Overview of hardness test of precision roller chain

1. Overview of hardness test of precision roller chain

1.1 Basic characteristics of precision roller chain
Precision roller chain is a kind of chain widely used in mechanical transmission. Its basic characteristics are as follows:
Structural composition: Precision roller chain consists of inner chain plate, outer chain plate, pin shaft, sleeve and roller. The inner chain plate and outer chain plate are connected by pin shaft, the sleeve is sleeved on the pin shaft, and the roller is installed outside the sleeve. This structure enables the chain to withstand large tensile and impact forces during transmission.
Material selection: Precision roller chain is usually made of high-quality carbon steel or alloy steel, such as 45 steel, 20CrMnTi, etc. These materials have high strength, high toughness and good wear resistance, which can meet the use requirements of the chain under complex working conditions.
Dimensional accuracy: The dimensional accuracy requirements of precision roller chain are high, and the dimensional tolerances of pitch, chain plate thickness, pin shaft diameter, etc. are generally controlled within ±0.05mm. High-precision dimensions can ensure the meshing accuracy of the chain and sprocket, and reduce transmission errors and noise.
Surface treatment: In order to improve the wear resistance and corrosion resistance of the chain, precision roller chains are usually surface treated, such as carburizing, nitriding, galvanizing, etc. Carburizing can make the surface hardness of the chain reach 58-62HRC, nitriding can make the surface hardness reach 600-800HV, and galvanizing can effectively prevent the chain from rusting.
1.2 Importance of hardness testing
Hardness testing is of great significance in the quality control of precision roller chains:
Ensure chain strength: Hardness is one of the important indicators for measuring material strength. Through hardness testing, it can be ensured that the material hardness of the precision roller chain meets the design requirements, so as to ensure that the chain can withstand sufficient tension and impact during use, and avoid chain breakage or damage due to insufficient material strength.
Evaluate material properties: Hardness testing can reflect the microstructure and performance changes of the material. For example, the surface hardness of the chain after carburizing treatment is higher, while the core hardness is relatively low. Through hardness testing, the depth and uniformity of the carburized layer can be evaluated, so as to judge whether the heat treatment process of the material is reasonable.
Control production quality: In the production process of precision roller chains, hardness testing is an effective means of quality control. By testing the hardness of raw materials, semi-finished products and finished products, problems that may occur in the production process, such as material defects, improper heat treatment, etc., can be discovered in time, so that corresponding measures can be taken to improve and ensure the stability and consistency of product quality.
Extend service life: Hardness testing helps to optimize the materials and manufacturing processes of precision roller chains, thereby improving the wear resistance and fatigue resistance of the chain. The high-hardness chain surface can better resist wear, reduce the friction loss between the chain and the sprocket, extend the service life of the chain, and reduce the maintenance cost of the equipment.
Meet industry standards: In the machinery manufacturing industry, the hardness of precision roller chains usually needs to meet relevant national or international standards. For example, GB/T 1243-2006 “Roller Chains, Bushing Roller Chains and Toothed Chains” stipulates the hardness range of precision roller chains. Through hardness testing, it can be ensured that the product meets the standard requirements and improves the market competitiveness of the product.

