|Title of Invention||
"AN IMPROVED RING LUBRICATED COMBINED JOURNAL AND THRUST BEARING"
|Abstract||An improved ring lubricated combined journal and thrust bearing for use in primary air fans in boiler auxiliary equipment of thermal power plant comprising a combined journal and thrust bearing having a plurality of thrust pad sections (2) supported by a correspondingly numbered runners (9) mounted on a rotating shaft (3); and an oil ring (1) mounted on a rotating journal of said combined journal and thrust bearing, characterized in that said oil ring (1) is fabricated with a trapejoidal cross section having a plurality of grooves on an inner diameter made of a bronze material, and in that each of said thrust pad section (2) is given a taper in a rotational direction of said bearing.|
|Full Text||This invention relates to improvements in ring lubricated combined journal and thrust bearings used in primary air fans in boiler auxiliary equipment of different rating at thermal power stations.
U. S. Patent No. 3544179 describes a ring lubricated combined journal and thrust bearings. However/ such bearings are self - contained/ oil ring lubricated, water cooled and spherical seated and can take both radial and thrust loads. The radial load is due to self weight of the fan rotor and axial load is due to reaction forces on the fan blades. The magnitude of these loads are of the order of 2 tonnes both radial and thrust bearing in a typical 7" dia PA Fan used in 210 MW thermal units.
Ring lubricated bearings are most economical and reliable compared to pressure-fed bearings, as there is no seprate oil circulation system. In ring lubricated bearing, the oil ring mounted on the journal rotates when the rotor starts rotating and picks up oil from the sump beneath it and feeds to the bearing. Oil delivered by the oil ring depends upon ring material/ geometry of the ring, oil viscosity and depth of immersion.
Disadvantage associated with the oil ring used in U.S I Patent No. 3544179 is that it is restrictive from the point of view of ring geometry/ weight and material of the
ring. Therefore/ this oil ring needs improvement
to deliver more quantity of oil to the bearing, so that the
excessive bearing temperatures can be reduced.
Another disadvantage is that the thrust bearing used in combined journal and thrust bearing of U.S. Patent No. 3544179 is a flat plate design and in this thrust bearing, there is no geometrical wedge and hence it is only suitable for smaller thrust loads. If the loads are excess, the flat plate design may fail due to rubbing of thrust plate with thrust collar. Therefore, the flat plate design of thrust bearings needs improvement for reliable operation of the bearing .
An object of the present invention is to propose an improvement in ring lubricated combined journal and thrust bearings used in primary air fans in boiler auxiliary equipments and capable of taking additional thrust load .
Yet another object of the present invention is to propose an improvement in the oil ring exhibiting a better performance.
Still another object of the present invention is to propose an improvement in oil ring having a greater oil delivery for the bea'ring and reduction in operating temperature.
Further object of the present invention is to propose an improvement in the oil ring wherein the weight of the modified ring is a greater than the present design
thereby giving better life.
Still further object of the present invention is to propose an improvement in the oil ring having improved hydro-dyanmic pressure distribution properties in the thrust bearing clearance.
According to this invention there is provided a ring lubricated combined journal and thrust bearings used in primary air fans in boiler auxiliary equipments having an oil ring with trapezoidal cross section and multiple grooves.
Further objects and advantages of the present invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings and wherein:
Fig. 1 shows the test bearing the oil ring (1) /thrust plate (2), shaft (3) locking cap (4) and locking screw (5);
Fig. 2: shows the oil ring used of U.S.. Patent No. 3544179 with oil groove (6);
Fig., 3 shows the modified oil ring developed with five oil grooves (7) ;
Fig. 4 shows the flat land thrust plate (8) Runner (9) of existing design;
Fig. 5 shows the taper land thrust plate (10), with taper
1 in 1000 ( 11) .
Improvements in ring lubricated combined journal and thrust bearings for primary air fans in boiler auxiliary equipment in the present embodiment of a bearing of size 7 " dia with the following design modifications is shown in Fig. 1.
(i) Oil ring design is modified for more oil delivery for the bearing/ and
(ii) Thrust plate design is rnodifed for taking more thrust loads for better performance.
i) Modif ied_Oil_R ing__Design_ (Pig. 3) - An optimum oil ring design for the 7" dia bearing has a width of 1 inch having a trapezoidal cross-section. It has five oil grooves effecting more oil delivery. The material is of bronze instead of Brass now being used. A comparison of oil ring details of existing and modified design are given below ( shown in Figs 2 and 3 respectively).
