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1 ernsthardnesstesters.com guide to hardness testing

2 2 INTRODUCTION 3 Introduction This guide to hardness testing is intended to be a practical aid for the operators of the ERNST hardness testers and a reference for first time users. For those who wish to study the explanation in detail, here is a list of the most important standards to be considered: Härteprüfung nach Rockwell C, A, B, F 513 T1 Härteprüfung nach Rockwell N und T 513 T2 Härteprüfung nach Vickers 5133 Härteprüfung nach Brinell 5351 Richtlinien für die Gestaltung und Anwendung von Aufnahmevorrichtungen 512 Umwertungstabellen 515 Härtevergleichsplatten 5133 Note: The references (1), (2)... (11) mentioned in the guide are reported in the appendix.

3 4 5 table of contents General guidelines for hardness testing Table of contents Introduction 3 General guidelines for hardness testing 5 Rockwell principle 7 Application field of the different Rockwell scales 11 Testing of cylindrical surfaces 13 Advantages and limitations of the Rockwell method 14 Modification to the Rockwell principle 15 Brinell method 17 Definition of the Brinell tests 19 Application field of Brinell test 2 Advantages and limitations of the Brinell method 22 Testing according to the Rockwell principle with Brinell penetrators and loads 23 Vickers method 24 Application field of Vickers method 25 Advantages and limitations of the Vickers method 26 Shore method for metals - Knoop method 27 Use of the hardness conversion tables and test blocks 28 Appendix (see the references mentioned in the guide) 29 Hardness tester comparison table 32 General guidelines for hardness testing Among all kinds of inspections, that are carried out in a workshop, testing of hardness is the most diversified. Testing can be made at 3 kgf (2943N) or with some hundreds grams; in laboratories, testing is made even with few grams. It is possible to test the hardness of heavy castings as well as of pins for horology, from the hardest sintered materials to the softest alloys. There are so many methods and hardness scales to be used that even those who have a considerable workshop experience can get confused when facing such problems. Modern electronics has contributed much to improve hardness testing equipment, permitting high accuracy, data processing of test results, statistical analysis, graphics, etc. The electronics, of course, finds its main application in reading of the results and control of the functions, while the original mechanical principles are still valid and indispensable. The following notes are a valid aid to reduce the confusion; the test methods Rockwell, Brinell and Vickers will be widely explained in depth later on. When choosing a hardness tester, we think one should first consider the following main points: 1. test load 2. hardness range 3. accuracy of results 4. adaptability of the tester to shape and dimension of the work piece 5. budget 1. Test load Generally, the test force should not cause a penetration more than 1/1 of thickness of the work piece or of the surface treatment. When possible, it is advisable to work with a quite heavy load, that permits a more accurate test result, as the test surface is usually subject to decarburisation during treatment; besides, with a heavy load, testing is less influenced by surface condition. On the other hand, a too strong impression can damage the work piece and initiate a crack on highly stressed parts. When choosing the force, it is important to evaluate the homogeneity of the material: cast iron is a typical case that normally requires a heavy load.

4 6 7 General guidelines for hardness testing ROCKWELL PRINCIPLE 2. Hardness range When testing materials with a hardness of over 5 HRC (steel of 485 HB approx) it is advisable to use a diamond indenter; steel or carbide penetrators can be used with materials of a lower hardness. The Brinell method does not make use of the diamond indenter and for this reason it cannot be applied for testing of tempered steel; the Rockwell method is more versatile, because it employs diamond indenters as well as steel penetrators. The Vickers test makes use of a pyramidal diamond indenter and can work on all hardness ranges, even if it finds its main application in laboratories rather than in workshops. 3. Accuracy Accuracy of the instrument depends also on the working method: well prepared surfaces, steady measuring time, regular inspections of the instrument with test blocks, are all elements that improve this factor. When possible, it is advisable to work with a static system instead of a dynamic one. The accuracy of the instrument becomes critical when working with light loads. 4. Adaptability of the instrument to shape and dimensions of the work piece It is possible to move the work piece under the tester as well as the tester over the work piece. The first case concerns bench instruments, that allows holding and clamping of the part during testing; such instruments are suitable for testing of small and medium parts (1). The second case concerns portable testers that can be clamped to the work piece (2), or simply placed on large and irregular parts. Portable testers applying heavy load are dynamic system (3); those applying light load can be also static system (4). Testing on particularly difficult parts should be evaluated from time to time. 5. Budget Here, several factors are taken into consideration: price, versatility, measuring time and involvement of the operator. The first two aspects become important in case of occasional testing and for checking of odd shaped parts or treatment, such as for handicraft or small enterprises. However, in case of testing on a production line, the rapidity and the possibility to employ unskilled personnel become key-factors when choosing an instrument. Rockwell principle For a better understanding, the different steps of the Rockwell method are illustrated and numbered in the figure A, showing the dial indicator, that records the displacements of the penetrator FIGURE A - Drawing of the rockwell principle 1. First, a preliminary test force Fo is applied (preload), determining a light penetration; after that, the dial indicator must be reset to zero. 2. Gradually and avoiding any impact, an additional test force (F1) is applied to reach the required test load (F). With this force applied, the penetrator penetrates according to the hardness of the material self. One must wait until penetration is completed. The dial indicator shows the penetrator s displacement. 3. The additional force F1 can be removed, returning to the preload; in this way, the indenter remains in the indentation, but all elastic strains given by the load application will be eliminated. The dial indicator will show the difference of penetration between preload and test load. Indenters, preloads, test loads and unit of measurement are standardized in two groups: standard Rockwell and Superficial Rockwell.