2. Hardness test standards

2.1 Domestic test standards
my country has formulated a series of clear and strict standards for the hardness test of precision roller chains to ensure that product quality meets the requirements.
Standard basis: Mainly based on GB/T 1243-2006 “Roller chain, bushing roller chain and toothed chain” and other relevant national standards. These standards specify the hardness range of precision roller chains. For example, for precision roller chains made of 45 steel, the hardness of the pins and bushings should generally be controlled at 229-285HBW; for carburized chains, the surface hardness must reach 58-62HRC, and the depth of the carburized layer is also clearly required, usually 0.8-1.2mm.
Testing method: Domestic standards recommend the use of Brinell hardness tester or Rockwell hardness tester for testing. The Brinell hardness tester is suitable for testing raw materials and semi-finished products with low hardness, such as chain plates that have not been heat treated. The hardness value is calculated by applying a certain load on the surface of the material and measuring the indentation diameter; the Rockwell hardness tester is often used to test finished chains that have been heat treated, such as carburized pins and sleeves. It has a fast detection speed, simple operation, and can directly read the hardness value.
Sampling and testing parts: According to the standard requirements, a certain number of samples should be randomly selected for testing from each batch of precision roller chains. For each chain, the hardness of different parts such as the inner chain plate, outer chain plate, pin, sleeve and roller should be tested separately. For example, for the pin, one test point should be taken in the middle and at both ends to ensure the comprehensiveness and accuracy of the test results.
Result determination: The test results must be determined strictly in accordance with the hardness range specified in the standard. If the hardness value of the test part exceeds the range specified in the standard, such as the hardness of the pin is lower than 229HBW or higher than 285HBW, the chain is judged as an unqualified product and needs to be re-heat treated or other corresponding treatment measures until the hardness value meets the standard requirements.

2.2 International Testing Standards
There are also corresponding standard systems for the hardness testing of precision roller chains in the world, and these standards have wide influence and recognition in the international market.
ISO standard: ISO 606 “Chains and sprockets – Roller chains and bushing roller chains – Dimensions, tolerances and basic characteristics” is one of the widely used precision roller chain standards in the world. This standard also makes detailed provisions for the hardness testing of precision roller chains. For example, for precision roller chains made of alloy steel, the hardness range is generally 241-321HBW; for chains that have been nitrided, the surface hardness must reach 600-800HV, and the depth of the nitriding layer is required to be 0.3-0.6mm.
Testing method: International standards also recommend the use of Brinell hardness testers, Rockwell hardness testers and Vickers hardness testers for testing. The Vickers hardness tester is suitable for testing parts with higher surface hardness of precision roller chains, such as the roller surface after nitriding treatment, because of its small indentation. It can measure the hardness value more accurately, especially when testing small size and thin-walled parts.
Sampling and testing location: The sampling quantity and testing location required by international standards are similar to those of domestic standards, but the selection of testing locations is more detailed. For example, when testing the hardness of rollers, samples need to be taken and tested on the outer circumference and end faces of the rollers to comprehensively evaluate the hardness uniformity of the rollers. In addition, hardness tests are also required for the connecting parts of the chain, such as connecting chain plates and connecting pins, to ensure the strength and reliability of the entire chain.
Result judgment: International standards are more stringent in judging the hardness test results. If the test results do not meet the standard requirements, not only will the chain be judged as unqualified, but other chains of the same batch of products will also need to be double-sampled. If there are still unqualified products after double sampling, the batch of products must be reprocessed until the hardness of all chains meets the standard requirements. This strict judgment mechanism effectively guarantees the quality level and reliability of precision roller chains in the international market.

3. Hardness test method

3.1 Rockwell hardness test method
The Rockwell hardness test method is one of the most widely used hardness test methods at present, especially suitable for testing the hardness of metal materials such as precision roller chains.
Principle: This method determines the hardness value by measuring the depth of the indenter (diamond cone or carbide ball) pressed into the surface of the material under a certain load. It is characterized by simple and fast operation, and can directly read the hardness value without complex calculations and measuring tools.
Scope of application: For the detection of precision roller chains, the Rockwell hardness test method is mainly used to measure the hardness of finished chains after heat treatment, such as pins and sleeves. This is because these parts have a higher hardness after heat treatment and are relatively large in size, which is suitable for testing with a Rockwell hardness tester.
Detection accuracy: The Rockwell hardness test has a high accuracy and can accurately reflect the hardness changes of the material. Its measurement error is generally within ±1HRC, which can meet the requirements of precision roller chain hardness testing.
Practical application: In actual testing, the Rockwell hardness tester usually uses an HRC scale, which is suitable for testing materials with a hardness range of 20-70HRC. For example, for the pin of a precision roller chain that has been carburized, its surface hardness is usually between 58-62HRC. The Rockwell hardness tester can quickly and accurately measure its hardness value, providing a reliable basis for quality control.