I nproved_ Existinq
material Bronze Brass
Outside diameter 332.6 mm 330.0mm
Inside diameter 304.0 mm 307.0mm
W idth 25 .4 mm 2 0 .0 mm
Thickness 14.3 mm 11.5 mm
No. of Oil grooves 5 One at centre
obtained from Roll ing
Weight 2 250 gm 694 gm
ii ) Modified thrust bearina Desiqn .
: Thrust bearing
design is modified by incorporating the taper land instead
of flat land provided by existing design. Each sector of
thrust pad (10) is given a taper 1 in 1000 (11) in the direction
of rotation. It provides more clearance i. e. 70 µ m in the inlet edge than the outlet edge. All the other dimensions of the existing design are kept unchang ed. The details of the flat plate thrust bearing and taper land thrust bearing are shown in Figs. 4 and 5 respectively.
The design modifications of proposed oil ring and thrust bearing are developed as an experiment alongwith the complete bearing of 7" dia and was retrofited in place of existing bearing as per Patent No. 3544179. The bearing performance was tested and oil delivery by oil rings were measured at different loads and speeds. The table below shows the measured oil flow rate with existing T section oil rings with that of the modified oil rings. It is found that the modified oil rings were pumping 50% more oil to the bearing clearance than the oil rings of the existing d es ig n .
OIL DELIVERED AT 1 TON LOAD
Speed RPM T-Section Modified PERCENTAGE
OIL FLOW O iL Flow INCREASE
OIL FLOW Oil Flew
RATE (ml/mt) Rate (ml/mt)
5 00 40 50 2 5%
1000 48 68 41%
1500 50 75 50%
Radial and thrust loads upto 2 Tons were applied on the Test bearing. Thrust bearing temperature was measured
at 1000 RPM and 1200 RPM. Table below shows the measured thrust bearing babbit temperature ov er ambient for taper land and flat land thrust bearing. It is found that thrust bearing temperatures were reduced with the taper land by 10oC at the rated para met res.
As already mentioned/ the modified oil rings helped in pumping more oil and the taper land thrust plate design helped in supporting more thrust load and resulted in a r aduction ot 10oC bearing temperature is considered a substantial improvement in the cearing design.
Although the principles of the invention have been set forth hereinabove with reference to specific embodiment,, / it is to be understood that these are by way of illustration, and that variations on modifications may be affected without departing from the scope and spirit of the invention as defined by the appended claims.
1. An improved ring lubricated combined journal and thrust bearing for use in primary air fans in boiler auxiliary equipment of thermal power plant comprising a combined journal and thrust bearing having a plurality of thrust pad sections (2) supported by a correspondingly numbered runners (9) mounted on a rotating shaft (3); and an oil ring (1) mounted on a rotating journal of said combined journal and thrust bearing, characterised in that said oil ring (1) is fabricated with a trapejoi-dal cross section having a plurality of grooves on an inner diameter made of a bronze material, and in that each of said thrust pad sections (2) is given a taper in a rotational direction of said bearing.
2. The bearing as claimed in claim 1 wherein a width of said trapejoidal cross section of said oil ring(l) is 1" when a diameter of said bearing is selected at 7".
3. The bearing as claimed in claim 1 wherein diamentional parameters of said taper in said thrust pad Sections (2) is such that a clearance in an inlet edge of the thrust pad sections exceeds by 70 /urn than that available in an outlet edge.
4. The bearing as claimed in claim 1, wherein an inside diameter of said oil ring (1) if selected at 304.oo mm, an outside diameter to be maintained at a value higher by 9'/.
5. The bearing as claimed in claim l wherein the number of said grooves provided in said oil ring (1) is five.
6. An improved ring lubricated combined journal and thrust bearing substantially as herein described and illustrated.
|Indian Patent Application Number||448/DEL/1996|
|PG Journal Number||30/2004|
|Date of Filing||01-Mar-1996|
|Name of Patentee||BHARAT HEAVY ELECTRICALS LIMITED|
|Applicant Address||BHEL HOUSE SIRI FORT, NEW DELHI-110049, INDIA.|
|PCT International Classification Number||F16D 1/06|
|PCT International Application Number||N/A|
|PCT International Filing date|