WO2014009053A1

WO2014009053A1 - Oven comprising surface radiator

Info

Publication number: WO2014009053A1
Application number: PCT/EP2013/061072
Authority: WO
Inventors: Gerhard Brendel
Original assignee: SLF Oberflächentechnik GmbH
Priority date: 2012-07-11
Filing date: 2013-05-29
Publication date: 2014-01-16
Also published as: EP2872845A1; DE202012102570U1; PL2872845T3; EP2872845B1; HUE048018T2

Abstract

Disclosed is an oven for surface-treated tools, comprising a usage chamber which accommodates the powder-coated tool, a convection heater which has a heating unit, a bellows and air supply ducts that guide the air that is heated and displaced by the bellows through the usage chamber and past the tool, the usage chamber having a radiation heater, the radiator of which, when functioning as an infrared radiator, optionally emits medium-wave infrared radiation and, when functioning as a dark radiator, emits long-wave infrared-radiation, and is aligned such that its radiation radiates into the interior of the usage chamber, and is arranged in the usage chamber in a three-dimensional arrangement so as to surround the tool, it being proposed in said oven that the radiator be disposed as a surface radiator so as to form three boundary panels in the form of wall, floor or covering surfaces of the usage chamber in a manner that surrounds the tool.

Description

"Oven with surface spotlight"

Description:

The invention relates to a furnace according to the preamble of claim 1.

From DE 10 2008 059 81 1 A1 a generic oven is known. The possibility of being able to paint-coat powdered or wet-varnished workpieces by combining radiant and convection heating and, at the same time, different

To use radiant heaters with a different waviness of the heat rays, in practice leads to excellent painting results. To generate the infrared radiation, hot air is passed through pipelines, with the pipes then emitting the radiation to the outside.

Apart from the use of a generic oven for baking a powder coating, the oven can also be used to dry the surface of a workpiece on which adhesive water is, or for drying

Workpieces whose surface is coated by means of a cathodic dip coating (KTL). Purely by way of example and without restricting the oven described to this intended use, the oven is described below as a baking oven for powdered workpieces, which is part of a

Powder coating is used to apply that to the workpiece melt applied powder and create a so-called burn-in.

The invention has for its object to improve a generic oven to the effect that the effect of heat on the surface of the workpiece as evenly as possible.

This object is achieved by a furnace having the features of claim 1.

In other words, the invention proposes not to guide the hot gas through individual tubes, each of which may be referred to as a line radiator, but rather to heat a larger area with the hot gas, so that the radiator forms a surface radiator. The surface radiator is designed such that it forms three boundary plates, which limit the usable, accessible for the positioning of the workpiece interior of the utility chamber. These boundary plates surround the workpiece on at least three sides, for example in the form of two opposite wall surfaces and a floor or ceiling surface connecting the two wall surfaces.

Advantageously, the boundary plates can be designed double-walled, so that the hot gas can be guided within these double-walled boundary plates. This allows a large-scale and direct heat transfer from the hot gas to the plate surface. Compared with z. As the ability to run the hot gas in pipes and to couple them thermally to a boundary plate, there is a better efficiency and the possibility of faster, more precise temperature control.

It is provided that no free distribution of the hot gas between the two surfaces of the double-walled Begren- but to divide the space between the double-walled boundary plate in several heating channels, so that the hot gas is guided within the heating channels. In this way, flow-calmed areas within a double-walled boundary plate can be avoided, which could lead to a comparatively cooler zone and accordingly unequal temperature distribution due to the reduced there hot gas flow. The first boundary plate in the flow direction can also be configured without such heating channels; especially in the then subsequent boundary plates, the heating channels are advantageous.

Advantageously, one of the three boundary plates, which is referred to as a first boundary plate, have an inlet opening through which the hot gas can flow into this first boundary plate. The three boundary plates are fluidically connected to each other, so are in fluid communication with each other and thus with the inlet opening, so that the hot gas can flow through all three boundary plates. A second of the three boundary plates has an outlet opening through which the meanwhile hotter hot gas can flow out of this second boundary plate. Inlet and outlet openings are not arranged close to each other in such a way that a short-circuit-like short connection between inlet and outlet opening would result, but the two inlet and outlet openings are arranged in such a way, in particular in connection with the mentioned heating channels. that the largest possible possible contacting of the surfaces facing the workpiece with the hot gas is ensured, so that even the most uniform heat distribution within the furnace is ensured by this way.