5 8 9 ROCKWELL PRINCIPLE ROCKWELL PRINCIPLE Standard Rockwell (5) The standard Rockwell method employs only one conical diamond indenter having a 12 angle and.2 mm radius on the diamond point (see figure B) and several hard metal ball penetrators, whose diameter is always given in inches: 1/16 1/8 ¼ ½ Example With a diamond indenter and a difference of penetration of.82 mm, the Rockwell number is given by: 1- (82 2)= 59 Rockwell. Conversely, with a ball penetrator and the same difference of penetration, the Rockwell number is different: 13- (82 2)= 89 Rockwell. In instruments having a dial indicator, that shows the penetrator s displacements, the dial is generally divided into 1 graduations, so that a complete revolution corresponds to.2 mm. Dial indicators have two series of numbers: black numbers for testing with diamond indenter; red numbers for testing with ball penetrator. The zero setting must be done always on the black zero (13 red). In case of digital instruments, the test results are directly shown on a display at the end of the test cycle. Combining the different penetrators and loads, it is possible to obtain a wide range of hardness scales, as shown in table 1 FIGURE B - Profile of a rockwell core indenter Preload is constant: 1 kgf (98.1 N). Test loads (preload + additional load) can be: 6, 1, 15 kgf (588.4, 98.7, 1471 N). load kgf penetrator C D A diamond G B F ball 1/16 scale HR K E H ball 1/8 P M L ball 1/4 V S R ball 1/2 numbers black red NotE: According to the current DIN norms, preloads and loads of the different test methods (Rockwell, Brinell, Vickers) have to be given only in N (Newton). However, for practical reasons the original indication in kgf is still used. The unit of measurement of the standard Rockwell method corresponds to.2 mm penetration. The hardness number must increase according to the hardness, while the difference of penetration between preload and load decreases as the hardness increases. Therefore, the Rockwell hardness number is obtained subtracting from 1 (by diamond indenter) or from 13 (by any other ball penetrator) the difference of penetration expressed in units of.2 mm. Example TABLE 1 - Standard rockwell scales When working with diamond indenter and load at 15 kgf, hardness will be called HRC, where H means Hardness, R the Rockwell method, C the scale in use. The hardness number is placed before this abbreviation, for example 6 HRC.

