NOZZLE STRIP FOR A BLOW BOX FOR THERMAL PRE-TENSIONING OF GLASS PANELS

Description

[0001] The invention relates to a nozzle bar, a blowing box equipped therewith and a device containing it for thermally prestressing glass panes.

[0002] The thermal tempering of glass panes has been known for a long time. It is also frequently referred to as thermal prestressing or annealing. By way of example, reference is made to patent documents DE 710690 A, DE 808880 B, and DE 1056333 A from the 1940s and 1950s. A glass pane heated to just below its softening temperature is subjected to a stream of air, which causes rapid cooling (quenching) of the glass pane. This creates a characteristic stress profile in the glass pane, with compressive stresses on the surfaces and tensile stresses in the core of the glass pane. This has two effects on the mechanical properties of the glass pane. First, the fracture resistance of the pane is increased, and it can withstand higher loads than an untempered pane.Secondly, if the glass breaks after penetration of the central tensile stress zone (e.g., by damage from a sharp stone or by deliberate destruction with a pointed emergency hammer), it does not break into large, sharp-edged shards, but into small, blunt fragments, thus significantly reducing the risk of injury.

[0003] Due to the properties described above, thermally tempered glass panes are used in vehicles as so-called single-pane safety glass, particularly as rear and side windows. Especially in the case of passenger cars, the panes are typically curved. The bending and tempering process is combined: the pane is softened by heating, formed into the desired curved shape, and then subjected to a cooling airflow, thereby generating the prestress. This process utilizes so-called blowing boxes. (quench box, quench headThe blowing chambers are used, to which the airflow is directed by powerful fans. Inside the blowing chamber, the airflow is divided into several channels, each terminated in a nozzle bar. The nozzle bars have a side surface with a series of blowing or nozzle openings directed at the glass pane, striking it with the airflow distributed by the blowing chamber. The curved glass pane is typically moved between an upper and a lower blowing chamber, and the chambers are then brought close to each other and to the pane surfaces for tempering. The entire apparatus with the two blowing chambers is often referred to as a tempering station.

[0004] The aforementioned side surfaces of commonly used nozzle strips are generally flat or curved, and the nozzle strips themselves are essentially cuboid or curved cuboids. The nozzle strips thus act as barriers to outflowing air, preventing it from flowing efficiently primarily between the nozzle strips, i.e., parallel to their direction of extension, and not perpendicular to them. This can have significant disadvantages, particularly when pre-stressing highly three-dimensionally (spherically) curved discs. The concave surface of such a strongly curved disc forms a kind of basin, potentially obstructing the outflow of heated air in the only remaining direction of flow. This can lead to an airlock, which hinders the cooling of the disc surface and thus reduces pre-stressing efficiency.

[0005] Blowing boxes with nozzle strips of the type described above are disclosed, for example, in DE 3612720 C2, DE 3924402 C1 and WO 2016054482 A1.

[0006] Other types of blowing boxes or tempering devices are also known in which the airflow is not divided into channels closed by nozzle bars. For example, the blowing box may have a cavity closed by a plate which is provided with openings (nozzles) in a two-dimensional pattern, thereby dividing the airflow and distributing it over the glass pane to be tempered.

[0007] To increase pre-tensioning efficiency, it is desirable to allow for a faster flow of the heated air. Higher pre-tensioning efficiency enables the generation of higher voltages or the more energy-efficient generation of a given voltage profile.

[0008] Blowing boxes are also known that are equipped with attached, for example, screwed-on, freestanding nozzles. Such nozzles have been described both for blowing boxes whose cavity is closed by a nozzle plate and for those in which the gas flow is divided into channels closed by a nozzle bar. Examples include US 4519829 A, US 4711655 A, EP 0463971 A2, GB 505 188 A, US 2013 / 255319 A1, US 4 662 926 A, EP 0 719 242 B1, and EP 0 002 055 A1. In principle, such nozzle bars allow for faster cooling because the spaces between the nozzles open additional drainage channels, even perpendicular to the direction of the nozzle bars. However, the multi-part design of nozzle strips and attached nozzles makes manufacturing more difficult and reduces the mechanical stability of the blowbox system.

[0009] WO 03 / 101898 A1, JP 5445974 B2, US 4494972 A, EP 2805926 A1, DE 102008017729 A1, US 2008 / 127678 A1, US 4749401 A, JP 200927488 A and US 2194760 A each show devices in which an object is blown on by a blowing device.

[0010] The present invention is based on the objective of providing an improved nozzle strip for blowing boxes for the thermal tempering of glass sheets. The nozzle strip should enable improved tempering efficiency, particularly when tempering highly three-dimensionally curved sheets, exhibit high mechanical stability, and be easy to manufacture.

