FURNACE FOR HEAT TREATMENT OF METAL BARS The invention relates to a heat treatment furnace for metallic section bars of various kind, made by extrusion and cut and stretched at the required lengths on a transfer and stretching plant arranged upstream the same furnace, this furnace being fit to permit the metallic section bars heat treatment by performing the operative steps in a fully automatic manner, with stay times on the furnace which are considerably shortened and a high productive capacity and less employ of personnel for furnace management. Heat treatment furnaces for metallic section bars of various kind, and particularly aluminium section bars, are well known, in which the section bars are extruded, cut and stretched at the required sizes on a transfer and stretching plant arranged upstream the same furnace. These metallic section bars are assembled on maps and conveyed up to the plant end portion by suitable conveyer means provided on the same plant, and afterwards they are loaded manually and/or automatically into boxes having adequate holding capacities (of approx. 70-80 units each one), and such boxes are then introduced in a longitudinal direction inside the furnace on a reciprocally stacked condition, with the different section bars arranged at a reciprocal contact, and these boxes are maintained on the furnace for so long times as to cause the various section bars to be submitted to the required heat treatment, generally for approx. 6-8 hours, and thereafter the boxes are extracted from the furnace and the section bars picked up for being utilized. However, the so structured furnaces have some drawbacks. In fact, at first the employ of boxes for holding the different metallic section bars needs several complicated and difficult operations, with the continuous presence of personnel, in order to load firstly the boxes with such section bars, then to introduce the boxes on the furnace and finally to extract them from the furnace and to unload the heat treated section bars. Moreover, under these circumstances it isnt'possible to avoid that the section bars are stacked in a not correct manner on the boxes, and that they may move and be subjected to shakings during the displacement of boxes, and consequently may be dented and damaged on the surface at a different extent. A further drawback of this section bars conveying system consists in that the furnace access, during the introduction and extraction of boxes with the section bars with respect to the furnace, is allowed by requiring the temporary opening of the doors of both the inlet and the outlet zone of the same furnace, with consequent loss of heat outwards and temporary decreasing of the furnace inner temperature, and need of an additional heating for increasing such temperature at the required levels. In this way, this additional heating involves unavoidably a larger energetic requirement, longer cycle times and lesser furnace productive capacities. The present invention has the object to eliminate the described drawbacks in a heat treatment furnace for

metallic section bars, by means of a furnace made in such a manner that to allow all the section bars loading and unloading operations to be fully automatically performed, with criteria different than those known hitherto, and such that to rationalize the section bars heat treatment with reduced energetic consumptions, lesser employ of personnel and higher productive capacity. This furnace is made with the substantially described constructive characteristics, with particular reference to the accompanying drawings, wherein : - Fig. 1 shows a schematic front view of a furnace according to the invention ; - Fig. 2 shows a schematic side view of the furnace of Fig. 1, cuts along the line A-A; - Fig. 3 shows a side view of a driving mechanism employed on the present furnace; - Fig. 4 shows a front view of the driving mechanism of Fig. 3, displaced on a first operative position; - Fig. 5 shows a front view of the driving mechanism of Fig. 3, displaced on a second operative position.

A furnace 6 according to the invention is shown schematically in the above mentioned Figures, which furnace is provided for the heat treatment of extruded metallic section bars, preferably of aluminium section bars, which are conveyed by means of suitable conveying means from an extruding, cutting and stretching plant of the section bars which is arranged upstream the same furnace. As particularly visible on Figs. 1 and 2, such heat treatment furnace comprises substantially a closed metallic box-like structure 7 having large size, delimiting an inner chamber 8 with a large capacity of holding metallic section bars, where air is heated at a determinate operation temperature, preferably at max. 250° C, by means of generators constituted by methane gas burners of the radiating tube type (not indicated), and where hot air is circulated by means of a series of ventilators (not shown) adequately arranged outside the furnace, and joined through pipe unions with the inner chamber 8, in a manner to distribute uniformly hot air into such inner chamber. The furnace box-like structure 7 is disposed near the end portion of the conveyer means (not shown) and is so structured, as it will be described, as to receive the metallic section bars conveyed from these conveyor means and adequately arranged on groups or maps, and to introduce such section bars in the inner chamber 8, by conveying them therethrough and maintaining them there for a time required for being submitted to the requested heat treatment, and finally to unload the treated section bars from the furnace, and all these operations are effected automatically as it will be described later. Furthermore, such furnace box-like structure 7 has its width extended in the same direction of the conveyer means and nearby the end portion thereof, so that to be able to receive the section bars conveyed by such conveyor means, and to introduce them inside the furnace, and has its length extended orthogonally to said conveyor means, so that to convey

all the section bars in this direction for the entire duration of heat treatment thereof, from the inlet side near said end portion to the unloading side situated on the opposite position.

