7. Joining

Talking book

When the piece is finished and ready, we can join it to another piece by using permanent or temporary joints.

7.1. Permanent joints

Talking book

Welding and soldering is the process of joining metal together, using pressure and heat on the surface. There are several types:

Soft soldering

Hard soldering

Oxyacetylene welding

We use a tin-lead alloy. This is heated with an electric soldering iron, which reaches temperatures of 400°C.

Uses: Join tinplate, sheets of metal, brass and electronic and electrical components.

Brass or copper is heated with a blowtorch to a temperature of 800°C.

Uses: Copper and brass; alloys of steel, bronze or cast iron.

An oxyacetylene blowtorch is used which can reach temperatures of over 3000°C.

Uses: Sheets of steel in construction and in the shipbuilding and car industries.

Other permanent joints:

Rivets	Press fit joint	Adhesives
This is a metal tube with a head at one end. It is inserted into the openings of the pieces to be joined together and then, with a tool known as a riveter, a head is placed onto the other end, joining the pieces.	In this type of joint, a pin with a slightly larger diameter than the opening is inserted into the opening using a hammer or pressure. Sometimes you have to pre-heat the hollow section to dilate the opening.	There are different types: hot melt adhesives, waterproof and instant glues. Before gluing the pieces together, you should scratch the surface to improve its adherence.

7.2. Temporary joints

Talking book

Finishing includes techniques that corrects imperfections on the surface, polishes and protects metals from damp and rust.
Joints can be permanent or temporary. Soldering and welding are the most common. Both use high temperatures and pressure on the surface.

If you use temporary joints, they can be joined and separated again without breaking the joint or damaging the pieces.

Nuts and bolts	Screws	Threaded stay bolts
The bolt is inserted through the pieces that need to be joined together. Washers are used so that the pieces don't break and to secure the joint.	A screw joins one piece to another where there is a threaded hole. If the screw threads the hole as it is going in, we say it is a self-drilling screw.	This bolt has grooves at both ends, but the middle section is smooth.
Keyed joint	Splined shafts	Sliding joints
With a piece of metal called a key, you can join two objects by putting the key in a groove.	The two pieces have grooves so that they fit together when joined together. The assembled pieces can rotate.	Two objects that are joined together that can move or slide over each other.

Why are some pieces of imitation jewellery covered in gold?

What is this technique called?

Soft soldering	Hard soldering	Oxyacetylene welding

What kind of welding or soldering would you use to join pieces together for the following objects: electronic components, the hull of a ship, a large bronze statue, a street lamp?

Electronic components:

The hull of a ship:

A large bronze statue:

A street lamp:

Find out what kinds of joints these pieces have: a metal drawer, the casing of a dishwasher, the metal frame on a pair of glasses, a tap.

a metal drawer
the casing of a dishwasher
the metal frame on a pair of glasses
a tap

screws
screws, nuts and bolts
screws
sliding joints

What types of finishing and joints are used in drinks cans?

What are you going to use for your flower?

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7. Joining

7.1. Permanent joints

7.2. Temporary joints

Activity 26

Activity 27

Activity 28

Activity 29