R2 Working properties of materials

Posted: October 10, 2010 in Resistant Materials

Initial knowledge – 1

Current working knowledge – 2.5

I have a basic knowledge of working properties of the more common materials  used in workshops and schools but when looking at suitable materials for each of my projects I decided to get a more in-depth knowledge of the different variations of  materials and their working properties, some of these were not suitable for the projects in hand but I felt I could include them in my audit as a reference point for the future

When designing my plate rack I had to decide what would be an appropriate material to produce it from.  After researching various modern kitchens I decided that I would produce the majority of the product from some form of metal, but first I had to undertake research on what would be an appropriate metal to form it from and that started by looking into the properties of metal in general.  This has been extracted from ed215

There are three categories of metal, ferrous metals, non-ferrous and alloys.

Ferrous metals such as cast iron and stainless steel contain iron, they are almost all magnetic and unless they have been treated they corrode easily.  Non-ferrous metals such as copper brass and tin contain no iron, they are not magnetic and are more resistant to corrosion.  Pure metals consist of one single element and have only one type of atom in them.  They are often too soft and so they are rarely used alone as they do not have sufficient working properties.  These are obtained by alloying metals.  This is done by mixing two or more metals in their liquid state to produce a metal alloy that increases in strength, machineability or casting  properties including the likes of brass, aluminium and copper.

Aesthetically an obvious property of many metals is that it reflects light, leading them to have a shiny appearance, in the case of my plate rack I decided to use sheet aluminium which has a very reflective finish compared to other metals, however it is true that some metals are more reflective than others.  For example lead is very dull.

lead block

Metal has a high thermal conductivity and can often feel cold to touch; this is because they are good heat conductors and move heat quickly away from your body.

Along with conducting heat, metal is extremely efficient in conducting electricity.  At a simple level heat and electric energy is transferred quickly through the electrons which are free to move, although not all metals conduct equally well.  For instance copper is a very efficient conductor of both heat and electricity and so is used in electrical wiring, however metals such as zinc or titanium conduct far less efficiently so would be of little use in this instance.

Most common metals have a high melting point which is usually above 500 degrees Celsius and so are solid at room temperature.  However there are a few exceptions, most notably mercury which is liquid at room temperature and has an unusually low melting point of -39 degrees Celsius and is used in thermometers to measure heat.  Other metals that melt below 100 degrees Celsius include sodium gallium and potassium.  The high melting point of most metals is due to strong attractive forces between tightly packed atoms and a considerable amount of heat energy is needed to break these forces to turn a solid metal into liquid.

liquid mercury

Metals are malleable and ductile, malleability measures the ease of which a material can be bent and ductility is the extent to which a material can be drawn out or deformed without breaking.  This means we can shape metals into almost any shape we like.  Gold is a particularly ductile metal whereas something like lead is not.

The elasticicity of a metal is its ability to regain its original shape once it has been deformed.  The more deformed it has become yet is still able to return to its original form the more ‘elastic’ it is.  Metals tend to bend rather than break and so have a greater elasticity compared to other traditional materials such as glass or stone.

All of these properties derive from metals very regular structure which allows layers of atoms to slip over each other as the metal is deformed.

Most metals are strong in their solid state and some can support loads of 250,000 times its own weight.  The high strength of metals such as iron and steel and the fact they are relatively easy to extract and purify make them popular in the construction industry.  Other metals combine high strength with being light weight such as titanium and aluminium and so are popular in the aerospace industry amongst others.

Most metals have a great toughness which means they have a great ability to withstand impact and it is measured in terms of the amount of energy it can absorb without fracturing.

Metals hardness is defined as its resistance to being scratched, and although most common metals are considered to have a great resistance, the alkali metals on the far left of the periodic table are very soft and could be cut with a sharp blade.

periodic table

Metals used outdoors are corroded by rainwater or acid rain, metals in seawater corrode much faster because of the presence of dissolved salts.  The rate of corrosion is directly linked to metals reactivity.  Potassium and sodium are highly reactive and burst into flames when coming into contact with cold water.  Magnesium and calcium would not remain intact for a day in a wet environment.  A metal such as iron will rust (a chemical reaction with water and oxygen in the air) over a period of around a month whereas metals such as gold and silver which are some of the least reactive will not corrode at all.

rusty metal

Surprisingly despite its high reactivity, aluminium is not particularly easy to corrode.  The reason being that exposed aluminium reacts with oxygen in the air and the oxide layer that forms as a result effectively protects the metal underneath from any further reaction.  This made aluminium perfect for my plate rack as I included a draining system, the aluminium comes into contact with water but it does not rust.  However if a scratch is made in the aluminium you will see shiny metal, within a few seconds this will fade to a whiter shade as the aluminium and oxygen react.

