Glass manufacturing – Processes – Glass preform treating
The invention relates to a method of adjusting the cooling air of a glass tempering machine, in which method cooling air is led to a tempering area for cooling the glass exiting a tempering furnace.
The invention also relates to an equipment for adjusting the cooling air of a glass tempering machine, the equipment comprising at least one fan and a channel system for leading cooling air to a tempering area for cooling the glass exiting a tempering furnace.
When tempering glass, the temperature of the glass is increased above the softening point of glass in the tempering process. For this purpose tempering furnaces are used, currently typically what are known as oscillating roller furnaces. After the tempering furnace the glass is led to temper cooling. Tempering thin glasses, typically with a thickness of 2.8 to 3.8 mm, requires a high tempering pressure provided by a fan, e.g. a pressure of about 20 to 25 kPa. The alternative is to use the combined effect of fan air and compressor air, whereby an about 8 to 10 kPa tempering pressure is sufficient with the tempering effect practically emanating from the compressor. Thin glasses are tempered either in a separate tempering zone through which the glasses are conveyed without stops. After the tempering zone, the glasses are led to an after cooling unit where they are oscillated in a reciprocating manner upon rollers. The blast pressure of the tempering zone is provided e.g. by series connected high-pressure fans. Such a separate tempering zone involves expensive equipment and structural investments. Furthermore, said tempering zone cannot be utilized in connection with glasses with a thickness of 4 mm or more, the after cooling unit operating as their tempering unit. Tempering thin glasses may be implemented also without a separate tempering zone by blowing pressurized air at the glasses both by fans and by the compressor. This, however makes the anisotropy pattern of the glass quite uneven as the air jets are formed spotlike. Furthermore, a separate compressor is needed, and, in order to increase the capacity, the compressor should be expanded with increased capacity.
On the other hand, when tempering thick glasses, the blast pressure has to be sufficiently low. Typically this problem is solved by adjusting the speed of rotation of the fan motors. Fl 77,216 discloses an alternative way to achieve low blast pressure. Said publication describes a solution with at least two fans, fan channels between the fans and the air delivery chamber, and a bypass channel connecting the fan channels. A gate valve is disposed after the bypass channel
between the fan channel and the air delivery chamber, the plate being in throttle position when one fan is switched on with the guide vane control closed and another fan is switched off with the guide vane control partially or entirely open. The air is led by the bypass channel
to the channel of the other fan, from where it exits via the open guide vane control. This way, the gate valve being in its maximum throttle position, the desired minimum pressure is achieved for the nozzles. Said solution and adjusting the speed of rotation of the fan motors require, however, a completely separate solution in tempering thin glasses.
It is the object of the present invention to provide a method and an equipment for avoiding the above mentioned drawbacks and for implementing temper cooling simply within a wide range of glass thickness.
The method of the invention is characterized in that the tempering area is reduced by closing a closing device that can be opened and closed, whereby a tempering zone with a pressure that can be raised sufficiently high for tempering thin glass can be formed out of the reduced tempering area.
The blast pressure unit of the invention is characterized in that it comprises a closing device for directing blast air at only a part of the tempering area, whereby a tempering zone with a pressure that can be raised sufficiently high for tempering thin glass can be formed out of the reduced tempering area.
It is an essential idea of the invention that the tempering area can be reduced by a closing device, whereby a tempering zone with a pressure that can be raised sufficiently high for tempering thin glass can be formed out of the reduced tempering area. Furthermore, the closing device can be opened for the after cooling of thin glasses or the tempering of thicker glasses, for example. It is the idea of still another preferred embodiment that the tempering area is reduced to a tempering zone of half the size of the tempering area. It is the idea of another preferred embodiment that the equipment comprises at least two fans which can be connected both in series and in parallel by means of channel systems and a gate valve.
It is an advantage of the invention that the tempering result achieved is very even. Furthermore, space is saved as no separate tempering zone is needed even for thin glasses. This also lowers acquisition costs. A separate compressor is not needed either, but instead two moderately sized fans are sufficient to provide tempering air to the entire thickness area of the glass.
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Ladas and Parry
Uniglass Engineering Oy
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