Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TUBE CLEANER FOR HARD DEPOSITS
Field of the Invention
The present invention relates to a tube cleaner or
scraper that is f luid driven through a tube to remove deposits,
specifically very hard deposits, from the inner surface of the tube
wall.
Background of the Invention
A variety of heat exchangers use a series of tubes
through which a cooling medium is passed so as to cool the tubes,
while another medium of higher temperature is in contact with the
exterior of the tubes, with heat transfer effected through the tube
walls. For example, in steam condensers in large power plants, a
series of small tubes are provided for heat transfer. After a
period of time, impurities or minerals in the water flowing through
the tubes tend to deposit on the inner surface of the tube wall
and, in addition to narrowing the cross-sectional flow area of the
tube passageway, such deposits form an insulating layer and detract
from the heat transfer capabilities of the tubes.
In order to remove deposits or encrustations, a scraper
element is inserted into one end of a tube, while the condenser is
out of service, and the scraper element is driven by fluid
pressure, usually by pressurized water, through the tube, the
scraper element scraping the deposits from the inner surface of the
tube wall and the pressurized fluid flushing the loosened deposits
from the tube. Depending upon the physical nature and chemical
composition of the deposits, various types of scrapers have been
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proposed. Examples of earlier tube scrapers are given in US
2,170,997, US 2,418,509, and 2,734,208 to C.M. Griffin, while
US 4,281,432 to George E. Saxon shows an improved tube cleaner
with a flexible rubber skirt. These types of scrapers are
adapted for use to remove general fouling and less tenacious
deposits from tubes. In US 5,153,963, to Gregory J. Saxon and
Daniel C. Lyle, a tube cleaner is disclosed for use in removing
thick hard deposits, or thick scales that chip off in
relatively large pieces, such as a scale containing calcium or
silicon, the cleaner having freewheeling cutting wheels that
cut through the scale and fracture the scale for removal from
the tube.
While the aforementioned tube cleaners are suited to
their purpose, there are certain deposits that are not readily
removed by such prior tube cleaners. One such difficulty
removable deposit is a very thin, brittle scale of a
crystalline structure that fractures into very small granular
pieces. Such scales are tenacious deposits.
Summar of the Invention
The invention provides a tube cleaner for removing
thin hard deposits on an inner surface of a tube, comprising: a
shaft having a nose portion and a tail portion, said tail
portion having secured thereto an outwardly and rearwardly
extending flexible skirt; a plurality, but less than four,
spaced apart scraper elements axially disposed along said
shaft; each said scraper element being formed of a single piece
of metallic material and having a radially outwardly extending
base portion and a plurality of rearwardly extending outwardly
biased fingers with each finger terminating as an outwardly
extending blade portion having an arcuate blade section, the
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radius of the arc being substantially smaller than the inside
radius of the tube for minimal contact, with adjacent fingers
of said scraper element being of a different length; and
adjacent said scraper elements being arranged on said shaft
such that blade portions of adjacent scraper elements are
axially displaced. The scraper elements are each preferably
formed from a single piece of spring steel.
Description of the Drawings
The invention will become more readily apparent from
the following description of a preferred embodiment thereof
shown, by way of example only, in the accompanying drawings,
wherein:
Figure 1 is a side elevational view of an embodiment
of the tube cleaner of the present invention;
Figure 2 is a front end or nose view of the tube
cleaner illustrated in Figure 1;
Figure 3 is a plan view of a scraper element in flat
state prior to bending the fingers and blade portions;
Figure 4 is a view similar to Figure 3 showing the
scraper element after bending to arrange the fingers and blade
portions into the desired configuration;
Figure 5 is a schematic view showing the contact of a
blade portion of a scraper element to remove hard scale from a
tube; and
Figure 6 is a cross-sectional view of a tube after
passage of a tube cleaner of the present invention through the
tube to remove hard scale.
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Detailed Description
A tube cleaner for hard deposits has two or three scraper
elements spaced along a shaft, which elements have fingers that
terminate as blades, the blades making a substantially point
contact with the .tube wall. The present tube cleaner is
specifically adapted for the removal of thin, hard deposits from
the tube wall inner surface, such as deposits of between 0.005 to
0.010 inch of manganese or iron oxide scales, which, while not
substantially restricting flow of a heat transfer fluid through the
tube, tend to act as an insulating material and has a deleterious
affect on the heat transfer capability of the wall of the tube.
Referring now to Figures 1 and 2, a tube cleaner 1 for
hard deposits of the present invention, is illustrated having a
shaft 2, with one end, or a nose portion 3, and a second end, or
tail portion 4, the tail portion 4 having secured thereto an
outwardly and rearwardly extending skirt 5. Spaced axially along
the shaft 2, between the nose portion 3 and tail portion 4, are two
or three scraper elements 6, illustrated as three scraper elements
6, 6~ and 6~. Each scraper element 6 is formed of a single price
of metal, preferably spring steel, such as SAE 1050 carbon annealed
spring steel. Each scraper element 6 has a radially outwardly
extending base portion 7 and a plurality, preferably six,
rearwardly extending fingers 8, with each finger 8 terminating as
an outwardly extending blade portion 9. The scraper elements 6 are
constructed such that adjacent fingers 8 of the scraper element 6
are of different lengths, as seen by reference to Figure 2.
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The scraper elements are of a size such that the blade
portions 9, at rest position, extend radially outwardly from the
shaft 2 a distance greater than the inner diameter of a tube to be
cleaned. Thus, the outwardly biased scraper elements 6 must be
slightly forced to a position closer to the shaft 2 in order to
insert the tube cleaner 1 into the tube to be cleaned. The outward
biasing of the scraper element f finger 6 then ensures contact of the
blade portions 9 with the inner surface of a tube during movement
of the tube cleaner through the tube.
