1、THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS United Engineering Center 345 East 47th Street New York, N. Y. 1 O0 17 iASME SI-L 82 m 0759670 0083944 5 m 7 , I -. ASME GUIDE SI -1 ASME 0rientati.on. and Guide for Use of SI (Metric) Units NINTH ED March 24,1982 llTlON THE AMERICAN SOCIETY OF MECHANICAL
2、 ENGINEERS United Engineering Center 345 East 47th Street New York, N, Y. 1 O01 7 No part of this docment may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher / Copyright O 1982 THE AMERICAN SOCIETY OF MECHANICAL ENGINEE
3、RS All Rights Reserved Printed in U.S;A. BOARD ON METRICATION J. G, Langensteh, Chairman Kurt Wessely, secretary W, P. Adkins J. T. Blackburn, Jr. J. S, Castorina O, J. Fisher W. P. Gobell, Jr. F. T, Gutmann Carl Handen F. R. Jackson R. G. Jobe J. G. Langenstein Samuel Leland J. B. Levy R. J. Mann W
4、. G. McLean J. W. Murdock D. H. Pai J. J, Pohl, Jr. P. C. Quo K. J. Simila C, E. Smith A. M. Smolen D. H, White C. J. Wilson B. D. Ziels Con tents SECTIONS 1 . Backgraund and Policy . 1 2 . History of the International System 3 3 . SIBaseUnits . 4 4 . Supplementary Units 5 5 . PreBxes . 5 7 . Rules
5、for Use of SI Units in ASME Publications 9 8 . Conversion and Rounding . 10 9 . Dimensioning . 16 11 . Units Accepted Temporarily. . 18 6 . The Coherence of Derived Units in SI . 7 10 . Units Outside the International System 17 12 . Units Not to be Used in ASME Documents. . 19 13 . SI Units for ASME
6、 Use. 21 14 . Introducing SI Units in ASME Publications . 23 15 . Introducing SI Units in Tables 24 16 . Methods of Reporfing SI Equivalents for Existing Standards Under Revision . 24 TABLES 1 . SI Base Units . 5 2 . SI Unit Prefwes 6 4 . Some Derived Units Withovt Names 9 S . Units in Use With the
7、Inteqational System . 18 6 . Units Used With the International System in Specialized Fields . -18 7 . Units To Be Used With the International System for a Limited Time . 19 8 . CGS Units with Special Names . 20 10 . List of SI Units for ASME Use. . 21 APPENDICES . Appendix1 25 Appendix2 26 Appendix3
8、 28 Appendix4 29 Appe4dix5 30 Appendix7 . . ! . 32 Appendix8 33 Appendix9 34 Appendix10 . 36 3 . Derived Units With Names . 9 9 . Other Units 20 Appendix6 31 V ASME Guide SI-1 ASME Orientation and Guide for Use of SI (Metric) Units Ninth Edition March 24, T982 SECTION l. BACKGROUND AND POLICY The 19
9、67 Regional Administrative Conference passed the following resolu- tion: “Form a working committee to propose and implement constructive solutions to problems associated with conversion to the metric system.” In 1968 a Special Committee on Metric Study was established by the Council of ASME. This co
10、mmittee has held a series of meetings which culmi- nated in the following Council policy: 1. 197O:The ASME anticipates the displacement of the usage of US. customary units by the usage of. SI* (metric) units in-many fields. 2, 1970-The ASME believes that both U.S. customary and the SI systems of uni
11、ts, modules, sizes, ratings, etc., will continue in use in the foresee- able future. 31 1970-Because of the increasing international commitment 0f.U.S. engi- neering and U.S. industry and commerce, the ASME recognizes the need for an accelerated growth in the capability in and between both -systems
12、by the mechanical engineering profession. 4. 1970-The ASME will encourage and assist the development of this “dial capability” by specific and positive actions, including the fol- (a) Contribute to the continuing development of the International (b) .Develop .and disseminate data to facilitate conve
13、rsion and insure (c) Provide and promote education in the fundamentals and applica- . lowing: System, particularly to meet engineering requirements. correspondence between the U.S. customary and SI. tion of both systems. *International System 1 ASNE SI-L 82 I 0759b70 00839LI9 Y 1- (d) Encourage and
14、guide theuse or inclusion of SI units as appropriate (e) Work with ANSI to develop and implement U.S. national poli- 5. 1970-The ASME will continue to support the National Bureau of Standards of the -Department of Commerce in its “Metric Study,” pursuant to Public Law 90472.Its.membership will be ke
15、pt informed of all significant NBS actions. 6. 1972-For the purpose of moving forward the ASME will maintain close liaison with legislative activities concerned with increased use of the International Metric System (SI). 7. 1973-The Society encourages the initiation of a coordinating volun- tary nat
16、ional program of conversion to SI usage. 8. 1973-As of July 1, 1974, SI units (in addition to any other units) will be required in ASME papers and in revised, reaffirmed and new engi- neering standards. 9. 1974-The ASME will cooperate fully with the American National Metric Council (ANMC), and other
17、 societies and agencies to minimize duplication of effort . 10. 197741 units shall be included in standards at the appropriate time as determined by industry, government, public and society needs consis- tent with nationd plans for coordinating and managing development of SI standards. . The ASME Me
