In the year 1933, Dr. Sendzimir invented the first Sendzimir mill, which was used to produce steel strip with width of 800 mm, and 0.13 mm thickness. Nowadays, there are over 400 mills working in 35 countries. 90% of cold rolled stainless steel strip is produced by Sendzimir mill, besides, huge quantity of silicon steel plate, non-ferrous metal and low carbon steel are being rolled by Sendzimir mill in the world.
Now, the smallest 20 high mill can produce strip products with only 100 mm width and only a few micron thickness; yet the widest is 2 meters. The highest working speed is over 1000 m/min.
Multi-row mills
In total, Sendzimir now has over 265 cluster mills to their credit as well as 55 Z-High®Mills and 16 Planetary mills in over 43 countries.
A Z-Mill or Sendzimir Mill is a machine for rolling steel. Unlike a traditional rolling mill this 20-high cluster mill configuration utilizes cascaded supporting rolls to apply force on the small work rolls in the center. This allows the application of a higher roll pressure without bending the work rolls, which would result in poor metal quality. Thus very hard and elastic materials can be rolled.
2. Varieties of cluster mills and their roll arrangements
Backing bearings have been specially developed for cold rolling mills of the cluster type, but can also be used for other applications, e.g. straightening or bending machines. Backing bearings are roller bearings having a particularly thick-walled outer ring and can be mounted on stationary support shafts to form back-up or straightening rolls. The forces from the work rolls are transmitted via the support shaft and a system of support saddles to the roll or machine stands. The picture below shows the arrangement of the backing bearings on theeight support shafts of a 20-roll mill.
Bearing A, D, E and H undertake 60% rolling force Bearing B, C, F and G undertake 40% rolling force
20-roller cold rolling mill
① Back shaft ② Middle roller ③ Working roller ④ Backing bearing – type 2 ⑤ Support bracket
Backing bearings based on cylindrical roller bearings have two or three rows of rollers and are available as full complement bearings (without cage) or as caged bearings, with or without integral flanges or flange rings. The advantage of the bearings without flanges lies in their particularly simple geometrical form and their very high radial load carrying capacity.
Backing bearings for Multi-row (cluster) mills
Cylindrical roller backing bearings without flanges or flange rings cannot accommodate any axial load. It is therefore necessary to position thrust washers of bronze or plastic between the side faces of the outer ring and the support saddles.
4. Backing Bearings Tolerances
Because of the narrow tolerances required for the thickness of the rolled material, backing bearings are produced with a running accuracy to P4 specifications, or better. In addition, the tolerances for the cross sectional height of the bearings is very tight see below table.
table – Tolerances for cross sectional height
cross sectional
Cross sectional height H
Cross sectional height H
height group
tolerances
tolerances
max
min
–
mm
mm
A
0
-0.005
B
-0.005
-0.010
C
-0.010
-0.015
4
0
-0.002
3
-0.002
-0.004
2
-0.004
-0.006
1
-0.006
-0.008
0
-0.008
-0.010
Depending on the tolerance range, the backing bearings are normally graded in three groups where the height difference is 5 μm. The position of maximum wall thickness is marked by an arrow on the side faces of the inner and outer rings. The consecutive number of the bearing is marked to the left of this arrow and the cross sectional height group is marked to the right.
variation of bearing section heights
5. Backing Bearings Measurement for bearing section height
Measurement equipment
Backing bearings measurement equipment
6. EVERGLORY Backing Bearings Advantages
6.1 Backing Bearings Service life comparison
EVERGLORY Backing Bearings Service life comparison
6.2 Backing Bearings Thickness of hardened layer
Thickness of hardened layer
Thorough countless tests and experiments, we found that the best material for Sendzimir backing bearing is not case hardened steel G20Cr2NiaA, although this kind of material is traditional.
In JIS standard, GCr9 is used in order to achieve the best performance. In Chinese GB standard, we use GCr18Mo toreplace it.
The main difference between G20Cr2Ni4A and GCr18Mo is their hardened layer. GCr18Mo has hardened layer of up to 8 mm.
6.3 Backing Bearings Cost comparison
EVERGLORY Backing Bearings Cost comparison
6.4 EVERGLORY Backing Bearings Features of Type 1
The outer ring does not have the flange, the rolling elements of the first row and the second row are guided by the double-row comb cage and the rolling elements of the third row are guided by the single-row comb cage. The axial guiding of the rolling element is conducted by the movable flange on the inner ring.
This kind of backing bearing does not have the sealing. The bearing without the sealing can be applicable to the rolling emulsion lubrication; the emulsion can flow in and out from the bearing without block.
Backing Bearing Type 1
6.5 EVERGLORY Backing Bearings Features of Backing Bearing Type 2
There are three flanges in the outer ring of these double-row backing bearing. The rolling element is guided by the double-row comb cage.
