CA1119373A

CA1119373A - Method and apparatus for heat treatment of fibrous mats

Info

Publication number: CA1119373A
Application number: CA000304353A
Authority: CA
Inventors: Jean A. Battigelli; Francois Bouquet
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-06-09
Filing date: 1978-05-29
Publication date: 1982-03-09
Also published as: IE47077B1; BR7803686A; NO148183C; NO782002L; AR215712A1; IT1096627B; PL207522A1; IT7824226A0; PT68162A; IL54873A0; IL54873A; PH16009A; ZA782948B; FI63071B; AU3694378A; EP0000111B1; FR2394041A1; YU136978A; DE2860695D1; NZ187494A

Abstract

ABSTRACT OF THE DISCLOSURES
A technique is disclosed for heat treatment of fibrous mats, especially mats formed of mineral fibers such as glass and carrying a heat hardenable binder material, such as a thermosetting resin.
The method and the equipment disclosed provide for continuous feed of the mat through a curing or treating oven having a plurality of heat treat-ment zones or areas. In one form of the method and equipment, the heat treatment in at least one zone is effected by circulation of a heated gas, such as air, through the mat in said zone, and the mat is also subjected to heat treatment in a localized area lying within said zone by passage of a second heated gas through the mat, the second heated gas having a pressure higher than that in the surrounding portions of said zone.

Description

METHOD AND APPARATUS
FOR HEAT TREATMENT OF FIBROUS MATS

Background and Statement of Objects:

In the production of fibrous insulating mats, especially mats formed of glass or similar mineral fibers, it is customary to initially form the mat by depositing the fibers on a perforated moving conveyor, usually with the aid of suction boxes provided under the flight of the conveyor on which the fibers are deposited. It is also customary to deposit a fiber binder on the fibers either before or during the buildup of the mat on the conveyor, such binder having adhesive characteristics and usually comprising a heat curable or hardenable material, such as a thermosetting resin, for instance, a phenol formaldehyde resin sprayed on the fibers in a solution or a suspension in a volatile liquid, such as water.

The layer or blanket of relatively loose fibers on the collecting conveyor is thereafter customarily deliv-ered to what is commonly referred to as a mat curing oven through which the mat is fed by additional perforated con-veyor means, frequently comprising a pair of endless con-veyors having adjacent flights presented toward each other in spaced relation and serving to determine the thickness of the mat to be formed. Such a mat may be more or less dense, depending upon the extent of compression applied by the pair of conveyors in the mat curing oven.

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During passage of the mat through the oven, the mat is subjected to heat treatment to effect curing of the fiber binder and thereby to effect stabilization of the mat at the desired thickness.

For the purpose of effecting the curing of the binder, various techniques have been employed; but quite commonly, the technique includes passage of heated air through the mat, for which purpose circulation boxes or manifolds are arranged in pairs at opposite sides of the feed path of the mat through the curing oven, such ovens quite com-monly including several such pairs of circulation boxes, with provision for establishing different temperature con-ditions sequentially through the series of pairs, so as to regulate the curing temperature applied at different zones in the path of the mat through the curing oven.

It is a principal object of the present invention to provide not only for the heating to effect curing of the binder by the primary heating system in the general manner heretofore contemplated, but in addition, the inven-tion contemplates employment of a second independent heating system comprising at least one pair of manifolds of rela-tively small size operating in relatively small localized areas at opposite sides of the path of the mat, this pair of manifolds serving to pass through the mat a heated gas having a pressure and temperature sufficiently high to raise the temperature of the core portion of the mat to a higher value than that attained in the core portion in the areas surrounding said localized areas. Moreover, the heated gas of this "secondary" binder curing system is preferably passed through the mat in a localized area located in the mid or downstream portion of the feed path so that the sur-face layers of the mat have already been cured and stabilized by the primary heating system. This initial stabilization of the surface layers of the mat makes possible the use of relatively high pressure in the secondary heating system without disrupting the fibers of the mat.

