Dear Search Engineer: Any idea where I can find Brinell, Vickers, and Rockwell hardness conversion tables for ductile cast iron?—G.D. in London
Dear G.D.: They don't call me the Search Engineer for nothing! I did a Google® search and came up with the perfect site for you, direct from the UK—www.gordonengland.co.uk/hardness/hardness_conversion_1c.htm. There are tables and tests for all the requested information and more. Bookmark the site, old chap!
Dear Mr. Search Engineer: If I subtract two-phase coherent signals that have random white noise (each signal having the same RMS noise) and measure the standard deviation, do I need to divide the result by the square root of two to get the true standard deviation or RMS noise? I need to do something like this to remove fixed pattern noise and dc offset from a video signal to be able to measure purely random noise.—V.K. in MA
Dear V.K.: If the white noise in the signals is independent, you need to multiply the standard deviation by 1.414. If the signals in each channel are 180° out of phase, you will get twice the signal level of a single channel. The net result is two times the signal and 1.414 times the noise for a net gain in SNR of 1.414 (3 dB). If the signals in each channel are in-phase, you will get no signal and 1.414 times the noise of a single channel.
Dear Mr. Search Engineer: I'm looking for any high-temperature compatible adhesive that can be used to adhere a thermocouple to a crucible at temperatures of 2,000C.—R.S. in OH
Dear R.S.: Sorry, but at the temperature you indicated, thermocouple materials melt. The answer is to use an indirect infrared-type readout if you need to have a view of the object. I'd suggest that you try to wedge the thermocouple into or onto the crucible.
Dear Search Engineer: I'm looking for a simple and relatively low cost method of installing flexible plastic hinges between 12 × 24-inch sheets of 1/8-inch thick polypropylene or polythylene. Hinge rotation is 180° allowing the adjacent sheets to fold back and stack in contact face-to-face. Hinges need to be flexible and last approximately 3,000 cycles. I'm interested in methods of producing such hinges (either formed into single 24 × 24-inch sheets to produce two hinges between 12 × 24-inch sheets, or separately attached hinges to two 12 × 24-inch sheets).—G.D. in IL
Dear G.D.: You can mechanically coin a hinge into a sheet of PP or PE. Nip press must have 1/8 inch radius on one side, flat on the other, thickness reduction ratio at the pinch should be about 4:1. Of course, the other option you could consider would be to run an extruded hinge in PP and weld it to PP sheet.
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