1. Standard Blocks

To control various industrial hardness testers,it is important to verify all related factors, including indenters, static and dynamic loads, indentation measurement, and sample pieces. Hardness blocks allow overall control of these complicated factors in the field. Therfore, it is imperative that a uniform surface hardness is displayed by all our test blocks, that the main factors of secular change are eliminated and, if possible, that the characteristics of their materials are similar to those of materials in practical use. Our company, which was established in 1939 by Shoichi Yamamoto, is the first dedicated manufacturer of standard test blocks in Japan, and has maintained its reputation as the best and the foremost company in this field.

2. ISO 9001 Quality System

We received a certificate dated December 26,1997, issued by Japan Quality Assurance Organization (JOA), stating that Yamamoto's quality management system for hardness blocks complies with the requirements of the following standards. The register certificate No. is JQA-2078 ISO 9001-2000 I JIS Q 9001 : 2000.

3. Characteristics of Our Hardness Blocks
Shows detailed specifications of our test blocks and their materials.

3. 1 Materials and manufacturing process

To maintain one highly uniform  surfacehardness, strict quality control of materials must be ensured for each test method. Our blocks are first cut from a plate material to avoid being affected by center segregation. Next, after machining to the required shapes, heat treatment is carefully applied to the blocks to get a stable microstructure and the required hardness level. For such cases, a very accurate conversion relationship has been already obtained especially between Shore hardness (HS), which is the Japanese original standard, and Vickers hardness (HV) values using eutectoid carbon steel. After heat treatment is completed, the blocks are ground, lapped, and then undergo a through advance. In  this  case, at  least three readings should be taken, and  a X-R controlling method adopted. Measuring locations should be  selected over the working surface to  represent the  hardness of the  whole block surface. Serial No. (side), hardness value, and inspection date of  hardness blocks are  checked against the  attached inspection sheet. The warranty period shall be three years from polishing process, followed by wet buffing to improve measuring precision and achieve the most accurate and consistent hardness available in the world. Care is taken so that the surfece is not adversely affected, which could result in surface hardness irregularities, and a routine microscopic structure inspection is performed as required across the finished test surface for possible variations caused in the processes.

3. 2 Hardness measurement of standard blocks

Each 20-block lot that has undergone heattreatment and other finishing processes is subjected to hardness tests to check for variations in hardness, and to determine reliable, measurement-based reference values.

4. Integrated Precision of Hardness Testers and Hardness Blocks

Force, indenter, indentation measurement and movement conditions, etc., should be separately inspected to metrically verify the integrated precision of hardness testers. Industrial adjustments of these conditions focus upon ISO standards. On the other hand, indirect verification of a tester with test blocks is used to integrally verify these respective conditions. It is quite natural, therefore, the uncertainty factor due to the material to be additionally considered, as   well as metrical  accuracy values. We do our utmost in material selection, heat treatment, and other processes to achieve the world's highest accuracy.

5. Best Use of  Test Blocks

5.1  Choice of test blocks

Normally, the general accuracy of a tester needs to be indirectly verified with blocks for at least the three ranges -high, middle, and low ranges of scales -in which a tester is being used. Routine inspections should be performed with blocks in the high frequency ranges in use.

5.2 Notes

Concerning hardness management with blocks, testers should be directly verified in the  inspection date, although the  blocks are considered to  be  effective for  five  years. Flaws and  attachments on  the  front or  back surface, as  well  as  re-processing of  blocks, are  strictly forbidden. (This similarity applies to  anvils used.)

6. Durability of Our Blocks

Secular changes of  all  our  blocks areeliminated by  a  sufficient heat treatment process, regardless of  the  block type. Due  to work hardening near and  around the  perimeters of  indentations, the  usable test  area is  limited, as JIS  prescribes it  to be 4d (d=diameter of  the indentation) as  spaces between indentations. To  make the  maximum use  of  a  block, indentations should be made evenly over the  test surface. For  this  purpose, we recommend dividing the  working surface. (See the figure at  the  left.) For the  durable limits specified in  Table 3, reduce the  numbers to  half  if  the  highest level of accuracy is  required.