Although the arrangement of the invention is adapt-able to the curing of a wide variety of mats and fibrousblankets, for reasons noted just above, the invention is especially advantageous in the curing of binder in rela-tively dense mats, because the pressure and temperature conditions employed in the secondary heating system of the present invention promote rapid penetration of the heat into the interior of even quite dense and thick fibrous products; and since the secondary high pressure air is applied after the surface layers of the mat have been stabilized, this rapid penetration is accomplished without disruption of the fibers.

In a typical installation in which the primary heat curing system involves the use of pairs of hot air circulation manifolds or boxes arranged in sequence along the feed path through the oven, the invention contemplates, as a secondary heat curing system, the introduction of at least one additional pair of hot air circulation manifolds having relatively small localized areas lying within the zone or area of one of the pairs of boxes of the primary system. In this installation, it is contemplated that the heated air of the secondary system operating in the local-ized area have a pressure higher than that of the air em-ployed in the primary system. When employed in this con-figuration, the primary air circulation system serves notonly to supply heat needed for the curing of the binder, but in addition, it serves also as a means for preventing escape or loss into the atmosphere of air leaking from the secondary system which operates at higher pressure.

By the employment of both primary and secondary systems, and by the employment of a higher pressure in the secondary system, the rapid penetration of the heat into the interior of the mat being cured in the localized area of the secondary manifolds, is highly effective in expedit-ing attainment of the binder curing temperature in the inter-ior or core portion of the mat; and it is an object of the invention to provide for rapid attainment of a binder curing temperature sufficiently high to initiate exothermic reac-tion of the binder resin. The attainment of such an exother-mic temperature will result in continuance of the bindercuring, even if succeeding zones of the curing oven are not maintained at the same elevated temperature. Therefore, in the overall curing operation, the use of the secondary high pressure system in the localized downstream curing areas effects an overall economy of the total fuel expended to accomplish the curing.

.37~

It is a further object of the invention to provide novel structural arrangements for introducing the hiyh pres-sure manifolds of the secondary system in the localized areas of the circulation boxes of the primary system, these structural arrangements providing for minimization of short-circuiting and leakage and also providing automatically for yielding of some of the shielding elements without break-age thereof, in the event of buildup of resin or other deposits on the conveyors serving to carry the mat through the curing oven.

From the foregoing general explanations and also from the following detailed description, it will be seen that the invention provides a method for heat treating a fibrous mat carrying a heat hardenable fiber binder in order to harden the fiber binder, the method comprising feeding the fibrous mat through a heat treating zone in which a first heated gas is passed through the mat from one side face to the opposite side face of the mat, and passing a second heated.gas at a pressure higher than that of said first gas through a localized area of the mat within said zone, which area is smaller than the total area of said zone. It will also be seen that the method comprises feed-ing the fibrous mat in a feed path through a heat treating zone in which the mat is heated to a binder curing tempera-ture, and passing a heated gas through the mat in a local-ized area extended across the mat in said zone at a temperature - .

3~3 and pressure providing for heating of the interior portion of the mat in said localized area to a temperature higher than the temperature established in the interior portion by the heating of the mat in an adjoining region of said zone upstream of said localized area.

, It will further be seen that the invention provides apparatus for heat treating a fibrous mat, the apparatus comprising conveyor mechanism for advancing the fibrous mat through a feed and treatment path, at least one pair of gas circulation boxes arranged at opposite sides of the mat in said path and defining a region of treatment in which gas is passed through the fibrous mat between circulation boxes at opposite sides of the mat, gas supply and exhaust ducts respectively connected with said circulation boxes and providing for passage of heated gas through the fibrous mat in said treatment region, a pair of supply and exhaust gas circulation manifolds positioned within a pair of said circulation boxes and defining a localized treatment area within and smaller than said treatment region, and located downstream of at least a portion of the treatment region, and heated gas circulating means associated with said mani-folds and circulating heated gas through the fibrous mat at a pressure higher than that of the gas passed through the fibrous mat between said circulation boxes.