6 1 APPLICATION FIELD 11 ROCKWELL PRINCIPLE OF THE DIFFERENT ROCKWELL SCALES Superficial Rockwell (6) The Superficial Rockwell method employs the same penetrators of the Standard Rockwell. The diamond indenter, however, although having the same profile, requires more a higher accuracy of the angle and of the radius. In fact, light loads give a little indentation, and in case the diamond point is not perfect, the results will be wrong. Preload is constant: 3 kgf (29.43N). Loads (preload + additional load) can be: 15, 3, 45 kgf (147.1, 294.2, N). The unit of measurement of the Superficial Rockwell method corresponds to.1 mm penetration. In the Superficial Rockwell test the zero setting is made at 1 ( dial indicator), whether when using a diamond indenter or a ball penetrator. In fact, dial indicators are divided into 1 graduations, where a revolution corresponds in this case to.1 mm. Example With a diamond or ball indenter and.82 mm penetration, the hardness will be given by: 1-82= 18 Superficial Rockwell. The test load followed by a letter, as shown in table 2, indicates the superficial Rockwell scales. The hardness number is placed before this abbreviation, for example 65 HR3 T. Application field of the different Rockwell scales As known, there are several standard Rockwell and Superficial Rockwell scales: the choice of a certain scale depends on the hardness of the material, minimum thickness of the work piece or of the hardened layer (in case of surface treatment as carburising, nitriding, etc.) The hardness of the material determines the penetrator to use: cone diamond indenter or ball penetrator. The diamond indenter is used for tempered steel or hard metal; it is not suitable for testing of steel having a resistance lower than 785 N/mm2. Steel ball penetrators are used for soft metals: the softer the material, lighter the load will be and larger the ball diameter. For example, the HRB scale (1/16 ball and 1 kgf test load) does not allow testing of soft material as the HRL scale does (1/4 ball and 6 kgf load). Generally, the largest balls are used for testing of plastics or similar only. The Rockwell method allows testing of plastic even under load. When testing very thin sheets or hardened layers, the indentation made by the penetrator during load application will influence a large area of the material, all around the indentation self. If deformation appears on the opposite side of the work piece, the test results will be wrong. Therefore, for testing of thin pieces, the load to be applied should not give a deformation higher than the minimum thickness of the part, avoiding in this way that the indentation breaks through on the opposite side of the specimen. This is a general rule for all methods of hardness testing. For each kind of testing, the minimum measurable thickness must be evaluated and considered. However, there are no specific rules, because these depend on the kind of material to be tested. Conventionally, the minimum measurable thickness is intended to be 1 times the penetration depth (see table 3). load kgf HR scale 45 45N 45T 45W 45X 45Y 3 3N 3T 3W 3X 3Y 15 15N 15T 15W 15X 15Y penetrator diamond 1/16 ball 1/8 ball 1/4 ball 1/2 ball TABLE 2 - Superficial rockwell scales

7 12 APPLICATION FIELD 13 OF THE DIFFERENT ROCKWELL SCALESv TESTING OF CYLINDRICAL SURFACES F kgf HRC ,41,33,26,19,14,9 3,69 8,47,36,26,17 45,91,77,63,37,25 6,9,8,7,6 15 1,8 1,6 1,4 1,2,8 TABLE 3 - Minimum measurable thickness by Rockwell method with cone diamond indenter Testing of cylindrical surfaces Testing conditions are different when working on a cylindrical surface than on a flat surface. In case of large diameters, the differences are not relevant; on the contrary, when testing small diameters, compensation is needed, increasing the results by a certain quantity according to the diameter and the hardness of the work piece (see table 4). The same is valid also for hardened surface layers (carburising, etc.), where normally the scale HRA is used (cone diamond-6 kgf). The most common Rockwell hardness scales are: HRC (cone diamond 15 kgf) This is the most typical Rockwell scale, used for testing of tempered, hardened or deeply carburised parts. When speaking of Rockwell hardness, we generally mean the HRC scale. This can generate some confusion, as sometimes the HRC hardness is requested for testing of parts that require different Rockwell scales or hardness methods. The HRC scale can be converted in other scales using conversion tables that must be considered an approximation only. HRA (cone diamond 6 kgf) Principally used for cemented and hard metal parts, where the hardness of carbide could generate splintering of the diamond. For this reason, heavy loads are not advisable. HRB (1/16 ball penetrator 1 kgf) Generally used in Europe for brass alloys (copper, bronze, etc) and in the USA for ferrous alloys until approx. 686 N/mm² SUPERFICIAL ROCKWELL or SUPER ROCKWELL The scales: HR15N, HR3N, HR45N (cone diamond) are suitable for testing of parts having thin layers. The scales: HR15T, HR3T, HR45T (1/16 ball penetrator) are suitable for testing of thin samples. SCALE HR C-D-A SCALE HR 15N-3N-45N Diameter of the work piece , 3, 3,5 4,5 1,5 2,5 3, ,5 2, 3, 2, 2,5 3,5 4,5 1,5 2, 1,5 2, 2,5 3,5 1,5 1,5 2, 2,5 1,5 2, TABLE 4 - Correction values for Rockwell test on cylindrical surfaces with diamond indenter (to be added to the hardness result) 1,5

