Spelt fiberglass or fibreglass, depending on if you are in the US or the UK, fibreglass is basically plastic reinforced with fibre. The fibre itself is made from bindings of numerous, fine fibres of glass. The fibres may be flattened into a lamina – referred to as a chopped strand mat – or woven into a fabric. The underlying plastic environment, is either a thermoplastic or a thermoset polymer (resin or plastic) matrix, – often relying on thermosetting polymers like epoxy, polyester resin or vinylester that act as binders.
Fibreglass is also known by other names – glass-reinforced plastic (GRP), glass-fibre reinforced plastic (GFRP), and GFK. GFK stands for the German Glasfaserverstärkter Kunststoff.
Thermoset plastic is pliable and easy to mould, above a defined temperature. It solidifies on cooling, whereas, thermoset plastic (commonly called thermoset), is a polymer that results from irreversible hardening of soft solid or viscous prepolymer, or resin. This process of hardening happens through curing.
Fibreglass has relatively common application in industry, making significant appearances in many home appliances, and all sorts of vehicles, for instance. It is less expensive and more flexible, than carbon fibre. Compared with metals, it is stronger by weight, and it can be moulded into complex shapes. Everyday applications are rife in the aviation, automotive, maritime, and building construction industries. Bath tubs and enclosures, swimming pools, septic tanks, water tanks and reservoirs, water tanks, roofing, pipes, cladding, surfboards, casts, and so forth, are few of the plenty around you that you never thought had fibreglass in them.
Glass fibre is many times referred to as fibreglass, thus the composite is also known as fibreglass reinforced plastic. Here, fibreglass is the complete glass non-enforceable composite material, not merely the glass fibre within it.
Fibreglass – a historical background
Man has engaged in the production of glass for a long time in history, and glass fibres have been produced for hundreds of years. The earliest fibreglass patent was however only awarded in the US in 1880, to Prussian inventor, Hermann Hemmesfahr (1845-1914).
Games Slayter, accidentally discovered a way to mass produce glass strands, in 1932. Slayter was a researcher, and directed compressed air at a stream of molten glass, resulting in fibres. A patent using this method of producing glass wool, was first applied for in 1933. A first implementation called Fiberglas (single‘s’) was unveiled in 1936, by the Corning company. It was simply glass wool, with fibres, entrapping plenty of gas, making it useful as an insulator, at especially scourging temperatures.
Du Pont pushed the limits of possibility with fibreglass, by developing a resin to suitably combine fibreglass with plastic, to produce a composite material.
Russia and the US both distinctly, employed fibreglass in transportation. While Russia built a Passenger boat using plastic materials, the US built a fuselage and aircraft wings. A 1946 prototype of the Stout Scarab, was the first vehicle to have fibreglass. The model did not however, make it to production
Fibreglass strength and integrity
Perhaps most important for a steely final fibreglass structure, is that the fibre surface must be entirely free of defects. This allows the fibres to attain gigapascal tensile strengths. A bulk piece of glass that is defect-free, is as strong as glass fibres, if it is free of defect.
It is however, impractical to produce and maintain bulk material in a defect free state, external to controlled laboratory conditions.
Pultrusion is the fibreglass manufacturing process. To make them suitable for reinforcement uses, the manufacturing process employs large furnaces, to gradually melt silica sand, kaolin clay, dolomite, fluorspar, colemanite, limestone and other liquids, until a homogeneous liquid forms. This liquid is then extruded through bushings, – bundles of very tiny orifices (5-25 micrometres in diameter for E-glass, 9 micrometres for S-Glass).
Using a chemical solution, the resulting filaments are then coated (sized), before being bundled, to provide a roving. The individual filament diameter and the number of filaments per roving, determine its weight, which can be expressed, in either of two ways:
- Yield – yards per pound. Typical standard yields include are 675yield, 450yield, and 225yield.
- Tex – inverted from yield, this represents grams per kilometre (km). Typical standard Tex are 2200tex, 1100tex, and 750tex.
A smaller yield value means a heavier roving, while a smaller Tex value, means a lighter roving.
Rovings are ultimately directly used in composite applications, like filament winding (pipe), pultrusion, gun roving, in which the glass is chopped by an automated gun, into short lengths and dropped into a resin jet, or an intermediary step, to make fabrics like chopped strand mat (CSM) – a binding of small randomly-inclined cut-lengths of fibre, knit fabrics, woven fabrics or uni-directional fabrics.
Chopped strand mat is a reinforcement type, employed in fibreglass. It is a stream of glass fibres, laid randomly across each other, and kept together, with a binder. The hand lay-up technique is used to process CSM. Here, sheets of material are placed on a mould, and brushed with a resin. The binder will dissolve in resin, allowing the material to easily conform, to various shapes, when wetted out. On curing the resin, the hardened product can be taken from the mould and finished. Chopped strand mat makes fibreglass isotropic, with in-plane material properties.
The roving is then coated or primed, to protect the glass filaments, for processing and manipulation, and guarantee resin matrix bonding, permitting transfer of shear loads, from the glass fibres, to the thermoset. This bonding prevents localised failure, arising from a slip in the matrix.
Individual structural glass fibre is stiff, exhibiting strong tension and compression, along its axis. While the fibre may be weak in compression, it is the fibre’s long aspect ration that is responsible for this illusion, as a typical fibre is long and narrow, buckling quite easily.
On the other hand, glass fibre is weak in shear – across the axis. This means, if a collection of fibres can be arranged permanently, in a preferred direction within a material, and are prevented from buckling in compression, the material will be preferentially strong in that direction.