-5a-~1~9373 Brief Description of Drawings:
~ Iow the foregoing and other objects and advantages are attained will appear more fully from the following descrip-tion referring to the accompanying drawings, in which -Figures la and lb, taken together, illustratea longitudinal sectional view through a mat curing oven according to the present invention embodying a sequence of six pairs of hot air circulation boxes providing the primary system for the heat treatment or curing, and further a secondary system embodying two pairs of localized high pressure manifolds, one pair being disposed in each of the last two of the primary or low pressure circulation boxes;
Figure lc is a fragmentary view similar to a portion of Figure lb but illustrating an alternative embodiment in which two pairs of high pressure or secondary circulation boxes are enclosed in one of the pairs of the low pressure circulation boxes;
, -5b-B WS~

... . . . . .

Figure 2 is a transverse sectional view on an enlarged scale taken through one of the pairs of primary hot air circulation boxes, as indicated by the section line

2-2 applied to Figure la;

Figure 3 is a fragmentary longitudinal sectional view on the scale of Figure 2, illustrating one of the pairs of primary or low pressure circulation boxes having a pair of secondary or high pressure manifolds disposed therein;

Figure 4 is a view on the same scale as Figures 2 and 3 but illustrating a transverse section through a pair of secondary or high pressure circulation boxes, this view being taken as indicated by the section line 4-4 on Figure lb; and Figure 5 is a fragmentary view on a smaller scale than Figure 4 but illustrating a modification of the high pressure air circulation system.

Detailed Description of the Drawings:

In the drawings, the reference numeral 6 indicates the overall enclosing structure of the mat curing oven in which the conveyor equipment and the hot air circulation systems are arranged.

, ;373 As seen in Figures la and lb, in the lower por-tion of the oven, rotative supporting elements or rollers 7-7 are provided for mounting the lower endless conveyor, the upper and lower flights of which are indicated in Fig-ures la and lb only by dot-dash lines, these conveyor flights appearing in greater detail at 8a and 8b in Figures 2, 3 and 4. As seen in Figures la and lb, rotative supports or rollers 9-9 are also provided for the upper conveyor, which is indicated in Figures la and lb only by dot-dash lines; but the lower and upper flights of which appear in greater detail at lOa and lOb in Figures 2, 3 and 4. Each :
of the conveyors is made up of a multiplicity of links which are pivotally interconnected and which carry rollers 12 adapted to ride on the tracks indicated at 13. The links carry trans-verse ribs indicated at 11. Conveyors of this type are driven through the mounting rollers.

The rollers 9 and also the tracks 13 for the upper conveyor are mounted upon a frame structure 14 made up of longitudinal and transverse members interconnected so as to provide for adjustable positioning of the upper conveyor with respect to the lower conveyor. This adjustment may be effected by screw jacks indicated at 15 in a manner well understood in this art and forming no part of the present invention per se.

By virtue of the adjustability of the upper con-veyor, the space between the conveyor flights 8a and lOa, which are the runs presented toward the fibrous mat, may be altered in order to establish the desired density or thickness of the product being made.

At the upstream or input end of the oven, a con-veyor, indicated diagrammatically at 16, is provided, the conveyor here illustrated representing a perforated conveyor such as commonly employed for the collection of fibers to form a mat or blanket. Suction boxes, such as shown at 17, may be employed for assisting the collection of the fibers and for maintaining them in position on the conveyor.
Suction fans 17a are connected with the suction boxes.
The fibrous blanket carried by this conveyor 16 is delivered to the sizing rolls Rl-R2, which are preferably adjustable in order to regulate the thickness of the mat being intro-duced into the oven; and after delivery of the partially sized mat from the rolls Rl-R2, the mat enters between the conveyor flights in the curing oven.

Interiorly of the oven, the primary or low pres-sure air circulation boxes are provided in pairs. In the embodiment illustrated in Figures la and lb, six such low pressure pairs of boxes appear, the zones or regions of these pairs being generally indicated by the letters A, B, C, D, E and F. These pairs of boxes each include a pair of generally rectangular box-like structures 18 and 19 which are closed on all sides except for the side presented toward the conveyor flights 8a or lOa. Each box 18 is mounted on fixed structure below the upper flight 8a of the lower conveyor; and each box 19 is mounted on the vertically ad-, .
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justable framing 14 for the upper conveyor, so that theupper boxes move with the upper conveyor when its position is adjusted.

