GB1601862A - Apparatus and process for forming a mineral wool fibreboard product - Google Patents

Description

(54) APPARATUS AND PROCESS FOR FORMING A MINERAL WOOL FIBERBOARD PRODUCT (71) We, ARMSTRONG CORK COMPANY, a Corporation organized according to the laws of the Commonwealth of Pennsylvania, United States of America, of Lancaster, Pennsylvania 17604. United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to apparatus and a process for forming a mineral wool fiberboard product from an intimate mixture of mineral wool fibers and a thermosetting powdered binder.

Low-density fiberboard products having excellent acoustical properties are readily available. Generally speaking, air laid products are formed from intimate mixtures of glass fibers and thermosetting resinous binders. However, although slurry board forming processes for manufacturing satisfactory low-density good acoustical fiberboard products from shorter mineral wool fibers are known, such shorter fibers present several problems relative to satisfactory mat and board formation using dry laid systems.

The desirability of having an alternate fiber souce for forming dry laid acoustical boards having good physical and acoustical properties from mixtures of fibers and resinous binder has led to a consideration of utilizing mineral wool fibers, usually produced as a by-product of steel manufacture from slag, as a replacement for the more common longer glass fibers.

It has been noted that the formation of a satisfactory board product from the mineral wool presents difficulties due to short fibers, variability in length, tendency to ball or clump and static build-up in processing. Thus, for forming a dry laid mineral fiberboard product, a special apparatus has had to be devised, and this invention concerns both the design of the special apparatus and the process in which such apparatus is utilized in forming the desired product.

The invention provides apparatus for forming a mineral wool fiberboard product comprising: (a) means for separating mineral wool fibers and means for intimately mixing said fibers with a thermosetting powdered binder, (b) means for entraining said mixture of fibers and binder in an air stream including means for directing said air stream into a mat-forming zone formed by converging upper and lower forming wires or belts, (c) means for exhausting air through said forming wires and arranged so that the fiber and binder mixture is collected as two layers on the forming wires with the two layers becoming consolidated at a nip opening formed between the converging wires, and (d) compacting and heating means for compacting and curing the mat of fibers and resin to form a mineral fiberboard product, The invention also provides a process for forming a mineral wool, resin-bonded acoustical insulating fiberboard product comprising: (a) mixing mineral wool fibers and powdered thermosetting binder, (b) introducing the mixture into an air stream and directing the entrained mixture into a mat-forming zone formed by converging upper and lower forming wires, (c) exhausting air through said wires to build up layers of fiber and binder thereon, and (d) consolidating and heating said layers to cure the resin and form the fiberboard product.

In the preferred process of the invention bales of mineral fibers as received, usually from a steel manufacturer, are broken up and then further subjected to mechanical disintegration operations whereby the individual clumps are further broken down into mixtures of individual fibers. These are then conveyed beneath a feed for a thermosetting powdered binder and fed through further mixing apparatus whereby the fibers and powdered binder are intimately mixed. At this point, the fibers and binder are entrained in an enclosed air stream and carried into the board-forming chamber. The board-forming chamber comprises two driven endless forming wires, the upper wire forming the collection means on which one layer of fibers and binder is deposited, and the lower-forming wire forming the collection means on which a second layer of fibers and binder is deposited. The wires are trained to converge at a nip opening wherein the two layers of fibers and binder are consolidated. Vacuum means are positioned above the upper wire and below the lower wire whereby air is withdrawn from the air stream carrying the fibers and binder, so that fibers and binder are deposited as the upper and lower layers on the forming wires. After exiting from the nip opening formed between the upper and lower wires, the consolidated board-forming mat is passed into an oven sandwiched between lower and upper foraminous driven belts, which engage the board-forming mat to compress it while heated air is passed therethrough to cure the binder material.

After exiting from the oven, finishing operations such as painting and cutting the boards to size may be performed.

Preferably, an open mesh glass fabric is introduced over the lower-forming wire or belt prior to deposition of fibers and resin from the air stream.

A liquid binder may be applied to the glass fabric mat prior to its introduction into the forming chamber to form a better bond between the glass fabric mat and the fibers formed thereover.

