Abstrict A Coriolis mass flow meter incorporates a measuring tube whose
wall is of fiber-reinforced polyether ether ketone (PEEK) and has
an internal coating of pure polyether ether ketone (PEEK). The measuring
tube is corrosion-resistant and has high pressure resistance. A
method of manufacturing the measuring tube is also described.
Claims 1. A Coriolis mass flow meter, having a measuring tube which may
be excited to oscillations, wherein the measuring tube comprises
fiber-reinforced polyether ether ketone having an internal coating
of pure polyether ether ketone.
2. The Coriolis mass flow meter according to claim 1 wherein the
fibers in the fiber-reinforced polyether ether ketone have at least
one predefined orientation.
3. The Coriolis mass flow meter according to claim 2 wherein said
fibers extend in the lengthwise direction of the measuring tube
and/or in a helix shape, preferably in a double helix shape.
4. The Coriolis mass flow meter according to any one of claims
1 through 3 wherein the fiber-reinforced polyether ether ketone
comprises graphite fiber-reinforced polyether ether ketone.
5. The Coriolis mass flow meter according to any one of claims
1 through 3 wherein the measuring tube has a wall made of said
fiber-reinforced polyether ether ketone and the internal surface
of the wall is completely covered with said internal coating made
of pure polyether ether ketone.
6. The Coriolis mass flow meter according to claim 5 wherein said
wall is wound from fiber-reinforced polyether ether ketone strips
and/or the internal coating is wound from pure polyether ether ketone
strips.
7. The Coriolis mass flow meter according to claim 5 wherein said
wall has a greater wall thickness at selected locations to be reinforced
than at other locations.
8. The Coriolis mass flow meter according to claim 5 wherein said
wall and said internal coating have a bond produced through tempering.
9. A method for manufacturing a measuring tube for a Coriolis mass
flow meter, said method comprising the steps of winding at least
one strip of pure polyether ether ketone on a mandrel and winding
at least one layer of fiber-reinforced polyether ether ketone around
said strip.
10. The method according to claim 9 wherein said at least one
layer is of graphite fiber-reinforced polyether ether ketone.
11. The method according to claim 9 or 10 wherein the fibers of
said fiber-reinforced polyether ether ketone are oriented in at
least one predefined direction.
12. The method according to claim 11 wherein said fibers are oriented
in the lengthwise direction of the measuring tube and/or in a helix
shape, preferably in a double helix shape.
13. The method according to claim 9 or 10 including the step of
providing additional reinforcement layers of fiber-reinforced polyether
ether ketone at selected locations on the measuring tube.
14. The method according to claim 9 or 10 including the step of
winding said at least one strip so that adjacent windings thereof
partially overlap one another.
15. The method according to claim 14 including the step of bonding
the winding overlaps through heating, preferably under elevated
pressure.
16. The method according to claim 9 or 10 including the step of
etching an outer surface of said strip wound on the mandrel, preferably
by chemically etching, before said layer is wound around the strip.
17. The method according to claim 9 or 10 including the step of
tempering the measuring tube.
18. The method according to claim 17 wherein the tempering is
performed at a temperature between 80.degree. C. and 120.degree.
C., preferably at 100.degree. C.
19. The method according to claim 18 wherein the tempering is
performed for a duration of 3 to 5 hours, preferably for 4 hours.
20. The method according to claim 18 wherein the tempering at
the temperature between 80.degree. C. and 120.degree. C. is followed
by further tempering at a lower temperature, between 50.degree.
C. and 80.degree. C. preferably at 60.degree. C.
21. The method according to claim 20 wherein the further tempering
at the lower temperature is performed for a duration of 3 to 5 hours,
preferably for 4 hours.
Description [0001] The present invention relates to a Coriolis mass flow meter,
having a measuring tube which may be excited to oscillations, and
a method for manufacturing a measuring tube for a Coriolis mass
flow meter.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Coriolis mass flow meters are well known from practice.
In this type of mass flow meter, at least one measuring tube is
excited to oscillations, so that Coriolis forces may be generated
in a medium flowing through the measuring tube. These Coriolis forces
and/or deflections of the measuring tube generated therefrom are
detected in order to be able to thus conclude the mass flow rate,
e.g., via the phase shift of the deflections of the measuring tube
at its inlet and/or outlet side. In this regard, a general reference
is made to "K. W. Bonfig, Technische Durchflu.beta.messung
[Technical Flow Rate Measurement], 3rd edition, 2002 Vulkan-Verlag
GmbH, pp. 215-226".
[0004] 2. Description of Prior Art
[0005] Measuring tubes for Coriolis mass flow meters are frequently
manufactured from metallic materials, such as stainless steel, titanium,
tantalum, etc. However, attempts to use non-metallic materials for
a measuring tube of a Coriolis mass flow meter are also known. According
to DE 41 19 396 C1 for example, the measuring tube of a Coriolis
mass flow meter comprises carbon obtained through pyrolysis of non-meltable
plastics. Furthermore, a Coriolis mass flow meter having a measuring
tube made of ceramic is known from DE 100 37 784 A1. Coriolis mass
flow meters having a measuring tube made of a non-metallic material
may be advantageous because, among other reasons, they are also
usable for flow rate measurement in the presence of chemically aggressive
media, i.e., they have a high corrosion resistance.