This kind of bearing is applicable to the entire lubrication mode (see Figure Grouping mark of the section height). The bearing with sealing or without sealing can be provided according to the different lubrication mode.
Backing Bearing Type 2
6.6 EVERGLORY Backing Bearings Features of Backing Bearing Type 3
There is the flange in the inner ring and outer ring of the double-row full filled backing bearing.
This kind of backing bearing does not have the sealing and it is applicable to the lubrication of emulsion.
Backing Bearing Type 3
7. Backing Bearings Installation and Disassembling
The inner ring of the backing bearing bears the point load and the loose fit shall be adopted in the installation on the axle.
Caution!
Some backing bearing do not have the self-hold facility, the inner ring shall not be pushed in the adjustment to prevent the falling of the rolling element. The components of the bearing can not be disassembled or exchanged in the process of installation and disassembling.
8. Backing Bearings Grouping of the section height
The tolerance reduction of the mill bar needs the high bearing precision, especially the requirement of the tolerance of the outer ring runout and section height of the bearing. This relies on the grouping of the manufacturing tolerance with high requirement and the tolerance of all the components to reach.
The backing bearing is classified into 3 to 7 tolerance groups of section height I to VII each one is 3μm or 5μm tolerance Table 1
Group of section height
Tolerance of section height (μm)
I
0-0.005
II
-0.005-0.010
III
-0.010-0.015
Table 1 Group and tolerance of section height
Each backing bearing has the name marks of the group and tolerance of the section height (Figure 1), The mark is located at the maximum wall thickness (Figure 2). In order to reduce the fluctuation of the wall thickness of the inner ring, all the inner ring marks of the bearing must be in the same place one the back shaft.
Caution !
All the backing bearings installed on the same back shaft must be in the same tolerance group, as Figure 1 is shown.
Figure 1 Grouping mark of the section height
Figure 2 Mark of the maximum wall thickness
8.1 Backing Bearings Axial location – Figure 3
Once the backing bearing and the support base is installed, all the support bases, backing bearing and support shaft must be located.
Figure 3 Back shaft, backing bearing and back axial location
9. Backing Bearings Lubrication
The lubrication is a design factor. The lubricant and lubrication mode shall be confirmed in the design of the rolling mill backing bearing.
The lubricant shall be uniformly distributed on the rolling element in the design backing bearing.
Caution!
The lubrication mode, they dose and viscosity of the lubricant is decided by the working conditions of the backing bearing. It must be ensured that the backing bearing is lubricated before the starting up of the rolling mill.
9.1 Backing Bearings Rolling emulsion lubrication – Figure 4
Using the rolling emulsion lubrication is the most economic and this mode is always used in a lot of rolling mills. Since the viscosity of the rolling emulsion is very low, much lubrication oil is needed to flow through the bearing. The high-speed lubricant of the backing bearing can prevent the outer things from entering the bearing. The backing bearing without sealing is applicable to the rolling emulsion lubrication.
Figure 4 Rolling emulsion lubrication backing bearing
The lubrication oil flows from the backing bearing to enter its own circulating system, thus the oil with high viscosity is used. This change will greatly improve the service life of the backing bearing. The design of the measurement of the oil inlet and oil outlet must be paid attention to . The bearing with the lip sealing is applicable to the recycle oil lubrication.
Figure 5 Recycle lubrication backing bearing of the rotary axial sealing
9.3 Backing Bearings Oil gas lubrication – Figure 6
The lubricating oil shall be blow into the bearing by the clean and dry pressed air. Since the gas sealing, the slight pressure produced in the backing bearing can prevent the intrusion of the external things. The oil particle will stick on the inner surface of the bearing and only a little oil will escape from the exhaust hole. The supply measures about the design of lubricant of which the viscosity is not less than ν=220 mm2/s shall be discussed with the manufacturer of the lubrication equipment. The bearing with the gap sealing is applicable to the oil gas lubrication.
Figure 6 Oil gas lubrication – backing bearing with the gap sealing
10. Backing Bearings Maintenance
Maintenance: The backing bearing must be inspected when it operates for some time. The bearing shall be disassembled from the axle to check whether there is damage or pollution or not.
The backing bearing in the machine frame will bear the different loads. The bearing of the backing bearing on the support roller which bears the higher load shall be exchanged with the bearing on the support roller which bears the lower load. The inner ring shall be turned 90ºin the installation after the disassembling each time. The abrasion of the bearing can be kept uniformly in this way.
The backing bearing must be inspected in the limited time cycle according to the required quality of the rolling materials and the surface of the outer ring shall be ground if it is necessary.
Since the heat treatment of the outer ring, the outer ring can conduct the regrinding without losing the hardness. This removes the indentation, wearing zone and others caused by the wear scar and foreign impurity to make the surface smooth. The stage regrinding is suggested. The independent regrinding details can be consulted through contacting us.