In an advantageous embodiment, these heating channels may be delimited by ribs, which are located inside the double-walled are arranged boundary plates. The two walls of a double-walled boundary plate may, for example, form two sections of such a heating channel, and two adjacent ribs form two other sections of the same heating channel, so that overall a heating channel with, for example, approximately rectangular cross-section can be created. Also by this measure, a direct contacting of the hot gas is made possible with the boundary plate, without the need for separate pipes within the double-walled boundary plates. The ribs thereby advantageously connect to one of the two walls of a double-walled heat transferring. Even if they are not airtight on the opposite wall of the double-walled boundary plate, nevertheless a sewerage of the hot gas is effected and thus enables a defined air distribution of the hot gas within the double-surface boundary plates by means of the ribs to the desired uniform surface temperature of the radiating onto the workpiece wall to reach the boundary plate. Advantageously, however, the ribs can connect the two walls of the double-walled boundary plate with each other.

Regardless of whether the ribs are in contact with only one or both walls of a double-walled delimiting plate, it may in any case be provided that they are always in contact with that wall of the double-walled delimiting plate which is directed towards the workpiece. The contact between the rib and the wall of the boundary plate is designed as a heat-conducting contact, so that the heat energy of the hot gas is passed via the rib on the wall of the boundary plate. In this way, a high efficiency in the heating of the boundary plates is made possible.

Due to the heat transfer from the hot gas to the boundary plates, the hot gas cools down in the course of its flow. Around To ensure the most uniform possible surface temperature of the three boundary plates, can therefore be advantageously provided to remove from the first flowing into the boundary plates hot gas initially less heat energy percentage, in the subsequently flowed boundary plate, however, from the hot gas to remove more heat energy percentage and finally in the third of Hot gas flowed through limiting plate percent more heat energy to remove in order to achieve in this way in the three boundary plates as equal as possible energy input and the same surface temperatures as possible. For this purpose, advantageously, the number of ribs, which are provided in the double-walled boundary plates, increase in the flow path of the hot gas. In this way, an increasingly larger heat transfer surface is used to direct heat energy from the hot gas into the workpiece facing surface of the restriction plate.

Alternatively, one can achieve a uniform surface temperature as possible, provided instead of the mentioned ribs, the flow-through cross-section of a boundary plate smaller than the cross section of upstream boundary plate, so that gradually, from one to the next boundary plate, always lower free Flow cross sections result. By reducing the cross-section compared to the upstream boundary plate to achieve a higher flow rate of the hot gas, which has a higher heat transfer coefficient and thus a higher heat transfer result. Compared to the design of the boundary plates with the mentioned ribs, however, results in an increased flow resistance, so that z. B. a higher drive power of a hot gas fan is required.

Whilst a boundary plate as a whole, seen macroscopically, is substantially planar, extending in a plane Plate can be configured, can be considered in detail, the workpiece directed to the surface of the boundary plate advantageously be designed profiled from a completely flat configuration deviating and rather uneven. In this way it is supported that the infrared radiation emitted by this surface is emitted in several directions, so that in this way undercuts, depressions u. Like. Of the workpiece are better achieved by the radiation, whereby the painting result is improved.

It can be advantageously provided that the profilings in the workpiece surface facing the boundary plate is designed not only in the manner of a vertical offset, but that the surface has inclined surface portions and that obliquely to the plane in which the boundary plate extends. By means of these inclined surface sections, an obliquely directed radiation of the thermal energy is supported. For example, the inclined surface sections can be created by the surface of the boundary plate having a straight or rounded wavy course.

Apart from radiant heating, the oven also allows convection heating of the workpiece. If the oven is used to burn a powder coating in a workpiece, a combined heating effect can advantageously be used: After the components have been heated at the beginning of the heating exclusively by the radiant energy, is switched to the convection heating after reaching the desired component temperature. For this purpose, a recirculation mode of the furnace is switched on. In this case, air flows down from supply air ducts, which are located above the lateral boundary plates. This air heats up as it flows past the side boundary plates so that the side boundary plates act similar to the surface of a heat exchanger. In the lower area of the utility room the two supply air streams, which have flowed downwards on the two opposite sides of the working space, collide and are directed upwards to an exhaust air duct, where the air is drawn in and from there to the supply air ducts. For example, the exhaust duct can be located centrally on the ceiling of the work space. In recirculation this air is then fed via fans back to the two supply air ducts.