Each box is also provided with an opening communi-cating with a duct for either supply or exhaust of the treat-ment gases, such openings being indicated at 20. The supply or inlet and the discharge or exhaust openings are respec-tively marked with plus and minus symbols _ 11+~ or n_n.
It will be noted that in the first pair of boxes A, the supply opening 20 is arranged in the lower box 18 toward the upstream end of the box, with respect to the direction of feed of the product through the oven; and the exhaust opening is arranged in the upper box 19 of this pair, near the downstream end.

The same general pattern is repeated in the boxes of the second pair indicated at B. In the third pair of boxes, indicated at C, the inlet opening is in the upper box 19 at the upstream end and the exhaust opening is in the lower box of the pair toward the downstream end.

In the zone indicated at D for the fourth pair of boxes, the pattern of inlet and outlet openings is the same as for pairs A and B. In the pair of boxes E, the arrangement of inlet and outlet conforms with that mentioned above in connection with zone C; and in the pair F, the arrangement shown conforms with that of the boxes D. It is to be understood that these relationships may be altered . .

in order to vary the manner in which the curing is effected;
and different flow conditions may be employed in connection with products of different types, thickness and/or densi-ties, as is known in this art. In addition, a smaller or a larger number of circulation boxes and treatment zones may be utilized, according to the nature of the product being made. Still further, the flow through certain boxes may be shut off if desired.

Before considering the structure and operation of the high pressure air circulation system contemplated by the present invention, attention is called to the ~act that the overall enclosure of the oven 6 is provided with a gas exhaust system including the ducts 21, and the exhaust fan 22, the latter delivering gases removed from the inter-ior of the oven into and through an appropriate precipitator 23 for separation of suspended solids. The osen walls 6, in effect, comprise a hood surrounding the interior com-ponents of the oven including the heated gas circulation boxes and manifolds; and the leakage which occurs is with-drawn from the oven enclosure by the exhaust system just described.

Figure 2 illustrates on an enlarged scale a trans-verse section through the low pressure boxes of zone C.
Here it will be seen that the gas supply line 24 is con-nected with the upper or supply box 19 and that the exhaust duct 25 is connected with the lower exhaust circulation box 18. Vanes l9a serve to distribute the incoming gas over the width of the conveyor and thus over the width of .. ,:
.: .

the mat being treated. The gases discharged through the connection 25 are delivered to a heater 26 with which a burner 27 is associated, and these gases are drawn through the heater by the fan 2~ and delivered by the fan into the supply duct 24. This gas heating and circulation system may be employed for more than one of the pairs of low pres-sure boxes, or if desired, separate circulation systems may be used.

To accommodate vertical motion of the upper con-veyor and the parts mounted therewith, the supply duct 24 extends through an oversized opening 29 in the wall of the oven, and a flexible closure bellows 30 may be used to sub-stantially seal the joint between the supply duct and the wall of the oven. In addition, the duct 24 is provided with a slip joint 24a to accommodate the vertical adjust-ment. --In considering the high pressure gas circulation system, attention is first directed to certain features of construction of the conveyors. As above noted, these conveyors are made up of links 11 which are pivotted to each other in an endless loop, one such loop being provided for each conveyor. The individual links (see for example Figures 2 and 3) extend across the width of the conveyor and have rollers 12 associated therewith as mentioned above, and each link has a base plate 31 which is apertured at intervals across the width of the conveyor (as clearly appears in Figure 2), and is provided with projecting ribs or flanges .. . .

32 forming transverse passages extended through the links fox the flow of the gases from the low pressure supply boxes or high pressure supply manifolds, through the mat carried by the conveyors and then through the apertures and passages s in the links of the other conveyor and into the exhaust boxes or manifolds.

