About 80% of the known chemical elements are metals.
- Metals are opaque lustrous elemental chemical substances that are good conductors of heat and electricity and, when polished, are good reflectors of light.
- Most elemental metals are malleable, ductile, and are generally denser than the other elemental substances.
- Metals are structurally distinguished from nonmetals by their atomic bonding and electron availability.
- The electron band structure of metals is characterized by a partially filled valence band. The “free electrons” lost from the outer shells of metallic atoms are available to carry an electric current.
- The defining property of a metal is that it is an element with a positive thermal coefficient of resistivity, meaning the electrical resistivity of a metal continuously increases as temperature increases.
There are a number of different grades that have some significantly different properties and machining qualities. Aluminium also forms a number of different alloys.
You can braze aluminium with zinc/aluminium alloys – one commercially available brazing rod is Durafix.
Parting Aluminium on the lathe can be tricky, so some simple rules to make this easier.
Easy to machine and get a crisp clean finish, when turning in the lathe use HSS tools and use zero or a very small top rake. I find it best to machine brass dry. These properties mean brass is great for creating patterns.
Types: Brass is an alloy of copper and zinc, but often other elements such as aluminium, iron, manganese, tin and lead are added. The result is a number of different types, standards and historical descriptions of brass.
Brass fittings should not be used in boilers due to dezincification.
A low melting point, good fluidity, castability, excellent machinability and wear resistance, cast irons have become an engineering material with a wide range of applications, including pipes, machine and car parts. There are a few worthwhile hints and tips when machining cast iron.
Noted for being ductile and having good electrical and thermal conductivity. It forms the basis of a number of alloys e.g. brass and bronze.
C101 – High conductivity – used in the electrical/electronic component industries.
C106 – available in sheet & strip in coil and tube it has excellent welding properties. It also can be offered in highly polished finishes for architectural purposes.
Annealing: Heat until it glows dull red, then cool (either slowly or by plunging it in water), the copper becomes very soft and easy to bend and work.
Machining: Not the easiest material to turn. I find turning it fast with cutting oil and very sharp tools and it will be fine. The problem with copper is it is malleable and so flows very easily. This means cutting tools need to be sharp to avoid smearing the copper onto the part being machined.
High Speed Steel
Used a lot for cutting tools.
The image to the right shows some blank pieces ready to be ground to shape and then used as lathe cutting tools.
The machinability index is relative ease of machining a metal. American Iron and Steel Institute rated AISI 1212 steel which is equivalent to EN1A in the UK as 100%. This sets a baseline from which you can compare the machinability of different materials.
Oil Hardening Steel: Heat the steel to 770 to 800°C and soak at this temperature for 3/4 hour per inch (25.4mm) thickness of material. Quench in a bath of oil inserting the heaviest end of the piece first (this way relieves stresses and reduces distortion). Further heat treatment at 100 to 120°C for a short while and then allowing the piece to cool naturally in air will reduce the stresses further and the possibility of cracking. Note: the higher the carbon content the lower the hardening temperature of steel.
I’ve used mild steel for a hammer head and then hardened the faces – small planishing hammer.
Surface Treatments of Mild Steel: there are a lot of different options for the surface treatment/finish of mild steel. Gun Blue is one option, but there are lots of other options.
Traditionally an alloy containing 80% tin and 20% lead.
The image shows a pewter flywheel on a solenoid engine. The outer surface has a hammered finish.
An alloy of copper with 3.5 to 10% of tin and a significant phosphorus content of up to 1%. Phosphor bronze has many uses where resistance to fatigue, wear and chemical corrosion are required.
Corrosion resistant steel in common use for medical and cooking amongst many other uses. A common material for inlet and exhaust valves on model engines.
Many different grades and qualities of steel that I think I need to just create a whole page that just lists all of the steels and a description of their various properties.
Nowadays tools are often referred to as being made from “carbide” – what they actually mean is Tungsten Carbide. The reason for using Tungsten Carbide is it has some great properties:
melting point 2,785–2,830°C
hardness of 9 on Mohs scale, 2600 Vickers number
Some tungsten carbide tools consist of a mild steel shank with a piece of tugsten carbide brazed in place and then ground to shape.