IE47077B1 - Heat treatment of fibrous mats - Google Patents

Abstract

1. Apparatus for heat treating a fibrous mat carrying a heat hardenable fiber binder comprising conveyor mechanism for advancing the fibrous mat through a treatment path, gas circulation boxes arranged at opposite sides of the mat in said path and defining a zone of thermal treatment, 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 zone, characterized in that it comprises in the downstream part of the treatment zone a pair of supply (33) and exhaust (38) gas circulation manifolds positioned within the circulation boxes (18, 19) and defining a localized treatment area within and smaller than said treatment zone, and heated gas circulating means associated with said manifolds and circulating heated gas through the fibrous mat at a pressure higher than that of the gas passed through the fibrous mat from one circulation box to another one.

Description

METHOD AND APPARATUS FOR HEAT TREATMENT OF FIBROUS MATS Abstract of the Disclosure; 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 treatment 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.

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 •4 7 0 7 7 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 delivered to what is commonly referred to as a mat curing oven through which the mat is fed by additional perforated conveyor means, frequently comprising a pair of endless conveyors 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.

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 7 ϋ 7 7 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 cora5 monly including several such pairs of circulation boxes, with provision for establishing different temperature conditions 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 invention contemplates employment of a second independent heating system comprising at least one pair of manifolds of relatively 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 surface 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 5θ without disrupting the fibers of the mat. -44 7 0 7 7 Although the arrangement of the invention is adaptable to the curing of a wide variety of mats and fibrous blankets, for reasons noted just above, the invention is especially advantageous in the curing of binder in relatively 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 beat 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 localized area have a pressure higher than that of the air employed in the primary system. When employed in this configuration, the primary air circulation system serves not only 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. 7 0 7 7 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 expediting 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 reac10 tion of the binder resin. The attainment of such an exother mic temperature will result in continuance of the binder curing, 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.

It is a further object of the invention to provide novel structural arrangements for introducing the high pres20 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 shortcircuiting 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. 7 077 The present invention provides apparatus for heat treating a fibrous mat carrying a heat hardenable fiber binder comprising a conveyor mechanism for advancing the fibrous mat through a treatment path, gas circulation boxes arranged at opposite sides of the mat in said path and defining a zone of thermal treatment, 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 zone, the apparatus having in the downstream part of the treatment zone a pair of supply and exhaust gas circulation manifolds positioned within the circulation boxes and defining a localized treatment area within and smaller than said treatment zone, and heated gas circulating means associated with said manifolds and circulating heated gas through the fibrous mat at a pressure higher than that of the gas passed through the fibrous mat from one circulation box to another one.

Advantageously, the conveyor mechanism comprises a pair of perforated endless conveyors having spaced conveyor flights presented toward the fibrous mat to engage and advance 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 the perforated conveyors and through the fibrous mat between said flights, said circulation manifolds 7 0 7 7 being defined in part by a Wall element lying close to a flight of a perforated conveyor, and mounting means providing freedom for displacement of the wall element away from the conveyor flight.

Preferably, the wall element, positioned above the conveyor flight, is displaceable upwardly away from the conveyor flight and is downwardly moveable toward the conveyor flight under the influence of gravity, while stop means limit the downward movement of the wall element toward the conveyor flight.

Conveniently, the wall element positioned below the conveyor flight is displaceable downwardly away from the conveyor flight, means urging the wall element upwardly towards the conveyor flight, and stop means limiting upward movement of the wall element toward the conveyor flight. ! Advantageously, the apparatus comprises at least two pairs of gas circulation manifolds defining at least two localized treatment areas each within but smaller than said treatment zone, the pairs of manifolds being spaced from each other in the upstream and downstream directions of the feed path of the fibrous mat. 7 0 7 7 Briet Description of Drawings: How the foregoing and other objects and advantages are attained will appear more fully from the following description referring to the accompanying drawings, in which 5 Figures la and lb, taken together, illustrate a 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; 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.

As seen in Figures la and lb, in the lower portion 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 Figures 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 10a and 10b 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 transverse ribs..

Conveyors of this type are driven through the mounting rollers. 4 7 0 7 7 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 nvention per se.