[0011] The problem is solved according to the invention by a nozzle bar according to independent claim 1. Preferred embodiments are set forth in the dependent claims.

[0012] The nozzle bar according to the invention for a blowing box for the thermal tempering of glass panes has a side surface provided with a series of nozzle openings, which are designed to impart an airflow through the nozzle openings to the surface of a glass pane. The nozzle openings can also be referred to as blowing openings or nozzle outlets. Each is the end of a passage or bore extending through the entire nozzle bar, which is referred to as a nozzle and through which a gas is directed from a gas channel (air channel) of the blowing box onto the pane surface. The nozzle opening is the outlet opening of the passage (nozzle), while the inlet opening (nozzle inlet) is typically formed on the opposite side surface.Typically, such a nozzle has a section that follows the inlet opening and tapers towards the outlet opening in order to efficiently and aerodynamically guide the air from the air duct into the respective nozzle.

[0013] Compared to conventional nozzle bars with a smooth side surface, the nozzle bar according to the invention is advantageously further developed in that the nozzle openings are arranged on crenellated protrusions of the side surface.

[0014] Alternatively, the nozzle bar according to the invention can be considered to be advantageously further developed compared to conventional nozzle bars in that an area of ​​the side surface between each adjacent nozzle opening is recessed.

[0015] The nozzle bar is thus designed with crenellations and intervening crenellation windows (i.e., gaps between the crenellations). The nozzle openings are arranged on the upper surface of the crenellations. The crenellation windows provide additional drainage channels, allowing the air heated after being blown onto the disc surface to also flow out perpendicular to the direction of extension of the nozzle bar, thereby improving the pre-tensioning efficiency. This is a major advantage of the present invention.

[0016] A further advantage of the invention becomes apparent when a close proximity of the nozzle strip to the glass pane is desired, for example, to increase tempering efficiency. In such cases, there is a risk that the nozzle strip will collide with the pane or the tempering mold on which the pane is mounted. In the nozzle strip according to the invention, the points of collision are located on the projecting, crenellated protrusions, which can be easily shortened by removing material to prevent collisions.

[0017] The nozzle strip according to the invention can also be understood as a nozzle strip with raised or projecting, freestanding nozzles arranged on a side surface, which is further developed compared to known designs in that the nozzles are formed integrally with the nozzle strip. This ensures high mechanical stability of the nozzle strip and makes it easier to manufacture than in the case of separately screwed-on nozzles.

[0018] The nozzle strip preferably has a single row of nozzle openings arranged substantially along a line. The crenellated protrusions are arranged along the same line. Preferably, exactly one nozzle opening is arranged on each crenellated protrusion on the side surface of the nozzle strip, typically located substantially in the center. The row of nozzle openings preferably extends over at least 80% of the length of the nozzle strip.

[0019] The nozzle openings preferably have a diameter of 4 mm to 15 mm, more preferably 5 mm to 10 mm, and most preferably 6 mm to 8 mm, for example 6 mm or 8 mm. The distance between adjacent nozzle openings is preferably 10 mm to 50 mm, more preferably 20 mm to 40 mm, for example 30 mm. This ensures good preloading results. Here, "distance" refers to the distance between the respective centers of the nozzle openings.

[0020] The height of the crenellated projections is preferably at least 10 mm, more preferably at least 30 mm. The height is preferably from 10 mm to 150 mm, more preferably from 30 mm to 100 mm, for example 40 mm or 60 mm. This ensures effective drainage of heated air between the crenellations and simultaneously sufficient stability of the nozzles. For the purposes of the invention, the height of the crenellated projection refers to the dimension along the direction of extension of the nozzle.

[0021] When selecting the width of the ridges, the diameter of the nozzle openings should be taken into account to ensure sufficient nozzle wall thickness. The wall thickness should be at least 1.5 mm to achieve sufficient ridge stability. Consequently, the width of the crenellated ridges preferably has a value equal to the diameter of the nozzle opening plus 3 mm. For example, the width of the crenellated ridge is from 10 mm to 30 mm or from 12 mm to 22 mm. For the purposes of this invention, the width of the crenellated ridge refers to the dimension along the direction of extension of the nozzle array (arrangement of nozzle openings).

[0022] The distance between adjacent crenellated projections is preferably at least 5 mm, more preferably at least 10 mm. The distance is preferably from 5 mm to 30 mm, more preferably from 10 mm to 20 mm. This ensures efficient drainage of heated air. Here, the distance refers to the distance between the facing edges of the crenellations. This distance thus corresponds to the width of the crenellated windows.

