Machinery's Handbook, 31st Edition
646 Shrinkage Fits Temperatures for Shrinkage Fits.— The temperature to which the outer member in a shrinkage fit should be heated for clearance in assembling the parts depends on the total expansion required and on the coefficient α of linear expansion of the metal (i.e., the in - crease in length of any section of the metal in any direction for an increase in temperature of 1 degree F). The total expansion in diameter that is required consists of the total allow ance for shrinkage and an added amount for clearance. The value of the coefficient α is, for nickel-steel, 0.000007; for steel in general, 0.0000065; for cast iron, 0.0000062. As an example, take an outer member of steel to be expanded 0.005 inch per inch of internal diameter, 0.001 being the shrinkage allowance and the remainder for clearance. Then . . . t t 0005 00000065 0005 769 degrees F # α = = = ° The value t is the number of degrees F that the temperature of the member must be raised above that of the room temperature. ANSI/ASME Standard Limits and Fits This American National Standard for Preferred Limits and Fits for Cylindrical Parts, ANSI/ ASME B4.1-1967 (2009; out of print), presents definitions of terms applying to fits between plain (non threaded) cylindrical parts and makes recommendations on preferred sizes, allow ances, tolerances, and fits for use wherever they are applicable. As of 2009, this standard was in accord with the recommendations of American-British-Canadian (ABC) conferences up to a diameter of 20 inches, with experimental work thereafter carried on with the objective of reaching agreement in the range above 20 inches. The recommendations in the standard are presented for guidance and for use where they might serve to improve and simplify products, practices, and facilities. They have practical application for a wide range of products. Note: At the time of this publication, even though ANSI/ASME B4.1-1967 was no longer officially in print, it was still available for reference and not yet revised or superseded. Factors Affecting Selection of Fits.— Many factors, such as length of engagement, bear ing load, speed, lubrication, temperature, humidity, and materials must be taken into con sideration in the selection of fits for a particular application, and modifications in the ANSI/ASME recommendations may be required to satisfy extreme conditions. Subse- quent adjustments may also be found desirable as a result of experience in a particular application to suit critical functional requirements or to permit optimum manufacturing economy. Definitions.— The following terms are defined in this standard: Nominal Size: The nominal size is the designation used for the purpose of general identification. Dimension: A dimension is a geometrical characteristic such as diameter, length, angle, or center distance. Size: Size is a designation of magnitude. When a value is assigned to a dimension, it is referred to as the size of that dimension. (It is recognized that the words “dimension” and “size” are both used at times to convey the meaning of magnitude.) Allowance: An allowance is a prescribed difference between the maximum material limits of mating parts. (See definition of Fit ). It is a minimum clearance (positive allow ance) or maximum interference (negative allowance) between such parts. Tolerance: A tolerance is the total permissible variation of a size. The tolerance is the difference between the limits of size. Basic Size: The basic size is that size from which the limits of size are derived by the application of allowances and tolerances. Design Size: The design size is the basic size with allowance applied, from which the limits of size are derived by the application of tolerances. Where there is no allowance, the design size is the same as the basic size.
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