Most metals readily form compounds with oxygen (oxides), chlorine (chlorides), sulphur (sulphides and sulphates) and carbon (carbides and carbonates).  A metal can be displaced from its compounds by a more reactive metal.   A classic example of displacement is the reaction between aluminium and iron oxide.  The aluminium being more reactive displaces the oxide and aluminium oxide and iron remain.  This is a highly exothermic reaction and generates a lot of heat and the heat released is sufficient to melt the iron that is produced.

It is possible to silver plate or copper plate an item made of a more reactive metal simply by placing it in a solution of silver nitrate or copper sulphate.  The more reactive metal displaces the silver (or copper) from the compound in the solution allowing the pure silver or copper to form on the surface of the item.

The primary example for extracting metal ore is form the ground via minine are 3 different types:

Open pit mining is used for large amounts of ore, soil and rock are moved from the surface to reveal the ore, forming a large open pit spanning up to 900 meters across.

Open cast mining is similar to open pit but it is done mainly near the surface, not requiring deep excavation with only the surface being removed.

Finally there is shaft mining where a tunnel is dug either into a mountain or deep into the ground, from the shaft tunnels are dug, and the ore is drilled or blasted away in chunks and taken to the surface by either conveyor belts or by hoists and pulley system

Having worked with aluminium I found it easy to bend and cut and fairly rigid and stable once bent into shape.  It is also easy to turn on the lathe and it is easy to obtain a fantastic finish with the use of the automated control and by taking tiny amounts off at a time.  It is easy to drill and therefore lent itself well to joining through riveting.  One of the problems I found with aluminium is that because it is soft it is susceptible to scratching and can also become dull if not polished regularly through simple finger marks that build up on the shiny surface.  When polished though it can look extremely presentable and it was easy to file and finish.  The only other metal I have had a little play with is copper and I found that it actually had quite similar properties to aluminium in that it was easy to manipulate and file

mining for metal

Again when manufacturing my ambiance light for ed217 I undertook research to look at the different type of plastics that were available  and there working properties, the following research is an extract from that electronic folio:

I think that the majority of my ambience light will be made of plastic. This is due to the fact that it is relatively inexpensive, it has the ability to be coloured or transparent if necessary, it is easy to mould and shape and it lends itself well to computer aided manufacture and so can be mass-produced. There are many different plastics available so I have researched a few and their properties so I can make an informed decision about what my light will be predominately made of:

ABS : A terpolymer made from three monomers, acrylonitrile, butadiene and styrene. Acrylonitrile and styrene provide chemical resistance, butadiene adds impact resistance and makes the plastic suitable for furniture and computer housings etc.

Acrylic: A hard thermoplastic made from acrylic acid or a derivative of acrylic acid. It is best known as a glass substitute and can also be known as trade names such as Perspex, Lucite and Plexiglas, It is strong and rigid and comes in various different opaque colours or transparent. It is also easy to form under heat, I feel this would be well suited for my ambience light.

  computer casing

Amino plastics: Plastics made from ammonia based compounds, namely urea formaldehyde and melamine formaldehyde.

Bakelite : This is really just a trade name but it is used frequently as a generic name for phenol formaldehyde (phenolic).

Cellophane : A Du Pont trade name for film made from regenerated wood pulp (cellulose).

Cellulose : The fibrous matter in all plant cells, with a long chain molecular structure. The most common sources used for making plastics are cotton fibres and wood pulp

Cellulose acetate: Is a tough thermoplastic made from cellulose in the form of cotton linters, treated with acetic acid and acetic anhydride. It can be used for many domestic mouldings such as spectacle frames, toothbrush handles, and as transparent packaging film.

Cellulose acetate butyrate: A thermoplastic made from cellulose treated with acetic and butyric acids. Transparent, opaque or coloured, with excellent moulding qualities, used where more moisture resistance and dimensional stability than cellulose acetate is required, this is possibly the plastic that was used in vase mood light featured in the existing ideas slide show

Copolymer: A plastic made by polymerizing two monomers, for example styrene and acrylonitrile .

Elastomer: A synthetic plastic with the flexible properties of rubber.

Epoxy resin: A very tough thermosetting resin used as a coating, or reinforced to make mouldings or laminates.

Epoxy Resin

Ester : A compound produced by the reaction between an acid and an alcohol.

GRP : Glass reinforced polyester, such as polyester resin strengthened by glass fibres, making the resin, which has no strength of its own, into a very tensile material. It is mainly used to build boats, furniture and cars.

