Question 1

How should you select the gauge for a digital Rockwell hardness tester?

Accepted Answer

Taiwan Nakazawa Co., Ltd. answers for you: Digital Rockwell hardness testers feature functions such as Rockwell scale selection, plastic Rockwell scale selection (optional function), and hardness conversion between various hardness scales. They are suitable for hardness determination of ferrous metals, non-ferrous metals, and non-metallic materials.
The A scale is suitable for measuring metals with hardness values exceeding 67HRC, such as tungsten carbide, hard alloys, hard thin plates, and surface-hardened parts, with a measurement range of 20-85HRA. The B scale is used to measure the hardness of non-ferrous metals and their alloys, annealed steel, and other low-hardness parts, with a hardness range of 25-100HRB. The C scale is suitable for hardness testing of specimens such as carbon steel, tool steel, and alloy steel that have undergone quenching or tempering treatment, with a measurement range of 20-67HRC.

Question 2

What are the precautions for using a digital Rockwell hardness tester?

Accepted Answer

1. When a digital Rockwell hardness tester begins to measure hardness, the first test point should not be used. This is due to concerns that poor contact between the specimen and the anvil may lead to inaccurate measurements. After the first point is tested and the hardness tester is in a normal operating state, formal testing of the specimen can begin, and the measured hardness values can then be recorded.
2. When replacing the anvil, care must be taken to wipe the contact parts clean. After replacement, test several times with a steel sample of a certain hardness until the hardness values obtained twice in succession are identical. The purpose is to ensure that the parts where the indenter or anvil connect with the testing machine are tightly pressed and in good contact, avoiding any impact on the accuracy of the test results.
3. For specimens with relatively complex shapes, corresponding shaped spacer blocks should be used, and testing can proceed once they are fixed. Cylindrical specimens should generally be placed in a V-slot for testing.

Our company is a firm specializing in providing metal detection and analysis instruments, producing high-quality products such as metallographic pre-processing equipment, metallographic cutting machines, metallographic mounting machines, micro-Vickers hardness testers, and Rockwell hardness testers. Welcome to Taiwan Nakazawa Co., Ltd. to make your purchase.

Question 3

What structural factors are often overlooked when purchasing a hardness tester?

Accepted Answer

1. The structural rigidity of the hardness tester. The structural rigidity of the hardness tester stipulated by the state cannot exceed 1.5 degrees. This requirement is seldom met by manufacturers, and this standard directly affects the measurement accuracy of the hardness tester. This is related to the technical expertise of each manufacturer, and many small manufacturers are likely to fail at this stage.
2. Perpendicularity ≤ 0.08/100. This means that the indenter of the hardness tester and the platform must be perpendicular. Naturally, the smaller this number, the better. Many manufacturers manufacture based on feeling—as long as it looks perpendicular, it is fine. Some use perpendicularity measuring instruments or similar tools, which involves significant error; most rely on visual inspection, which is non-standard.

The hardness testers represented by our Taiwan Nakazawa Co., Ltd. have high precision and stable performance, with a complete range of hardness tester specifications and models suitable for various products and tests across all walks of life.

Question 4

What factors are often overlooked when purchasing a hardness tester?

Accepted Answer

1. Coaxiality is less than Φ0.2mm. Specifically, this means that the upper indenter and the lower lifting screw must be on the same vertical axis, and the error cannot exceed Φ0.2mm. This is also not something that can be achieved through visual inspection.
2. Repeatability must be good. This parameter is a comprehensive evaluation of a hardness tester. If the results are different every time, what is the use of buying such a machine?

Our company, Taiwan Nakazawa Co., Ltd., specializes in the production of precision metallographic testing equipment, such as metallographic cutting machines, metallographic grinding and polishing machines, Vickers hardness testers, metallographic mounting machines, and other precision equipment. Friends in need are welcome to come and make a purchase.

Question 5

Why do errors occur when using a digital Rockwell hardness tester?

