FI116463B - Convection heating oven for heat-treated glass plate - Google Patents

Description

116463

CONVECTION HEATING OVEN FOR HEAT TREATED GLASS PLATE

The invention relates to a convection heating furnace of a heat-treatable glass sheet into which the glass sheet comes along a conveying path such as rotatable rolls and the furnace further includes heating resistors for heating the air to be blown against the glass sheet at least a portion of each heating air heating heater resistor is located in 10 free contact with the air flow, and each channel further comprises an extension below the resistance line, and in the extension a base portion provided with air outlet openings.

EPO 0 910 553 B1 discloses a glass plate heat treatment furnace having elongated air blowing ducts, according to the preceding recital 15. These ducts are provided with duct heating resistors which, by means of special reflector surfaces, are adjusted to radiate mainly downwards towards the glass. Blowing air comes from the top of the ducts toward the heating resistors partially surrounding the reflector troughs and bypasses the troughs, and continues down toward the special irradiated plates. 20 The radiation plates receive, due to the reflector troughs, strong thermal radiation from the heat resistors, and the radiation plates are also intentionally made into thick panels *, *. · To allow the air to warm up as they pass through their openings. No airflow. : Rinse the heating resistors so they have a high surface temperature and emit * I * '· ·' strong heat radiation.

LV 25 • ·

The disadvantage of the furnace described above is that the glass is largely heated by radiation, even if the air is blown, since the radiation plates of the solution are above the glass and • · · ;; * Temperature significantly higher than glass. Especially in a certain way • »T coated glasses reflect the radiation and do not heat up with radiation heating.

30 The furnace will require additional reflector troughs along the heating resistors, as well as massive openings underneath the * ·· 'resistors, which will still respond slowly to • ·' / · / · heating control. The use of heating resistors as radiant heaters, which have: very high surface temperatures, inevitably results in a clear reduction in their service life.

116463 2

To eliminate the disadvantages of the above furnace solution and to bring the glass heating mode closer to perfect convection heating, a new convection heating furnace has been developed, characterized in that to reduce the channel in a tight spot.

The invention has the advantage that the glass is heated almost exclusively by convection, whereby the solution is suitable for all types of coated glass. The heating resistors are 10 directly in a strong air flow, so that their surface temperature does not rise very much above the temperature of the blown air. As a result, the life of the resistors is prolonged and their impact on the environment is also small. The air discharge nozzles are openings made in a lightweight plate structure. The plate structure is substantially at the same temperature as the strong air flow therethrough, since the radiation of the heating resistors 15 does not substantially heat the plate structure. The quality of the material of the sheet structure and its surface also makes it possible to influence that the sheet structure hardly emits heat radiation to the glass. Individually adjustable heating resistors can be mounted parallel to or across the ducts. The heating resistors can also be installed in both furnaces at the same time.

20

In the following, the invention will be explained in more detail with reference to the accompanying drawing, in which

k I

Figure 1 illustrates part of a heating furnace according to the invention in which some of the heating components on a glass plate are obliquely depicted on the side.

Fig. 2 shows an end view of the blowing duct, f Fig. 3 shows the installation of a heating resistor mounted transversely to the duct.

,. Figure 1 shows a portion of a glass heat treatment furnace comprising walls (not shown) and a conveyor path formed by rotating rolls 3 on which the glass sheet 1 is * »* · '! Can be transferred as desired during and after the process. To guide the blowing air to • 30 the surface of the glass 1, the oven includes elongated channels 2, which in this example are '*; · 'Mounted in the direction of travel of the glass 1. The ducts 2 are supplied with blowing air from one or more »», · i blowers through the distribution ducts 4. Inside the passageways 2 are located heating elements' 5 which are parallel to the passageways 2. The passageways 2 extend downwardly below the heating elements 5 and terminate in the perforated bottom portions 9. At least the bottom part 9 is 5 3 116463 thin sheets and has holes 7 therein, 8 preferably with the punching tool also forming collars down the holes (Figures 1-3) .Tin-sheet refers to a sheet having a thickness of less than 3 mm.

The heating elements 5 are in channel 2 in a relatively high air flow and the air flow passes close to the elements 5. As a result, the elements efficiently release heat to the air and the temperature of the elements does not rise high. Their surface temperature remains substantially lower than in the case of radiant heating, in which case they must emit considerable 10 radiated power to the environment. The blowing air passes through the resistor, warms as a result, and continues to warm up through the apertures of the base portion 9 toward the glass 1. Due to the expanded shape of the base portion 9, the blowing holes 7,8 cover the glass surface. However, there is sufficient space between the ducts 2 to return air up to the suction side of the fan.

