WO1997044286A1

WO1997044286A1 - Controlling tempering process in tempering furnace

Info

Publication number: WO1997044286A1
Application number: PCT/FI1997/000302
Authority: WO
Inventors: Jukka Vehmas
Original assignee: Uniglass Engineering Oy
Priority date: 1996-05-22
Filing date: 1997-05-21
Publication date: 1997-11-27
Also published as: FI100526B2; FI100526B; AU2900597A; FI962161A0

Abstract

A method and an equipment for controlling the tempering process in a tempering furnace provided with rollers. Information concerning the shape and loading degree of a glass load on a loading table (1) is automatically read into the memory of a control system, and the tempering process is controlled based on the loading information read. This way heat is supplied to the desired locations, and a good and even tempering result is achieved irrespective of operator skills.

Description

CONTROLLING TEMPERING PROCESS IN TEMPERING FURNACE

The invention relates to controlling the tempering process in a tem¬ pering furnace provided with rollers, in which method the adjustments of the tempering process are controlled by a control system. The invention also relates to an equipment for controlling the tem¬ pering process in a tempering furnace provided with rollers, the equipment comprising a control system for controlling the adjustments of the tempering process.

Current glass tempering machines employ what are known as os- dilating roller furnaces in which glass is heated mainly by radiation. In the tempering process the temperature of the glass is increased above the sof¬ tening point of glass in order to enable the glass to be tempered. Said tem¬ perature is between 610 and 625°C depending on the thickness of the glass. The glass is then cooled at desired speed typically using forced convection whereby air jets are blown at the glass from above and from below. This method enables high heat-transfer coefficients, necessary when thin glass is concerned in order to achieve a sufficient temperature difference between the surface and centre of the glass. Examples of oscillating roller furnaces are dis¬ closed in FI patents 62,043 and 83,072. Before the glasses are transferred to the furnace, they are placed on a loading table, usually manually, in accordance with the instructions sup¬ plied by the manufacturer of the machine. The main point in the instructions is that the load must be balanced, i.e. that the whole loading table is evenly filled with glass. The minimum distance between the glasses is also determined. The heating resistors of the furnace may be given what is known as a heating profile, whereby the operator selects desired temperatures or heating effects for a certain resistor or for a certain part of the furnace. However, the main principle is always that the loading is performed in accordance with the in¬ structions, and the profile and the loading are compatible. This, however, re- quires that the operator is able to perform the loading correctly and control the heating furnace so that it corresponds with the load. However, all or part of the glasses may be too massive or too few or may have a difficult shape, and hence the loading table does not fit the glasses to be tempered in accordance with the instructions, resulting in the loading being contrary to instructions. This may easily lead to at least partial failure of the heating. At its worst this may cause the heat balance of the furnace to disappear, i.e. a part of the fur- nace is excessively cooled or heated and the furnace is incapable of restoring its former state.

It is the object of the present invention to provide a method and an equipment for avoiding the above mentioned drawbacks. The method of the invention is characterized in that information concerning the shape and loading degree of the glass load is automatically read into the control system and the tempering process is controlled based on the loading information read.

The equipment of the invention is characterized in that it comprises means for reading loading information automatically into a control system, and a control system for controlling the tempering process based on the loading information read.

It is an essential idea of the invention that information concerning the loading, such as shape and degree, are read automatically into the mem- ory of the control system, and the tempering process is controlled based on said information. It is the idea of a preferred embodiment that the information is read into the memory from a moving load when it is being transferred from the loading table into the furnace. It is the idea of still another preferred em¬ bodiment that the information is read optically. It is the idea of a third preferred embodiment that measuring devices reading the information are arranged for each longitudinal upper resistor line.

The information obtained may be easily used for controlling the en¬ tire tempering process, e.g. for controlling the heating of the furnace or the automatic unloading of glass from the unloading table, etc. The loading infor- mation travels with the load through the entire tempering process, whereby the system is constantly aware of the location of a certain piece of glass in the process. The information read into the memory is stored in an appropriate form, whereby it can be easily utilized, i.e. the control system of the system remains sufficiently rapid without any unreasonable need to increase its ca- pacity. By reading the information concerning the load from a moving load op¬ tically, the reading devices can be kept simple and the reading of the load easy and fast. By adapting a measuring device for each longitudinal upper resistor line, information concerning the load is obtained by means of which it is easy to make decisions about controlling the upper and lower resistors. By means of the invention, the heat in the furnace can be directed at the desired place, for example, allowing the entire load to be heated as homeothermic as possible, and in this way the temperature of the glass can be kept within a strict temperature tolerance, i.e. desired homogenous surface optics and tem¬ pering results are achieved. Furthermore, a lower average output temperature of the load, lower energy consumption, and a higher capacity are achieved. The invention will be described in more detail in the attached draw¬ ings in which

Figure 1 schematically shows a top view of the arrangement of the invention in partial section, and

Figure 2 shows the arrangement of Figure 1 seen in the travel di- rection of the glass.

