FIELD OF THE INVENTION
The present invention generally relates to Journal spring assembly in a coal
pulveriser. More particularly the present invention relates to a method of
replacing a conventional spring assembly with bearing less spring assembly in
Bowl Mills in an operating thermal power plant.
BACKGROUND OF THE INVENTION
In a bowl mill, raw coal is fed through a center feed pipe so that coal falls at the
center of a rotating bowl. The bowl is lined with replaceable hard liners called
bull ring segments. Due to the centrifugal force, the coal starts moving towards
the bowl periphery in a spiraling fashion. The bowl mill is operated in such a
manner that coal comes between a grinding roll and the bullring segments and
get crushed. The crushed coal is then carried by the hot air under pressure to a
classifier section, and through a fuel piping network for further transportation to
the boiler for firing. When coal comes between the bowl and a roller assembly
constructed in the form of bed, the roller assembly is pushed upwards. At this
time, the pre-loaded journal spring assembly imparts the required grinding
pressure, on a Journal Opening Cover (JOC) by pressing down a Journal
Assembly on to the bull ring segments. There are at least three journal
assemblies kept at 120 degrees apart. Similarly, there are three journal spring
assemblies provided to press them down.

A conventional journal spring assembly consists of two springs set inside a spring
canister. The springs are guided by a pressure spring stud. The spring
compression can be set manually (even when mill is online) by adjusting an
adjustable bolt of the Journal spring, which are provided with a ball bush bearing
and a thrust bearing. Free movement of said adjusting bolt is ensured by
greasing the bolt by a grease nipple. After adjusting the spring compression to a
desired value, the spring is locked in place using a Spring bolt lock nut, a bearing
guard, and a bearing guard jam nut. The moment of inertia of the ball bush
bearing due to load is restricted by a retainer ring. The damage of the bearings
due to entry of coal dust is restricted by an 0-ring, and a seal pressure spring
clamp. The deflection in the springs is controlled by a piston ring. As the bowl
mills are operated in dusty working conditions, it is difficult to maintain the
conventional journal spring assembly having bearings and ball bushings. One of
the major disadvantages is that due to entry of dust into the bearings, the
bearings undergo frequent seizure and damage. Replacement of these bearings
in remote sites is costly and cumbersome. The additional shock loads are created
when hard to grind foreign materials enter the mill resulting in quick damage to
the bearings.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method of replacing a
conventional spring assembly with bearing less spring assembly in Bowl Mills in
an operating thermal power plant which is simpler and easy to maintain.
Another object of the invention is to propose a method of reducing downtime
replacing a conventional spring assembly with bearing less spring assembly in
Bowl Mills in an operating thermal power plant which is simpler and easy to
maintain.
A another object of the invention is to propose a method reducing number of
parts and cost of manufacture of replacing a conventional spring assembly with
bearing less spring assembly in Bowl Mills in an operating thermal power plant
which reduces manufacturing cost and time.
A still another object of the invention is to propose a method reducing
procurement cycletime of replacing a conventional spring assembly with bearing
less spring assembly in Bowl Mills in an operating thermal power plant which
reduces manufacturing cost and time.
SUMMARY OF THE INVENTION
Accordingly, there is provided a method of replacing an existing journal spring
assembly with a bearing-less spring assembly in bowl mills in an operating
thermal power plant, the bearing-less spring assembly comprises a spring cup

fitted on a journal opening cover by at least a first coupling device consisting of a
hexagonal screw, a spring washer, and a machined washer, the spring cup
provided with a pressure spring assembly; a spring support cover releasably
attached to said journal opening cover by at least one second coupling device
consisting of a spring washer, a bolt retainer clamp, a pressure hexagonal bolt,
and a hexagonal nut; and a spring extension cap for assembly on the spring
support cover, the method comprising the steps of removing the existing journal
opening cover by gas-cutting and grinding the cut surface; welding a round plate
on the spring support cover; enlarging the bore diameter to accommodate the
spring support cover of the bearing-less spring assembly; drilling a plurality of
equally-spaced through holes to accommodate the spring support cover; drilling
equally spaced tapped holes to assemble the pressure cup.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Conventional spring assembly (Prior art).
Figure 2: Bearing-less spring assembly according to the invention,
Figure 3: Modification of Journal Opening Cover (gas cutting and step
removal) according to the invention.
Figure 4: Modification of Journal Opening Cover (Plate welded on JOC top
side) according to the invention.

Figure 5a: Modification of Journal Opening Cover (Before enlargement of
bore diameter) according to the invention.
Figure 5b: Modification of Journal Opening Cover (After enlargement of
Bore diameter) according to the invention
Figure 6: Modification of Journal Opening Cover (drilling holes PCD) accord-
ing to the invention.
Figure 7: Modification of Journal Opening Cover (drilling tapped holes)
according to the invention.
Figure 8: Bowl Mill Cross - Section.
DETAILED DESCRIPTION OF THE INVENTION
The modification of the conventional Journal spring assembly (JOC) according
to the invention is performed as follows:
a) Process of removing a conventional spring assembly from JOC
JOC is removed from the Pulveriser and placed on a maintenance platform
using an overhead crane of the mill handling system. A socket head set
screw (item No.25 of Figure 1) is removed. The bearing Guard jam nut (item
No. 13 of Figure 1) and bearing guard nut (item No. 6 of Figure 1) are
removed along with the trfrust bearing (item No. 16 of Figure 1) and o-ring