8 14 ADVANTAGES AND LIMITATIONS 15 OF THE ROCKWELL METHOD MODIFICATION TO THE ROCKWELL PRINCIPLE Advantages and limitations of the Rockwell method Among the commonly used hardness methods, Rockwell is the only one that allows direct reading of the hardness value without need of optical reading as per Vickers and Brinell methods. Therefore, it is the most rapid method and the only one that can be fully automated. The instruments working according to the Rockwell principle are the most popular, because they are less subject to operators influence. Even if, according to the standards, the test surface must be carefully smooth, among the different methods for hardness testing, the Rockwell test is the least influenced by surface roughness. The main limitations are due to the fact that between maximum and minimum load there is only a 1:1 ratio. In hardness testing, the most required loads by foundries and workshops are included in the range between 1 and 3 kgf. For example, a Rockwell scale suitable for testing of cast iron or of steel sheets having a thickness lower than.15 mm does not exist. To overcome the limitation on light loads, instruments working according to the Rockwell principle are produced to work also with non-standardized light loads (2), (8). Although the Rockwell method employs a wide range of hardness scales, for a range of materials of high importance, such as untreated steel, there is not a specific scale. In this case, it is advisable to employ an instrument working according to the Rockwell principle with Brinell loads and penetrators (see page 23) Modification to the Rockwell principle The main disadvantage of the traditional Rockwell instruments is that the accuracy of testing depends to a large degree on the perfect contact between the work piece and its support, usually called the anvil. When removing the additional load and returning to the preload, the unique deformation registered by the dial indicator should be the indentation self (see part 3 of the Rockwell method description). This can happen only if the work piece is in perfect contact with the anvil; if there is a slight oil coat, some grease or other, a little movement occurs during load application, when added to the indentation depth, gives a wrong result, decreasing the hardness value. Because it is not always possible to work in perfect conditions, for example in heat treatment or workshop environments, this is an important consideration. To overcome this problem, almost all our instruments (AT-series, TWIN, BRE-AUT, COMPUTEST SC, DYNATEST SC) work according to a modification to the Rockwell principle, shown in figure C. A support on the test surface gives the penetration depth. Therefore, any movement of the part, elevating screw or stand, does not influence the test result. Thanks to this method, the same advantages of the Brinell and Vickers principle are reached.

9 16 17 MODIFICATION TO THE ROCKWELL PRINCIPLE BRINELL METHOD Brinell method In the Brinell method, a carbide ball penetrator (ball diameter is expressed in mm) is pressed on the test surface (flat and smooth) with a certain load and for a certain time (normally 15 seconds). The indentation diameter is measured with an optical system (microscope or profile projector); in case the indentation is not perfectly round, the medium value will be considered. FIGURE C - Variant to the Rockwell principle (test reference and penetrator) j The assembly (a+b) moves down on to the test piece and the penetrator moves back producing a resistance equivalent to the preload value. Zero setting is automatic. k The test load is applied. l The load is removed while the preload remains applied. The dial indicator shows the penetrator s displacement between j and l. In case of movement of the test piece, the measurement reference (b) follows the surface avoiding the typical error of the original Rockwell principle. The same method is used also in Superficial Rockwell measurement. Sfera The Brinell hardness (HB) is given by the relation between the applied load and the rounded shape given from indentation, according to the formula: HB= 2F π D(D- D 2 -d 2 ) where F is the load expressed in kgf, D the ball diameter in mm and d the indentation diameter in mm. Our instruments have a third component that should not be confused with the penetrator shroud (b). In bench testers, this component is called clamping shield. The clamping shield is used for locking of the test piece, avoiding the use of any special support; the clamping shield can be easily removed if needed. In portable testers, this component is called base, it is interchangeable and helps creating a perfect support on the test piece. FIGURE D - Drawing of the Brinell principle Having the load, the ball diameter and the indentation diameter, Brinell hardness can be deduced from the specific tables. Normally, the Brinell method employs balls having the following diameters: 1, 5 and 2.5 mm. Test loads are: 3, 1, 75, 5, 25, 187.5, 125, 62.5, kgf (2942, 987, 7355, 493, 2452, 1839, 1226, 612.9, 36.5 N).

