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Blog January 7, 2016

by Bob Miller

Hardfacing Preheating Part 2

Bob Miller is a Materials Engineer for Postle Industries. With over 45 years experience in the field of Wear Resistant Technology he offers tips, and techniques for the highest quality hardfacing on your equipment.

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Fig. 1 Tapping two chemical sticks together allows you to determine a temperature minimum and maximum with a single scratch on the workpiece.

The recommended instrument for measuring a preheat temperature is a pyrometer. However chemical sticks, which melt at a predetermined temperature can be used as an alternative. The difficulty with using a single chemical stick is that you can only determine that the workpiece is above or below a certain prescribed temperature. In other words, if you have a chemical stick labeled 400°F (210℃), the melted stick only tells you that the workpiece is above 400°F (210℃). The actual temperature could be 500°F (260℃), 600°F (316℃), or higher. To overcome this difficulty Postle Industries recommends using two chemical sticks. One labeled at the minimum preheat temperature and a second one labeled at a temperature 50°F (28℃) higher. For example, if the minimum preheat temperature is 400°F (210℃), then chemical stick number one must be labeled "400°F" (210℃), and a second chemical stick should be labeled "450°F" (232℃). Another example, if the preheat temperature is 550°F (288℃), then the first chemical stick should be labeled "550°F" (288℃), and the second chemical stick should be labeled "600°F" (316℃).

It is common practice to tape the two chemical sticks together (see Fig 1). When measuring the temperature of the workpiece, simply scratch the surface with the chemical sticks together. The first chemical stick should melt, and the second should remain solid. This ensures that the workpiece is somewhere between the minimum and maximum preheat temperature. If the two chemicals sticks melt on contact with the workpiece, then the maximum preheat temperature has been exceeded. If the two chemicals sticks do not melt at all, then the minimum preheat temperature has not been achieved.

If you have a question or a comment on this blog or any hardfacing product or issue please contact Bob Miller or call Corporate Headquarters at (216) 265-9000(USA).