11. Backing Bearings Grinding mandrel
The special grinding mandrel (Figure 7) can be used in the regrinding of the type 2. The mandrel can be provided through discussion.
The grinding mandrel focuses on the backing bearings through the rolling element and track of the outer ring. The same grinding technology is adopted in the bearing of the support roller which bears the same load operation on the rolling mill. To reduce the circular runout of the mandrel, the elastic clasp must be accurately ground before the regrinding of the bearing of the support roller.
Figure 7 Backing bearing type 2 of graphical diagram:
①Grinding mandrel ②Plastic retainer③Backing bearing ④Wrench bolt⑤Lock nut ⑥Envelope of backing bearing⑦Elastic clasp ⑧Support washer⑨Retainer
12. Backing Bearings Internal Designs
12.1 Backing bearings without axial guidance, without seals
backing bearings design 1
Double row cylindrical roller backing bearing with one integral flange on both inner and outer rings, cage-guided roller complement
backing bearings design 2
Double row cylindrical roller backing bearing with one integral flange on both inner and outer rings, cage-guided roller complement and annular lubrication groove in the inner ring bore
backing bearings design 3
Three-row full complement cylindrical roller backing bearing with flangeless outer ring and two loose flange rings on the inner ring.
backing bearings design 4
Three-row full complement cylindrical roller backing bearing with the flangeless outer ring and two loose flange rings on the inner ring and two annular lubrication grooves in the inner ring bore.
backing bearings design 5
Three-row caged cylindrical roller backing bearing with the flangeless outer ring and two loose flange rings on the inner ring, cage-guided roller complement.
backing bearings design 6
Three-row caged cylindrical roller backing bearing with flangeless outer ring, two loose flange rings on the inner ring, cage-guided roller complement and two annular lubrication grooves in the inner ring bore.
backing bearings design 7
Three-row caged cylindrical roller backing bearing with flangeless outer ring, two loose flange rings on the inner ring, inner ring guided roller complement and two annular lubrication grooves in the inner ring bore.
backing bearings design 8
Three-row caged cylindrical roller backing bearing with two integral flanges in the outer ring, cage-guided roller complement and two annular lubrication grooves in the inner ring bore.
12.2 Backing bearings with axial guidance without seals
backing bearings design 9
Double row caged cylindrical roller backing bearing with three integral flanges in the outer ring, two loose flange rings on the inner ring, cage-guided roller complement and annular lubrication groove in the inner ring bore.
backing bearings design 10
Three-row full complement cylindrical roller backing bearing with two integral flanges in the outer ring and two loose flange rings and two loose guide rings on the inner ring.
backing bearings design 11
Three-row caged cylindrical roller backing bearing with two integral flanges in the outer ring and two loose flange rings and two loose guide rings on the inner ring, cage-guided roller complement.
backing bearings design 12
Three-row full complement cylindrical roller backing bearing with four integral flanges in the outer ring and loose flange rings on the inner ring.
backing bearings design 13
Three-row caged cylindrical roller backing bearing with four integral flanges in the outer ring and loose flange rings on the inner ring, cage-guided roller complement.
12.3 Sealed backing bearings with axial guidance
backing bearings design 14
Double row full complement cylindrical roller backing bearing with three integral flanges in the outer ring, two loose flange rings on the inner ring, radial shaft seals, no lubrication holes.
backing bearings design 15
Double row caged cylindrical roller backing bearing with three integral flanges in the outer ring, one integral and one loose flange ring on the inner ring, cage-guided roller complement, and radial shaft seals.
backing bearings design 16
Double row caged cylindrical roller backing bearing with three integral flanges in the outer ring, two loose flange rings on the inner ring, cage-guided roller complement, and “Fey-ring” seals.
backing bearings design 17
Double row caged cylindrical roller backing bearing with three integral flanges in the outer ring, two loose flange rings on the inner ring, cage-guided roller complement and annular lubrication groove in the inner ring bore.
backing bearings design 18
Three-row caged cylindrical roller backing bearing with two integral flanges in the outer ring, two loose flange rings on the inner ring which forms a gap-type seal with the outer ring raceway, cage-guided roller complement.
backing bearings design 19
Three-row full complement cylindrical roller backing bearing with two inserted flanges in the outer ring, which form a gap-type seal with the flanges on the inner ring.
backing bearings design 20
Three-row caged cylindrical roller backing bearing with four integral flanges in the outer ring, one integral flange and one loose flange ring on the inner ring, cage-guided roller complement.
Hi, I’m Peter Wong, the funder of EVERGLORYINDUSTRY.com, I’ve been running a factory in China that makes backing bearings, Crusher bearings and other rolling bearings for 14 years now, and the purpose of this article is to share with you the knowledge related to backing bearings and other rolling bearings from a Chinese supplier’s perspective.