An embodiment of the invention will be explained in more detail below with reference to the purely schematic representations. It shows

Fig. 1 is a vertical section in the longitudinal direction by a

Furnace used to burn a powder coating into a workpiece,

Fig. 2 is a longitudinal section in the horizontal direction through the

Oven of Fig. 1,

3 shows a vertical cross section through the furnace,

Fig. 4 is a rear view of the oven, and

Fig. 5 is a vertical cross section through the furnace, with

Flow arrows for the air duct in convection operation of the furnace.

In the drawings, 1 in total denotes a furnace which serves to burn a powder coating on the surface of a workpiece. The furnace 1 has a utility chamber 3, within which a hatched indicated workpiece 2 may be, wherein the hatching illustrates the largest possible dimensions of the workpiece 2 and the workpiece 2 is formed in practice considerably more irregular than the rectangular, in Fig. 3 apparent contour For example, the workpieces to be treated may be machine components or machine assemblies, and the dimensions that the workpiece 2 may have are usually several in length, width, and height Meter. 1, 2 and 4, the workpiece 2 is not shown hatched, but here are each marked with the respective plurality of reference numerals shown in a figure 2, the outer lines of the purely schematically cuboid workpiece 2.

The useful chamber 3 is bounded on three sides by limiting plates: a first limiting plate 4 forms a side wall of the useful chamber 3, and on the opposite side a second limiting plate 5 forms the opposite side wall. Simplifying is in each case of a boundary plate 4, 5 or 6, the speech, but in fact the wall and bottom surfaces of the utility chamber 3 are created by modular juxtaposed segments, depending on the length of the useful chamber. 3 In the illustrated embodiment, each five such segments form one of said boundary plates 4, 5 or 6, which deviating from this embodiment, in each case a non-segmented, a continuous boundary plate can be provided.

The three boundary plates 4, 5 and 6 are fluidically connected to each other. For this purpose, curve pieces 7 are provided, which are designed as well as the boundary plates 4, 5 and 6 double-walled. The curve pieces 7 form in the illustrated embodiment, a non-divided, continuous interior, while the other hand, not curved, but substantially flat boundary plates 4, 5 and 6 each have a plurality of ribs 8, extending between the two walls of the double-walled boundary plates 4, 5 and 6 extend. In this way, a plurality of heating channels 9 is created within the boundary plates 4, 5 and 6 respectively.

From Fig. 2 it can be seen that the number of ribs 8 in the individual boundary plates 4, 5 and 6 is different. Since the drawings are purely schematic, only the difference in the number of ribs 8 is shown, while the actual conditions, ie the arrangement density of the ribs 8, may differ from the illustrated conditions: In the first limiting plate 4 hot gas flows, which then between the relatively far apart spaced ribs 8 by heating channels 9 flows with a correspondingly großformatigem cross section. From the first boundary plate 4, the hot gas then passes through a curve piece 7 in the middle boundary plate 6, which forms the bottom of the utility chamber 3. Due to the hitherto performed heat release from the hot gas to the first limiting plate 4, the hot gas already has a slightly lower temperature. In order to remove approximately the same heat output from the hot gas, the middle boundary plate 6 has a higher number of ribs 8, which are arranged at a comparatively smaller distance from each other, so that in total the heat transferring, in contact with the hot gas surface of the middle boundary plate 6 is larger than in the first limiting plate. 4

By a further curve piece 7 then passes the still further cooled hot gas into the space of the second boundary plate 5, which forms the first boundary plate 4 opposite wall surface of the Nutzkammer 3. Within this second boundary plate 5, the distance between two adjacent ribs 8 is again lower and accordingly the heat transfer surface between hot gas and boundary plate 5 again larger, in order to ensure sufficient heating of the second boundary plate 5, also in view of this even lower temperature levels of the hot gas, so that the Workpiece 2 around the three boundary plates 4, 5 and 6 provide the most uniform heating power for baking the powder coating or to ensure the most uniform heating of the workpiece in other uses of the furnace. As can be seen in particular from the enlarged detail of FIG. 2, the boundary plates 4, 5 and 6 are each configured double-walled, with an outer, flat surface 10 and an inner, directed to the workpiece 2 surface 1 1. This inner surface 1 1, which is directed to the workpiece 2, has in the illustrated embodiment, only surface portions which are obliquely aligned to the plane of the boundary plate 5, namely by this surface 1 1 zigzags, ie has a waveform of exclusively straight lines , In the drawing, the inclination of the surface portions is shown for illustrative purposes, the actual inclination may be chosen flat. First, the heat transfer surface of the boundary plate 5 is enlarged on its side facing the workpiece by the zigzag wave pattern of the surface portions in comparison to a flat configuration of this surface. Secondly, a diffuse radiation distribution of the heat radiation is supported, which also includes the achievement of undercuts, the penetration of the radiation into depressions and the like. Like. Supported on the workpiece 2 and thus improves the burn-in.