seal pressure spring clamp (item No. 17 of Figure 1). The journal spring
adjusting bolt (item No. 10 of Figure 1) and the grease nipple (item No.29 of
Figure 1) are removed along with the spring bolt lock nut (item No. 11 of
Figure l)and the ball bush bearing (item No. 19 of Figure 1). The JOC is then
reversed and placed on the maintenance platform. The hexagonal socket
head cap screw (item No. 23 of Figure 1) and the spring washer (item No.
31 of Figure 1) is removed. A pressure spring cup connecting the hexagonal
bolt (item No.22 of Figure 1) is removed along with the hexagonal nut (item
No. 26 of Figure 1) and the lock washer (item No.27 of Figure 1). The spring
cup (item No.05 of Figure 1) is removed. The spring seat (item No.04 of
Figure 1) is removed along with the spring adjusting stud (item No. 08 of
Figure 1), that the pin (item No. 20 of Figure 1). The pressure springs (item
No. 01 of Figure 1) are then removed. The precision hexagonal bolt (item No.
21 of Figure 1) and the lock washer (item No. 28 of Figure 1) are removed.
The spring clamp cylinder (item No. 02 of Figure 1) is removed along with the
pressure spring clamp (item No.03 of Figure 1), the retainer ring (item No. 14
of Figure 1), the thrust bearing pressure spring clamp (item No. 15 of Figure
1), the piston ring (item No. 18 of Figure 1), The bearing sleeve (item No. 12
of Figure 1) and the 0-ring, pressure seal spring clamp (item No. 17 of Figure
1). The spring adjusting bolt bushing (item No.09 of Figure 1) is then
removed. The hexagonal socket head cap screw (item No.24 of figure 1) is
removed along with the lock washer (item No.30 of Figure 1). The spring
adjusting bolt seat (item No. 07) is removed.

b) The process of JOC modification
i) The step on the cover is removed by gas cutting operation (refer
Figure 3). Grinding operation is performed to remove burrs and improve
surface quality for further machining.
ii) A round plate is welded on the spring support cover area (refer Figure 4)
to accommodate a longer new bearing less spring assembly.
iii) The Existing bore diameter is enlarged (Figure 5a and 5b) to
accommodate the modified spring support cover (item No.03 of Figure 2
iv) Equally spaced through holes are drilled (Refer Figure 6) to accommodate
the modified spring support cover (item No.03 of Figure 2).
v) Equally spaced tapped holes are drilled (refer Figure 7) to assemble a
new pressure spring cup (item No. 01 Figure 2).
c) The invented Bearing less spring assembly and the process of assembly
of the same with JOC.

The invented bearing less spring assembly consists of a modified spring cup
(item No. 01 of Figure 2) which is fitted on to the modified Journal Opening
Cover (JOC) using a hexagonal screw (item No. 06), a spring washer (item No.
07) and a machined washer (item No. 08). The pressure spring assembly (item
No. 02 of Figure 1) is fitted into the modified spring cup. The modified spring
support cover (item No.03 of Figure 2) is then assembled on to the modified JOC
cover using a spring washer (item No. 13 of Figure 2), a bolt retainer clamp
(item No. 05) of Figure 2), a pressure hexagonal bolt (item No. 10 of Figure 2)
and a hexagonal nut (item No. 11 of Figure 2). The spring compression can be
adjusted using a hydraulic spring compression kit, a hexagonal nut (No.9), a
spring washer (item No. 14) and a high tensile stud (item No. 12). After adjusting
the spring compression, the spring extension cap (item 04) is assembled.

WE CLAIM :
1. A method of replacing an existing journal spring assembly with a bearing-
less spring assembly in bowl mills in an operating thermal power plant, the
bearing-less spring assembly comprises:
a spring cup fitted on a journal opening cover by at least a first coupling
device consisting of a hexagonal screw, a spring washer, and a machined
washer, the spring cup provided with a pressure spring assembly;
a spring support cover releasably attached to said journal opening cover
by at least one second coupling device consisting of a spring washer, a
bolt retainer clamp, a pressure hexagonal bolt, and a hexagonal nut; and
a spring extension cap for assembly on the spring support cover, the
method comprising the steps of:-
removing the existing journal opening cover by gas-cutting and grinding
the cut surface;
welding a round plate on the spring support cover;
enlarging the bore diameter to accommodate the spring support cover of
the bearing-less spring assembly;

- drilling a plurality of equally-spaced through holes to accommodate the spring
support cover;
- drilling equally spaced tapped holes to assemble the pressure cup.
2. The method as claimed in claim 1, wherein a device is used to adjust the
spring compression of the bearing-less spring assembly.
3. The method as claimed in claim 2, wherein the device comprises a hydraulic
spring compression kit, a hexagonal nut, a spring washer, and a high tensile
stud.

ABSTRACT

The invention relates to a method of replacing an existing journal spring assembly with a bearing-less spring assembly in bowl mills in an operating thermal power plant, the bearing-less spring assembly comprises a spring cup fitted on a journal opening cover by at least a first coupling device consisting of a hexagonal screw, a spring washer, and a machined washer, the spring cup provided with a pressure spring assembly; a spring support cover releasably
attached to said journal opening cover by at least one second coupling device consisting of a spring washer, a bolt retainer clamp, a pressure hexagonal bolt, and a hexagonal nut; and a spring extension cap for assembly on the spring
support cover, the method comprising the steps of removing the existing journal opening cover by gas-cutting and grinding the cut surface; welding a round plate on the spring support cover; enlarging the bore diameter to accommodate the spring support cover of the bearing-less spring assembly; drilling a plurality of equally-spaced through holes to accommodate the spring support cover; drilling equally spaced tapped holes to assemble the pressure cup.