Metallic Fibres

8/3/2019 Metallic Fibres

1/28

METALLIC FIBRES


2/28

INTRODUCTION Metallic yarns or threads, have been known for more than

3000 years

Gold and silver were hammered into extremely thin sheets,then cut into ribbons and worked into fabrics.

The metal threads were twisted, doubled or wrappedaround

some other thread such as cotton. With the advancement of technology, metal/conductivetextiles found extensive functional applications.

These materials have high electrical conductivity and radarreflecting property, yet are lightweight and flexible.

Various methods have been developed to coat fibers andtextile materials by metals.

sputter coating coating metal powder with binders electro less coating

vacuum deposition


3/28

Many technical applications demand properties which cannot

be obtained by simply processing common textile material

into single textile fabric.

A manufactured fibres composed of metal, plastic-coatedmetal, metal-coated plastic, or a core completely covered bymetal.

Thus, metallic fibres are fibres produced from metals, which

may be alone or in conjunction with other substances. These metal filaments were made by beating soft metals and

alloys, such as gold, silver, copper and bronze, into thin

sheets, and then cutting the sheets into narrow ribbon-like

filaments. The filaments were used entirely for decorative purposes,

providing a glitter and sparkle that could not be achieved by

other purposes.


4/28

Expensive to produce and inflexible and stiff ribbon-like cross-

section provided cutting edges that made for a harsh, rough

handle; they were troublesome to knit or weave, and they had

only a limited resistance to abrasion. The development of modern techniques of surface-protection

has brought cheaper metals into use; aluminium foil.

for example, may be anodized and dyed before being slit

into filaments which are colorful and corrosion-resistant. It is used as a decorative material.

The filaments are weak and inextensible, and are easily

broken during wear; they lack the flexibility that is essential in a

genuine textile fiber.


5/28

TYPES OF METALLIC (M.C.) FIBRE

Aluminium is, however, the metal most commonly selected,and it is sandwiched between cellulose acetate butyrate,

cellophane (cellulose) or polyester films. The following are the types of yarn commonly produced:

(1) Acetate Butyrate, Aluminium Foil:

A continuous flat monofilament composed of aluminium foillaminated on both reflective surfaces with cellulose acetatebutyrate film.

(2) Cellophane Aluminium Foil:

A continuous flat monofilament composed of aluminium foillaminated on both reflective surfaces with Cellophane film.

(3)Polyester, Aluminium Foil:

A continuous flat monofilament composed of Aluminium foillaminated on both reflective surfaces with polyester film.


6/28

(4) Polyester, Aluminum Metallized Polyester:A continuous flat monofilament composed of aluminiummetallized polyester laminated on its metallized surface or

surfaces with

polyester film.(5) Polyester, Aluminium Metallized, Non- Laminated:

A continuous, flat monofilament composed of a single layerof aluminium metallized polyester protected on its metallized

surface. Metal fibres are defined as fibres composed of metals,plastic coated metals or metal-coated plastics. Single component metallic fibres are fine drawn metalfilaments. These fibres are mostly used as reinforcing elements incomposite materials. For this, the fiber should have high modulus and tenacity,better thermal expansion co-efficient, resistance to solvents

and comparatively lower density.


7/28

The filaments are generally fabricated by one of the following

techniques: Those are

(a) wire-drawing technique,

(b) melt-forming technique,(c) Powder metallurgical process and

(d) Vapour deposition method.

WIRE-DRAWING Wire-drawing method is very well known and common.

Encasing the sheath or core wire with a matrix. The matrixmay be plastic, glass or ceramic.

The matrix imbedded wires are heated to a temperature, tosoften or melt the metal core. Simultaneously the sheathmaterial is also softened.

Drawing the wire at high temperature.


8/28

Melt-Forming Technique

Similar to the principle of melt spinning. Because of low viscosity at high temperature, as soon as the

molten filament comes out of the spinnerette, it breaks into

separate droplets.

However, it can be extruded and processed by a modifiedtechnique. The principle of the technique is as follows:

(i) Melting of the metal in a furnace.

(ii) Solidification of the molten metals immediately after

extrusion by means of a chill block or chill wheel. Instantaneous solidification takes place by surface contact of

the molten metal with the chilled surface.

The chill roll melt spinning technology is very common forthe production of metal fibres.


