Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTIVE MEMORANDUM
This invention relates generally to pumps such as for example centrifugal
pumps
including centrifugal slurry pumps and also to a method of handling components
therefor.
Centrifugal slurry pumps are used in a large variety of industrial processes,
especially in
the grinding and grading stage of ore during mineral processing.
Ore slurries are highly abrasive causing great wear and tear to those parts of
the pump in
contact with the slurry, which requires slurry pumps to undergo frequent
servicing.
In the processing of copper ore, a slurry pump typically processes
approximately 2,000
tonnes of ore per hour, including about 20 tonnes of copper content.
Depending on the slurry pump size and weight, from 12 to 30 tonnes, its
replacement
takes from 8 to 16 hours and each replacement therefore causes a production
loss of at
least 150 to 300 tonnes of copper.
For this reason there have been advances in the design and development of
slurry
pumps to extend the pumps' operating time between services. One of the typical
solutions is to protect the pump casing with metallic or elastomeric
sacrificial internal
liners.
However, in the state of the art there is no technical solution to reduce the
period of time
it takes to change out a slurry pump, this being the technical problem that
the present
invention solves.
Figure la is a cutaway elevation view of a slurry pump without a sacrificial
liner, and
Ib is the elevation view of the pump front face.
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Figure 2a is a cutaway elevation view of a slurry pump with a sacrificial
liner, and
figure 2b is the elevation view of that same pump front face.
Figure 3a is a cutaway elevation view of a slurry pump in a preferred
embodiment of
the invention. Figure 3b is the elevation view of that same pump front face.
Figure 3c
is a cutaway elevation view of a preferred embodiment of the impeller fixing
mechanism which is the object of the present invention. Figure 3d is a cutaway
axial
elevation view of a preferred embodiment of the fixing mechanism corresponding
to the
pump frontal face, and figure 3d is the view corresponding to the pump rear
face.
The description of the invention shall be based on these figures.
A slurry pump without liners, figures 1a and lb, comprising a base 2 that is
connected
to subbase I by means of bolts 17. Subbase 1 is anchored to the ground. Base 2
supports the slurry pump which consists of a casing, 3, or "wet end" according
to the art
and a rotating drive shaft 14, with a torque release mechanism, 27, where the
shaft 14 is
connected by means of coupling 15 to the impeller system of shaft 16. Wet end
3
comprises a metallic casing formed by two members, the casing frontal face 4a
and the
casing rear face 4b. Both faces are connected to each other by bolts 10.
Frontal-face 4a
is connected to the inlet or suction pipe 6 by means of bolts 8. The wet end
is fixed to
base 2 by bolts 13 that are located in the rear face 4b. On the inside of the
wet end is
impeller 5 which is screwed onto shaft 14. The slurry enters through inlet
pipe 6 under
the suction produced by the rotating impeller 5 and is propelled from the pump
via
outlet pipe 7 which is connected to the slurry pump by bolts 9.
A pump with a sacrificial liner differs from the preceding pump in that the
inner
surfaces of casing faces 4a and 4b have a covering or lining 18a and 18b as
shown in
figure 2a.
Because of the pump weight which, depending on the pump size, varies between
12 to
30 tonnes, including base 2, handling the pump requires the use of chain
blocks or
cranes, for which purpose the wet end comprises flanges 11 having orifices 12,
such
flanges are located at the outer side of casing faces 4a and 4b.
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The pump high rotation speed demands the precise alignment between shafts 14,
16 and
impeller 5.
Presently, the servicing of centrifugal slurry pumps is performed in two ways:
By Total Replacement of Pumpor
Pump Liner and Impeller Replacement by Dismantling in situ.
Total Replacement of Pump
Total replacement of pump requires the following procedure:
1. Disconnect suction pipe 6 and discharge pipe 7 from the pump by
removing bolts 8 and 9, respectively.
