Abstract:
A method comprising the claimed oven, blowing units, and heaters inside a blowing chamber in an oven where convection air is blown through nozzle rows and wherein a roll space and a suction space are separated with the help of pressure from each other by extending the length and/or width of a spacer plate which measures essentially larger than the length and/or width of a spacer plate or by arranging gaps or part which constricts the flow of the convection air between the roll space and the suction space where the gaps or part has an effect on the pressure of suction channels, suction channels extension, or of the suction space so that the convection air is sucked at least mainly from the rolls space through the mentioned suction channels, suction channels extension, and the suction space.

Description:
Object of the invention is a method for tempering glass in an oven in which oven the glass is moved while resting on rolls in horizontal plane and during the heating of the glass a significant part of heating occurs with convection air which is circulated with the help of one or several blowing units which air is heated with heaters which are located inside a blowing chamber and are mainly longitudinal regarding the oven after which the air is blown towards the glass through nozzle rows. 
     BACKGROUND 
     A Finnish patent FI-111006 and a U.S. Pat. No. 7,290,405, FIGS. 10 and 11 show a convection arrangement which in practice has proven to be very efficient and well functioning. In the arrangement the pipes of the heaters must be taken through each air channel (nozzle section). The sealing between pipes and channels must be made well. There is a large number of points to be sealed. Making of perforations and sealings causes unnecessary costs and loss related to escape of convection air. The requirement of an efficient convection is the fact that convection air showers meet the glass with great speed. Arrangements according to the FIGS. 7, 8, and 9 of the patent FI-111006 has also been realized but have been found to be much weaker. The reason is the fact that return air cycle interferes with convection air showers and reduces the incidence speed of the air showers coming from the nozzles to the glass. Figure A clarifies the disadvantage of the return flow for convection showers. The capacities of these kind of convection arrangements are approximately 20-40% lower than the methods according to the FIGS. 10 and 11 of the patent FI-111006 depending on the glass type. In addition to that convection air showers should have a heating profile required by each load of glass. Air flowing to the sides also weakens hugely the heating profile. The method according to the patent FI-111006 has thus been found to be the best and the most inexpensive convection arrangement in which method convection air shower areas and exit air areas alternate in relation to the direction of motion of the glass on transversal sectors. The methods according to the FIGS. 1-6 of the patent FI111006 cannot be realized so that they would be technically correct regarding the air flow and reasonable regarding their costs. 
     One section which has disadvantages in the patents FI111006 and FI20030482 the patent application 2013 0238 relates to the changing of the heaters. It must be performed at the end of the oven because the heaters are long and they are inside casings or pipes. The other disadvantage of the heaters is the fact that the adjusting of the temperature of the oven in a longitudinal direction is difficult, an example is the transverse heaters of the oven described in the patents FI111006 and FI20030482. The third disadvantage is the fact that the mentioned ovens FI 20030482 have long nozzle casings and the oven FI111006 has long pipes for the heaters. The control of their thermal expansion is difficult in relation to other structures, especially in relation to blowing units located in stationary points. Sealings in the thermal expansion points are difficult to realize and escape of the convection air causes loss of power and energy loss. 
     Efficiency of the convection can be increased, the temperature profile can be improved, the loss of convection air can be reduced and costs can be cut when one acts in the innovative way described in the following: 
    
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a prior art solution. 
         FIG. 2  shows a prior art solution. 
         FIG. 3A  is illustration of a cross section of the oven. 
         FIG. 3B  is illustration of a cross section of the oven. 
         FIG. 4A  is illustration of a side view of the oven arrangement. 
         FIG. 4B  is illustration of a side view of the oven arrangement. 
         FIG. 5  shows an alternative return circulation of the air. 
         FIGS. 6A, 6B  and &amp;C show details of the part between the wall of the oven and blowing unit. 
         FIG. 7  is illustration of structure of two blowing units. 
         FIG. 8  is illustration of the oven structure. 
         FIG. 9  shows the upper part of the oven lifted to an upper position. 
         FIG. 10  shows a sealing arrangement between the heaters and the wall of the blowing chamber. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a disadvantageous return air flow which is directed sidewards which return air flow interferes with the efficiency of the convection air showers. This disadvantage can advantageously be removed in the way which is described in this application. 
       FIG. 2  shows an efficient convection according to the patent FI111006 during which blowing units (BU) are arranged inside the tempering oven one after another above the rolls  4 . The heaters  5  are most advantageously installed inside the pipes which pipes penetrate the walls of the nozzle casings which are located to be an extension to the blowing chamber  3 . 