As shown in the embodiment of Figures la and lb, a high pressure manifold system HPl is associated with the pair of low pressure boxes E, this high pressure system and the pair of low pressure boxes E being illustrated in enlarged longitudinal section in Figure 3 and in enlarged transverse section in Figure 4. From Figures lb and 3, it will be seen that the high pressure manifold system is substantially smaller than the low pressure boxes and further that the high pressure manifold system lies within the low pressure boxes. The high pressure supply manifold is indi-cated at 33; and from comparison of Figures 3 and 4, it will be noted that this manifold extends across the width of the conveyor, above the flight lOa, and of the mat being treated, but is of relatively short dimension in a direction upstream and downstream of the feed path of the mat. A
supply duct 34 is connected with the high pressure supply manifold, this duct passing through an oversized opening 35 in the wall of the oven and the opening being closed by a flexible bellows seal 36. Duct 34 has a slip joint 34a to accommodate vertical motion. In the interior of the high pressure supply manifold, vanes 37 are provided to insure distribution of the high pressure gases over the : ., . . :

3~

width of the conveyor. A high pressure exhaust manifold 3~ is provided below the flight 8a of the lower conveyor and the exhaust manifold is connected with the duct 39 in order to discharge the high pressure gases after they have passed through the mat being treated~ The duct 39 delivers the withdrawn gases to a heater 40 having a burner 41 from which the gases are withdrawn by the fan 42 which recir-culates the gases to the supply duct 34.

As in the low pressure system, the high pressure duct and circulation system, including the heater 40 and the fan 42, may be employed for more than one high pressure system; or if desired, separate heaters and fans may be utilized for different high pressure systems.

Although distributing vanes 37 are provided in the supply manifold 33, these are not needed in and are preferably omitted from the exhaust manifold 38.

Figure 5 schematically illustrates an alternative form of heater which may be employed for heating the high pressure gases in the circulation system. Here, a heat exchanger diagrammatically indicated at 43, is introduced into the exhaust manifold 39 in advance of passage of the gases through the fan or blower 42. Figure 5 also indicates an alternative arrangement of the high pressure supply and exhaust manifolds 33 and 38; in this illustration, the supply manifold 33 being located below the mat being treated and the exhaust manifold 38 being located above the mat.

Because of the employment of relatively high pres-sure gases in the high pressure system, it is of importance to minimize gas leakage, and this requires provision of special sealing devices, an example of such devices being particularly illustrated in Figure 3. Here it will be seen that at each side of the upper or supply manifold 33, a supporting structure 44 is provided, this structure serving to mount a pair of wall elements 45, one located at each side of the manifold 33. Each of these wall elements is pivotally mounted as indicated at 46, so that the wall ele-ment may be swung or displaced upwardly away from the upper surface of the conveyor flight lOa. At a point opposite to the pivot 46, the wall element 45 is provided with a flange cooperating with a stop or abutment 47 which serves to limit downward movement of the wall element and thus prevents contact of the wall element with the upper surface of the conveyor flight lOa. Each of these wall elements 45 is of trough-like configuration, being extended across the entire width of the conveyor; and it is contemplated that these elements have a flat lower surface and that they be mounted in close proximity to the upper surface of the conveyor flight lOa, thereby providing sealing action pre-venting any substantial lateral flow or leakage of the high pressure gas being used in the high pressure manifold system.
In a typical installation, in the normal operating position of each wall element 45, the element will be spaced from the upper surface of the flight lOa a distance of the order of a few millimeters, for instance, from about 3 to 5mm.

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~: ...

These displaceable sealing wall elements are pro-vided so that the sealing elements may be normally posi-tioned much closer to the conveyor than would be possible if they were fixed in position. Displacement away from the conveyor will readily occur in the event of the accumu-lation on the conveyor of irregular deposits of resin or fibers, as tends to occur from ti~e to time in the operation of such equipment. Since the elements 45 are automatically displaceable, if a lump or deposit is encountered, no damage to the equipment will occur, even when the wall elements are mounted for normal operation very close to the surface of the conveyor.