10 18 19 BRINELL METHOD DEFINITION OF BRINELL TESTS In Brinell testing, the following steps are to be considered: 1. The standards require that the indentation diameter is between.24 and.6 of the ball diameter; to meet this condition, there must be a certain relation between the ball diameter and the load, conforming to the material to be tested. Of course, when testing a soft material with a ball having a small diameter and a heavy load, the ball will penetrate too much; conversely, when testing a hard material with a large ball diameter and a light load, the indentation cannot be read as it is smaller than.24 with respect to the ball diameter. 2. In Brinell principle, there is a fundamental relation F/D 2 between the force (kgf) and the diameter of the ball squared (mm), that is characteristic of every single test. The most common ratios are: 3, 1, 5, 2.5 (for particularly soft material it is possible to use a lower ratio). For example, having a 1 mm ball and 3 kgf load, the ratio is 3. In fact, 3:12 = 3 With a 5 mm ball and 125 kgf load, the ratio will be 5. Of course, harder is the material, higher will be the ratio to use. 3. The relation F/D 2 is important, because test results change according to the ratio in use. In fact, the same material tested with 1mm ball and 1 kgf load (ratio HB1) will give a different hardness when tested with 1mm ball and 5 kgf load (ratio HB5). On the contrary, if the material is tested with 2.5mm ball and 62.5 kgf load (ratio HB1), the result will be the same as the first test, since in both cases the ratio in use is the same (supposing that the material is homogeneous and without layers of different hardness). Definition of Brinell Tests The abbreviation HB means Brinell Hardness, where H is the hardness and B means Brinell. The Brinell hardness number is placed before the HB abbreviation, which is followed by the ball diameter in mm, load in kgf (or N) and load application time in seconds. Ball diameter mm Carico kgf ,5 2,5 187,5 62,5 31,2 15,6 Ratio HB3 HB1 HB5 HB2,5 TABLE 5 - Brinell test and ratio F/D 2 Example: 35 HB 2.5/187.5/15 For portable instruments, the abbreviation HB is followed by the ratio F/D 2 (for example, 35 HB3). For the various ratios, please see table 5.

11 2 21 APPLICATION FIELD OF BRINELL TEST APPLICATION FIELD OF BRINELL TEST Application field of Brinell test As reported in the previous chapter, the hardness of the material determines the ratio of the test. Once the ratio has been determined, the load will be decided according to these elements: 1. Minimum measurable thickness of the test material (see table 6) Ball F HB mm kgf ,5 187,5 HB3 2,4 1,6 1,2,8,6, , 1,3,8 3 HB , 5,3 4, 3,2 2,1 1,6 HB1 1 3 HB3 9,6 6,3 4,8 3,2 2,4 1,9 TABLE 6 - Minimum measurable thickness in Brinell test 2. Homogeneity of the material. In case of non-homogenous material, it is advisable to work with heavy load. 3. Ability to measure the indentation, whether using a microscope or profile projector, it will be easier on a larger indentation that on a smaller one. The following is a summary of the Brinell tests on the different materials Steel Always HB3. The Brinell test is fundamental for steels, because of an exact constant relationship existing between the Brinell hardness and tensile strength (with ratio.36 for carbon steels, chrome and chrome-manganese;.34 for nickel-chrome steels). Example: 225 HB3x.x36x9.87= N/mm 2 This is the only non-destructive test for determining the tensile strength of steel. The Brinell method, however, is not suitable for tempered steel that requires the diamond indenter. Soft iron is generally tested with HB3, even though the indentation diameter exceeds half of the ball diameter. Cast iron Always HB3. Because of the poor homogeneity of this material, it is advisable to work with the heaviest load compatible with the minimum thickness of the work piece. Generally, the load 3 kgf is used. Light alloys HB1 or HB5. Particularly soft alloys require HB 2.5. Copper alloys HB1 for bronze (if particularly hard even HB3) and HB5/HB1 for brass.

