FI20210006A1 - Improvement and cost reduction for convection heated glass tempering machines - Google Patents

Abstract

The convection process is improved by making the convection units in such way that the convection air and the furnace air cannot disturb each other. The all the convection air is blown onto the glass and roller space and it is returned directly from there to the blower. The duct work is minimized by air boxes. The efficiency is improved by suction in between the nozzle boxes.

Description

IMPROVEMENT AND COST REDUCTION FOR CONVECTION HEATED GLASS TEMPERING

MACHINES Glass tempering machines are normally heated by a blower operated convection system. The convection air is heated by heaters into the matrix configuration.

The nozzle boxes must be narrow to reach high capacity. If they are narrow, the more of them are needed which increases costs. The air delivery duct manufacturing is costly, too. The connection of ducts to the nozzle boxes is problematic and costly in narrow spaces. Normally a convection heating machine consists of several convection units depending on the furnace length.

The mixing of the furnace air and convection air circulation is problematic. Especially at the ends of the furnace, as outside air tends to mix with the convection air. Blower suction causes always causes a small under pressure, (small vacuum), nears the vicinity of the blower intake opening.

The furnace top section tends to be high with ducts to nozzle boxes.

Certain cost savings have been invented like the patent US 7,290,405. However, it also needs pipe nozzles to function well. This method does not have any radiation. Its heater change is troublesome.

The effectiveness of convection has reduced from what they were 25 and over 10 years ago due to the cost savings. The convection processes have also deteriorated.

NOVEL IDEA WHICH OFFERS HIGHER EFFICIENCY AND SAVES EXPENSES This patent application includes ways to improve the process, increase convection effectivity and reduce costs. The improvement consists of the following steps:

1. Make the convection totally independent convection air circulating unit. It will affect the furnace air extremely little, if any. This is made by enclosing the convection suction chamber into a totally enclosed chamber.

2. Reduce the duct manufacturing costs and make the convection air delivery to the nozzle boxes easy.

3. Suction in between the nozzle boxes improves the efficiency of the convection. S30 Convection unit with effective nozzle boxes S Fig, 1 shows a cross section of the furnace with a convection unit inside. The convection S unit, more exactly the blower return space (BRS), (blower suction chamber) is a totally x enclosed box. The only way out are the nozzles. The only way in is from between the & nozzle boxes. The furnace air does not interfere or mix with the convection air all the O 35 vacuum, even small is downwards. S Blower return space (BRS) is the suction chamber of the blower (B). It is behind the end N cover plate (CPE). “E” means between the convection units and furnace doors, N (lengthwise the furnace. The blower has preferably 2 outlets. Both outlets deliver air directly into two air boxes (AB), see section A- A. Perforated plate (PP) is useful since, 1 without them, the dynamic air pressure would enter into the nozzle boxes. In case extra good design is required, perforated plate shape (PPE) would make it. From air boxes there are connections directly to the nozzle boxes (NB). In the figure there are 2 nozzle boxes in one matrix (M). Dotted lines are not well seen, see section B — B.

Matrixes, (M) are shown by dashed lines. There is a thermocouple (TC) for each matrix. At the furnace doors 2 thermocouples. Glass is moving on the rollers (R). The return air (AR) comes from between the nozzle boxes into the blower return space (BRS).

Section A- A shows 2 convection units. The blower (B) delivers the convection air (FA) directly into the air boxes (AB). The air boxes are connected directly to the nozzle boxes (NB) in an easy way. One air box would also work but would require much more complicated arrangement. Air boxes save quite a lot of expenses compared to duct work. All nozzle boxes are identical. The arrows (RA) indicate return air flow to the blower return space (BRS).

Thermocouple and electric wires are not shown in the figure. The side cover plate (CPS) makes the blower return space (BRS) an enclosed box. Mark (PP) indicates the perforated plate (PP). The section B — B explains further why 2 air boxes are practical arrangement. Sec. B — B indicates how inexpensive and easy it is to deliver convection air from the air box (AB) directly to the nozzle boxes (NB). The nozzle box feed opening is (NBF). In the opening it is good to use a perforated plate to eliminate the dynamic air pressure of the convection air to enter the glass through the nozzles. The arrow (AD) means the obvious air direction moving in the nozzle box.

The sec. C—C of sec. A - A of figure 1 and its top view describes the arrangement above the convection unit. Blower dimension of 1500 rpm. are not easily located in the length of the matrix or convection unit. This is why the blower air delivery (BAD) has to be parallel or almost parallel to the rollers blowing the convection air in the same direction. Air box is marked with (AB). The blower casing (BC) and impeller (Im) together form a blower.

This applies to the blowers with two outlets. The cover plates (CPE) and (CPS) form the N enclosed box at the 4 sides of the convection unit. Top cover plate (CPT) and the blower N casing (BC) do the same at top of the convection unit.

S S Fig.2 shows 2 types of effective nozzle boxes (NB). The nozzles (NO) in the “face” (OP) of z 35 nozzle box impinge convection jet (CJ) on to glass (G). Radiation is marked (RAD). In the = left hand side of the figure the heater (H) and the heat transfer plate (S) are inside of the S nozzle box. It is not handy since the heaters need to be changed periodically.

