Handbook-Appendices

4 Appendix C Tests for Identifying Metals Spark Test. Occasionally, it may be necessary to attempt to weld a metal that cannot be readily identified by surface appearance alone. It is not hard to distinguish aluminum from stainless steel, and easy to distinguish copper from brass, or lead from almost any other metal. It is not easy to distinguish ordinary low-carbon mild steel from some of the low-alloy steels, or to distinguish malleable cast iron from ordinary gray cast iron. However, there are some simple tests you can perform which will help you identify at least the major class of ferrous metal, and by so doing help you decide whether welding is possible, and what type of welding rod or flux may be best suited to the job. The best and simplest of all tests, at least so far as the ferrous metals are involved, is the spark test. A power- driven high-speed grinding wheel will produce spark patterns which are quite distinctive. Try to do the grinding so that the spark stream is thrown horizontally against a reasonably dark background. The spark patterns typical of six major types of ferrous metals are shown on the facing page. Study them carefully before you run a test; you can’t look at the page and at the spark stream simultaneously. Here are a few notes to supplement the patterns and descriptions given on the facing page: Gray cast iron vs. malleable cast iron: Difference between actual spark patterns may be less than indicated by our sketches. Under identical test conditions, malleable iron spark stream should always be longer than gray iron stream, with less breakdown into sprigs and small sparks near the wheel. If spark test is inconclusive, apply chip test. White cast iron vs. gray cast iron: The white iron pattern is not shown, since white iron can usually be distinguished by its color. Under the same test conditions, length and volume of spark stream from white iron will be less than for gray iron. Low-carbon steel vs. wrought iron: Chief difference lies in color of spark stream near wheel. It will always be white for the steel, straw yellow for the iron, although both will appear white farther out. (continued on p.6)