2. Disconnect coupling 15 to disengage shaf114 from driveshaft 16.
3. Remove bolts 17 which connect the complete pump assembly to its
subbase 1.
4. Remove the complete pump assembly from the pump location by means
of a chain block or crane and transport the complete pump assembly to
repair facility for maintenance.
5. Transport to the pump location a new complete pur.pp assembly by
means of chain block or crane.
6. Connect the complete pump assembly to sub-base 1 by means of bolts
17.
7. Connect coupling 15 which joins pump shaft 14 and driveshaft 16.
8. Perform alignment of shafis 14 and 16.
9. Connect suction pipe 6 and discharge pipe 7 to pump by means of bolts 8
and 9, respectively.
Such procedure presents the following disadvantages:
1. The entire pump assembly 2, including the entire mechanical system,
bearing housing, packing gland and lubrication, not shown in the figures,
comprising shaft 14, implying a greater investment cost.
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2. The weight to be handled, considering the complete pump assembly, is
of about 12 to 30 tonnes, of which 4 to 10 tonnes corresponds to the
weight of base.
3. Alignment of the pump drive shaft must be extremely accurate to avoid
vibration and prevent equipment damage. This is an arduous task and
requires much time.
4. Total pump replacement procedure takes over 8 hours.
Pump Liner and Impeller Replacement by Dismantling in situ.
Replacement of pump with elastomeric liners, by dismantling in situ, requires
the
following steps:
1. Disconnect pump from suction pipe 6 and discharge pipe 7 by removing
bolts 8 and 9, respectively.
2. Place lifting slings on the pump casing front or suction section 4a.
3. Open wet end 3 by removing bolts 10.
4. Remove front section of pump casing 4a and store temporarily
5. Dis-engage torque release mechanism 27.
6. Secure impeller 5 with a special lifting device that maintains impeller in
a vertical position, while allowing rotation of shaft 14 in reverse
direction for disconnection and permit removal of the impeller 5.
7. Place lifting slings on the rear pump casing rear section 4b.
8. Remove bolts 13 which join the pump casing rear section 4b with the
pump base 2.
9. Remove the rear pump casing section 4b and store temporarily. . to
remove and replace liner.
10. Re-install the rear pump casing section 4b with a new liner in place to,
pump base 2, by means of bolts 13.
11. Install the new impeller 5 by using the special device that keeps impeller
in a centralised vertical position.
12. Re-engage the torque release mechanism.
13. Rotate shaft 14 in its normal rotation direction for connection to the
impeller.
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14. Install the front pump or suction casing section 4a with new liner
installed and close the pump up by fastening bolts 10.
This procedure does not require the re-alignment of the shafts stage, however
it presents
the following disadvantages:
1. It requires many steps that take much working time, especially steps 3
and 11.
2. It requires using a special lifting device mounted on a chain block which
keeps the impeller in a centralized vertical position for both
disconnection and re-connection.
3. Total pump wet end liner and impeller replacement procedure takes over
8 hours.
The main common problem of such procedures is the time it takes for pump liner
and
impeller replacement purposes, which causes a production drop.
Due to the large mineral processing through-put, reduction in the amount of
time the
pump is off-line has a great impact in the plant productivity and
profitability.
In the current state of the art there is no procedure to replace slurry pump
liners in less
than 8 hours. This is the technical problem that is solved by the present
invention.
According to one aspect of the present invention there is provided a
centrifugal pump in
which a pump wet end comprises a casing with or without inner pump linings and
one
impeller which freely rotates inside the casing by means of a shaft,
CHARACTERIZED
in that it has a fixing mechanism which immobilizes and fixes the impeller in
a
centralised position and a system for tightening and loosening the fixing
mechanism.
Preferably, the fixing mechanism, comprises two elements concentric with the
pump
shaft, the first element attached to face and the second element attached to
face.
Preferably the fixing elements are circular ring-shaped, having a diameter
between
0.95D and ID, where D is the impeller diameter.
