MATERIALS AND MOLDING METHODS 



4-5 



they are somewhat more open in structure, Fig. 4-4. As a result, these fabrics are much 

 easier to wet out. Strengths tend to be more isotropic than either woven roving or fiber- 

 glass cloths. Interlaminar shear strengths are improved. Limited test data indicates that 

 these spun roving products are intermediate in their properties between standard chopped 

 strand mats and woven rovings. Thickness per ply, using the contact or hand lay up mold- 

 ing method, are greater per unit of weight than woven roving, and are somewhat less than 

 equivalent weight mat laminates. 



Mat, Preforms and Chopped Strands 



Mat: Consists of chopped strands of fiberglass, Fig. 4-5 randomly deposited, to form 

 a sheet or layer. The layer of chopped strands is usually bonded or held together by a high 

 solubility resin binder, compatible with molding resins, Fig. 4-6. Another type of mat 

 does not use a binder, but is made from rando'm strands of glass stitched together into a 

 layer. During manufacture, needles are driven through the mat causing some of the glass 

 strands to act as stitching. 



Random fiberglass mat reinforcement is more economical than both woven roving and 

 cloth reinforcements. Mats are available in weights of 3/4 ounce to 3 ounce per square 

 foot. The 1-1/2 ounce and 2 ounce weights are the most suitable for boat hull construction 

 since maximum economical build-up can be achieved with required conformity to hull forms 

 and ease of material handling. 



The advantages of mat reinforcement are: 



Low cost per square foot and thickness. 



Equal physical properties in all directions. 



Good interlaminar bond due to interlocking action of fibers. 



Can be molded or formed into moderate complex surfaces. 



Fig. 4-5. Chopped Strands 



Fig. 4-6. Mat - Resin Bonded 