9/28

POWDER METALLURGICAL METHOD

By this method, metal powders are mixedwith binders and extruded at Hightemperature.

The extruded material is further processedfor compactness.


10/28

VAPOUR DEPOSITION METHOD

According to this method a heated core in filament form

E.g., a tungsten wire is continuously drawn through a sealeddeposition chamber.

A vaporized reactant is introduced in the chamber, which isdecomposed and deposited on the core to produce acomposite filament.

This is generally done by pyrolysis of boron halide on aheated tungsten wire at 1500C

The filaments thus formed is chemically treated by orthermally post treated to remove surface defects. Thechemical post treatment consists of etching by somechemicals and the thermal post treatment is done to removeresidual stresses.

Some of the metal fibres commonly used for composites are:Steel, bronze, alumina, boron, tungsten, copper-tin alloy,

nickel-aluminium alloy.


11/28

Manufacturing of Metallic Yarn

Extrusion and Metal coating

Metal coating with a binder

Vacuum Deposition. Sputter coating

Electroless Plating


12/28

Extrusion and metal coating Used for decorative purpose.

The tinsel yarns used to add glitter to fabrics were madeby flattening thin wire or sheets of noble metals like gold orsilver.

The aluminium foil strips coated on both sides by celluloseacetate-butyrate, to prevent them from tarnishing, wereused.

All of these yarns had poor compatibility with the moreflexible and extensible textile yarns.

The metal foil, metalized pigment and colouring matter

might be considered the meat.The meat is placed between two layers of transparentplastic film.

The adhesive used between layers to bind all the layers

together into one film might be compared to thebutter that holds the bread and meat together.


13/28

The raw material is a roll of aluminium foil of 0.00045 inchthickness and 20 inch wide.

To both sides of the sheet is applied a thermoplasticadhesive to which has already been added the requiredcolouring matters.

The adhesive-coated foil is heated to about 90-95C, and a

sheet of cellulose acetate-butyrate transparent film islaminated to each side of the foil by passing through squeezerollers at a pressure of 2000 lb/in.


14/28

The laminated material is then slit into filaments of therequired width, the most popular width being 1/64 inchalthough other sizes from 118 inch to 1/120 inch are also

made.


15/28

Gold is the most important colour which is produced by theaddition of an orange-yellow dyestuff to the adhesive.

Silver is simply the colour of the aluminium itself. Other

colours such as bronze, peacock blue and red are obtained byusing the suitable pigment.


16/28

Metal coating with a binder

High leafing aluminium pastes (65-70%) areincorporated into a polymeric carrier, likesynthetic rubber, PVC, polyurethanes, silicones,acrylic emulsions, etc., and spread coated on the

fabric. The coating method may be conventional knife

or roller coating.

The adhesion, flex, and chemical resistance of

the coated fabric depend on the type of polymerused, but they are not highly reflective.


17/28

Vacuum deposition In this process, the substrate to be coated is placed

in a chamber over a set of crucibles containing themetal to be coated in the form of a powder/wire.

The chamber containing the whole assembly isevacuated to 0.5-1 torr.

The crucible is heated by resistance heating to meltthe metal.

The temperature of heating is so adjusted that thevapour pressure of the metal exceeds that of thechamber pressure, so that substantial evaporation ofthe metal takes place.

The temperature required for aluminium is about

1200C.


18/28

The production speed is quite high, ranging from150-500 m/min.

The items to be coated should be pretreated forproper adhesion of the metal.

Continuous metal film coatings can be formed onjust about any surface, film, fiber or fabric with

thickness ranging from micron to millimeter. Several metals can be vacuum evaporated, most

common being aluminium, copper, silver, and gold.

Difficulty arises in the case of metals, whichsublime rather than melt and boil.


19/28

Sputter coating The equipment consists of a vacuum chamber

containing an inert gas, usually argon, at 10-3 to 10-1

torr. The chamber is equipped with a cathode (target),

which is the source of the coating material, and ananode, which acts as a substrate holder.

The argon ions are accelerated toward the cathode ata high speed due to high electric potential.

If the kinetic energy of the striking ion is higher thanthe binding energy of the surface atoms of thematerial of the target, atoms are dislodged orsputtered from its surface by a cascade of collisions.

Typically, the threshold kinetic energy of the ionsshould be between 10-30 EV for sputtering from thesurface.


20/28

Considerable heat is generated during thesputtering process, and it is necessary to cool thetarget.

