US 3363036 A
Description (OCR text may contain errors)
Jan. 9, 1968 w. G. CRAIG METHOD OF FORMING A FIBER MAT Filed Sept. 21, 1965 INVENTOR. WILLIS G. CRAIG ATTORNEY United States Patent Ofiice 3,3fi3,@35 Patented Jan. 9, 1368 3,363,036 METI-IQD F FGRMIN-G A FIBER MAT Willis G. Craig, Willoughby, Ohio, assignor, by mesne assignments, to Koppers Company, Incorporated, Pittsburgh, Pin, a corporation of Delaware Filed Sept. 21, 1965, Ser. No. 489,030 4 Qlairns. (Cl. 264-91) This invention relates to the production of fiber mats, and more particularly to an improved process for the production of mats of low density and'high strength.
Fiber mats impregnated with resinous or bituminous materials are in wide use as roofing elements and the like. It is desirable that the mats to be impregnated have the highest possible strength, but at the same time their density, in terms of weight of fibrous material per unit area, should be as low as possible.
When fibers are matted by deposition on a surface in random arrangement, the strength of the mat is roughly proportional to the degree to which the fibers cross each other. In known methods for making fiber mats, the degree of crossing has been largely a matter of chance, and consequently the mats are subject to wide variation in strength and density.
A principal object of the present invention, therefore, is to produce uniform fiber mats of high strength and low density.
A further object is to provide a method for preparing fiber mats containing a high percentage of crossed fibers.
A further object is to produce improved fibrous mats suitable for impregnation with plastic or bituminous substances.
Other objects will in part be obvious and will in part appear hereinafter.
The present invention constitutes an improvement over methods for the preparation of fiber mats which comprise forming, on a continuously moving, endless mesh belt, a loosely piled mass of fibers less than 8 inches long which are randomly arranged and distributed throughout the mass, and compacting said mass by applying suction thereto from beneath said belt. According to the present invention, the fibers are propelled angularly downward in diverging streams by a plurality of successive gas currents from a fiber source of substantially less width than said belt, said gas currents being directed so as to cause at least one reversal in the horizontal component of the direction of flow of said fibers, whereby fibers are caused to disperse evenly over substantially the entire width of said belt.
The fibers used in the method of this invention may be selected from a wide variety of readily available fibrous materials. Suitable materials include glass, cotton, silk, wool, fortisan, ramie, flax, hemp, rayon, acetate, asbestos, nylon, acrylonitrile polymers and copolymers, polyesters such as polyethylene terephthalate and the like. Of these, glass fibers are preferred because of their economic availability, structural strength and stability. When glass fibers are used, the resulting mats have a glass density of about 0.01-0.05 pound per square foot. In the remainder of this specification, reference will frequently be made to the use of glass fibers; however, it should be understood that other fibrous materials may be substituted therefor.
Short glass fibers are preferred in the method of this invention. In general, the fibers should be less than eight inches long, preferably about 1-6 inches and desirably about 2.5 inches. Methods for chopping fibers into these lengths are known in the art; according to a typicfl method, a continuous glass fiber strand is passed between two rollers revolving in opposite directions, one of which has blades mounted circumferentially thereon at approximately equal intervals.
In the drawings, FIGURE 1 represents a side view of a typical apparatus suitable for carrying out the method of this invention. FIGURE 2 is a top view of the apparatus of FIGURE 1. FIGURE 3 is a side view of a second embodiment of the apparatus of this invention.
Referring to FIGURES l and 2, 1 represents an endless belt of suitable mesh construction (e.g., a chain mesh belt). This belt may be of any suitable width, typically about 30-40 inches. It may travel horizontally but is preferably inclined as shown, the direction of travel thereof being upward. Above the belt is a hopper 3 for supplying chopped fiber strands; the width of this hopper is substantially less than that of belt 1, and is typically about 6-10 inches.
A suitable guide means 5, such as a fishtail chute, is directed angularly downward from hopper 3. This guide means is constructed so as to enable the fibers traveling through it to diverge, until at the point where they con tact belt 1 they cover substantially its entire width. Associated with guide means 5 is a gas jet 7, which provides a high-velocity stream of gas, preferably air, for the purpose of propelling the chopped fibers downward in a diverging stream via guide means 5. A second gas jet 9 is likewise directed divergently downard, but the horizontal component of its flow direction is opposite to that of gas jet 7. Underneath belt 1 is a suction means 11 for applying suction through the belt.
The operation of the apparatus of FIGURE 1 may be described as follows: Belt 1 travels upward at a velocity suitable for the production of a fiber mat of the desired density. Chopped fibers are supplied through hopper 3 and are conveyed angularly and divergently downward by a current of gas from gas jet 7 via guide means 5 to the point of contact with the gas current from gas jet 9. This current reverses the horizontal component of the direction of flow of the fibers and propels them angularly and divergently downward to a point opposite suction means 11. Thence, the fibers are attracted to the belt Where they form a low-density, interlocked mat.
In the embodiment of the invention shown in FIGURE 3, gas jet 9 is associated with a second guide means a whose width increases until at its lower end, it corresponds substantially to the width of belt 1. A third gas jet 1!), located at the opening of guide means 6, is directed downward. The method of use of this apparatus is similar to that of the apparatus of FIGURE 1. The fibers passing through guide means 5 are contacted by gas jet 9 and directed thereby through guide means 6 to the point of contact with gas jet 10, which propels them directly onto the belt at a point opposite suction means 11.
As already stated, the density of glass fiber mats prepared by the method of this invention is usually in the range of about 0.01-0.05 pound per square foot. The velocity of the belt and the gas jet pressures may be adjusted to afford products with the desired density within that range. Similarly, the directions of travel of the fibers between hopper 3 and belt 1 may be varied to suit conditions. Typically, gas jet 7 is directed at about an angle from the vertical, gas jet 9 at about 45, and the gas pressure in each may be about 5075 pounds per square inch.
The reversal of direction of fiber travel in the process of the present invention causes the fibers to attain a highly random configuration as they are deposited on the belt. The result is a large number of crossed fibers, and hence a high mat strength.
Subsequent to their formation, mats made by the process of this invention may be impregnated or bonded with asphalt, synthetic resins or similar materials by a method such as that described in U.S. Patent 2,811,769, for the formation of roofing elements or similar objects.
What is claimed is:
1. In a rnethodfor preparing a fiber mat which comprises forming, on a continuously moving, endless mesh belt, a loosely piled mass of fibers less than 8 inches long which are randomly arranged and distributed throughout the mass, and compacting said mass by applying suction thereto from beneath said belt, the improvement which comprises propelling said fibers angularly downward in diverging streams by a plurality of successive gas currents from a fiber source of substantially less Width than said belt, said gas currents being directed so as to cause at least one reversal in the horizontal components of the direction of flow of said fibers, whereby said fibers are caused to disperse evenly over substantially the entire Width of said belt.
l 2. The method of claim 1 wherein the fibers are glass fibers. I
3. The method of claim 1 wherein the gas is air. 4. The method of claim 1 wherein there is a single 5 reversal in the horizontal component of the direction of flow of said fibers.
References Cited UNITED STATES PATENTS 3/1962 Urbanetti 264-121 3,158,668 11/1964 Johnson 264-121 ROBERT F. WHITE, Primary Examiner.
15 J. R. HALL, Assistant Examiner.