       FIG. 3A  shows a cross section of the oven  1  in which oven the blowers  2  are located at both sides of the blowing chamber  3 . The air from the blowers is directed from between the heaters  5  to the rows  6   n  which are penetrated into the wall  9 , the convection showers are directed to the glass G which moves on the rolls  4 . 
       FIG. 3B  corresponds to  FIG. 3A  with the difference that the blowers which blow in two directions are located in the middle of the oven, such as is shown also in  FIG. 2 . 
     The blowing chamber extends to two sides of the blower but is combined underneath the blowers. Also the space underneath the blowers now belongs to the suction space. Depending on the output of the blower  2  they can be arranged to blow also into two consecutive blowing units regarding the direction of the oven in order to cut the costs. 
     The section A-A of  FIGS. 3A and 3B  shows how air is returned from the roll space  8  to the suction channel  7   c  shown as a section and along the channel into  7   d  which is part of suction space  7 . The suction space comprises the whole upper part of the roll space  8  excluding the blowing chamber  3  and the blowers  2 . 
       FIG. 4A  is a side view of the oven arrangement which arrangement comprises blowing units BU one after another and a gap G 1 , is left between them. G 1  is part of suction space between the blower unit. The majority, even almost all return air can be returned by utilizing the gap G 1  into the suction space  7  in which case the width of the oven can be made smaller by reducing the measure  7   d  and the pressure loss of the return air flow can be reduced. Part of the air can further be returned along the channels  7   c  and along the space  7   d . The parts  3   e  in the drawing illustrate intermediate ducts which combine the blowing chambers  3  to each other. Their purpose is to balance air flow between the blowing chambers  3  and enable the usage of the machine even though one of the heaters  5  might be broken.  FIG. 4A  also shows the essential feature of the invention, return air flows must be constricted above the roll space  8  and underneath the actual suction channels  7   c  by gaps  7   co  and  7   cov  so that the desired, controlled air flow can be created. 
       FIG. 4B  shows an embodiment of the invention with the help of which a greater part or even nearly all return air can be returned through the gap G 1 . So that the flow in the direction of the oven in the roll space  8  would not increase so that it would interfere with the convection air showers, it is possible to add suction channels extensions  7   ce  above the suction channels  7   c  which channels are transverse in relation to them and longitudinal in relation to the oven. Through these channels a majority of the convection air produced by each blowing unit BU can be sucked into the suction space  7  through the gap G 1 . The section A-A in the figure illustrates suction channels  7   c  and suction channels extension  7   ce  at the location of the channel  7   c . The section B-B is a section between the suction channels  7   c . The nozzle casing extends from one edge of the oven to the other in which case the convection air showers cover evenly the width of the whole oven. 
       FIG. 5  shows an alternative return circulation of the air during which air channels which are like the suction channels  7   c  and suction channel extensions  7   ce  are not used but the return air is circulated into the suction space and back to the blowers in the return air space  7   i  which is between the lower wall of the blowing chamber  3  and the spacer plate  9   i  either in a longitudinal direction regarding the oven to the gap G 1  or in a lateral direction to a space  7   d  or in both directions. There are gaps in the spacer plate  9   i  for tubular nozzles  6   t  or tubular nozzle rows  6   tn  are attached to them through which convection air showers are directed to the glass G. Gaps  7   co , are pierced into the spacer plate  9   i  and gaps  7   cov  are left small enough which create the needed restriction which is needed to create the pressure difference between the roll space  8  and the suction space  7 . The return air flows to the space  7   i  between the spacer plate  9   i  and the lower wall of the blowing chamber  3  and further to the suction space  7 . For example largish gaps which are made for the tubular nozzles, separate holes or elongated holes can be used as gaps depending on how the nozzle rows are arranged and how underpressure distribution which is advantageous for the return air flows can be created. When the length of the tubular nozzles is adjusted to be such that they extend to the level of the spacer plate  9   i , the return air flow moving in to the suction space  7  does not interfere with the convection air showers. 
       FIGS. 6A, 6B and 6C : Details are shown of the part between the wall of the oven and the blowing unit at the location of the suction channel  7   c  and/or details of the method according to the way shown in the  FIG. 3 . It shows how the roll space  8  must be separated at least mostly at the location of  7   d , which is a part of the suction space  7  so that at most only minor underpressure is directed directly to the roll space  8 , but underpressure and air flow are directed in a controlled way through the suction channel  7   c , (suction channel extension  7   ce ) or through the return air space  7   i.    