12 22 ADVANTAGES AND LIMITATIONS Testing according to the Rockwell principle 23 OF THE BRINELL METHOD with Brinell penetrators and loads Advantages and limitations of the Brinell method The main advantage offered by the Brinell method consists in the possibility of employing heavy loads using rugged and easy-to-use instruments. Furthermore, the indentation can be read by a microscope or an eyepiece. Testing is possible even if positioning of the piece is not perfect, as required by Rockwell method. Brinell testing is not sensitive to the deflection of the testpiece. It is possible to derive the tensile strength value simply by multiplying the Brinell hardness number by a certain factor, changing according to the test material. Deformation of the indentation may show existing stress in the test material. The main limitation of this method is due to the optical reading of the indentation that may cause measurement errors due to the operator. Furthermore, an accurate surface preparation is needed to obtain reliable results. For these reasons, the Brinell method cannot be considered a quick test and it is not suitable for testing of high volumes. To overcome this problem, the choice is often to work according to the Rockwell method but using Brinell penetrators and loads (see the next chapter) (9). In case of testing of cylindrical surface, it is necessary to create a flat area on the test surface (1). Testing according to the Rockwell principle with Brinell penetrators and loads As said at the previous chapter, to overcome the different limitations of the Brinell method, the Rockwell testers are generally used to perform tests with Brinell penetrators and loads. In fact, the main part of Rockwell instruments as well as the Rockwell loads, work also with Brinell loads (62.5, 125, kgf / 612.9, 1226, 1839 N). In this case, the difference of penetration between preload and load gives the indentation measure. Test results are directly shown on the display or on the dial indicator in Rockwell numbers that will be converted in Brinell numbers using the proper table. This method, however, is not a real Brinell test, since this would require the optical reading of the indentation. In fact, the results given by the table are not the same for all the materials: for example, the conversion for steel is different from the one for cast iron. Nevertheless, this method is more convenient in the case of high volume testing, as it allows avoiding the optical reading and the surface preparation required by the classic Brinell test. When testing steel, it is possible to use a special calibrated scale for the direct reading of tensile strength in kgf/mm 2 - N/mm 2. To increase the accuracy in the case of high volume testing, the range of Ernst testers give the operator the possibility to introduce a new and temporary calibration of the Brinell scale, based on Brinell test blocks where the indentation has been made by classic Brinell tester.

13 24 25 VICKERS METHOD APPLICATION FIELD OF VICKERS METHOD Vickers method The working principle is the same as the Brinell one, but in this case it employs only one indenter, being a pyramidal diamond with square base having an angle of 136 between the opposite faces. After the indentation is made, the two diagonals will be measured and as these are almost never the same, the average value will be considered. Application field of Vickers method In the Vickers method it is possible to compare the results obtained at different loads to each other. This is possible, because the Vickers method makes use of only one penetrator and because the Vickers number represents the specific load per mm 2 on the indentation. For example, when testing on the same material at 3 kgf (294.3 N) and afterwards at 1 kgf (9.81 N) the result will be the same (supposing that the material is homogeneous and without different hardness layers). Even in the presence of layers, the Vickers method can be applied, using increasing loads to determine the case depth. It is important to consider that when test loads are lighter than 2 grams, even if the material is homogeneous, there will be an increase of the hardness number, because of the manifestation of the phenomenon s of residual stress. Also for the Vickers method, the minimum measurable thickness is considered to be 1 times the penetration depth (see table 7). FIGURE E - Drawing of Vickers principle As per the Brinell hardness number, the Vickers number is given by the relationship between the applied load and the surface area of the indentation, according to the formula: 2F 136 F HV=. sen = d 2 2 d 2 where F is the load expressed in kgf and d the diagonal (or average of the diagonals) given in mm. Of course, also in this case to obtain the Vickers hardness the proper table must be consulted. There are different test loads, but the most common used are: 1, 2, 5, 1, 3 kgf (9.81, 16.62, 49.5, 98.1, N). It is possible to work with loads lighter than 1 kgf (9.81 N) entering in this way the micro-indentation hardness fi eld, whose main application takes place in metallographic laboratories. F kgf The abbreviation for Vickers testing is HV (H= hardness, V=Vickers), followed by the test load expressed in N or kgf and in some cases by the load application time. The hardness number is placed before the abbreviation. Example: 715 HV 5/15 The Vickers test is especially suitable for testing of small or thin parts or parts having superficial treatment, where there is the need to work with light loads; the Vickers method is to be avoided for testing of non-homogeneous materials, such as cast iron. HV ,2,19,12,9,6,5,4,4,3,3 1,43,28,19,14,12,1,8,7,6 2,62,39,28,19,16,14,12,1,9 5,62,44,31,25,22,18,15,14 1 1,4,87,62,43,36,31,25,22,19 TABLE 7 - Minimum measurable thickness by Vickers testing