Accepted Answer

Taiwan Nakazawa Co., Ltd. answers for you: Possible causes of error include: the error in hardness testing for inclined, spherical, and cylindrical parts is greater than that for flat surfaces.
When the indenter presses into the surface of such parts, the resistance around the indentation point will be smaller than that of a flat surface, and there may even be phenomena of deviation or slipping. As the indentation depth increases, the hardness value decreases. The smaller the radius of curvature and the greater the slope, the more significant the decrease in the hardness value. Diamond indenters are also more easily damaged. For these types of parts, a dedicated workbench should be designed to ensure the workbench and the indenter are concentric.

Question 6

Why are there errors when using a digital Rockwell hardness tester?

Accepted Answer

Taiwan Nakazawa Co., Ltd. answers this question for you. Different surface finishes will exhibit different effects during Rockwell hardness testing.
For surfaces with low surface finish, the hardness will appear relatively high during high-hardness testing; conversely, the hardness will appear relatively low. A rough surface with tool marks, when cooled during quenching, or a relatively hard surface layer will result in a higher hardness value. On the contrary, during high-temperature tempering of quenched and tempered parts, the surface structure with tool marks transforms first, leading to lower tempering resistance and thus a lower hardness value. When testing parts with a surface finish below Δ7, it is necessary to use a discarded grinding wheel for fine grinding, then file it smooth with a file, or polish it with a fine hand-held grinding wheel, and then wipe it clean.

Question 7

What factors can cause errors when using a digital Rockwell hardness tester?

Accepted Answer

Taiwan Nakazawa answers for you: Causes of error include: the surface of heat-treated parts may have salt stains, sand, or other substances. When a load is applied, the part may slip. If grease is present, it will act as a lubricant when the diamond head presses in, reducing friction and increasing the indentation depth. This will cause the measured hardness value to be lower. For the tested area of a part, a thin and loose oxide scale layer will decrease the hardness value, while a thick and dense oxide scale layer will increase the hardness value. For parts whose hardness is to be measured, the oxide scale must be removed, and they must be wiped clean and free of any dirt.

Question 8

How should one proceed with a practical pointer type Rockwell hardness timer?

Accepted Answer

1. Place the specimen on the workbench, rotate the handwheel to make the workbench rise slowly and lift the indenter. The small pointer of the indicator dial should point at the green dot, and the large pointer should point at marks C and B (if there is a slight deviation, the dial can be rotated to align it).
2. After the pointer position is aligned, press the motor start button to apply the main load to the indenter.
3. Once the indicator pointer's rotation has clearly come to a halt, the main load will be unloaded immediately.
4. Read the corresponding scale value from the indicator. When using a diamond indenter, read according to the black figures on the outer ring of the reading dial. When using a steel ball indenter, read the value according to the red figures on the inner ring of the reading dial.
5. Loosen the handwheel, lower the workbench, and then you can slightly move the specimen to select a new position to continue the test.

The hardness testers produced by our Taiwan Nakazawa Co., Ltd. have high precision and stable performance, with a complete range of hardness tester specifications and models suitable for various products and tests across all walks of life.

Question 9

What are some tips for using a digital Vickers hardness timer?

Accepted Answer

During the digital Vickers hardness tester test, a set test force is applied. After pressing into the surface of the specimen and dwelling for a certain period, the main test force is unloaded, and the Vickers hardness value of the metal material is determined based on the degree of indentation on the specimen surface.
The hardness value of a digital Vickers hardness tester is determined by the size of the indentation; the larger the degree of indentation, the lower the hardness; conversely, the higher the hardness. Generally speaking, according to conventional concepts, the larger the numerical value, the higher the hardness. When we conduct a hardness test, if the hardness tester is not in a horizontal position, or if a certain test area of the part has poor contact with the workbench, or if the support point is unstable, the hardness value will be lower.
In such cases, the measured value will be low. Solution: Use a level to measure the horizontality, then level the hardness tester or ensure that the workpiece and the workbench support are stable.