The elements 45, located above the conveyor, func-tion automatically under the action of gravity to returnto the position in close proximity to the conveyor, after being displaced by any deposit of resin or fibrous material.
The width of the flat bottom surface of each of the trough-shaped elements 45 is preferably at least as great as any two adjacent passages through the conveyor ribs, so that the desired sealing function will be performed, regardless of the relative position of the conveyor ribs with respect to the wall element in the path of movement in the conveyor.

Similar displaceable wall elements 48 are asso-ciated with the flight 8a of the lower conveyor, these wallelements being arranged for downward displacement away from the lower surface of the conveyor flight 8a and being urged upwardly by springs 49. Similar pivots and limiting stops - , are provided for the lower elements 48, but the lower ele-ments being displaceable downwardly under the action of obstructions encountered as the conveyor flight passes the high pressure system, springs instead of gravity are relied upon to return the wall elements 48 to their normal operat-ing position.

Each of the wall elements 45,45 and 48,48 is pro-vided with an inclined surface, such as indicated at 50, at the upstream side of the element, in order to facilitate the displacement action under the influence of foreign bodies carried by the conveyors.

From Figures lb, 3 and 4, it will be noted that in the high pressure manifold system HPl, the supply mani-fold 33 is located above the conveyor and in the low pres-sure circulation box with which the low pressure gas supplyconnection communicates, the discharge manifold of this high pressure system being located in the discharge box of this low pressure system.

By reference to Figure lb, it will also be seen that in the low pressure zone F, the high pressure system HP2 is inverted with relation to the arrangement shown in zone E. Thus, in Figure lb, the high pressure supply mani-fold 33 is located below the mat in the low pressure sup-ply box and the high pressure exhaust manifold 38 is located above the mat in the low pressure exhaust box.

3~3 In the alternative arrangement of Figure lc, two high pressure circulation systems are shown as mounted with-in a single pair of low pressure boxes. Thus, the high pressure supply manifolds 33a and 33b are located in side-by-side relation with an intervening displaceable sealing wall element such as the sealing elements described above in connection with Figure 3; and the cooperating high pres-sure exhaust manifolds 38a and 38b are mounted within the low pressure exhaust box below the mat, with a displaceable wall element lying between the two high pressure exhaust manifolds of the type described above in connection with Figure 3. Outboard displaceable wall elements are also associated with the manifold systems of Figure lc in the manner which will now be understood.

Although the high pressure air circulation systems contemplated according to the present invention may be em-ployed in association with any of the treatment zones, A
to F, it is particularly advantageous to employ such high pressure circulation systems in association with the low pressure circulation boxes downstream of about the mid region of the feed path and preferably at least 2/3 of the length of the feed path from the entrance end of the oven. Thus, in accordance with one preferred embodiment appearing in Figures la and lb, two high pressure circulation systems are indicated in general at HPl and HP2, these being located respectively within the low pressure zones E and F, being the last two in the embodiment of Figures la and lb.

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3~

Where two high pressure systems are incorporated in a single pair of low pressure boxes, it is preferred to arrange the two high pressure supply manifolds at the same side of the mat, and preferably within the low pres-sure supply box, because this will minimize leakage prob-lems, with consequent loss of heat.

Operating Conditions:

As will be understood, the operating conditions will vary in accordance with a number of factors, including the thickness and density of the mat being formed, the com-position and characteristics of the binder being used, and also the amount of binder employed. However, some general guidelines, with regard to the operating conditions, are presented herebelow.

First, it is contemplated that the low pressure circulation established by the circulation boxes 18 and l9, in the zones A to F inclusive, should include some zones in which the gases pass upwardly through the mat, and some zones in which the gases pass downwardly through the mat.
Also, it is contemplated that the gases circulated through the boxes 18 and l9 in different zones may be at different temperatures, depending upon the characteristics of the mat and the binder used, as is already known in the opera-tion of mat curing ovens having multiple zones of treatment.
An appropriate temperature range for the gas supplied to g.3~3 circulation boxes 18 and 19 is ~rom about 150C to about 300C, when employing common types of fiber binders, such as phenol formaldehyde binders.