Alternatively and preferably, an open weave thermoplastic netting is laid over the glass fabric mat prior to the deposition of fibres and binder thereon, the thermoplastic material of the netting having a melting point below the oven curing temperature required for setting the resin binder so that the thermoplastic melts during curing of the binder and serves to bond the glass fabric mat to the fiber board product. Of thermoplastic materials that can be used there may be mentioned polyethylene and polypropylene. The thermoplastic netting preferably has a weight of between 1/2 and 1 ounce per square yard. The use of the open mesh glass fiber mat results in two advantages, first that it acts as a carrier for the board-forming mat throughout the several stages in the process and secondly that it forms a decorative surface which becomes integrally bonded to the board during the board formation stage.

In forming a mineral fiberboard product from a mixture of mineral wool fibers and powdered binder, it has been found to be desirable to adjust the air flow through the wires in the forming chamber so as to insure that the layer of fibers and resin initially formed on the respective foraminous belts is both resin enriched and comprised predominantly of the finer fibers. By "resin enriched" is meant that the initially formed layers, which eventually form the outer portions of the final board product, contain more resin than the inner portion of the board. This combination of finer and higher resin composition results in a fiberboard product of enhance physical properties.

The invention will now be described in greater detail by way of Example with reference to the drawings in which Figure I shows schematically one form of apparatus for carrying out the process of the invention; and Figure 2 shows schematically a part of a modified form of apparatus.

In the drawings, the large arrows show the direction of fabrication. As shown in Figure 1, at the outset, bales of mineral wool 3 are placed on a conveyor 4 and separated at 5 from where they are conveyed up an inclined conveyor 6 under a flail 7, which is the point of initial separation of the fibers 8. From the top of conveyor 6 the fibers drop onto conveyor 9 and are fed to an inclined pinned feeder conveyor 10. At the top of conveyor 10 the excess fibers are combed by the rotary comb 11 to level the feed and the feed is doffed by roll 12 into a weigh pan 13 which controls the rate of fiber feed.

The fibers are then dropped from pan 13 onto a feeder conveyor 14 which feeds the fibers into the first of two separating devices 15. Separating device 15 consists of a licker in 16, feed rolls 17 and 18, clearer roll 19 and brush 20.

From separating device 15, the fibers drop onto a feeder conveyor 22 and pass under a feed 23 for the powdered thermosetting binder 24. The mixture of fibers and binder then passes through the second separating device 25, which is of the same construction as separating device 15. Here the fibers and resin are intimately and homogeneously blended and substantially all the clumps are separated into individual fibers, although some small clumps may remain.

From separating device 25 the fiber-binder blend drops into the venturi of an enclosed air distribution and forming system including ducts and fan (not shown) for creating a vacuum in the forming chamber. The enclosed duct 26 leading into the evacuated forming chamber 27 is of plexiglass which effectively minimizes static buildup from the separating and mixing operations. Air infeed is supplied through duct 28 and the fibers and binder are entrained in the air stream created between duct 28 and the evacuated forming chamber 27.

The entrained fibers and resin in the air stream in duct 26 pass into the forming chamber 27. This air stream is created by the vacuum established in the enclosed areas behind the upper driven forming wire 30 and lower driven forming wire 31. Fans (not shown) evacuate the air through ducts 32 at the top of forming chamber 27 and ducts 33 at the bottom of forming chamber 27. Means (not shown) control the velocity of the air stream such that the amounts of resin and fiber as well as fiber types can be classified as the fiber-resin mats 35 and 36 are being built up on forming wires 30 and 31.

An open mesh glass fabric 37, which does not impede air flow, is fed from an unwind stand 38 beneath an adhesive applicator 39 and over lower forming wire 31 at a point just prior to the point at which mat buildup starts. Mats 35 and 36 are consolidated onto the fabric 37 and to each other at a nip opening 40 formed by the convergence of forming wires 30 and 31, the adhesive on fabric 37 serving to establish a more firm and integral bond between the fabric and consolidated board forming mat 41. Fabric 37 acts as a carrier throughout the remaining processing steps, which include consolidation in zone 45 and consolidation and cure in oven 46.

A lower driven metal mesh belt 47 and upper driven metal mesh belt 48 convey the fabric and board forming mat into and through oven 46 wherein the thermosetting resincontaining mat is cured under compression to form the acoustical insulating board which is cooled at 49, has paint applied at 50 and is cut to size at cut-off saw 51. Recirculated heated air is supplied to oven 46 through upper ducts 52 and 53 and removed through lower ducts 54 and 55.

