Heat treatment oven

Abstract: A device at a heat treatment oven of the type using a com­ bination of radiation heat and convection heat, and where in connection to the oven chamber are provided means (4, 19) arranged to circulate the oven atmosphere through the oven chamber and a channel (20, 21) situated outside the oven chamber and back to the oven chamber, whereby the device incorporates a gas burner (7) arranged at combustion to emit its flame in a direction, which at least partly touches or coincides with the circulation channel (20, 21) for the oven atmosphere, and where the gas burner (7) is arranged to direct its flame into a vessel (22), provided in the cir­ culation channel (20, 21) for the circulating atmosphere.

Description: For heat treatment purposes of different types there have been developed different types of ovens for drying, hardening and food processing. An oven type, which has been developed in a number of different, well operating embodiments, during the last decade, is the IR-oven, which with a plurality of infrared radiators heat the goods to be treated in the oven. By particular steps it has hereby been possible to adapt the heating effect and the heat distribution in a desired manner, whereby ovens entirely or partly equipped with IR-elements, have proven themselves very well suited for many different purposes. For the purpose of combining the IR radiation with convection heating it has in certain types of ovens beside IR-elements in the oven walls also been provided an electric heating battery, which gives convection heating. This gives the heat treatment an improved flexibility, which is desirable in many connections. Such a heat treatment oven is known from WO 87/01186. US-A-3 324 844 refers to a gas-fired oven having a heat-distribution system having two gas-fired heat exchangers located in lateral large ducts along opposite sides of the oven chamber. Each of the two heat exchangers has an elongated burner tube extending along the chamber and having a series of spaced apart flame ports. Overlaying each burner is a collector formed as a downwardly opening elongated channel for collection of combustion products and having a plurality of vertical straight heat tubes connected to said collector and extending from the collector at the bottom of the heat exchanger to the top thereof where the vertical heat tubes communicate with flues. This oven gives no heating of the return air, its heating efficiency is not so good and the two burners thereof causes difficulties in guiding the heating of the oven and may cause uneven heating. During the years to come it is expected that electrical energy will be subjected to substantial price rises and it may even happen that there will be a shortage of electricity. On the other hand it is expected that supply and use of natural gas will increase substantially as the pipeline systems for natural gas is built out. For adaption to this expected new situation, the purpose of the present invention is to provide a heat treatment oven for reducing the electricity dependency of an IR-oven combined with convection heating of the aforesaid type and instead to use gas heating for the convection part of the heating, and this has been achieved at a heat treatment oven of the type using a combination of radiation heat and convection heat, and having a circulation channel situated outside the oven chamber and means in connection to the oven chamber for circulating the oven atmosphere through the oven chamber, through the circulation channel and back to the oven chamber, and comprising a device incorporating a gas burner arranged to emit its flame created during combustion in a direction, which at least partly touches or coincides with said circulation channel for the oven atmosphere, whereby the gas burner is arranged to direct its flame into a vessel, which vessel is constituted by a coiled, corrugated tube, which is positioned in the circulation channel for the oven atmosphere. The invention hereinafter will be further described with reference to an embodiment illustrated in the accompanying drawings. Fig. 1 shows in a view from above an oven portion according to the invention. Fig. 2 is a side view of a part of the oven according to the invention. Fig. 3 shows in bigger scale a cross section through the oven according to the invention, and Fig. 4 is a schematical detail view, partly in section of the oven according to the invention. Fig. 1 shows from above a combined oven zone as a parallelepipedic housing 1 incorporating a number of oven sections 2, and an infeed lock-gate 3 provided at one end thereof. Each one of the oven sections 2 is provided with a blower motor 4, air inlet 5 and a connection 6 for a gas burner 7 and a fume outlet 8. All gas burners 7 are connected to a main gas conduit 9, whereas all fume outlets 8 are connected to a collecting duct 10 for fumes, in which duct is provided a fume fan 11, which during operation creates a suction effect at all fume outlets 8. In Fig. 2 is shown a side view of a portion of the combined oven zone 1 according to Fig. 1. The gas burner, the gas conduit and the fume ducts have been omitted from this figure for the sake of clarity, whereas it instead is shown how the oven is equipped with a number of exhaust terminal devices 12, which via feed conduits 13 communicate with a main conduit 14 for exhaust air from the oven. In this view is also symbolically shown how the oven is equipped with electrical connections 15. At the infeed side is schematically shown how the objects 16, which shall travel through the oven for treatment, are conveyed into the oven e.g. on a conveyor track 17. Fig. 3 shows a cross section through an oven chamber section 2 according to Fig. 1 and 2, and as can be seen from this view the oven chamber walls are internally provided with IR-elements 18, which give a radiation heating of goods traveling through the oven chamber. The blower motor 4 positioned on top of the oven housing drives an impeller 19, which produces air circulation in the oven, whereby the oven atmosphere is caused to move upwards through a central air shaft 20, and thereafter downwards through a tapering, annular shaft 21 arranged concentric with the first central air shaft 20, and through which annular shaft the air is again introduced into the oven chamber through not shown slots provided in the oven walls, and from the bottom of the oven chamber through said central shaft 20, for a repeated closed cycle. In the tapering, annular shaft 21 is provided a coiled tube 22, having one of its ends is connected to the connection 6 for the gas burner 7, whereas its opposite end is connected to the connection 8, shown in Fig. 1, leading to the main fume conduit. The gas burner 7 is connected to the main gas conduit 9 via a gas valve 23, a stop valve 24 and a reduction valve 25. The fume outlet, which is not shown in the figure, as earlier mentioned, communicates with a main fume conduit (10 in Fig. 1) in which is provided a fume fan 11, which creates a suction at the connection 8. Fig. 4 shows schematically, in perspective and in bigger scale the coiled tube 22 with its connections 6 and 8 to the gas burner 7 and to the fume outlet resp. As can be seen from this view the tube 22 is corrugated and it is of course manufactured from a material, which is not destroyed or influenced by the temperatures created by the gas burner at one end of the tube. Due to the corrugation the heat transferring surfaces of the tube are increased, thus that a good heat transfer to the oven atmosphere is achieved, and which moves downwards through the annular, tapering space 21 in which the tube 22 is provided. In this manner and by means of this design is achieved a good heating of the oven atmosphere recirculating in the oven chamber, without need of increased electric consumption, and by appropriate adjustment (which is however no part of the present invention) it is possible easily to set required proportions of IR-radiation heat and convection heat in relation to the requirements in different applications and occasions of use.