Besides, as visible from said Figures, the present furnace substantially comprises a loading unit, arranged at the furnace inlet, and provided for introducing the section bars assembled on maps in the furnace inner chamber 8, a transfer unit 13 for the section bars maps, arranged on the inner chamber 8 and provided for transferring selectively the section bars maps for the entire length of such inner chamber, and an unloading unit arranged at the furnace outlet and provided for unloading from the furnace the section bars maps transferred through the transfer unit 13 and heat treated in the inner chamber 8. All the driving mechanisms of the various units are controlled automatically and adequately protected, so as to reduce the risks of accidents, and are controlled by means of corresponding P. L. C. electric control circuits, which are interfaced with a P. L. C central control system and supplied by a main electric power supply (not indicated), complete with all the components for supplying the various control circuits of the units referred to. The arrangement and operation of the different section bars loading, transfer and unloading units are now described, by referring always to the above Figures and also to Figs. 3-5. The loading and unloading units (not indicated) are made identical to each other, as a respective elevator with powered rollers (not indicated), which is supported by a corresponding stiff structure made of an electric welded steel and extended vertically (not indicated), which is secured outside the furnace, said elevators being controlled in a manner to be displaced contemporaneously, with vertical movement directions opposite to each other, and are adapted to support the section bars maps in such a way that one of these elevators determines the lifting of such section bars, from the level of the conveyer means to different heights, for the functions hereinafter described, and the other elevator determines the lowering of the section bars from the respectively attained height to the level of further conveyer means (not indicated), situated on the furnace unloading side and provided for transferring all the heat treated section bars towards the packing area. Such elevators are controlled automatically with slow motions through electronic control circuits and electric gear motors, and are associated with corresponding furnace openings, which are closed by respective automatic openable doors 12 and 14, so as to let the section bars to pass through the same openings during the loading and unloading operations, and at the end of these operations the doors are closed again on the openings, thereby minimizing loss of hot air of the furnace inner chamber outwards. Moreover, the elevators are associated with limit stop sensors detecting the position of the section bars maps, and providing for enabling the control circuits, with consequent movement of the same elevators and displacement at the required height level thereof, in presence of section bars to be treated which are transferred up to the

relative elevator, and such sensors also provide for disenabling these control circuits and therefore to stop the elevator movement, when section bars are not present. In turn, the transfer unit 13 is constituted by a plurality of horizontal rectilinear plates 21, identical and overlapped to each other at the different height levels, for the entire furnace extent, which are anchored to the furnace base 10 by means of a structure made of electric welded steel and connected together by means of bolts. These plates, of fixed type, are subdivided transversally the furnace on a series of single sliding paths 22 separated from each other, which extend from the inlet to the outlet of the furnace, in the present example formed by 6 paths the function of which is to transfer the section bars from the inlet to the outlet of the furnace as it will be described, each path being structured on its upper side with a set of stationary bars or idle rotating rollers (not indicated) for the entire extent thereof, except the end portions of these sliding paths which are structured with powered rollers 15, for allowing respectively the section bars transferred by the furnace inlet elevator to be automatically arranged on the sliding paths, and the section bars to be unloaded with the furnace outlet elevator from the sliding paths. These plates are formed by adequately dimensioned and reciprocally joined section bars, the upper surface of which is covered by a layer of heat-resistant material, preferably of the type kevlar, which in addition to resist to high temperatures protects the section bars from any possible dent along the entire respective sliding path. Moreover, the transfer unit 13 is constituted by a plurality of horizontal rectilinear plates 24, of movable type, which are co-operating with the fixed plates and displaceable with respect to these latter in the manner and for the scopes which will be described later. Such movable plates 24 are provided on each sliding path, for the entire longitudinal extent of the same paths, and are preferably adaptable on the fixed plates, as visible on Figs. 4 and 5, said movable plates being structured on their upper side with movable bars 25, which are arranged longitudinally the furnace, parallelly the stationary bars or idle rotating rollers of the fixed plates, and being also covered by a layer of heat-resistant material, identical to that of the fixed plates. The scope of the movable plates 24 is to effect the transfer step by step of the section bars along the different sliding paths 22 parallel to each other, with a series of movements adapted to determine the lifting and the translation in a longitudinal direction of these section bars, and then the lowering of this movable plate and the consequent laying down of the section bars, and the return on the starting position of the shifted movable plate, with a translation movement inverse to the preceding one. In this way, the laying down of these section bars on the following zone allows to clear the rest surface of the previous zone, by making it available for laying down the following section bars, in which condition the section bars are progressively transferred towards the outlet. In particular, these movements are effected

