1、Designation: B478 85 (Reapproved 2016)Standard Test Method forCross Curvature of Thermostat Metals1This standard is issued under the fixed designation B478; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.
2、 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 thermostat
3、 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 rega
4、rdedas 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 user
5、 of this standard to become familiarwith all hazards including those identified in the appropriateSafety Data Sheet (SDS) for this product/material as providedby the manufacturer, to establish appropriate safety and healthpractices, and determine the applicability of regulatory limi-tations prior to
6、 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 temperature is
7、 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 aspecimen of th
8、ermostat 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 typical c
9、ross 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. On the tra
10、cks 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 signal when
11、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 steel para
12、llel 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).6. Sampling6.1 The method of sampling shall be mutually agree
13、d uponbetween the manufacturer and the purchaser.7. Preparation of Sample for Measurement7.1 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
14、be cut in a mannerthat will not tend to alter the inherent cross curvature. It isrecommended that a shear with sharp blades and the properclearance be used. The shearing should impart no burrs to the1This test method is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and
15、is the direct responsibility of SubcommitteeB02.10 on Thermostat Metals and Electrical Resistance Heating Materials.Current edition approved May 1, 2016. Published May 2016. Originallyapproved in 1968. Last previous edition approved in 2008 as B478 85 (2008).DOI: 10.1520/B0478-85R16.Copyright ASTM I
16、nternational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1specimen. 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 beflat longitudinally
17、.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 carriage over the parallel an
18、d 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 specimen contact the para
19、llel, 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 thickness within 60.000
20、1 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 convex,the results obtai
21、ned 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 micrometer depth gage, i
22、n. (or mm),H = micrometer depth gage reading at highest point ofspecimen, in. (or mm),t = specimen thickness, in. (or mm).FIG. 1 Specimen RelationshipsFIG. 2 A Typical Design of ApparatusB478 85 (2016)2NOTE 6Cross curvature varies by the square of the width for the sameradius of curvature. For examp
23、le, if the cross curvature of a strip 3.00 in.(76.2 mm) is 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
24、 for strips of low width-thicknessratio.10. Report10.1 The report shall include the following:10.1.1 Type of material,10.1.2 Thickness of specimen,10.1.3 Width of specimen,10.1.4 Percentage reduction of specimen,10.1.5 Test temperature,10.1.6 Base reading of micrometer depth gage,10.1.7 Micrometer d
25、epth gage 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
26、sourcesof 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 take
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30、 address 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). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 85 (2016)3
