DE29923271U1 - Device for the contactless, localized heating of material by means of radiation - Google Patents

Description

Device for contactless, localized heating of material using radiation

field of use

In industrial production, there is often a need to heat materials (e.g. workpieces or samples) at specific points. Examples include annealing, brazing, melting, shrinking, gluing, drying or soft soldering of plastics and metals.

State of the art

A non-contact method in which thermal radiation energy can be limited to a small area and the heat input can be regulated is irradiation with light from a light source (German patent specification No. 498501 dated May 23, 1930). The radiation energy can be varied by the power of the light source, the duration of the radiation and the type of focusing. It is absorbed on the surface of the workpiece to be heated and converted into heat. The absorption behavior of the irradiated workpieces is therefore of crucial importance and a light source should be selected whose wavelength is in a range in which the light is absorbed very well.

In light soldering, part of the rays emitted by a light source are focused at a focal point using a semi-ellipsoidal reflector and directed to a soldering point. In a product from Royonic, the light is additionally bundled using a lens system, which absorbs a considerable part of the light output. Since this system is used for the slow and "gentle" heating of

However, if electronic components are used in conjunction with a sub-heater, the comparatively low power density is sufficient.

In another repair system (DE 196 39 993 A1), the light from a halogen spotlight is bundled with an ellipsoidal reflector and guided through a capillary glass tube, which makes it possible to combine the handling function of a suction pipette with the function of a soldering tool. Better focusing is to be achieved by tapering the capillary tube.

In a system with a high-pressure xenon lamp, light is also bundled with an ellipsoidal reflector and coupled into a flexible light guide at the second focal point (Stellbrink, L.: "Soldering with light", Productronic (1994) 4, pp. 31-32). The focus can be changed by adjusting the optics.

In these systems with semi-ellipsoidal reflectors, the light is not focused on the second focal point in a considerable part φ* of the radiation elevation angle, but leaves the reflector as scattered light. This loss angle φ* is approximately 90° for an ellipse with a numerical eccentricity of 0.6-0.7 (as recommended by Wiesner, P. in his final report on the DFG project "Surface hardening with high-energy lamps Wi 1209/3-1"). This scattered light is lost as power for heating the processing area and may disrupt the process because it heats the environment. Furthermore, the maximum light exit angle or opening angle φ for semi-ellipsoidal reflectors is equal to the loss angle φ*. If the emerging light cone is influenced by a lens, further power losses occur because commercially available lenses can only absorb light up to an opening angle of approximately 60°. Radiation components that lie outside this angle are reflected into the environment.

The aim is therefore a reflector shape with a low loss angle φ* and a small opening angle φ.

An extension of the reflector from a half-ellipse (seen in a section along the axis of rotational symmetry of the reflector) to almost a full ellipse reduces the loss angle φ*, but the opening angle φ increases. A shortening of the ellipse reduces the opening angle φ, but the loss angle φ* increases. A change in the numerical eccentricity changes the size of the image of the light source at the focal point.

Another approach is shown in the German patent application DE 43 45 010 A1 with a reflection element consisting of an ellipsoidal main reflector and an additional ellipsoidal reflector, which are connected to one another via a spherical ring reflector. A radiation focal point of the first reflector lies in the coupling surface of the latter. This reduces the loss angle φ*, while the opening angle φ does not change.

Description of the invention

The invention is based on the problem that when focusing by means of an ellipsoidal reflector, power losses occur because at a loss angle φ* radiation does not hit the reflector and is therefore not focused on the second focal point, and furthermore because the opening angle φ may be larger than the permissible light entry angle of a downstream lens.

The invention is intended to ensure that as much of the available heat radiation from a heat source as possible reaches a processing location.

This is achieved by a device having the features of patent claim 1, because one of the reflector surfaces can now extend far into the rotational symmetry plane of the reflector arrangement. Advantageous further developments are specified in the dependent claims.

An essential idea of the invention is that a reflector arrangement is composed of several rotationally symmetrical reflector surfaces in such a way that the radiation emitted by a heat radiator, in particular a lamp, is reflected by single or multiple reflection from surrounding reflector surfaces onto a reflector surface arranged behind or around the heat radiator in such a way that it is guided as near-axis radiation through a radiation exit opening, i.e. in such a way that the opening angle φ is smaller than with a comparable ellipsoidal reflector, preferably less than 60°. Furthermore, the loss angle φ* is very small, i.e. even smaller than the opening angle φ.

