A glass heating process and a glass tempering furnace

Abstract

The invention relates to a glass heating and tempering process and to a glass tempering furnace in which a glass sheet (G) is heated by a combination of convection air and radiation. Convection air is generated in pressurised convection units (CU) and directed through nozzle boxes (NB) towards the glass sheet (G), while radiation heating is provided by heating wires (Hw) arranged to heat metal structures adjacent to the glass. A plate (S, RPG) is positioned between the heating wires and the glass sheet. Additional heaters and temperature sensors are arranged in the convection air circulation to increase heating capacity and enable controlled and uniform heating of the glass.

Description

[0001] A glass heating process and a glass tempering furnace

[0002] The invention relates to a glass heating process, in which a glass sheet is conveyed through a heating section and is heated by convection air and radiation. The invention is also related to a glass tempering furnace.

[0003] BACKGROUND

[0004] Glass tempering furnaces are known to exhibit several characteristics affecting their operational performance and product quality. The capacity of a glass tempering furnace depends primarily on the heating speed. In general, the time required for tempering and cooling of the glass is substantially shorter than the heating time. Exceptions are observed for thick glass sheets, typically in the range of 15-19 mm, for which the tempering temperature and pressure are lower. In such cases, cooling pressure may be increased until the end of the cooling cycle. Heating speed in a furnace is influenced by both heating power and convection power (kW / m2). While increased convection power only raises energy consumption (kWh / m2), increased heating power can reduce overall energy consumption by shortening the heating time.

[0005] The quality of the glass, including straightness and optical characteristics, is highly dependent on focused heating. Focused heating using convection is generally more effective than radiation-based heating in achieving the desired glass quality.

[0006] Economic considerations are also significant. Many existing tempering machines do not incorporate convection air heating, making them less costly to manufacture. Prior to patent application EP 2115911.1, heating speeds in conventional furnaces were relatively low. Notwithstanding existing technologies, glass tempering processes continue to face several technical challenges:

[0007] A. Radiation heating wires are typically positioned approximately 300 mm from the glass. If the distance is insufficient, thermal shock may occur when cold glass enters the furnace, adversely affecting the lifetime of the heating wires.

[0008] B. Nozzle boxes having a height of approximately 300 mm may experience substantial heat variations, potentially causing deformation. Such deformation can complicate or prevent the replacement of heating elements and may also increase manufacturing costs.C. The intensity of radiation decreases rapidly with distance, following an inverse fourth-power relationship. Radiation sources located close to the glass can create extremely high air temperatures.

[0009] D. Radiation width diminishes with increased distance from the glass, and sufficient space must be allocated for convection jets. Absence of adequate convection airflow can significantly reduce heating speed.

[0010] E. Service time for maintenance operations should be minimized, and service procedures should be straightforward. This consideration is particularly relevant for components such as additional heaters and convection units.

[0011] F. Economic factors are taken into account where practicable in furnace design and operation.

[0012] Furthermore, graphical representations provided in the prior art are not necessarily scalable, and the description primarily illustrates principles of operational improvement without providing detailed design solutions.

[0013] Accordingly, there remains a clear need to develop improved glass tempering furnaces that can address the aforementioned limitations, providing enhanced heating efficiency, improved glass quality, reduced energy consumption, and simplified maintenance, without compromising operational reliability or economic feasibility.

[0014] BRIEF DESCRIPTION

[0015] It is an object of the present invention to provide a glass heating and tempering process, and a corresponding furnace, which overcome or at least alleviate one or more of the limitations identified in the prior art. In particular, the invention aims to enable efficient and uniform heating of glass sheets, to allow controllable convection and radiation heating, to facilitate maintenance and replacement of heating elements, and to optimize energy consumption during the tempering process.

[0016] The objects of the invention are attained with a process and a furnace that are characterised by what is stated in the independent patent claims. Some advantageous embodiments of the invention are disclosed in the dependent claims.

[0017] The invention relates to a glass heating and tempering process and to a glass tempering furnace in which a glass sheet is heated by a combination of convection airand radiation. Convection air is generated in pressurised convection units and directed through nozzle boxes towards the glass sheet, while radiation heating is provided by heating wires arranged to heat metal structures adjacent to the glass. A plate is positioned between the heating wires and the glass sheet. Additional heaters and temperature sensors are arranged in the convection air circulation to increase heating capacity and enable controlled and uniform heating of the glass.

[0018] When reference is made in the text to upper or lower parts, or to directions such as up or down, this refers to a situation in which the glass tempering furnace is in use, i.e. , when a glass sheet is positioned substantially horizontally.

[0019] In a first embodiment of a glass heating process according to the invention, a glass sheet is conveyed through a heating section and is heated by convection air and radiation. In one advantageous embodiment of the invention, the convection air is generated and heated in one or more pressurised convection units, radiation heating is provided by heating wires arranged to heat metal structures adjacent to the glass, and a heat transfer plate and / or a radiation plate glass is arranged between the heating wires and the glass, and the plate or plates are arranged substantially parallel to, or at an angle relative to, a travelling direction of the glass sheet such that uniform heating of the glass sheet is achieved.

[0020] In yet another embodiment of the glass heating process according to the invention, the convection air is directed in a matrix arrangement over the glass, wherein the matrix comprises a plurality of rows of convection jets or nozzles in nozzle boxes, and the matrix provides substantially uniform heating across the top and bottom surfaces of the glass.

