Composite Processing

Question 1

Why is it hard to process composites

Answer 1

Composites are more complex, consisting of two or more phases that needs to orient the reinforcing phase

Processing for composites has had less refinement over the years

Question 2

Closed mold processes

Answer 2

Like plastic processing

Question 3

Filament winding

Answer 3

Continuous filaments that have been dipped in liquid resin are wrapped around a rotating mandrel,

Question 4

Pultrusion

Answer 4

Produces long, straight sections of constant cross section. Like extrusion but addapted to include continuous fibre reinforcement

Question 5

Roving

Answer 5

A collection of untwist
Shed continuous strands in a convenient form for handling and processing

Question 6

Yarn

Answer 6

A twisted collection of filaments

Question 7

Cloth

Answer 7

A fabric of woven yarns

Question 8

Woven rovings

Answer 8

Fabric consisting of untwisted filaments. Produced by unequal number of strands in two directions, posses greater strength than one direction

Question 9

Mat

Answer 9

A felt consisting of randomly oriented short fibres held loosely together with a binder, sometimes in a carrier fabric

Question 10

When is reinforcing agent incorporated into a polymer matrix

Answer 10

During shaping or before shaping

Question 11

Prepregs

Answer 11

Consist of fibres impagnated with partially cured thermosetting resin to facilitate shale processing. Completion of curing occur during or after shaping.

Question 12

Advantages of prepregs

Answer 12

Fabricated with continuous filaments thus increasing strength and modules of the final product Economic production

Question 13

Open mold processes

Answer 13

Starting materials applied to the mold in layers, building up to desired thickness. This if followed by curing and part removal.

Question 14

Advantages of open mold processes

Answer 14

Mold costs much less that than if two matching molds were used

Question 15

Disadvantages of open mold

Answer 15

Only part in contact with mold is finished, other side is rough

Question 16

Hand lay up

Answer 16

Shaping method where successive layers of resin and reinforcement are manually applied to an open mold. Final piece usually needs to be trimmed.

Question 17

Steps involved in a hand lay up

Answer 17

1) mold is cleaned and treated with mold release
2) thin get coat is applied which becomes outer surface
3) when get coat is partially set, successive layers of resin and fibre are applied, fibres being mat or cloth. Each layer is rollled to fully impregnate and remove air bubbled. Or use prepregs (already impregnated layers)

4) part is cured

5 fully hardened part is removed from mold

Question 18

Advantage of metal mold

Answer 18

Durability. High thermal conductivity so heat curing system can be implemented or heat can dissipate easier.

Question 19

What type of products are suited to hand lay up

Answer 19

Large in size but low in production quantity

Question 20

Spray up

Answer 20

Alternative to step 3 I. Hand lay up. Liquid resin and chipped fibres are sprayed onto open mold. Satay gun equipped with chopped mechanism which feeds in continuous filaments thus increasing and cuts them before added to resin streams. Mixing action result in random orientation. Rolling generally required for each layer

Question 21

Hand lay up vs spray up

Answer 21

In spray up filament can be oriented as desired and contains much less filament

Question 22

Why is automated machine usually,y better that
N portable for spray up

Answer 22

Labour efficiency and environmental protection. Some emissions from liquid resins can be hazardous but this can operate in sealed off areas

Question 23

Disadvantages of pray up over hand lay up

Answer 23

Not as strong

Question 24

Curing

Answer 24

Accomplishes cross linking of the polymer, transforming is from liquid to highly plastic conditim

Question 25

What impacts curing

Answer 25

Time, temp and pressure

Question 26

How can heat be applied to increase curing

Answer 26

Oven curing, usually also equipped to draw a partial vacuum Infrared heating Autoclave which also allowed for controlled pressure

Question 27

Autoclave

Answer 27

An enclosed chamber equipped to apply heat and/or pressure at controlled levels

Question 28

Filament winding

Answer 28

Process in which resin impregnated continuous fibres are wrapped around a rotating mandrel that has the internal shape of desired product before being cured and removed.

Question 29

Steps of filament winding (most common)

Answer 29

Band of fibre roving is pulled through resin bath immediately before being wound. Continuous winding will complete a surface of one filament thick. Operation repeated to form additional layers, each with criss cross pattern with the previous until part thickness obtained

Question 30

What methods can fibre be impregnated before filament winding

Answer 30

Wet winding- filament pulled through liquid resin before winding Prepreg winding- partially cured resin are wrapped around a heated mandrel Post imprégnation- filaments are wound onto a mandrel then impregnated by brushing or other technique