[0023] The depth of the crenellated projection preferably corresponds to the width or depth of the nozzle bar, but can also be larger or smaller. As with the width, the minimum wall thickness must be taken into account when determining the depth of the projections. The depth of the crenellated projections preferably has a value equal to the diameter of the nozzle opening plus 3 mm. The depth is the dimension perpendicular to the height and width of the crenellations as defined according to the invention.

[0024] The length and width of the nozzle array depend on the design of the blowbox and its gas channels for which the nozzle array is intended. Typical values ​​for the length of the nozzle array (measured along the direction of extension of the nozzle row) range from 70 cm to 150 cm, and for the width / depth (measured perpendicular to the length in the plane of the nozzle openings) from 8 cm to 15 cm, preferably from 10 to 12 mm. The number of nozzle openings is determined by the length of the nozzle array and the spacing between the nozzles.

[0025] In a preferred embodiment, the individual crenellated projections have a substantially cuboid shape, although the corners and edges may be rounded for manufacturing reasons or due to deliberate design. Such a shape is easy to produce and stable. However, other shapes are also possible, for example, the shape of a circular cylinder or a truncated cone or pyramid.

[0026] According to the invention, the crenellated protrusions are at least curved and have no straight sections, resulting in a wave-like profile in side view. The nozzle openings are arranged on the crests of the waves, while the crenellated windows are essentially defined by the troughs. In other words, the surface of the nozzle strip with the nozzle openings is curved and has no flat sections or partial surfaces. This shape of the crenellated protrusions is easy to manufacture and avoids the formation of edges in the crenellated windows where glass fragments from damaged or broken panes can become wedged or caught. This significantly simplifies the cleaning of the nozzle strips after glass breakage.In this case, the height of the crenellated protrusion is defined as the distance between the line connecting the wavelengths and the line connecting the lowest points of the wave troughs. The width and spacing of the crenellations can be approximately measured at half their height. The described shape of the nozzle bar should occur at least in sections / areas, with this section / area preferably comprising at least 80% of the nozzle bar. Ideally, essentially the entire nozzle bar is designed in the curved shape, with the two terminal crenellations being exceptions, for example, if the side surfaces of the terminal crenellations facing away from the other crenellations are flat for manufacturing reasons.

[0027] The nozzle bar preferably contains aluminum or steel and is preferably manufactured from these materials. These materials are easy to machine, allowing for cost-effective manufacturing of the nozzle bar, and ensure advantageous stability of the nozzle bar during long-term use.

[0028] The nozzle strip can be manufactured starting from a cuboid workpiece or a workpiece in the form of a curved cuboid. A crenellated structure is formed on one side edge by material removal. On the opposite side edge, recesses can be formed by material removal, preferably using a countersink, in particular a conical countersink, which create the tapered sections of the nozzles. The nozzles can be formed by drilling before, after, or between the described work steps. The nozzle inlet, the transition between the tapered recesses and the bore, or the nozzle opening can be deburred to enable an improved flow profile. Material removal is preferably carried out by laser cutting or waterjet cutting.

[0029] The invention further comprises a blowing box equipped with at least one nozzle bar according to the invention. The blowing box serves to actuate the surface of a glass pane for thermal tempering. The blowing box is a device with an internal cavity and has a gas supply line through which a gas flow can be introduced into the interior of the blowing box. The gas flow is typically generated by means of a fan or several fans connected in series. Preferably, the gas supply line can be closed, for example, by means of a slide or a flap, so that the gas flow into the internal cavity can be interrupted without switching off the fans themselves.

[0030] Opposite the gas inlet, a number of channels adjoin the inner cavity, into which the gas flow is divided during operation. These channels can also be referred to as nozzle fins, ribs, or ridges. The channels typically have an elongated, essentially rectangular cross-section, with the longer dimension essentially corresponding to the width of the cavity and the shorter dimension ranging from 8 cm to 15 cm. The channels are typically arranged parallel to one another, so that they are evenly distributed along the entire lateral boundary of the cavity. The number of channels typically ranges from 10 to 50.

[0031] In a preferred embodiment, the inner cavity is wedge-shaped. The boundary of the cavity bordering the channels can be described as two lateral surfaces that converge at an acute angle. The channels typically run perpendicular to the line connecting said lateral surfaces. Consequently, the length of a channel is not constant but increases from the center to the sides, so that the inlet opening of the channel connected to the cavity is wedge-shaped, and the outlet opening forms a smooth, typically curved surface. The outlet openings of all channels typically form a common smooth, curved surface. Due to the described wedge-shaped design of the cavity and the described arrangement of the channels, the gas flow is distributed particularly efficiently among the channels, resulting in a very homogeneous gas flow across the entire effective area.