[0021] In yet another embodiment of the glass heating process according to the invention, a ratio between radiation heating and convection jet heating is adjustable at a design stage of the heating section, such that a maximum radiation heating capacity is structurally limited, while a convection heating capacity is selectively increased by heating the convection air by means of at least one additional heater.

[0022] In yet another embodiment of the glass heating process according to the invention, that additional heaters are provided in one or more convection pipes, air ducts, pressure boxes, or suction chambers, and the additional heaters are selectively controllable to increase convection air temperature and heating speed of the glass.

[0023] In yet another embodiment of the glass heating process according to the invention, thermocouples are arranged to sense return airflow to suction chambers, and thetemperature readings are used to control the switching or power reduction of heaters and / or additional heaters to maintain temperature of the convection air matrix within desired limits

[0024] In yet another embodiment of the glass heating process according to the invention, the nozzle boxes are at an angle relative to the travelling direction of the glass sheet such that convection jets provide uniform heating without causing optical distortions in the glass.

[0025] In a first embodiment of glass tempering furnace according to the invention, the glass tempering furnace comprises rollers for supporting a glass sheet in a heating section, one or more convection units for generating and heating convection air, nozzle boxes arranged in the heating section, and heating wires arranged to provide radiation heating. In one advantageous embodiment of the invention, the heating wires are configured to heat metal structures adjacent to the glass, and the convection units are pressurised, and the furnace comprises a heat transfer plate and / or a radiation plate glass, and the plate or plates are arranged between the heating wires and the glass, and the plate or plates are arranged substantially parallel to, or at an angle relative to, a travelling direction of the glass sheet such that uniform heating of the glass sheet is achieved.

[0026] In yet another embodiment of the glass tempering furnace according to the invention, the convection units comprise one or more impellers for pressurising convection air through air ducts to the nozzle boxes.

[0027] In yet another embodiment of the glass tempering furnace according to the invention, the glass tempering furnace comprises a pressure box configured to direct convection air to the nozzle box.

[0028] In yet another embodiment of the glass tempering furnace according to the invention, the nozzle boxes comprise rows of nozzles arranged at an angle relative to the travelling direction of the glass sheet to form a convection matrix for uniform heating. In yet another embodiment of the glass tempering furnace according to the invention, the glass tempering furnace comprises convection pipes, that are elongated hollow structures arranged to convey and direct convection air from a convection unit to the nozzle boxes, the pipes being configured to allow controlled heating of the convection air by internal or surrounding heating elements, and to protect the heating elements from direct cooling by the convection air.In yet another embodiment of the glass tempering furnace according to the invention, additional heaters are arranged in convection pipes or pressure boxes to increase convection air temperature and heating speed.

[0029] In yet another embodiment of the glass tempering furnace according to the invention, the furnace comprises a suction chamber arranged downstream of the nozzle boxes in the convection air flow, the suction chamber being configured to collect convection air returning from the nozzle boxes and to guide the convection air back to the convection unit.

[0030] In yet another embodiment of the glass tempering furnace according to the invention, the return air to the suction chambers passes above the heaters of the air channels and / or radiation / convection pipes or radiation pipes, or alternatively, the return air flows through the pressurized convection air ducts before entering the suction chambers.

[0031] In yet another embodiment of the glass tempering furnace according to the invention, the nozzle boxes are substantially parallel to the rollers.

[0032] In yet another embodiment of the glass tempering furnace according to the invention, thermocouples are arranged to measure temperatures in the return flow of convection air to the suction chamber, providing feedback for controlling the heaters. In yet another embodiment of the glass tempering furnace according to the invention, the radiation plate glass is arranged to protect the glass and heating wires from thermal shock and cooling effects of convection air.

[0033] In yet another embodiment of the glass tempering furnace according to the invention, the radiation plate glass is removable along at least the length of a convection unit. In yet another embodiment the radiation plate glass is arranged to protect the radiation / convection pipes or radiation pipes from thermal shock.

[0034] In yet another embodiment of the glass tempering furnace according to the invention, the radiation plate glass is removable along the length of the convection units and / or nozzle boxes to facilitate maintenance or replacement of heating wires and other components. In yet another embodiment the heat transfer plate is removable. In yet another embodiment of the glass tempering furnace according to the invention, the additional heaters and / or convection pipes are arranged to provide matrixheating along the width and / or length of the glass sheet, optionally divided into multiple heating zones.

[0035] In yet another embodiment of the glass tempering furnace according to the invention, the heating wires are wound on ceramic pipes and / or protected by ceramic rings to prevent short circuits and thermal shock.

[0036] In yet another embodiment of the glass tempering furnace according to the invention, the convection unit is substantially enclosed on all sides except for gaps leading to the nozzle boxes and suction chamber, minimising leakage and energy waste. In yet another embodiment of the glass tempering furnace according to the invention, one or more radiation pipes are provided in the heating section, each radiation pipe comprising one or more heating elements arranged to radiate heat directly to the glass sheet.

[0037] In yet another embodiment of the glass tempering furnace according to the invention, one or more of radiation plate glass have a wall thickness of less than 6 mm. In yet another embodiment of the glass tempering furnace according to the invention, the radiation plate glass is positioned in such a way that minimum distance from the glass is 200 mm.