continuously and automatically at such speeds as that each section bars map which is introduced in the furnace employs the same time for passing from the inlet to the outlet side of the furnace, thereby resulting submitted to the ageing heat treatment under the same conditions. In particular, in the case of aluminium section bars this treatment normally occurs in a time of 3 hours. In order to provide for movements of this kind, a possible driving mechanism suitable for this scope is now described by way of a not limitative example. This mechanism is substantially constituted by a set of extended shafts 26 with limited rotation, housed transversally the furnace inner chamber 8, parallelly to each other, and driven in rotation by a control unit 27 arranged outside the furnace, near one of the furnace sides, and provided for operating all the movements of the movable plates 24 under control of P. L. C. electric circuits, which are independent and interfaced with further P. L. C electric circuits operating the furnace heating generators, and the P. L. C. central control system. Each shaft 26 supports both a first set of lever cams 28 and a second set of lever cams 29, provided near the respective movable plates 24 and fixed plates 21, where each cam 28 of the first set is axially spaced away from each cam 29 of the second set and is secured at its one end portion to the rotating shaft 26 and at its other end portion supports a pressure roller 30, which is steadily pressed against the lower surface of the corresponding movable plate 24 (or is secured to this latter in an articulated manner), and where each cam 29 of the second set is secured at its one end portion to the rotating shaft 26 and is articulated at its other end portion to a bracket 31, secured to the lower surface of the corresponding fixed plate 21, and these cams are adequately angularly offset from each other so that when the shaft is driven in a rotation direction the movable plate, which is initially displaced on its lowered rest position where it is housed in the relative fixed plate 21, is firstly gradually raised up to its operative position shown on Fig. 4, where it is fully raised from such fixed plate, then this movable plate maintained on this maximum lifted position is translated in the advancing direction turned toward the furnace outlet, in which condition the section bars laid down on the movable plate 24 are advanced one step, thereafter this movable plate is lowered at the same height of its starting position, on its operative position shown on Fig. 5, and consequently the section bars are laid down on the consecutive zone, and finally this movable plate is returned back on its rest position with a translation movement inverse to the preceding one. The movements of the movable plate are produced by employing adequate driving mechanisms acting on the same movable plate. Preferably, these driving mechanisms are constituted by a set of jacks with worm screw, acting on the cams 28 of the movable plates 24, in such a way as to raise firstly and then to lower the same plates, so as to remove the section bars from such plates, and thereafter to lay down such section bars on the subsequent zone, as well as are constituted by

a set of gearmotors with worm screw acting on the movable plates 24 in a manner to translate them in the advancing direction, and additional gearmotors acting onto said movable plates in a manner to translate them in the opposite direction, up to the starting rest position. Finally, the present driving mechanisms are constituted by a set of rack-sprocket gear wheels joining the longitudinal bars of the movable plates, in such a way as to transmit the motive power for the movement without breaks and jolts, thereby avoiding any possible damage of the material being treated, and the assembly step by step movement is ended automatically after a pre- established number of advancing steps, such that to maintain the material being heat treated in the furnace interior for the established time. Obviously, instead of the described manner, the section bars step by step advancement along the movable plates is also possible to be obtained in a different manner and with different driving mechanisms, provided that a section bars automatic advancement through the furnace within the established times is always obtained, which times are such that each section bars map is submitted to the needed treatment, thus without departing from the protection sphere of the present invention. The operation of the so realized furnace appears already evident from the description of the structural characteristics of the same furnace. In fact, each section bars map transferred by the conveyor means in this furnace arrives at the furnace end portion and by means of a set of powered rollers arranged here is conveyed toward the outer elevator, which latter is raised firstly to the fixed plate situated at the higher level, where such map is laid down in this position, and thereafter such elevator is subsequently raised at the respectively lower levels, by laying down a map here from time to time. Afterwards, the map loading operations are repeated with the same sequence, in such a manner that each plate is always filled with the same number of maps, which therefore are progressively transferred in the advancement direction, and as soon as a set of maps arrives at the furnace outlet is picked up selectively by the outer elevator and transferred by the same towards the conveyer means which transfer it towards the storage area, while a new set of maps is ulteriorly introduced in the furnace through the outer elevator, acting synchronously with the preceding elevator, in which condition the furnace is always filled with maps and therefore may be maintained always at the same operation temperature. Consequently, this furnace allows the more homogeneous and even heat treatments for all maps to be performed, by eliminating the map loading and unloading boxes and the operations needed for these boxes, and by minimizing any loss of heat outwardly during the rapid automatic map loading and unloading operations, which circumstance allows the need of repeating furnace pre-heating after each treatment cycle to be avoided.