The arrangement shown in Figure 2 is identical with that of Figure 1 except as far as the feed of the glass fabric mat 37 is concerned. Instead of adhesive applicator 39 as used in the arrangement of Figure 1 there is provided a porous open mesh thermoplastic netting 62 from a roll 63 on an unwind stand (not shown). Netting 62 is fed round the glass fabric mat 38 and is carried with the glass fabric mat .37 beneath a tensioning roll 60 and over a mounthope roll 61 and, as in the arrangement of Figure 1 pass onto the lower forming wire 31 at a point just prior to the point at which mat building starts.

The following Examples in which "Durez" and "Varcum" are trade marks, illustrate the invention: Example 1 A typical bale of mineral wool has fibers having fiber diameters of from about 1 to 10 microns, with about 84% having diameters between 2.5 and 6.0 microns. The length distribution is as follows: o to 0.25 millimeters 48% 0.25 to 0.50 millimeters 34.5% 0.50 to 0.75 millimeters 10.9% greater than 0.75 millimeters balance Mineral fibers in bales, as received from Bethlehem Steel, are separated and weighed, establishing a feed of fibers into separating device 15 to 29.9 pounds per minute (13.6 kilograms per minute). A powdered thermosetting first-step phenol formaldehyde resole resin (Durez 24652) is fed at 23 onto the fibers on conveyor 22 at a rate of 5.3 pounds per minute (2.4 kilograms per minute) and the fiber and resin are intimately mixed in separating device 25 and fed into the enclosed plexiglass duct 26. The line speed established at these rates of feed is about 75 inches per minute (1.9 meter per minute).

The air entering through duct 28 in which the fibers and resin is entrained is at a velocity of about 4000 cubic feet per minute (113.2 cubic meters per minute). At the entrance to the forming chamber 27, the velocity of the air stream is about 11000 cubic feet per minute (311.4 cubic meters per minute). The velocity of the air passing through the upper forming wire 30 is about 4000 cubic feet per minute (113.3 cubic meters per minute) and through the lower forming wire, about 7000 cubic feet per minute (198.2 cubic meters per minute). The air stream passing into the forming chamber 27 and through the forming wires 30 and 31 acts as a classifier. such that the finger fibers initially build up on the wires with the coarser fibers building up thereover. The two mats of fiber and resin built up on the forming wires are then consolidated into a unitary board forming mat 41 about 52 inches wide at the nip opening 40 formed by the converging forming wires and further consolidated in zone 45.

As discussed hereinbefore, an open mesh glass fabric 37 is drawn off an unwind stand 38, under an adhesive applicator 39 and then over the lower wire screen 31 just prior to fiber-resin buildup. A suitable glass fabric utilized in this example is a J.P. Stevens Style 1635-52"-O-MC weighing 3.95 ounces per square yard. Any open mesh fabric or scrim can be used as long as it does not interfere with air flow during mat buildup and does not deteriorate at the oven temperatures. Thus, some plastic cloths could be used instead of glass cloth or scrim. The adhesive utilized is a polyvinyl acetate homopolymer (Vinac AA65), although other liquid adhesives could be used equally as well, for example a liquid urea-melamine formaldehyde resin (Diaron 96-611).

The consolidated board forming mat with the glass cloth facing layer is then carried through the oven 46 by the driven metal mesh belt 47 and is further consolidated during resin cure by the driven metal mesh belt 48. The oven temperature is about 350"F., although heated air at between 300 and 400"F. could be passed through the board to effect cure, the temperature being related to line speed and board thickness.

After exiting from the oven 46, the board is cooled at 49 by passing cooling air therethrough, back painted at 50 and cut to size at 51.

The above process forms a 2-inch (5.1 centimeter) thick board having a glass fabric facing and a density of about 0.65 pounds per board foot (124 kilograms per cubic meter). As measured by Federal Specification PBS-C.2, it has an 18 to 19 N.I.C. (noise isolation class) and a noise reduction coefficient of about 90.

By raising the velocity of the air through the top wire 30 to 8000 cubic feet per minute (226.5 cubic meters per minute) and by lowering the air velocity through the bottom wire 31 to 3000 cubic feet per minute (84.9 cubic meters per minute), most of the finer fibers are deposited solely on the upper wire, resulting in an improvement in N.I.C. to 20 and in noise reduction coefficient to 95.

The forming wires utilized should have openings large enough to allow free air flow, but fine enough to block passage of resin and fibers. A Fourdrinier wire cloth of 24 x 18 mesh (0.7 millimeter x 0.98 millimeter opening) works well. The size of-the openings of the metal mesh belting is less critical since the board forming mat is formed but must also allow for air passage.