SUMMARY OF THE INVENTION
[0006] It is the object of the present invention to specify a Coriolis
mass flow meter of this type and a method of this type for manufacturing
a measuring tube of a Coriolis mass flow meter, by which a mass
flow rate measurement of chemically aggressive media is made possible,
with optimal adaptation of the parameters of the Coriolis mass flow
meter, such as temperature and pressure resistance, to the particular
application being made possible at the same time.
[0007] On the basis of the Coriolis mass flow meter described at
the outset, the object derived and described above is achieved in
that the measuring tube is of fiber-reinforced polyether ether ketone
and has an inner coating made of pure polyether ether ketone.
[0008] The present invention thus provides the combination of polyether
ether ketone, also known as PEEK, in fiber-reinforced form with
pure PEEK as the inner coating, "pure" in this context
meaning that the PEEK is provided as such, i.e., without fiber reinforcement.
The term "pure" is not meant in this case to indicate
a particular degree of purity so that no fiber reinforcements are
to be provided in the pure PEEK, but rather the addition of other
material is not excluded. According to a preferred embodiment of
the present invention, however, PEEK which is practically free of
additives is used as the "pure" PEEK, in order to ensure
high corrosion resistance of the inner coating.
[0009] In principle, a fiber material of a type which is added
to the PEEK without orientation may be used for the fiber-reinforced
PEEK. However, according to a preferred embodiment of the present
invention, the fibers provided for reinforcement in the PEEK should
have at least one predefined orientation. Furthermore, it is preferable
in this case for the fibers to run in the lengthwise direction of
the measuring tube and/or in a helix shape, preferably in a double
helix shape.
[0010] In principle, multiple fiber materials are usable for reinforcing
the polyether ether ketone. However, according to a preferred embodiment
of the present invention, graphite fiber-reinforced polyether ether
ketone is used.
[0011] In principle, it is possible to use fiber-reinforced polyether
ether ketone and/or pure polyether ether ketone only partially for
the measuring tube. However, according to a preferred embodiment
of the present invention, the wall of the measuring tube is made
of fiber-reinforced polyether ether ketone and the inner surface
of the wall is completely covered with an internal coating made
of pure polyether ether ketone. It is particularly preferred in
this case for the wall of the measuring tube to be wound from fiber-reinforced
polyether ether ketone strips or layers and/or the internal coating
to be wound from pure polyether ether ketone strips or layers.
[0012] Furthermore, according to a preferred embodiment of the
present invention, the wall of the measuring tube made of fiber-reinforced
polyether ether ketone may have a greater wall thickness at certain
locations to be reinforced than at other locations. In other words,
additional windings and/or layers of the fiber-reinforced polyether
ether ketone may be applied to those certain locations during the
manufacturing of the wall of the measuring tube.
[0013] The transition from the fiber-reinforced polyether ether
ketone to the inner coating made of pure polyether ether ketone
may be arbitrary in principle. However, according to a preferred
embodiment of the present invention, the wall made of fiber-reinforced
polyether ether ketone and the internal coating made of pure polyether
ether ketone have a bond produced through tempering.
[0014] On the basis of the method described at the beginning for
manufacturing a measuring tube for a Coriolis mass flow meter, the
object derived and described further above is achieved in that at
least one strip made of pure polyether ether ketone is wound on
a mandrel and at least one layer made of a fiber-reinforced polyether
either ketone is wound around the pure polyether ether ketone strip.
[0015] In this case, according to a preferred embodiment of the
present invention, as already noted above, that layer is of graphite
fiber-reinforced polyether ether ketone.
[0016] As also already noted above, in principle fiber-reinforced
polyether ether ketone of the type in which the fibers used for
reinforcement are randomly oriented is usable. However, according
to a preferred embodiment of the present invention, fiber-reinforced
polyether ether ketone whose fibers provided for reinforcement are
oriented in at least one predefined direction is used. According
to an especially preferred embodiment, the fiber-reinforced polyether
ether ketone is wound up in this case in such a way that the fibers
in the windings or turns run in the lengthwise direction of the
tube and/or in a helix shape, preferably in a double helix shape.
In this way, a measuring tube is obtained which is highly resistant
to pressure and has a moderate temperature expansion.
[0017] Furthermore, according to a preferred embodiment of the
present invention, selected points or locations on the measuring
tube to be reinforced may be provided with additional reinforcement
windings or layers made of fiber-reinforced polyether ether ketone.
These reinforced points or locations of the measuring tube may be
used, for example, to attach additional components to the measuring
tube and/or to fasten the measuring tube in an external pipeline
system.
[0018] Furthermore, according to a preferred embodiment of the
present invention, the windings or turns of the pure polyether ether
ketone which are next to one another may be wound so that they partially
overlap one another. In this case, the overlaps may also be bonded
to one another by heating, preferably under increased pressure.
