along with the other measurements. Once both the internal and external measurement thermocouples reached 500°F, the machine was set to maintain the temperature for one hour and the time on the data recorder and power meter were noted. After one hour, the machine was turned off and the temperature was recorded for another hour after making note of the time on the data recorder. Throughout the test, the amount of time required to set up and tear down was recorded. Direct Flame A 100-lb cylinder of propane was used with a Belchfire® fuel gas and compressed air torch. The valve was rotated on a turntable while the flame impinged on the exterior surface of the valve — Fig. 3. The valve was not insulated at all, which is in accordance with typical industry practices. The data recorder was placed on top of a piece of pipe tacked to the valve so as to not tangle the thermocouple leads. Only the two data recorder thermocouple leads were used for this test. The data recorder was turned on and the flame and rotation were started. Once both thermocouples reached 500°F, the time was noted and the maintenance time started. Preheat maintenance was determined by monitoring the temperature and cycling the torch on and off manually. This human element can add some degree of inconsistency. After one hour of preheat maintenance, no additional heat was applied and the temperatures were recorded for one hour after making note of the time on the data recorder. Throughout the test, the amount of time required to set up and tear down was recorded. Experimental Results Time Time was evaluated based on time to preheat to 500°F, time difference between inside and outside reaching 500°F, time to set up, and time to tear down. Preheat Time When analyzing preheat time, induction produced the best results with both the inside and outside of the valve reaching the minimum 500°F in 0.6 h. The outside of the valve reached the minimum A B C 500°F in only 0.5 h. There was minimal difference in the results from flame and resistance preheating. Achieving 500°F on the outside with the propane required 1.02 h, while the inside required 1.1 h. The outside with the resistance required 0.78 h, while the inside required 1.75 h. Therefore, resistance heating required the greatest amount of time to achieve through-thickness preheating. Overall, the method that brought the inside and outside to the target temperature the fastest was induction. Setup and Tear-Down Time The flame method required the least amount of setup and tear-down time, 54 JANUARY 2014 Fig. 4 — Comparison between the temperature rise on the inside and outside vs. the energy used. A — Propane heating; B — resistance heating; C — induction heating.
Welding Journal | January 2014
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