Various Open and Closed Mould Process:
Prototype: Working with your team the process begins with the creation of an exact prototype of your part based on your specifications.
Hand lay: The process of applying resin (usually polyester) to a reinforcement (usually fiberglass) and consolidating (removing the air) by hand with a brush and or roller within a one-sided open mold.
Spray up: Another option used to apply resin inside an open mold, the resin is sprayed, which speeds the process.
LRTM: A composite molding process with two counter molds (male and female). Typically, the molds are joined, vacuum clamped, and resin is injected using vacuum assist into the mold cavity.
Closed molded parts feature a two-sided Class “A” exterior finish, and superior part-shape accuracy and quality. These parts can be fairly simple, flat shapes, or more complex shapes, such as head doors for a recreational boat.
Synthetic fibres are made from polymers, many of which are obtained from petroleum. Some common synthetic fibres are nylon, rayon, terylene, acrylon and cashmilon. They can be placed into two groups.
1. Fibres made from cellulose
2. Fibres made by joining monomers.
Synthetic materials are cheap, strong and attractive for clothing. They are easy to maintain as they are easy to wash, light in weight and resistant to wrinkles, moths and molds. When a new synthetic fibre is developed, it is given a new name by the trade commission. In order to receive such a name, the new product must have useful properties for the consumer.
Manufacture of synthetic fibres
Most synthetic fibres are made by forcing liquids through tiny holes in a metal plate and allowing them to harden. A wide range of liquids produces a great variety of fibres. The metal plates are called spinnerets. They are made of gold or platinum because these metals are not affected by most chemicals. The size of the spinneret is about the size of thimble and it has 10 to 150 small openings, depending on the thickness of the strand wanted. Different synthetic fibres are made from different raw materaials.
It is also called artificial silk. Rayon is made from cellulose. There are several varieties of rayon. Buyt rayon produced by the viscose process is the most important. The ingredients for making viscose rayon are
1. Cellulose (C6H10O5),
2. Sodium hydroxide (NaOH),
3. Carbon disulphide (CS2), and
4. Sulphuric acid (H2SO4).
Manufacture of rayon:
The manufacture of rayon involves the following steps.
1. Cellulose in the form of wood pulp is treated with NaOH.
2. On adding CS2, it dissolves completely and a yellow syrup-like liquid called viscose is formed.
3. Viscose is forced through the fine holes of the spinneret into a solution of dilute H2SO4. Silk-like threads are formed. This product is viscose rayon.
Uses of rayon:
Rayon can be mixed with cotton or wool, which makes it more suitable for our needs. It is a good fabric or sarees. When mixed with cotton it makes a good dress material. Aprons and caps are preferably made of rayon. On mixing it with wool, it serves as a good fibre for making carpets. Bandages and lints for dressing wounds are made of rayon. Hosepipes and conveyor belts are also made from rayon.
Perspiration weakens rayon fibres and they lose strength when wet.
Acetate is another well-known fibre made from wood pulp. The reaction between wood pulp (cellulose) and acetic acid is the basis for this manufacture of this fibre. Acetate is made of fibres that do not wrinkle or shrink as much as rayon. It is an efficient smoke remover, thus it is used in cigarette filters.
Acetate fibres melt when burned. They are destroyed by pressing with very hot iron. Some dry-cleaning solvents dissolve the fibres.
Nylon is a polymer made of polyamide chains. The basic materials for making nylon are coal and petroleum. The polymer is squirted through spinneret holes to form nylon threads. The strands are then stretched four times their original length. The stretching forces the molecules to line up, giving nylon an increased strength and making it more elastic. Nylon is light weight, fine and durable. It is resistant to moths and molds. It absorbs very little water, therefore it dries quickly.
Uses of nylon:
Hammocks, fishing nets tyre cords, ropes, bristles of brushes and parachute fabrics are all made of nylon fibre. As nylon is elastic in nature, it is a good material for making stockings and socks. Nylon sarees are quite common in our country.
Nylon has a few weaknesses, as it absorbs very little moisture it is difficult to dye. It produces static electricity when rubbed. Being a non-cellulose fibre, it requires low to moderate ironing heat.
Acrylic and polyester are non-cellulose fibres. They are manufactured from petroleum products. Terylene and Dacron are examples of polyesters. These fibres are easy to wash; they dry quickly, and resist chemicals and wrinkles. They are difficult to dye. These fibres blend well with natural fibres in making cloth. Terylene is often mixed with cotton to make terycot, with wool, it gives terywool. Clothes made of these are more comfortable to wear than pure terylene.