[0032] Each channel is closed at its end opposite the cavity by a nozzle bar. The nozzle bar has a plurality of openings, which are referred to as nozzles, and through which the gas flow of each channel is further divided. At least one of the channels, preferably all channels, are equipped with a nozzle bar according to the invention with crenellated projections.

[0033] The channels are typically formed by sheet metal and closed off by the nozzle bar. The side sheets preferably have a straight edge at the channel outlet. The channel is closed off by the lower part of the nozzle bar, opposite the side surface with the nozzle outlets on the crenellated protrusions. The sheet metal does not extend up to the crenellated protrusions. Such sheets are simpler and require less material to manufacture. Furthermore, the fact that no sheet metal is placed in the space between the crenellated protrusions of adjacent nozzle bars increases the clearance for the outflowing gas.

[0034] The nozzle strips are preferably designed and mounted such that the crenellated projections of adjacent nozzle strips are offset. Each projection is thus located adjacent to the "crenellated windows" of the two neighboring nozzle strips.

[0035] The blow box thus divides the gas flow from the gas supply line, which has a comparatively small cross-section, across a large effective area via the channels and nozzles. The nozzle openings represent discrete gas outlet points, which are nevertheless numerous and evenly distributed, so that all areas of the surface are cooled essentially simultaneously and uniformly, thus providing the disk with a homogeneous prestress.

[0036] At least one nozzle bar of the blow box according to the invention is a nozzle bar according to the invention with the crenellated projections. Preferably, the majority of the nozzle bars are designed according to the invention, and particularly preferably all nozzle bars. The advantages then become especially apparent.

[0037] The distance between adjacent nozzle bars (measured from their respective centers) is preferably from 15 mm to 50 mm.

[0038] The invention further comprises a device for the thermal tempering of glass panes. The device includes a first blowing box and a second blowing box arranged opposite each other so that their nozzles point towards one another. The blowing boxes are spaced apart from each other so that a glass pane can be positioned between them. Typically, the nozzles of the first blowing box (upper blowing box) point downwards, in particular vertically downwards, and the nozzles of the second blowing box (lower blowing box) point upwards, in particular vertically upwards. A glass pane can then advantageously be moved horizontally between the blowing boxes.

[0039] The device preferably also includes means for changing the distance between the first and second blowing boxes. This allows the blowing boxes to be moved relative to each other and away from each other. Preferably, both blowing boxes are moved towards each other or away from each other simultaneously. The movable blowing boxes increase the tempering efficiency. After the glass pane has been inserted between the blowing boxes in their more widely spaced position, the distance between the blowing boxes and thus to the glass pane is reduced, thereby generating a stronger gas flow on the glass surface.

[0040] The device also includes means for moving a glass pane, suitable for moving a glass pane into the space between the two blowing boxes and out of said space again. For this purpose, a rail, roller, or conveyor system can be used, for example. The glass pane can optionally be supported on a frame during transport.

[0041] The design of the blowing chambers and their gas channels and nozzle bars is preferably adapted to the shape of the sheet being tempered. The nozzle openings of one blowing chamber create a convexly curved surface, and the nozzle openings of the opposite blowing chamber create a concavely curved surface. The degree of curvature also depends on the shape of the sheet. During tempering, the convex blowing chamber faces the concave surface of the sheet, and the concave blowing chamber faces the convex surface. This allows the nozzle openings to be positioned closer to the glass surface, increasing tempering efficiency. Since the sheets are usually transported to the tempering station with the concave surface facing upwards, the upper blowing chamber is preferably convex and the lower one concave.

[0042] Shown, but not claimed in the patent claims, is an arrangement for thermally prestressing glass panes, comprising the device according to the invention and a glass pane arranged between the two blowing boxes.

[0043] Also shown, but not claimed in the patent claims, is a method for thermally prestressing glass panes, wherein (a) a heated, tempered glass sheet, having two main surfaces and a circumferential side edge, is arranged flat between a first blowing box and a second blowing box, so that the two main surfaces can be supplied with a gas stream, wherein the first blowing box and / or the second blowing box is equipped with at least one nozzle bar according to the invention; (b) the two main surfaces of the glass sheet are supplied with a gas stream by means of the two blowing boxes, so that the glass sheet is cooled.

[0044] Preferably, at least one blow box or both blow boxes are predominantly or exclusively equipped with nozzle bars according to the invention.

[0045] The glass pane is preferably transported between the blowing boxes on rollers, rails, or a conveyor belt. In an advantageous embodiment, the glass pane is arranged on a mold with a frame-like support surface (frame mold).

