1.5 The use of finishes

Comprehensive practice questions covering material forming, redistribution, and all forms of finishing for paper, boards, polymers, metals, and woods as described in the lecture notes.

What is a die cutter?

A machine using a hydraulic press and a plywood substrate with cutting dies and creasing rules to cut a net from paper, card, or polymer film.

How is 'redistribution' defined in material shaping?

Shaping materials by melting them and reforming them in a mould that resembles the finished product or component.

What is 'wastage' in the context of stock material shaping?

Shaping stock material by machining it using processes such as milling, turning, and routing.

When are redistribution processes such as injection moulding or casting typically used?

When the product is too complex to be manufactured by any other method.

How do fabrication methods compare to forming and redistribution in terms of speed?

Fabrication methods are generally much slower than manufacturing by forming and redistribution.

Why do most polymer redistribution processes use thermoplastics?

Because they can be heated and re-shaped.

What is the primary use of knock-down (KD) fittings?

They are useful where it is important to supply products flat-pack.

What is 'self-finished' material?

A material that has an acceptable finish after processing.

What are the four general aims of an applied finish?

To prevent the material from absorbing moisture, protect against decay or corrosion, protect against insect attack, and enhance the appearance.

What polymer mixture is usually used for lamination via encapsulation?

A mix of PET and ethylene-vinyl acetate (EVA).

What are the two ways surface coating lamination of papers and boards can occur?

Liquid lamination or film lamination.

For what specific application is liquid lamination used to protect from UV light and moisture?

Signage.

What term refers to an embossed area that does not have any ink or foil applied?

Blind emboss.

Which two materials are typically used to make the male and female dies for embossing?

Stainless steel or brass.

How is 'debossing' different from 'embossing'?

It produces an imprinted depression which sits below the surface of the paper or card rather than a raised design.

What is foil blocking?

The application of heat and pressure to a metallic paper (foil) to create areas of depth and texture.

What happens if the heat is too high during the foil blocking process?

The foil will bubble and peel.

What is UV varnishing?

A process providing a smooth finish using specific machinery that instantly cures the varnish under a UV light.

What is spot varnishing?

Varnish that is applied via a plate or set of plates to specific areas or spots rather than the whole surface area.

In printing, what does the term 'substrate' mean?

The material on to which the print ink is applied, such as paper or boards.

What are the common applications for screen printing?

Posters, display boards, and textile t-shirts.

What does the abbreviation CMYK stand for in the four-colour process?

Cyan, Magenta, Yellow, and Key (Black).

What is the function of a registration mark in colour printing?

It is a quality control (QC) check to ensure all four colours have printed in the correct place to avoid blurring.

Which printing process is considered the least expensive due to its simple operation and use of fast-drying water-based inks?

Flexographic printing.

What are the image and non-image areas of offset lithographic plates called based on their water/oil attraction?

Image areas are oleophilic (absorb oil) and non-image areas are hydrophilic (absorb water).

For what volume of print runs is offset lithography typically suited?

Medium and long print runs, specifically $1,000$ or more.

What allows digital printers to be ideal for mass customisation?

The option of different designs on each page and the use of fast-drying inks.

Why are polymers considered 'self-finishing'?

They require no additional finishing process once manufactured because surface textures and colors are produced during the moulding process.

How are pigments added to polymers during injection moulding?

Pigment particles can be added into the hopper during manufacture or used in pre-pigmented granules.

Give an example of a smart polymer product mentioned in the text.

'Glow in the dark' polymer stars made with phosphorescent pigment additives.

What are the benefits of using acrylic spray paints on polymers in the automotive industry?

Improved aesthetics, protection against UV light/weathering, and allowing for mass customisation like colour-coded bumpers.

What is overmoulding?

Moulding a second polymer, often TPE, over specific parts of a product to provide grip or texture.

Describe the twin shot injection moulding process.

A machine uses a rotating mould with two cavities; the first part is moulded, the mould rotates $180^{\circ}$, and the secondary overmoulding is applied in one cycle.

Why does steel rust while other metals with oxide layers might not?

Steel has a porous oxide layer that allows moisture to penetrate.

What is electroplating?

Using a metal to coat a base metal to provide a protective layer and greater aesthetic appeal using an electrolyte solution and direct current.

What is the temperature required for polymer dip coating set-up?

$230\,^{\circ}\text{C}$.

What is tin plating commonly used for?

To provide a non-corrosive coating to food cans by passing steel sheets through molten tin at $320\,^{\circ}\text{C}$.

What is galvanising?

Dipping steel into molten zinc at approximately $460\,^{\circ}\text{C}$ to provide a barrier against corrosion.

How does powder coating apply the resin to the product?

The product is negatively charged and the thermoset polymer resin is positively charged, resulting in a strong attraction before baking.

What are metal sealants primarily used for in the automotive industry?

As an additional bodywork barrier against weathering, road salts, and insect attack.

What is the process of anodising?

An electric current passes through a sulphuric acid electrolyte from the positive anode (the part) to a negative cathode to build up the aluminium oxide layer.

How does cathodic protection work using sacrificial anodes?

A more electrochemically active metal is joined to a less active metal; the more active metal corrodes while the base metal is protected.

Which two methods of cathodic protection are mentioned?

Impressed current and sacrificial anodes.

What is the cause of 'wet rot' in wood?

Alternating wetness and dryness which allows moisture to remain below the surface, leading to breaking down of fibers by fungus.

Which insects are mentioned as attacking wood products?

Furniture beetle (woodworm) and deathwatch beetle.

What are the qualities of polyurethane varnish as a wood finish?

It provides a hard, tough, heatproof, and waterproof finish.

How is pressure treating of wood carried out?

Wood is placed in a pressure vessel with copper sulphate and other salts, where vacuum and pressure force the preservative deep into the fibers.

What is the purpose of yacht varnish?

It is suitable for woods outside all year round (like boat parts) to increase toughness, hardness, and weather resistance.

For what length of time can pressure treating protect wood from rot and weathering?

Up to $50$ years.

In wood preparation, why should sanding only be done in the direction of the grain?

To avoid scratching the wood surface.