FIELD OF INVENTION
The present invention relates to an improved method of replacement of oil seal
in journal shaft assembly in bowl mills in an operating thermal power plant. More
particularly, the invention relates to an improved method of said replacement that saves
a significant amount of man-hours avoiding the hazards of total dismantling of the shaft
assembly and again assembling the same.
BACKGROUND OF THE INVENTION
In a bowl mill, the coal is crushed and pulverized to powder form between
the grinding rolls and rotating bowl. The coal on the bowl moves along with the bowl
and gets entrained between the grinding rolls and the bowl and causes rotation of
the grinding roll opposite to the bowl rotation. To facilitate the free rotation of the
grinding roll, it is mounted on the journal housing of the journal shaft assembly. The
journal housing is mounted on the stationary journal shaft by means of two taper
roller bearings.
Oil is filled in the journal housing for smooth operation, cooling and lubrication
of the bearings while in operation. The whole journal shaft assembly is inside the
mill and is surrounded by the coal powder being pulverized and moving upwards

towards the outlet. To avoid leakage and prevent the contamination of oil by the
surrounding coal powder inside the mill, the journal shaft assembly is made leak-
proof by means of oil seals and journal housing covers. These oil seals need regular
replacement after a particular duration of time as these are worn out due to the
rotation of the journal housing cover upper along with the journal housing &
grinding roll.
In the conventional method for the replacement of oil seals, the whole
journal shaft assembly is required to be dismantled.
With the existing design of Journal housing cover upper, the replacement of the
oil seals requires the following steps (refer figure-1):
1. Draining of the oil (140) in the journal shaft assembly by removing the Pipe
plug (85).
2. Removal of seal air connections.
3. Removal of Journal opening covers.
4. Mounting the tilt out brackets on the journal opening frames.
5. Place the chain pulley in appropriate positions on the cross beams.
6. Removal of the fasteners (100) and Journal housing liner (95).

7. Removal of the fasteners (110) and seal keeper (105) fastened to the
journal housing cover upper (15).
8. Removal of the fasteners (80) connecting the journal housing cover upper
(15) to the journal housing (40).
9. Removal of fasteners (80) and journal housing cover lower (75).

10. Removal of fasteners (55) and journal bearing keeper (45).
11. Removal of taper roller bearing (35) at the journal shaft bottom end along
with the journal housing (40) & grinding roll (60).
12. Removal of the taper roller bearing (35) at the journal shaft flange end.
After completing the above mentioned steps, the oil seals will be replaced
with new oil seals.
After replacement of the oil seals, all the above steps are to be repeated in a
reversed manner for the reassembly of the journal shaft assembly. Additionally heating
of the bearings is required before assembling the bearings.
The whole process of replacement of oil seal from one journal shaft assembly
requires 200 man-hours, equipment like tilt out bracket, chain pulleys, heaters for

heating the bearings and miscellaneous items required during the process. This also
reflects that the mill has to shut down for the same duration as mentioned above.
In this whole process there are chances for the damage of bearings due to
dismantling and reassembly.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose an improved method of
replacement of oil seal in journal shaft assembly in bowl mills in an operating thermal
power plant, which is capable of avoiding hazards of dismantling and assembly of the
journal shaft assembly.
Another object of the invention is to propose an improved method of
replacement of oil seal in journal shaft assembly in bowl mills in an operating thermal
power plant, which is able to make the process of replacement economical by saving
significant man-hours.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Journal Shaft Assembly showing the position of oil seals (in Prior Art).
Figure 2: Modified Journal Shaft Assembly according to the invention showing the
modification of Journal housing cover upper and slot cover.

Figure 3: Modification of Journal housing cover upper according to the invention.
Figure 4: Slot cover according to the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The outer surface of the journal housing cover upper (15) is machined to make
two flat surfaces 180 degrees apart. On each of the face one elongated hole is
incorporated. Adjacent to this elongated hole, 4 numbers of M8 tapped holes are
incorporated. The elongated holes are covered by slot covers. The new oil seals to be
used are of split type (i.e., split at one end) to facilitate easy installation and removal.
As shown in Fig. 2 the proposed simple method of replacement of oil seal in the
journal shaft assembly consists of the following.
i) The outer surface of the journal housing cover upper (15) is machined to
make two flat surfaces 180 degrees apart.
ii) On each of the machine flat face, one elongated hole in incorporated.
iii) Adjacent to this elongated hole, four numbers of M8 tapped holes are
incorporated. The elongated holes are covered by slot covers (16) and the slot cover

