Stuffing box seal having braided packings and lip seal rings in combination with a shaft sleeve

A sealing device for a shaft rotating relative to a frame, particularly for a pump shaft, wherein a protective sleeve surrounding the shaft is fixedly mounted for rotation with the shaft; a collar step surrounding the sleeve is fixedly mounted on the frame; a sealing device surrounding the sleeve is non-rotatingly mounted within the frame and includes a lantern ring for connection to a source of lubrication liquid; an annular ring with a sealing lip is inserted between the collar step and lantern ring; and a packing braid is disposed between the lantern ring and a device for compressing the braid.

The invention relates to a sealing device for a rotating shaft. 
OBJECTS OF THE INVENTION 
The present invention has for its object a sealing device for a rotating 
shaft, and particularly for a rotating shaft for a pump. 
More precisely, the present invention has for its object a sealing device 
surrounding the rotating shaft which makes it possible effectively to 
isolate the pump part proper in which the liquid traversing the pump 
circulates from the mechanical part for rotating and for guiding the shaft 
of the pump, 
It will be understood that this is very important, particularly in 
paper-making industries where the pumps must place liquids in circulation, 
which liquids may be very corrosive and highly likely to damage the 
mechanical parts of the pump, and in particular, the bearings thanks to 
which the shaft is mounted to rotate inside the frame of the pump. 
In the known rotating shaft sealing devices, a stuffing box is most often 
found which is disposed around the shaft inside a packing box, such seal 
often being completed by an annular recess or lantern ring for 
introduction of a liquid for lubricating the packings. To make the 
stuffing box, different types of braids are used, particularly braids of 
tallowed hemp, Teflon .RTM.-coated braids which may be based on hemp or 
aramide fiber. Furthermore, in the known systems, the lubrication liquid 
is most often introduced under pressure and may consist in the injection 
of the liquid itself which circulates in the pump. 
It will also be understood that, when such a pump is used continuously, it 
is, on the one hand, necessary that the sealing device has a life duration 
as long as possible in order to reduce the frequency of interventions 
which increase the duration of non-availability of the pump and that, in 
particular, the sealing device changing operations may be carried out 
conveniently without this causing too long a period of non-availability of 
the pump. 
In addition, in order to avoid having to change the shaft itself of the 
pump, the shaft part disposed opposite the sealing device is covered with 
a metallic sleeve most often made of bronze or stainless steel. It so 
happens that these types of sleeves present the drawback of being altered 
relatively rapid by the effect of friction of the sealing devices which 
reduces to zero the function of the sleeve. 
It is an object of the present invention to provide a sealing device for a 
rotating shaft, and particularly of a pump, which avoids the drawbacks 
mentioned hereinabove by increasing the life duration of the sealing 
device and simplifying the maintenance operations corresponding to the 
change of the sealing device. 
To attain that object, the sealing device for a rotating shaft comprises a 
frame surrounding the shaft, the sealing device being disposed between the 
shaft and the frame comprises: 
a protective sleeve surrounding the shaft for rotation with the shaft; 
a collar step surrounding the sleeve and held fixed in the frame; and 
a sealing device surrounding the sleeve held fixed in the frame which 
includes: 
a lantern ring with an annular recess held fixed in the frame for 
connection to a source of lubrication liquid; 
at least one annular ring with sealing lip between the collar step and 
lantern ring, the sealing lip cooperating with an outer face of the 
sleeve, and 
at least one packing braid disposed between the lantern ring and the collar 
step and a means for compressing the braid. 
It will be understood that, thanks to the arrangements of the invention, 
the seal between the collar step and the lubrication recess is ensured by 
the lipped sealing rings which makes it possible, on the one hand, to 
improve the seal, particularly between the pump and the lubrication liquid 
and, on the other hand, to simplify the maintenance operations since these 
lipped rings present a very long life. Further, the rings are disposed in 
the zone where the packing braids of the prior art solutions were in fact 
inaccessible due to the presence of the lantern ring comprising the recess 
for injection of lubrication liquid. 
According to a preferred embodiment of the invention, the protective sleeve 
is made of steel and is coated with a protective layer comprising 50 to 
70% of the addition metal and 30 to 50% of binding agent. Percentages of 
weight as is conventional in the art. 
Such a composition of the protection layer ensures a high mechanical 
strength of the outer face of the sleeve while presenting a considerable 
ease of employment. 
Other characteristics and advantages of the present invention will appear 
more readily on reading the following description of an embodiment of the 
invention given by way of non-limiting example.

