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Rockwell hardnes testing

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Rockwell hardnes testing

  1. 1. Rockwell Hardnes Testing
  2. 3. Rockwell Hardness Testing <ul><li>Test Principle: </li></ul><ul><li>Rockwell hardness Number (RHN) based on an inverse relationship to the measurements of the additional depth </li></ul><ul><li>Which an indenter is forced by a heavy (major) load beyond the depth resulting from a previously applied (minor) load. </li></ul>
  3. 5. <ul><li>Indenter: </li></ul><ul><li>120 degree sphero-conicall diamond indenter is used for hard material. </li></ul><ul><li>Hardened steel ball indenter with diameter of 1/16,1/8,1/4.1/2 inch. </li></ul>
  4. 6. Types of Test <ul><li>Two types of test based on load </li></ul><ul><li>Load Rockwell Superfical </li></ul><ul><li>Minor 10Kg 3 Kg </li></ul><ul><li>Major 60,100,150 Kg 15,30,45 Kg </li></ul>
  5. 7. Rockwell Scales <ul><li>There are 30 different scales ,depending on the combination of the indenter and the load. </li></ul><ul><li>64 HRC means RHN of 64 on C- scale, (diamond indenter and 150 Kg major load) </li></ul><ul><li>100 HRB means RHN 100 on B-scale (1/16 inch steel ball and major load 100Kg ) </li></ul><ul><li>81 HR 30 N means SHN 81 on 30 N-scale (30 N diamond indenter and major load 30 Kg) </li></ul>
  6. 8. Dial Gauge <ul><li>One revolution of the large pointer equals 1mm </li></ul><ul><li>There are 100 divisions to a revolution </li></ul><ul><li>Therefore ,1 division=0.01 mm </li></ul><ul><li>Dial gauge is connected to a plunger system in the head of a tester </li></ul><ul><li>By means of the index lever having 5:1 </li></ul><ul><li>Therefore depth for 1 division = 0.01x0.2=0.002 </li></ul>
  7. 9. <ul><li>Indentation depth caused by major load </li></ul><ul><li>HRC= 100 - -------------------------------------------------- </li></ul><ul><li>0.002 </li></ul>indentation depth caused by major load HRB= 130 - ------------------------------------------------ 0.002
  8. 10. Rockwell indentation One dimension on the dial gage - a depth of 0.002mm. Zero reference line –100 for C scale and-130 for B scale
  9. 11. Depth of indentation <ul><li>Indentation depth from minor to major load: in case of Rockwell test </li></ul><ul><li>(60HRC). </li></ul><ul><li>(100-60)x0.002mm= 0.08mm. </li></ul><ul><li>(130-Ball indentation reading)x0.002mm. </li></ul><ul><li>Superficial test </li></ul><ul><li>(regardless of the indenter used) </li></ul><ul><li>80HR30N </li></ul><ul><li>(100-80)x0.001mm=0.02mm </li></ul>
  10. 12. Factors that control Scale selection <ul><li>-Type of material, </li></ul><ul><li>-Specimen thickness , </li></ul><ul><li>-Test location , </li></ul><ul><li>-Scale limitation. </li></ul>
  11. 13. Type of Materials <ul><li>Hard materials such as steel or tungsten carbide diamond indenter would be used. </li></ul><ul><li>This limits to one of six Rockwell scale i.e C,A,D,45N,30N,15N. </li></ul><ul><li>Out of the above scales now determine which scale will guarantee accuracy, sensitivity and repeatability. </li></ul>
  12. 14. Specimen Thickness <ul><li>The material around the indentation is cold worked. </li></ul><ul><li>The extent of cold work area depends on the type of material and previous history of the testing material </li></ul><ul><li>The depth of material affects has been found by extensive experimentation to be the order of ten times the depth of indentation. </li></ul>
  13. 15. Test location <ul><li>If an indentation is placed with in the cold worked area (previous indentation). </li></ul><ul><li>The reading usually will be higher than that obtained had it been placed out side this area. </li></ul><ul><li>As a precaution three diameter from the centre of one indentation to another is sufficient for most material. </li></ul><ul><li>The distance from edge should be minimum of 2.5 diameter of indentation. </li></ul>
  14. 16. Scale limitation <ul><li>No upper limit to the hardness of a material that can be tested with a diamond indenter. </li></ul><ul><li>However C scale should not be used on tungsten carbide (material may fracture or indenter may damage). A scale is acceptable in this case. </li></ul><ul><li>Diamond indenter are not calibrated below values of 20. </li></ul>
  15. 17. Anvils <ul><li>The work piece must be supported by the proper anvil so that, </li></ul><ul><li>It can not slide, roll or sag during the test. </li></ul><ul><li>If not supported properly then accurate reading is obtained. </li></ul><ul><li>Or the indenter may damage. </li></ul>
  16. 18. Superficial hardness Rockwell hardness
  17. 19. Case hardened and Decarburization Parts <ul><li>Using several different scales case characteristics can be determined. e.g </li></ul><ul><li>parts shows 91 HR15 N and 62 HRC. This means same hardness at an appreciable depth . </li></ul><ul><li>91HR15N and 55 HRC. This means indenter has broken through a relatively thin case. </li></ul><ul><li>Decarburization can be detected by reversing the techniques described above. </li></ul>
  18. 20. Rockwell Testing at Elevated Temperature <ul><li>Tester in a furnace with provision of controlled atmosphere . </li></ul><ul><li>Facilities to move the specimen in the furnace. </li></ul>
  19. 21. Rockwell testing Machines <ul><li>Test load can be applied either dead weight or through springs. </li></ul><ul><li>Measuring device - a dial or digital meter. </li></ul><ul><li>Microprocessor to control the test process. </li></ul><ul><li>Bench type testing machine. </li></ul><ul><li>Production type. </li></ul><ul><li>Portable type machine </li></ul>

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