From Fig. 3 it can be seen that the first limiting plate 4 is in communication with an inlet opening 12 and at the opposite end of the Begrenzungsplattenanordnung the second limiting plate 5 is in communication with an outlet opening 14. The inlet opening 12 and the outlet opening 14 are each designed as air channels which extend over the entire length of the useful chamber 3, so that the hot gas is distributed over the entire boundary plates 4, 5 and 6 as large as possible over a large area and a uniform temperature distribution to the inner, to the workpiece 2 facing surfaces 1 1 of the boundary plates 4, 5 and 6 is achieved. Within each substantially flat boundary plates 4, 5 and 6, the hot gas is guided in the heating channels 9. On the other hand, in curve pieces 7, which are not characterized by ribs in different dene flow sections are divided, the hot gas can be distributed. The curved pieces 7 can thereby also be made simpler and more economical.

Workpieces that have areas with different thicknesses heat up at different speeds when heated with infrared radiation. Therefore, after a previously calculated time, or based on a temperature measurement of the thinnest part, in the baking oven 1, a circulating air for Konvek- tion heating of the workpiece 2 is switched on. Simultaneously with the connection of the circulating air, the beam wall temperature, ie the temperature measured at the boundary plates 4, 5 and / or 6, so far reduced until the circulating air reaches a previously set temperature of z. B. 200 ° C holds constant. The circulating air serves to ensure that thin-walled parts, which have already reached the temperature of the circulating air, do not continue to heat up due to the infrared radiation, but release their excess irradiated energy to the circulating air. Thick-walled parts, which have not yet reached the circulating air temperature, experience even steeper Temperaturanstiegsgradienten due to the switched circulating air, because these parts now not only the heat radiation, but additionally acts a heat transfer by forced convection.

To produce the circulating air three hot air blower 15 shown in FIG. 4 are provided in the rear region of the furnace 1, wherein two discharge channels 16 connect to the pressure side of the hot air blower 15, while the hot air blower 15 are in flow connection with a suction channel 17 on the suction side, so that as possible complete flow around the workpiece 2 with the hot air in convection operation of the furnace 1 is made possible. After the components have been heated at the beginning of the heating exclusively by the radiant energy, is switched to the convection heating after reaching the desired component temperature. For this purpose, a forced air operation of the furnace is switched on, wherein Fig. 5 illustrates the air flow through flow arrows:

In the outflow channels 16, a narrow blow-out slot 18 is arranged over the entire length, which can be seen in particular from FIG. 3. From the outflow channels 16, which are located above the lateral boundary plates 4 and 5, circulating air flows at a very high blow-off speed of, for example, 30 m / s downwards. The fact that overpressure prevails in the outflow channels 16 is indicated by the "+" signs drawn in parenthesis and this downwardly flowing air impinges on the boundary plates 4, 5 and 6 as a plane free jet and heats up as it does so As a result, the boundary plates 4, 5 and 6 function not only as infrared radiators but also as heat exchangers by releasing thermal energy due to forced convection to the circulating air In the lower region of the useful chamber 3, the two supply air streams, which have flowed downwards on the two opposite sides of the utility chamber 3, collide and are directed upwards to the intake channel 17, where the air is sucked in and from there in the circulating air process is again conducted to the outflow channels 16. That in the intake passage 17 a negative pressure ago is indicated by the "-" sign.

Because of the high air outlet velocity from the blow-out slots 18 in addition about 6 times the amount of air of the free jet from the work space 3 is induced. As illustrated in FIG. 5, the plane free jets resting against the left and right boundary plates 4 and 5 collide in the middle of the floor and are deflected upwards, so that a turbulent vertical flow is obtained in the work space 3. As a result, it is possible to achieve twice the speed of the ascent in normal circulating air ovens, whereby the electric drive train ventilation of fans only 50% of the drive power of the fans of a conventional convection oven.

Due to the superimposition of the infrared radiation with the convection, very short workpiece heating times are achieved without the risk of overburning the workpiece.