[0038] In yet another embodiment of the glass tempering furnace according to the invention, radiation provides high-intensity heating to the glass sheet beneath the heating element.

[0039] In yet another embodiment of the glass tempering furnace according to the invention, the nozzle boxes comprise a plurality of rows of nozzles forming convection jets directed towards the glass sheet, the rows being arranged substantially parallel to the travelling direction of the glass sheet.

[0040] In yet another embodiment of the glass tempering furnace according to the invention, the nozzle boxes are configured to maintain slight negative pressure or underpressure, enabling thermocouples positioned in the return air flow to accurately monitor the convection air temperature.

[0041] An advantage of the invention is that it enables more uniform heating of the glass sheet, thereby reducing optical distortions and improving product quality.A further advantage of the invention is that it allows controlled adjustment of convection and radiation heating, improving heating speed while maintaining energy efficiency.

[0042] Another further advantage is that removable heat transfer plates and / or radiation plate glass facilitate maintenance and replacement of heating components.

[0043] An advantage of the invention is that the arrangement of convection jets and nozzle boxes allows precise control of airflow, improving heating uniformity and process reliability.

[0044] DESCRIPTIONS OF THE FIGURES

[0045] In the following the invention will be described in detail, by way of examples, with reference to the accompanying drawings in which,

[0046] Figure 1 shows a table describing heating speed of glass

[0047] Figure 2 shows an embodiment of the invention,

[0048] Figure 3 shows a second embodiment of the invention,

[0049] Figure 4 shows a third embodiment of the invention,

[0050] Figure 5 shows a detail of the embodiment of Figure 2,

[0051] Figure 6 shows a fourth embodiment of the invention, and

[0052] Figure 7 shows a fifth embodiment of the invention.

[0053] DETAILED DESCRIPTION

[0054] The embodiments in the following description are given as examples only. Though the description may refer to a certain embodiment or embodiments in several places, this does not mean that the reference would be directed towards only onedescribed embodiment or that the described characteristic would be usable only in one described embodiment. The individual characteristics of two or more embodiments may be combined and new embodiments of the invention may thus be provided.

[0055] Figure 1 shows that there are 3 main steps to increase the heating speed of glass. Radiation (RAD) was used until the 1990’ies in glass heating. It was enough for clear glasses and coloured glasses. Then low emissivity glasses came to the market. They reflect radiation. Convection was needed. However, radiation and convection are needed for the good process. For highest heating speed is convection + radiation but correctly made.

[0056] 1. As figure 1 shows, no power (kW / m2) and no convection area (m2) no radiation are enough to heat the glass when heating starts.

[0057] 2. However, later heating progresses, the heaters are under-utilized.

[0058] 3. Heating speed can be heated also outside of nozzle boxes (NB). Basically, convection heating speed is basically unlimited, up to the point where convection material can be heated. Convection heating heats the glass only at the surface. Therefore, high heating speed causes stress on the glass, especially thick glasses, and low emissivity glasses. Glass start to break if heating speed is too high.

[0059] Furthermore, glasses need uniform heating, top and bottom and all over glass surface. This requires profiled convection, preferably matrix by convection of air.

[0060] Formula is Q = h x A x AT of maximum heating speed is Q amount of heat can be transferred to the glass / time unit

[0061] - h = just a factor. Normally heat transfer plate.

[0062] - A = convection area (m2)

[0063] - AT = the temperature of difference of convective material and convection air. - When temperature for glass is for example 20 °C to tempering temperature 620 °C is heated, the formula AT / 2 = 600 °C / 2 = 300 °C.

[0064] Heating speed depends on convection area. Convection areas need more heating power. Some more explanation of the previous main methods.Radiation heating wires (Hw) glow red or even yellow at the end of heating time. Heating wires turn dark when cold glass enters the furnace even if they are over 300 mm from the glass. Convection air (CA) drops down to 300 - 400 °C, depending on glass thickness and loading efficiency.

[0065] Figure 2 show a part of a glass heating furnace comprising a heating section where heating processes occur.

[0066] Figure 2 presents the heating wires (Hw) are protected from cooling effects of convection air (CA) by heat transfer plate (S). Heating wires (Hw) wound on ceramic pipe (CePi) radiate (RAD) heat all around. Ceramic ring (CR) prevents short circuits with metallic structures, primarily to the nozzle boxes (NB). Rollers (R) moving the glass under the nozzle boxes (NB).

[0067] Heating wires (Hw), ceramic pipes (CePi), and ceramic rings (CR) are called heaters (H). Also, other components may be called heaters. Functional parts of the furnace that produce heat are called heating elements. Other heating sources than electricity can be used, the most common is gas.

[0068] When cold glasses enter the furnace, the heating wires (Hw) are protected from cold shocks by radiation plate glass (RPG).

[0069] As heating progresses, heat transfer plate (S) and radiation plate glass (RPG) very hot by heating wires. They get hotter and hotter and heat transfer plate (S) radiate plate glass (RPG) radiate (RAD) glass (G) strongly because it is near the glass. The air is extremely hot near the radiation plate glass, also at 30 - 40 mm when convection jets (CJ) start from nozzles of nozzle box (NB).