Referring now to Figure 3, a scraper element 6 is
illustrated in flat form, as punched from spring steel, prior to
bending the fingers 8 and blade portions 9 into the desired shape.
The scraper element 6 illustrated has six fingers, a, b, c, d, a
and f. While the six fingers, as punched from spring steel, are of
the same length in flat condition, adjacent legs 8 are bent at
different points so as to provide different length of adjacent legs
8 upon completion of the formation of the scraper element. For
example, legs a and d are bent along line B, at a distance Ll from
the base portion 7, to provide long bent legs; legs b and a ale
bent along line B2, at a distance L2 from base portion 7, to
provide bent legs that are shorter than bent legs a and d; and legs
c and f are bent along line B3, at a distance L3 from base portion
7, to provide bent legs that are shorter than bent legs b and e.
Such an arrangement will result in a scraper element, after bending
to a desired shape (Figure 4) that will have adjacent fingers 8 of
the scraper element of different lengths, although a and d may be
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the same length, b and a may be the same length, and c and f may be
the same length. Although the bent legs 8 have different lengths,
the blade portions 9 are arranged such that they form a circle'
having a diameter ~ which is slightly larger than the inner
diameter of the tube that is to be cleaned with the scraper element
6. Thus, the distance from the shaft 2~to the outer arcuate edge
of the blade portion 9 is the same from all of the legs 6,
although the distance from adjacent blade portions 9 to the
outwardly extending base portion 7 will vary. The staggered -
lengths of the fingers 8 of the scraper element 6 of the present
invention is an important factor. If the fingers 8 were all of the
same length, the total force of insertion into a tube would be too
great to overcome by hand. With staggered finger lengths, however,
the force for entry is reduced by providing three stages of actual
insertion rather than a single stage for each scraper element 6.
As an example, the force required to insert conventional scrapers,
. such as those described in the Griffith patents referred to
hereinbefore, is about eleven (11) pounds of pushing force, while
with the scraper of the present invention, about forty-five (45)
pounds of ..force are required to -insert the tube scraper into an
open end of a tube, with scraper size and tube sizes being
comparable. Thus, the scraper of the present invention requires
about 4 to 5 times as much force to insert it into a tube as would
a comparable sized conventional scraper if the lengths are equal.
The staggered length enables the tube cleaner to be sized so as to
thus have more force perpendicular to the tube wall and still be
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loaded into the tube by hand. As an example, a tube cleaner 1
having scraper elements 8 has been prepared according to the
present invention where the lengths of the fingers, as measured
from the base 7 of the scraper elements 6 to the blade portions 9
of the scraper elements were as follows: fingers a and d = 0.670
inch, fingers b and a = 0.635 inch and fingers c and f - 0.600
inch, with the scraper elements 6 formed from SAE 1050 carbon
annealed spring steel, No. 2 finish, of a thickness of 0.030 inch.
The ability to form a scraper element from a single piece of metal,
rather than forming prior scraper blades from separate pieces that
had to be assembled, provides lower labor costs associated with
their formation and can also provide greater spring force than was
generated before.
The contact of a blade portion 9 of a scraper element 6
with the inner surface of a tube is shown in Figure 5. As
illustrated, a tube 11 has a wall 12 with thin, hard scale 13 on
the inner surface 14 of the wall 12. The blade portion 9 is of an
arcuate shape such that only minimal contact, by section 15 of the
blade portion 9 contacting the inner surface 14 of the wall 12,
with almost a point-to-point contact achieved, as the blade portion
scrapes through the thin hard scale 13, forming grooves 16.
Conventional scrapers generally are designed to maximize the
contact between a scraper blade edge and the inner surface of the
tube wall. To remove a thin, hard scale, however, such a design is
unusable. If the force required to fracture the scale were
generated at the same time as surface contact were maximized, the
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friction between the blade of the scraper and the tube wall would
be so great as to preclude fluidized pressure movement of a tube
cleaner through the tube. By minimizing the contact in the present
invention, a virtual point-to-point contact is provided, and a
significantly higher pressure can be applied by the scraper blade
9 to the tube wall 12 and the tube cleaner 1 can still be propelled
through the tube 11 by reasonable fluid pressures. It has been
found that the contact of a scraper blade with the inner tube wall
should be effected with a contact surface of between 0.003 - 0.009~~NCff
of the arc of the blade surface with the tube inner wall surface 13
so as to provide scraped grooves 16 in the thin, hard deposits.
The blade portion should also have a~ sharp edge such that a cutting
force is applied through the deposits.
The present tube cleaner, with the use of six fingers on
each scraper element will provide six spaced contact points on an
inner surface of a tube wall by each scraper element to remove
hard, thin scale and clean the tube wall to bare metal. With the
use of two or three, six-fingered scraper elements, that are
axially offset from each other, there will be twelve or eighteen
scraping grooves which, with removal of the hard, thin scale, will
greatly enhance the heat transfer of the tube. A tube 11 is shown
in Figure 6, after passage of a three scraper element tube cleaner
of the present invention with grooves 16 formed in the hard, thin
scale 13. By forming the grooves 16 through the deposits of hard,
thin scale 13, the heat transfer capability of the tube wall 12 is
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significantly increased to an extent such that complete removal of
the scale is not required.
As scale grows very slowly, subsequent cleanings result
in, over time, tubes that approach "as-new" condition after
multiple passes of the cleaner. .
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