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Preferably, the fixing elements comprise a flexible elastomeric member and a
stiff
backing part. Preferably, the elastomeric members thickness is about 10 mm to
25
mm and each member can have a different thickness. Preferably, the diameter of
stiff members is the same as that of members, and are formed by a flat base
and ribs
where the flat plate thickness is between 10 to 30 mm and the height of the
ribs is
between 20 to 50 mm.
Preferably, the fixing mechanism tightening system comprises two tightening
bolts,
which are screwed to the casing faces and abut against the rib of the fixing
mechanism member, and the loosening system comprises loosening bolts, with
nuts
and washers, the bolts freely pass through the casing holes, bolts are jointly
attached
to stiff part on the same rib where bolts are fastened. Preferably, the
tightening bolts
and loosening bolts are inserted there between and evenly spaced apart in a
circumference concentric to the shaft.
According to another aspect of the present invention there is provided a
procedure
for replacement of liners and impeller in a centrifugal pump, described above
comprising the following steps:
a. Disconnect pump from suction pipe and discharge pipe by removing
bolts, respectively.
b. Place lifting slings on the pump wet end.
c. Loosen nuts to allow axial displacement of members by tightening of
bolts until members make contact and press on the impeller faces.
d. Remove bolts that join the casing rear face to the pump base.
e. Dis-engage the torque release mechanism.
f. Rotate shaft in its normal reverse rotation direction for disconnection
from impeller.
g. Remove the complete wet end and take it to a repair facility.
h. Position the new wet end furnished with the impeller and assembled with
the impeller fixing mechanism and fasten it to base by means of bolts.
i. Engage the torque release mechanism.
j. Rotate shaft in its normal rotating direction for connection to impeller.
k. Release bolts to allow movement of members, release impeller by
rotating nuts, until members make contact with faces.
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Reduction of slurry pump liner and impeller replacement time implies the
reduction of
the number of steps to be taken. In the case of total replacement of the
slurry pump
steps 2, 3, 6, 7 and particularly step 8 relating to alignment are eliminated;
and in the
case of pump replacement by dismantling in situ, steps 3, 4, 6, 11 and 13 are
eliminated.
A preferred embodiment of the present invention comprises a mechanism that
temporarily fixes the impeller 5 to the faces of the casing sections 4a and
4b, in such a
way that the impeller 5 remains immobilized and perfectly centered in the wet
end 3,
therefore it can be connected to shaft 14 without the need for re-alignment,
that is to
say, such special mechanism allows removal of the entire pump wet end assembly
3
from the slurry pump without the impeller losing its position relative to
shaft 14,
therefore no re-alignment of impeller to pump shaft is required nor is the
slurry pump
required to be dismantled "in situ".
When impeller 5 is fixed and immobilized, the wet end 3 can be removed by
removing
bolts 13 only, without the need of disassembling shafts 14 and 16, in other
words,
disconnection of coupling 15 that connects the shafts is not required.
Consequently, no
re-alignment is needed as in the case of total replacement of pump, nor is it
necessary to
open the slurry pump wet end 3, as required in the case of "dismantling in
situ".
One of the preferred embodiments of the present invention involving the fixing
mechanism is shown in figures 3a, 3b, 3c and 3e.
Figure 3a is a cutaway elevation view of the pump with fixing mechanism, which
in this
preferred embodiment comprises two elements concentric with the pump shaft,
the first
element 19a attached to the face of front pump casing section 4a and the
second
element 19b attached to the face of rear pump casing section 4b.
