In my opinion it is that the convection air must be heated into the matrix configuration.
The reason is, that the silver glass reflects almost 100% of the radiation. Only convection guarantees uniform glass temperature. At the same time as the convection is heated, the capacity is increased. Actually all high capacity and well working convection systems are so called pure convection systems. It means that the radiation is colorless, weak radiation. In 1996 first such one is made by IANUA, it was followed by 2003 GLASSROBOTS. The capacity for 5 mm glass was > 25 loads/hour, for triple silver abt. 10% lower. These convection were made by narrow nozzle blocks. They also proved, that the convection heating was at least 60% faster than the radiation heating. In around 2004 Land Glass made the same using also matrix heating system based on FERACITAS patent US 7,2790,405. GLASTON followed 2010 using GLASSROBOTS principle and technology.
Only in 2011 FERACITAS used the patent US 7,290,405. It used a combination of heated convection air and radiation by “Smart Cycle”. The capacity was high for 5 mm clear glass, 23 load per hour. For triple silver glass it was 15 loads/hour. The convection area covered 2/3 of the heating area. The nozzle boxes were wide, 240 mm. This is why the convection was poor efficiency. The convection air return air flow disturbed the efficiency of the convection jets.
How to use matrix heating most accurately? Simultaneously get rid of the heating time parameter!
After the convection jets have impinged the glass surfaces under each matrix, the most accurate glass temperature reading can be obtained from the convection air return flow temperature. This should be made matrix by matrix by thermocouples. The best is to use 2 thermocouples for each matrix. The thermocouples can be common for the preceding or the following matrix.
An interesting and useful benefit is, that an automatic dispatch to tempering and reduction of the glass breakage in tempering can be combined. The red matrix (2 thermocouples) is the only one matrix under which the glasses are not hot enough for tempering. The automatic discharge takes place when the thermocouples show that the tempering temperature of the glasses has been reached. Then the control system tells “exit” command. The glass breakage is minimized and heating process will be fully repeatable. The other glasses under the other matrixes do not get overheated as the heaters in them are off. Besides, the temperature difference is small and the heating control system has all the time balanced the temperature between all the matrixes of each convection unit.
An example of the convection which works like a radiation heating furnace
The fact is, that the convection with the radiation is good for tempering of all glass types with exception of triple silver glass, because it reflects all the radiation. However, the inexpensive convection systems do not heat the convection air. This results in a very bad process for triple silver glass and a very low capacity particularly for triple silver glass.
This results in a low capacity and a great waste of the operators wages:
The capacities for 5 mm triple silver glass drop from over 20 loads per hour to max. 12 loads per hour. North Glass A-series furnaces also have over 90 kW heating power per m2 of the heating area. This, together with weak convection affirm, that the heating process is mainly the radiation. The capacity of North Glass for 5 mm clear glass is high. about 23 loads/hour.
The 100% convection means IANUA “CONVAIR” and GLASSROBOTS “RoboTemp” and also FERACITAS 100% convection coverage. The FERACITAS convection similar physical features like CONVAIR and RoboTemp, actually even better as FERACITAS convection jets do not blow all into the return air flow. The “cost” of this is less than 10% of the convection blower pressure delivery, about 40 pascals at 700 centigrade temperature.
The next idea may prove to be more effective. Even for the triple silver glass. Even without 100% convection coverage!
The heated air, passing through radiation on to the radiation heated glass surface creates a very high heat transmission coefficient. This is so high, that the the capacity can be expected to reach at least what has been available by IANUA “CONVAIR” and GLASSROBOTS “RoboTemp”. They reached with “pure convection”, (no efficient colored radiation) over 25 loads/hour 5 mm clear glass and max. about 10% less with triple silver glass. They also proved, that “pure convection” is at least 60% faster heating speed than the radiation. The schematic picture below shows the principle. It will be easy to change the top heaters. In INUA “CONVAIR and GLASSROBOT RoboTemp they were as long as the heating area. In GLASTON FC-series they are inside of the nozzle boxes, which tend to warp in hot conditions.
The necessary changes and possibilities
To avoid iridescence the heaters and nozzle rows of each matrix has to be designed in an angle to glass travel direction. The similar system is used in GLASTON FC-series and North Glass A-series. Also the patent “box construction” e.g. US 7,290,405 with the air return space can be used to reduce the convection fabricating cost. The similar design without the convection air return space can be used for nozzle box design to increase the heat transfer area from the heaters to the convection air.
