A thermally expanding laminate contains highly elastic reinforcing fibers, such as glass fibers, in the elastically compressed state, and a thermally softening, thermosetting plastic as a binder. In order to manufacture this laminate, first glass fiber mats are impregnated with a thermosetting plastic and thereupon one or more superposed mats are compressed in a press and raised to temperatures such that the plastic shall soften and the assembly then is cooled while still being compressed and while the plastic is solidifying to form the finished laminate. The expandable laminate preferably is used for electrically insulating spacers. Illustratively a laminate blank 4 is mounted between neighboring coil parts 5 of a stator of an electrical high-voltage machine. In the ensuing vacuum-pressure molding, which is conventional per se, of the stator to complete the soil insulation, the laminate blanks 4 are heated by the hot impregnation-soaking medium, the plastic of the laminate blanks being softened and these blanks then expand on account of the decompression of their compressed fiber material and entirely fill the gaps between the coil parts 5. The soaking medium totally filling the laminate pores then is jointly cured with the plastic of the laminate with the stator insulation.

The present invention relates to a process for forming a composite article in a resin transfer molding system. The process includes the steps of providing a fiber preform in a mold, injecting a matrix resin into the mold, allowing the matrix resin to impregnate the fiber preform, and heating the resin impregnated preform to at least about 200.degree. F. for sufficient time to produce at least a partially cured solid article. The matrix resin comprises 1) a liquid epoxy resin component selected from the group of a phenolic novolac epoxy resin,, a cycloaliphatic epoxy resin and mixtures thereof; 2) an epoxy diluent; and 3) at least one latent curing agent that cures only when subjected a temperature of at least about 200.degree. F. The partially cured solid article may be subjected to post-curing operations to produce a final composite article. The present invention also relates to a process for forming a composite article in a vacuum assisted resin transfer mold system.

A structural connection is obtained between elements (21, 22) of the reinforcement texture to be assembled by using at least one blocking means (23). The latter is made of a fibrous texture that is compacted prior to being inserted in a corresponding lodging formed in at least one of the elements of the reinforcement texture in order to conform with the shape of the lodging. The blocking means (23) then locks itself into the lodging by relaxation of its fibrous texture, as a result of a removal of the prior compacting. The blocking means can be in the form of a dowel (23) inserted inside aligned lodgings formed in the elements (21, 22) of the reinforcement texture to be assembled, or may alternatively be part of one of the elements of reinforcement texture to be assembled.

A composite sheet is made of a moldable resin and reinforcement fibers, where the resin is a thermoplastic resin, thermosetting resin or mixture thereof, and the reinforcement fibers are fibers centrifuged from a rotary process fiberizer, where the composite sheet has at least 5 distinct layers of reinforcement fibers per mm of thickness. The composite sheet has at least 10 distinct layers of reinforcement fibers, and preferably at least 30 distinct layers. At least 85 percent of the reinforcement fibers are monofilaments, and the reinforcement fibers are wool glass fibers.

Polyether-reinforced fiber-based materials, and methods for their manufacture, are disclosed. A representative material is a sheetlike ply having on one or both faces thereof a polyether-impregnated stratum extending depthwise into the ply thickness dimension no greater than about one-half the ply thickness dimension so as to leave a portion of the ply thickness dimension unimpregnated with polyether. The materials can comprise plural superposed plies wherein at least one ply has at least one polyether-impregnated stratum, such as polyether-reinforced corrugated paperboard. The polyether-reinforced materials have excellent compression strength and foldability. Each polyether-reinforced stratum is made by controllably applying a low-viscosity liquid mixture of an epoxy resin and a hardener, wherein the epoxy resin is substantially non-prepolymerized, to a fibrous web surface, then curing the resin mixture. The polyether-reinforced materials can be folded after curing and are useful for making cartons and other products.