Pass Design of Angle 55 × 55 × 6 mm
Design of Finishing Pass
Fig. 8.6 Cold Section of Angle 55 « 55 * 6 mm.
Area of Angle = t x (21 -t) + ax, where t and L are the thickness, length of angle and ax is the area of curvature.
Weight = , where density of steel is 7.85 gm/cc.
= 5.06 kg/m
If the length of bar is taken as 85 m (length of cooling bed is 90 m)
The input billet length will be 100 x 100 mm, its sectional weight is
It is recommended that the length of billet is to be taken as 5.0 m to have the standardization of the billet size in billet yard .Billet length of 5 m will give total length of bar of about 76 m at cooling bed, which is within limit.
Finishing temperature after the finished stand is to be ensured around 850°C to have better quality and properties of the finished angle.
At the temperature of 850°C, the co-efficient of elongation will be around 1.0102.
But the leg length in this case is to be kept to the cold section size i.e., 55 mm, to facilitate to rolling in negative size and to give more roll life even after the wear out of pass.
Computation of Thickness of other Passes of Angle Rolling
A thickness graph is to be prepared for co-efficient of reduction vs. pass number is shown below in the Fig. 8.7.
Fig. 8.7 Graph for computation of Co-efficient of Reduction for Closed Passes for Angle 55 x 55 x 6 mm.
It is seen from the graph that co-efficient of reduction is to be kept as minimum as possible in finishing passes, as to give more pass life due to less wear out of the finishing pass. Reduction then gradually increases in subsequent passes i.e., from pre-finishing passes going towards initial passings, whereas, it limited by angle of bite and motor capacity only.
The finishing pass should be designed with free widening. In this case, the finishing pass will so design, so that not only, it will facilitate to roll angles of size 50-65 mm size from the same pass, but also to roll thickness from 5 nun to 10 nun of same size from the same pass.
Fig. 8.8 Roll Diagram of Finishing Stand (Stand-12).
Pre-finishing Pass (Stand -10)
The computation of the pass and roll design of pre-finishing stand-10 is explained below and as shown in Fig. 8.9 and 8.10 below.
Fig. 8.9 Pass Diagram for Prefinishing Stand (Stand-10). Thickness of flange is taken as 7 min.
Spread is generally assumed as 30% for angle design Length,
Length of chord,
Assuming an 6% taper on each side Then,
As finishing and pre-finishing stands (stand 10 and 12) are not the part of a continuous group, the Nu and Nl0 are assumed as 300 RPM.
Fig. 8.10 Roll Diagram Pre-finishing Stand (Stand-10).
STRAND PASS (Stand-09)
With the help of thickness graph, computation of pass and roll design of stand 9 has been made and explained and shown in the Fig. 8.11 and 8.12.
Thickness of flange is taken as 8.5 mm, as per graph Fig. 8.7.
Fig. 8.11 Pass Diagram Stand-9.
Spread for angle design is taken as 30%
Length of chord,
Assuming a taper of 10% on each side Then,
Fig. 8.12 Roll Diagram stand-9.
With the help of thickness graph, computation of the pass and roll design of stand 8, has been made and explained and shown in the Fig. 8.13 and 8.14, below.
Fig. 8.13 Pass Diagram Stand-8.
Thickness of flange is taken as 11.0 mm, as per thickness graph Fig. 11.8. Spread for angle design is taken as 30%
Length of chord,
Assuming an 10% taper on each side Then,
Rolling Diameter Motor RPM,
Fig. 8.14 Roll Diagram Stand-8.
6.5.2 (Stand-6 & 7)
The stand 07 is a vertical stand and its purpose is to facilitate the rolling of different section/thickness from same scheme/pass, by reducing the width of work-piece with the help of vertical roll and to bring the width of stock fed to stand 8 to a correct calibrated size and to eliminate the variation in the input billet size
Fig. 8.15 Pass Diagram Stand-6.
The thickness of flange is taken as 14 mm with help of thickness graph (Fig. 11.8)
Spread for angle design is taken as 30%
It is assumed that this pass will be used for the rolling angle sizes from 50 x 50 to 65 x 65 mm
d = 28.5 nun assumed, based upon the sizes of angles to be rolled, average size comes to 51 nun
Here, it is assumed as 98°
Fig. 8.16 Roll Diagram Stand-6.