3.2 Brinell hardness test method
The Brinell hardness test method is a classic hardness test method, which is widely used in the hardness measurement of various metal materials, including the raw materials and semi-finished products of precision roller chains.
Principle: This method presses a hardened steel ball or carbide ball of a certain diameter into the surface of the material under the action of a specified load and keeps it for a specified time, then removes the load, measures the indentation diameter, and determines the hardness value by calculating the average pressure on the spherical surface area of ​​the indentation.
Scope of application: The Brinell hardness test method is suitable for testing metal materials with lower hardness, such as the raw materials of precision roller chains (such as 45 steel) and semi-finished products that have not been heat treated. Its characteristics are large indentations, which can reflect the macroscopic hardness characteristics of the material and are suitable for measuring materials in the medium hardness range.
Detection accuracy: The accuracy of Brinell hardness detection is relatively high, and the measurement error is generally within ±2%. The measurement accuracy of the indentation diameter directly affects the accuracy of the hardness value, so high-precision measuring tools such as reading microscopes are required in actual operation.
Practical application: In the production process of precision roller chains, the Brinell hardness test method is often used to test the hardness of raw materials to ensure that they meet the design requirements. For example, for precision roller chains made of 45 steel, the hardness of the raw materials should generally be controlled between 170-230HBW. Through the Brinell hardness test, the hardness value of the raw materials can be accurately measured, and the unqualified hardness of the materials can be discovered in time, thereby preventing unqualified materials from entering the subsequent production links.

3.3 Vickers hardness test method
The Vickers hardness test method is a method suitable for measuring the hardness of small-sized and thin-walled parts, and has unique advantages in the hardness test of precision roller chains.
Principle: This method presses a diamond tetrahedron with a vertex angle of 136° under a certain load into the surface of the material to be tested, keeps the load for a specified time, and then removes the load, measures the diagonal length of the indentation, and determines the hardness value by calculating the average pressure on the conical surface area of ​​the indentation.
Scope of application: The Vickers hardness test method is suitable for measuring materials with a wide hardness range, especially for detecting parts with high surface hardness of precision roller chains, such as the surface of rollers after nitriding treatment. Its indentation is small, and it can accurately measure the hardness of small-sized and thin-walled parts, which is suitable for detection with high requirements for surface hardness uniformity.
Detection accuracy: The Vickers hardness test has high accuracy, and the measurement error is generally within ±1HV. The measurement accuracy of the diagonal length of the indentation is crucial to the accuracy of the hardness value, so a high-precision measuring microscope is required for measurement.
Practical application: In the hardness test of precision roller chains, the Vickers hardness test method is often used to detect the surface hardness of rollers. For example, for rollers that have been nitrided, the surface hardness must reach 600-800HV. Through Vickers hardness testing, the hardness values ​​at different positions on the roller surface can be accurately measured, and the depth and uniformity of the nitriding layer can be evaluated, thereby ensuring that the surface hardness of the roller meets the design requirements and improving the wear resistance and service life of the chain.

