SIMPLE METAL WORK PROJECTS

Metal Finishing 

Metal finishing refers to any of the techniques used to create a decorative or protective surface on a metallic surface. Metals differ in their degree of luster. They range from very dull to very bright. Finishing is used to turn a very dull surface to a bright attractive one. Ferrous metals rust and some non-ferrous metals corrode when they are placed in humid or otherwise unfavourable environment. Certain kinds of finishing prevent rusting and corrosion.

Metal finishing is also performed for some other additional reasons. In electronics, for example, metal finishing is done to impart desirable electrical and magnetic properties to elements so treated. In the manufacture of precision apparatus, metal finishing is done to increase or reduce the sizes of precision parts. Metal finishing is also performed in the industry to alter certain surface properties of metals.

The methods of metal finishing which will be considered in this chapter are buffing and polishing, scratch brushing, spot and copper finishing, application of lacquer, enameling, electroplating, and painting.

 

Buffing and Polishing

Buffing is the smoothing and brightening of a surface by means of a device called a buffing wheel or belt, which is used to press a powdery abrasive to the surface. The buffing wheel or belt is made of a flexible material such as linen, felt, soft leather, or muslin.

The buffing wheel or belt is fixed to the rotating spindle of a buffing machine. Fine abrasive powder is then mixed with wax or melted animal fat to form a smooth paste. The paste is then plastered on the wheel or belt, and the machine switched on. As the wheel or belt rotates, the job is brought in contact with it. In this way, the surface of the job is progressively smoothened and brightened.

Polishing is done in much the same way as buffing. It involves smoothing a surface by the cutting action of small, hard, abrasive particles adhered to rotating wheels or belts made of felt, cloth, or leather. For ordinary polishing, silicon carbide, or aluminium oxide are the most often used abrasives. However, for extra fine polishing, ferric oxide powder, and jeweler’s rouge are two of the notable abrasives used. Another form of polishing involves the use of a specially made soft rubber having particles of an abrasive moulded into it.

In industry, buffering and polishing are done by use of big lathe-type machines.

 

Scratch Brushing

Scratch brushing involves the use of a brushing device to rapidly wipe the surface of metal in order to make it smoother and brighter. The brushing device may be a conventional brush or a wheel on which flexible wire bristles have been fixed.

This method is used for removing marks left by machining processes. It is also used for cleaning the surface of metal. Job, which is to be worked, is first gripped in a vice with the surface in a horizontal position for convenience. The brush is then rapidly run in one direction over the surface, several times. If the wheel brush is being used, it is held on a convenient axis and then rotated. As it rotates, it is brought in contact with the surface, which is being worked. Scratch brushing cannot produce surfaces as smooth as those obtainable by buffing or polishing.

 

Spot or Copper Finishing

Copper is a reddish metal. It is extremely ductile, malleable, and a particularly good conductor of electricity and heat. Copper is also resistant to corrosion. Because of these properties, there is much use for copper in industries.

Copper because of its relatively low cost is the best choice for making electrical conductors. In the workshop, copper is readily worked by hammering, cold-rolling, engraving etc. Copper is used for making cooking utensils, ornamental wares and so forth. Copper maintains its strength and toughness up to as high as 204°C. However, copper is not suited for casting.

Copper is also one of the metals, which can be used in the process called electroplating.

 

Lacquer

Lacquer is a substance that is applied to metals, woods, or ceramics, which after drying leaves a shiny, protective film on the surface. It is derived from chemical compounds of lac, cellulose, or resin. Lacquers are obtainable in a wide variety of colours.

A lacquer made from lac is usually dissolved in ethyl alcohol before use. When applied on a surface, the ethyl alcohol evaporates, leaving a hard, shiny film of lac. The evaporating solution in a cellulose lacquer is butyl acetate or butyl alcohol. In a resin lacquer, the evaporating solution is turpentine. In every case, after a lacquer is applied, on exposure to air, the solution will evaporate, leaving on the surface a coating of the lacquer.

Lacquers are extensively used in industries dealing with metals, wood, paper, fabrics, porcelain etc. The motor vehicle industry uses lacquers to produce a very glossy finish on vehicles. Beautiful coatings are produced on chromium, zinc, and brass by the use of acrylic-resin lacquers. The furniture industry uses lacquers to enhance the colours of woods and make their surfaces resistant to moisture penetration. Lacquers are also used in the paper industry to finish book covers, make glossy cardboards etc. Fabrics and parchments are coated with lacquers for the purposes of decoration and protection.

