FIELD OF THE INVENTION
The present invention relates to improved configuration of hydraulic cylinder system for
bending of work rolls and balancing of backup rolls in cold rolling mills. More
importantly, the present invention is directed to providing hydraulic cylinders of
actuators adapted to prevent failure of seals by providing a double acting compact type
seal capable of withstanding lateral load caused by axial shift of rolls. Advantageously
also, the piston head as well as piston rods of the cylinders are provided with single row
of same compact type seal according to the invention along with required modification
of cylinder cover, replacing the conventional seal in two rows to prevent failure of seal
due to built up of localized pressure. In the modified hydraulic cylinder of the present
invention, the ingress of roll coolant emulsion along with iron fines is avoided by
providing a double profile wiper introduced between cylinder cover and piston rod and
all seal components made of hydrolysis resistant material in order to prevent failure of
seal and scoring of barrel due to ingress of emulsion. The cylinder barrel is made of
high strength material like EN24 steel and the cylinder bore is honed to desired finish to
avoid the need for chrome plating which usually gets peeled off. The hydraulic cylinder
for actuators according to the invention is thus capable of ensuring uninterrupted
operation in TCM with consistent quality/shape profile of cold rolled strip without failure
of seals of cylinders and resultant wastage of hydraulic oil and is thus having prospects
of application of theses cylinders in bending of work rolls and balancing of backup rolls
in TCM in steel plants.
BACKGROUND ART
The rolling mills use various hydraulic actuators for operation and control of their
components. Hydraulic cylinders of some of these actuators are subjected to severe
loading conditions and are highly prone to leakages of oil mostly due to failure of seals.
Often undesirable deformation and/or scoring of piston and barrel are also observed in
these cylinders. Failure of cylinders not only hinders the production process but also
leads to quality defects on the rolled strips due to contamination of emulsion by the
leaked hydraulic oils. Each cylinder-failure causes huge revenue loss due to wastage of
hydraulic oil besides making the mill untidy.
One of the important actuators most of the cold rolling mills use is the roll bending
system, which is employed to control shape of the rolled strips. In this system, work

rolls are bent in negative and/or positive direction to alter the contour of roll gap at the
roll bite. Negative and positive bending of the work rolls are carried out respectively by
crown-in and crown-out type roll bending systems. Bending of the work rolls is done by
pressuring the chocks of rolls on both sides of the mill against the backup rolls using
hydraulic cylinders. These cylinders are fitted into the Maewest Block of the mill stand
and hydraulic oil pressure is varied from 0 to the order of 200-300 kg/cm2 for exerting
differential roll bending pressure as per requirements of shape correction.
Similar hydraulic cylinders are also used for balancing of the backup rolls. Using two
cylinders on each side of the mill the top backup roll is kept horizontal. It is essential to
control skew in the mill. The hydraulic cylinders used for bending of work rolls and
balancing of backup rolls are similar in design except they may have different stroke
length.
Cylinders for both the above stated applications are normally designed to withstand
only the axial load. When such cylinders are subjected to lateral loads, some of their
components such as seal, barrel, etc. are susceptible to premature failure. It is however
common in most of the mills that there is axial shift of rolls due to various reasons.
Under such conditions the cylinders are bound to get the lateral load. It is therefore
required to design the cylinders to withstand both the axial as well as lateral loads.
Selection of material and heat treatment method should be such that the barrel has
adequate strength and hardness to sustain the service condition. The hydraulic
cylinders are also exposed to the roll cooling emulsion which carries iron fines too. It is
often found that the emulsion ingresses into the cylinder and damages the seal and
barrel. Iron fines become the source for causing scratch mark on the bore of cylinder.
Normally bore of the cylinder is having hard chrome plating to avoid the generation of
scratch mark. On many occasions, however, it is found that the layer of chrome plating
gets peeled off causing more problems to the cylinder. It is therefore required to design
the cylinder with a mechanism to check the ingress of emulsion as well as iron fines.
Additionally alternative of chrome plating is required to be developed to avoid the peel-
off problem.
OBJECTS OF THE NVENTION
The basic object of the present invention is thus directed to providing an improved
configuration of hydraulic cylinder systems for bending of work rolls and balancing of
backup rolls in the cold rolling mills to avoid failures of cylinders and seals to ensure
uninterrupted operation with longer operating life and consistent shape profile of CR
strip.