Our company, Taiwan Nakazawa Co., Ltd., specializes in the production of precision metallographic testing equipment, such as metallographic cutting machines, metallographic grinding and polishing machines, Vickers hardness testers, metallographic mounting machines, and other precision equipment. Friends in need are welcome to come and make a purchase.

Question 10

What precautions should be taken when inspecting the standard block of a digital Rockwell hardness tester?

Accepted Answer

Taiwan Nakazawa answers for you: Digital Rockwell hardness testers feature functions such as Rockwell scale selection, plastic Rockwell scale selection, and hardness conversion between various scales. Among these, the test block is a simple comparison method to check the accuracy of your hardness tester. Before performing a test block inspection with a digital Rockwell hardness tester, always pay attention to the following matters:
1. Do not use a test block where old indentations have been ground away, because it cannot be certain whether the newly processed surface has the same hardness value as the original one.
2. If the digital Rockwell hardness tester is used across the entire given scale range, the high, medium, and low ranges of the scale should be checked. If only one or two ranges are used, test blocks with hardness values above and below those specific ranges can be selected.
3. The test block should be tested on a single side only; do not test on both sides. Using the bottom or side surfaces will not yield correct hardness values.
4. Use test blocks that are in good condition. Do not use a test block where the distance between indentations is less than at least 2.5 times the indentation diameter.

Question 11

How to prevent rust when maintaining a Rockwell hardness tester?

Accepted Answer

Taiwan Nakazawa Co., Ltd. answers for you: Although all components of the instrument have undergone anti-rust treatment, improper storage or repair can still lead to corrosion of some parts, especially in coastal areas.
The instrument is fully lubricated when leaving the factory and should not require further lubrication during use. Rockwell hardness testers should be wiped frequently with a soft cloth; take care to keep the anvil, indenter, extension rod, and hardness blocks dry and clean. The measuring surface of the hardness block must not be touched directly by hand.

Question 12

What is the basic principle of a digital Vickers hardness tester?

Accepted Answer

Taiwan Nakazawa Co., Ltd. answers for you: The basic principle of the digital Vickers hardness tester test is that the indenter uses a 136° angle pyramidal diamond indenter.
The loads for Vickers micro-hardness testing are: 1 kg, 2 kg, 3 kg, 5 kg, 10 kg, 20 kg, 30 kg, 50 kg, and 100 kg. Commonly used loads are 1 kg, 2 kg, 5 kg, 10 kg, 30 kg, and 50 kg. The required thickness of the specimen depends on the magnitude of the load.
The hardness indentation test is expressed by the load per unit area. A fixed selected test force (load) is applied to the surface of the sample, followed by a predetermined holding time (dwell) and the removal of the test force (unloading). A residual indentation remains on the surface of the sample in the shape of a square pyramid base. By measuring the length of its diagonals with a micrometer eyepiece, the diagonal length of the indentation is obtained. The hardness value is calculated by the ratio of the test force to the surface area of the indentation.

Question 13

What are the advantages of using a digital Vickers hardness tester?

Accepted Answer

Digital Vickers hardness testers are used for the measurement of Vickers hardness values of thinner workpieces. A diamond indenter in the shape of a regular quadrangular pyramid is used to press into the surface of the specimen under the action of a test force. After maintaining the force for a specified period, the test force is unloaded, and the length of the diagonal of the indentation on the specimen surface is measured.
The indentation of the digital Vickers hardness tester test is square, with clear contours and accurate diagonal measurements. Therefore, the Vickers hardness test offers very high precision among commonly used hardness testing methods, and its repeatability is also excellent, which is superior to Brinell hardness testing.
The measurement range of the digital Vickers hardness tester test is extensive, capable of measuring almost all metal materials used in industry today, from very soft materials to very hard materials.
The advantage of the digital Vickers hardness tester test lies in the fact that its hardness value is independent of the magnitude of the test force. As long as the material is uniform in hardness, any test force can be selected, and the hardness value remains unchanged. This is equivalent to having a unified scale across a very broad range of hardness, which is superior to the Rockwell hardness test.