DETAILED DESCRIPTION OF THE INVENTION 
Referring first to FIG. 1, the general structure of a pump on which the 
sealing device for a rotating shaft may be mounted will be described. This 
pump comprises a shell or housing 10 with its inlet conduit 12 and its 
outlet conduit 14. The shell 10 is extended by a pump body or frame 16 in 
which the rotating shaft 18 is mounted. On the first end 20 of the shaft, 
the rotor 22 of the pump is mounted, which rotor is, of course, disposed 
inside the shell 10. The second end 24 of the shaft is connected to a 
motor (not shown in the Figure). The shaft 18 is supported for rotation by 
two bearings 26 and 28 in known manner with suitable ball bearing 
assemblies. In this way, the rotor 20 is in overhang position with respect 
to the bearings 26 and 28. It will be understood that it is necessary to 
produce a seal between the interior of the shell 10 in which the fluid 
circulates and the mechanical part for supporting the shaft 18 for 
rotation, this mechanical part being essentially constitutes by the 
bearing assemblies 26 and 28. 
FIG. 1 schematically shows the sealing device 30 disposed between the shell 
10 and the first bearing 28. This figure shows the sealing device only 
schematically. However, it will be understood that the sealing device 
essentially comprises a stuffing box 32 which is fixed to the pump body 16 
and which surrounds the shaft 18 and serves to hold the sealing device 30. 
Referring now to FIG. 2, the sealing device 30 mounted inside the stuffing 
box 32 will be described in greater detail. As this figure shows, the 
shaft 18 is covered with a protective sleeve 40 which extends at least 
over the part of the shaft opposite the sealing device. The embodiment of 
the sleeve 40 will be described hereinafter in greater detail. 
The protective sleeve 40 is slidingly fitted onto the outer face of the 
shaft 18. 
As is well known, the stuffing box 32 comprises an inner countersink 
opening 42. Engaged around the shaft 18 are the different elements 
constituting the sealing device 30. Shown along the shaft 18 from its 
motor end 24 is a first bearing 26, a second bearing 28, and between the 
bearing 28 and rotor 22 shaft end 20, there are inside a countersink 
opening 42 a collar step 44, two elastomer annular sealing rings 46 and 
48, a lantern ring 50 including an annular recess 52 for the introduction 
of a lubricating liquid for the sealing device, and a plurality of packing 
braids 54, these components being maintained compressed in the countersink 
opening 42 by a rammer 56. As shown better in FIG. 1, the rammer 56 is 
maintained in place and tightened by screws, such as 58. 
The collar step 44 is of conventional type. It is made of bronze or of 
celoron and essentially constitutes an interchangeable wear piece. It thus 
makes it possible to avoid, particularly in the case of vibrations, wear 
of the shaft or of the stuffing box 32. The clearance e between the outer 
face of the sleeve 40 and the inner face of the collar step 44 is 
preferably very small, for example, of the order of 0.2 mm, in order to 
reduce the specific pressure of the liquid on the sealing device. 
The elastomer annular sealing rings 46 and 48 are disposed between the 
lubricating lantern 52 and the collar step 44. These two sealing rings are 
of the lipped type and comprise a fixation body 64 in contact with the 
wall of the countersink opening 42 and a deformable lip 60. Each lip 60 is 
incurved in the direction of the collar step 44 in order that, under the 
effect of the pressure, the lip 60 tends to be pressed against the shaft 
18. The nature of the elastomer employed to produce the rings 46 and 48 
depends on the fluids conveyed by the pump or on the lubricating liquid. 
It is also possible to provide rings 46 and 48 in which an annular spring 
62 is embedded in the lip 60 to increase the contact pressure between the 
lip and the outer face of the shaft. The sealing rings may preferably be 
made of the material marked under the Trademark VITON.RTM.. 
The lantern ring 50 may be of conventional type. It defines an annular 
recess for supplying lubricating liquid, comprises an inlet orifice 50 
which can be connected to a source of lubricating liquid, and it presents 
preferably an inlet orifice 50 opposite an orifice for outlet of the 
lubricating liquid (not shown in FIG. 2). This outlet orifice makes it 
possible to avoid any risk of overpressure of the lubricating liquid in 
this zone and, therefore, any risk of passage of the lubricating liquid 
towards the shell of the pump. 
Beyond the lantern ring 50, a plurality of packing braids 54 are inserted. 
The number of braids depends on the seal which it is desired to produce. 
The packing braids are preferably based on Teflon.RTM.-coated aramide 
fibers. 
It will be understood that this arrangement ensures a very effective seal 
between the pump proper and the mechanical members for guiding the shaft 
while allowing easy maintenance of the pump. In fact, it will be 
understood that the packing braids 54, after dismantling of the rammer 56, 
may be easily extracted from the stuffing box by any suitable means since 
access is free. On the other hand, concerning the sealing components 
disposed beyond the lantern ring 52 and which are therefore not accessible 
except during considerable dismantlings, the question is not raised since 
the lipped rings 46 and 48 have a very high mechanical resistance and do 
not require frequent replacement. It should be added that the chosen 
braids 54 also present a very high life expectancy, typically at least of 
the order of 12 months. 
The quality of the seal avoids the passage of the liquid pumped towards the 
mechanical part of the pump. This presents two principal advantages. On 
the one hand, the mechanical part is protected from corrosion due to the 
liquid circulating in the pump. On the other hand, losses of liquid are 
avoided which may be very important when the liquid has a high value. 
As indicated, the protective sleeve 40 is preferably constituted from a 
steel sleeve which is not stainless, but which may possibly be in certain 
cases, where a protective coating 66 of added metal is made. According to 
the invention, this protective coating has a thickness of about 1 mm. To 
produce the protecting layer of the sleeve, a mixture of 60% addition 
metal, more generally in a range between 50 and 70%, and of 40% of binding 
agent, more generally in a range from 30 to 50% weight is used. The 
binding agent allows a re-melting to allow the deposit and fixation of the 
added metal at a temperature of the order of 1200.degree. C. In known 
manner, the added material may be chromium carbide, tungsten carbide, or 
similar materials.