The picture below shows the “box construction” convection blower B as well as plate PL which is necessary to avoid outside air to the convection air. Further, the plate PL is necessary to give for the thermocouples (TC) the correct reading of the convection air return temperature. This kind of the plate should be used also for nozzle box designs.
Also the gaps in between the convection units should be reasonably closed so the Bernoulli laws, (patent US 9,624,120.) would work properly. (ARS in the figure below). Bernoulli laws works well, but it requires some more accuracy in manufacturing. This is, however, easy to achieve with a modern manufacturing technology. The method is covered by FERACITAS patent US 9,624,120.
A BIG QUESTION ARIZES; IS “PURE CONVECTION” NEEDED AT ALL?
GLASSROBOTS tried to increase the heating speed, (capacity) of IANUA CONVAIR by almost doubling the convection air volume, doubling the kW power of the convection blower motors for RoboTemp. The heating speed increase was practically nothing. At that time turbo convection SONIC of GLASTON were competing for the world record heating speed.
Later there are various attempts made by Land Glass, which is only has about 50% convection coverage and no effective radiation at all. Therefore the capacity is low. Also the thermocouple and heating control are far from the optimum. GLASTON FC-series has about 85% convection coverage, which does not explain the heating speed drop fully. HEGLA-Taifin has nozzle boxes across the furnace and it can change the heaters more easily from outside of the furnace, even without cooling the furnace. However, it uses even more convection power than GLASSROBOTS RoboTemp and FC-series. The exact power is not known. The heating speed is faster than FC-series.
My conclusion is, that about 100 – (150) mm. wide nozzles boxes are needed to reach a high capacity with acceptable convection air volume. This means expensive convection design with a big number of components or very big convection blowers and big motors. Higher pressures than 500 – 600 Pa are not feasible with the temperatures 680 – 700 centigrade. FERACITAS patent US 9,624,120 is the best alternative for the “pure convection” heating with high capacity.
What extra can be available by “pure convection” heating?
There are ways to do it very service friendly, like changing the heaters from outside, without cooling the furnace. There is also remarkably cheaper ways to make the convection than GLASTON FC-series and HEGLA-Taifin. FERACITAS can use the “box construction” expired patent of FERACITAS US 7,290,405. 1) The way maintain 100% convection coverage for high capacity with reasonable convection blower size. 2) This also maintains perfectly heating the convection air into the matrix configuration. The solution is using FERACITAS patent US 9,624,120 in a new way according to the patent application FI 20200070. The cross section of the furnace and one convection unit are shown below.
The blower can be located at the 2 sides of the furnace or also centrally. The large open areas between the convection boxes uniform under pressure at the top of the furnace even if the blowers are at the sides of the furnace.
The simple inventions have continued now 25 years since IANUA “CONVAIR was made. The processes have been made worse when trying to make cheaper convection heating furnaces. Alone the capacity can make increase operating costs very much especially in high labor cost countries. When tempering triple silver glass the operating cost difference can be € 200,000,- per year per machine in one shift work! With Feracitas capacity this means one shift work, low capacity almost 2 shift work!
Actually, IANUA CONVAIR used Tamglass Engineering technology also for software, heating control, everything, which was not patented by Tamglass. The CONVAIR glasses were excellent quality. Basically only matrix heating is new and beneficial process improvement.
A modern, good process and effective convection heating cannot be made without heating the convection air into the matrix configuration. M.O.T.
What else is new? Iridescence reduction in tempering section!
This is an improvement. FC-series is offering it as an option. It works. However, there are simple inventions, which can also improve it free of charge. Simultaneously it can reduce the power consumption.
Personally IANUA time for undersigned was initially the find a new job and get started my invention for complex glass bending and tempering and tempering, which was rejected by Tamglass Engineering/(GLASTON) in 1992. However, it also started the convection development ideas and patents in which I have been a pioneer for over 20 years. IANUA time also taught and proved me the ways to lower the costs for tempering section manufacturing. It further includes the tempering section operation easier this reduces the cost at the same time. The inventions are based on similar simple ideas like the improvements and lowering the costs of the convection. They are based on the very standard engineering.
Welcome to ask anything, which is not a novel idea.
Post time: Jan-04-2021