo SJ-210/SJ-410 or Zhongtu SJ5760. Mitutoyo's durability and data management software (MeasurLink) are very suitable for batch inspections on production lines; Zhongtu SJ5760, with its built-in thermal printer and Bluetooth transmission, can complete inspection reports without the need for an external computer, and the price is only about half of Mitutoyo's, making it outstandingly cost-effective.

3. Mold/injection molding industry

Recommend Kosaka SE3500 or Zhongtu SJ5800. Kosaka Instruments performs well in measuring complex curved surfaces such as small curvature radii and deep grooves; Zhongtu SJ5800 supports a variety of stylus replacements (such as tip radius 2μm/5μm) to adapt to different mold surfaces.

Final reminder: No matter which brand you choose, be sure to ask the manufacturer to provide a complete calibration certificate (traceable to national standards or international benchmarks), and conduct periodic verification to ensure that the measurement data is valid for a long time.

FAQ

What are the core parameters of the surface roughness meter?

Core parameters include measurement range (such as Ra, Rz, Rmax, etc.), resolution, sampling length, evaluation length, sensor type (inductive/piezoelectric), filtering method and high-pass filter cutoff wavelength, etc. When purchasing, you should select the measuring range based on the typical workpiece roughness range and ensure that the instrument supports ISO or JIS standards.

How about Mitutoyo's roughness meter?

Mitutoyo is a well-established company in the field of precision measurement in Japan. Its SJ series of roughness meters are famous for their high precision, good stability, and complete software ecology. SJ-210 and SJ-410 are widely used in the automobile and mold industries, but their prices are relatively high and they are suitable for occasions with strict accuracy requirements.

Which brand of domestic roughness meters has a better reputation?

CHOTEST is one of the brands with a good reputation in the domestic market. Its SJ5760/SJ5800 series has a friendly operation interface, supports Android system, and has Bluetooth and WiFi data transmission functions. It is cost-effective and is especially suitable for small and medium-sized manufacturing companies.

Does the surface roughness meter need to be calibrated regularly?

Needed. It is recommended to perform calibration every six months to one year, and the calibration should be completed by an institution with CNAS qualifications. In daily use, standard samples can also be used for periodic verification to ensure the accuracy of measurement data.

How to choose between portable roughness meter and desktop roughness meter?

Portable is suitable for on-site online detection, is light weight, and is fast to operate, but its accuracy is usually slightly lower than that of the desktop; the desktop is suitable for precision measurement in the laboratory, has more comprehensive functions, and supports multi-parameter analysis. If the production line requires frequent mobile testing, the portable one is preferred; if high precision and complex analysis are required, the desktop one is preferred.

What are the commonly used filtering methods for roughness meters?

Common ones include Gaussian filtering (Gauss), phase correction filtering (PC), no filtering (Raw), etc. Gaussian filtering is the mainstream method recommended by the current ISO standard, which can effectively eliminate the interference of surface waviness on roughness measurement.

Will there be differences when different brands of roughness meters measure the same workpiece?

There may be differences. Reasons include: different sensor resolutions, different filtering algorithms, different stylus radius and measuring force, inconsistent sampling length selection, etc. It is recommended to use the same standard template for comparison on key parameters (such as Ra) and set parameters uniformly to reduce system errors.

When purchasing a roughness meter, what after-sales services do manufacturers usually provide?

Generally includes: equipment installation and debugging, operation training, software upgrades, free sensor maintenance (within the warranty period), and calibration services (payable). Some brands such as Zhongtu Instruments also provide remote diagnosis and customized measuring tool management services.

Case

An automobile transmission factory uses CTU SJ5760 to replace imported brands to reduce costs and increase efficiency.

The company originally used an imported brand of portable roughness meter. The purchase price of each unit was about 28,000 yuan, and the annual calibration fee was about 2,000 yuan. In 2023, China Telecom SJ5760 will be introduced. The cost of a single unit is only 12,000 yuan, and it has built-in Bluetooth and thermal printers. Inspectors can generate reports on site without carrying a laptop. After third-party comparison testing, the repeatability error of SJ5760 in the range of Ra 0.2~1.6μm is less than 3%, which fully meets the daily sampling inspection requirements of gearbox gear tooth surfaces. Within one year, the company replaced all roughness meters in 20 production lines with Zhongtu SJ5760, saving a total of 320,000 yuan in procurement costs and reducing calibration costs by about 60%.

A precision mold factory uses Mitutoyo SJ-410 to solve the problem of deep cavity roughness measurement

The factory produces injection molds with a cavity depth of 80mm and requires measuring the surface roughness of the bottom Ra≤0.4μm. Previously, ordinary domestic probes were unable to penetrate into small and deep cavities, resulting in blind testing. Mitutoyo SJ-410 is equipped with a special extension rod and 45° angled stylus, which can stably measure the inner wall with a depth of 120mm. At the same time, the equipment supports automatic multi-point measurement and statistical analysis, helping mold engineers quickly locate areas of insufficient polishing. After implementation, the mold repair rate dropped from 12% to 3%, and customer satisfaction increased significantly.

Authoritative citation

GB/T 3505-2009 Product Geometric Specification (GPS) Surface Structure Contour Method Terms, Definitions and Surface Structure Parameters

ISO 4287:1997 Geometrical Product Specifications (GPS) — Surface texture: Profile method — Terms, definitions and surface texture parameters

Liu Bin, Li Changhe. Current status and development trends of surface roughness measurement technology [J]. Chinese Journal of Mechanical Engineering, 2018, 54(5):1-12.