[0070] When convection jets (CJ) impinge on the radiation plate glass (RPG), they may cause cooling of the RPG, in particular due to turbulence generated at the surface. The magnitude of this cooling effect depends on the inclination of the convection jets. When the inclination is as illustrated in Figure 2, the distance between the radiation plate glass (RPG) and adjacent heating elements can be reduced to even less than 30 mm without causing excessive cooling of the radiation plate glass. The convection jets (CJ) entrain the hot air layer formed adjacent to the radiation plate glass (RPG). This effect becomes significant when the glass temperature reaches approximately 400 °C. At a final stage of the heating process, the radiation plate glass (RPG) attains a high temperature, whereby the air in its vicinity iscorrespondingly heated to a high temperature level. As a result, the temperature of the convection air increases substantially compared with convection air heated solely by the heat transfer plate (S). The temperature increase depends on the proportion of radiation-heated air entrained into the convection air flow. For achieving this effect, the nozzle diameter is preferably small and the centre-to-centre spacing of the nozzles is correspondingly small. The temperature difference AT of the convection air impinging on the glass (G) increases progressively as the convection jets (CJ) strike the glass.

[0071] If the radiation panel is relatively thick, for example approximately 16 mm as used in certain known glass tempering furnaces, its heat conduction is slow even if the panel is made of metal. In such arrangements, the radiation intensity remains high because the panel is positioned close to the glass surface, typically at a distance of about 70 mm. For improved heating performance, the radiation plate glass (RPG) preferably has a thickness of less than 5 mm, whereby a reduced thickness results in an increased heating rate. In some embodiments the radiation plate glass thickness is between 1 to 6 mm. Such a thin radiation plate glass may be mechanically reinforced by suitable means. Likewise, the heat transfer plate (S) is preferably made as thin as practicable, for example having a thickness of about 2 mm based on experience.

[0072] The nozzle rows in the nozzle boxes (NB) are preferably arranged at a small angle relative to the travelling direction of the glass sheet. If the nozzle rows are arranged substantially perpendicular to the travelling direction, the convection jets (CJ) may cause optical distortions in the glass. For this reason, the nozzle boxes are preferably relatively short in the travelling direction. Convection jets directed substantially at a 90° angle to the glass surface cover the glass surface only in the width direction, whereas inclined convection jets allow a more uniform surface coverage and reduce sensitivity to manufacturing tolerances.

[0073] Nozzle boxes (NB) at 90-degree angle to glass travel direction may improve optical quality further. This is why there is a round figure of rollers (R).

[0074] Convection jets can be also of line type, not only from round nozzles.

[0075] Due to the small angle of nozzle boxes (NB) matrixes rhombus, diamond shape, but let us call it matrixes. In this it is matrix in radiation (RAD) and in convection.

[0076] Figure 3 illustrates a radiation pipe (RP) and convection pipes (CP), both comprising internal heating elements (H). The operating principle corresponds to that describedin connection with Figure 2, and the arrangement is also applicable to the embodiment of Figure 6. The upper illustration represents the lower right-hand side of a convection unit (CU).

[0077] Figure 3 depicts an arrangement providing near-maximum radiation heating (RAD) together with highly heated convection air (CA). Vanes (V) are arranged to guide the convection air such that it is heated by the radiation pipe (RP) before the convection air (CA) is conveyed to the suction chamber (SC) of the convection blower. Thermocouples (TC) are positioned near the glass (G) to measure the return airflow to the suction chamber (SC) of the convection blower. Their response is improved and faster when they detect the returning convection air. For this purpose, a slight underpressure, or small vacuum, must be maintained between the convection units (CU) or the nozzle boxes (NB), including any openings (HO) or piping. Rows of convection jets (CJ) are arranged to heat the glass sheet (G) located between nozzle boxes (NB) or convection units (CU), as illustrated in Figures 5 and 6.

[0078] The convection pipe (CP) may be loosely positioned within the nozzle box (NB), as illustrated in Case 2. This allows easy replacement of the heaters (H) along with the convection pipe (CP). However, such an arrangement may result in leakage of pressurized convection air, increasing energy loss and reducing the heating speed. In some embodiments the matrix is arranged like in figure 6. This is explained in the description of figure 6.

[0079] The lower part of Figure 3 shows that the convection pipe (CP) and the radiation pipe (RP) can heat the convection air (CA) to approximately one-quarter of the total heating capacity, while the radiation pipe (RP) provides about three-quarters of the radiation (RAD). Nevertheless, a significant portion of the convection air (CA) is heated by the radiation pipe (RP). Numerous possibilities exist to adjust the proportion of convection and radiation (%) as illustrated in Figure 6. While the radiation heating rate is limited, the convection heating rate is essentially unrestricted.

[0080] Figure 4 shows other heater types suitable for removing known technology problems. When voltage (U) is connected between heating wires, (Hw) they get very hot. It heats protection material (PM). In some embodiments, the protection material is magnesium oxide. Hot resistant sheet thin metal pipe surrounds protection material. Its diameter is + / - 10 mm and it glows red. This is used for example sauna heaters. It has a small power in kW. When many heaters (H) are connected to together, it has sufficient (kW) area (m2) to heat convection air (CA) and glass (G) by radiation(RAD). It could be in nozzle box without radiation plate glass (RPG), It would be ineffective for heating convection air (CA) through the heat transfer plate (S).

