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Strip steels for cans

Q1: Required properties

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Question For this application we need to consider what are the most important properties. From the list below select the three most important properties required by a drawn / wall ironed beverage (i.e. drinks) can.  

 

Strength

Red cross Strength is not a particularly important issue with strip steels used for drinks cans. In fact the general objective is to produce low strength steels in order to achieve a high level of formability, although the subsequent distribution of work hardened properties in the various portions of the finished can are critical to the can performance. So you need to look for a different property.

Toughness

Red cross Toughness is not very important here provided that the drinks can does not shatter when dropped, this is not a problem with strip steels so you need to look for another, more important, property.

Corrosion Resistance

Red cross This does need to be taken into account especially where the can is being used as a food container. For drinks cans the shelf life of the product is much less than say for a car body panel so corrosion protection is less critical and a different form of protection is used, i.e. tinplate and polymer coatings rather than galvanising + paint. Try another property.

Magnetic properties

Red cross Not really important for this application. Try another property.

Aesthetics

Red cross The appearance of the drinks can is very important and would be my fourth choice of property to consider. Many aspects of the appearance will be controlled by other properties which we will take into account. By appearance we mean ability to be coated (paint and protective layers e.g. polymer films), surface finish (i.e. no wrinkles, a consistent bright finish etc.). Try another property for one of the three most important.

Cost

Green tick Correct, cost is always an issue with design and materials selection, especially of mass produced items. In this case cost will be minimised because the steels are used in large quantities and, as low strength levels are all that are necessary, the alloying costs will be low.

Steel cleanliness

Green tick Correct, this is important as it will control the amount of rejected cans. A can is drawn down to a wall thickness of about 60 - 70µm and any inclusion in the steel will cause rupture/tearing of the can and hence rejection. This will then have implications for the cost of the product.

Fatigue resistance

Red cross For steel cans fatigue is not a crucial property as the cans do not typically receive significant load fluctuations that would lead to fatigue cracks forming. Also the expected life time of the can is relatively short minimising the need to worry about fatigue. Try another property.

Formability

Green tick Correct, this is an important property as a drinks can will start as a flat round blank that will be drawn into shape and we need to ensure that this can occur in a uniform manner giving good overall properties and little waste material.

Machinability

Red cross This is not a very important property in this case because the strip steels are stamped out and then pressed into shape so machining is not used. Try another property.

Weldability

Red cross to manufacture a drinks can the main body section is pressed out then the lid section is crimped into place meaning that welding is not required. Try another property.

Electrical properties

Red cross Not really important for this application. Try another property.

Wear resistance

Red cross Not really important for this application. Try another property.

Creep

Red cross Not really important for this application as creep in steels is only an issue at elevated temperatures and long exposure times, for example power plants where components may experience temperatures of 400°C+ for 20+ years. Try another property.

Recyclability

Red cross This is always important and becoming more so. Fortunately steel is one of the most easily recycled materials which makes it use favourable in this application. As steel is recyclable in general we need not consider this property to any great depth here. Try another property.

Surface hardness

Red cross This is not a critical property. Try again.

    

When you have correctly identified all three, they will be displayed in a 'Notepad', from where you can link to pages giving more detail.

NOTEPAD

Three most important properties for a drinks can:

  • Cleanness / consistency

  • Formability

  • Cost

 

 
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