Layering multiple fibres on top of each other, with each layer oriented in a distinct direction, helps to control the material’s overall stiffness efficiently. The plastic matrix in fibreglass permanently constrains the structural glass fibres, to directions chosen by the designer. With CSM however, this directionality is confined to a plane of two dimensions. Woven fabrics and unidirectional layers, show directionality of stiffness and strength that is controlled within the plane, in a more exact manner.
A thin shell construction is basically what a fibreglass component is, with an inside filling of structural foam, like we have with surfboards. This component can assume any arbitrary shape, the only limitations being the complexity and tolerances of the mould used, to manufacture the shell.
The mechanical functionality of materials heavily influences the combined performances of the resin, matrix and fibres. Take the case in extreme temperatures (>180 °C); the resin component of the composite may show dwindling functionality, due in part to deterioration of the bond, between resin and fibre. However, GFRPs are able to retain significant residual strength, under high temperature extremes (~200 °C).
Types of glass fibre used
In terms of composition, the most common glass fibre employed in fibreglass is E-glass. It is an alumino-borosilicate glass, with less than 1% w/w alkali oxides, (majorly used in glass-reinforced plastics). There is also A-glass, which is absolute alkali-lime, without boron oxide. E-DR-glass is another. It stands for Electrical/Chemical Resistance glass. It is of alumino-lime silicate, with barely 1% w/w alkali oxides and significant acid resistance.
C-glass is alkali-lime glass, containing an amount of high boron oxide, employed in insulation and glass staple fibres. D-glass got its name from the low Dielectric constant it has. It is borosilicate glass, while R-glass is alumino-silicate glass that has no MgO and CaO content, with high mechanical requirements, as Reinforcement and S-glass is alumino-silicate glass with high MgO content but zero CaO and high tensile strength.
By naming and use, pure silica (silicon dioxide) can be cooled in fused quartz form, to make glass without a definite melting point and can be used as glass fibre for fibreglass. The disadvantage is that, it must be worked at extremely high temperatures. To lower this temperature, other materials are thrown in as fluxing agents. These serve to lower the melting point of the glass. A-glass (Alkali-lime above) or soda lime glass, which is crushed and ready to be remelted, as cullet glass, was the first type of glass used for fibreglass.
E-glass (Electrical application) is alkali-free and was the first glass formulation used for continuous filament formation. Most fibreglass production globally is comprised of E-glass, and remains the single largest consumer of boron minerals worldwide. It easily lends itself to chloride ion attack and is a poor choice for marine applications.
S-glass (Stiff) supplies key tensile strength (modulus) where it matters, as with building and aircraft epoxy composite. It is called R-glass in Europe (Reinforcement), C-glass (Chemical resistance) and T-glass (Thermal insulator) – a North American variant of C-glass, – both defy chemical attack, and are common in insulation-grades of blown fibreglass.
Being lightweight, fibreglass is resoundingly versatile. It has good strength, weather-resistant finish and a variety of surface textures.
In World War II, fibreglass ably replaced moulded plywood in aircraft radomes, as it was transparent to microwaves. Civilian applications are more common today, the first being for boats and sports cars. Wider adoption is seen in the automotive and sports equipment sectors. For aircraft though, it is being replaced by carbon fibre, which is stronger by volume and weight.
Fibre rovings and pre-pregs are examples of manufacturing techniques that have broadened the possibilities of fibreglass applications, and tensile strength possible, with reinforced plastic.
To shroud antennas in telecoms, fibreglass has been employed. This is because of its RF permeability and diminished signal attenuation properties. Where signal permeability is unneeded, fibreglass can be used to conceal equipment, as it is easily moulded and painted to fit in, with surrounding structures and surfaces. It is also used in sheet-form electrical insulators and structural components commonly found in power-industry products.
The combined light weight and durability of fibreglass means it can be used in protective gear such as helmets. This can be seen in many sports.
Storage tanks, houses, oil and gas artificial lift equipment, piping, traffic lights, helicopter rotor blades, premium bicycles, auto body parts, refrigerators, new refrigerated vehicles (available from Glacier Vehicles if you call 0208 668 7579), commercial wind turbines, and sculptures are only a small number, of the many areas fibreglass is applied. Many areas of industry are increasingly seeing how fibreglass can improve efficiency across the board, making better products, than is now present.
Benefits of fibreglass in refrigerated vehicles
In preference to steel, fibreglass is the material of choice for modern refrigerated truck insulation. A refrigerated truck is primarily for reliable temperature control, and fibreglass has this property. If the refrigeration unit suddenly develops a fault, the cargo’s freshness will remain intact while the issue is resolved. Compared with steel, fibreglass truck bodies are more thermally efficient, by around 20-30%.
It is also cheaper to operate trucks with fibreglass bodies. When used for reefer trucks, the lighter fibreglass bodies provide better fuel economy, and electricity consumption. Insurance firms also offer coverage for a 10-year life cycle, on fibreglass. For steel, they do 5 years, or less.
There is also the payload capacity advantages of fibreglass, to consider. Steel is heavier and generally reduces the total payload capacity offered by the vehicle. This implies that anyone using steel-bodied trucks, might be conveying a larger truck, than is necessary. Exploiting any efficiency benefits is vital in the expensive refrigerated transport business.
How fibreglass truck bodies perform insulation
We already mentioned that fibreglass is a composite of plastic, reinforced with small glass fibres. It is strong, lightweight, and does not conduct heat, making it useful in refrigeration. Fibreglass traps heat between its fibrous strands, as it moves to a cold area, keeping the temperature in the colder area, stable.
This thermal efficiency makes fibreglass unbeatable, for refrigerated truck insulation for the foreseeable future.