What is the difference between a flat and a long product?
Long products are formed by grooved rolls
Flat products are formed by flat rolls
Name the parts of a rolling stand
a housing
b drive
c rolls
m motor
Name 4 arrangements of rolls
What are considered semi finished products?
slab, billet, bloom
Give the marked terms:
What are the two stages of milling operations? Describe them.
Roughing
to obtain base product with different dimensions
Finishing
to reach final shape and dimension
What is the typical strain rate and interpass time of a rolling row for cold strip rolling?
strain rate: 100 s^-1
interpass time: 0.4-4s
Describe the principle of a discontinous annealing furnace.
coils are stacked in furnace and heated at 700°C for 10h
What are the five steps in a coninous annealing oven?
welding
cleaning
reservoir
heating
cooling
What are the characteristics of steel plate rolling?
strain 0.1-0.4
strain rate 1-30 s^-1
interpass time: 8-10 s
housing has to support high loads
How many stands are normally used in each step for producing a round bar?
7-8 roughing stand
6-10 intermediate stand
10 finishing stand
How can the length that is being worked by the roll be calculated?
What is the continuity equation for rolling?
How can the friction coefficient be derivated?
l_d=working length
What is the maximum reduction in rolling?
Name the usual firction coefficient for steels and Al alloys in hot rolling.
steels: 0.2-0.5
Al alloys. 0.15-0.3
What is the usual friction coefficient in cold rolling?
<0.1 always lubricated
What is the ford equation and what is calculated by it?
S=rolling force
R=radious
How are the strain and stress calculated in rolling and what assumptions are necessary?
assumptions: plain strain(epsilon 3=0), absence of friction
Describe the pressure distribution on the roll with the presence of friction compared to no present friction.
Name the components of this formula:
P=rolling load
w_0=width of sheet
sigma_1=mean plain strain flow stress
L=length of contact
G=parameter based on friction length of contact and height reduction
What is the temperature distribution over the rolling process steps?
Heating
roughing
finishing
cold rolling
annealing
What is coiling?
The process of transferring a long product like for example a wire onto a coil for transportation.
Why should ferritic, low C steels be cold coiled and what does that mean?
Cold coiling: T<660°C carbo nitrides do not have time to precipitate
Hot coiling: T>660°C Al carbo nitrides have time to precipitate during coiling
How long does a steel need to be annealed for optimal thermal homogenization?
10-20h
What are the defects occuring in rolled products?
oxides
Surface cracks
lateral spread
barreling
Hot/Cold rolling
Internal cracks
What is undercrowning in rolling and what are the effects?
What materials are rolls made of and with which procedure are they made?
material: white cast iron, high-Cr steels
casting: static or centrifugal casting subsequent forging
What is the special feature of grooved rolls?
they are often coated by thermal spray
Describe the temperature over time distribution of the roll during a rolling process.
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