How is a finished metal product prepared and finished, and why are surface finishes applied to metal?
Finishing processes: removing sharp edges and burrs (deburring), cleaning and preparing the surface (emery cloth/abrasives), and applying a finish such as paint, lacquer or plating to protect the metal and improve its appearance.
How SQA National 5 Practical Metalworking covers finishing a metal product: removing sharp edges and burrs (deburring), cleaning and preparing the surface with abrasives, and applying a finish such as paint, lacquer or plating to protect the metal and improve its appearance.
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What this dot point is asking
A product is not finished when it is shaped and joined - the edges must be made safe and a finish applied. The SQA expects you to describe deburring, surface preparation and finishing (paint, lacquer, plating), and explain the two reasons a finish is applied: protection and appearance. The skill is applied in the practical activity and sampled by the case study.
Deburring and preparing the surface
A finish applied over a dirty, greasy or rough surface will not stick and soon flakes off, so preparation is as important as the finish itself. Emery cloth comes in different grades (coarse to fine): a coarser grade removes rust and scale quickly, then a finer grade smooths the surface and leaves a light key for paint to grip. Any oil or grease is wiped off with a degreaser at the end, because even a fingerprint can stop paint adhering.
Applying a finish
- Paint: a coloured coat, usually over a primer, that seals and colours the metal. Thin, even coats give the best finish.
- Lacquer/varnish: a clear coat that protects a bright metal (like brass) while letting its colour show.
- Oil/wax: a simple protective film, e.g. wiping bright steel tools with oil to stop them rusting.
- Plating (e.g. chrome, zinc): a thin layer of another metal applied to protect and give a bright, hard surface; galvanising coats steel with zinc to stop rust.
Putting it together
Try this
Q1. State what deburring means. [1 mark]
- Cue. Removing the sharp edges and burrs left after cutting, filing and drilling.
Q2. Give the two main reasons a surface finish is applied to metal. [2 marks]
- Cue. Protection (sealing it against corrosion and wear) and appearance (colour, gloss or a bright surface).
Q3. Explain why mild steel must be finished but brass need not be protected from rust. [2 marks]
- Cue. Mild steel is ferrous and rusts if left bare, so it needs a protective finish; brass is non-ferrous and does not rust.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA-style Describe4 marksA mild steel bracket has been made and is to be painted. Describe how you would prepare and finish it.Show worked answer →
Award up to 4 marks, 1 per correct stage. First remove any sharp edges and burrs left from cutting and drilling by filing or grinding them off (deburring), so the bracket is safe to handle and the finish will sit evenly (1). Clean the surface and rub it down with emery cloth (abrasive) to remove rust, scale and grease and to give a slightly keyed surface for the paint to grip (1). Apply a primer suited to steel, then the paint, in thin even coats, letting each coat dry (1). The paint seals the steel so it does not rust, and improves its appearance; mild steel must be protected because it is a ferrous metal that corrodes if left bare (1). A strong answer covers deburring, cleaning/keying, and a protective coat with a reason.
SQA-style Explain3 marksExplain why a surface finish is applied to a metal product, giving the two main reasons, and why mild steel in particular needs finishing.Show worked answer →
Award up to 2 marks for the two reasons and 1 for the mild steel point, to a maximum of 3. The first reason is protection: a finish such as paint, lacquer or plating seals the metal against moisture and air so it resists corrosion and wear and lasts longer (1). The second reason is appearance: it adds colour, gloss or a bright surface to make the product look attractive (1). Mild steel in particular needs finishing because it is a ferrous metal that contains iron, so if left bare it rusts quickly; a protective finish keeps the rust off (1). A clear answer gives protection and appearance and links rust to mild steel being ferrous.
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