4. Hardness testing instrument

4.1 Instrument type and principle
Hardness testing instrument is a key tool to ensure the accuracy of hardness testing of precision roller chains. Common hardness testing instruments are mainly of the following types:
Brinell hardness tester: Its principle is to press a hardened steel ball or carbide ball of a certain diameter into the surface of the material under a specified load, keep it for a specified time and then remove the load, and calculate the hardness value by measuring the indentation diameter. Brinell hardness tester is suitable for testing metal materials with lower hardness, such as raw materials of precision roller chains and semi-finished products that have not been heat treated. Its characteristics are large indentation, which can reflect the macroscopic hardness characteristics of the material. It is suitable for measuring materials in the medium hardness range, and the measurement error is generally within ±2%.
Rockwell hardness tester: This instrument determines the hardness value by measuring the depth of the indenter (diamond cone or carbide ball) pressed into the surface of the material under a certain load. Rockwell hardness tester is easy and fast to operate, and can directly read the hardness value without complex calculations and measurement tools. It is mainly used to measure the hardness of finished chains after heat treatment, such as pins and sleeves. The measurement error is generally within ±1HRC, which can meet the requirements of precision roller chain hardness testing.
Vickers hardness tester: The principle of the Vickers hardness tester is to press a diamond quadrangular pyramid with a vertex angle of 136° under a certain load into the surface of the material to be tested, keep it for a specified time, remove the load, measure the diagonal length of the indentation, and determine the hardness value by calculating the average pressure borne by the conical surface area of ​​the indentation. The Vickers hardness tester is suitable for measuring materials with a wide hardness range, especially for testing parts with higher surface hardness of precision roller chains, such as the roller surface after nitriding treatment. Its indentation is small, and it can accurately measure the hardness of small-sized and thin-walled parts, and the measurement error is generally within ±1HV.

4.2 Instrument selection and calibration
Selecting a suitable hardness testing instrument and accurately calibrating it is the basis for ensuring the reliability of the test results:
Instrument selection: Select a suitable hardness testing instrument according to the testing requirements of precision roller chains. For raw materials and semi-finished products that have not been heat treated, a Brinell hardness tester should be selected; for finished chains that have been heat treated, such as pins and sleeves, a Rockwell hardness tester should be selected; for parts with higher surface hardness, such as the roller surface after nitriding treatment, a Vickers hardness tester should be selected. In addition, factors such as the accuracy, measurement range, and ease of operation of the instrument should also be considered to meet the requirements of different testing links.
Instrument calibration: The hardness testing instrument must be calibrated before use to ensure the accuracy of its measurement results. The calibration should be performed by a qualified calibration agency or professional personnel in accordance with relevant standards and specifications. The calibration content includes the load accuracy of the instrument, the size and shape of the indenter, the accuracy of the measuring device, etc. The calibration cycle is generally determined according to the frequency of use and stability of the instrument, usually 6 months to 1 year. Qualified calibrated instruments should be accompanied by a calibration certificate, and the calibration date and validity period should be marked on the instrument to ensure the reliability and traceability of the test results.

5. Hardness test process

5.1 Sample preparation and processing
Sample preparation is the basic link of precision roller chain hardness testing, which directly affects the accuracy and reliability of the test results.
Sampling quantity: According to the requirements of national standard GB/T 1243-2006 and international standard ISO 606, a certain number of samples should be randomly selected for testing from each batch of precision roller chains. Normally, 3-5 chains are selected from each batch as test samples to ensure the representativeness of the samples.
Sampling location: For each chain, the hardness of different parts such as the inner link plate, outer link plate, pin shaft, sleeve and roller shall be tested separately. For example, for the pin shaft, one test point shall be taken in the middle and at both ends; for the roller, the outer circumference and end face of the roller shall be sampled and tested separately to comprehensively evaluate the hardness uniformity of each component.
Sample processing: During the sampling process, the sample surface shall be clean and flat, free of oil, rust or other impurities. For samples with oxide scale or coating on the surface, appropriate cleaning or removal treatment shall be carried out first. For example, for galvanized chains, the galvanized layer on the surface shall be removed before hardness testing.