[0081] Pressurized convection air is needed for convection jets (CJ). And this causes sealing problems. It could be solved quite easily, for example on the furnace roof, outside. This could be used as a vertical or inclined additional heater (AH) in figures 6 and 7. Sauna type heaters can be wound on a spiral, like thread, quite small radius, depending on the diameter (d). And in the nozzle boxes (NB), too. In nozzle boxes this should reduce convection air heating (CA) through heat transfer plate (S). Also, ceramic pipe (CePi) could be grooved in such a way, like thread, heating wire (Hw) would not slide down when hot vertical or inclined position. Heating wire could be “porcupine” wound, in a small radius and higher diameter on ceramic pipe (CePi) in grooved ceramic pipe for higher heating power (kW).

[0082] Figure 5 presents figure 2 heater (H) with radiation plate glass (GPR) in nozzle boxes (NB). Also figures 3 and 4 could be used, with limitations as explained. Figure 5 also shows a convection unit (CU) without the furnace frame and insulation. Convection unit (CU) is in this embodiment a completely enclosed box on top and 4 sides. Impeller(s) (IMP) shaft for convection blower would be through the top. The only way out is nozzles in nozzle boxes (NB). The way in is gaps between nozzle boxes to the suction chamber (SC). Convection unit maintains air circulation “in package” of convection units. The furnace outside air does not mix with hot convection air (CA). The convection unit length is about 1000 mm + / - 300. Gaps between convection units are about 100 mm. If convection unit (CU) is used, the furnace length consists of several convection units.

[0083] The difference of convection air at the heating time is about 50 - 120 °C higher than glass. The additional heaters (AH) main purpose is to increase heating speed by additional (AT). In figure 6 is also convection air matrix.

[0084] Thermocouples (TC), not shown in fig. 5, follow matrix rows of heaters (H). The same rows of nozzle boxes (NB) and matrix heaters (H) can be in convection units (CU).

[0085] - If matrix temperature is getting too high, heaters (H) are switched off momentarily or heating power is reduced.

[0086] - If convection unit nozzle box (NB) rows are getting too high, the heaters (H) are switched off momentarily or heating power is reduced.- Alternative: In case additional heaters (AH) are used all additional heaters are switched off momentarily or the heating power is reduced.

[0087] With convection unit (CU) service is easy. Top heaters (H) change is easy with radiation plate glass (RPG). All the heating and thermocouple wires are out of nozzle boxes (NB) and convection unit (CU).

[0088] A convection unit has convection blower(s) with impeller(s) (IMP) which pressurizes convection air through air duct (AD), to possible pressure box(es) (PB) and nozzle boxes (NB). Additional heaters (AH) are preferably in convection pipes (CP), They can be in air ducts (AD), pressure boxes (PB) or even in suction chambers (SC). The additional heaters (AH) can be installed through side walls and insulation on 1 side or 2 sides.

[0089] The additional heater (AH) and convection pipes (CP) may larger diameter to increase convection area (m2) but they need also more convection power, (kW / m2). If convection area and heating power is doubled compared to the nozzle boxes (NB) area, heating speed is increased about 60 - 70%.

[0090] Convection pipes can be square or rectangular, any shape, but round is the best because.

[0091] • Additional heaters (AH) replacement is easy.

[0092] • They have the most efficient heat transfer rate to convection air (CA), also because of COANDA effect.

[0093] • Convection pipes protect heating wires (Hw) from cooling effect and shocks of convection air. Lifetime of heating wire is higher,

[0094] • Convection pipe is fixedly heated at least in convection unit sides. The convection pressure is outside, leakage is minimal. Heating speed remains high, and energy waste is minimal.

[0095] To increase the heating speed, heating power is great abt. 100 kW / m2. It increases manufacturing cost. But unnecessarily high convection power 13 kW / m2increases power consumption, too. With this patent application nozzle boxes need 75 kW / m2and convection pipes max. 50 kW / m2, Convection power needs 5 kW / m2Figure 6. the upper figure is another type of convection unit (CU). The right-side figure 6 can be like the left-side figure or contrary.

[0096] There can be two additional heaters (AH) and convection pipes (CP) in one air duct (AD) to make heaters change easier. Both heating wires should be connected to the electric power supply from the roof of the furnace.

[0097] Impeller (IMP) pressurizes convection air (CA) in pressure boxes (PB) and it continues to air ducts (AD). The air ducts are substantially parallel to the glass travel direction and nozzle boxes (NB) are substantially parallel to the rollers (R).

[0098] Additional heaters (AH) are matrix heaters. They can be switched off momentarily or heating power is reduced if matrix temperature is getting too high.

[0099] The air ducts width (AD) = matrix air width and convection unit (CU) the length = matrix length.

[0100] If convection units (CU) and glasses (G) are getting to high temperature, all heaters (H) are switched off momentarily or heating power is reduced.

[0101] The heaters (H) are preferably in convection pipes (CP) even if they are in the nozzle boxes (NB). Figure 3 shows that the heaters (H) can be in radiation pipes (RP), Figure 3 upper figure includes nearly maximum amount of radiation (RAD) and very hot convection air (CA).

[0102] Matrix temperatures are detected by thermocouples (TC). The figure 3 and de-scrip-tion explains purpose of holes (HO).