The regulation of the process takes place in such a way that at the beginning of the baking or heating process of the control parameters, the surface temperature of a limiting plate 4, 5 and 6, respectively. In a combustion chamber, the hot gas is thus supplied with the required amount of heat in the recirculation mode in order to keep the desired temperature of the boundary plate 4, 5 and 6 constant.

After a certain time, when the maximum allowable temperature of the thinnest wall thickness of the component is reached, the surface temperature of a boundary plate 4, 5 and 6 is no longer used as a control parameter, but the maximum allowable temperature of the furnace air. The maximum permissible temperature of the furnace air usually corresponds to the desired final temperature of the workpiece or is slightly above it. The temperature of the thinnest wall thickness of the component can either be determined by means of temperature measurement, or the time to reach this temperature can be theoretically calculated beforehand. Usually, databases with times for various combinations of thinnest and thickest component wall thicknesses are stored in the controller for this purpose.

The furnace air can already be switched on at the beginning of the heating process, which is the fastest way of heating the component, because in this case the two types of heat transfer radiation and forced convection are superimposed from the beginning. In the case of sensitive coatings, on the other hand, it can be deliberately planned to switch on the circulating air later. In the case of a powder coating, for example, there is the danger that powder not yet gelled will be blown from the component by the circulating air. Therefore, it can be provided in this case, the circulating air zuzuschalten only after reaching a so-called fishing temperature, namely, when the powder is gelled and in particular is also angeliert on the component.

Claims

Furnace (1) for surface-treated workpieces (2), having a utility chamber (3) containing the powder-coated

Picking up workpiece (2),

a Konvektionsheizeinrichtung, which has a heating unit, a fan and the heated and blown by the fan air through the Nutzkammer (3) and on the workpiece (2) along leading air ducts, wherein the Nutzkammer (3) has a radiant heater whose radiator as infrared radiator either one medium-wave infrared radiation and as a so-called dark radiator emits a long-wave infrared radiation, and is oriented such that its radiation radiates into the interior of the useful chamber (3),

and in a three-dimensional arrangement, the workpiece (2) surrounding, in the Nutzkammer (3) is arranged, characterized

the emitter is configured as a surface emitter, such that it forms three boundary plates (4, 5, 6) surrounding the workpiece (2) as wall, floor or ceiling surfaces of the utility chamber (3).

Oven according to claim 1,

characterized,

the boundary plates (4, 5, 6) are designed as double-walled wall, floor or ceiling surfaces of the utility chamber (3),

wherein inside the double-walled wall, floor or ceiling surfaces hot gas leading heating channels (9) extend.

Oven according to claim 2,

characterized,

a first boundary plate (4) has an inlet opening (12) for the hot gas, and the three boundary plates (4, 5, 6) are in flow communication with the inlet opening (12),

and that a second boundary plate (5) has an outlet opening (14) for the hot gas,

wherein the inlet opening (12), the heating channels (9) and the outlet opening (14) are arranged such that the hot gas over a large area in contact with the workpiece (2) facing surfaces (1 1) of the boundary plates (4, 5, 6) is guided.

Oven according to claim 2 or 3,

characterized,

in that the heating channels (9) are delimited by ribs (8) which are arranged inside the double-walled boundary plates (4, 5, 6).

Oven according to claim 4,

characterized,

the ribs (8) connect heat-conducting to the surfaces (1 1) of the boundary plates (4, 5, 6) facing the workpiece (2).

Furnace according to claims 3 and 4,

characterized,

in that the first limiting plate (4), which has the hot gas outlet opening (12), has a first number of ribs (8) per unit area,

the second restriction plate (5) having the hot gas outlet port (14) has a second number of ribs (8) per unit area,

and the third restricting plate (6) disposed between the first restricting plate (4) and the second restricting plate (5) has a third number of ribs (8) per unit area,

wherein the first number is smaller than the third number, and the third number is smaller than the second number of ribs. pen (8) per unit area of the respective limiting plate (4, 5, 6).

Oven according to claim 2,

characterized,

in that the boundary plates (5, 6) each have a smaller free flow cross-section through which the hot gas can flow than the boundary plate (4, 6) upstream of the hot gas in such a way that from one to the next boundary plate (4, 5, 6) each results in a decreasing free flow cross section.

Oven according to one of the preceding claims,

characterized,

that the workpiece (2) directed surface (1 1) of a boundary plate (4, 5, 6) is profiled uneven profiled.

Oven according to claim 8,

characterized,

in that the profiled surface (11) comprises predominantly surface portions which are oriented obliquely to the plane in which the boundary plate (4, 5, 6) extends.