บทความ Rockwell Hardness Scale
Rockwell hardness scales
หน่วยความแข็งสเกลร็อกเวลล์
สเกลบ่งบอกถึงความแข็งของวัสดุ มีการนำมาใช้ครั้งแรกในปี ค.ศ.1919 ถูกคิดค้นโดย สแตนลีย์ พี. ร็อกเวลล์ จะใช้สัญญลักษณ์ HR ตารมด้วยตัวอักษรที่แสดงหน่วยที่เป็นไปได้ ซึ่งรายละเอียดอยู่ในตารางแนบท้าย ยกตัวอย่างเช่น “HRC 96” หมายถึง ความแข็ง 96 ในหน่วยร็อกเวลล์สเกล C ตัวเลขความแข็ง Rockwell โดยปกติมักจะใช้เพื่ออธิบายความแข็งของโลหะ ถึงแม้ว่าในบางครั้งจะใช้กับพลาสติกได้บ้าง
ค่าความแข็งสเกลร็อกเวลล์ ขึ้นอยู่กับความลึกของหลุมกด ที่วัสดุถูกกดโดยหัวกดเพชร หรือหัวกดบอล ซึ่งวิธีการทดสอบแตกต่างจากการทดสอบแบบบริเนลล์ แต่ค่าความแข็งขึ้นกับขนาดหลุมกดเช่นกัน
A scale indicating the hardness of materials, first used in 1919, when it was invented by Stanley P. Rockwell. The measurement has no units. The symbol is HR followed by a letter indicating one of a number of possible scales, described in the table below. For example, “HRC 96” means 96 on the Rockwell C scale. Rockwell hardness numbers are usually used to describe the hardness of metals, although they are also used for some plastics.
Like the Brinell hardness scale, the Rockwell scale is based on measuring the depth of the indentation made by pressing a diamond point, or a ball, into the material. Unlike the Brinell test, however, the Rockwell test makes two depth measurements. The ball (say) is brought in contact with the material to be tested. The preliminary force is applied for a set length of time, and then the depth of the indentation is measured. Then the force is increased in a set rate until it reaches the total force. This force is kept constant for a predetermined period, after which the force is reduced to the preliminary force level. After a set period of time, the depth of the indentation is measured for a second time. Usually the entire process is carried out by automatic machinery.
| Regular Rockwell Scales |
Scale Symbol | Indenter Type. If a ball, diameter in millimeters (diameter in inches) |
Preliminary force in newtons (kg-force) |
Total force newtons (kgf) |
Typical Applications |
|---|---|---|---|---|---|
| A | Spheroconical diamond | 98.07 (10) |
588.4 (60) |
Cemented carbides, thin steel, and shallow case hardened steel. | |
| B | Ball 1.588 (1/16) |
98.07 (10) |
980.7 (100) |
Copper alloys, soft steels, aluminum alloys, malleable iron, etc. | |
| C | Spheroconical diamond | 98.07 (10) |
1471 (150) |
Steel, hard cast irons, pearlitic malleable iron, titanium, deep case hardened steel, and other materials harder than 100 on the Rockwell B scale. | |
| D | Spheroconical diamond | 98.07 (10) |
980.7 (100) |
Thin steel and medium case hardened steel, and pearlitic malleable iron. | |
| E | Ball 3.175 (1/8) |
98.07 (10) |
980.7 (100) |
Cast iron, aluminum and magnesium alloys, and bearing metals. | |
| F | Ball 1.588 (1/16) |
98.07 (10) |
588.4 (60) |
Annealed copper alloys, and thin soft sheet metals. | |
| G | Ball 1.588 (1/16) |
98.07 (10) |
1471 (150) |
Malleable irons, copper-nickel-zinc and cupronickel alloys. | |
| H | Ball 3.175 (1/8) |
98.07 (10) |
588.4 (60) |
Aluminum, zinc, and lead. | |
| K | Ball 3.175 (1/8) |
98.07 (10) |
1471 (150) |
Bearing metals and other very soft or thin materials. Use smallest ball and heaviest load that does not give anvil effect. | |
| L | Ball 6.350 (1/4) |
98.07 (10) |
588.4 (60) |
||
| M | Ball 6.350 (1/4) |
98.07 (10) |
980.7 (100) |
||
| P | Ball 6.350 (1/4) |
98.07 (10) |
1471 (150) |
||
| R | Ball 12.70 (1/2) |
98.07 (10) |
588.4 (60) |
||
| S | Ball 12.70 (1/2) |
98.07 (10) |
980.7 (100) |
||
| V | Ball 12.70 (1/2) |
98.07 (10) |
1471 (150) |
||
| Superficial Rockwell Scales |
15N | Spheroconical diamond | 29.42 (3) |
147.1 (15) |
Similar to A, C and D scales, but for thinner gage material or case depth. |
| 30N | Spheroconical diamond | 29.42 (3) |
294.2 (30) |
||
| 45N | Spheroconical diamond | 29.42 (3) |
441.3 (45) |
||
| 15T | Ball 1.588 (1/16) |
29.42 (3) |
147.1 (15) |
Similar to B, F and G scales, but for thinner gage material. | |
| 30T | Ball 1.588 (1/16) |
29.42 (3) |
294.2 (30) |
||
| 45T | Ball 1.588 (1/16) |
29.42 (3) |
441.3 (45) |
||
| 15W | Ball 3.175 (1/8) |
29.42 (3) |
147.1 (15) |
Very soft material. | |
| 30W | Ball 3.175 (1/8) |
29.42 (3) |
294.2 (30) |
||
| 45W | Ball 3.175 (1/8) |
29.42 (3) |
441.3 (45) |
||
| 15X | Ball 6.350 (1/4) |
29.42 (3) |
147.1 (15) |
||
| 30X | Ball 6.350 (1/4) |
29.42 (3) |
294.2 (30) |
||
| 45X | Ball 6.350 (1/4) |
29.42 (3) |
441.3 (45) |
||
| 15Y | Ball 12.70 (1/2) |
29.42 (3) |
147.1 (15) |
||
| 30Y | Ball 12.70 (1/2) |
29.42 (3) |
294.2 (30) |
||
| 45Y | Ball 12.70 (1/2) |
29.42 (3) |
441.3 (45) |
The table is adapted from Table 1 of
Samuel R. Low.
Rockwell Hardness Measurement of Metallic Materials.
NIST Recommended Practice Guide.
Special Publication 960-5.
Washington: U.S.G.P.O. 2001.
Standards
ASTM E 18 – 2000, Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials.
ISO 6508-1 Metallic Materials – Rockwell hardness test (scales A, B, C, D, E, F, G, H, K, N, T) – Part 1: Test method, 1999-09-01
ISO 6508-2 Metallic Materials – Rockwell hardness test (scales A, B, C, D, E, F, G, H, K, N, T) – Part 2: Verification of testing machines, 1999-09-01
ISO 6508-3 Metallic Materials – Rockwell hardness test (scales A, B, C, D, E, F, G, H, K, N, T) – Part 3: Calibration of reference blocks, 1999-09-01
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