[0046] Preferably, the blowing boxes are positioned close together after the glass pane has been placed between them. This reduces the distance between the nozzle openings and the pane surface and increases the pre-stressing efficiency.

[0047] The gas stream is applied to the disc surfaces by introducing a gas stream into the inner cavity of each blow box, dividing it there and directing it evenly across the disc surfaces via the nozzle openings.

[0048] Air is preferably used to cool the glass pane. The air can be actively cooled within the tempering device to increase the tempering efficiency. However, typically, air that has not been specially temperature-controlled by active means is used.

[0049] The disk surfaces are preferably exposed to the gas stream for a period of 1 s to 10 s.

[0050] In a preferred embodiment, the glass pane to be tempered consists of soda-lime glass, as is common for window panes. However, the glass pane can also contain or be made of other types of glass, such as borosilicate glass or quartz glass. The thickness of the glass pane is typically from 0.2 mm to 10 mm, preferably from 0.5 mm to 5 mm.

[0051] In an advantageous embodiment, the inventive method follows directly after a bending process in which the initially flat glass sheet is bent. During the bending process, the glass sheet is heated to its softening temperature. The tempering process follows the bending process before the glass sheet has cooled down significantly. This eliminates the need to reheat the glass sheet separately for tempering.

[0052] Curved, prestressed glass panes are particularly common in the automotive sector. The glass pane to be prestressed according to the invention is therefore preferably intended as a window pane of a vehicle, particularly preferably of a motor vehicle and especially of a passenger car.

[0053] The nozzle strip according to the invention opens additional drainage channels for air flowing onto the glass surface through the areas between the crenellated protrusions. This advantage is particularly relevant when tempering glass panes that are strongly curved in the direction perpendicular to the extension direction of the nozzle strips, such that the nozzle strips can potentially act as barriers to the outflowing air. This occurs especially with panes that are strongly curved in two spatial directions (so-called three-dimensional or spherical curvature) with a high curvature depth. Such strongly curved panes form a kind of basin, so that gas cannot drain away as effectively, especially when using conventional cuboid nozzle strips, which present additional barriers to the outflowing gas.The method is therefore applied in a particularly advantageous embodiment to such a strongly curved glass pane, wherein at least the blowing box that is directed towards the concave surface of the pane is equipped with the nozzle strips according to the invention. The glass pane preferably has a bending gradient BG of at least 5 in the direction of curvature perpendicular to the direction of extension of the nozzle strips, more preferably at least 8, and particularly preferably at least 10. The bending gradient is defined as... BG = 100 × KT 0 , 5 × SL , where SL represents the so-called chord length, namely the length of the segment between the centers of the side edges in the direction under consideration, and KT represents the depth of curvature, namely the perpendicular distance of the geometric center of the pane from said segment. The terms chord length and depth of curvature are familiar to those skilled in the art. It has been shown that a significant swell effect occurs from the aforementioned bending gradient, and the invention demonstrates its advantages in a particular way. Since nozzle strips are generally arranged parallel to the top and bottom edges of the glass pane, which is usually the longer dimension of expansion of the pane, the minimum curvature described above preferably applies to the vertical direction of curvature, that is, the direction of curvature between the top and bottom edges. The top edge is the side edge of the pane that is intended to point upwards towards the vehicle roof in the installed position, while the bottom edge points downwards.An alternative bending gradient can also be described as . BG ′ = 100 × KT SL be defined.

[0054] Glass panes must have a minimum thickness to be thermally prestressed because the difference in cooling rates between the pane surfaces and the core is crucial for the formation of the characteristic compressive and tensile stress profile. Conventional blowing boxes can thermally prestress panes with a minimum thickness of approximately 3 mm. The improved prestressing efficiency achieved with the nozzle strips according to the invention can support efforts to thermally prestress even thinner panes. Thus, the method can also be used to prestress glass panes with a thickness of less than 3 mm.

[0055] The nozzle bar can be adapted to the glass geometry, especially at small distances, by shortening interfering nozzles. For example, in a test rig, the nozzle bar can be moved to the desired distance from a glass pane, and crenellated protrusions that collide with the glass pane or the supporting structure can be shortened by removing material to prevent collisions.

[0056] Also shown, but not claimed in the patent claims, is the use of a glass pane prestressed by the method in means of transport for traffic on land, in the air or on water, preferably as a window pane in rail vehicles or motor vehicles, in particular as a rear window, side window or roof window of passenger cars.

[0057] The invention is explained in more detail below with reference to a drawing and exemplary embodiments. The drawing is a schematic representation and not to scale. The drawing does not limit the invention in any way.