The resins that are used in fibre reinforced composites can also be referred to as ‘polymers’. All polymers exhibit an important common property in that they are composed of long chain-like molecules consisting of many simple repeating units. Man-made polymers are generally called ‘synthetic resins’ or simply ‘resins’. Polymers can be classified under two types, ‘thermoplastic’ and ‘thermosetting’, according to the effect of heat on their properties.
Thermoplastics, like metals, soften with heating and eventually melt, hardening again with cooling. This process of crossing the softening or melting point on the temperature scale can be repeated as often as desired without any appreciable effect on the material properties in either state. Typical thermoplastics include nylon, polypropylene and ABS, and these can be reinforced, although usually only with short, chopped fibres such as glass.
Thermosetting materials, or ‘thermosets’, are formed from a chemical reaction in situ, where the resin and hardener or resin and catalyst are mixed and then undergo a non-reversible chemical reaction to form a hard, infusible product. In some thermosets, such as phenolic resins, volatile substances are produced as by-products (a ‘condensation’ reaction). Other thermosetting resins such as polyester and epoxy cure by mechanisms that do not produce any volatile by products and thus are much easier to process (‘addition’ reactions). Once cured, thermosets will not become liquid again if heated, although above a certain temperature their mechanical properties will change significantly. This temperature is known as the Glass Transition Temperature (Tg), and varies widely according to the particular resin system used, its degree of cure and whether it was mixed correctly. Above the Tg, the molecular structure of the thermoset changes from that of a rigid crystalline polymer to a more flexible, amorphous polymer. This change is reversible on cooling back below the Tg. Above the Tg properties such as resin modulus (stiffness) drop sharply, and as a result the compressive and shear strength of the composite does too. Other properties such as water resistance and colour stability also reduce markedly above the resin’s Tg.
Although there are many different types of resin in use in the composite industry, the majority of structural parts are made with three main types, namely polyester, vinylester and epoxy.
Properties of Resins:
Properties such as strength and durability are used to describe various types of resins’ physical and chemical characteristics. Resins are generally known for having superior strength and exceptional durability under various laboratory and environmental conditions. In addition, some types of resin can have variable adhesive and mechanical properties. Synthetic resin has properties similar to those of natural resin, but they are chemically different.
Engineering applications use chemical resin to produce a product that is resistant to both impact and fatigue. Other important resin properties for engineering and chemistry purposes include insolubility and fire resistance. Resin products are designed to encompass all of these properties, because the products undergo extreme conditions in terms of water abrasion, temperature changes or direct impact. Some common chemical resins include polyoxymethylene, also known as Acetal; polycarbonate; and tetrafluoroethylene, also known as Teflon TFE.
Products made with chemical resins can include centrifuge ware, safety shields and filter ware. These products are designed to withstand extreme temperatures and aqueous chemical environments. Acetal is especially resistant to organic solvents and may be reinforced with glass fibers. Polycarbonate is a type of clear thermo-plastic that is non-toxic and extremely rigid. Tetrafluoroethylene products have superior chemical resistance.
Application of resins:
The hard transparent resins, such as the copals, dammars, mastic and sandarac, are principally used for varnishes and adhesives, while the softer odoriferous oleo-resins (frankincense, elemi, turpentine, copaiba) and gum resins containing essential oils (ammoniacum, asafoetida, gamboge, myrrh, and scammony) are more largely used for therapeutic purposes and incense.
Resin in the form of rosin is applied to the bows of musical string instruments because of its ability to add friction to the hair to increase sound quality.
Ballet dancers, as well as boxers in the old days, may apply crushed resin to their shoes to increase grip on a slippery floor.
Resin has also been used as a medium for sculpture by artists such as Eva Hesse, and in other types of artwork.
In the early 1990s, most ten-pin bowling ball manufacturers started adding resin particles to the covers of bowling balls. Resin makes a bowling ball tackier than it would otherwise be, increasing its ability to hook into the pins at an angle and (with correct technique) making strikes easier to achieve.
Resin is also used in stereo-lithography.
The analysis of filament-wound structures which assumes
(1) That the stresses induced in the structure are carried entirely by the filaments, and the strength of the resin is neglected.
(2) That the filaments possess no bending or shearing stiffness, and carry only the axial tensile loads.