     Parts  9   e  in  FIGS. 6A, 6B, 6C  illustrate alternative restriction ways. One restriction way may also be the sizing and design of the blowing chamber in such a way that the right kind of restriction can be created. 
       FIG. 7  shows the reciprocal location and the advantageous structure of two blowing units BU and their blowing chambers  3  as a side view of the oven in which figure the nozzle casing part  3   nb  of the blowing chamber is broadened at its lower part and correspondingly the suction channel  7   c  is broadened at its upper part. Thus the desired restriction and pressure difference between the roll space  8  and the suction channels  7   c  and the suction space  7  can be created. In addition to that the nozzles can be spread to a wider surface area in which case the heat transfer becomes more effective. 
       FIG. 8  shows the oven structure which is described earlier but for clarity reasons the mentioned descriptions of the inventive parts of the air flows are mainly left out. The figure shows how the heaters  5  have now been built to have approximately the length of the blowing chamber  3  and how the blowing chamber is divided above the heaters  5  into two parts along the line  3   s . The lower part  3   b  of the blowing chamber can be detached and lowered down either fully or can be equipped with hinges at its other edge. The heaters  5  which are located at the lower part of the blowing chamber  3  are most advantageously installed to the pipes. The heaters are attached at least nearly air-sealed to the walls of the blowing chamber at their ends or near their ends. 
     Underneath the glass an efficient convection heating is not needed because there is no coating underneath the glass. However, it is important to keep the temperature of the rolls  4  stable. Radiation is not good enough for this. That is why the heat transfer must be boosted with the help of the convection. Additionally, because the upper and lower heat regulation must be “synchronized”, the upper and lower heaters  5   b  must be located on top of each other in relation to each other. In order to perform the necessary heat transfer advantageously and in the right way, the best way to perform it is to install the heaters underneath the glass which heaters correspond to the length and location of the upper heaters. Most advantageously the needed addition of the heat transfer can be realized with convection and nozzle casings  3   db  from between the lower heaters from which heaters air showers are directed to the rolls  4  in different angles being measured from the horizontal plane so that the convection is directed to all rolls. 
       FIG. 9  shows how the upper part of the oven is lifted to an upper position when the heaters are being changed. Then the part  3   b  can be lowered downwards in which case the changing of the heaters can be done easily.  FIG. 9  shows the hinge alternative in order to lower the lower part  3   b  of the blowing chamber  3  into the lower position so that the heaters  5  can be pulled out and pushed in without the adjacent blowing unit BU interfering because there is no need to change the heaters. There is no need to present the cables of the heaters, connections, thermocouples and mechanisms of the lifting process because several known alternatives exist for them. The lifting device  10  can also be located on the top of the oven, if wanted. If one wants to lower down the lower part  3   b  in horizontal plane, the lifting devices are needed at both ends of the blowing chamber. 
     Organizing the needed additional length for the cablings, which is needed for lowering down the heaters, can be organized on top of the oven, if wanted, in which case a down/up movement possibility is arranged for them to that location. 
       FIG. 10 : A sealing arrangement between the heaters  5  and the wall of the blowing chamber  3  in which arrangement holes Dh, which are considerably larger than the outer diameter Dp of the pipe, are machined to the wall of the pressure chamber and to the holder Sh of the seal while the hole of the seal part S is only a little bit larger than the hole of the outer diameter of the pipe. When the outer diameter Do 2  of the holder of the seal is considerably larger than the outer diameter Do 1  of the seal and the hole, which is left for the seal, is only a little bit larger than the thickness of the seal, a good enough sealing can be achieved for the convection air while the tube for heaters  5  can move in longitudinal direction and at the same time the tube for heaters can also move radially in every direction. 
     By realizing the isolation of the upper convection from the roll space  8  according to the  FIGS. 6A, 6B, 6C, 7  with the arrangement in question the heaters  5  can be located immediately on top of the suction channels  7   c , suction channel extensions  7   ce  or on top of the return air space  7   i , most advantageously inside the pipes in which case numerous perforations can be avoided according to the  FIGS. 10 and 11  from the patent FI-111006. With the help of this method manufacturing costs, difficulties caused by thermal expansions and sealing problems can be considerably decreased. 
     The mentioned disadvantages on the page 1-2 can be removed and one can achieve a) heat regulation also in the longitudinal direction regarding the oven in which case a “matrix” heat regulation can be created with the transverse profile of the heat, b) easily performed changing of the heaters and c) controlling of the thermal expansions and at the same time a nearly complete removal of escape air when one acts in the inventive way described in the following.