14 26 ADVANTAGES AND LIMITATIONS SHORE METHOD FOR METALS 27 OF THE VICKERS METHOD KNOOP METHOD Advantages and limitations of the Vickers method The main advantage of the Vickers method consists in employing only one scale, that can range from the lowest to the highest hardness. For this reason this method is fundamental for researching laboratories. Any deformation of the indentation may reveal structural characteristics of the test material. As for the Brinell test, the Vickers method is not sensitive to any deflection of the work piece. In comparison with the Rockwell and Brinell values, the Vickers hardness number has a proper meaning, as it represents a specific load on an indentation having always the same shape. The limitation of the Vickers method is due to the low speed of operation, as the measurement of indentation has to be made optically (microscope or profile projector). The test area must be carefully prepared and polished. For this reason, perpendicularity of the indenter axis is a very important factor, as any inclination would give an irregular indentation. For these reasons, Vickers method is not recommended for testing in production lines. Finally, we can say that the Vickers method is more suitable for testing in laboratories than in workshops. To overcome these disadvantages, our range of testers are designed to read the Vickers hardness in a rapid and easy way (11). Shore method for metals This method is based on the following principle: a ball (or a rod with ball point) falls on the test piece and rebounds more or less according to the hardness of the material. This method does not find a common use, because even if the working principle is simple, the test accuracy depends on the mass of the work piece and on the perpendicularity of the fall axis. The test result is given in Shore points and it is the standardized for testing of large cylinders with high finish surface refinement. Some of our testers can be equipped with the Shore scale allowing a direct reading of this hardness (12). Knoop method Similar to the Vickers, this method employs a diamond indenter having a rhomboidal pyramidal shape with diagonals ratio 1:7 This method is used in the laboratories for testing at low loads.

15 28 USE OF THE HARDNESS CONVERSION TABLES APPENDIX - BENCH HARDNESS TESTERS 29 AND TEST BLOCKS (SEE THE REFERENCES MENTIONED IN THE GUIDE) Use of the hardness conversion tables The equivalence among the different hardness scales is the result of various empirical experiences, but it is important to keep in mind that there is no mathematical relationship between them. In fact, tables from different sources often show remarkable differences in the results. For this reason, the hardness values calculated with tables cannot be considered as absolute values, but approximations only. Generally, hardness conversion tables show also tensile strength values expressed in kgf/mm 2 and N/mm 2 for steels, with conversation ratios of.36 or.34 with respect to HB3. Use of hardness test blocks Generally, hardness testers are equipped with one or more hardness test blocks. These test blocks are made of a highly homogenous material, carefully treated. The blocks are calibrated on one side only. It is important to check the instrument with test blocks, in order to verify operation and accuracy. The minimum distance between the two centres of adjacent indentations or of an edge of the test block must be the following: - for Rockwell testing: 3 mm - for Rockwell N: 1 mm - for Rockwell T: 2 mm - for Brinell testing: from 2.5 to 6 times the indentation diameter, according to the hardness. When the test surface of the block is fully covered by indentations, the test block must be changed with a new one. With time, the hardness of the test blocks may change. We know for experience, that the hardness checked on some test blocks HRC 6 five years later has increased by.5-1 point HRC. For more information, please ask us for the leaflets. (1) Bench hardness testers as: NR3D R - Version Rugged and easy-to-use Rockwell hardness tester, with standardized preload and load. Test loads for Brinell testing. SR - Version Superficial Rockwell execution of NR3-DR. Test loads for Brinell testing. AT13 DR - Version Hardness tester for Rockwell testing according to a variation of the Rockwell principle with digital readout of test results (see page 1). Standardized preload and test loads. Test loads for Brinell testing. Four different stands available. DSR - Version Superficial Rockwell execution of AT13 DR. Test loads for Brinell testing. AT25X DR - Version Similar to AT13, with digital readout through microprocessor and touch screen Swift testing, data printing, statistics, tolerances, etc. Standard USB output and optional output modules: RS232, Bluetooth, Ethernet, Profibus, etc. 8 Languages - possibility to request optional languages Eight or more hardness scales available. Four test stands available. Test loads for Brinell testing. DSR - version Superficial Rockwell execution of AT25DR. Test loads for Brinell testing. ESATEST MTRX (ESATEST principle) Makes use of a testing principle, that allows testing of odd shaped parts difficult test points, as grooves, holes, involutes. With one test only, it is possible to display the hardness values at different loads. This is particularly helpful when testing of surface treated areas to learn immediately the case depth. Touchscreen