Figure 1 schematically shows a loading table 1 with rollers 2, upon which glass 3 is placed during loading. From the loading table 1 the glass 3 is transferred to a furnace 4. In the furnace 4 the glass 3 is heated to tempering temperature in a manner fully known per se. Resistors 5, for example, are used for heating. For the sake of clarity, Figure 1 only shows the first part of the furnace 4 and the resistors 5. Further, for the sake of clarity, the rollers by the furnace 4 are not shown.

When the furnace 4 is prepared to receive the following load, and the load is ready on the loading table 1 , the glass 3 is transferred to the fur- nace by rotating the rollers 2 in a manner fully known per se. At this point the glass sheets move in the direction of arrow A. The area between the loading area and the furnace typically comprises two to four rollers 2 upon which there is no glass 3 during loading. Detectors 6 are arranged in this area. During the transfer, the detector is able to register the glass 3 and the empty area be- tween the glass pieces 3 relative to time, whereby a point grid depicting the loading degree and shape can be established. This information may be modi¬ fied in the control system and be utilized in e.g. direct control of resistor power. Preferably there is one detector 6 per each longitudinal resistor line 5. In this case the information obtained by said detector can be very easily utilized for controlling the resistors 5.

The detectors 6, secured to a frame 7, are clearly seen in Figure 2. The detectors 6 are typically secured to e.g. a height of 15 to 25 mm above the glass 3. Hence the most advantageous distance between the detectors matches that between the resistors 5, being typically e.g. about 100 mm. The detectors 6 are optical detectors, controllable to transmit a beam, denoted by arrow B, at the stage when the glass 3 is transferred to the furnace 4. If there is glass 3 below a detector 6, at least part of the transmitted beam is reflected back as shown by arrow C, whereby the detector 6 registers that there is cur¬ rently glass 3 below it.

From the detectors 6 the information is transferred to the control system of the tempering process where said information can be utilized in a variety of ways. The resistors 5 may, for example, be divided into two or more parts in the longitudinal direction of the furnace 4, whereby resistor power may be directed at the right points. Furthermore, information concerning the loca¬ tion of each glass 4 in the tempering process is continuously available to the control system.

The drawing and the related description are only intended to illus¬ trate the idea of the invention. As to its details, the invention may vary within the scope of the claims. Thus, the information measured on the forming of the load and on loading degrees may be utilized at any stage of the tempering process. The information can be especially well utilized e.g. in preheating fur¬ naces.

Claims

1. A method of controlling the tempering process in a tempering furnace provided with rollers, in which method the adjustments of the temper¬ ing process are controlled by a control system, characterized in that information concerning the shape and loading degree of the glass load is automatically read into the control system and the tempering process is con¬ trolled based on the loading information read.

2. A method as claimed in claim 1, characterized in that the loading information is read into the control system from a moving load as it is transferred from a loading table (1) to a furnace (4).

3. A method as claimed in claim 1 or 2, characterized in that the loading information is read optically.

4. An equipment for controlling the tempering process in a temper¬ ing furnace provided with rollers, the equipment comprising a control system for controlling the adjustments of the tempering process, character¬ ized in that the equipment comprises means for reading loading information automatically into a control system, and a control system for controlling the tempering process based on the loading information read.

5. An equipment as claimed in claim 4, characterized in that the means for reading the loading information comprise at least one detector

(6), arranged immobile relative to a loading table (1), and that the glass (3) is arranged to move past the detector (6), whereby the loading information is read by the detector (6) from the moving load as it is transferred from the loading table (1) to the furnace (4).

6. An equipment as claimed in claim 5, characterized in that the detector (6) is an optical detector.

7. An equipment as claimed in claim 5 or 6, characterized in that one detector (6) is arranged per each resistor line (5) in the furnace (4).