Apparatus and method for making preforms in mold

Abstract

Apparatus and a method of preparing fiber preforms disperses fibers and binder on a forming support surface such that the materials are conditioned and then applied to the surface where the composite material solidifies. Reinforcing material, such as fiber, is mixed with binder, such as thermoplastic or thermoset materials, so that the materials adhere. Then, the adhesive mixture is dispersed in a controlled pre-determined weight ratio on the support surface where the mixture sticks to the support surface, cools and solidifies. The deposited mixture can be an open mat having interstices between fibers. The deposited mixture can also be shaped further into a final desired shape before complete solidification. This method eliminates the need for solvents and their associated problems. The process does not require a vacuum or plenum system to hold the reinforcing material in place. The preform can be made in any shape, including sections or asymmetric configurations and remain in mold while being processed to a composite molded article.

Description

FIELD OF THE INVENTION [0001] This invention relates to an apparatus and a method of making a preform, particularly for use in composite molded articles, and also composite molded articles. The apparatus and the method especially relate to making a structural preform for use with polymeric materials. BACKGROUND OF THE INVENTION [0002] High strength polymeric materials are being increasingly used to replace traditional structural materials, such as metal, in many applications. The polymeric materials have the advantage of lower weight and are often less expensive and more durable than metals. However, polymeric materials tend to be much lower in strength than metal. Unless polymeric materials are reinforced in some manner, they often do not meet the strength requirements for metal replacement. [0003] Thus, polymeric composites have been developed to meet such strength requirements. These composites are characterized by having a continuous polymeric matrix within which is embedded a r...

AI Technical Summary

Benefits of technology

[0014] An aspect of this invention provides an apparatus and a method in which a high strength structural preform and composite molded article can be made efficiently and at a lower cost.

[0017] An additional aspect of this invention provides an apparatus and a method that uses less components and thus reduces the capital entry and operational production costs.

[0018] This invention can be easily adapted to automated production and / or control.

Problems solved by technology

However, polymeric materials tend to be much lower in strength than metal.

Unless polymeric materials are reinforced in some manner, they often do not meet the strength requirements for metal replacement.

Otherwise, the composite will have weak spots where the reinforcement is lacking.

In addition, the individual fibers should be held in place to resist flowing with the molding resin as it enters the mold, which would disrupt the fiber distribution.

This means that the application of binder is at least a two-step process, which is not desirable from an economic standpoint.

Also, the use of solvents is encountered, which raises environmental, exposure and recovery issues.

Dealing with these issues potentially adds significantly to the expense of the process.

The procedure is also energy intensive, as the entire mat must be heated just to flash off solvent and cure the binder.

The curing step also makes the process take longer.

Use of the solvent-borne polymer binders is extremely messy.

There are also high maintenance costs associated with keeping the work area and the screen on which the mat is formed clean.

When a composite article is then prepared from a preform made in this way, the binder often interferes with the adhesion between the fibers and the continuous polymer phase, to the detriment of the physical properties of the final composite.

However, simply substituting a powdered binder in an air-directed method raises problems.

For example, powdered binders cannot be applied unless a veil is first applied to the screen to prevent the binder particles from being sucked through.

Again, this adds to the overall cost and adds a step to the process.

Airborne powders may also present a health and explosion hazard, depending on conditions of use.

Heating renders this process energy-intensive.

This method has problems with “lofting,” or inadequate compaction of the preform.

Lofting typically occurs because the thermoplastics are conventionally heated to any random temperature above their melting points, leading to a lack of uniformity in their cooling patterns and extensive migration along fiber surfaces.

This may result in formation of a lower density preform than desired, density gradients throughout the preform, and poor adhesion of the fibers to each other.

However, the application of the vacuum requires additional equipment in the form of a plenum arrangement and also requires additional control functions and labor to properly apply the fibers and vacuum.

Therefore, the material and operating costs are increased.

Images