Material Properties

Different metals have different properties, so if you are in the design stage of a project it is important to spend some time researching the limits and properties of materials and compare them to your requirements before you make your choices. Why spend a fortune on a pricey material when a cheaper alternative will do just as well for what you require?
Here is a basic break down of properties associated with metals and what they mean.

Tensile Strength

Tensile strength is the ability to withstand tensile forces. The object below is withstanding the combined tensile force of 4kN.

Ductility

Ductility is the ability to shape without cracking. For example if you wish to form a 90° bend into a thin steel bar it would have to be quite ductile to avoid it splitting and cracking along the bend. Heating the area to be bent can temporarily increase the ductility.

Density

Density is defined as the ratio of an objects mass to its volume. What makes one material less or more dense than another is down to how tightly packed the atoms are which make up that material, more atoms packed within a set area the more dense the material will be. An example of a low density metal would be Aluminium. An example of a high denisty metal would be Tungsten.

Hardness

Hardness is the ability to withstand indentation. There are a number of scales and systems used to measure the hardness of a material, for example Vickers, Brinell and Rockwell.

Brittleness

Something that is brittle is likely to shatter, crack, or split when struck with a certain force. For example glass is usually considered to be brittle.

Toughness

The resistance to fracture when stressed, this is different to tensile strength as the stress applied to find the tensile strength is just tension where toughness can be found by seeing how much energy the material can absorb before rupturing.

Malleability

Malleability is the ability of a material to be deformed without shattering or breaking, an example of a malleable material is Lead.

Yield Strength

The yield strength is defined as the stress at which a predetermined amount of permanent deformation occurs.

Young’s Modulus of Elasticity

Is defined as the ratio of the uni-axial stress over the uni-axial strain, for example a metal rod is being held at each end and is being pulled with forces of X at each of these ends, the rod is likely to stretch under these stresses and it’s the rods ability to return to its original shape once the forces are released which is measured as its modulus of elasticity. Strain is defined in mechanics terms as change in length divided by the original length.

Shear Modulus

Shear modulus describes a material’s response to shearing strains, this is when the material is under a force parallel to one of its faces, again this modulus is concerning the materials ability to return to its original shape.

Changing Properties of Metals

Carbon steel is a versatile material whose properties within limits can be altered to improve hardness and toughness by the addition of carbon and heat treatment.

However carbon steels have a number of limitations which makes them unsuitable for certain applications. These are:

-Poor resistance to oxidation
-Limited tensile, hardness and ductility when untreated
-Drastic quenching causes cracking and distortion
-Poor resistance to acid
-Large sections cannot be hardened
-Steel can soften at high temperatures

Hardening
Hardening is only possible via heat treatment on medium to high carbon steels, the metals are heated to certain temperatures depending on their carbon content (780°C to 850°C) then cooled quickly usually by quenching the metals in water or oil, the reason the metals are heated to these temperatures called their ‘austenitic crystal phase’ is because the crystal structures of the metals can then start to alter, forming bonds to create cementite as the carbon diffuses which is a very hard and brittle material.

% Carbon	Annealing Temperature
0.2%	850°C
0.5%	810°C
1.0%	780°C

Annealing
When annealing the metal is heated just above the re-crystallization temperature process and is left to cool slowly, for what is called a full anneal the metal is left to cool in the furnace, this allows the metal to cool off more gradually. Annealing changes the metals properties to become more soft and ductile, this is caused by the grain structure within altering and re-aligning at heat.

Hot Rolled Grain	Annealed Grain

Normalising
Normalising removes stresses within the grain structure of the metal thus making the metal more stable and ready for other processes. This is done by heating the metal to a higher temperature than that of the annealing process then leaving it to air cool.

Tempering
This gives the metal more malleability but taking away a small amount of hardness in the process. Tempering is done by heating the metal to a pre determined temperature which will depend on the level of malleability required. The size and the arrangement of the metals grain structure will affect the metals properties such as; hardness, ductility, malleability ect.

Basic Iron/Carbon Phase Graph

This graph shows the basic relationship of carbon content in steel when hardening with heat treatment, as the graph shows high carbon steels can become very hard at the cost of ductility.

Ferrite Phase
-High ductility
-Poor tensile strength
-Low hardness

Pearlite Phase
-High tensile strength
-Increasing hardness
-Less ductility

Cementite Phase
-Brittle
-Low ductility
-Lower tensile strength

Low Carbon	Mild Steel	Medium Carbon	High Carbon
Applications: -Car body panels -Filing cabinets Properties: -Malleable -Very ductile -Soft	Applications: -Automotive parts -Brackets Properties: -Low hardness -Medium tensile strength -Good ductility	Applications: -Hammers -Chisels Properties: -Medium hardness -Good tensile strength -Medium ductility	Applications: -High speed tooling Properties: -Hard -Brittle -Low ductility

MATERIAL HANDLING

Bases on Design features and operational characteristics, material handling equipment may be broadly classified as:

Hoisting Equipment’s:

It constitute a group of equipment which are employed mainly for lifting or lowering of unit load or piece goods in batches. This group of equipment’s can be further sub classified into:

1. Pure Hoisting Machineries

• Jack
• Winches
• Hand Hoists
• Pulley Blocks

2. Cranes

• EOT Crane
• Jib Crane
• Cantilever Crane

3. Elevators

• Lift
• Bucket Elevators

Conveying Equipment’s:

It comprises of a number of equipment which are employed for handling principally bulk load (occasionally piece goods or unit load may also be handled) in continuous flow. Such machines do not have separate lifting or lowering gear. This group of equipment also can have further sub classifications as:

1. Belt Conveyor

2. Hydraulic Conveyor

3. Pneumatic Conveyor

4. Apron Conveyor

5. Screw Conveyor

6. Flight Conveyor

Surface/ Overhead Equipment’s:

These are the group of equipment’s which are employed for handling unit load or bulk load in batches on a horizontal surface. This group of equipment may be further sub classified into:

1. Truck and Lorries

2. Railway Cars and Wagons

3. Fork Lifts

4. Overhead mono-rail / Equipment

5. Scrapers and Skidders

Types of Material Handling Equipment Loads:

It usually classified into:

1. Unit Load

2. Bulk Load

Unit Load:

Unit loads are those which are counted by numbers or units. A component of a machine, a complete machine, a structural element, a beam, a girder, building block are some examples of unit load.

Sometimes certain quantities of free flowing materials can be placed in a container and can be handled as unit load. Hoisting equipment are primarily used for handling unit load. Unit loads are usually specified by it’s weight.

Bulk Load:

When the load is in the form of particles or lumps of homogeneous materials or powder like materials, which can not be counted by numbers, it is called as “Bulk load”.

Examples are:

Sand, Cement, Coal, Mineral, Stone, Clay etc.,

A bulk material may be classified by it’s:

1. Bulk Density

2. Lump-Size

3. Flowability

4. Abrasiveness

5. Miscellaneous Characteristics