ASTM B478-85 pdf free.Standard Test Method for Cross Curvature of Thermostat Metals.
This procedure provides the means for defining themagnitude and direction of cross curvature (an inherent prop-erty in thermostat metal).
A 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. On the tracks is assembled a movable carriage formounting a micrometer depth gage. 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.Electronic Contact Indicator, sensitive,low-current, togive a signal when the micrometer depthgage rod completesthe electrical circuit across the indicator terminals by touchingthe specimen or the parallel.Parallel, hardened and ground steel, 1/4 by 3/s by 6 in.(6by 10 by 150 mm).The method of sampling shall be mutually agreed uponbetween the manufacturer and the purchaser.
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 be 3/4 in.(20 mm). It must 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 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 beflat longitudinally.
Lay the steel parallel on the surface plate with the 1/4 -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 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 specimen 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. ASTM B478 pdf download.