Embodiments of the invention

Figures 1 to 3 each show, in longitudinal section, a schematic embodiment of a device according to the invention.

Figure 4 shows the use of the device in a light soldering system.

Further embodiments are shown schematically in Figures 5 and 6.

The entire reflector R (see Figure 4) has, according to Figure 1, several reflector surfaces with a common rotational symmetry axis ROT, namely:

1. a continuously curved collecting surface RS, which is arranged on the side opposite a radiation outlet opening LA as seen from a heat radiator L,

2. a reflector surface RA1, which is connected to RS, and

3. a reflector surface RA2, which is connected to RA1 and extends to a radiation exit opening LA, i.e. almost to the rotational symmetry axis ROT.

A beam &khgr; shows the mode of operation. Starting from the heat radiator (light source) L, the beam hits the reflector surface RA1 and is guided to the reflector surface RA2 (the so-called counter surface), from there to the reflector surface (collecting surface) RS and from there to the radiation exit opening (light exit opening) LA (see Figure 1 in the lower section). The last part of the beam path (between RS and LA) runs close to the axis, i.e. so close to the rotational symmetry axis of the reflector surfaces that it lies within the maximum opening angle ϕ that the downstream lens (O in Figure 4) (not shown in Figure 1) allows. This applies to all beams &khgr; in a range &agr; of the radiation elevation angle, i.e. between the beams a and b (see Figure 1 in the upper section).

The light exit opening LA is designed as a replaceable aperture B. The emerging rays cross in the light exit opening LA, forming a beam waist here. Since the reflector arrangement is closed up to the light exit opening, there is almost no scattered light outside the light cone leaving the reflector. One or more openings OL in the collecting surface RS are used to position the heat radiator L with its socket F.

• · fr * &phgr; ·

Figure 2 shows a further embodiment of the device according to the invention. In this case, a further reflector surface RE is arranged between the collecting surface RS and the reflector surface RA1, the shape of which is ellipsoidal, so that the light source L is located in one of the two focal points and the light exit opening LA is located in the other focal point.

Rays in a range β of the radiation elevation angle, i.e. between the rays c and a* (see Figure 2 in the upper area), strike the ellipsoidal reflector surface RE and are reflected from there directly through the JKk light exit opening LA (see ray y in Figure 2, in the lower area). Rays in the range α* of the radiation elevation angle, i.e. between the rays a* and b* (see ray x* in Figure 2, in the lower area), are guided through the light exit opening LA by multiple reflection.

Figure 3 shows a further embodiment of the device according to the invention. Here, the collecting surface RS is arranged between the light source L and the radiation exit opening LA. Rays in a range γ of the radiation elevation angle, i.e. between the rays b** and d (see Figure 3 in the upper area), strike the reflector surface RA3 and are reflected from there onto the collecting surface RS and from there directly through the light exit opening LA (see ray ζ in Figure 3, in the lower area).

Rays in the range α** of the radiation elevation angle, i.e. between the rays a** and b** (see Figure 3 in the upper area), are guided through the light exit opening LA by triple reflection at RA1, RA2 and RS (ray x**).

Figure 5 shows an embodiment in which a reflector surface RA3 emits rays over a wide range of the radiation elevation angle.

(for example z1, z2, z3) is reflected onto a reflector surface RS, which causes a further reflection in the direction of a light exit opening LA. It is noteworthy that the radiation is only reflected twice here.

In Figure 6 (similar to Figure 2) a part of the radiation is reflected only once at a reflector surface RE (ray y* between the boundary rays c* and a*). Other rays (ray z* between the boundary rays a* and b*) are reflected twice.

The advantage of Figures 5 and 6 is that only relatively small losses occur due to the small number of reflections.

Application example

The light soldering system according to Figure 4 allows individual, high-quality solder joints to be produced cost-effectively?*- It can be used both for reflow soldering with solder paste and for soldering with solder wire.

With the reflector arrangement R described above, the radiation emitted by the light source L is focused onto the radiation exit opening LA, which in turn is imaged with an objective O onto a processing point BS, where the material to be locally heated is located.

The system is supplemented by a solder wire feed unit LZ and a pyrometer P for non-contact temperature measurement at the processing point BS.