Claims: A heat treatment oven of the type using a combination of radiation heat and convection heat, and having a circulation channel (20, 21) situated outside the oven chamber and means (4, 19) in connection to the oven chamber for circulating the oven atmosphere through the oven chamber, through the circulation channel and back to the oven chamber, and comprising a device incorporating a gas burner (7) arranged to emit its flame created during combustion in a direction, which at least partly touches or coincides with said circulation channel (20, 21) for the oven atmosphere, characterized therein that the gas burner (7) is arranged to direct its flame into a vessel (22), which vessel is constituted by a coiled, corrugated tube, which is positioned in the circulation channel (20, 21) for the oven atmosphere. A heat treatment oven as claimed in claim 1, characterized therein that the vessel (22) is closed and provided with a fume outlet (8) situated outside the oven. A heat treatment oven as claimed in claim 1, characterized therein that the tubular channel (22) is arranged in a portion of the channel (21), has an interior separated from the oven atmosphere, and is at one end (6) connected to said gas burner (7), which directs its flame directly into the tubular channel (22), which at its opposite end (8) is connected to a fume discharge conduit. A heat treatment oven as claimed in claim 2 or 3, characterized therein that a fume fan (11) is connected to the fume outlet (8) or provided in the fume discharge conduit (10), said fan being arranged during operation to create a suction effect in the vessel or in the tubular channel (22) respectively.

Inventors: KARLSSON LARS, KARLSSON, LARS
Applicants: TRILINE AB
Application year: 1990
Main classification: F24C15
IPC codes: F24C15, F24C3