(16) is fixed to the journal housing cover upper (15) by using M8 counter sunk hex
socket heat screws (17).
iv) Seal keeper (105) fastened to the journal housing cover upper (15) can be
dismantled and there exists a space between oil seals (20) and the journal housing
cover (15) which facilitates the removal and assembly of the oil seals (20).
v) Split Oil Seals (i.e., split at one end) (20) will be used to facilitate easy
installation and removal of the same.
With this modification the method of replacing the oil seals is listed in the
following steps:
1. Removal of the fasteners (110) and Seal keeper (105) fastened to the
journal housing cover upper (15).
2. Removal of screws (17) and slot covers (16).
3. Removal of the existing oil seals (20) by pushing it upwards using screw
drivers.
4. In case of continuous oil seals (20) without any splits, it has to be
cut for removal from the journal shaft (5).
5. Placing the new oil seals (20) in the journal housing cover upper (15).
6. Fastening the slot covers (16) to the journal housing cover upper (17).
7. Fastening the seal keeper (105) to journal housing cover upper (15) with
fasteners (110).

The whole process of replacement of the oil seal for one journal shaft
assembly can be completed within 16 man-hours or 2 man-days.
The modification of journal housing cover upper eliminates the following steps
which are required with the pre art process of oil seal replacement:
1. Draining of the oil (140) in the journal shaft assembly by removing the Pipe plug
(85).
2. Removal of seal air connections.
3. Removal of Journal opening covers.
4. Mounting the tilt out brackets on the journal opening frames.
5. Place the chain pulley in appropriate positions on the cross beams.
6. Removal of the fasteners (100) and Journal housing liner (95).
7. Removal of the fasteners (80) connecting the journal housing cover upper (15) to the
journal housing (40).
8. Removal of fasteners (80) and journal housing cover lower (75).
9. Removal of fasteners (55) and journal bearing keeper (45).

10. Removal of taper roller bearing (35) at the journal shaft bottom end along with the
journal housing (40) & grinding roll (60).
11. Removal of the taper roller bearing (35) at the journal shaft flange end.
12. Heating the taper roller bearings (35) before re-assembly.

13. Re-assembly of journal housing (40) & grinding roll (60).
14. Re-assembly of taper roller bearings (35).
15. Fastening the journal bearing keeper (45) to Journal Shaft (5) with fasteners (55).

16. Fastening the journal housing cover lower (75) to Journal housing (40) with
fasteners (80).
17. Fastening the journal housing cover upper (15) to Journal housing (40) using
fasteners (80).
18. Fastening the journal housing liner (95) to Journal housing (40) with fasteners
(100).

19. Tilting of the journal shaft assembly to place it back inside the mill.
20. Opening the cap (130), filling the lubrication oil (140) in the journal shaft assembly
through the pipe (120) mounted on the journal shaft (5).
21. Controlling the quantity of oil (140) by checking the oil level using dip stick to
ensure oil quantity is sufficient or not. Then closing the pipe (120) with the cap (130).
22. Adjusting the gap between the grinding roll (60) and the bowl by adjusting the
journal stop bolt with the help of its special spanner and hammer.
23. Removal of chain pulley.
24. Removal of tilt out bracket.
25. Fastening the Journal opening cover to the separator body.

WE CLAIM
1. An improved method of replacement of oil seal in journal shaft assembly in bowl
mills in an operating thermal power plant implementing a modification of journal
housing cover upper (15), comprising;
machining the outer surface of journal housing cover upper (15) to make two flat
surfaces 180 degrees apart;
incorporating one elongated holes machined on each of the said flat surfaces;
machining four tapped holes adjacent to said elongated holes to fix a slot cover
(16) to cover the said elongated holes with screws (17);
removing fasteners (110) to dislodge seal keeper (105) from the journal housing
cover upper (15) to create a space between oil seal (20) and journal housing cover
(15);
removing existing oil seals (20) by pushing it upwards using screw drivers and
cutting the oil seal (20), if required, to remove from the journal shaft (5);
wherein the new split oil seals (i.e., split at one end) (20) are implemented to
facilitate replacement of oil seal when the said oil seal is placed in the journal housing
cover upper (15) and then the slot cover (16) is fastened to the journal housing cover
upper (15) with screws (17) and the seal keeper (105) is fixed to the journal housing
cover upper (15) with fasteners (110).

2, An improved method of replacement of oil seal as claimed in claim 1, wherein
the slot cover is fastened to the journal housing cover by M8 counter sunk hexagonal
socket head screws.