[0103] Some examples of additional heaters (AH) are shown in description and figure 4. If vertical additional heaters (AH) were used, the air ducts (AD) would continue down at the ends of convection unit (CU). From there starts pipelines convection air duct to nozzle boxes (CANB). When convection jets (CJ) have impinged on glass (G) they return between nozzle boxes to pipeline convection air to suction chamber (CASC). This is why they are in the same position of side view, in figure 6. The pressure boxes (PB) could be also in the top part of convection unit (CU). In that case matrix heated convection air (CA) could be directed to the nozzle boxes (NB). Air ducts need to be shaped in other ways to ensure heat transfer from matrix heaters to the convection air (CA).With this convection unit (CU) convection heating and radiation (RAD) heating can be divided in percentual proportion quite freely. Explained in figure 3 but more in the following:

[0104] - Additional heaters (AH) are used in embodiment shown in figure 6 for matrix heating only. Additional heaters could be used to increase heating speed, AT, easily in pressure boxes (PB).

[0105] - Radiation pipes can heat convection air (CA) a lot, also without remarkable radiation (RAD) decrease, especially with vanes (V) as figure 3.

[0106] - For example, radiation pipe (RP) can be lower to the glass surface. This is a remarkable increase in radiation strength.

[0107] - There may be high diameter convection pipes (CP) in wide nozzle boxes (NB). This is not reducing convection air temperature and not radiation effect. And it is cheaper to manufacture throughputs of side walls and insulation is less and the number of component and cables are reducing. (The heaters (H) must be put through the sidewalls and insulation).

[0108] Experience from 1990 up to this patent application, physical facts of figure 1 and description, the heating speed is based to the table below. It is approximate,

[0109] "

[0110]

[0111] 1. Note 1 : a) Additional heaters are used all the time, (heating time is 150 seconds), b) Formula of convection heating states that when convection heating starts from X °C and it continues to temperature Y °C it must have multiplication factor . c) increases at the end of heating time convection air temperature is 900 °C instead of700 °C. d) because they are matrix heaters, they heat convection air 75% of the capacity, e) There are 4 convection pipes dia.70 mm, length 400 mm / each, A = 0,45 m3, Convection air heating speed 23 loads / hour. Additional heating speed is = a) * b) * c) * d) = 1 * >2 * 900 / 700 * 0,75 * 23 loads / hour = 10 loads / hour for triple silver glass. Heating speed for clear glass 26 / 23 = over 10 % higher.

[0112] 2. Note 2: Experience from 1996 that “pure” convection is 10 loads / hour faster than radiation for 5 mm clear glass (G). More for clear glass.

[0113] 3. Note 3: a) radiation starts to affect at 500 °C when the heating is near the radiation. Radiation heated air has 1300 °C temperature at the end of heating time. b) Proportion of convection air 2 / 1 to radiation (RAD) heated air.

[0114] c) Formula factor, (see note 1), 1 / 2. d) Heating time 80 seconds of total heating time 150 seconds, f) Average clear glass / triple silver glass 23 + 27 = 25 loads / hour. Heating speed increase = a) * b) * c) * d) = 1300 / 500 * * * 80 / 150 * 25 loads / hour = 9 loads / hour.

[0115] Known competitive capacities for clear and 5 mm triple silver glasses:

[0116] A major Chinese manufacturer, producing approximately 250 tempering machines per year, reports a clear glass capacity of 23 loads per hour. The manufacturer heats the convection air very little, resulting in a capacity of only 13 loads per hour for triple silver glass. This highlights that heating the convection air is essential, not only for triple silver glass but also for other low-emissivity glass types.

[0117] Another heating process manufacturer which heats convection air by heater transfer plate (S) and which does not have radiation (RAD), has heating process which capacities are clear glass 26 loads / hour and triple silver glass 22 loads / hour.

[0118] Pressure boxes (PB) could easily in figure be added additional heaters (AH) and convection pipes (CP), AT, further, they would add capacity even further especially triple silver glass. Clear glass capacity is enough if it is over 40 loads / hour? Additional heaters (AH) electricity supply could be through the furnace roof and insulation in round bars (BA), about 10 mm diameter, isolated from metal structures. Bars (BA) could be connected by glamps (GL) to the heating wires of additional heaters (AH) or by other means.The lower figure of No. 6 shows that insulation (INS) thickness is problematic. In roof of the furnace, it should be at least 300 mm. There is one possibility for connecting outside of the furnace. The convection unit length 1200 mm and height 500 mm + nozzle boxes + air ducts. Convection pipe (CP) diameter is 70 mm. The impeller (IMP) diameter is 400 mm.

[0119] There could be two convection pipes in one air duct (AD). In continuous furnaces, like in bending and tempering, there might be need to heat glasses at higher temperature for bending. In this case 100 mm of hotter glass might be advantageous. There should be insulation in convection pipes (CP) + convection pipe end could be closed firmly. A long convection unit (CU) would not cause problems. The additional heaters (AH) should be placed at 1200 mm C - C length of the furnace. In the end of the furnace, it is easy. Convection pipes could be horizontal.

[0120] Figure 7 shows the top convection unit (CU) at the top of the glass (G) and bottom convection / radiation arrangement without furnace frame and insulation. The heating speed at the top of glass (G) is high. Therefore, it must be on the lower side of glass, too.

