GCSE Resistant Materials Components, Adhesives and Applied finishes Summer Examination 2011

GCSE Resistant MaterialsGCSE Resistant MaterialsComponents, Adhesives and Components, Adhesives and

Applied finishesApplied finishesSummer Examination 2011

Components and AdhesivesComponents and Adhesives

Knock down fittings (KD)

Many DIY and furniture stores sell their products flat packed in cardboard boxes. This makes it easy to take them hoe in a normal family car.

It is easier to assemble products with knock down fittings. They often come in a variety of shapes and sizes to carry out different functions.

They are designed to be used with a screw driver or an allen key, this is often supplied in the packaging with the furniture. KD fittings are used to join metallic products such as steel tube TV stands and timber based products such as kitchen cupboards.

These are non permanent joints, usually locks and brackets (plastic/metal) which allows something like furniture to be assembled and taken apart again easily.They are used instead of traditional wood joints, they are fast to use but not as strong as a glued wood joint.


Examples of Knock down fittings:

Knock down half block: screws directly into two cabinet parts to hold them at 90 degrees. Can become weaker if altered too much. Knock down full block/modesty block: screws to two parts and then is joined with a single machine screw.Frame connector: Very strong joining method Cam Lock: A large thread on the screw is designed to grip well into chip board. Turning the cam can pull two parts together to join.Worktop connector: Act the same as a cam lock.Corner plate: Allows a table leg to be fitted to a table frame without tools. Captive nut: The nut bites into the timber. The bolt is then screwed into a hard nut in order to preserve cutting into soft timber.


Other Fixtures and Fittings:Other examples of fixtures and fittings are varied, a few common ones are explained here:

Magnetic catch: Simple to fit, but visible when a door is open.Bolt: Often used to fix a pair of doorsToggle catch: Used for holding lids closed.Drawer runners: Allow doors to slide much more easily than traditional methods.Lid Stay: These come in all shapes and sizes. Used for holding flaps open and for limiting door opening.


Hinges are available in a number of materials (steel, brass, nylon) and can be coated to match a piece of furniture. The part of a hinge that moves is known as the knuckle.

There are 4 different types of hinges;

Tee hinge – often used for sheds and garden gates. (outside) the longer ‘strap’ allows the hinge to support a greater weight.Butt hinge – most common hinge used for doors. One part of the hinge is set into the door and the other into the door frame.Pivot hinge – this type of hinge allows you to life a door from its frame, again one part is screwed to the door and the other into the frame.Flush hinge – this hinge is screwed directly to the surface and are much easier to fit than a butt hinge. They are often used to lightweight jobs.


Mechanical methods of joining materialsMechanical joining systems allow parts to be dismantled at a later date without damaging the material. Mechanical joining systems may include nuts, bolts, rivets, screws and nails.

Nails

Nails are quick and easy to use. They only need a hammer, plus a nail punch if you wish to drive the head below the surface. Parts can usually be knocked apart with little surface damage created. Nails are mostly made of mild steel, but other materials such as stainless steel, copper, and aluminum are used for specific purposes. Some mild steel nails are galvanised to be used outdoors.


Screws

Wood screws can be used to joint together a variety of materials. The shape of the screw will vary according to the type of material being joined. It will also vary in length and diameter. Screws are commonly made from steel, but brass, stainless steel, and other materials are also used. Some steel screws are available with zinc or chrome plating.

Joining with screwsThe correct method for joining with screws is as follows:1.Drill a pilot hole into the material being joined.2.Drill a clearance hole into the material that needs to be fixed to allow the screw to slide through to the part being joined too. 3.Countersink the clearance hole so that the head of the screw can be driven level with the surface of the wood/material.


Screws and bolts are used with wood, metals and plastics, and there are different types available to use with each of these materials. Wood screws often require a pilot hole to be drilled before the screw is inserted. As the screw is turned by the screwdriver, the thread pulls it into the wood. The screws have a different type of head for the jobs for example round, countersunk, slotted and cross heads. Self tapping screws have hardened threads and are designed to cut there own threaded holes in hard materials such as metals and hard plastics.Machine screws have a straight shank and are used with washers and nuts, the head types vary and can be tightened with a screwdriver or Allen key.Screws and bolts are usually made from steel, brass or stainless steel.


Nuts and BoltsFor fixing metal parts together it is more usual to use nuts and bolts. Both systems are non permanent and can be taken apart easily. Like screws, nuts and bolts come in a variety of shapes and sizes.

RivetsRivets are a convenient way of joining metals without the use of heat which is needed for welding. A whole is needed for the rivet to fit into. The end of the rivet is hammered when fitted.Rivets cannot be undone however, to remove them they have to be drilled out.A pop gun rivet allows rivets to be fitted from one side, for more awkward projects.


Adhesives: Types of Glue

Adhesives are used to bond materials together to form a permanent joint. There are a wide variety of adhesives to choose from depending on the materials being joined together.

Preparation

Preparation of the materials is important, all adhesives need the material to be clean and free from oil and dust to allow the material to achieve the maximum grip.Some areas may need to be covered with masking tape to prevent the adhesive from spreading over other areas.Some adhesives will require the surface to be ‘keyed’ to allow maximum traction so sanding the material may be required.


PVA – Polyvinyl Acetate is used for wood.There are two types of PVA, one can be used for interior work, and one for exterior use. This means that one is waterproof and the other is not. PVA for use outside is more expensive but can withstand damp. It can take 4 – 24 hours to dry.