[0058] They show: Fig. 1 a perspective view of a nozzle strip, Fig. 2 a cross-section through the nozzle strip according to Figure 1 Fig. 3 shows a cross-section through two blow boxes as part of a device according to the invention for thermal pre-stressing, Fig. 4 shows a further cross-section through the device made of Figure 3 , rotated by 90°, Fig. 5 a top view of the nozzle bars of a blow box, Fig. 6 a flow diagram of an embodiment of the method according to the invention, Fig. 7 a side view of a design of the nozzle bar according to the invention and Fig. 8 an illustration of the bending gradient BG.

[0059] Figure 1 and Figure 2Figures 1 and 2 show a detail of an embodiment of the nozzle strip 1 for a blowing box for the thermal tempering of glass panes. The nozzle strip 1 is made of aluminum, which is easy to machine and advantageously lightweight. The nozzle strip has a width of, for example, 11 mm, with the dimensions being designed to close the gas channels of an associated blowing box. As is typical for nozzle strips of this type, the nozzle strip 1 according to the invention is designed with a series of nozzles 4. Each nozzle 4 is a passage (bore) between two opposing side surfaces of the nozzle strip 1. The nozzles 4 are designed to direct a gas flow out of the associated blowing box, the gas flow entering the nozzle 4 via a nozzle inlet 5 and exiting the nozzle 4 via a nozzle opening 2.The side surface of the nozzle bar 1 with the nozzle inlets 5 must therefore face the blow box in the installed position, while the side surface with the nozzle openings 2 faces away from the blow box.

[0060] According to the invention, the side edge of the nozzle strip 1, on which the nozzle openings 2 are arranged, is formed with crenellated projections 3, with each nozzle opening 2 being arranged on one such projection 3. The advantage of this arrangement is that drainage channels are formed through the areas between adjacent crenellations (the "crenellated windows"). These drainage channels allow gas, which has been directed onto the surface of a glass pane for thermal tempering, to drain away more efficiently and quickly, thereby accelerating heat transfer. The cooling of the glass surface occurs more rapidly, thus increasing the tempering efficiency. This increased tempering efficiency can, in turn, be utilized in two different ways: Predetermined stress values ​​can be achieved with lower gas flows, allowing the tempering process to be carried out with reduced energy consumption. With a given gas flow, higher stress values ​​can be achieved in the glass pane, and in particular, thinner glass panes can also be thermally tempered.

[0061] These advantages are particularly evident in the case of discs that are strongly curved in two spatial directions (three-dimensionally curved, spherically curved), where the gas outflow is hindered due to their boiler shape.

[0062] The remaining side surfaces of nozzle bar 1 are smooth and flat.

[0063] The geometric dimensions of the exemplary embodiment are summarized below. However, they are only to be understood as examples and are not intended to limit the invention in any way.

[0064] The crenellated projections 3 have a width b of 15 mm, a height h of 40 mm, and a depth t of 11 cm, where the depth t essentially corresponds to the width of the nozzle bar 1. The distance a between adjacent projections 3 is 15 mm. The distance between the centers of adjacent nozzle openings 2 is 30 mm.

[0065] The individual nozzles have a significantly widened nozzle inlet 5, followed by a tapered section. The nozzle diameter then remains constant at 6 mm up to the nozzle opening 2.

[0066] Figure 3 and Figure 4Figure 1 shows an embodiment of the device for thermally tempering glass panes. The device comprises a first, upper blowing chamber 10.1 and a second, lower blowing chamber 10.2, which are arranged opposite each other such that the nozzle openings 2 are directed towards each other. The device further comprises a transport system 15 with which a glass pane I to be tempered can be transported between the blowing chambers 10.1 and 10.2. The glass pane I is supported horizontally on a frame 16, which has a frame-like support surface on which a circumferential edge region of the glass pane I rests. The actual transport device 15 consists, for example, of rails or a roller system on which the frame 16 is movably mounted. The glass pane I is, for example, a pane of soda-lime glass intended as a rear window for a passenger car.The glass pane I has undergone a bending process, whereby it has been brought into the intended curved shape at a temperature of approximately 650 °C, for example by gravity bending or press bending. The transport system 15 serves to transport the glass pane I, while still heated, from the bending device to the tempering device. There, the two main surfaces are subjected to an airflow via the blowing boxes 10.1 and 10.2 to cool them rapidly and thus create a characteristic profile of mechanical tensile and compressive stresses. The thermally tempered glass pane I is then suitable as so-called single-pane safety glass for use as an automotive rear window. After tempering, the pane is transported again by the transport system 15 from the space between the blowing boxes 10.1 and 10.2, making the tempering device available for tempering the next glass pane.The device also includes means for moving the blowing boxes 10.1 and 10.2 towards and away from each other. Once the glass pane I has reached its intended position between the blowing boxes 10.1 and 10.2, the distance between the blowing boxes 10.1 and 10.2 and between them and the pane surfaces is reduced to achieve a greater cooling effect through the airflow. After pre-stressing, the distance is increased again to allow the glass pane I to be transported away without damaging itself or the nozzle strips 1. The transport direction of the glass pane I is in . Figure 3 represented by a grey arrow.

