Steel Times on Byblock
Wire rod blocks are extremely compact and productive units. However, due to their
rigid nature of gearboxes, trying to provide them with a suitable roll pass design
can be incredibly complex. A sophisticated software program is now available,
speeding pass design and mechanical design operations by some thousand times.
ROLL PASS DESIGN SOFTWARE FOR WIRE ROD BLOCKS (*)
By Annibale Izzo, Linebow (**)
Roll pass design calculations for bar and rod mills are based on two parameters:
the elongation coefficient - designated Lambda - which is the ratio between the
exit cross sectional areas at stands N and N+1; and the transmission ratio -
designated Tau - which is the ratio between the rotational speeds of the rolls at
stands N+1 and N. Lambda is a typical parameter in rolling technology while Tau
is a typical parameter in gearing technology.
When applying these parameters to two types of rolling mills - the continuous bar
mill, and the mill fitted with a wire rod block for precision shaping of the final bar -
Lambda is important to both, but Tau is only important in the wire rod block section
of a mill. A continuous bar mill with 'N' stands has N independent motors, each with
an individually-set speed (rpm). The N-stand wire rod block has a single motor,
powering each stand through N gearing mechanisms.
Basic laws of rolling
The elongation coefficient is defined as the ratio between cross sectional areas of
the product exiting stands N and N+1, rather than between the lengths exiting N+1
and N. This is made possible by the first law of rolling, which states that the
volume is a constant: ie cross-sectional area x length = constant.
But there is a second, fundamental law of rolling, which states that the flow is a
constant: ie cross-sectional area x linear speed = constant.
This law provides the 'mechanism' with which it is possible to perform roll
pass design in continuous bar mills.
Continuous bar mills
Generally speaking, the roll pass designer starts from an initial billet, a
finished round and a mill with N stands1. Through a number of formulae, a proper
distribution of the Lambda coefficients is achieved. This means determining
N cross-sectional areas A' [mm^2], hence N linear speeds LS [m/s]. Then
the shape and dimensions of N grooves are calculated, each capable of
delivering a bar with cross-sectional area A'.
In a program for electronic roll pass design, the algorithm controls that
each groove is correctly filled. While applying the proper spread formulae,
two important factors are calculated: working diameter WD [mm] and forward
slip FS. These allow the mill settings to be completed, with rotational
speeds RS [rpm] defined by the formula:
RS=60000*LS/(PI*WD*FS).
Wire rod blocks
Generally speaking, the roll pass designer starts from an entry round (with
an entry speed), a finished round and an N-stand block (with N-1 values of
Tau). Exit bar speed is immediately calculated and, through approximate
values of forward slip and working diameter, the related rotational speed is
determined. This means determining N rotational speeds, hence N linear
speeds, and N cross-sectional areas A'. Then the dimensions of N grooves
(N/2 ovals and N/2 rounds since alternate stands have oval and round passes)
are calculated, each capable of delivering an oval or round section with
cross-sectional area A'.
In a program for electronic roll pass design, the algorithm controls that
each groove is correctly filled AND that each exit cross-sectional area
Q' (from calculated groove dimensions) is almost identical to A' (from the
law of constant flow).
The BYBLOCK program
BYBLOCK is the most recent, and most sophisticated program produced by the
software house Linebow2,3. It is dedicated to the design of wire rod blocks.
Running on a 486DX/66 processor, the program can take just 18 seconds to
design an entire 8-stand block. The time required by a human designer to
obtain the same performance without software could be anywhere between
5 and 50 hours.
Although it may seem irrelevant to summarize the various steps of the design
process in the two types of mills examined, it does lead to better understanding.
By comparing the two cases, we can see their inverted approach to the problem.
In continuous bar mills we start from N values of Lambda to calculate
cross-sectional areas, then linear speeds, then working diameters (WDs),
then forward slips (FSs) and then rotational speeds.
In wire rod blocks we start from N-1 values of Tau to calculate rotational
speeds, then linear speeds, then cross-sectional areas. At this stage only
WDs and FS can be calculated.
Apparently, in block design we do not initially have enough elements to
calculate WDs and FSs. This leads to BYBLOCK operation being divided in
two loops, a "first approximation" and a "second approximation".
