Engineering Studies
Home > Engineering Studies > Lifting Devices > Forming Processes - Rolling
Engineering materials: Structure/property relationships in forming processes
Suggested Answers
Activity 1
Go to the following web site and answer the questions below
http://www.bluescopesteel.com/navajo/display.cfm/objectID.5248A606-DDF6-4E80-B74FA4A95B3F5107#rolling 
- Cast steel is a relatively weak mass of coarse, uneven metal crystals. Describe the benefits of rolling cast metals and list some of the properties, which are achieved by this process.
Rolling causes this coarse grain structure to re-crystallise into a much finer grain structure, giving greater toughness, shock resistance and tensile (stress) strength.
- Justify the reason for heating steel slabs, blooms and billets to 1200°C prior to rolling.
This is done to make it easier to roll the steel (i.e. less force required) and it removes the rough, flaky surface, or scale.
- Cold rolling has quite a different effect on the finished product when compared to hot rolled steel. Describe some of these differences.
Cold rolling is carried out at room temperature and is rolled at very fast speeds using lubricants to reduce friction. Cold rolling increases strength, makes steel thinner and produces a bright smooth surface.
Activity 2
Go to the following web site and answer the following questions
http://www.steelstrip.co.uk/coldrolled.htm
- List some reasons for cold rolling following a hot rolling process
- Reduce the thickness
- Improve the surface finish
- Improve the thickness tolerances
- To offer a range of 'tempers'
- As a preparation for surface coating
- Explain the term ‘reversing mill’ when applied to cold rolling mills.
A reversing mill is where the steel enters the rolling mill from one side, passes through the other side and then comes back through the mill again. Normally it will go left to right through the mill a number of times being rolled a little thinner each time it goes through.
Activity 3
- What does the amount of strain, introduced during cold rolling, have on the rolled metal?
The amount of strain introduced determines the hardness and other material properties of the finished product.
- Cold rolled steel can be produced in various 'conditions'. Compare some of the characteristics and differences of 'skin rolling' and 'quarter hard rolled' stock.
In skin rolling, the metal is reduced by 0.5 to 1.0% and results in a surface that is smooth. It is more ductile and further forming and stretching operations can be performed. 'Quarter hard' has higher reductions, up to 50%. This increaes the yield point; grain orientations and material properties assume differnece properties along the grain orientation. Ductility decreases.
- Describe some of the 'bend' possibilites for 'quarter hard', 'half hard' and 'full hard' meterial.
'Quarter hard' material can be bent (perpendicular to the direction rolling) on itself without fracturing. 'Half hard' can be bent 90°, 'full hard' can be bent 45°, giving these materials great amounts of bending deformation, without fracturing.
Activity 4
- Which of the four sets of three microstructures depicts a structure representative of the descriptions of the jib members in terms of forming.
Group (c) elongated grains in the long members and tubes and equiaxed grains in the cross members (struts).
- Justify your selection in terms of working stress requirements and structural properties.
Elongated grains better resist induced bending stresses due to loads raised at different positions along the jib. (Note the position of ‘head tensioning’ ties to each end of the jib).
- Which member has the least bend strength property?
The cross braces have the least bend resistance as they act as struts to resist compressive forces.
Activity 5
From your knowledge of forming processes and structure/property relationships, select and justify the best possible position, on the steel plate, (for the ‘oxy-cut’ profiles for the side panels) to make the Support Arm. Your selection must achieve the best possible bend strength for the panels.
Option ‘B’ would be selected, as this would have the elongated grains running horizontally and providing the best possible bend resistance due to the ‘dead weight’ of the crane and working stresses.
|