[0067] Blowing boxes 10.1 and 10.2 are blowing boxes of the type described, for example, in DE 3924402 C1 or WO 2016054482 A1. They have an inner cavity 11 to which an airflow is supplied via a gas supply line 12, represented in the figures by a gray arrow. The airflow is generated, for example, by two fans (not shown) connected in series, which are connected to blowing boxes 10.1 and 10.2, respectively, via the gas supply line 12. The airflow can be interrupted by a shut-off flap 13 without having to switch off the fans.

[0068] Opposite the gas supply line 12, channels 14 adjoin the cavity 11, through which the airflow is divided into a series of partial flows. The channels 14 are designed in the form of a hollow rib, which in one dimension is essentially as long as the cavity 11 and in the dimension perpendicular to it has a significantly smaller width, for example, approximately 11 mm. The channels 14, with their elongated cross-section, are arranged parallel to one another, so that the endpoints of all channels lie essentially on a straight line that runs perpendicular to the direction of extension of the elongated channels. The number of channels 14 shown is not representative and serves only to illustrate the operating principle.

[0069] The cavity 11 is wedge-shaped – along a first dimension, the depth of the cavity 11 is greatest in the center of the blowbox and decreases outwards in both directions. In the second, perpendicular dimension, the depth remains constant for a given position of the first dimension. The channels 14 are connected to the wedge-shaped cavity 11 along the aforementioned first dimension. They therefore have a depth profile complementary to the wedge shape of the cavity 11, with the depth being smallest in the center of the channel 14 and increasing outwards, so that the air outlet of each channel 14 forms a smooth, but typically curved, surface. The air outlets of all channels 14 form a common smooth surface.

[0070] Figure 3 and Figure 4 Two cross-sections are shown at an angle of 90° to each other. Figure 3Figure 1 shows the cross-section along the aforementioned second dimension of the blowbox 10.1, 10.2 perpendicular to the orientation of the channels 14, so that the individual channels 14 can be seen in the section. The depth of the cavity 11 is constant in the section plane. Figure 4 Figure 1 shows the cross-section along the aforementioned first dimension of the blow box 10.1, 10.2 along the orientation of the channels 14. Here the wedge-shaped depth profile of the cavity 11 can be seen, while in the section plane there is only a single channel 14, whose depth profile can also be seen.

[0071] Each channel 14 is closed at its end opposite the cavity by a nozzle bar 1. The nozzle bar 1 divides the airflow of each channel 14 into further partial flows, each of which is directed through a nozzle 4. Each partial flow enters the nozzle 4 from the channel 14 through the nozzle inlet 5, exits the nozzle 4 through the nozzle opening 2, and then strikes the surface of the glass pane I.

[0072] Figure 5Figure 1 shows a section of a top view of the nozzle openings 2 of a blow box 10.1, 10.2. The number of nozzle bars 1 is again not representative and serves only for illustration. It can be seen that the adjacent nozzle bars 1 are arranged offset from each other, so that a crenellated protrusion 3 of one nozzle bar 1 is adjacent to a "crenellated window" of the two adjacent nozzle bars 1. This arrangement achieves the most uniform possible distribution of the nozzle openings 2.

[0073] Figure 6 shows an exemplary embodiment of the method for thermally prestressing glass panes using a flowchart.

[0074] Figure 7Figure 1 shows an embodiment of the nozzle strip 1 according to the invention. The crenellated projections 3 are not cuboid in shape. Instead, the surface of the nozzle strip 1 with the nozzle openings 2 is curved. In the illustrated side view of the nozzle strip (i.e., the top view of the surface that connects the surface with the nozzle openings 2 to the opposite surface and is arranged along the length of the nozzle strip 1), a wave profile with convex crests and concave troughs is formed. The nozzle openings 2 are arranged on the wave crests. Since the surface with the nozzle openings 2 has no flat sections, no edges form between the crenellated projections 3 in which glass fragments could become trapped. Therefore, this nozzle strip 1 is easier to clean after glass breakage.

