Noise control materials

#This invention relates to noise control and provides novel noise reducing materials which are particularly applicable to the reduction of noise from internal combustion engines.

#According to the present invention, we provide a noise reducing material comprising a laminate including a layer of reinforced thermoplastics material comprising a matrix of low rigidity, i.e., pliant, thermoplastic material reinforced with fibrous material and, bonded to said layer, a layer of metal which has a density of at least 7 gm/cc.

#Although the layer of reinforced thermoplastic material is preferably bonded directly to the metal layer, it may also be separated from the metal layer but bonded to it by at least one other layer which is interposed between and bonded to each of the metal layer and the layer of reinforced thermoplastic material.

#The invention is illustrated in the attached drawings in which

#FIG. 1 is a cross-sectional elevational view not to scale of a rocker box cover (sometimes known as a tappet cover) of an internal combustion engine clad with a laminate according to the invention,

#FIG. 2 is an enlarged cross-sectional view through one of the reinforced thermoplastic layers of the laminate,

#Referring to FIGS. 1 and 2 there is shown a conventional press-stamped sheet metal rocker box cover 2 clad over substantially its entire surface by a laminate 4 which is bonded to the metal cover by a layer of adhesive 6. The laminate comprises a 2 mm thick inner layer 8 of bitumen reinforced with asbestos fiber bonded by means of a layer 10 of a polymeric adhesive to a 0.85 mm thick sheet 12 of lead which in turn is bonded by means of a layer 14 of polymeric adhesive to a 2 mm thick outer layer 16 of bitumen reinforced with asbestos fiber. The external surfaces of the clad cover are coated with a layer 18 of oil resistant paint. The rocker box cover 2 is attached to the cylinder head of the engine in conventional manner by bolts passing through the passages 20.

#Each of the layers 8,16 of bitumen reinforced with asbestos fiber comprises a matrix 30 of bitumen and a plurality of laminae 32 of staple asbestos fibers, there being about four such laminae per mm of thickness of the layer and the fibers of each lamina being randomly oriented in the plane of the lamina.

#FIG. 3 is a diagrammatic representation of a four cylinder diesel engine 40 having a rocker box cover 42, cylinder head 44, cylinder block 46, engine side plates 48, crankcase 50, sump 52 and front plate or timing gear cover 54. The rocker box cover, side plates, sump and front plate are each clad over part or all of their respective surfaces with a laminate 56 having the formulation described with reference to the rocker box cover of FIG. 1.