Novel brass material presents design challenge

A novel process produces uniform brass filaments for the thermally conductive component of vehicle brake pads to improve heat dissipation.

Fibretech has applied its rapid solidification "melt overflow" process to produce the first "filial brass" - uniform brass filaments for the thermally conductive component of vehicle brake pads to improve heat dissipation.

The melt overflow process, first developed in 1992, has previously been used to spin semicontinuous or, alternatively, discrete, short lengths of other metals and alloys, mainly for reinforcement in a variety of composites or for use in automotive applications such as catalytic exhaust systems for cars and motorcycles.

Peter Rooney of Fibretech explains the elegant simplicity of the process: "Basically we can take metal feedstock and melt it.

The melt is open-topped and has a prominent, accessible lip.

In contact with the reserve of melt is a plunger which advances into the melt, displacing the surface upwards, until the molten charge displays a meniscus at the overflow point.

A large water-cooled drum, spinning rapidly contradirectional to the potentially overflowing melt, is advanced until contact is made with the meniscus, at which point controlled pickup of the molten metal occurs.

The type of product required determines the choice of drum surface.

If semicontinuous filament is to be the product, then the drum surface is machine-turned to create the characteristic of the filaments.

Rapid air-cooling takes place, typically at rates around 50,000K/s, place and thermal contraction causes the, now solid, filaments to self-release.

They fly free from the drum rather like the candyfloss machine at the fair.

An interesting feature of the process, and one often beneficial in heat exchange or binding applications, where surface area is important, is the cross-sectional shape of the filaments.

These are probably best described as a 'kidnoid', being kidney shaped resulting from the molten metal quenching around and against the cooled fins of the drum.

Should short filaments be required the drum has grooves cut at the appropriate position for the size of fibre specified.

In all other respects the technique is the same as for the semicontinuous filaments.

These short filaments have a consistent length and cross section".

Rooney continues: "Some 18 months ago we decided to address the potential market for precisely formed brass fibres to be used in brake-pad applications.

In this application it is important also to remember that the graded brass swarf used to enhance heat-removal from disc brakes consists of nonuniform, random particles.

Obviously this is less than ideal for consistent performance so the uniform fibres produced by the Fibretech process confer a major quality/performance advantage.

Melting copper and zinc in the required ratio in the crucible produces the feedstock for our process in this case.

Depending on the purity of the alloy required, we can start with a choice of recycled, refined or primary metals.

By simply changing the copper/zinc ratio we can easily produce fibres in brass to any European, American or world standard specification.

After some trials we found we could successfully produce either filaments of brass in lengths of approximately one metre, or alternatively short micro-fibres, both of these in diameters from 50 to 300 microns.

At this early stage the full analytical data on the properties of these fibres is not yet available, however we have initiated a formal research programme at Cambridge University (with the Materials Science and Metallurgy Group headed by Professor Bill Clyne) investigating the joining and sintering of these novel materials.

In the case of brake pads, trials are in progress, with considerable interest being shown in Fibretech's unique ability to produce a wide variety of copper alloys including lead-free brass.

Meanwhile we are seeking, via Copper Development Association and other dissemination media, to popularise the material and find new applications".

Copper Development Association Consultant Ken Kempson has a broad appreciation of material and manufacturing techniques.

Kempson's reaction to the new material was enthusiastic, stating: "The unique Fibretech process itself has been a source of interest to me since its inception and it was no surprise to find that the brasses can form good fibres by this method.

I can see that new markets may develop for this novel form of brass since designers and engineers now have the potential to find applications for short and semicontinuous filaments and this could represent something of a culture shock with exciting future possibilities.

The Fibretech system offers a simple method of producing fibres of a consistent length and cross section in any brass alloy.

It is a one-stage process that eliminates the need for any subsequent hot or cold working processes.

To my knowledge there does not exist an alternative technology to the melt overflow method of forming these copper zinc filaments; it therefore creates a totally original brass product and represents an important break-through in cupro-technology.

A further stimulating thought results from considering the aesthetics of the filaments.

Without any post-processing they look, for all the world, like spun gold.

There must be many major decorative and architectural outlets for the product.

Fibretech are to be congratulated for bringing such a product onto the market.

I think we have a significant 'watch-this-space' situation ahead".

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