A further object of the present invention is directed to providing an improved
configuration of hydraulic cylinder systems for bending of work rolls and balancing of
backup rolls in the cold rolling mills wherein seals would be capable to withstand lateral
thrust and loading caused by axial shift of the rolls.
A still further object of the present invention is directed to providing an improved
configuration of hydraulic cylinder systems for bending of work rolls and balancing of
backup rolls in the cold rolling mills adapted to prevent seal failure due to high localized
pressure of hydraulic oil.
A still further object of the present invention is directed to providing an improved
configuration of hydraulic cylinder system for bending of work rolls and balancing of
backup rolls in the cold rolling mills adapted to avoid ingress of roll cooling emulsion
and iron fines into the cylinder causing scoring of barrel or damage of seals.
A still further object of the present invention is directed to providing an improved
configuration of hydraulic cylinder system for bending of work rolls and balancing of
backup rolls in the cold rolling mills adapted to guide the piston rod for proper linear
movement during its reciprocation motion and avoid localized stress generation in seals.
A still further object of the present invention is directed to providing an improved
configuration of hydraulic cylinder system for bending of work rolls and balancing of
backup rolls in the cold rolling mills wherein all seal components are made of hydrolysis
resistant material to avoid damage of seals by water present in roll coolant emulsion.
A still further object of the present invention is directed to providing an improved
configuration of hydraulic cylinder system for bending of work rolls and balancing of
backup rolls in the cold rolling mills wherein high strength steel material is used for the
cylinder barrel and its process of manufacture is selected to avoid warpage of cylinder
barrel during operation.
A still further object of the present invention is directed to providing an improved
configuration of hydraulic cylinder system for bending of work rolls and balancing of
backup rolls in the cold rolling mills wherein cylinder bore is fabricated to eliminate
problem of peel-off of chrome plating and resulting failure of the system.
A still further object of the present invention is directed to providing an improved
configuration of hydraulic cylinder system for bending of work rolls and balancing of
backup rolls in the cold rolling mills adapted to save wastage of expensive hydraulic oil
due to leakage due to seal failure and avoid consequent shop floor hazard.
A still further object of the present invention is directed to providing an improved
configuration of hydraulic cylinder system for bending of work rolls and balancing of
backup rolls in the cold rolling mills which avoid premature failure and resultant
downtime and loss of production.
A still further object of the present invention is directed to providing an improved
configuration of hydraulic cylinder system for bending of work rolls and balancing of
backup rolls in the cold rolling mills adapted to avoid contamination of roll coolant
emulsion and thereby improving the surface quality of rolled product.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to Hydraulic cylinder system
for bending of work rolls and/or balancing of backup rolls in the cold rolling mills,
adapted to avoid leakage of oil due to failure of seals, comprising
a cylinder barrel;
a piston with piston rod for reciprocating motion in said cylinder barrel;
double acting compact type seal adapted to withstand lateral load free of oil leakage
due to failure of seal on at least one of said piston and piston rod;
a cylinder cover housing said piston rod with seals.
A further aspect of the present invention is directed to Hydraulic cylinder system,
wherein said double acting compact type seal comprising
a main seal;
energizer for providing extra elasticity to the main seal;
back up rings to prevent bulging of the main seal;
guide rings to withstand thrust/lateral load on the cylinder.
A still further aspect of the present invention is directed to said Hydraulic cylinder
system, wherein all the seal components are made from hydrolysis resistant material.
According to an advantageous aspect of the present invention directed to said Hydraulic
cylinder system, wherein said compact type seal on piston rod is adapted to guide the
rod for proper linear movement during its reciprocation motion.
Also in said Hydraulic cylinder system, said piston is adapted to incorporate said double
acting compact type seal and extrusion gap is controlled to avoid extrusion of seal
under pressure and motion.
A still further aspect of the present invention is directed to said Hydraulic cylinder
system, wherein said cylinder barrel is made from high strength steel material,
preferably EN 24 steel, and obtained of forging and machining processes.
Also said cylinder barrel is heat treated to attain a core hardness of 320-340BHN and
bore of cylinder is honed with surface Ra<0.3.
According to a further aspect of the present invention said Hydraulic cylinder system is
adapted for maximum roll bending pressure sustained by said hydraulic cylinder is in
the range of 200 to 300 kg/cm2.
A still further aspect of the present invention is directed to said Hydraulic cylinder
system, wherein a double profile wiper is introduced between cylinder cover and piston
rod to prevent ingress of roll coolant emulsion as well as iron fines.