The pressure conditions established may also vary, and these pressure conditions may be measured in various ways. The pressure in the supply box and the pressure in the exhaust box will, of course, vary because of the drop in pressure incident to passage of the gas through the mat.
In typical operating conditions, the pressure in the supply box of the low pressure systems may be of the order of from about S to 30mm of water.

With regard to the high pressure circulation sys-tems, it is contemplated that where more than one such system is utilized, for instance, in the configuration illustrated in Figure lb where one high pressure system HPl is located in low pressure zone E and another high pressure system HP2 is located in low pressure zone F, it is contemplated that one of these high pressure systems should be arranged to pass the treatment gas through the mat in one direction and the other high pressure system be arranged to pass the gas through the mat in the opposite direction. Thus, as indicated by the arrow in Figure lb, the high pressure system HPl is shown as delivering the gas downwardly and the high pressure system HP2 is shown by the arrow as delivering the gas upwardly. This will serve to maintain substantial uniformity of the treatment throughout the thickness of the mat.

.. ... . .

With regard to the pressure and temperature em-ployed in the high pressure systems, it is further pointed out that some benefit may be achieved by the employment of both low pressure and high pressure systems in combina-tion in the same curing oven, even if the temperature of the high pressure system is not higher than or even lower than the temperature in the low pressure system. The reason for this is because the high pressure will cause more rapid and effective penetration of the heat to the interior of the mat than is the case with the low pressure system.

The high pressure system may be operated over a substantial range; but in general, should be at least several times preferably at least 10 to 20 times the pre-ssure of the low pressure system. For example, the pressure in the supply manifolds of the high pressure systems may be upwards of about 300 to 600mm of water.

In a typical case where the temperature of the air in the low pressure systems is from about 150C to about 300C, the temperature in the high pressure systems may desirably be from about 200C to about 350C.

~ n a typical installation, the high pressure systems may have a discharge flow of about 5,000 Nm3/h, when the discharge flow of the low pressure circulation system is about 30,000 Nm3/h. The high pressure gases are concentrated in the localized relatively small areas as compared with the low pressure gases, and those localized areas in a typical case may comprise about 10% of the area of the treatment zones established by the low pressure boxes.

: . . .

.3~

The temperatures and pressures will also vary depending upon the speed of advancement of the mat being formed and on the number of treatment zones in the mat cur-ing oven. The use, accordin~ to the invention, of both high and low pressure air circulation systems, is particu-larly effective from several standpoints, including the fact that for given binder curing effect, this may be accom-plished in fewer treatment zones and with a substantially shorter overall length of the curing oven. This is due to the fact that the high pressure systems are particularly effective in bringing the interior portions of the mat up ~`
to curing temperature in a short time. It is also advan-tageous that the high pressure systems will rapidly bring the temperature of the binder to the level where exothermic reaction will occur even in the core portion of the mat;
and this temperature will then be maintained more readily, even beyond the localized area of the high temperature mani-folds. `

Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A method for heat treating a fibrous mat carry-ing a heat hardenable fiber binder in order to harden the fiber binder comprising feeding the fibrous mat in a feed path through a heat treating zone in which the mat is heated to a binder curing temperature, and passing a heated gas through the mat in a localized area extended across the mat in said zone at a temperature and pressure providing for heating of the interior portion of the mat in said local-ized area to a temperature higher than the temperature estab-lished in the interior portion by the heating of the mat in an adjoining region of said zone upstream of said local-ized area.

2. A method as defined in Claim 1 in which the heating of the mat in said adjoining region is effected by passing heating gas through the mat at a pressure lower than that of the gas passed through the mat in said local-ized area.

3. A method as defined in Claim 2 in which the temperature of the heated gas passed through the localized area is from about 150°C to about 350°C and in which the temperature of the heated gas passed through the adjoining region is from about 150°C to about 300°C.

4. A method as defined in Claims 2 or 3 in which the pressure of the heated gas through the mat in said local-ized area is at least several times that of the heated gas passed through said adjoining region.

5. A method as defined in Claims 2 or 3 in which the pressure of the heated gas passed through the mat in said localized area is at least 10 to 20 times that of the heated gas passed through the adjoining region.