18、tric Study Committee maintains contact with the National Bureau of Standards and various technical societiesinvolved in the change to SI and has developed educational material and reports to the membership. The committee also developed sociefy positions on metric legislation. The U.S. Metric Study R
19、eport was submitted t Congress for study and imple- mentation in July, 1971. This report -recognized that “ngineeringstandards have served as a keystone in our domestic industrial development, as they have in other industrialized nations.” It notes that only a small portion of U.S. standards are coo
20、rdinated by the American National Standards Institute (ANSI) which represents the -U;S. on the International Electrotechnical Commission (IEC) and in the International Organization for Standards (ISO). Many IEC and IS0 recommendations are not compatible with U.S. Standards, The report further states
21、: “If U.S. practices ar to-be reflected in inter- national recommendations, active participatiob on the drafting committee is essential.” With the trend to use the International System of Units “further national standards which do not include SI units are ot likely to receive due consideration in th
22、e development of international standards.” Since dimensional specifications in different metric countries are incom- patible as frequently as those in countries using the inch unit for measure- ment “a change-to SI dos not by itself make patible.” The re- port continues, “a few dimensional specifica
23、tions based on the inch and U.S. in Codes and Standards and other ASM,E publications. cies regarding international standardization. 2 i ASME SI-L 82 m 0759670 0083950 O 1 engineering .practices are used internationally and have been incorporated in IEC and IS0 recommendations. Likewise, there are a
24、few specifications based on metric units used throughout the world including the U.S.” The report states that a change in both metric and nonmetric countries is required to achieve international standardization. A review of practices incorporated in standards could result in new practices and standa
25、rds “which will conserve raw materials, improve the quality of products and reduce costs.” ASME is a charter subscriber to the American National Met hwever, if the symbols are derived from proper names, capital roman type is used for the fist letter. *The kilogram is the only base unit with a prefix
26、. SECTION 4. SUPPLEMENTARY UNITS The General Conference has not yet classified certain units of the ntei- national System under either base units or derived units. These SI units are assigned to the third class called “supplementary units” and may be regarded either as base units or as derived units
27、, The two supplementary. units are the radian for plane angle (symbol rad) and the steradian for solid angle.(symbol sr), SECTION 5. PREFIXES Decimal multiples and submultiples of the SLunits are formed by means of the prefixes detailed in Table 2 on next page. Only one multiplying prefix is applied
28、 at ne time to a given unit, cg., nanometer (nm), not millimicrome- ter (mpm). 5 TABLE Z-9 UNIT PREFIXES Amount dtiples and Submultiples Prefixes Symbols Pronounciations Means 1000000000000000000 1ooo00000b000000 1000000000000 1000 000, 000 1000 000 1000 100 10 10f8 1CP 1o12 IO9 lo6 103 IO2 10 exa E
29、 peta P tera T upper case is to be used only at the beginning of a sentence. The rule for capitalka- tion of unit symbols is as follows: if a unit is named for a person, the first letter of the symbol. is capitalized, as in V for volt or Hz for hertz; otherwise the unit symbol is in lower case, as i
30、n lm for lumen or lx for lux. The eiip tion is the symbol L for liter. This rule applies to all SI units. :ASME SI-L 82 m 0759670 008395b L m TABLE 3-DERIVED UNITS WITH NAMES Expression in Terms Ouantity Name Symbol Formula of SI Base Units Frequency hertz HZ 11s or S” S? Frce newton . N m-kg*s“ me
31、kg S- Energy, work -joule J N* m m2*kg. 1st signif- one less signif- . 10.5 yd X 0,9144 icant digit of icant digit m/yd = 9.6102 m orig. value which rounds to 9.6 m 8.1.1 Rounding of Temperatures Temperatures can be rounded to the nearest whole degree or a multiple of whole degrees. 8.2 Rounding of
32、Toleranced Values There are several methods used to determine the number of significant digits to be retained in converted.values. Following are three common prac- tices. 8.2.1 Rounding tnward This practice rounds the converted values to within the range of the origi- nal dimension and tolerance. Fo
33、r example, 0.880 .t. 0.003 inch is 0.877 to 0.883 inch which equals 22,2758 to 22.4282 millimeters. Two.decimalplaces in millimeters could be considered comparable to three decimal places in inches when considering the accuracy required and the measuring equipment that would be used in machining or