5.2 Test operation steps
The test operation steps are the core of the hardness test process and need to be strictly operated in accordance with standards and specifications to ensure the accuracy of the test results.
Instrument selection and calibration: Select the appropriate hardness test instrument according to the hardness range and material characteristics of the test object. For example, for carburized pins and sleeves, Rockwell hardness testers should be selected; for raw materials and semi-finished products that have not been heat treated, Brinell hardness testers should be selected; for rollers with higher surface hardness, Vickers hardness testers should be selected. Before testing, the hardness test instrument must be calibrated to ensure that the load accuracy, indenter size and shape, and accuracy of the measuring device meet the requirements. Qualified calibrated instruments should be accompanied by a calibration certificate, and the calibration date and validity period should be marked on the instrument.
Testing operation: Place the sample on the workbench of the hardness tester to ensure that the sample surface is perpendicular to the indenter. According to the operating procedures of the selected hardness test method, apply the load and maintain it for the specified time, then remove the load and measure the indentation size or depth. For example, in Rockwell hardness testing, a diamond cone or carbide ball indenter is pressed into the surface of the material under test with a certain load (such as 150kgf), and the load is removed after 10-15 seconds, and the hardness value is directly read; in Brinell hardness testing, a hardened steel ball or carbide ball of a certain diameter is pressed into the surface of the material under test under a specified load (such as 3000kgf), and the load is removed after 10-15 seconds. The indentation diameter is measured using a reading microscope, and the hardness value is obtained by calculation.
Repeated testing: To ensure the reliability of the test results, each test point should be tested repeatedly for multiple times, and the average value is taken as the final test result. Under normal circumstances, each test point should be tested repeatedly 3-5 times to reduce measurement errors.

5.3 Data recording and analysis
Data recording and analysis is the last link in the hardness testing process. By sorting and analyzing the test data, scientific and reasonable conclusions can be drawn, providing a basis for product quality control.
Data recording: All data obtained during the test process shall be recorded in detail in the test report, including sample number, test location, test method, hardness value, test date, test personnel and other information. Data records should be clear, accurate and complete to facilitate subsequent reference and analysis.
Data analysis: Statistical analysis of the test data, calculation of statistical parameters such as the average hardness value and standard deviation of each test point, and evaluation of the uniformity and consistency of hardness. For example, if the average hardness of the pin of a batch of precision roller chains is 250HBW and the standard deviation is 5HBW, it means that the hardness of the batch of chains is relatively uniform and the quality control is good; if the standard deviation is large, there may be quality fluctuations in the production process, and further investigation of the cause and improvement measures are required.
Result determination: Compare the test results with the hardness range specified in the national or international standards to determine whether the sample is qualified. If the hardness value of the test location exceeds the range specified in the standard, such as the hardness of the pin is lower than 229HBW or higher than 285HBW, the chain is judged as an unqualified product and needs to be reheat treated or other corresponding treatment measures until the hardness value meets the standard requirements. For unqualified products, their unqualified conditions should be recorded in detail and the reasons should be analyzed so as to take targeted improvement measures to improve product quality.

6. Factors affecting hardness test

6.1 Impact of test environment

The test environment has an important influence on the accuracy of the hardness test results of precision roller chains.

Temperature influence: Temperature changes will affect the accuracy of the hardness tester and the hardness performance of the material. For example, when the ambient temperature is too high or too low, the mechanical parts and electronic components of the hardness tester may expand and contract due to heat, resulting in measurement errors. Generally speaking, the optimal operating temperature range of Brinell hardness tester, Rockwell hardness tester and Vickers hardness tester is 10℃-35℃. When this temperature range is exceeded, the measurement error of the hardness tester may increase by about ±1HRC or ±2HV. At the same time, the influence of temperature on the hardness of the material cannot be ignored. For example, for the material of precision roller chain, such as 45# steel, its hardness may increase slightly in a low temperature environment, while in a high temperature environment, the hardness will decrease. Therefore, when conducting hardness testing, it should be carried out in a constant temperature environment as much as possible, and the ambient temperature at that time should be recorded so as to correct the test results.
Humidity influence: The influence of humidity on hardness testing is mainly reflected in the electronic components of the hardness tester and the surface of the sample. Excessive humidity may cause the electronic components of the hardness tester to be damp, affecting its measurement accuracy and stability. For example, when the relative humidity exceeds 80%, the measurement error of the hardness tester may increase by about ±0.5HRC or ±1HV. In addition, humidity may also form a water film on the surface of the sample, affecting the contact between the hardness tester indenter and the sample surface, resulting in measurement errors. For the hardness test of precision roller chains, it is recommended to be carried out in an environment with a relative humidity of 30%-70% to ensure the reliability of the test results.
Vibration influence: Vibration in the test environment will interfere with hardness testing. For example, the vibration generated by the operation of nearby mechanical processing equipment may cause the indenter of the hardness tester to have a slight displacement during the measurement process, resulting in measurement errors. Vibration may also affect the load application accuracy and stability of the hardness tester, thereby affecting the accuracy of the hardness value. Generally speaking, when performing hardness testing in an environment with large vibration, the measurement error may increase by about ±0.5HRC or ±1HV. Therefore, when performing hardness testing, you should try to choose a place away from the vibration source and take appropriate vibration reduction measures, such as installing a vibration reduction pad at the bottom of the hardness tester, to reduce the impact of vibration on the test results.