6. A method as defined in Claims 2 or 3 in which the pressure of the heated gas passed through the mat in said adjoining region is from 5 to 30 mm of water.

7. A method as defined in Claim 1 in which said localized area is located in the feed path of the mat through the heat treating zone downstream of at least the mid region of said path.

8. A method for heat treating a fibrous mat carry-ing a heat hardenable fiber binder in order to harden the fiber binder comprising feeding the fibrous mat through a heat treating zone in which a first heated gas is passed through the mat from one side face to the opposite side face of the mat, and passing a second heated gas at a pres-sure higher than that of said first gas through a localized area of the mat within said zone, which area is smaller than the total area of said zone.

9. Apparatus for heat treating a fibrous mat carrying a heat hardenable fiber binder comprising conveyor mechanism for advancing the fibrous mat through a feed and treatment path, at least one pair of gas circulation boxes arranged at opposite sides of the mat in said path and defin-ing a region of treatment in which gas is passed through the fibrous mat between circulation boxes at opposite sides of the mat, gas supply and exhaust ducts respectively con-nected with said circulation boxes and providing for pas-sage of heated gas through the fibrous mat in said treatment region, a pair of supply and exhaust gas circulation mani-folds positioned within a pair of said circulation boxes and defining a localized treatment area within and smaller than said treatment region, and located downstream of at least a portion of the treatment region, and heated gas circulating means associated with said manifolds and circu-lating heated gas through the fibrous mat at a pressure higher than that of the gas passed through the fibrous mat between said circulation boxes.

10. Apparatus as defined in Claim 9 in which the conveyor mechanism comprises a pair of perforated endless conveyors having spaced conveyor flights presented toward the fibrous mat to engage and advance or feed the mat through the treatment path, the gas circulation boxes being disposed at the outboard sides of said conveyor flights and having openings presented toward said flights for circulation of heated gas through perforated conveyors and through the fibrous mat between said flights, and further characterized in that said circulation manifolds are defined in part by a wall element lying adjacent to a flight of one of said perforated conveyors, and mounting means providing freedom for displacement of said wall element away from the adjacent conveyor flight.

11. Apparatus as defined in Claim 10 in which the wall element is positioned above the conveyor flight and is displaceable upwardly away from the conveyor flight and is downwardly moveable toward the conveyor flight under the influence of gravity, and stop means limiting downward movement of the wall element toward the adjacent conveyor flight.

12. Apparatus as defined in Claim 10 in which the wall element is positioned below the conveyor flight and is displaceable downwardly away from the conveyor flight, means urging the wall element upwardly toward the conveyor flight, and stop means limiting upward movement of the wall element toward the conveyor flight.

13. Apparatus as defined in Claim 9 in which at least two pairs of gas circulation manifolds are provided defining at least two localized treatment areas each within and smaller than said treatment region, the pairs of mani-folds being spaced from, each other upstream and downstream of the feed path of the fibrous mat.

14. Apparatus as defined in Claim 13 in which the supply manifolds of said pairs are located in the circu-lation box at one side of the feed path and in which the exhaust manifolds are located in the circulation box at the other side of the feed path.

15. Apparatus as defined in Claim 13 in which the supply manifolds of said pairs are located in the sup-ply circulation box at one side of the feed path and in which the exhaust manifolds of said pairs are located in the exhaust circulation box at the other side of the feed path.

16. Apparatus as defined in Claim 9 in which a plurality of pairs of circulation boxes are arranged at opposite sides of the feed path, and in which a plurality of pairs of circulation manifolds are provided, at least one pair of manifolds being positioned in one pair of circu-lation boxes and at least one pair of manifolds being posi-tioned in another pair of circulation boxes.

17. Apparatus as defined in Claim 10 in which the conveyors each comprise a series of interconnected links having reinforcing ribs spaced from each other in a direc-tion paralleling the feed path, and in which the displace-able wall element has a dimension in a direction paralleling the feed path at least twice the gap separating two adjacent reinforcement elements of the conveyor links.