© In the right hand side of the nozzle box the heaters are outside convection jets (CJ) pass O through the radiation. The heater is outside of the nozzle box, in which case the heaters 40 are easy to change.

The convection air return flow back to blower takes place in between the nozzle boxes. 2

Fig. 3 shows other types of nozzle boxes. They would be preferred in case there is an under pressure, small vacuum inside of the blower return space (BRS). There is a congestion of the convection air in between the glasses and the nozzles. This will cause a serious efficiency loss especially in case the nozzle boxes are wide, well over 100 mm. Fig. 4 is a cross section of one matrix with two nozzle boxes and heaters in between the air boxes (AB). It describes an improved convection efficiency. This is easy and inexpensive to increase suction in between the nozzle boxes. This naturally means higher under pressure, (a small vacuum) inside of the blower return space (BRS). If the air boxes (AB) are connected by duct (ADAB) there will be convection air pressure inside of the duct. The narrow ducts (ADNB) take the convection air to the nozzle boxes (NB) in a very uniform manner. The narrow duct increases the heat transfer area of the heat transfer plate (S) above the heaters (H). The result is higher convection air temperature. The convection air will return to the blower return space (BRS) through air return gaps and the openings in between the air return space (ARS). When the gap width (g) is small the suction is high in the air return gap. The openings from the blower return space (BRS) to the air return space (ARS) must be sufficiently large so that the vacuum is at least almost the same in both of them until the air return gaps (ARG) . The suction reduces the congestion of the convection air in between the glasses and nozzles. This allows the wider nozzle boxes and/or convection efficiency, (capacity) is increased. The pipe nozzles would increase the convection efficiency further. This belongs to the Bernoulli equation explained next.

Bernoulli system. Fig. 5 describes an option of the figure 1 with the detail of one matrix as shown in figure

4. In this case the Bernoulli system is made in a different way (as first invented by the inventor). A blower (B) with two outlets delivers the convection air (BAD) into ducts (AD). N The air duct leads directly into the air delivery box (ADB). It and the novel system are N located behind matrixes (M). The matrixes are separated by dashed lines. S One duct also could be used since the air delivery box (ADB) has a very large area, it S covers basically all the area of the convection unit. z 35 The thermocouples are marked with (TC). The arrows (RA) mean the return air flow. = Long arrows mean option under fig. 7 description. S Cover plate (CP) makes the blower return space an enclosed box as the sides are also S enclosed. All the air flow outside of the convection unit is under it as above explained. O The return air flow into the blower return chamber (BRS) is different as per description of 40 figure 6. The convection air circulation does not interfere or mix with the furnace air as all the under pressure (vacuum) and suction is from below, in between the nozzle boxes. 3

The difference comes from the option of figure 7. Fig. 6 shows a cross section of one matrix with 3 nozzle boxes and 3 heaters.

The pressurized convection air from the air delivery box (ADB) is distributed by narrow ducts (ADNB) to the nozzle boxes.

The duct length in horizontal direction is at least nearly as long as the nozzle boxes.

Narrow ducts are useful because the convection air enters into them and the nozzle boxes uniformly.

Another advantage of narrow ducts is that in this way the heaters (H) heat the heat transfer plate (S) in a larger area than in the case of normal nozzle boxes.

This way heats the convection air to the higher temperature.

According to the Bernoulli law the blower (B) must cause an under pressure, (small vacuum) into the blower return space (BRS). The practical vacuum is 7 % +/- 3 % of the blower air delivery pressure depending on the dimensioning, (cross sectional area) of the convection air return flow.

Theoretically much higher vacuums are possible.

On the other hand, Bernoulli equation is practically always valid.

However, it causes effective suction only when vacuum is the range is over 3% of the air delivery pressure.

The vacuum is transferred from the blower return space (BRS) to the air return space (ARS) by the sufficiently dimensioned air return pipes (ARP). Relatively large cross section of the air return space (ARS) keeps vacuum the same at the whole horizontal length of the air return space.

In this way also the suction level is maintained the same at the same length.

The sufficient cross section of the air return space (ARS) also secures that only 1 pipe (ARP) is needed.

The advantages of the suction are explained earlier in the description.

The air return pipes can be square or rectangular shapes, too.

Sec.

A — A of figure 6 shows the air return pipes ARP (2 of them in the figure in between every nozzle box) and the air delivery openings for ducts (ADNB) from air delivery box (ADB) to the nozzle boxes.

The 2 oblique rectangle openings on two sides of the picture describe the air duct AD entrances into the air delivery box (ADB). As the nozzle boxes need to be in an angle to the glass travel direction, the furnace convection width must be wider than the nominal loading width.

The rectangle opening shapes save some of the furnace width.

N 30 Fig. 7 describes one of the most important subjects of convection efficiency.

The figure is N a part of the nozzle boxes shown from the glass upwards.

The heaters (H) are shown <Q darkened.