34、inspecting this dimension. The 22.2758 to 22.4282 range would therefore round to 22.28 to 22.42. Note that the lower limit is rounded up and the upper limit is iounded down. Abnt SI-L 82 0759670 0083960 3 The advantage of this practice is that absolutely every part mg the converted dimension and tol
35、erance would also meet the inch dimension and tolerance. The disadvantage to this practice is that folerance is always de- creased. In .this example the tolerance reduction is 0.0124 mm (0,00049 inch), approximately 8%. 8.2.2 Rounding Based on Decimal Places This practice assumes that the number of
36、decimal places reflects the in- tended precision. Millimeter dimensions are then rounded to one less place than the inch dimension and tolerance, but no less than a certain number of decimal places - generally two decimal places. h this case 0.880 f 0.003 inch equals 22.3520 f 0.0762 mm, which would
37、 be 22.35 f 0.08 mm. The in- crease in tolerance is f 0.0038 or a total of 0.0076 mm (0.0003 inch), or approx. 5%. 0.75 * 0.01 inch .equals 19.050 f 0.254 mm which would be 19.05 1?- 0.25 mm,a decrease in total tolerance of 0.098 mm (0.00031 inch). The practice of basing the number of decimal places
38、 in the converted value on the number of decimal places in the original dimension presumes that the number of decimal places in the original dimension reflects the intended precision. This practice may be most suitable for conversion of millimeters to inches where the designer is aware that the dime
39、nsions are to be con- verted. When converting millimeters to inches, inches would be expressed to one more decimal place than the millimeter dimension. Thus, when expressing the width of a bracket, 150 mm could be shown and the conversion to 5.9 inches would be satisfactory. However, when showkg the
40、 internal diameter of a ball bearing, 150.000 mm would be required to get a conversion to 5.9055 inches. 8.2.3 Rounding Based on Total Tolerance Using another practice, the number of decimal places is determined by the size of the total tolerance applied to the dimension. The following chart may be
41、used: Total Toleran Converted Value In Inches In Millimeters At La Least Than Shall be Rounded To 0.000 04 0.0004 0.000 4 0.004 0.004 O .O4 O .O4 - 4 places (0.0001) 3 places (0.00 1) 2 places (0.01) 1 place (0.1) - 0.880 t0.003 inch equals 22.3520 k 0.0762 mm. The total tolerance is 0.006 inch whic
42、h is between 0.004 and 0.04 inch. Thus the dimension and tolerance would be rounded to 2 decimal places, 22.35 f 0.08 mm. 13 ASNE SI-1 82 0757670 0083961 5 m J 8.3 Numerical Values in Formulas Formulas which use letter symbols to represent physical quantities should be valid with any units used. How
43、ever, in practice, fo-rmulas.may have coeffi- cients which contain unit conversion factors asiwell as empirical or other factors. Such formulas are tailored for use with specific units, and the engi- neer may wish to “convert” them so that a specific set of SI units can be used directly. It is essen
44、tial that any “unit-tailored” formula.beaccompanied by clear directions for correct units to be used. 8.3.1 describes a recommended method ofhandling units. 8:3.2 describes a method of converting formulas which contain coefficients r empiricd fac- tors which depend on the units used. 8.3.1 If a form
45、ula is in unit-independent form, units can be most simply determined as numerical values are substituted. Example: The .power which -can be safely transmitted by a rotating, - round shaft is given by pz” 7D3 W A. 16- . . in which T is the allowable shear stress . D is the diameter of the shaft o is,
46、 the aigular speed of the shaft . For the values .E- / T = 6000 lbf/in2 = 41.4 MPa = 41.4 X lo6 N/m2 D = 1.00 in = 0.0254 m . W = ,1000 rev/min = 104.7 rad/s the substitution is carried out as follows: . I n (6000 lbf/in2) (1 ,O0 in)j (1000 revlmin) (2n rad/rev) 16 (12 in/ft)(33 O00 fGlbf/min HF) P
47、=. = 18.7 HP P = - (41.4 X lo6 N/m) (0,0254 m)3 (104.7 rad/s) n 16 = 13 900 N m/s = 13.9 kW The results agree since 18.7 HP 0.7457 kW: ( HP ) =.13.9 kW, properly rounded. A check of the units should-be made by algebraic “cancelling; prior to carrying out bf the multiplication and/or division. If the
48、 formula is to .be used repeatedly to give horsepower in terms of diameter in inches and angular speed in rev/min, with a shear stress of 6000 14 ALflE SI-L 82 O759670 0083962 7 psi, it may be “unit-tailored by incorporating the appropriate conversion factors with the n/16 and 6000 psi as follows: .
49、 ! n (6000 16f/in2) (277 rad/rev)D3 o P= 16 (12 in/ft) (33 O00 ft lbf/min HP) - D3 o - 53.5 in3 rpm/HP It is sound practice to write the units of the factor 53.5; thus when values such as D = 1.00 in and o = 1000 rpm are substituted, (1 .O0 in)3 (1000 rpm) 53.5 in3 - rpm/W P= = 18.7 HP all units except HP cancel properly upon multiplication and- division. 8.3.2 A formula may have the general form A= K- B* C” where K is a constant which may contain a unit conversion factor as well as other factors,
