1、Designation: B 478 85 (Reapproved 2008)Standard Test Method forCross Curvature of Thermostat Metals1This standard is issued under the fixed designation B 478; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisio
2、n. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of crosscurvature of thermostat metals.NOTE 1This test method is not limited to thermost
3、at metals and canbe used for other materials for which the cross curvature must bemeasured accurately.NOTE 2This standard includes means for calculating cross curvaturefor widths other than that of the specimen having the same radius ofcurvature.1.2 The values stated in inch-pound units are to be re
4、gardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the us
5、er of this standard to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet (MSDS) for this product/materialas provided by the manufacturer, to establish appropriatesafety and health practices, and determine the applicability ofregulatory limitation
6、s prior to use.2. Terminology2.1 thermostat metal, na composite material, usually inthe form of sheet or strip, comprising two or more materials ofany appropriate nature, metallic or otherwise, which by virtueof the differing expansivities of the components, tends to alterits curvature when its temp
7、erature is changed.2.2 cross curvature, nthe deviation from flat across thewidth, measured as a chord height. It is expressed in inches ormillimetres.3. Summary of Test Method3.1 The test method for cross curvature consists of measur-ing the chord height deviation from flat across the width of aspec
8、imen of thermostat metal (Fig. 1).NOTE 3The highest point will normally be at or near the center of thespecimen.4. Significance and Use4.1 This procedure provides the means for defining themagnitude and direction of cross curvature (an inherent prop-erty in thermostat metal).5. Apparatus5.1 FixtureA
9、 typical cross curvature fixture is shown inFig. 2. It consists of a base which has a flat ground surface onits top side. For convenience a granite surface plate, as ispictured, can be used. To it are attached side frames to supportrod or bar tracks which are parallel to the top surface of thebase.
10、On the tracks is assembled a movable carriage formounting a micrometer depth gage.5.2 Micrometer Depth Gage, for measuring the position ofthe specimen to the nearest 0.0001 in. (0.0025 mm). The tip ofthe gage rod shall be radiused.5.3 Electronic Contact Indicator, sensitive, low-current, togive a si
11、gnal when the micrometer depth-gage rod completesthe electrical circuit across the indicator terminals by touchingthe specimen or the parallel.5.4 Parallel, hardened and ground steel,14 by38 by 6 in. (6by 10 by 150 mm).NOTE 4Parallelism of the rods, on which the micrometer carriagetraverses, to the
12、steel parallel when laid on the surface plate shall be suchthat when the carriage is traversed and micrometer readings are takenalong the length of the parallel, no reading shall be different from anyother reading by more than 0.0002 in. (0.005 mm).1This test method is under the jurisdiction of ASTM
13、 Committee B02 onNonferrous Metals and Alloys and is the direct responsibility of SubcommitteeB02.10 on Thermostat Metals and Electrical Resistance Heating Materials.Current edition approved Nov. 1, 2008. Published November 2008. Originallyapproved in 1968. Last previous edition approved in 2003 as
14、B 478 85 (2003).FIG. 1 Specimen Relationships1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Sampling6.1 The method of sampling shall be mutually agreed uponbetween the manufacturer and the purchaser.7. Preparation of Sample for M
15、easurement7.1 The most important step in preparing the specimen formeasurement is cutting it to length. The length shall beapproximately equal to the width. The minimum length of aspecimen shall be34 in. (20 mm). It must be cut in a mannerthat will not tend to alter the inherent cross curvature. It
16、isrecommended that a shear with sharp blades and the properclearance be used. The shearing should impart no burrs to thespecimen. It is recommended that after shearing the specimento length the specimen be allowed to set for 10 min beforetesting so that it can stabilize its shape. The specimen shall
17、 beflat longitudinally.8. Procedure8.1 Lay the steel parallel on the surface plate with the14-in.(6-mm) face down and its length parallel to the travel of themicrometer and directly under the tip of micrometer gage rod.Take a base reading of the micrometer depth gage by slidingthe micrometer carriag
18、e over the parallel and turning themicrometer thimble down until contact of the tip of the rod ismade with the parallel as is indicated by the electronic contactindicator. Back off the micrometer thimble and move thecarriage away. Lay the specimen on the parallel so that the twoside edges of the spe
19、cimen contact the parallel, the convex sideof the specimen is up, and the specimen is centered to avoidtilting or uneven contact to the parallel. Then move themicrometer carriage over the sample and take a micrometerreading at the highest point on the specimen. Remove thespecimen and determine its t
20、hickness within 60.0001 in.(60.0025 mm) by means of micrometer calipers havingradiused anvils. Take all measurements at a temperature of 756 1F (24 6 0.5C) with sufficient time allowed for the sampleto have reached temperature stabilization.NOTE 5When low expansion side of the thermostat metal is co
21、nvex,the results obtained shall be referred to as positive ( + ) and when the highexpansion side is convex, the results obtained shall be referred to asnegative ().9. Calculation9.1 Calculation of cross curvature is as follows:C 5 B 2 H 2 twhere:C = cross curvature, in. (or mm)B = base reading of mi
22、crometer depth gage, in. (or mm),H = micrometer depth gage reading at highest point ofspecimen, in. (or mm),t = specimen thickness, in. (or mm).NOTE 6Cross curvature varies by the square of the width for the sameradius of curvature. For example, if the cross curvature of a strip 3.00 in.(76.2 mm) is
23、 0.09 in. (2.3 mm), the cross curvature of a strip 1.00 in. (25.4mm) wide having the same radius of curvature would be 0.01 in. (0.3mm). This relationship may be influenced by mechanical distortion of theedges in slitting or trimming to width for strips of low width-thicknessratio.10. Report10.1 The
24、 report shall include the following:10.1.1 Type of material,10.1.2 Thickness of specimen,10.1.3 Width of specimen,FIG. 2 A Typical Design of ApparatusB 478 85 (2008)210.1.4 Percentage reduction of specimen,10.1.5 Test temperature,10.1.6 Base reading of micrometer depth gage,10.1.7 Micrometer depth g
25、age reading at highest point onspecimen, and10.1.8 Cross curvature (including positive or negative sign).11. Precision and Bias11.1 The reliability of the results of the measurement ofcross-curvature depends primarily on the method of samplepreparation and the test conditions. The most common source
26、sof variation in the test results relate to the quality of the shearededge of the test specimen, and the uniformity of the testtemperature.11.2 Quantitative determination of precision and bias is inprogress.12. Keywords12.1 chord height; cross curvature; thermostat metalASTM International takes no p
27、osition respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsib
28、ility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to
29、ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the addre
30、ss shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).B 478 85 (2008)3
