Pressing and bending steel plates

Working in Industry...

Background information

Rolled steel is used extensively in industry.

Steel sheet, (a few mm thick), or steel plate, (6 mm or more in thickness), is

pressed into cylinders and cones, and steel can be pressed around specific

arcs to form bends or angles.

These are pressed to great accuracy and are then assembled to make bulk

storage containers, ductwork, piers for oil rigs, panels for the hulls of ships,

etc.

TW Woods Construction is a heavy engineering and steel fabrication company

based at Tomago, NSW.

http://www.twwoods.net.au

The steel plates that are used in the production of these items

range in thickness from 6 mm to 70 mm.

TW Woods has several hydraulic roll presses that are used to

bend the steel plate into the required shape.

During the pressing process the steel is deformed in such a way that matter is ‘squished’

along the length from the inner surface of the steel plate to the outer surface.

i.e. the inner half of the steel is compressed as it is forced around the roller while the

outer half is stretched.

The section of the plate that is exactly in the middle, (with regard to the thickness),

is not affected. The length of the middle section of the steel plate is called the ‘mean

running’.

Mean

running

Mean

running

Mean

running

Part 1

When the thickness of the steel doesn't matter...

In this example, the label is so thin that when it is wrapped around the tin there is no "stretching"

or "squashing". We can calculate the circumference of the tin using

and measure/cut the label as the same length.

The diameter of the tin is approximately 73 mm.

Calculate the circumference of the tin and

hence, how long the label will need to be to wrap

around the tin.

Show working out...

Answer...

So, the circumference of the tin is approximately 229 mm and the label is

measured as being 230 mm.

229 mm is close

enough to 230 mm

So, the thickness of the label doesn't effect our calculations.

TIN

LABEL

73 mm

230 mm

= = = =

Example 1 Making a cylinder in sheet metal (1 or 2 mm thick)

Flues take the waste gases and smoke from a gas or wood heater and vent them

outside the house.

A flue is made from cylindrical sections which are joined together. Sections are

typically 900 mm or 1000 mm in length. The diameter may be from 100 mm to

305 mm (or more) depending on the size of the heater. The sections are rolled

from sheets of stainless steel, galvanized steel, or copper depending mainly on

the appearance required.

The picture shows part of the flue for a home fire place. It is made from rolled

stainless steel. It has a diameter of 230 mm and is 900 mm in length.

Find the dimensions of the rectangle of stainless steel sheet from which

each section is made. (Allow an additional 5 mm on the length to allow the

edges of the rolled cylinder to be overlapped and joined together).

230 mm

900 mm

900 m

m

?

1 or 2 mm thick

(thickness doesn't matter)

Calculate the dimensions of the steel sheet

from which the flue should be cut when d = 230 mm.

Show working out...

Answer...

The stainless steel sheet would need to be cut to a

length of 900 mm and a width of 728 mm.

90

0 m

m

728 mm

230 mm

900 mm

Now try for yourself...

The flue pictured forms part of a

chimney.

Calculate the dimensions of the sheet of

steel from which the 615 mm length

should be cut.

Allow an additional 5 mm to join the flue

together once rolled. Answer...

Now try for yourself...

The flue pictured forms part of a

chimney.

Calculate the dimensions of the sheet of

steel from which the 615 mm length

should be cut.

Allow an additional 5 mm to join the flue

together once rolled.

The chimney flue pictured bellow needs to be 2.7 m in length and have a diameter of

100 mm to meet specifications. Sections of flue are produced in lengths of 900 mm. An

additional 5 mm should be allowed to join each section of flue once it has been rolled.

a) How many sections of flue are required?

b) Calculate the dimensions of steel sheet required to fabricate

one section of flue, allowing for extra 5 mm.

c) Calculate the total amount of steel sheet required to

produce the entire chimney. Give your answer to the

nearest mm2.

d) Can all 3 sections be cut from 1 m2 sheet? Justify your

answer using mathematical calculations.

e) 1 m2 of steel sheet costs $15.90 per sheet. In terms of

dollars and cents, how much money is wasted in producing

the flues?

Part 2

For a cylinder made from steel which is 60 mm thick, or even 6 mm thick,

the effects of bending the steel can’t be ignored.

When the thickness is 6 mm or more it is called plate steel rather than sheet steel.

When thickness does matter...

Remeber...

Example 2 Pressing a cylinder from steel plate

Suppose that we have to make a cylinder from 60 mm steel plate such that

the cylinder has a height of 1500 mm and external radius of 900 mm.

(Note that in the manufacturing industry lengths are expressed in mm.)

It is most important to have the steel plate cut very accurately, (within 1 mm),

to the correct length and width before it is pressed. The pressing process can’t be

adjusted to correct any errors in the dimensions of the plate – if we press an

incorrectly sized plate we will get an incorrectly sized cylinder.

15

00

mm

? mm

60 mm

We know that the steel plate will have to be 60 mm thick and 1500 mm wide,

but how long must it be?

It appears that the length of the plate will have to be equal to the outside

circumference of the cylinder

C = 2 x pi x r = 2 × pi × 900 = 5655 mm (correct to the nearest mm).

If we act on this calculation and cut a sheet of 60 mm thick steel into a

rectangle of length 5655 mm by 1500 mm, then roll it, we will get a cylinder

of the correct height but the radius will be incorrect.

Why?

In the rolling process the outside material is stretched as it is rolled,

which means that the outer circumference will be more than 5655 mm,

which then means that the external radius will be greater than 900 mm.

How do we solve the problem?

We must work with a length measurement that does not change during

the rolling process, i.e. we must work with the mean running.

Step 1 Calculate the radius of the mean running

The radius of the circle produced with the mean running as its

circumference is (900– 30) mm or 870 mm.

Step 2 Calculate the circumference of the mean running, which is the required length to

cut

Using C = 2 x pi x RM we obtain C = 2 × pi × 870 = 5466 mm (correct to the nearest mm).

Now we know that the 60 mm thick steel plate has to be cut to a length of 5466 mm

and a width of 1500 mm.

1500 m

m

5466 mm

60 mm

Example 3 Pressing a cylinder from steel plate

Step 1 Calculate the mean running

The mean radius is 635 mm.

Note that when working with inside units, RM = RI + ½ × T.

(i.e. the radius of the mean running is the interior radius plus half the thickness).

70 mm

Step 2 Calculate the dimensions of the sheet of steel

Length required = circumference of mean running

= 2 × pi × 635

= 3990 mm

The steel required is 3990 mm long, 800 mm wide and 70 mm thick.

800 m

m

3990 mm

70 mm

70 mm

Student question... Use the mean running to calculate the dimensions of the steel plate

required to roll the section pictured below.

Assessment for Learning Activity

Additional Resource Links • Bend Angle and Angle at Centre • Terminology used in bending