Annular seal for self-cleaning sludge centrifuges

The invention pertains to a displaceable annular seal for self-cleaning sludge centrifuges where the sludge contents are ejected through a peripheral slit which is defined upwardly by the upper bowl part, and downwardly by the annular seal which consists of a relatively soft and elastic sealing part and a relatively stiff and hard reinforcement part which are joined by glueing or in a similar manner.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to annular seals for self-cleaning sludge 
centrifuges. 
2. Description of the Prior Art 
Annular seals for self-cleaning sludge centrifuges are well known, such as 
shown in Danish Patent No. 127041. The annular seal disclosed in this 
patent has its soft ring part joined to the reinforcement part in such a 
way that the soft material covers the reinforcement part's top in such a 
manner that the soft material seals directly against the upper bowl part 
when the slit is closed. This arrangement has shown itself to be 
accompanied by serious drawbacks as the soft material is squeezed between 
the two hard parts, has a tendency to flow outwardly under the influence 
of the centrifugal force, and is quickly eroded in its exposed position by 
the outflowing solid particles. Furthermore, in such an arrangement it is 
difficult to perform so called "partial shots" because the soft material 
is not able to "bite" the sludge flows over. These disadvantages of the 
prior art are overcome by the present invention. 
SUMMARY OF THE INVENTION 
A displaceable annual seal for self-cleaning sludge centrifuges in which 
the sludge contents are ejected through a peripheral slit which is defined 
upwardly by the upper bowl part and downwardly by the lower bowl part and 
by the annular seal which is mounted on a ring piston, includes a soft 
elastic sealing part which is fastened to a relatively stiff and hard 
reinforcement part in the surface which faces the inner space of the 
centrifuge, with the upper edge of the reinforcement part directly 
touching the upper bowl part. Such an embodiment has the result that the 
soft sealing material, which for example may be rubber, is protected 
against the centrifugal pressure against the reinforcement ring which 
directly touches the upper bowl part. Thus, the sealing material is not 
squeezed and cannot flow outwardly. Nevertheless, the soft material seals 
because, since it cannot be compressed, it is deformed upwardly against 
the upper bowl part by the fluid pressure in the centrifuge. In most 
cases, depending on the degree of hardness of the sealing material, the 
sealing material will, when the slit is opened, move together with the 
reinforcement ring without flowing over its edge. Thus, it will be lying 
more or less protected against the erosive effect of the outflowing 
material. 
An important improvement in the annular seal in accordance with the present 
invention is accomplished by providing a sharpened upper edge for the 
reinforcement ring. A sharp edge bites well, and offers only a limited 
area of attack to the hydro-static pressure emanating from the fluid 
inside the centrifuge which might cause the centrifuge to become leaky. As 
a result of this preferred arrangement, the forces which keep the 
centrifuge closed may be kept to a minimum. Both characteristics are 
important for the performance of a "partial shot". Preferably, the upper 
edge of the aforementioned reinforcement ring is hardened while the upper 
bowl part is furnished with a non-hardened erosion ring. If relatively 
hard sealing materials are employed, it is preferably advantageous to 
provide the sealing part with a relatively broad upper edge which is on a 
level with the upper edge of the reinforcement part because such a 
material cannot be deformed very much. If, instead, relatively soft 
sealing materials are employed, preferably the sealing part is separated 
from the reinforcement part by a groove between their respective upper 
edges or the upper edge of the sealing part is divided by a groove. This 
arrangement has the advantageous effect that the upper edge of the seal 
can flow out downwardly into the groove when the slit is open so that it 
does not flow over the sharp edge of the reinforcement ring, and the upper 
edge of the seal is raised up by the pressure of the fluid generated in 
the groove and is pressed against the upper bowl part when the slit is 
closed. This arrangement also protects the material against erosion. 
Preferably, the life of the seal may be increased by making the inside 
edge of the aforementioned groove of the sealing part higher than the 
upper part of the reinforcement ring. This additional material enhances 
the dependability of the seal. 
Under certain circumstances, it may be beneficial to preferably provide a 
rounded or relatively broad upper edge for the reinforcement part with the 
upper bowl part which is opposite to it being furnished with a soft 
sealing ring. In this manner the collision between the annular seal and 
the upper bowl part is softened when the centrifuge is closed with great 
force. When the slit is opened the sealing part is deformed along its 
surface that adjoins the inner surface of the centrifuge. By this, the 
sludge lodging in this area is moved and loosened which has the very 
important effect that the sludge is ejected more easily. In order to 
enhance this effect the annular seal may preferably be formed with the 
inner surface of the sealing part forming a concave angle surface against 
the interior of the centrifuge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention shall be explained in detail below in connection with 
the drawings, which in FIGS. 1-4 show parts of a self-cleaning sludge 
centrifuge together with various preferred embodiments of the annular seal 
in accordance with the invention in sectional view. Referring now to the 
drawings in detail, FIGS. 1-3 show an upper bowl part 1 and a lower bowl 
part 2 with a sludge ejection slit 3 located between the two. The lower 
bowl part 2 preferably is surrounded by a ring shaped piston 4, which is 
vertically displaceable relative to lower bowl part 2. Piston 4 preferably 
carries an annular seal 5-6 consisting of an outer stiff reinforcement 
ring 5 and an inner relatively soft sealing ring 6. The upper bowl part 1, 
as shown and preferred in FIG. 1, can be provided at the slit 3 with a 
replaceable erosion ring 7. The sludge preferably collects in a triangular 
sludge space 8 which is preferably defined by, among other parts, the 
inner surface 9 of the sealing ring 6, which in FIG. 1 is preferably shown 
as having a concave angle area 10 which, by the opening movement of the 
annular seal, is preferably reshaped into a convex area by which the 
sludge is loosened. In FIG. 1 the upper edge of the hard reinforcement 
ring 5 is shown as being sharp, whereas in the embodiment of FIG. 3 it is 
shown as being rounded and in the embodiment of FIG. 4 as being relatively 
flat. As illustrated in FIG. 3, by way of example, the embodiments shown 
in FIGS. 3 and 4 make it possible to employ a seal ring 11 in the upper 
bowl part 1. As also shown and preferred in FIG. 1, the upper edge of seal 
ring 6 is on the same level as the upper edge of the reinforcement ring 5. 
However, as shown and preferred in the embodiments of FIGS. 2 and 4, a 
groove 12, 13, respectively, is provided between the sealing ring 6 and 
the reinforcement ring 5, and in the sealing itself. In both cases the 
sealing ring 6 is shown to preferably extend over the level of the 
reinforcement ring 5. It is also possible to form the sealing ring 6 on a 
level with or below the level of the upper edge of the reinforcement ring 
5. In all of the aforementioned FIGS. 1-4, the slit 3 is preferably shown 
open in order to show distinctly the manufacturing shape of the annular 
seal which, naturally, changes when the slit is closed.