Many powdered thermosetting binders may be used including those extended with thermoplastic resins. Typical powdered binders are the one-step phenol formaldehyde resole resins such as Durez 24652 and 24-655 Varcum and the two-step phenol formaldehyde novalac resin such as 29-574 Varcum.

Example 2 An intimate mixture of mineral wool (as in Example 1) and a powdered thermosetting one-step phenol formaldehyde resole resin (Durez 24652) is fed at a rate of about 29.9 pounds per minute (13.6 kilograms per minute) for the mineral fibers and a rate of 5.3 pounds per minute (2.4 kilograms per minute) for the resin into the enclosed duct 26. The line speed established at these rates of feed is about 75 inches per minute (1.9 meter per minute).

The air entering through duct 28 in which the fibers and resin are entrained is at a velocity of about 4,000 cubic feet per minute (113.2 cubic meters per minute). At the entrance to the forming chamber 27, the velocity of the air stream is about 11,000 cubic feet per minute (311.4 cubic meters per minute). The velocity of the air passing through the upper forming wire 30 is about 4,000 cubic feet per minute (113.3 cubic meters per minute) and through the lower forming wire, about 7,000 cubic feet per minute (198.2 cubic meters per minute (198.2 cubic meters per minute). The air stream passing into the forming chamber 27 and through the forming wires 30 and 31 acts as a classifier, such that the finer fibers initially build up first on the wires with the coarser fibers building up thereover. The two mats of fiber and resin built up on the forming wires are then consolidated into a unitary board forming mat 41 about 52 inches (132 centimeters) wide at the nip opening 40 formed by the converging forming wires and further consolidated in zone 45.

The open mesh glass fabric 37 is drawn off an unwind stand 38 and a thermoplastic extruded film which has been embossed and oriented to give an open mesh porous netting 62 is drawn off unwind stand 63 over the fabric coming off unwind stand 38. The two layers 37 and 62 are led under tension roll 60, over the mount hope roll 61 and then over the lower wire screen 31.

A suitable glass fabric utilized in this example is a J.P. Stevens Style 1635-52"-O-MC weighing 3.95 ounces per square yard. The open mesh thermoplastic netting is a high density polyethylene extruded film which has been embossed and oriented to give porous mesh netting. It is produced by Hercules Incorporated under the trademark Delnet X-230 and weighs .52 ounces (14.7 grams) per square yard. Neither the open mesh glass fabric 37 nor the open mesh thermoplastic netting 62 impedes air flow during mat build-up.

The consolidated board forming mat with the glass cloth and thermoplastic netting facing layer is then carried through the oven 46 by the driven metal mesh belt 47 and is further consolidated during resin cure by the driven metal mesh belt 48. The oven temperature is about 350"F., although heated air at between 300"C and 400"F. could be passed through the board to effect cure, the temperature being related to line speed and board thickness.

During board curing, the thermoplastic open mesh netting melts to form an adhesive layer whereby the open mesh glass fabric facing layer is securely adhered to the board.

After exiting from the oven 46, the board is cooled at 49 by passing cooling air therethrough, back painted at 50 and cut to size at 51.

The above process forms a 2-inch (5.1 centimeter) thick board having a glass fabric facing and a density of about 0.65 pounds per board foot (124 kilograms per cubic meter). As measured by Federal Specification PBS-C.2, it has an 18 to 19 N.I.C. (noise isolation class) and a noise reduction coefficient of about 90.

The N.I.C. of the board can be raised to 20 and its noise reduction coefficient to 95 by raising the velocity of the air through the top wire 30 in the forming chamber to 8,000 cubic feet per minute (226.5 cubic meters per minute) and by lowering the air velocity through the bottom wire 31 to 3,000 cubic feet per minute (84.9 cubic meters per minute).

Hercules Incorporated provide a number of open mesh thermoplastic nettings which are formed of an extruded film, which has been passed through an engraving roll to form openings therein and to orient the film. Most are of high density polyethylene, although some are of polypropylene. It will be obvious to one skilled in the art that any open mesh thermoplastic netting material which will not impede air flow during the board forming operation and which in turn will melt to form an adhesive layer during the cure cycle in the oven would work equally as well. Generally speaking, the mass or weight of the fabric should be between about 1/2 ounce per square yard to 1 ounce per square yard (14.15 grams to 28.3 grams) in order to form an adequate bond without wasting excessive material.