Rolling Constant = F x Dkx —
Where, F is the area of metal, Dk is rolling diameter,
N6 is the Speed of Motor, which is assumed as 300 rpm and i is the reducer ratio.
Then constant for intermediate group works out to
As explained earlier, the function of pass-7 is to press the flanges and buckle them to make to the stock to enter easily in pass-8, which is the first forming pass, designed with fixed angle i.e., 90°.
Fig. 8.17 Pass Diagram Stand-7.
The angle is considered between 95 to 105 degree and it is generally taken same as of pass 6 i.e., 98°.
Rolling Diameter, Dk = Dav _
= 460 - = 439.2 mm
Pass design of stand 5, has been done as shown in the Fig. 8.19, shown below:
Fig. 8.19 Pass Diagram Stand-5.
AH6 is assumed as 26 mm.
Here, height of pass is so selected, so that it can cover the total height of pass 6.
And the spread in the pass is assumed about 25%, as there is restricted spread fr om side of the pass. Then spread will be
6.6.2 Stand 1 to 4
Pass design of stand 1 to 4, has been done with square -rectangular system as explained below:
The roll pass design of square -rectangular is the simplest form of roll pass design system. Here, stand 1 to 4 will have square- rectangular design system.
First of all, it is to be decide first, which stand will have box pass and which stand will have barrel pass.
It is preferred to have box pass in first stand for following reasons:
- • To take care of sectional variation of incoming billets.
- • To shed of scale from the hot billet. It also acts as scale shedding pass.
- • To avoid slipping of metal and better stability of work-piece.
- • Take care of the variation of temperature, to avoid bending of piece, which will facilitate easy tilting by 90° before the stock enters in to stand-2. Likewise box pass is also recoimnended in Stand-4, which has to provide
the feeding of correct metal to the first cutting passes, stand-5 of angle design.
Other left over stands of roughing stands i.e., 2 and 3, can have barrel passes, as these barrel passes will help in avoiding the tedious roll changing of stands of roughing group. Which takes a lot of time in roll changing, while changing from one section to another. Only disadvantageous is that there is no control over the section, as there will be free widening in barrel passes.
(a) Roughing Group Pass-4 (Vertical Stand)
The design of box pass of stand-4 is shown below (Fig. 8.20). The root of pass should be equal or within ±2 mm of the incoming width of the stock to facilitate the smooth entry of bar and to avoid faster wear out of pass.
Fig. 8.21 Roll Diagram of Stand-4, (b) Roughing Group Pass-1 (Horizontal Stand)
Fig. 8.22 Pass 1 (Box Pass).
(c) Computation of Rolling Diameter for Roughing Group
Here, Dk for roughing group (Stand 1 to 5), will be worked out as follows:
- (i) Pass 2 and 3: These two passes are barrel passes, Dk for this two passes will be the Dc i.e., collar diameter. Dk for stand 2 and 3 will be 523 and 510 mm respectively, which will be also Dc of these two stands.
- (if) Pass 1 and 4: These two stands have box passes. For Box passes i.e., for stand 1 and 4, Dk will be the pass diameter, which comes to 476 and 392 mm for stand 1 and 4 respectively.
(Hi) Pass 5: As stand 5 is the first cutting pass of angle design, Dk of sand 5,works out in same manner as shown for other closed passes of angle design.
(d) Computation of Motor Speed N
Rolling Constant = f x Dk* —
Where, F is the area of metal,
DK is rolling diameter, i is the reducer ratio
(i) Stand-1: Here, it is recommended to use box pass (Fig. 8.22). The advantage of using box pass at stand-1 are numerous like stability of work-piece is more in box pass compare to the barrel pass where chances of twisting is less. It also acts as scale shedding pass, which in turn will help to improve the quality of product. The amount of spread is also less compare to barrel pass.
It is not part of the continuous group. Here, speed is kept such that to facilitate easier bite and should not give any chance of slipping of the metal, which effects adversely the mill equipments. Here, speed is assumed as 300 rpm.
Sometimes, ragging of rolls, use of sand and forced biting is given in stand-1 to facilitate smooth bite in stand-1.
Diameter of stand-1 plays a vital role in the biting of billets. The use of minimum diameter rolls should be avoided.
N2 is the Speed of Motor, Which is assumed as 300 lpm Then Constant for roughing group works out to
(ш) Stand-3 (iv) Stand-4