Consulting-Specifying Engineer - August 2007 - (Page A8)

INDUSTRIAL PROCESSING E N E RGY SOLUTION S CE NTE R New Tools Available for Heat Treating Steel Improvements in Speed, Efficiency, Emissions AT A GLANCE ❯ Wide range of applications in steel industry tube and bar, for example—and for fabricated steel products. have quick enough payback at the old energy prices.” That has changed. A widespread tool used in indirect gas-ﬁred heat treating is the combustion tube. Controlled gas combustion takes place within the tube, and exhaust gases exit the other end. A common style is the U-tube, which radiates heat for its entire length. In recent years, researchers and manufacturers have looked for ways to increase the efﬁciency of this device. One concern was that the U-tube and similar devices radiate much of their energy along the combustion leg, and not as much on the exhaust leg. ❯ Industrial operators look for improved efﬁciency, higher output incentive for system upgrades heat tubes extend tube life INDIRECT TREATMENT MORE WIDELY USED The treatment process encompasses both direct exposure of the treated metal within a zone that includes combustion gases and indirect treatment where the product is treated separately from combustion gases. Treatment temperatures range from 500°F to 2,100°F, and treatment times run from a few seconds to many hours. Indirect heat treatment systems are more widely used for ferrous metals because this method avoids unwanted oxidation effects, and because it can be more precisely controlled. Commonly, natural gas is the fuel of choice for an indirect heat treatment system. ❯ Rising energy costs provide ❯ Flameless combustion, ceramic H eat treating is a process widely used to change or stabilize the physical characteristics of a range of iron and steel products. Heat treating processes include annealing, tempering, quenching, solution heat treating and heat soaking. SEARCH FOR WAYS TO INCREASE THERMAL OUTPUT Bennett indicates that in many furnaces, radiant tube ﬁring rates have been limited by the need to avoid hot spots that can cause premature tube failure. “This has resulted in conservative transfer rates across the tube walls, limiting productivity and furnace turnaround time. That, in turn, increases energy consumption per weight of product,” he says. He indicates that two different approaches are being taken to get past this bottleneck. One is the use of ceramic or microalloyed radiant tube materials that will tolerate higher temperatures. The other is to squeeze greater performance out of the tube by improving its temperature uniformity with burners that induce recirculating ﬂow within the tube, reducing hot spots and permitting the tube to operate at higher average temperatures and heat ﬂux rates. OWNERS LOOKING FOR BETTER METHODS WIDE VARIETY OF APPLICATIONS The objective of the treatment varies: Increase or decrease hardness, strength, toughness or ductility; or to relieve internal stresses that were acquired from stamping, forging or cutting. The actual change in the metal’s characteristics comes through modiﬁcation of its crystalline structure. Within the last century these processes and the associated changes in the product been studied at a microscopic or crystalline level. Our current knowledge of metallurgy has given the ability to precisely modify the characteristics of steel to better meet the needs of users. Heat treatment is widely used both in steel manufacture—sheet, With rising energy costs and growing restrictions on emissions, many heat treating operators have looked for process improvements. Technological developments in the last decade have made such improvements available. Owners are looking for ways to reduce energy bills, reduce emissions, keep systems on line and achieve more even heating. New technologies make signiﬁcant contributions to these goals. Janus Technology is an engineering consulting ﬁrm specializing in industrial combustion and heat processing. Richard Bennett, Janus president, observes that “Many of the new technologies have been around for a while, but were dismissed in the past because they didn’t A8

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - August 2007

Contents M/E Roundtable Giants 100 Pullout Poster Giants Stand Tall: CSE Giants 100 Report Electrical Design for Tall Buildings HVAC and Fire Safety for Elevator Systems How to Beat the Codes GAS Technology Supplement Recovering Waste Heat from Boilers New Applications for Tankless Water Heating Systmes Techniques Improve for Powder Coating MDF New Tools Available for Heat Treating Steel Direct Drive Engines

Consulting-Specifying Engineer - August 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.