HIPS : High impact polystyrene

LLDPE : Linear low density polyethylene, a new type of low density polythene.

Melalmine : Melamine formaldehyde, a thermoset produced by reacting (triaminotriazine) with formaldehyde. It is a tough glossy plastic usually strengthened with a filler of wood pulp.

Monomer: A simple low molecular weight compound. Polymerization links monomers together to form high molecular weight polymers.

Nylon: Not one material but a group of very tough and flexible materials called polyamides. Thermoplastic and usually found as fibres or used solid, as gears, zips and more recently as dyed jewellery.

Nylon and plastic fasteners

Phenolic: abbreviated version of phenol – formaldehyde. Phenolic is usually reinforced with a filler, but cast phenolic has no filler and can be translucent. It can be easily coloured and is used decoratively for jewellery, radio cabinets and all kinds of ornaments this could also be used for my light but it is not as readily available to myself as acrylic.

Polycarbonate : A very tough thermoplastic, usually found as a substitute for glass, for example: vandal proof telephone kiosks, bullet proof shields, baby bottles and picnic ware. Again this may have been suitable but I feel there is more versatility with acrylic as it is easier to manipulate.

Polycarbonate sheeting

Polyesters : Complex ester compounds which are thermosetting and can be polymerized at room temperature, for example GRP.

Polymer : Another word for a plastic material: one which has been made from chains of molecules of one or more monomers. Polymers (plastics) are organic substances, made from hundreds or thousands of molecules linked together in a repeating chain pattern (also known as macromolecules).

Polymerization : The chemical process of linking monomers to form new compounds called polymers. For example, ethylene is polymerized into polyethylene, (polythene for short).

Polypropylene : A thermoplastic polymerized from propene, very close to polythene in molecular structure, but harder, stronger and less flexible.

Polystyrene : A brittle. water white thermoplastic polymerized from styrene – (phenylethylene). The brittleness is overcome by adding some butadiene, which results in toughened polystyrene also known as high impact polystyrene (HIPS), a copolymer of butadiene and styrene. Expanded polystyrene is the rigid white foam used for packaging.

After working with acrylic I have realised that it has many uses and good properties and uses.  It seems to have been the material of choice for a lot of people on the course.  You can produce some nice effects with the use of coloured acrylic and in particular the live edge perspex.  It is easy to cut on the laser cutter and it is easy to produce some intricate interesting designs and lettering using this process.  It is easy to bend but once in a fixed position becomes very brittle as I unfortunately found out when  carrying out ED216.  Although it has a good quality look and fantastic clarity or colour when the protective film is removed it too is prone to easy scratching and so it is important to only use it for the right applications as it would become tired looking if constantly being moved around and banged about.  Although it is a thermoplastic when it  is reheated it is very hard to get it completely back to its normal shape (especially with large pieces) and although perfectly usable it can remain a little bit warped.  If over heated it can also have a tendency to bubble, tarnishing the surface.

I enjoy working  with wood but I have not really had the chance to work with any hardwood as of yet.  The wood I have worked with predominantly is pine and plywood as well as man made boards such as MDF.  I found pine easy to cut and finish but although it is strong and stable it is soft and so can be quite easy to make dents in if it is dropped etc.  Again I had to do research on the properties of wood and here is some information I found.

Properties of Wood

Grain. – Wood is composed of long, hollow wood cells, or fibers, sometimes accompanied by vessels of varying diameters. The character and direction of these fibers constitute what is termed the grain of the wood. As these fibers separate and break more easily lengthwise than across, we say that wood splits with the grain. If the fibers run very straight, the wood is straight-grained; if crooked, then it is called cross-grained.  Many causes affect the regularity of the grain: the stem itself may be crooked, it may be straight, but the fibers run spirally around it, or there may be sets of fibers alternating in spiral directions; branches and wounds also cause cross-grain.

If the cells are small and compact, the grain is said to be fine, as in box-wood if is nearly uniform in size and thickness, the wood is even-grained, as in maple.  The cells may vary greatly in size and thickness, and have large vessels in the spring growth, which would give rise to coarse-grained wood, as in the oak, ash, and chestnut.

Fig. 15.   Warping of planks cut from an unseasoned log.warping of planks from an unseasoned log

The appearance given by the annual rings and medullary rays to the surface of the wood differs very much with the kind of wood and the part of the log from which the board is sawed. Special cuts are made to obtain the best effect of these markings. To show silver-grain, the face of the board should be parallel, or nearly so, with the medullary rays.  The birch is an excellent example of this effect. Maple and ash are frequently seen with a wavy or curled grain. For veneers, which are about one sixteenth of an inch in thickness, wood with a very irregular grain is selected, such as walnut roots and knots, and knurls of mahogany.  In some old maple-trees an appearance called bird’s-eye, due to a small circular inflection of the fibers, gives to the wood a fine effect.