By virtue of the adjustability of the upper conveyor, the space between the conveyor flights 8a and 10a, 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 conveyor, 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 R1-R2, which are preferably adjustable in order to regulate the thickness of the mat being introduced into the oven; and after delivery of the partially sized mat from the rolls R1-R2, the mat enters between the conveyor flights in the curing oven.

Interiorly of the oven, the primary or low pressure 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 10a. 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 adjustable framing 14 for the upper conveyor, so that the upper boxes move with the upper conveyor when its position is adjusted.

Each box is also provided with an opening communicating 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 respectively marked with plus and minus symbols - + or It will be noted that in the first pair of boxes A, tbe 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 i 7 0 7 7 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. Xn 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 densities, 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 fact 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 interior of the oven into and through an appropriate precipitator 23 for separation of suspended solids. The oven walls 6, in effect, comprise a hood surrounding the interior components of the oven including the heated gas circulation boxes and manifolds; and the leakage which occurs is withdrawn 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 connected with the upper or supply box 19 and that the exhaust duct 25 is connected with the lower exhaust circulation box 18. Vanes 19a 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 28 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 pressure boxes, or if desired, separate circulation systems ]_5 may be used.

To accommodate vertical motion of the upper conveyor 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 sub20 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 adjustment.

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 pivot ed to 7 0 7 7 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 for 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 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 HP1 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 indicated 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 10a, 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 4‘?o77 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 width of the conveyor. A high pressure exhaust manifold 38 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 recir15 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 25 form of heater which may be employed for heating the high pressure gases in the circulation system. Here, 7 0 7 7 a heat transfer device, 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 pressure 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 bt seen that at each side of the upper or supply manifold 33, a «upporting -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 element may be swung or displaced upwardly away from the upper surface of the conveyor flight 10a. 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 10a. Each of these wall elements 45 is of trough-like configuration, being extended across the entire width of the conveyor; end 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 10a, thereby providing sealing action preventing 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 10a a distance of the order of a few millimeters, for instance, from about 3 to 5mm.

These displaceable sealing wall elements are provided so that the sealing elements may be normally posi10 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 accumulation on the conveyor of irregular deposits of resin or fibers, as tends to occur from time 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 eguipment 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, function automatically under the action of gravity to return to 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 trough25 shaped elements 45 is preferably at least as great as any two adjacent passages through the conveyor rl b«, so that the desired sealing function will be performed, regardless 4-7 0 7 7 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 associated with the flight 8a of the lower conveyor, these wall elements 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 elements 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 thei. normal operating position.

Each of the wall elements 45,45 and 48,48 is provided 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 HP1, the supply manifold 33 is located above the conveyor and in the low pressure circulation box with which the low pressure gas supply connection communicates, the discharge manifold of this high pressure system being located in the discharge box of this low pressure system. 7 0 7 7 By reference to Figure lb, it will else, be seen that in the low pressure 2one 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 mani5 fold 33 is located below the mat in the low pressure supply box and the high pressure exhaust manifold 38 is located above the mat in the low pressure exhaust box.

In the alternative arrangement of Figure lc, two high pressure circulation systems are shown as mounted with10 in a single pair of low pressure boxes. Thus, the high pressure supply manifolds 33a and 33b are located in sideby-side relation with an intervening displaceable sealing wall element such as t}ie sealing elements-described above in connection with_Figure 3; and the cooperating high pres15 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 employed 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 -20Λ-70 7 7 pressure circulation boxes downstream of about the mid region of tn^ 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 HP1 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.

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 pressure supply box, because this will minimize leakage problems, 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 composition 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 IB and 19, 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 19 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 operation of mat curing ovens having multiple zones of treatment. An appropriate temperature range for the gas supplied to circulation boxes 18 and 19 is from about 15°*θ to about JOO’C 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 mit.

In typical operating conditions, the pressure in the supply box of the low pressure systems may be of the order of from about 5 to '30mm of water.