The hardness testers represented by our Taiwan Nakazawa Co., Ltd. have high precision and stable performance, with a complete range of hardness tester specifications and models suitable for various products and tests across all walks of life.

Question 14

What are the applications of Rockwell hardness testers in castings?

Accepted Answer

Rockwell hardness testers are commonly used for the hardness testing of cast iron. For workpieces with fine grains that do not have sufficient surface area for Brinell hardness testing, Rockwell hardness testing can also be performed. For pearlitic malleable cast iron, chilled cast iron, and steel castings, the HRB or HRC scales can be adopted. If the material is non-homogeneous, several readings should be measured and their average value should be taken.

Our company is a firm specializing in providing metal detection and analysis instruments, producing high-quality products such as metallographic pre-processing equipment, metallographic cutting machines, metallographic mounting machines, micro-Vickers hardness testers, and Rockwell hardness testers. Welcome to Taiwan Nakazawa Co., Ltd. to make your purchase.

Question 15

What kind of working environment should a hardness tester operate in?

Accepted Answer

Hardness is one of the commonly used indicators for evaluating the mechanical properties of metal materials. The essence of hardness is the ability of a material to resist the indentation of another harder material.
Hardness tester testing is a rapid, economical, and simple experimental method for evaluating the mechanical properties of metals. Its purpose is to determine the suitability of the material or the effect of special hardening or softening treatments performed for the material's intended use.
We should place the hardness tester in a dry and clean environment, far from damp places, and ensure indoor ventilation (use in a smoke-free location).
Commonly used hardness testers include Rockwell hardness testers, Vickers hardness testers, digital Rockwell hardness testers, Brinell hardness testers, etc.

Our company, Taiwan Nakazawa Co., Ltd., specializes in the production of precision metallographic testing equipment, such as metallographic cutting machines, metallographic grinding and polishing machines, Vickers hardness testers, metallographic mounting machines, and other precision equipment. Friends in need are welcome to come and make a purchase.

Question 16

What methods can be used to reduce the measurement error of a Leeb hardness tester?

Accepted Answer

Taiwan Nakazawa Co., Ltd. answers for you:
1. For hollow materials such as pipes, try not to impact the cross-section on the side; alternatively, adding a support inside the pipe wall is difficult but very effective. When measuring solid pipes with a curved surface diameter of 20mm-100mm, a curved surface support ring must be selected.
2. For thin plates, the thickness should be above 5mm (try not to choose a hardness tester for workpieces below 5mm). When measuring, grease should be applied evenly on the back of the measurement site to achieve dense coupling with the platform, pressing out the air in between so it cannot move. Do not apply too much grease.
3. Ensure the surface finish of the metal material has an RA of less than 7um; the better the surface finish, the higher the accuracy of the hardness value.
4. For solid cylinders, to ensure the stability of the workpiece, a V-shaped anvil should be added for smaller cylinders.
5. When measuring hardness, efforts should be made to improve the surface roughness, weight, and degree of coupling of the workpiece. If the surface roughness is poor and difficult to process while the workpiece is large, select a G-type impact device.

Question 17

What are the applications of hardness testers in the quenching process of straight seam welded pipes?