[0121] Radiation (RAD) heats rollers (R) and glass by gaps of rollers. This is not enough; convection must be used to increase heat transfer. Bottom heaters (H) can be radiation pipes (RP). The bottom matrix is the same size as the top matrix.

[0122] The convection unit (CU) and bottom C-C have the same length. Further, bottom nozzle boxes (NB) should be under the rollers (R). Convection jets (CJ) should be directed at the third roller bottom both sides. Turbulence is enough for the roller above the nozzle box (NB).

[0123] If C - C distance is over 1000 mm long, roller and glass need convection jets (CJ) rows in between the C - C distance. This should be arranged preferably pipe nozzles (PN).

[0124] The computer calculation speeds are now fast. And radiation plate glass (RPG), heat transfer plates (S) or radiation pipes (RP) are thin. Therefore, their response time for radiation (RAD) and convection air (CA) heating is short. The air HO makes thermocouples (TC) faster and more accurate at convection unit and nozzle boxes (NB). The Proportional-Derivate-Devices (PID) are good but unnecessary and expensive. Contractors with ON / OFF can do the same thing cheaper.There is 1 thermocouple (TC) following bottom temperature.

[0125] If the top matrix temperature gets too hot the top matrix heaters are switched off momentarily, bottom matrix heater (H) will follow immediately.

[0126] If the heaters (H) or additional heaters (AH) in top temperature, get too high, the bottom additional heaters (AH) get off momentarily.

[0127] The top temperature follows bottom temperature by difference + or - or 0 difference always. This is decided by the furnace operator when making receipt of this glass. Also receipt of convection blower speed is decided by the operator. It depends on emissivity and thickness of glass. Later convection blower speed is reduced.

[0128] In conventional furnaces all cables and control wires are brought to the same point. When the furnace top part must be elevated to service position. There is a certain device which can do this.

[0129] The most cables and wires are between top and bottom heaters and thermocouples wires between the heaters which are relatively short, heating 10 - 20 kW. These heaters and wires can be connected near electric and control cabins. This is possible if the cables and wires are elevated to the walking height level between the furnace and cabins. When top parts of the furnace is elevated to service position, the cables and wires are almost straight. These should be lifted between cabins and the furnaces to the walking height level. When the top part of the furnace is in service position the cables are almost straight. This is the big savings in cables and installation of cables.

[0130] Glass tempering profitability is dependent how much glass tempering costs / m2The highest capacity and low manufacturing cost reduce cost level to $ or € / m2extremely low. 2 or 3 tempering machines cost a lot but 1 tempering machine ac-cord-ing to this patent application costs a little bit more. It is the price of radiation plate glass (RPG) + additionally heaters (AH) - cost saving presented in this pa-tent application. Otherwise.

[0131] • High heating speed is giving more production (m2) in time unit.

[0132] • Energy waste can be 40 % in glass tempering. Higher heating speed reduces inversely proportional up to 50% of energy waste.

[0133] • Labor costs reduce inversely to the heating speed.Most normal thicknesses of tempered glasses are less than 8 mm thick. Heating speed is far more important than quenching and cooling process.

[0134] Some advantageous embodiments of the arrangement and the method according to the invention have been described above. The invention is however not limited to the embodiments described above, but the inventive idea can be applied in numerous ways within the scope of the claims.

Claims

Patent claims1. A glass heating process, in which a glass sheet (G) is conveyed through a heating section and is heated by convection air (CA) and radiation (RAD), characterised in that- the convection air (CA) is generated and heated in one or more pressurised convection units (CU),- radiation heating is provided by heating wires (Hw) arranged to heat metal structures adjacent to the glass (G), and- a heat transfer plate and / or a radiation plate glass (S, RPG) is arranged between the heating wires (Hw) and the glass (G), and- the plate or plates are arranged substantially parallel to, or at an angle relative to, a travelling direction of the glass sheet such that uniform heating of the glass sheet is achieved.

2. The glass heating process according to claim 1 , characterized in that the convection air (CA) is directed in a matrix arrangement over the glass (G), wherein the matrix comprises a plurality of rows of convection jets (CJ) or nozzles in nozzle boxes (NB), and the matrix provides substantially uniform heating across the top and bottom surfaces of the glass (G).

3. The glass heating process according to claim 2, characterised in that a ratio between radiation heating (RAD) and convection jet heating (CJ) is adjustable at a design stage of the heating section, such that a maximum radiation heating capacity is structurally limited, while a convection heating capacity is selectively increased by heating the convection air (CA) by means of at least one additional heater (AH).

4. The glass heating process according to any of claims 1 to 3, characterized in that additional heaters (AH) are provided in one or more convection pipes (CP), air ducts (AD), pressure boxes (PB), or suction chambers (SC), and the additional heaters (AH) are selectively controllable to increase convection air temperature (CA) and heating speed of the glass (G).

5. The glass heating process according to any of claims 1 to 4, characterized in that thermocouples (TC) are arranged to sense return airflow to suction chambers (SC), and the temperature readings are used to control the switching or power reduction of heaters (H) and / or additional heaters (AH) to maintain temperature of the convection air matrix within desired limits.

6. The glass heating process according to any of claims 1 to 5, characterized in that the nozzle boxes (NB) are at an angle relative to the travelling direction of the glass sheet such that convection jets provide uniform heating without causing optical distortions in the glass (G).