16 APPENDIX - BENCH HARDNESS TESTERS (SEE THE REFERENCES MENTIONED IN THE GUIDE) 3 31 (SEE THE REFERENCES MENTIONED IN THE GUIDE) For more information, please ask us for the leaflets. Automatic hardness testers as: BRE-AUT (8) Automatic hardness tester for Brinell testing with variable loads from 5 to 3 kgf. Suitable for custom in line applications. (see our Automatic hardness testers leaflet)**** APPENDIX - BENCH HARDNESS TESTERS (2) (4) Portable hardness testers as: COMPUTEST SCX Tester with direct reading of test results on LCD backlit display. Seven or more hardness scales available. Static testing on flat and cylindrical surfaces and on different metals. Test load 5 kgf. USB and RS232 output. TWIN Hardness tester for testing of Rockwell and Superficial Rockwell hardness. Test head displacement, load change and load application are automatic. 45 mm penetrator s stroke. Insensitive to any deflection of the work piece. It is possible to remove the elevating screw assembly for working in line. The electronics permits further different functions. Standard USB output and optional output modules: RS232, Bluetooth, Ethernet, Profibus, etc. 8 Languages - possibility to request optional languages Touchscreen. AT35X DRT-M - version Motorized hardness tester, upgrade of the AT13 and AT25 series, especially designed for high-volume testing (approx. 1 pieces/h). It can be integrated into custom in-line applications for a completely automated testing process Standard USB output and optional output modules: RS232, Bluetooth, Ethernet, Profibus, etc. 8 Languages - possibility to request optional languages Touchscreen. OMNITEST Omnitest is suitable for all standardized and common test methods, such as: Rockwell, Superficial Rockwell, Brinell, Vickers and Knoop (on request). Omnitest is equipped with an integrated PC operated by Windows XP, high resolution (2 mega pixels) USB camera with LED lighting source. Software for fully automatic measurement of all indentations with possibility to operate manually. Omnitest performs the hardness testing with loads from 9,84 N to 2451 N (1-25 kgf). The indentation image can be captured and memorized with possibility to be recalled until the test protocol has been issued or the data have been exported. DYNATEST SCX Similar to Computest SCX, but with heavy load (more than 1 kgf). Four or more hardness scales available. Unique of its kind, this instrument allows the accuracy of a bench hardness tester thanks to the heavy load. USB and RS232 output. HANDY ESATEST X (ESATEST principle ) Portable execution of the MTR model. Weight of the instrument 1.5 kg. Selectable load from 1 to 1 kg. USB and RS232 output. (3) STE Dynamic or static-dynamic system working with calibrated pins. Test load 158 kgf. Test results in Brinell scale and tensile strength. In compliance with the Brinell 3 D2 standards. APPENDIX - CASE DEPTH ANALYSIS (SEE THE REFERENCES MENTIONED IN THE GUIDE) Case depth analysis: HTD15 Automatic system for case depth analysis with hard metal penetrator; based on the principle of depth measure according to the surface of the test piece. Measurable thickness.5mm - 1.3mm, maximum test load 15kgf (14 71N). HTD4 Automatic system for case depth analysis with hard metal penetrator; based on the principle of depth measure according to the surface of the test piece. Measurable thickness.5mm - 2.7mm, maximum test load 4kgf (39 227N).

17 32 HARDNESS TESTER COMPARISON TABLE HARDNESS TESTER COMPARISON TABLE 33 PORTABLE HARDNESS TESTERS BENCH HARDNESS TESTERS AUTOMATIC HARDNESS TESTERS CASE DEPTH ANALYSIS ste computest scx dynatest scx handy esatest X esatest mtrx NR3 AT13 AT25X AT35X twin bre-aut omnitest htd9s htd4 MATERIAL STEEL LIGHT ALLOYS CAST IRON X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X PLASTIC X X SIZE AND SHAPE OF THE PART TO BE TESTED IRREGULAR LARGE SMALL THIN INTERNAL INVOLUTES/ GEARS X X X X X X X X X X X X X X X X X X X X X X X X X X X X x x x x X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X HARDNESS ROCKWELL BRINELL VICKERS X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X

18 NOTES 35

19 ERNST HÄRTEPRÜFER SA Via Cantonale 36A I CH-6814 Lamone - Switzerland Tel I Fax I sales.ernstsa@ernsthardnesstesters.com EN-15 We deserve the right to make modifications