GB1110659A - Process for making fibrous articles - Google Patents

Abstract

1,110,659. Moulding fragmentable structures. HAWLEY PRODUCTS CO. 9 May, 1966, No. 20436/66. Heading B5A. [Also in Divisions D1 and F3] Nose and tail fairings (30, 31) (Fig. 6, not shown), of elliptical shape for aircraft rocket launchers and which fragmentize into small pieces to avoid damage to the aircraft upon launching of rocket, are moulded from a fibrous preform, e.g. of 70% sulphate cellulose fibres, 23% mechanical (shredded wood) and 7% ground wood, with 1À8% of melamine formaldehyde (on the dry fibre weight) to improve the wet strength, which preform is accreted by suction from a slurry on to a porous screen and is then dried under pressure between a preferably movable smooth-faced female die 40 and a preferably fixed male die 50 which is provided with interlacing axially and circumferentially extending grooves 52, 53 into which the fibrous structure of the preform is displaced to form axially and circumferentially extending raised ribs (35, 34) on the interior of the moulding whereby the fibrous structure of the ribs and in the moulding therebeneath is less dense than that of contiguous areas thereof and, when impregnated with a brittle resin, forms regions of a higher resin to fibre ratio which are more brittle and at which fracture occurs upon launching of the rocket. The ribs (34, 35) of 0-09 to 0À12 inch thickness and “ inch width enclose less brittle areas of approximately 2 sq. inches of 0À06 inch thickness. The front portion (A) of the nose fairing (30) may be dip impregnated with brittle phenol or melamine formaldehyde resins from an alcohol or an alcohol-water solvent mixture and the rear portion (B) may be impregnated with a high impact polystyrene in toluene or mixed solvents, a styrene/acrylonitrile/butadiene, or a polymethylmethacrylate resin whereby the fragmentation of the front portion (A) precedes that of the rear portion (B). The phenol or melamine resin dip impregnated fairing is rapidly heated to drive off the solvent and subsequently cured for a longer period in an oven. The polystyrene impregnant is usually applied in two dipping operations followed by air drying. The dies 40 and 50 are preferably heated by hot gases supplied by one or more respective burner nozzles 45, 57 to the rear of the moulding surfaces thereof and the moulding surface 51 of the male die 50 is provided with a plurality of small drain grooves 61 which connect, via an annular recess 62 in the base of the die, to a vacuum space 64. The die flanges 47, 48 are spaced by a brass ring 60. Glass, mica or asbestos fibres may also be employed in the moulded fairing.