Said double profile wiper comprising
an external lip made of metal to wipe out iron files and other small particles from piston
rod in motion;
an inner rubberized lip as seal for preventing the ingress of emulsion.
Further in said Hydraulic cylinder system, air breather provided in the cylinder is
extended using fabricated tubes to prevent entry of emulsion through it.
The objects and advantages of the present invention are described in greater details
with reference to the following non limiting accompanying illustrative drawings.
BRIEF DECSRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: is the schematic illustration of the compact type seal configured to resist
lateral load in the modified hydraulic cylinder of the present invention.
Figure 2a-b: is the schematic illustration of the sectional view of the cylinder with piston
assembly showing the location of the piston seal and the seal of piston rods according
to the cylinder configuration of the present invention.
Figure 3: is the schematic illustration of the sectional view of the double profile wiper
according to the present invention to prevent ingress of roll coolant emulsion and iron
fines carried with it inside cylinder.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS
The present invention is directed to providing an improved configuration of hydraulic
cylinders for actuators for bending of work roll and balancing of backup rolls avoiding
leakage of hydraulic oil due to failure of seals and/or cylinder barrel and thus causing
interruption of production and inconsistent quality/shape profile of rolled strips.
Cold rolling mills use hydraulic cylinders for bending of work rolls and balancing of work
rolls. These cylinders often fail prematurely if not designed properly especially to
withstand the lateral load experiencing from axial shift of rolls. Seal may also get
damaged due to localised high pressure in the fluid. Ingress of emulsion and iron fines
decreases the life of seal and may cause scoring of the barrel and piston. Hard chrome
plating may not be required in such cylinders as they are susceptible for getting peeled-
off.
An improved configuration of hydraulic cylinders for these applications has been worked
out for preventing their premature failure. It includes use of superior material for barrel,
provision of compact type seal for piston and rod, introduction of wiper at cylinder gland
and honing of bore in place of hard chrome plating. One set of the modified cylinders
are also manufactured and installed at the last stand of a 5 stand Tandem Cold Mill in
one of the plants of the applicants for their performance evaluation. Studies with the
cylinders of improved design revealed that there was no case of failure with them for
over 18 months. Besides the maximum roll bending pressure could be increased by
about 20%.
The aspects of constructional configuration of the hydraulic cylinders according to the
present invention to avoid particular type of failure of components/function are
illustrated as follows.
(a) Preventing failure of seal under lateral loading:
The conventional piston seal (not designed to withstand the side load) is changed with a
double acting compact type seal. Accompanying Figure 1 shows schematically this type
of seal comprising main seal(A), energizer(B), backup rings(C) and guide rings(D). The
energizer(B) is useful in giving extra-elasticity to the main seal(A). The backup rings(C)
are provided to prevent bulging of the main seal(A) and the guide rings(D) are able to
withstand the thrust on the cylinder. Design of piston is modified to incorporate the new
type of seal. Extrusion gap is controlled to avoid extrusion of seal under pressure and
motion.
(b) Preventing failure of seal due to built up of localised pressure:
Some of the hydraulic cylinders are provided with two rows of seal on the piston as per
conventional design. It is possible to build up high localised pressure in the fluid present
between the two seals during movement of the piston. This localised pressure can be
sufficient to damage the seal through bursting action. To avoid this possibility single
row of seal is used on the piston in the cylinder configuration of the present invention.
The provision of single row double acting compact type piston seal has been illustrated
in the accompanying Figure 2. Similar to piston seal, compact type seal is also used for
piston rod. In addition to strengthening the seal, it guides the rod for proper linear
movement during its reciprocating motion. Otherwise it is possible to have localised
stress generation in the piston seal due to unguided movement of the rod. To
incorporate the compact type seal for piston rod, suitable modification is carried out in
the cylinder cover.
(b)Preventing failure of seal and scoring of barrel due to ingress of emulsion:
In the existing design of cylinders there is possibility of ingress of emulsion inside it
through the recess available between rod and cylinder cover. The emulsion contains
iron fines whose concentration may go to as high as 700 ppm. Water present in
emulsion also damages the seal if the latter is not made of hydrolysis resistant material.
The iron fines, due to their abrasive nature, are capable of damaging the seal as well as
leaving scoring marks on the inside wall of barrel.
For meeting the twin requirements of preventing ingress of emulsion as well as of iron
fines, a double profile wiper is introduced between cylinder cover and piston rod.
Accompanying Figure 3 schematically illustrates the double profile wiper wherein the
external lip of the wiper is made of metal to wipe out iron fines and other smaller
particles. The inner rubberised lip acts as seal for preventing the ingress of emulsion.