Contact adhesives (Evostick) are very strong, it is usually rubber based and is used for household items like floor tiles. It is applied to both surfaces and left to go tacky until it is applied. Contact adhesives can give off harmful fumes so need to be applied in well ventilated areas. Works well with woods, metals and plastics and take 6 – 8 hours to dry.

Epoxy resins (Araldite) is two substances (resin and hardener) that are mixed in equal parts. Both are thick liquids (one is clear and the other yellow).Once the two substances are mixed they will stick almost anything, ceramic to ceramics, metals to woods, woods to plastics etc. Epoxy resins will need about 15 minutes to harden and can be more expensive. Drying time ½ hour – 6 hours.


Superglue (Cyanocrylate)Superglue is however more expensive than an epoxy resin. It will stick to skin so care is required. Superglue is a clear thin liquid, after application the glue will require some small pressure to create a strong bond. Drying time is instant.

Liquid solvent cementThis is used commonly for plastics. Tensol is a good example. Tensol is used in orthopaedic surgery to attach artificial joints to bones. It is a watery, clear liquid and is applied with a brush. Joint pressure is required when drying. Tensol generates very strong and harmful fumes, so a well ventilated space is required. Drying time 10mins.

Cleaning the joint

It is important to clean the materials after using glues andadhesives as they can have a damaging impact on paint orvarnish if applied.

Surface PreparationSurface Preparation

It is essential that surfaces are fully prepared before any finish is applied. This helps to improve the quality of any work.

Preparing a wooden surface

A sharp plane will produce the flattest, smoothest surface but does require some skill.Mechanical sanding using a band facer, disc sander, or palm sander will usually provide a flat finish but will leave some sanding marks.Abrasive paper should be used to create a good finish. Glass paper and a sanding block will help. Abrasive papers come in different grades from course to fine. It is important to sand in line with the grain to avoid scratches.

Surface PreparationSurface Preparation

Preparing a metal surface

Edges of metal should be smoothened with a file. You can draw file in order to get rid of any burring on the edges. Emery cloth, a type of abrasive paper, can be used also to smoothen metal when wrapped around a file. Oil can also be added to get a better finish.White spirits help to clean edges on metal, as well as remove grease and oil.

Preparing a plastic surface

Most plastics are self coloured and have an immaculate surface finish. Protective coatings that are already in place should be kept on the plastic for as long as possible to prevent damage. When Cut the edges will need preparing. Again you can use a file for this process and follow this by using abrasive papers. (Silicon Carbide Paper)

Applied FinishesApplied Finishes

Finishes for wood

Wax: Wax adds shine to a surface of wood and gives some protection. The two types commonly used are beeswax and silicon polish. Wax comes in a solid form and is rubbed into the surface of the wood with a cloth. Once it is dried it is buffed to create a natural, shiny surface .

Oil: Oil adds shine to a surface of wood and provides protection. There are a number of varieties, teak oil, Danish oil, and linseed oil being the most common.Oil comes in liquid form and is rubbed into the surface of the wood with a cloth.

Stain: stain changes the colour of wood but provides little protection. Stain is applied evenly with a cloth over the surface of the wood. Once it has dried it needs to be sealed with a sealer.


French Polish: French polish adds a deep shine to the surface of wood and gives some protection. This is a traditional and very skilled process. It comes in liquid form and is a mixture of beeswax and methylated spirits. It is applied with a rubber (cotton wool wrapped in cloth). A number of coats need to be applied.

Sealer: Sealer adds shine to the surface of wood and gives good protection. Sanding sealer and MDF sealer are the most common types. Sealer is liquid in form and is brushed onto the surface of the wood, but needs to be sanded down with glass paper.

Varnish: Varnish adds shine and gives good protection. Varnishes can also come in a variety of colours, the most common types are polyurethane and acrylic. It is brushed onto the surface of the wood and needs to be rubbed down with wire wool. Extra coats can be applied to produce a deeper shine. Paint: Paint is available as matt, silk or gloss in a number of colours. The most common types are oil based, water based and solvent based. They are applied by brushing onto the surface of the wood. Solvent based are more commonly known as spray paints. Water based acrylic paints are ideal for children's toys as they are non toxic.


Finishes for metal

Paint: Paint adds colour to the metal and is available in a matt, silk or gloss finish to gives good protection. Solvent based paints are the most commonly used for metals.There are a few stages in painting with metals, a primer coat, which is rubbed back, an undercoat, also rubbed down, and then a first top coat. To get a deeper colour/shine more coats are applied.

Lacquer: Lacquer adds a clear shine to metal and gives good protection. It is generally solvent based and comes in the form of a spray can. It can be quick drying and does not leave brush strokes.

Oil bluing: Oil Bluing adds a blue/black colour to steel and helps to give protection. The metal is then placed into an oil bath. The oil sticks to the hot metal and then is left to cool.

Anodising: anodising adds vivid colours to aluminum, it gives excellent protection and hardens the surface. This is an industrial process that involves the use of electrolysis.


Plating: Plating involves coating a metal with another metal, this changes the appearance of the metal and helps to protect the material. This is how chrome is plated for alloys.

Galvanising: as is with plating, galvanising involves coating the metal with another metal. It changes the appearance of the metal into a dull grey but helps with protection. In order to galvanise steel it needs to be dipped into molten zinc.

Plastic dip coating: Plastic dip coating adds colour to the metal and gives strong protection to the metal. The metal is heated in an oven to 200 degrees. It is then dipped into a fluidising bath of powdered polythene. This sticks to the metal and is allowed to cool.

Documents

GCSE Resistant Materials Components, Adhesives and Applied finishes Summer Examination 2011