FIELD OF THE INVENTION
The present invention generally relates to an improved Labyrinth joint, using split
type IBC(Inner Bearing Cap), in large rating Flame Proof A.C. Induction Motor,
mounted with sleeve bearings. More particularly, the present invention relates to
an improved labyrinth joint on flexible rotor of a Flame proof A.C. Induction
motor with Sleeve bearings to achieve a desired flame paths to restrict leakage
of flame.
BACKGROUND OF THE INVENTION
Basic requirement of all flame proof motors are to comply with the requirement
as per IS/IEC 60079-1 with regard to the flame path (shortest path through a
flame proof joint from the inside to the outside of an enclosure) and a gap
(distance between the surfaces of the flameproof joint).
In the prior art Labyrinth joints, Cast iron bearing Housing (7) are used. This is a
magnetic material and is restricted in its use to make labyrinth joint for Flame
proof motor fitted with sleeve bearings.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved labyrinth joint
adaptable in flame proof motor with sleeve bearings used in hazardous gas
group areas IIA and IIB such that they facilitate ease in assembling and
dismantling.
SUMMARY OF THE INVENTION
According to the invention, there is provided an improved labyrinth joint, in
particular for two pole motors with flexible rotors and sleeve bearings. The
invention proposes use of special split type inner bearing cap (IBC) which is easy
to manufacture and facilitates ease in assembly of the joint and can also be
dismantled during maintenance of the motor without difficulty.
The labyrinth joint so produced is able to provide appropriate flame paths
between the rotating components and stationary surfaces. The Outer part of the
IBC is made up of fabricated steel and is fixed over the motor End-shield from
inside, by using at least six number fasteners. Inner part of the IBC is made up
of non-sparking material brass and is suitable to mount on the outer part with
the help of 8 nos. fasteners.
The split type IBC is accommodated in same bearing housing as of the prior art.
An Outer ring made up of cast iron is fixed over the inner part of IBC and a Shaft
ring of forged steel is shrink fitted over the shaft, collectively produces a
labyrinth joint as stipulated in IEC-60079-1 2007.
Thus, the present invention proposes the use of IBC in two pieces, along with
Outer ring of cast iron and a Shaft ring made up of forged steel to form a
labyrinth joint. The outer part of IBC is made up of steel and inner part is made
of non-sparking material brass. The improved labyrinth joint is adaptable for
Flame Proof A.C Induction Motor with sleeve bearings, as per clause 8.2.1 of
IEC-60079-1, 2007.
The proposed labyrinth joint is applicable to flame proof motors having Sleeve
Bearings used in-the gas group llA and llB only. Flame proof motor with sleeve
bearings are not allowed in IIC group of gases.
The invented labyrinth joint is unique and its components can be produced with
ease in any lathe machine ad avoiding intricate machining and difficult to
manufacture.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG-1 - Section layout of a flame proof motor with flexible rotor and sleeve
bearings for which labyrinth joint is proposed.
FIG-2 - Shows schematic of a labyrinth joint as per prior art.
FIG-3 - Shows schematic of a labyrinth joint as per the present invention.
FIG-4 - Schematic of a typical split type inner bearing cap (IBC).
FIG-5 - Schematic of a typical shaft ring.
FIG-6 - Schematic of a typical outer ring.
DETAIL DESCRIPTION OF THE INVENTION
FIGURE - 1 shows a typical Cross Sectional Layout of a large capacity, for
example a llOOkw H.T. Induction motor in TETV (Totally Enclosed Tube
Ventilated) construction. This motor rotates on Sleeve Bearings. Rotor geometry
including Core, and Shaft results in flexible operation of the Rotor. The figure
also shows use of labyrinth joint inside the machine on both DE and NDE Side of
the motor with detail-W.
FIGURE - 2 shows a typical labyrinth joint as per prior art. In this arrangement
a Bearing Housing (7) made up of Cast Iron is used for fixing of Anti friction
bearings (11, 12). An Outer ring (8) and Bearing Housing (7) are fixed over End-
shield (6) by high tensile strength fasteners. A shaft ring (9) made of forged
steel is mounted on Shaft (10) which is rigid in construction. Requirement of
length of the flame path is maintained as per IEC-60079-1.
FIGURE-3 Shows a labyrinth joint as per the invention. In this arrangement the
bearing housing used in the prior art is eliminated and a split type IBC (2A, 2B) is
used. Top half of the IBC (2A) is fixed over the End-shield (1) from inside of the
motor. Bottom half of the IBC (2B) is fixed over the top half (2A) by using
fasteners. Outer ring (3) is push fitted over the bottom half of IBC (2B). A shaft
ring (4) made of forged steel is shrink fitted over flexible Shaft (5).
WE CLAIM:
1. An improved labyrinth joint on flexible rotor of a Flame proof A.C.
Induction motor with Sleeve bearings to achieve a desired flame paths
to restrict leakage of flame, the improvement is characterized by
following steps:
- a split type inner bearings cap (IBC) (2A, 2B), each half
provided at both driving end (D.E) and non-driving end
(N.D.E) for achieving desired flame path;
- a cast iron Outer ring (3) push fitted over a bottom half of the
IBC (2B);
- a shaft ring (4) made of forged steel shrink fitted over a flexible
shaft (5) wherein a top half (2A) of the IBC is releasably fixed
over the bottom half (2B) by fastening means.
2. The labyrinth joint as claimed in claim 1, wherein the bottom half of
The IBC (2B) is made of non-sparking material brass.

ABSTRACT

The invention relates to an improved labyrinth joint on flexible rotor of a Flame
proof A.C. Induction motor with Sleeve bearings to achieve a desired flame paths
to restrict leakage of flame, the improvement is characterized by following steps:
a split type inner bearings cap (IBC) (2A, 2B), each half provided at both driving
end (D.E) and non-driving end (N.D.E) for achieving desired flame path; a cast
iron Outer ring (3) push fitted over a bottom half of the IBC (2B); a shaft ring
(4) made of forged steel shrink fitted over a flexible shaft (5) wherein a top half
(2A) of the IBC is releasably fixed over the bottom half (2B) by fastening means.