Accepted Answer

Taiwan Nakazawa answers for you:
1. Vickers hardness testers are an important means of testing the surface hardness of heat-treated straight seam welded pipes.
2. Surface Rockwell hardness testers are also very suitable for testing the hardness of surface-quenched workpieces. Surface Rockwell hardness testers offer three scales to choose from. They can test various surface-hardened straight seam welded pipes with an effective hardening depth exceeding 0.1mm. This is of great significance for welded pipe processing and machinery manufacturing plants.
3. When the surface heat-treatment hardened layer is thick, a Rockwell hardness tester can also be used. When the thickness of the heat-treated hardened layer is between 0.4 and 0.8mm, the HRA scale can be adopted; when the hardened layer thickness exceeds 0.8mm, the HRC scale can be adopted.
4. If a part requires high local hardness, local quenching heat treatment can be performed using methods such as induction heating. Such straight seam welded pipes usually need to have the position of the local quenching heat treatment and the local hardness value marked on the drawings. The hardness testing of straight seam welded pipes must be conducted within the designated area. Rockwell hardness testers can be used as the hardness testing instrument to test HRC hardness values; if the heat-treated hardened layer is shallow, a surface Rockwell hardness tester can be used to test HRN hardness values.

Question 18

What are the storage and usage conditions for a hardness tester?

Accepted Answer

1. The hardness tester should be used and stored in a place that is dry, free of corrosive media, and without vibration, to ensure that the precision of the instrument is not compromised and to ensure a smooth testing process and reliable readings.
2. For the diamond cone indenter used during the process, an inspection of the hardness tester's dimensions and surface finish should be conducted once a year. After each hardness test is completed, the indenter should be wiped clean and stored in its dedicated box.
3. Lubricating oil should not be added to the measuring mechanism of the hardness tester; however, a small amount of lubricating oil can be injected into friction components such as the lifting screw of the loading platform and the handwheel to ensure operational flexibility.
4. During the testing process, touching the parts with hands is not allowed to avoid causing inaccurate test results or damaging the diamond tip.
5. Depending on the situation, the hardness tester should be checked using standard blocks 1-3 times a year. Every month, a thorough inspection should be conducted and verified through the application of certificates issued by the competent department during the course of work.

The hardness testers produced by our Taiwan Nakazawa Co., Ltd. have high precision and stable performance, with a complete range of hardness tester specifications and models suitable for various products and tests across all walks of life.

Question 19

What are the reasons for the variation in Rockwell hardness tester readings?

Accepted Answer

Taiwan Nakazawa introduces for you, regarding the loading mechanism section:
(1) Check whether the testing table is firmly installed on the screw, whether the screw is loose, and whether the testing table is level.
(2) Poor clamping of the indenter or damage to the tip of the indenter.
(3) If the sliding poise on the loading lever is loose, it will cause the test force to be unstable; the sliding poise should be tightened.
(4) Check whether the knives and knife seats on the loading lever are loose; if they are loose, the knives and knife seats should be tightened.
(5) The shoulder plane of the upper part of the spindle and the working surface of the knife seat fixed on the frame are not smooth and flat, causing instability of the test force; the working surfaces should be adjusted or ground.
(6) If the edges of the three knives on the loading lever are not on the same plane or are not parallel to each other, the lever ratio will fluctuate frequently, easily causing instability of the test force. In this case, the knives should be ground or adjusted so that their edges are on the same plane and parallel to each other.

Question 20

How do you calculate the depth of the indentation left after a Rockwell hardness test?

Accepted Answer

1. HRA, HRC, and HRD scales. The Rockwell hardness value is HR=100-h/0.002, and the residual indentation depth is h=(100-HR)×0.002mm. For example, when the hardness value is 62HRC, the residual indentation depth is h=(100-62)×0.002=0.076mm.
2. HRB, HRF, HRE, HRG, HRH, and HRK scales. For the HRB, HRE, and HRF scales, the Rockwell hardness value is HR=130-h/0.002, and the residual indentation depth is h=(130-HR)×0.002mm. For example, when the hardness value is 80HRB, the residual indentation depth is h=(130-80)×0.002=0.1mm.

Our company, Taiwan Nakazawa Co., Ltd., specializes in the production of precision metallographic testing equipment, such as metallographic cutting machines, metallographic grinding and polishing machines, Vickers hardness testers, metallographic mounting machines, and other precision equipment. Friends in need are welcome to come and make a purchase.

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