Method of forming discrete length fibers

#This invention relates to a method of forming discrete length fibers, and in particular to a method of forming discrete length reinforcement fibers suitable for use in reinforcement mats, reinforcement preforms, and other types of reinforcement structures.

#Discrete length reinforcement fibers are useful in the manufacture of many different types of reinforcement structures. For example, the fibers can be used in reinforcement mats for reinforcing articles such as roofing shingles. The reinforcement mats can be made with a single type of fiber, with commingled fibers of different types (e.g., carbon fibers and thermoplastic fibers), or with layers of different types of fibers.

#The discrete length reinforcement fibers can also be used in reinforcement preforms. Structural composites and other reinforced molded articles are commonly made by resin transfer molding or structural resin injection molding. These molding processes have been made more efficient by first creating a reinforcement fiber preform that is the approximate shape and size of the molded article, inserting the preform into the mold, and injecting the resin into the mold around the preform.

#FIG. 1 is a perspective view illustrating the dispensing of discrete length fibers that are formed according to the method of the invention.

#FIG. 2 is a side view showing a mechanism for feeding continuous fibers, a cross-section of a cutting assembly useful for cutting the continuous fibers to form discrete length fibers according to the method of the invention, and a cross-section of a nozzle for dispensing the discrete length fibers.

#FIG. 3 is a perspective view of a portion of thc cutting assembly of FIG. 2, showing multiple rotary cutters moving in orbit along an inner circumference of a ring to cut continuous fibers into discrete length fibers.

#Referring to the drawings, FIG. 1 illustrates an apparatus 10 for forming and dispensing discrete length fibers 12 according to the method of the invention. A cutting assembly (not shown in FIG. 1) for forming the discrete length fibers is mounted inside a housing 14 attached to the end of a robot arm 16. The robot arm is positioned to deposit the discrete length fibers onto a collection surface 18, such as a preform molding surface. The robot arm can be provided with a hydraulic system (not shown) or other similar system to enable the arm to be positioned adjacent or above any portion of the collection surface. The movement of the arm can be controlled by a computer (not shown) according to a predetermined pattern so that a desired pattern of discrete length fibers is laid down on the collection surface. The arm need not be robotized or automated, and could even be stationary with the collection surface being moveable.

#The cutting assembly 20 illustrated in FIGS. 2 and 3 is an example of an apparatus useful for forming discrete length fibers 12 according to the method of the invention. In a first step of the method, a first engagement member is moved in orbit relative to a second engagement member. The term “a first engagement member” means one or more first engagement members, and the term “a second engagement member” means one or more second engagement members. The first and second engagement members are any structures capable of cooperating with each other to engage the continuous fiber and thereby cut it into discrete length fibers.

#Preferably, one of the first and second engagement members is a cutter, and the other of the first and second engagement members is a ring. The cutter can be any type capable of cutting the continuous fiber into discrete length fibers. Preferably, the cutter is a rotary cutter including a curved cutting blade. In the embodiment shown in FIGS. 2 and 3, the first engagement members of the cutting assembly are three rotary cutters 22 having circular cutting blades 24. The cutting blades are preferably formed of a metallic material or a hard polymeric material.