Air breather provided in the cylinder is also extended using fabricated tubes to prevent
entry of emulsion through it. All the seal components in present cylinder configuration
are made of hydrolysis resistant materials to improve the life of seal even in case of
ingress of roll coolant emulsion.
(d) Preventing failure of cylinder barrel:
To prevent warping of cylinder barrel, material of higher strengths is used in the
present configuration. EN24 steel with yield strength of minimum 780 N/mm2 and
ultimate tensile strength of 1200 N/mm2 is preferably used as cylinder material
according to the invention. Entire barrel with flange is made by forging followed by
machining processes and no weld joint is allowed to minimise residual stress in it.
Complete barrel is heat treated (hardened and tempered) to achieve core hardness of
320-340 BHN. Bore of cylinder is honed with surface Ra < 0.3 finish, instead of hard
chrome plating to avoid the risk of getting peeled off.
While the above basic steps are implemented to ensure uninterrupted operation of the
hydraulic cylinders of the present invention for work roll bending and/or balancing of
back up rolls for longer operating life, eliminating frequent cylinder failure as well as
leakage of hydraulic oil due to seal failure, there are some more optional advantages of
the hydraulic cylinders according to the present invention. These include controlling
shape of the rolled products and reducing down time by checking the premature failure
while minimising hydraulic oil consumption. It not only helps in saving the hydraulic oil
but also reduces the contamination of emulsion and thereby in improving the surface
quality of rolled products thus ensuring for environment friendly operation.
The objects and advantages of the present invention are described in greater details
with reference to the following accompanying illustrative Example I:
Example I:
A 5-stand Tandem Cold Mill, engaged in rolling of TMBP, sheet gauge and galvanising
steels in varying sizes (gauge 0.20-1.60 mm and width 650-1250 mm), using work roll
bending and backup roll balancing cylinders as per the basic design specifications as
shown in Table 1 has been selected for implementation of hydraulic cylinders of the
present invention.
Table 1 Basic specifications of existing cylinders (as per old design)
These cylinders of the above specification were found to be failing prematurely which
was causing surface defects on cold rolled products, high mill delays and loss of
hydraulic oil. The level of yearly failure at each stand was around 20 for work roll
bending cylinders and 3 for backup roll balancing cylinders.
In order to attend to solve the problems existing in the prior design, a total of 8 sets of
roll bending cylinders (bore 125 mm, rod 85 mm, stroke 50 mm) and 4 sets of
balancing cylinders (bore 125 mm, rod 85 mm, stroke 210 mm) have been
manufactured as per the improved design, incorporating the inventive features as
discussed earlier. All the cylinder assemblies are made suitable for working pressure of
220 bar, test pressure of 315 bar and medium as mineral oil at maximum temperature
of 70 °C. Each cylinder is tested for proof pressure test, no-load cycle test and internal
leakage test at test pressure of 315 kg/cm2 after its manufacturing as per IS 10585. It
was also tested ultrasonically for any internal crack or defects.
For validating the design of modified cylinders, their performance has been subjected to
test under actual running condition. Since stand 5 of the mill was most critical for the
point of view of shape control, these cylinders are installed at this stand. Performance
of the cylinders has been monitored with respect to their capacity of bearing the
bending pressure and giving stipulated life in the running condition.
Studies carried out with the modified cylinders revealed that they worked efficiently
without any failure of seal and barrel for over IV2 years. Significant reductions in
mechanical delay and consumption of lubricating oil have been achieved after
introduction of the modified cylinders. By reducing the failure rate of cylinders using
improved design parameters, there has been reduction in annual mill delays by about
74 hrs. Higher operating life of the cylinders helped avoiding contamination of emulsion
with the hydraulic oil. Importantly, there has been no leakage of hydraulic oil from any
of the cylinders. It is estimated that over 7200 litres of oil could be saved every year
using the modified cylinders. The level of benefits shall further increase after
introducing the modified cylinders at all the stands of the mill.
In addition to the longer life of the modified cylinders, there has been additional
advantage of increasing roll-bending pressure. The maximum bending pressure
achieved increased to over 200 kg/cm2 without any problem, as compared to
conventional value of 170 kg/cm2. With higher bending pressure it was possible to
control shape defects in more flexible manner.