Figure 2 shows the installation position of the ducts directly from the end of the duct 2.

The distance s between the base part 9 and the glass 1 is adjusted to be about 50 - 70 mm. The bottom part 9 is far from the heating element 5, the distance is about 70-120 mm. As a result, the element 5, through radiation, does not heat the base member 9 very much. The temperature of the base member 9 comes very close to the temperature of the blowing air. The surface temperature of the heating element 5, in turn, is about 50 to 200 ° C higher than the temperature at which the air flowing past •. '· · Piya. Em. the temperature difference largely depends on the speed at which the air passes the elements 5.

1 · ...: Fig. 3 shows an exemplary embodiment in which openings for heating elements 5 are formed in the transverse direction of the channel 2 and that in the space between the channels 2 there are protective sleeves 6,: · '25 which both adjust the channels 2; distance to prevent the elements 5 significantly * ··· 'radiating out of the spaces between the channels. The ducts 2 also allow their shape and height to allow the elements 5 to be mounted simultaneously in the longitudinal and transverse directions of the glass. The thermal power of the elements 5 at the sleeves 6 can be adjusted, for example, by using fewer turns of the resistance wire per unit length 30.

Under the glass plate 1, a heating arrangement similar to that of Fig. 1 may be made upside down: with the channels 2 parallel to the rolls 3 and in the intermediate spaces thereof. The blowing openings 7 in the corners of the bottom portions 9 then face the rolls 4 116463 3 and warm them. Other types of solutions for heating under glass are also possible, for example, heating methods with a higher proportion of radiation.

It is essential for the invention that the heating intensity of the various parts of the glass can be adjusted by means of separate heating elements 5 which are individually adjustable. Preferably, the elements 5 are adjacent to each other in the direction of the elements, i.e. in the direction of travel of the glass, so that each has its own feed and thus its own adjustment. If necessary, the adjustment of the heating elements on the surface of the glass 1 alone can be used to obtain the exact desired heat-volume distribution.

In addition, the fans and the air distribution ducts 4 can further control the air velocities and the distribution of the air volumes into the various duct systems 4 and thereby also influence the temperature distribution of the glass. The general control of the fans can also influence the nature of the heating, i.e. the proportion of convection with respect to radiation. The large amount of air to be blown and its speed move the heating method towards near-perfect convection heating.

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Claims (9)

116463 A convection heating furnace for a heat-treatable glass sheet (1) into which the glass sheet enters along 5 conveyor paths, such as on rotatable rollers (3), and further comprising heating resistors (5) for heating air blown against the glass sheet (1); ) for blowing said air against the glass sheet and the air blowing ducting comprises elongated channels (2) in the direction of movement of the glass sheet (1), within which at least a portion of the heating resistor (5) 10 for each blowing air is in free contact with the airflow; and in the extension the base portion (9), wherein the base portion (9) is provided with air blowing openings (7, 8), characterized in that, to lower the surface temperature of the heating resistor (5) and reduce the radiant heat transfer mmitysvastuksen 15 (S) into the said site of an air flow duct (2) narrowest point. Convection heating furnace according to Claim 1, characterized in that the expansion bottom part (9) is a thin plate and that due to the strong convection blowing 20 and / or the surface quality selected for the plate, substantially little heat radiation is provided in the glass; '* For sending. Convection heating furnace according to claim 1, characterized in that Γ! the air blowing openings (7, 8) of the base part (9) are collar holes made in the thin plate. 25 • · The convection heating furnace according to claim 1, characterized in that:, · the heating resistors (5) are placed in a strong air flow to limit their surface temperature t> «up to 300 ° C higher than the temperature of the air * I« .. ' . »« T · · 30 »I A convection heating furnace according to claim 1, characterized in that I t * • ·; the heating resistors (5) are located in a strong air flow to limit their surface temperature up to 200 ° C higher than the temperature of the air which has passed said resistance. 116463 A convection heating furnace according to claim 1, characterized in that the temperature of the base (9) is substantially the same as the temperature of the air blown into the glass plate (1). Convection heating furnace according to claim 1, characterized in that the heating resistor (5) is located in the duct (2) parallel to the duct (2). A convection heating furnace according to claim 1, characterized in that the heating resistor (5) is located transversely to the duct (2) and is led to pass therethrough. A convection heating furnace according to claim 1, characterized in that, for controlling the temperature distribution and temperature rise of the glass (1), the power of the heating resistors (5) is individually adjustable by the furnace control system and the rotational speed of the blower.