The basic options
The software is designed to be used either by a roll pass designer or a mill
manufacturer. On entering the program, the user is prompted with the following
options:
if you know entry round area and finished round diameter, press A
if you know number of stands and finished round diameter, press B
if you want to force round diameters at even stands, press C
Options 'A' and 'B' are equivalent. Option 'A' advises the number of stands
to use (in any block it is possible to de-activate pairs of stands); option 'B'
advises about a suitable value of entry cross-sectional area.
Option 'C' is particularly important for block designers and manufacturers.
The values of Tau are not requested but calculated, and the program is
challenged with an input of N/2 round diameters. That is, in an 8-stand block,
you can ask to have (for example) round 10 mm at stand 2, round 8.5 mm
at stand 4, round 7 mm at stand 6 and round 6 mm at stand 8.
Automatic and semi-automatic modes
Each of the three basic options allows the choice of either automatic mode or
semi-automatic mode. The difference between the two is in roll gap values,
which are assigned by the program or provided by the designer.
To show how the semi-automatic mode can be useful, let us first assume that
we are working in automatic mode. At a certain stand, the pass dimensions are
calculated. However, to attain the required cross-sectional area, the exit bar width
becomes larger than the maximum pass width. This should abort the process.
However, the designer would then be left without any indication of how to resolve
the problem.
Instead of aborting, BYBLOCK beeps and carries out the design report anyway,
underlining the irregular figures. By restarting BYBLOCK in semi-automatic mode
the designer can fix the problem (see example).
Manual mode
Option 'B' allows the choice of the manual mode which is used if a roll has to be
changed out of schedule due to damage. Maybe there are no rolls available with
exactly the same diameter, or the available rolls have grooves which almost
(but not fully) match the original ones.
For such accidents, the necessary roll gap changes to counterbalance the new
configuration have to be determined on the shop floor. This is automatically done
by BYBLOCK in manual mode.
Input data
Option 'B' covers all three operating modes: automatic, semi-automatic and manual.
Because normally a block is located after a bar mill, the first question is "Source
stand?". If we have a 16-stand bar mill followed by an 8-stand block, the answer to
this question is 16: block stands will then automatically be labelled 17 to 24.
Answering zero allows the block stands to be labelled 1 to 8.
For an N-stand block, a list of input data comprises:
Items of data
Number of source stand 1
Number of block stands 1
Block reduction ratio (global Tau) 1
Finished round diameter 1
Entry round area (suggested) 1
Entry round speed 1
Rolled stock material (Carbon steels) 3
Entry round temperature 1
Nominal roll diameters N
Actual roll diameters N
Roll surface hardness N
Roll material N
Block reduction ratios N-1
Relief angles for rounds N/2
Spread correction coefficients (suggested) N
Roll gaps (semi-auto only) N
______________________________________________________________________________
Web Site
For further details and for free demonstration software, visit the Internet at
http://www.passdesign.com (***)
______________________________________________________________________________
Working example
To illustrate the application of the program, part of the report produced when
using BYBLOCK's automatic mode (option B) to make rounds of 5.5 mm diameter
on a bar mill of 16 stands followed by an 8-stand block is shown.
The program display below suggests that entry round cross-sectional area could
be 89.5152 mm^2, and we accept this by pressing ENTER.
B L O C K D E S I G N F O R R O U N D 5.5
The ABCD Steel Company Ltd.
Number of stands 8 - option B
Initial section is a round from stand 16
Entry round area 89.5152 mm^2
Entry round speed 18 m/s
Entry round temperature 1100 °C
Final round diameter 5.5 mm
Final speed 66.1 m/s
Rolling temperature - calculated
Theoretical mill throughput 43.0 t/h
Rolled stock: carbon steel with C = 1 ; Mn = 1 ; Cr = 1 [%]
The input data can be read from the roll pass design report shown in Fig 1 which
has been condensed in this example for stands 17-22 to show only geometric data.
The data should be read against the relevant head, OV (oval pass) or RD (round
pass) as indicated against each stand number.