7. A glass tempering furnace comprising rollers (R) for supporting a glass sheet (G) in a heating section, one or more convection units (CU) for generating and heating convection air (CA), nozzle boxes (NB) arranged in the heating section, and heating wires (Hw) arranged to provide radiation (RAD) heating, characterised in that the heating wires are configured to heat metal structures adjacent to the glass (G), and the convection units are pressurised, and the furnace comprises a heat transfer plate and / or a radiation plate glass (S, RPG), and the plate or plates are arranged between the heating wires (Hw) and the glass (G), and the plate or plates are arranged substantially parallel to, or at an angle relative to, a travelling direction of the glass sheet such that uniform heating of the glass sheet is achieved.

8. The glass tempering furnace according to claim 7, characterised in that the convection units (CU) comprise one or more impellers (IMP) for pressurising convection air (CA) through air ducts (AD) to the nozzle boxes (NB).

9. The glass tempering furnace according to claim 7 or 8, characterised in that the glass tempering furnace comprises a pressure box (PB) configured to direct convection air (CA) to the nozzle box (NB).

10. The glass tempering furnace according to any of claims 7 to 9, characterised in that the nozzle boxes (NB) comprise rows of nozzles arranged at an angle relative to the travelling direction of the glass sheet (G) to form a convection matrix for uniform heating.

11. The glass tempering furnace according to any one of claims 7 to 10, characterised in that the glass tempering furnace comprises convection pipes (CP), that are elongated hollow structures arranged to convey and direct convection air (CA) from the convection unit (CU) to the nozzle boxes (NB), the pipes being configured to allow controlled heating of the convection air by internal or surrounding heating elements (H), and to protect the heating wires (Hw) from direct cooling by the convection air.

12. The glass tempering furnace according to any one of claims 7 to 11 , characterised in that additional heaters (AH) are arranged in convection pipes (CP) to increase convection air (CA) temperature and heating speed.

13. The glass tempering furnace according to any one of claims 7 to 12, characterised in that the furnace comprises a suction chamber (SC) arranged downstream of the nozzle boxes (NB) in the convection airflow, the suction chamber being configured to collect convection air returning from the nozzle boxes and to guide the convection air back to the convection unit (CU).

14. The glass tempering furnace according to claim 13, characterized in that the return air to the suction chambers (SC) passes above the heaters (H) of the air channels and / or radiation / convection pipes (RP / CP) or radiation pipes (RP), or alternatively, the return air flows through the pressurized convection air (CA) ducts (AD) before entering the suction chambers (SC).

15. The glass tempering furnace according to any one of claims 7 to 14, characterised in that the nozzle boxes (NB) are substantially parallel to the rollers (R).

16. The glass tempering furnace according to claim 14 or 15, characterised in that thermocouples (TC) are arranged to measure temperatures in the return flow of convection air (CA) to the suction chamber (SC), providing feedback for controlling the heaters (H, AH).

17. The glass tempering furnace according to any one of claims 7 to 16, characterised in that the radiation plate glass (RPG) is arranged to protect the glass (G) and heating wires (Hw) or radiation / convection pipes (RP / CP) or radiation pipes (RP) from thermal shock.

18. The glass tempering furnace according to any one of claims 7 to 17, characterised in that the radiation plate glass (RPG) is removable along at least the length of a convection unit (CU).

19. The glass tempering furnace according to any one of claims 7 to 18, characterised in that the radiation plate glass (RPG) is removable along the length of the convection units (CU) and nozzle boxes (NB) to facilitate maintenance or replacement of heating wires (Hw) and other components.

20. The glass tempering furnace according to any one of claims 7 to 19, characterised in that the heat transfer plate (S) is removable.

21. The glass tempering furnace according to any one of claims 7 to 20, characterised in that the additional heaters (AH) and / or convection pipes (CP) are arranged to provide matrix heating along the width and / or length of the glass sheet (G), optionally divided into multiple heating zones.

22. The glass tempering furnace according to any one of claims 7 to 21 , characterised in that the convection unit (CU) is substantially enclosed on all sides except for gaps leading to the nozzle boxes (NB) and suction chamber (SC), minimising leakage and energy waste.

23. The glass tempering furnace according to any of claims 7 to 22, characterized in that one or more radiation pipes (RP) are provided in the heating section, each radiation pipe comprising one or more heating elements (Hw) arranged to radiate heat directly to the glass sheet (G).

24. The glass tempering furnace, according to any of claims 7 to 23, characterized in that one or more of radiation plate glass (RPG) have a wall thickness of less than 6 mm.

25. The glass tempering furnace, according to any of claims 7 to 24, characterized in that the radiation plate glass (RPG) is positioned in such a way that minimum distance from the glass (G) is 200 mm.

26. The glass tempering furnace according to any one of claims 7 to 25, characterised in that the nozzle boxes (NB) comprise a plurality of rows of nozzles forming convection jets (CJ) directed towards the glass sheet (G), the rows being arranged substantially parallel to the travelling direction of the glass sheet.

27. The glass tempering furnace according to any of claims 7 to 26 characterised in that the nozzle boxes (NB) are configured to maintain slight negative pressure or underpressure, enabling thermocouples (TC) positioned in the return airflow to accurately monitor the convection air (CA) temperature in the suction chamber.

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