Woods in which the grain runs alternately in different directions, though hard to split and very difficult to work and finish, usually furnish an ornamented grain, such as mahogany.

Density. – This property depends on the more or less complete thickening of the walls of the wood-cells, and also upon the number and size of the vessels. Certain operations, such as turning, carving, and wood-engraving require dense or close-grained woods.

Porosity. – A porous wood has large, thin-walled cells and many open vessels. Its open grain is easily filled with preserving liquids which adapts it for framing and timber work generally, if such a wood is to be finished, the pores must be filled before a good surface can be obtained. As a rule, porous woods are soft and light, while dense woods are hard and heavy.

Weight and Hardness. – It sometimes happens that the entire cell is replaced by the thickened cell-wall, and this, together with deposits of oily and resinous substances, make an exceedingly hard and heavy wood. On the contrary, we have very light woods, even lighter than cork, these are composed of thin-walled cells filled with air. Between these extremes are found many gradations of weight and hardness, but woods are generally spoken of as hard or soft, and heavy or light. The hard and heavy woods are stronger and more durable than the softer and lighter ones.

The weight is expressed by a number, which shows the weight of the wood compared with the weight of an equal bulk of water, taken as the standard.

During the process of drying, wood becomes lighter and harder and so, lignum-vitse and most of the palms are quite soft and easily cut when green, but after drying are worked with great difficulty.

Strength. – The strength of wood depends on peculiar powers of resisting various forces brought to bear upon it. Thus, lignum-vitse and the oaks are noted for their stiffness, or resistance to bending, which is probably due to the interlacing of their fibers. Young hickory, lance-wood, and others are very elastic, bending readily and returning to their former position without injury to the structure. Black or swamp ash and young white oak split easily into long and strong strips or bands such as those used for making chair-seats or baskets. Very little force is required to break the fibers of whitewood, birch, and mahogany across the grain. Pine, ash, and maple break easily but with a splintered fracture. In some palms this splintering occurs to such a degree, that walking-sticks may be transformed into very dangerous weapons, which has given rise to laws in some countries restricting their use. Rattan, oak, and hickory, when bent short, have the individual fibers unbroken, but separated from each other; and are therefore tough woods. Hard and dense woods resist compression, while soft woods yield to pressure and are indented; and more so when the pressure is applied on the sides than on the ends of the fibers. This compressibility of the softer woods is taken advantage of in gluing up joints, where the pieces are forced into perfect contact by the pressure of the screws. To secure a good joint with hard woods it is necessary to use the greatest care in preparing and cutting the pieces. The cohesion of the particles of the fibers, when strains are applied lengthwise, is very great, several tons being required to fracture pine one inch square.

Colour. – As the heart-wood becomes lignified, coloring-matters are deposited within the substance of the cell-wall, giving to each kind its characteristic colors; these are exhibited in great variety, including every shade of color between the white of satin-wood and the black of ebony. In • the same wood there may be variations of tint, or even color, in the annual rings and medullary rays, enhancing the beauty of its appearance. The sap-wood receives none of the color-pigments, and therefore is always light or even white. As a rule, exposed surfaces, whether varnished or not, become darker; and this darkening, besides indicating age, gives to the surface a more agreeable effect than that of new wood. It is for this reason, as well as deception, that new cabinetwork of hard wood is stained to imitate the effects of age. Colour combined with a figured grain constitutes the intrinsic ornament of wood.

Durability. – At great age a slow oxidation of the constituents of the cell-wall takes place in the interior of the heart-wood of standing trees, thus rendering the wood softer and brittle, and an easy prey to the fungi and insects. Dampness, by promoting fungus growths, is very destructive to cut timber, few woods withstanding its injurious influence; especially is this so when there are alternating dampness and dryness as seen in those portions of a building or structure in contact with the soil. Most woods if kept dry and protected from insects with paint or varnish, will last for ages, as illustrated by ancient pieces of furniture. Nearly all woods are perfectly preserved if kept immersed in water, which is shown by the wood of vessels that have been sunk for a hundred years or more, and which finds application in laying the foundations of stone for large buildings and bridges upon the tops of piles driven below the water-mark. Many woods like cedar and camphor-wood have within their substance oils and resins which protect them from the fungi and insect life.

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