The sputtered atoms and ions condense on thesubstrate to form a thin film of coating.

The relative rates of deposition depend on sputter

yield, which is the number of atoms ejected perincident ion.

The method is applicable to a wide range ofmaterials and gives more uniform coating withbetter adhesion than simple vapour deposition.

The process is however, more expensive, and therate of deposition is lower (30 m/min)


21/28


22/28

Electroless plating

It is a process to deposit metal film on a surface,without the use of electrical energy.

Unlike electroplating where externally suppliedelectrons act as reducing agent, in electrodes

plating, metallic coatings are formed as a result ofchemical reaction between a reducing agent andmetal ions present in solution.

In order to localize the metal deposition on aparticular surface, rather than in the bulk of thesolution, it is necessary that the surface should actas a catalyst.


23/28

Such an autocatalytic process is the basis of electrolesscoatings.

Compared to electroplating, electroless coating has thefollowing advantages:(l) Nonconducting materials can be metallized.(2) The coating is uniform.(3) The process is simple and does not require electrical energy

Electroless coating is, however, more expensive.

A typical plating solution consists ofa. Metal saltb. Reducing agentc. Complexing agents, required in alkaline pH and also

to enhance the autocatalytic process

d. Bufferse. Stabilizers, which retard the reaction in the bulk andpromote autocatalytic process.

Some important coatings are copper, nickel, Silver etc

Ph i l ti


24/28

Physical properties Metallic (m.c.) fibres are flat, ribbon-like filaments, commonly

3.2-0.2 mm (1/8-1/128 in) width.

They are smooth-surfaced, and may be coloured or uncoloured. Tenacity:

Acetate Butyrate, foil : 2.6 cN/tex (0.3 g/den).Polyester, foil : 6.2 cN/tex (0.79 g/den).Polyester, metallized : 11.0 cN/tex (1.25 g/den).

Elongation:Acetate Butyrate, foil : 30 percent.Polyester, foil : 140 percent.

Polyester, metallized : 140 percent.

Elastic Recovery:Acetate Butyrate, foil : 75 percent at 5 percent elongation.Polyester, foil : 50 percent at 5 percent elongation.

Polyester, metallized : 100 percent at 5 percent elongation.

Flex Resistance:


25/28

Flex Resistance:Acetate Butyrate, foil : 1Polyester, foil : 18Polyester, metallized : 70

Abrasion Resistance:Acetate Butyrate, foil : fair.Polyester, foil : good.Polyester, metallized : Excellent.

Effect of Moisture Regain:

Acetate Butyrate, foil : 0.1 per cent.Polyester, foil : 0.5 percent.Polyester, metallized : 0.25 per cent.Thermal Properties:

Softening point : 205-240C Acetate Butyrate, foil : 205C.

Polyester : 232C.

Effect of Sunlight:Some loss of strength on prolonged exposure.

CHEMICAL PROPERTIES


26/28

CHEMICAL PROPERTIES

AcidsGenerally good resistance.

AlkalisAcetate Butyrate : good resistance to weak alkalis;degraded by strong alkalis.Polyester: these also show similar characteristics.

Metal foil types are more resistant. General

Acetate Butyrate : Similar to acetate yarn. Not affected by sea water, chlorinated water, or

perspiration.

Generally resistant to bleaches, but sensitive tocaustic soda used in peroxide bleaching.

Also sensitive to copper sulphate and sodiumcarbonate at high temperatures.


27/28

Effect of Organic SolventAcetate Butyrate: Attacked by acetone, ether,

chloroform, methyl alcohol, tetrachloroethane.

Not attacked by benzene, carbon tetrachloride,ethyl alcohol, perchloroethylene, trichloro ethylene.

Polyester: Attacked by acetone, benzene,chloroform, tetra chloroethane, trichloroethylene.

Not attacked by carbon tetra chloro ethyl alcohol,methyl alcohol, perchloroethylene, white spirit.Insects and microorganismsNot attacked.

Electrical PropertiesMetallic (m.c.) fibres conduct electricity - themetallized types having a lower conductivity thanthe foil types.


28/28

USES

Upholstery Carpets

Stainless steel fibers are also used in

carpets. Tire cord, missile nose cones,

work clothing such as protective suits,

space suits, and cut resistant gloves for butchers

Metallic Fibres

Documents

Transcript of Metallic Fibres