Heater for billets

#This invention relates to apparatus for heating an elongated piece of material such as a metallic billet to a temperature at which the material can be worked by compressive forces. The invention is particularly useful for heating a billet of aluminum to a temperature at which it can be effectively extruded. The invention utilizes an arrangement in which the billet is passed through a small, elongated chamber which, itself, is within a larger chamber of high temperature gases. The two chambers are separated by baffle means shaped to provide elongated, narrow throats. Adjacent these throats, jets of high pressure, heated gas are discharged through the throats against the billets as the billets pass through the apparatus. The gas discharged under pressure to form the jets is at a substantially lower temperature than the gas in the vicinity of the jets. The jets effectively entrain quantities of the high temperature gas from the surrounding area and mix it with the cooler, high velocity gases and impinge the mixture on the surface of the billet. By reason of the impingement technique, the rate of thermal transfer between the gases and the billet is substantially increased and the heating is more uniform.

#No flame is used either impinging upon or in the vicinity of the billet. In the preferred method of heating the gases, an electrical heating source is utilized but other thermal sources can be utilized. Since an electrical heat source does not require an adequate supply of oxygen to support combustion, the heated gases can be recirculated as much as once each second past the heating source. This represents a very considerable savings in thermal energy.

#The use of the jets to force the heated gases to impinge upon the surface of the billet substantially accelerates the rate of heat transfer. Thus, the time the billet has to remain in the apparatus to attain the desired temperature is materially reduced. Thus, again the thermal efficiency of the unit is increased. The particular design of the unit in which an efficient aspirating zone is provided adjacent the jet nozzles assures entrainment of a high percentage of the high temperature gases, thus, effecting rapid heat transfer.

#FIG. 1 is a somewhat schematic plan view of the invention;

#FIG. 2 is a sectional elevation view of the invention taken along the plane II--II of FIG. 1;

#FIG. 3 is a sectional elevation view taken along the plane III--III of FIG. 1;

#Referring to FIG. 1, the numeral 10 indicates an elongated billet heater consisting of a preheater section 11 and, in addition, at least one and, in the particular embodiment illustrated, three primary heating sections 12, 12a and 12b. The sections are arranged in tandem, and are so designed as to form a continuous tunnel extending from a billet receiving opening 13 to a billet discharge opening 14. Each section has its own individual heat source such as the heating elements 15. Each section has its own individual fan system 16 for circulating the primary or high temperature gases. Each section has its own individual fan unit 17 for pressurizing and circulating the secondary air. In FIG. 1, these are only illustrated schematically.

#FIGS. 3 and 4 illustrate a typical, single zone or section such as the preheater section 11 or any of the primary heating sections 12, 12a or 12b. In the preferred embodiment of this invention, each of these sections is approximately ten feet in length. Each section has a plurality of suitably spaced rollers 20 forming a billet transporting track 21 extending along the center of the apparatus. The billets enter through the entrance 13 and are pushed along the track 21 by any suitable means such as the billets being supplied one after the other with the one entering at the right-hand end of FIG. 1, forcing the lead billet out through the discharge opening 14 on the left-hand end of FIG. 1. Each section has a pair of the heaters 15 mounted to the roof of the unit (FIGS. 1 and 3). Each zone or section has its own separate fan assembly 16 driven through belts or other suitable means by an externally mounted electric motor 23.

#At the beginning or upstream end with respect to the direction of movement of the billets through the apparatus, each section is equipped with a plenum chamber 30 (FIGS. 4 and 6). As will be seen in FIG. 2, an opening 31 is provided below the plenum chamber to permit the billet B to pass. The plenum chambers 30 serve as separators or dividers between each of the sections. They also serve as the air supply for the hereinafter described secondary or pressurized air system.