Utilizing a 90" peel test, the peel strength measured for boards produced in accordance with this invention ranged between about 170 to 350 grams with a nominal reading of 250 grams. This compared with a liquid adhesive system, such as that used in Example 1, which only yielded nominal 100 gram peels using the 90" peel test. The 90" peel test measures the weight (in grams) required to cause delamination between the fabric facing and the fiberboard.

WHAT WE CLAIM IS: 1. An apparatus for forming a mineral wool fiberboard product comprising: (a) means for separating mineral wool fibers and means for intimately mixing said fibers with a thermosetting powdered binder, (b) means for entraining said mixture of fibers and binder in an air stream including means for directing said air stream into a mat-forming zone formed by converging upper and lower forming wires, (c) means for exhausting air through said forming wires whereby the fiber and binder mixture is collected as two layers on the forming wires the two layers becoming consolidated at the nip opening formed between the converging wires, and (d) compacting and heating means whereby the mat of fibers and resin is compacted and cured to form a mineral fiberboard product.

2. Apparatus as claimed in claim 1, wherein the air exhaust system behind said wires is adjustable whereby the layer of fibers and binder initially formed on at least the upper of said wires is composed of a layer of binder and predominantly fine fibers.

3. Apparatus as claimed in claim 1 or claim 2, wherein means are provided for positioning an open mesh glass fabric between the lower forming wire and the layer of fibers and resin being formed thereover, said fabric acting as a carrier for the board-forming mat throughout the remainder of the process.

4. Apparatus as claimed in claim 3 wherein means are provided for applying a liquid adhesive onto the glass fiber mat prior to its entry into the forming chamber whereby a bond is attained between the glass fiber mat and the mineral fibers in the board-forming mat.

5. Apparatus as claimed in claim 3, wherein means are provided for applying an open mesh thermoplastic netting over the glass fabric mat to lie between the mat and the fibers to be deposited thereon.

6. Apparatus as claimed in any one of claims 1 to 5, in which the means for directing the fibers and binder into the mat-forming zone is a plexiglass duct.

7. Apparatus as claimed in claim 1 substantially as described herein with reference to and as shown in Figure 1 of the drawings.

8. Apparatus as claimed in claim 1 substantially as described herein with reference to and as shown in Figure 2 of the drawings.

9. A process for forming a mineral wool, resin-bonded acoustical insulating fiberboard product comprising:

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

**WARNING** start of CLMS field may overlap end of DESC **. layer is then carried through the oven 46 by the driven metal mesh belt 47 and is further consolidated during resin cure by the driven metal mesh belt 48. The oven temperature is about 350"F., although heated air at between 300"C and 400"F. could be passed through the board to effect cure, the temperature being related to line speed and board thickness. During board curing, the thermoplastic open mesh netting melts to form an adhesive layer whereby the open mesh glass fabric facing layer is securely adhered to the board. After exiting from the oven 46, the board is cooled at 49 by passing cooling air therethrough, back painted at 50 and cut to size at 51. The above process forms a 2-inch (5.1 centimeter) thick board having a glass fabric facing and a density of about 0.65 pounds per board foot (124 kilograms per cubic meter). As measured by Federal Specification PBS-C.2, it has an 18 to 19 N.I.C. (noise isolation class) and a noise reduction coefficient of about 90. The N.I.C. of the board can be raised to 20 and its noise reduction coefficient to 95 by raising the velocity of the air through the top wire 30 in the forming chamber to 8,000 cubic feet per minute (226.5 cubic meters per minute) and by lowering the air velocity through the bottom wire 31 to 3,000 cubic feet per minute (84.9 cubic meters per minute). Hercules Incorporated provide a number of open mesh thermoplastic nettings which are formed of an extruded film, which has been passed through an engraving roll to form openings therein and to orient the film. Most are of high density polyethylene, although some are of polypropylene. It will be obvious to one skilled in the art that any open mesh thermoplastic netting material which will not impede air flow during the board forming operation and which in turn will melt to form an adhesive layer during the cure cycle in the oven would work equally as well. Generally speaking, the mass or weight of the fabric should be between about 1/2 ounce per square yard to 1 ounce per square yard (14.15 grams to 28.3 grams) in order to form an adequate bond without wasting excessive material. Utilizing a 90" peel test, the peel strength measured for boards produced in accordance with this invention ranged between about 170 to 350 grams with a nominal reading of 250 grams. This compared with a liquid adhesive system, such as that used in Example 1, which only yielded nominal 100 gram peels using the 90" peel test. The 90" peel test measures the weight (in grams) required to cause delamination between the fabric facing and the fiberboard. WHAT WE CLAIM IS:

1. An apparatus for forming a mineral wool fiberboard product comprising: (a) means for separating mineral wool fibers and means for intimately mixing said fibers with a thermosetting powdered binder, (b) means for entraining said mixture of fibers and binder in an air stream including means for directing said air stream into a mat-forming zone formed by converging upper and lower forming wires, (c) means for exhausting air through said forming wires whereby the fiber and binder mixture is collected as two layers on the forming wires the two layers becoming consolidated at the nip opening formed between the converging wires, and (d) compacting and heating means whereby the mat of fibers and resin is compacted and cured to form a mineral fiberboard product.

