© Boardworks Ltd 20051 of 19 Resistant Materials Adhesives These icons indicate that teacher’s...

© Boardworks Ltd 20051 of 19

Resistant MaterialsAdhesives

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Learning objectives


Lea

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es To understand that different adhesives are used with different materials and for different purposes.


There are two basic ways of joining materials:

In this section we are going to look at adhesives.

1. temporary, using nuts and bolts, etc.

2. permanent, using adhesives.

Joining components


Early adhesives were made from animal bones.

They were strong but limited: they had to be heated to melt in small pots in the workshop and were damaged by heat, water and fungus.

Modern glues are made from synthetic polymers instead!

Early adhesives


When adhesives fail to stick things together it is usually because of poor surface preparation. Dust and grease are particular hazards. Grease from your hands may also make the surface unsuitable for joining.Prepare the surface before applying any adhesive, ensuring there is no dust, grease or water on the surface. A smooth surface is needed for PVA while a rough surface is required for epoxy resin.

Adhesives


safe to usenot effective in damp conditions, although a waterproof PVA is availablequick drying (it takes 2–4 hours to dry).

PVA is a white, ready-mixed liquid, used for joining porous materials including wood.It is:

PVA will not fill gaps – you must make sure that the pieces fit together well and use a clamp to join the two pieces. Excess glue can be removed with a damp cloth.

PVA


Using PVA


is a powder which has to be mixed with waterneeds to be clamped while settingis stronger than PVAcan be used as a filler.

Waterproof synthetic resin wood glues, such as Cascamite, are used for building boats or making outdoor furniture.

Synthetic resins

Cascamite:


Apply an even layer to both surfaces to be joined.Wait for 10–15 minutes until the surfaces are touch dry. They do not need clamping.The surfaces will stick as soon as they touch each other.The pieces need to be lined up carefully as they can not be repositioned.

Contact adhesives can be used to join dissimilar materials, such as plastic laminate and MDF.

Caution! Use contact adhesives in a well ventilated area

because of fumes.

Contact adhesive


The two parts are mixed together.The hardening process starts immediately and cures to full strength within 24 hours.

Epoxy resin adhesives, such as Araldite, come in two parts: the resin and the catalyst (hardener).

Epoxy resin can be used to join a wide range of dissimilar materials, but works best on a slightly rough surface.It is expensive but very strong.

Epoxy resin adhesive


Surfaces must be in contact before the adhesive is applied.Reacts with the surface of the acrylic.Needs a large gluing area to work effectively.

Tensol cement is used solely for joining acrylic. It is a solvent-based adhesive which dissolves the surfaces being joined.

Caution!Tensol is harmful if used incorrectly.

It evaporates quickly and must be used in a well ventilated area because of fumes.

Tensol cement


Dichloromethane adhesive for plastics


quickconvenientmessyuseful for modelling – its quality is too poor for production work.

Hot melt glue is:

Caution!Care needs to be taken with the hot glue – it can burn!

Hot glue


A very simple adhesive is double sided tape.

quick to useeasy to useinexpensive.

It is:

Double sided tape is widely used in the construction and assembly of road signs.

It is ideal for joining clean, large, flat surfaces.

Double sided tape


The adhesive used in post-it notes does not damage books or other surfaces it is attached to. The note is held securely in place until you want to remove/reposition it.

An unusual technological problem was to find an application for an adhesive that was just not very sticky.

The solution?Post-it notes!

Non-sticky adhesives


Adhesives work by adhering (sticking) to the surfaces being joined.

Some materials have surfaces that are difficult for adhesives to stick to.

Polythene and polypropylene are difficult to glue.

Nylon cannot easily be glued so nuts, bolts, screws or rivets are usually used instead.

Because its surface is not sticky, nylon is used as a bearing material.

Difficult to join materials


If you are using adhesives, be aware of the possibility of fumes.

Wipe up any spillages.

Some adhesives are skin irritants, so wear gloves when working with them.

Reading the instructions on the tins is a useful starting point for finding out about each adhesive.

All adhesives need to be stored and used appropriately.

COSHH regulations cover the storage and use of these substances.

Health and safety


Adhesives game


Key points


Key

po

ints

Adhesives are used to permanently join materials.

PVA and cascamite are used to join wood.

Contact adhesives and epoxy resins can be used to glue dissimilar materials.

Tensol cement is used for joining acrylic.

When using adhesives be sure to follow the storage and usage instructions.

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