Claims (18)

1. Device for the contactless, localised heating of material by means of concentrated radiation, in particular light, from a heat radiator (L), having the following features: a) a rotationally symmetrical reflector arrangement (R) is provided for the rays of the heat radiator (L), which has at least a first and a second continuously curved reflector surface (RA2, RS) with a common rotational symmetry axis (ROT) on which both the heat radiator (L) and a radiation outlet opening (LA) are arranged, b) the reflector surfaces (RA2, RS) are designed and aligned in such a way that the rays falling on the first reflector surface (RA2) during operation are reflected onto the second reflector surface (RS) and from there are guided directly through the radiation outlet opening (LA), characterized by the following feature: a) the beam waist of the rays leaving the reflector arrangement (R) during operation lies in the radiation exit opening (LA). 2. Device according to claim 1, characterized in that on that side of the radiation outlet opening (LA) which faces away from the heat radiator (L) there is an objective (O) for the rays guided through the radiation outlet opening (LA), which projects the radiation outlet opening (LA) onto the part of the material (BS) to be heated. 3. Device according to claim 1 or 2, characterized in that the first reflector surface (RA2) is arranged on that side of the heat radiator (L) on which the radiation outlet opening (LA) is also located. 4. Device according to one of the preceding claims, characterized in that the reflector arrangement (R) is designed in the shape of a hood and the heat radiator (L) arranged therein has a plurality of ring-shaped, continuously curved reflector surfaces (RA1, RA2, RE) arranged next to one another, which are designed and aligned in such a way that they guide the rays emitted by the heat radiator, in particular light source L, onto the second reflector surface (RS) in such a way that they are reflected from there through the radiation exit opening (LA) and leave the reflector arrangement (R) as rays close to the axis. 5. Device according to one of the preceding claims, characterized in that the first reflector surface (RA2) extends so far to the radiation exit opening (LA) or to its border that, during operation, it reflects all rays which come directly from the heat radiator (L) or from a reflector surface (RA1) in the immediate vicinity of the radiation exit opening (LA) or its border. 6. Device according to one of the preceding claims, characterized in that the first reflector surface (RA2) extends only so far as to the axis of rotational symmetry (ROT) that it does not intercept a significant part of the rays which are thrown during operation by another reflector surface (RS) in the direction of the receiving opening of the objective (O). 7. Device according to one of the preceding claims, characterized in that the diameter of the radiation exit opening (LA) is smaller than one tenth of the maximum diameter of the reflector arrangement (R). 8. Device according to one of the preceding claims, characterized in that a third reflector surface (RA1) is provided which can be directly irradiated by the heat radiator (L) and from which, during operation, those rays come which fall on the first reflector surface (RA2). 9. Device according to claims 1 to 8, characterized in that the rays falling on the first reflector surface (RA2) during operation come directly from the heat radiator (L). 10. Device according to one of the preceding claims, characterized in that a fourth reflector surface (RE) is provided, which reflects rays, which come directly from the heat radiator (L) during operation, directly through the radiation opening (LA). 11. Device according to one of the preceding claims, characterized in that a fourth reflector surface (RE) is arranged between the second reflector surface (RS) and the first reflector surface (RA2) as part of a hollow ellipsoid and is shaped such that those radiation components of the heat radiator (L) which are emitted during operation within a range (β) of the radiation elevation angle assigned to the fourth reflector surface (RE) are thrown through the radiation exit opening (LA) after only one reflection. 12. Device according to one of the preceding claims, characterized in that the enclosure of the radiation exit opening (LA) is designed as a replaceable aperture (B). 13. Device according to one of the preceding claims, characterized in that the reflector arrangement (R) consists of several separate parts. 14. Device according to one of the preceding claims, characterized in that the radiation exit opening (LA) is closed by a protective glass. 15. Device according to one of the preceding claims, characterized in that an objective lens (O) and/or a protective glass has a visible light filtering effect. 16. Device according to one of the preceding claims, characterized in that it comprises a heat detector (P) with which the temperature at critical areas of the material to be heated can be determined. 17. Device according to one of the preceding claims, characterized in that the guidance of a gas flow for cooling components of the heat radiator (L), its holder (F) and parts of the reflector arrangement (R) through channels is integrated in the reflector arrangement (R). 18. Device according to one of the preceding claims, characterized in that it comprises a device for axial and radial adjustment of the heat radiator (L).