O The convection jets must not be slowed down by the return air flow.

Their temperature z should not change before they impinge on the glass surface.

The vertical jets (VJ) impinge on the glass straight, in 90 degrees angle.

The radiation on the way and on the glass S surface increases the heat transfer from jets to the glass.

It is good for heating speed. 2 The inclined jets, arrows (lJ) pass through the radiation and impinge on the radiation O heated glass surface.

The heat transfer ratio from the air onto the glass is very high.

The jets also have larger convection areas. 4

These effects should not be reduced. Or if they are “must be” reduced, it should be as little as possible. This is why inclined jets (lJ) should be sucked on the other side of the nozzle box in between the two vertical jet nozzles. The sucking effect can be improved if there are sucking holes on the other side of the nozzle box for the inclined jets (lJ). The air return gap (ARG) should be made narrower or eliminated totally to maintain the Bernoulli equation at the selected level. Fig. 8 describes a slightly different optional method of figure 1 and/or 5. The air return pipes (ARP) of the fig. 5 are shown on the lowest part of the figure. Around them is the air delivery box marked as (ADB). For figure 1 there would be the ducts (ADAB). The blower outlets (BAD) deliver the convection air into the air boxes (AB) in fig 1. Respectively to the air ducts (AD) in fig 5. In this option a small part of the return air flow is taken from holes (Ho) made into the cover plates (CPE) leading to the air return space (BRS). The Bernoulli equation should be kept in mind. The holes are located above every matrix and thermocouples (TC). In this case the thermocouples would read the return air temperature of the two matrixes of the successive convection units. At the furnace doors there should be an additional plate in between the furnace doors and the thermocouples in order not to mislead the thermocouple temperature readings. The plate should cover the area of the holes (Ho) and should reach down to the level of the nozzle outlets. The small pipe type openings (O) could take a fraction of the air return flow from between the convection unit and the furnace wall to the blower return space (BRS). This applies fig 5 only. For fig 1 it would be best to make this opening differently. This would be a gap type opening on the furnace side wall of the last nozzle boxes. These openings should also follow the principles of Bernoulli equation. All the nozzle boxes need to be installed in an angle to the glass travel direction. This is required to make optically good glass, without iridescence. This is a must if the heaters are outside of the nozzle boxes. The angle is determined by the matrix length. The whole length of the matrix should get an equal amount of convection and radiation onto the = 30 glass. The oscillation length and the oscillation length variation can be considered to S reach the excellence of glass guality.

N - There may be variations of nozzle boxes as shown in figures 2 and 3 and channels (ADNB) © as shown in figure 4 and 6. = 35

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Claims (11)

THE PATENT CLAIMS:

1. The glass tempering convection heating process in which the glasses are heated by convection air and convection air is heated by heaters (H) and the glasses (G) are moved on the rollers (R) and the air is blown on onto the glasses from nozzle boxes (NB) through the nozzles is known in that the blower return space (BRS) is a closed box and under it convection air is blown onto the glass (G) from nozzle boxes (NB) as convection jets (Vj and/or IJ) and the convection air is returned back to the blower return space (BRS) in between the nozzle boxes.

2. The glass tempering process according to the patent claim 1 is known in that there is an under pressure, (vacuum) in convection blower return space (BRS).

3. The glass tempering process according to the claim 2 is known in that a small part of the convection air return flow (RA) is taken from holes (Ho) in the end cover plates (CPE) on two sides of the convection unit above every matrix and the thermocouples (TC) are in between the convection units under the holes (Ho)

4. The glass tempering process according to the claim 1 —3 are known in that at least the inclined convection jets (lJ) blow onto the radiation heated glass surface (RAD).

5. The convection heated glass tempering machine according to the claims 1—4 is known in that the blower (B) outlet (BAD) is directly connected to at least one air box (AB) and the air box is directly connected to the openings of (NBF) of the nozzle boxes (NB).

6. The convection heated glass tempering machine according to the claim 5 is known in that the air box (AB) has channels (ADAB) and the channels are connected to the narrow ducts (ADNB) and the nozzle boxes (NB).

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7. The convection heated glass tempering machine according to the claims 2 and 3 are S known in that the blower return space (BRS) is connected to the air return pipes N (ARP) and the air return pipes are connected to the air return spaces (ARS).

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8. The glass tempering machine according claims 5 - 7 are known in that the nozzle box = 35 (NB) has a hollow type space made for the heaters (H) outside of the nozzle box and O there are convection nozzles on two sides of the heater.

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9. The glass tempering machines according to the claim 7 is known in that the N convection nozzles direct inclined convection jets (lJ) so that they impinge the glass 40 under the heaters (H) and the nozzle boxes may have nozzles for vertical jets (VJ), too.

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10. The glass tempering machines according to the claims 5 — 9 are known in that the nozzle boxes are in an angle to the glass travel direction.

11. The glass tempering machines according to the claims 5-7 and 10 are known in that the nozzle boxes have heaters (H) and the heat transfer plates (S) inside the nozzle boxes.

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