It is thus possible by way of the present invention to providing improved hydraulic
cylinder systems for actuators for work roll bending and balancing of back up rolls in
cold rolling mills which ensure longer operation without failure of seals or leakage of oil
even with higher roll bending pressure of about 200 kg/cm2 and thereby ensure
consistent quality of cold rolled strip by maintaining required roll gap as well as strip
shape/profile. The hydraulic cylinders according to the invention thus ensure cost
effective operation with higher productivity, requiring less involvement of maintenance
as well as operating personnel while minimizing rejection of finished products.
We Claim:
1. Hydraulic cylinder system for bending of work rolls and/or balancing of backup rolls
in the cold rolling mills, adapted to avoid leakage of oil due to failure of seals and/or
cylinder barrel, comprising
a cylinder barrel;
a piston with piston rod for reciprocating motion in said cylinder barrel;
double acting compact type seal adapted to withstand lateral load free of oil leakage
due to failure of seal on at least one of said piston and piston rod;
a cylinder cover housing said piston rod with seals.
2. Hydraulic cylinder system as claimed in claim 1, wherein said double acting compact
type seal comprising
a main seal;
energizer for providing extra elasticity to the main seal;
back up rings to prevent bulging of the main seal;
guide rings to withstand thrust/lateral load on the cylinder.
3. Hydraulic cylinder system as claimed in anyone of claim 1 or 2, wherein all the seal
components are made from hydrolysis resistant material.
4. Hydraulic cylinder system as claimed in anyone of claim 1 to 3, wherein said compact
type seal on piston rod is adapted to guide the rod for proper linear movement during
its reciprocation motion.
5. Hydraulic cylinder system as claimed in anyone of claim 1 to 4, wherein said piston is
adapted to incorporate said double acting compact type seal and extrusion gap is
controlled to avoid extrusion of seal under pressure and motion.
6. Hydraulic cylinder system as claimed in anyone of claim 1 to 5, wherein said cylinder
barrel is made from high strength steel material, preferably EN 24 steel, and obtained
of forging and machining processes.
7. Hydraulic cylinder system as claimed in anyone of claim 1 to 6, wherein said cylinder
barrel is heat treated to attain a core hardness of 320-340BHN and bore of cylinder is
honed with surface Ra<0.3.
8. Hydraulic cylinder system as claimed in anyone of claim 1 to 7, wherein maximum
roll bending pressure sustained by the hydraulic cylinder is in the range of 200 to 300
kg/cm2.
9. Hydraulic cylinder system as claimed in anyone of claim 1 to 8, wherein a double
profile wiper is introduced between cylinder cover and piston rod to prevent ingress of
roll coolant emulsion as well as iron fines.
10. Hydraulic cylinder system as claimed in anyone of claim 1 to 9, wherein said double
profile wiper comprising
an external lip made of metal to wipe out iron files and other small particles from piston
rod in motion;
an inner rubberized lip as seal for preventing the ingress of emulsion.
11. Hydraulic cylinder system as claimed in anyone of claim 1 to 9, wherein air breather
provided in the cylinder is extended using fabricated tubes to prevent entry of emulsion
through it.
12. A double acting compact type seal adapted for use in hydraulic cylinder systems
comprising
a main seal;
energizer for providing extra elasticity to the main seal;
back up rings to prevent bulging of the main seal;
guide rings to withstand thrust/lateral load on the cylinder.
13.A double profile wiper for use in hydraulic cylinder systems adapted for preventing
ingress of materials in the cylinder comprising:
an external lip made of metal to wipe out metallic and like fines and other small
particles from piston rod in motion; and
an inner rubberized lip as seal for preventing the ingress of fluid /emulsion and the like.
14. Hydraulic cylinder system for bending of work rolls and/or balancing of backup rolls
in the cold rolling mills substantially as herein described with reference to the
accompanying drawings.

There is disclosed an improved configuration of hydraulic cylinder system for bending of
work rolls and balancing of backup rolls in cold rolling mills adapted to prevent failure of
seals by providing a double acting compact type seal capable of withstanding lateral
load caused by axial shift of rolls. The piston head and the piston rod of the cylinders
are provided with single row of same double acting compact type seal with modification
of cylinder cover to prevent failure of seal due to built up of localized pressure. The
ingress of roll coolant emulsion along with iron fines is avoided by providing a double
profile wiper introduced between cylinder cover and piston rod. The cylinder barrel is
made of high strength material like EN24 steel and the cylinder bore is honed to desired
finish and no chrome plating. The hydraulic cylinders ensure longer operating life with
higher maximum roll bending pressure.