 

Enamel

Enamel is a glassy substance applied to the surface of metal so as to create a smooth, glossy layer. Enamel consists principally of powdered lead-potash glass, or lead-soda glass to which certain metallic oxides have been added. The metallic oxides are used to produce a wide range of colours.Because of this, varieties of articles such as metal utensils, kitchen appliances, bathroom fixtures, are covered with enamel.

Enamel provides decorative and tough protective surfaces for these goods. Metal articles, which have been treated with enamel, are collectively called enamel ware.

Not all metals can be enameled. Only those which can resist the high temperature (816?C) at which enameling is performed can be so treated. Examples of such metals are copper, silver, tin, and gold. Enameling in industry is performed in two ways. The first involves liquefying the enamel and then applying it as paint on the surface of the metallic article. The article is then transferred to the heating device. In the second method, the metallic article is heated, after which the enamel is evenly sprinkled on its surface while it is still at the appropriate temperature.

In both methods, heat melts the enamel and causes it to adhere strongly to the metallic surface. Enameling is different from glazing. The latter refers to the application of a glassy substance to the surfaces of ceramic wares for the purposes of decoration and protection.

 

Electroplating

Electroplating is the process of depositing a thin film of metallic material on a surface by means of an electric current. It is done chiefly to alter the surface properties of the article. Although electroplating is mostly used for coating metals, it is also sometimes used for coating non-conducting surfaces such as wood, plastics, leather, and ceramics.

When used on metals, electroplating is usually done for one or more of the following reasons.

1. Making the metal resistant to corrosion or oxidation.
2. Addition of colour or improvement of attractiveness.
3. Improving electrical conductivity.
4. Creating resistance to wear.
5. Improving optical reflectivity.
6. Imparting desirable magnetic properties.
7. Increasing dimensions of worn or undersized parts.

Several metals are used for electroplating articles. The most common ones are tin used in a process called tinning, nickel, chromium, silver, gold, copper, and zinc.

Tin, a white metal is used for coating steel on both sides, forming what is called tin plate. Tin plate is mostly employed in the production of tin cans, as well as paper clips, and pins. Zinc is used on nuts, bolts, nails, and other fasteners. Chromium and nickel are plated on motor vehicle bumpers and machinery among other uses. Gold is used on jewelry and medals. Silver is used on cutlery, cups, plates, and other tableware. Copper is used on steel to produce ornamental wares.

When an article is to be electroplated, it is made a part of an electrolytic cell in which a solution of the metal to be used as coating constitutes the electrolyte. The article is connected to the cathode while the anode is the same as the metal in the electrolyte. A direct current is used for electroplating. When the current is switched on the electrolyte begins to dissociate into its component ions. The metallic ions move towards the cathode and attach to the object being electroplated. A larger current, a longer period of electroplating, or a stronger concentration of metallic ions in the electrolyte will each result in the deposition of a thicker layer of the metal coating on the object being electroplated.

 

Painting

The application of paint is also employed in metal finishing. Apart from metals however, painting is done on a wide range of materials.

Paints are sometimes used toproduce various colours and designs on metal surfaces.

The process of painting metals is much similar to those of painting wood or plastered walls. Before painting a piece of metal, the surface should be entirely clean of grease, dirt, and other impediments. Two thin layers of the paint usually are sufficient for most metals.

 

Some Simple Metalwork Projects

Some simple projects, which you can do in your school workshop, are the following:

1) Bottle opener

Bottle opener is a simple device used for opening caps of bottled drinks.

 

2) Key holder

Key holder is a simple device used for holding keys of locks so as to make them handier.

 

3) Pen knife

Pen knife is a simple handy device used for cutting or plying loose any stuck items whenever necessary. Take note that a pen knife is not a toy and you must always be careful when using it, so as to avoid injury to yourself and other people.

 

4) Scraper

Scraper, is a simple device used for scraping away material from a wooden surface to make it smoother.

To make any of the projects listed above just follow these steps:

1. Make a freehand sketch of the object to be made.
2. Determine the dimensions, which you may like to use. However, to make things more straightforward for you, just use the dimensions included on Fig 7.1 shown here. Write the dimensions in the appropriate places in your freehand sketch.
3. Study your freehand sketch to identify and correct any faults, which you notice in the design. Using scissors to cut out what is obtained of the object on the paper.
4. Obtain a piece of sheet metal 3mm thickness. Thicker metals may be more difficult for you to work with.
5. Place the paper cutting on the piece of metal and using a scriber, as much as possible, accurately trace the shape of the desired object on the metal piece.
6. Using the hacksaw, cut the piece of metal to the size of object already traced out on it.
7. Cut the internal shape of the object traced out on the metal using a cold chisel.
8. Grind the internal and external edges of the object using a hand file to ensure bluntness of the edges. In the cases of the pen knife and scraper, the cutting edges must be ground to sharpness.