hit counter script Finishes for Materials

Finishes for Materials     

A finish is in simple terms a coating, layer or skin applied to the material. The finish will be applied for one or more of the following reasons: .
 

               1) To protect the material from moisture, wear, abrasion, fungus, mould or insect attack.
               2) To change the materials appearance, its colour or texture.
               3) To enhance the materials durability, surface hardness or other properties.

 

Finishes for metals

 

Type of finish

Description

Examples

Polishing

Polishing creates a shiny surface through the action of rubbing or the application of chemicals.  These remove the oxides on the surface of the metal. The process of polishing needs repeating regularly to maintain shine.

 

Wet & dry paper of the correct grit or a buffing wheels with compound of the correct grade work on the principle of rubbing over the surface of the metal. Abrasives may also be applied in paste form or as a liquid which evaporates quickly leaving a residue of powder which can be removed with a suitable cloth.  

 

The correct chemical must be used or the workpiece will be damaged.

Some polishes react with zinc, a major component of brass and also a protective surface on steel.

Bronze and brass artefacts, aluminium, Jewellery.

 

Lacquer can be applied to protect polished surface.

Plastic coating

The metal is heated to about 150C and dipped into a box of fluidised powdered plastic which melts onto the surface of the metal sealing it. The correct temperature of the metal can be gauged by the colour of the heated metal. In school the metal is generally heated using a brazing hearth.

Its very efficient in coating the handles of everyday artefacts.

Powder coating

http://en.wikipedia.org/wiki/Powder_coating

The most common way of applying the powder coating is to spray the powder using an electrostatic gun. The gun imparts an electric charge on the powder, which is then sprayed to the object which is grounded. The powder sticks to the object. The object is then heated in an oven at the required temperature and the powder melts to form a coating which is allowed to cure leaving a hard plastic coating on the object.

 

 

 

 The powder may be a thermoplastic or a thermoset polymer. It is normally used to create a hard finish on metals. Powder coating is mainly used for coating of metals, such as "white goods", aluminium extrusions and automobiles, although some other materials (like MDF-medium-density fibreboard) also can be coated in this way. http://en.wikipedia.org/wiki/Powder_coating

Enamel

enamel (or vitreous enamel, or porcelain enamel in American English) is the colorful result of fusion of powdered glass to a substrate through the process of firing, usually between 750 and 850 degrees Celsius. The powder melts and flows to harden as a smooth, durable vitreous coating on metal, glass or ceramic. It is often applied in a paste form and may be transparent or opaque when fired. Vitreous enamel can be applied to most metals. A powdered glass is melted and fused onto the metal. This requires high temperatures. This finish is very heat resistant.

 

http://en.wikipedia.org/wiki/Vitreous_enamel

Jewellery, baths, pots and pans, oven liners

Paint

Painting a metal surface depends on the type of metal it is and the state of the surface. For ferrous metals it is desirable to first degrease the surface with white spirit or some propriety solvent (remove oil and grease). Then the surface needs to be cleaned either with a wire brush or emery cloth followed by a metal primer (this allows good adhesion of paint to the surface of the primed metal) followed by a few coats of the desired metal paint.

If it is a rusty surface, first all traces of rust should be removed followed by the application of anti-rust treatment. When dry the surface can be primed and painted. Certain manufacturers produce paint that can be applied directly to a rusty surface.

 

Special Metals Primer
Promotes adhesion for metal finish paints on non-rusting metal surfaces such as aluminium, galvanized and stainless steel, chrome, brass and copper.

Ferrous and non ferrous surfaces such as Aluminium, brass and chrome items.

Galvanising

a chemical process that is used to coat steel or iron with zinc. This is done to reduce rusting of the ferrous item. Zinc coatings prevent oxidation of the protected metal by forming a barrier, and acting as a sacrificial anode. Abrasion damages the Galvanised surface.

 

Car bodies are galvanised via electroplating followed by painting with rust inhibitors. Nuts, bolts, screws hinges are routinely galvanised giving them an attractive finish. 

Oil blacking

To oil black small parts, heat it till the ferrous metal surface changes to a dull  blue grey colour (not orange or red hot!). Dip it in oil and remove immediately. "Dry" oil off with a flame. Repeat if necessary. Dipping the hot metal into oil leaves the metal with a thin blue/black surface layer that protects it from rust.

Gun barrels are oil blacked as are many pieces of industrial components.

Chrome plating

Chrome plating is a finishing treatment utilizing the electrolytic deposition of chromium. The most common form of chrome plating is the thin, decorative bright chrome, which is typically a 10 µm layer over an underlying nickel plate. It imparts a mirror-like finish to items such as metal furniture frames and automotive trim. Thicker deposits, up to 1000 µm, are called hard chrome and are used in industrial equipment to reduce friction and wear and to restore the dimensions of equipment that has experienced wear.

http://en.wikipedia.org/wiki/Chrome_plating

 Precision Shafts, castings, chrome plated car exhausts, bicycle wheels, Chrome plated Toilet and washbasin fittings etc


Finishes for plastics

Most plastics do not require a finish as they are not susceptible to corrosion or deterioration. Plastics tend to acquire the surface finish of the mould used to form them and are rarely finished after manufacture.  http://www.tep.org.uk/a2z_glossary/a2z/finishes.htm

 

Type of finish

Description

Examples

Smoothing a plastic edge Use a smooth file along the edge of the plastic to get rid of scratches and other marks.  Hold the file at an angle and let it slide over work lightly until the edge of the plastic looks smooth. Then use 220 grit sand paper followed by  400+ grit wet & dry paper with the aid of a sanding block.  