2. Apparatus as claimed in claim 1, wherein the air exhaust system behind said wires is adjustable whereby the layer of fibers and binder initially formed on at least the upper of said wires is composed of a layer of binder and predominantly fine fibers.

3. Apparatus as claimed in claim 1 or claim 2, wherein means are provided for positioning an open mesh glass fabric between the lower forming wire and the layer of fibers and resin being formed thereover, said fabric acting as a carrier for the board-forming mat throughout the remainder of the process.

4. Apparatus as claimed in claim 3 wherein means are provided for applying a liquid adhesive onto the glass fiber mat prior to its entry into the forming chamber whereby a bond is attained between the glass fiber mat and the mineral fibers in the board-forming mat.

5. Apparatus as claimed in claim 3, wherein means are provided for applying an open mesh thermoplastic netting over the glass fabric mat to lie between the mat and the fibers to be deposited thereon.

6. Apparatus as claimed in any one of claims 1 to 5, in which the means for directing the fibers and binder into the mat-forming zone is a plexiglass duct.

7. Apparatus as claimed in claim 1 substantially as described herein with reference to and as shown in Figure 1 of the drawings.

8. Apparatus as claimed in claim 1 substantially as described herein with reference to and as shown in Figure 2 of the drawings.

9. A process for forming a mineral wool, resin-bonded acoustical insulating fiberboard product comprising:

(a) mixing mineral wool fibers and powdered thermosetting binder, (b) introducing the mixture into an air stream and directing the entrained mixture into a mat-forming zone formed by converging upper and lower forming wires, (c) exhausting air through said wires to build up layers of fiber and binder thereon, and (d) consolidating and heating said layers to form the fiberboard product.

10. A method as claimed in claim 9 wherein the amounts of air exhausted through the forming wires is adjusted so that predominantly all of the fine fibers are preferentially deposited on the upper forming wires.

11. A method as claimed in claim 9 or claim 10, which includes the step of supplying an open mesh fabric over the lower forming wire just prior to the fiber-binder layer build-up, said fabric acting as a facing layer in the final product and a carrier for the board-forming mat during the board formation steps.

12. A method as claimed in claim 11, wherein said open mesh fabric is a glass fabric.

13. A method as claimed in claim 11 or claim 12 wherein an adhesive is applied to the open mesh fabric before the fiber-binder mixture is deposited thereon.

14. A method of manufacturing a dry laid mineral wool resin bonded fiberboard product faced with an open mesh fabric, wherein a mixture of the fibers and binder forming the board product is entrained in an air stream and deposited on two converging wires which form a mat-forming zone, air being exhausted through the wires, and wherein an open mesh fabric is positioned between the lower forming wire and the layer of fibers and resin being formed thereover, with the fabric acting as a carrier which becomes adhered as a facing layer during oven cure, which comprises feeding an open weave thermoplastic netting between the open mesh glass fabric and the fiber and resin layer being formed thereover, said thermoplastic netting being of an open porous structure such that air flow during the forming operation is not impeded, and consolidating and heating to cure the resin, the thermoplastic netting having a melting point below the curing temperature required for setting the resin binder in the resulting mineral fiber board.

15. A method as claimed in claim 14, wherein said thermoplastic netting is polyethylene or polypropylene netting.

16. A method as claimed in claim 14 or claim 15, wherein the weight of the thermoplastic netting is from ounce per. square yard to 1 ounce per square yard.

17. A method as claimed in any one of claims 14 to 16, wherein the open mesh fabric is a glass fabric.

18. A method as claimed in claim 9 conducted substantially as described herein with reference to Figure 1 of the drawings.

19. A method as claimed in claim 14 conducted substantially as described herein with reference to Figure 2 of the drawings.

20. A fiberboard product whenever produced by a process as claimed in any one of claims 9 to 19.