6.2 Operator influence
The operator’s professional level and operating habits have an important impact on the accuracy of the hardness test results of precision roller chains.
Operating skills: The operator’s proficiency in hardness testing instruments directly affects the accuracy of the test results. For example, for a Brinell hardness tester, the operator needs to accurately measure the indentation diameter, and the measurement error may cause a deviation in the hardness value. If the operator is not familiar with the use of the measuring tool, the measurement error may increase by about ±2%. For Rockwell hardness testers and Vickers hardness testers, the operator needs to correctly apply the load and read the hardness value. Improper operation may cause the measurement error to increase by about ±1HRC or ±1HV. Therefore, the operator should undergo professional training and be proficient in the operation methods and precautions of the hardness testing instrument to ensure the accuracy of the test results.
Testing experience: The testing experience of the operator will also affect the accuracy of the hardness test results. Experienced operators can better judge the problems that may arise during the test and take corresponding measures to adjust them. For example, during the test, if the hardness value is found to be abnormal, experienced operators can judge whether there is a problem with the sample itself, or the test operation or instrument fails based on experience and professional knowledge, and deal with it in time. Inexperienced operators may handle abnormal results improperly, resulting in misjudgment. Therefore, enterprises should focus on cultivating the testing experience of operators and improve the testing level of operators through regular training and practice.
Responsibility: The responsibility of operators is also crucial to the accuracy of hardness test results. Operators with strong sense of responsibility will strictly follow the standards and specifications, carefully record the test data, and carefully analyze the test results. For example, during the test, the operator needs to repeat the test for each test point several times and take the average value as the final test result. If the operator is not responsible, the repeated test steps may be omitted, resulting in reduced reliability of the test results. Therefore, enterprises should strengthen the responsibility education of operators to ensure the rigor and accuracy of the test work.

6.3 Impact of equipment accuracy
The accuracy of the hardness testing instrument is a key factor affecting the accuracy of the hardness test results of precision roller chains.
Instrument accuracy: The accuracy of the hardness testing instrument directly affects the accuracy of the test results. For example, the measurement error of the Brinell hardness tester is generally within ±2%, the measurement error of the Rockwell hardness tester is generally within ±1HRC, and the measurement error of the Vickers hardness tester is generally within ±1HV. If the accuracy of the instrument does not meet the requirements, the accuracy of the test results cannot be guaranteed. Therefore, when selecting a hardness testing instrument, an instrument with high accuracy and good stability should be selected, and calibration and maintenance should be performed regularly to ensure that the accuracy of the instrument meets the test requirements.
Instrument calibration: The calibration of the hardness testing instrument is the basis for ensuring the accuracy of the test results. Instrument calibration should be performed by a qualified calibration agency or professional personnel and operated in accordance with relevant standards and specifications. The calibration content includes the load accuracy of the instrument, the size and shape of the indenter, the accuracy of the measuring device, etc. The calibration cycle is generally determined according to the frequency of use and stability of the instrument, usually 6 months to 1 year. Qualified calibrated instruments should be accompanied by a calibration certificate, and the calibration date and validity period should be marked on the instrument. If the instrument is not calibrated or the calibration fails, the accuracy of the test results cannot be guaranteed. For example, an uncalibrated hardness tester may cause the measurement error to increase by about ±2HRC or ±5HV.
Instrument maintenance: Maintenance of hardness testing instruments is also a key link to ensure the accuracy of test results. During the use of the instrument, the accuracy may change due to mechanical wear, aging of electronic components, etc. Therefore, enterprises should establish a complete instrument maintenance system and regularly maintain and service the instrument. For example, regularly clean the optical lens of the instrument, check the wear of the indenter, calibrate the load sensor, etc. Through regular maintenance, problems with the instrument can be discovered and solved in a timely manner to ensure the accuracy and stability of the instrument.