Polishing acrylic

Use a buffing wheel and the correct buffing compound.  Compounds have an abrasive grit in an oil base.   Buffing compounds are a solid bar that you apply to the wheel while the wheel is turning on the buffer.  Hold the compound to the wheel for a few seconds, do not over apply compound to the wheel, you will only waste the compound. Run the rough edge of the acrylic against the turning wheel moving the sheet back and forth so as not to “burn” the acrylic. Buffing acrylic sheet is easy and produces crystal clear edges.

http://www.sdplastics.com/acrylic.html

http://www.delviesplastics.com/buffing%20compounds.htm

Acrylic polish applied on cut edges.


Finishes for Woods

 

Type of finish

Description

Examples

Paint

http://www.diydata.com/techniques/painttechniques/paintsurfaces.htm

 

Use glasspaper to get a smooth finish over the entire surface. Apply knotting solution to any knots (follow manufacturers' instructions). Fill any voids with a suitable filler and smooth using glasspaper. Brush off all dust.

 

Apply a coat of wood or universal primer.

 

Internal timber - Apply undercoat and at least 1 top coat.

External timbers - apply undercoat and at least 2 top coats.

 

All types of wooden constructions, both internal and external.

Water/spirit based dyes

Dyes by themselves provide little protection to the wood. To afford protection the wood can be wax polished, French Polished, or varnished.

Application  http://www.blackfriar.co.uk/default.asp

The wood to be dyed must be new, clean, dry and free from grease. Ensure the surface is smooth by lightly sanding along the grain with fine abrasive paper.  First test Dye on an off-cut or inconspicuous area to check the colour is that required. Dye can be applied by brush but is best applied using a lint-free cloth rubbing the dye in the direction of the grain. Avoid streaks in the finish by taking care not to overlap the dye. Wipe the surface with a cloth after application to remove any surplus dye. If using a brush, apply 1 thin coat, followed by a second coat if there is still suction in the wood. Again, wipe off any surplus dye with a cloth. When the dye is thoroughly dry, the wood may be either wax polished, French Polished, or varnished, as desired.  

Furniture

French polish

Very seldom used in schools. Basically the polish is rubbed into the smooth material and buffed into it providing it with a high shine. It is muscle building work to french polish an item. It is also very time consuming to apply. The subsequent surface is neither heat resistant or water resistant but it looks very good with an enhanced and shiny grain pattern.

 Internal high quality furniture.  

Varnish

http://www.blackfriar.co.uk/default.asp

 

Varnishes can be used to provide a wooden artefact with a tough and durable surface and some resistance to heat, boiling water, knocks, dilute acids, alkalis and stains. It can also be used to give furniture new life and bring out the natural grains and colours of wooden surfaces. Varnishes are available for both internal and external use.

 

APPLICATION

Ensure surface to be varnished is clean, dry, sound and free from wax and oil. If preparing bare wood sand it to a smooth surface always working with the grain of the wood. If varnishing a previously coated surface sand lightly to provide a key. Where it is suspected wax may have been used, clean surface thoroughly with white spirit prior to sanding.apply varnish evenly, using light strokes, following the grain of the wood.

 

Rub the varnished surface lightly with a slightly damp cloth and allow to dry. For best results 3-4 coats are recommended. If more than 24 hours elapse between coats, lightly rub the surface down with fine glasspaper, working with the grain and then remove the dust. If you're applying by spray, thin the varnish with up to 10% white spirit and spray as normal.

External wood- boats/yachts, furniture.
Internal furniture

Tannalising

(Treated Timber)

This is timber which has been impregnated with wood preservative under controlled conditions . Pressure treated timber has a long service life and is protected against fungal and insect attack.

Suitable timbers for treatment are all softwoods, commonly used hardwoods and exterior grade plywoods.


 

Fence posts, decking,  joists, battens,

Wax finishes

This uses natural waxes such as beeswax, carnauba etc to seal and enhance the wood, adding lustre and shine while controlling moisture. These waxes are not water or heat resistant. http://www.tep.org.uk/a2z_glossary/a2z/finishes.htm

 

Internal furniture only

Oil finishes

These use natural and blended oils to seal and enhance the wood. They offer some moisture resistance and surface protection, some will accept a high shine others a matt or satin look.http://www.tep.org.uk/a2z_glossary/a2z/finishes.htm

 

Teak oil, Tung oil, Danish oil, linseed oil, olive oil (for food contact woods).

Cellulose sealant (sanding sealant)

A nitro-cellulose materials that dries very rapidly sealing the wood and raising the grain to enable a smoother finish to be achieved. The wood will then accept a wax finish. http://www.tep.org.uk/a2z_glossary/a2z/finishes.htm

 

Internal furniture only.