With regard to the high pressure circulation systems, 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 HP1 is located in low pressure zone E and another high pressure system BP2 is located in low pressure zone F, it is contemplated that one of these high pressure systems should be arranged to pess the treatment gas through the mat in one direction and the other high pressure system be arranged to pass the -22A7077 gas through the mat in the opposite direction. Thus, as indicated by the arrow in Figure lb, the high pressure system HP1 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 employed 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 combination in the same curing oven, even if the temperature of the high pressure system is not higher than or even lewer 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 pressure of the low pressure system. For example, the pressure in the supply manifolds if the high pressure systems may be upwards of about 300 to 600 mm of water.

In a typical case where the temperature of the air in the low pressure systems is from about 150C to about JOO’C the temperature in the high pressure systems may desirably be from about 200*C to about 35O*C . -2347 U 7 7 In a typical installation, the total of the gases employed in the low pressure circulation systems may be about 30,000 Nm^/h. in such a typical case, the high pressure systems may use heated gas in an amount about 5,000 Nm^/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.

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 curing oven. The use, according to the invention, of both high and low pressure air circulation systems, is particu15 larly effective from several standpoints, including the fact that for given binder curing effect, this may be accomplished 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 advantageous 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 manifolds.

Claims (10)

1. CLAIMS:1. Apparatus for heat treating a fibrous mat carrying a heat hardenable fiber binder comprising a conveyor mechanism for advancing the fibrous mat through a treatment path, gas circulation boxes 5 arranged at opposite sides of the mat in said path and defining a zone of thermal treatment, 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 zone, the apparatus having in the downstream part of the treatment zone a 10 pair of supply and exhaust gas circulation manifolds positioned within the circulation boxes and defining a localized treatment area within and smaller than said treatment zone, and heated gas circulating means associated with said manifolds and circulating heated gas through the fibrous mat at a pressure higher than that of the gas passed through 15 the fibrous mat from one circulation box to another one.

2. Apparatus as defined in Claim 1, 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 the mat through the treatment path, the gas circulation 20 boxes being disposed at the outboard sides of said conveyor flights and having openings presented toward said flights for circulation of heated gas through the perforated conveyors and through tne fibrous mat between said flignts, said circulation manifolds being oefined in part by a wall element lying close to a flight of a perforated 25 conveyor, and mounting means providing freedom for displacement of the wall element away from the conveyor flight. -254-7077

3. Apparatus as defined in Claim 2,in which the wall element, positioned above the conveyor flight,is displaceable upwardly away from the conveyor flight and is downwardly moveable toward the conveyor flight under the influence of gravity, while stop means limit the downward 5 movement of the wall element toward the conveyor flight.

4. Apparatus as defined in Claim 2,in which the wall element positioned below the conveyor flight is displaceable downwardly away from the conveyor flight, means urging the wall element upwardly towards the conveyor flight, and stop means limiting upward movement of the wall 10 element toward the conveyor flight.

5. Apparatus as defined in Claim 1, which comprises at least two pairs of gas circulation manifolds defining at least two localized treatment areas each within but smaller than said treatment zone, the pairs of manifolds being spaced from each other in the upstream and 15 downstream directions of the feed path of the fibrous mat.

6. Apparatus as defined in Claim 5,in which the supply manifolds of said pairs are located in the circulation box at one side of the feed path and the outlet manifolds are located in the circulation box at the other side of the feed path. 20

7. Apparatus as defined in Claim 5,in which the supply manifolds of said pairs are located in the supply circulation box at one side of the feed path and the exhaust manifolds of said pairs are located in the exhaust circulation box at the other side of the feed path.

8. Apparatus as defined in Claim 1, which comprises a plurality 25 of pairs of circulation boxes arranged at opposite sides of the feed path, and a plurality of pairs of circulation manifolds r at least one pair of -2617077 manifolds being positioned in one pair of circulation boxes and at least one pair of manifolds being positioned in another pair of circulation boxes

9. Apparatus as defined in Claim 2,in which the displaceable wall element has a dimension in a direction parallelling the feed path at least twice as great as the spacing between two projecting ribs of the links of the conveyor.

10. Apparatus for heat treating a fibrous mat, substantially as herein described with reference to the accompanying drawings.