1 Consolidated form of information displayed. The full display is shown for stands 23 & 24
______________________________________________________________________________
OV b1t h1t b1r h1r r maxw gap dnom dwor [mm]
RD drn h1r b1r maxw gap dnom dwor [mm]
17 OV 13.68 7.73 12.96 7.73 7.99 13.03 1.00 210 204.32
18 RD 9.28 A 25 9.28 9.27 9.77 1.00 210 202.45
19 OV 13.21 6.13 11.80 6.13 8.65 12.30 1.00 210 205.57
20 RD 7.83 A 25 7.83 7.82 8.17 1.00 210 203.76
21 OV 10.72 5.39 9.60 5.39 6.68 9.90 1.00 170 166.26
22 RD 6.61 A 25 6.61 6.61 6.83 1.00 170 164.93
23 OV b1t h1t b1r h1r r maxw gap dnom dwor [mm]
8.85 4.60 8.07 4.60 5.40 8.05 1.00 170 166.98
----- -----
cE3 area slip speed revs temp K 28 P 2 M 26 N
-234 27.99 1.0237 57574 6433 1152 277 22 250 169
mm^2 mm/s rpm °C N/mm^2 kN N m kW
grwa = 7.7 grwb = 8.9 grwc = 8.9
HSC: 100; KSC: 4 tau = 1.1667
24 RD drn h1r b1r maxw gap dnom dwor [mm]
5.57 A 25 5.57 5.57 5.68 1.00 170 165.90
cE3 area slip speed revs temp K 23 P 1 M 15 N
-278 24.38 1.0137 66088 7505 1160 224 12 150 118
mm^2 mm/s rpm °C N/mm^2 kN N m kW
grwa = 8.2 grwb = 9.9 grwc = 9.9
HSC: 100; KSC: 4
Block reduction ratio: 3.059718
Global elongation coefficient: 3.67157
Total power required (just for rolling): 1123 kW
DATE (MM-DD-YY): 10-09-1996
HOUR: 23:12:50
Processing time: 18 s
______________________________________________________________________________
The full display is presented for stands 23 and 24 which include the relevant
calculated data for these stands. The value of Tau (reduction ratio between
stand N and stand N+1) is shown only for stand 23 but is indicated at each
stand N in the full display.
The reduction ratios are:
17->18 1.116300
18->19 1.198700
19->20 1.164300
20->21 1.199600
21->22 1.167900
22->23 1.201500
23->24 1.166700
And the relief angles (A) for rounds:
25 25 25 25
During the 18 seconds of processing two beeps were heard meaning that one
irregular situation occurred (at stand 23 underlined values).
To fix the problem, launch BYBLOCK again, set the semi-automatic mode
and assign gap=1 mm at stands 17-20 and gap=0.5 mm at stands 21-24. It works!
If you are curious to know the results, in that position the new report
shows b1r=8.07 and maxw=8.47. And, with the new gap configuration, the processing
time fell to 13 seconds.
Key to symbols
OV oval pass
RD round pass
cE3 is 1000 times the Suppo/Izzo spread correction coefficient cw4
HSC is the roll surface hardness [Shore C]
KSC is a code for roll material (4 is tungsten carbide)
grw (in 3 versions) is the bite angle [degrees]
A is relief angle for rounds [degrees]
b1t is theoretical width of current roll pass
h1t is theoretical height of current roll pass
maxw is max width of groove on the roll barrel
r is radius of oval
drn is theoretical round diameter
dnom is roll barrel diameter
dwor is working diameter
K is roll pressure in current pass [Newton/mm^2 and kg/mm^2]
P is roll force in current pass [kiloNewton and t]
M is roll torque in current pass [Newton.m and kgm]
N is rolling power in current pass [kW]
REFERENCES
1) U. Suppo, A. Izzo, P. Diana, "Anwendung eines elektronischen Rechners zur
Rundstahlkalibrierung", Archiv für das Eisenhüttenwesen, 46 (1975),
Nr. 7 Juli
2) A. Izzo, "Automating roll pass design for rounds", Steel Times, July 1988
3) A. Izzo, "Un précieux logiciel pour votre précieux matériel (de
laminage)", La Revue de Métallurgie - CIT, Avril 1994
4) A. Izzo, "Spread formulae" in World Wide Web site
http://www.passdesign.com (***)
(*) Published by Steel Times, Jan 1997, p 14-15
(**) Via Garda 2, Ivrea, Italy. Phone +39 0125 616 768, fax +39 02 700 500 073,
e-mail info@passdesign.com
(***) URL updated January 2001