The fixing elements 19a, in figures 3c and 3d and 19b, in figure 3e are
similar and are
split-annular shaped, therefore there will be a simultaneous common
description of
them. Fixing elements 19a and 19b comprises a flexible clastomeric member 20a
and
20b, respectively, and stiff backing parts 21a and 21b on which the tightening
bolts 22a
and 22b operate, being screwed to the casing faces 4a and 4b, respectively. In
addition,
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in the stiff backing parts 21a and 21b is the loosening system consisting of
loosening
bolts 23a and 23b, nuts 24a and 24b, and washers 25a and 25b. Bolts 23a and
23b
freely pass through the holes 26a and 26b in pump casing section faces 4a and
4b,
respectively.
Figures 3b and 3d show the distribution of bolts 22a and 23a, which are
inserted and
evenly spaced apart in a concentric circumference with the shaft. Figure 3e
shows a
similar form for bolts 22b and 23b.
The elastomeric members 20a and 20b are split-annular shaped with a 0,95D to
ID
diameter, where D is the impeller diameter with a 10 mm to 25 mm thickness
depending
on the pump size, the thickness of both members can be different but within
the
specified degree.
Stiff inembers 21a and 21b have the same diameter of members 20a and 20b, and
are
fonned by a flat base and ribs providing greater stiffhess and serving as
support for
tightening bolts 22 and as a base for the loosening bolts 23 where they are
jointly
positioned.
The thickness of the members' flat base 21 is ranked between 10 to 30 mm and
the ribs
height between 20 to 50 mm, which makes members 21 to have a total projected
height
of between 30 and 80 mm.
To fix the impeller, nuts 24a and 24b are firstly loosened, which allows free
movement
of loosening bolts 23a and 23b. When tightening bolts 22a and 22b, elements
19a and
19b move toward impeller 5 until making contact and pressing on the impeller
surface
immobilizing and keeping impeller fixed in a centered position with respect to
shaft 14.
To unlock the impeller, bolts 22a and 22b are firstly loosened and nuts 24a
and 24b of
loosening bolts 23a and 23b are rotated.
By using this preferred fixing mechanism of the present invention the complete
pump
wet end replacement procedure comprises the following steps:
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1. Disconnect pump from suction pipe 6 and discharge pipe 7 by removing
bolts 8 and 9, respectively.
2. Place lifting slings on the entire pump wet end 3.
3. Loosen nuts 25a and 25b to allow displacement of members 19a and 19b
by tightening bolts 22a and 22b until members 19a and 19b make
contact and press on the impeller 5 front and rear faces.
4. Remove bolts 13 which fasten the casing rear face 4b to the pump base
2.
5. Dis-engage the torque release mechanism 27.
6. Rotate shaft 14 in its normal reverse rotation direction for disconnection
from impeller 5.
7. Remove the wet end 3 and transport it to a repair facility.
8. Position the new wet end furnished with the impeller 5 assembled and
restrained in the centralized position by the fixing mechanism and fasten
it to base 2 by means of bolts 13.
9. Engage the torque release mechanism.
10. Rotate shaft 14 in its normal rotational direction for re-connection to
impeller 5.
11. Release bolts 22a and 22b to allow movement of members 19a and 19b
by rotating nuts 24a and 24b, until members 19a and 19b make contact
with faces 4a and 4b.
The following are the advantages of this procedure that makes use of the
impeller fixing mechanism, the object of the present invention:
= There is a maximum of plant operating down-time of less than 2 hours.
= It does not require disconnection of the pump shaft drive coupling..
= There is no need for re-alignment of the pump shafts.
Throughout this specification and the claims which follow, unless the context
requires
otherwise, the word "comprise", and variations such as "comprises" or
"comprising",
will be understood to imply the inclusion of a stated integer or step or group
of integers
or steps but not the exclusion of any other integer or step or group of
integers or steps.
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The reference in this specification to any prior publication (or information
derived from
it), or to any matter which is known, is- not, and should not be taken as an
acknowledgment or admission or any form of suggestion that that prior
publication (or
information derived from it) or known matter forms part of the common general
knowledge in the' field of endeavour to which this specification relates.
The reference numerals in the following claims do not in any way limit the
scope of the
respective claims.