[0075] Figure 8The bending gradient BG is illustrated using a schematic cross-section through a glass pane I. The bending gradient BG describes the extent of the bending of the glass pane. The bending gradient is defined as BG = 100 × KT 0 , 5 × SL The chord length SL denotes the length of the line segment between the midpoints of the lateral edges in the direction under consideration. The depth of curvature KT The vertical distance from the geometric center of the pane to the aforementioned line segment is indicated. The bending gradient BG ultimately specifies the slope of a straight line through the geometric center of the pane and the midpoint of the side edge, which is indicated in the figure by a dashed line. The larger the bending gradient BG, the more bowl-shaped the glass pane I is, and the more advantageous the effect of the present invention becomes, namely the improved efficiency through the provision of additional air drainage channels. Example

[0076] Rear windows with a vertical bending gradient greater than 8 and a horizontal bending gradient greater than 4 were prestressed using a blowing box according to the invention and a conventional blowing box with cuboid nozzle strips. With the same distances between the glass pane and the blowing boxes, the fan speed, and thus the airflow velocity, was controlled so that the same fracture pattern was produced with the nozzle strip according to the invention as with the conventional one. The fracture pattern is characterized by the number and size of the fragments when the glass pane breaks and is a measure of the degree of prestressing achieved. It was found that the nozzle strip according to the invention enabled energy savings of greater than 5%. This result was unexpected and surprising to those skilled in the art. Reference symbol list:

[0077] (1) Nozzle bar (2) Nozzle opening / outlet opening of nozzle 4 (3) Crested protrusion of nozzle bar 1 (4) Nozzle (5) Nozzle inlet / inlet opening of nozzle 4 (10.1) First / upper blowing box (10.2) Second / lower blowing box (11) Blowing box cavity 10 (12) Blowing box gas supply line 10 (13) Shut-off flap in the gas supply line 12 (14) Blowing box channel / nozzle bridge 10 (15) Glass pane transport system (16) Glass pane frame (b)Width of the crenellated elevation 3 (h)Height of the crenellated elevation 3 (t)Depth of the crenellated elevation 3 (a)Distance between adjacent elevations 3 (I) Glass pane SL tendon length KT curvature depth

Claims

1. Nozzle strip (1) for a blow box for thermally prestressing glass panes, which nozzle strip has a row of nozzles (4) each having a nozzle inlet (5) and a nozzle opening (2) for impinging on a surface of a glass pane (I) with a stream of air through the nozzle openings (2), wherein the nozzle openings (2) are arranged on merlon-like elevations (3) of a side surface of the nozzle strip (1), which are implemented integrally with the nozzle strip (1), wherein the merlon-like elevations (3) are curved at least in regions such that the side surface of the nozzle strip (1) with the merlon-like elevations (3) has no planar sections, yielding a wave-like profile when viewed from the side, wherein the nozzle openings (2) are arranged on the wave peaks.

2. Nozzle strip according to claim 1, wherein the nozzle openings (2) are arranged at a mutual distance of 10 mm to 50 mm.

3. Nozzle strip according to claim 1 or 2, wherein the nozzle openings (2) have a diameter of 4 mm to 15 mm, preferably of 5 mm to 10 mm.

4. Nozzle strip according to one of claims 1 through 3, wherein the height (h) of the elevations (3) is from 10 mm to 150 mm, preferably from 30 mm to 100 mm.

5. Nozzle strip according to one of claims 1 through 4, wherein the width (b) of the elevations (3) corresponds at least to the diameter of the nozzle openings (2) plus 3 mm.

6. Nozzle strip according to one of claims 1 through 5, wherein the distance (a) between adjacent elevations (3) is at least 5 mm, preferably at least 10 mm.

7. Nozzle strip according to one of claims 1 through 6, wherein the nozzles (4) have a section tapered in the direction from the nozzle inlet (5) to the nozzle opening (2).

8. Nozzle strip according to one of claims 1 through 7, wherein the nozzle strip (1) contains aluminum or steel.

9. Blow box (10.1, 10.2) for thermally prestressing glass panes, comprising a hollow space (11), a gas feed line (12) connected to the hollow space (11), and a row of channels (14) connected to the hollow space (11), wherein at least one channel (14) opposite the hollow space (11) is completed with a nozzle strip (1) according to one of claims 1 through 8.

10. Apparatus for thermally prestressing glass panes, comprising - a first blow box (10.1) and a second blow box (10.2) that are arranged opposite one another such that the nozzle openings of the first blow box (10.1) and of the second blow box (10.2) face one another, wherein the first blow box (10.1) and / or the second blow box (10.2) is equipped with at least one nozzle strip (1) according to one of claims 1 through 8; and - means for moving a glass pane (I) into an intermediate space between the first blow box (10.1) and the second blow box (10.2).