7. Determination and application of hardness test results

7.1 Result determination standard
The determination of the hardness test results of precision roller chains is strictly carried out in accordance with relevant standards to ensure that the product quality meets the requirements.
Domestic standard determination: According to national standards such as GB/T 1243-2006 “Roller Chain, Bushing Roller Chain and Toothed Chain”, precision roller chains of different materials and heat treatment processes have clear hardness range requirements. For example, for precision roller chains made of 45 steel, the hardness of the pins and bushings should be controlled at 229-285HBW; the surface hardness of the chain after carburizing treatment must reach 58-62HRC, and the depth of the carburized layer is 0.8-1.2mm. If the test results exceed this range, such as the hardness of the pin is lower than 229HBW or higher than 285HBW, it will be judged as unqualified.
International standard judgment: According to ISO 606 and other international standards, the hardness range of precision roller chains made of alloy steel is generally 241-321HBW, the surface hardness of the chain after nitriding treatment must reach 600-800HV, and the depth of the nitriding layer is required to be 0.3-0.6mm. International standards are more stringent in judging the results. If the test results do not meet the requirements, not only will the chain be judged as unqualified, but the same batch of products will also need to be doubled for sampling. If there are still unqualified products, the batch of products must be reprocessed.
Repeatability and reproducibility requirements: To ensure the reliability of the test results, each test point needs to be tested repeatedly, usually 3-5 times, and the average value is taken as the final result. The difference in test results of the same sample by different operators should be controlled within a certain range, such as the difference in Rockwell hardness test results generally does not exceed ±1HRC, the difference in Brinell hardness test results generally does not exceed ±2%, and the difference in Vickers hardness test results generally does not exceed ±1HV.

7.2 Application of results and quality control
The hardness test results are not only the basis for determining whether the product is qualified, but also an important reference for quality control and process improvement.
Quality control: Through hardness testing, problems in the production process, such as material defects and improper heat treatment, can be discovered in time. For example, if the test finds that the chain hardness is lower than the standard requirement, it may be that the heat treatment temperature is insufficient or the holding time is insufficient; if the hardness is higher than the standard requirement, it may be that the heat treatment quenching is excessive. According to the test results, the company can adjust the production process in time to ensure the stability and consistency of product quality.
Process improvement: Hardness test results help optimize the manufacturing process of precision roller chains. For example, by analyzing the hardness changes of the chain under different heat treatment processes, the company can determine the optimal heat treatment parameters and improve the wear resistance and fatigue resistance of the chain. At the same time, hardness testing can also provide a basis for the selection of raw materials to ensure that the hardness of the raw materials meets the design requirements, thereby improving the overall quality of the product.
Product acceptance and delivery: Before the product leaves the factory, the hardness test results are an important basis for customer acceptance. A hardness test report that meets the standard requirements can enhance customer confidence in the product and promote product sales and marketing. For products that do not meet the standards, the company needs to reprocess them until they pass the hardness test before they can be delivered to customers, which helps improve the company’s market reputation and customer satisfaction.
Quality traceability and continuous improvement: The recording and analysis of hardness test results can provide data support for quality traceability. When quality problems occur, companies can trace the test results to find the root cause of the problem and take targeted improvement measures. At the same time, through the long-term accumulation and analysis of test data, companies can discover potential quality problems and process improvement directions, and achieve continuous improvement and enhancement of quality.