[0019] In principle, it is not absolutely necessary to treat the
external surface of the pure polyether ether ketone strip wound
on the mandrel before the fiber-reinforced polyether ether ketone
layer or strip is wound around it. However, according to a preferred
embodiment of the present invention, the external surface of the
pure polyether ether ketone wound on the mandrel is etched before
the fiber-reinforced polyether ether ketone is wound around it,
preferably by chemical etching.
[0020] Furthermore, according to a preferred embodiment of the
present invention, the measuring tube having the pure polyether
ether ketone with the fiber-reinforced polyether ether ketone wound
around it is tempered, i.e., subjected to a heat treatment. In this
case, the tempering is preferably performed at a temperature between
80.degree. C. and 120.degree. C., preferably at approximately 100.degree.
C. This temperature treatment should be performed for a duration
of 3 to 5 hours, preferably for approximately 4 hours. A temperature
treatment of this type should be sufficient in principle. However,
according to a preferred embodiment of the invention, this treatment
is followed by a further tempering at a lower temperature, preferably
at a temperature between 50.degree. C. and 80.degree. C., most preferably
at a temperature of approximately 60.degree. C. This tempering at
the lower temperature is preferably performed for a duration of
3 to 5 hours, and most preferably for approximately 4 hours.
[0021] In principle, the shape of the measuring tube achieved through
the winding of strips or layers on a mandrel may be used as is for
a Coriolis mass flow meter. However, adaptations of the measuring
tube, particularly at the points reinforced through additional windings
of fiber-reinforced polyether ether ketone, may be derived by mechanically
processing the original measuring tube, e.g., through metal cutting
methods.
[0022] There are now manifold possibilities for specifically designing
and refining the Coriolis mass flow meter according to the present
invention and the method according to the present invention for
manufacturing a measuring tube for a Coriolis mass flow meter. For
this purpose, reference should be made to the dependent claims and
to the following detailed description of a preferred embodiment
of the present invention with reference to the accompanying drawings.
[0023] In the drawings:
[0024] FIG. 1 is a longitudinal sectional view of a Coriolis mass
flow meter according to a preferred embodiment of the present invention,
and
[0025] FIG. 2 is a cross-sectional view on a larger scale of the
measuring tube of the Coriolis mass flow meter shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] FIG. 1 shows a Coriolis mass flow meter according to a preferred
embodiment of the present invention, whose measuring tube 1 is manufactured
as described below.
[0027] A mandrel (not shown) having a diameter of 25.4 mm is wound
with a film strip made of pure PEEK having a thickness of 0.05 mm
with a lateral overlap of 5 mm on each side. The film strips are
then bonded to one another at their overlaps by heating them under
pressure. The external surface of the pure PEEK wound on the mandrel
is then chemically etched, using a chromic acid solution, in order
to improve the bonding with a layer made of fiber-reinforced PEEK
to be wound on the pure PEEK as will now be described.
[0028] After the just-described chemical etching of the external
surface of the pure PEEK wound on the mandrel, two layers of graphite-fiber-reinforced
PEEK having a thickness of 0.125 mm each are wound onto the pure
PEEK. For the graphite-fiber-reinforced PEEK, a material of a type
in which the graphite fibers are oriented in a predefined direction
is used. In this case, the two layers of the graphite fiber-reinforced
PEEK are wound in such a way that the orientation of the graphite
fibers corresponds to the lengthwise direction of the measuring
tube 1. Subsequently, two additional layers of graphite fiber-reinforced
PEEK having a thickness of 0.125 mm each are applied in such a way
that the orientations of the graphite fibers in relation to the
lengthwise direction of the measuring tube 1 are +82.5.degree. and
-82.5.degree., respectively. Therefore, the graphite fibers in additional
layers of the graphite fiber-reinforced PEEK extend substantially
in a double helix shape around the measuring tube 1. Depending upon
the orientation of the direction of the fibers provided for reinforcing
the PEEK, the dynamics, the thermal properties, and the pressure
resistance of the measuring tube 1 may be determined. Thus, the
wall 5 of the measuring tube 1 has a thickness of 0.5 mm, the internal
coating 6 has a thickness of 0.05 mm, so that tube 1 has an overall
wall thickness of 0.55 mm.
[0029] Further layers of graphite-fiber-reinforced PEEK may be
applied at predefined points or locations 2 on the measuring tube
1 to be reinforced, as is shown in FIG. 1. These reinforced points
or locations 2 are used for attaching other components of the Coriolis
mass flow meter, such as an internal cylinder 3 and/or for fastening
the measuring tube 1 in a housing 4 for the Coriolis mass flow meter.
As may also be seen from FIG. 1 these points or locations 2 to
be reinforced may be additionally mechanically processed or shaped
in order to achieve conically extending surfaces.
[0030] Subsequently, the measuring tube 1 is preferably tempered,
at 100.degree. C. for four hours and subsequently at a lower temperature
of 60.degree. C. for a further four hours.
[0031] Using this method, a measuring tube 1 for a Coriolis mass
flow meter having a length of 620 mm, an internal diameter of 25.4
mm, and an external diameter of approximately 26.4 mm is achieved.
The tube has a construction as is shown in FIG. 2 which figure
is a section through the measuring tube 1 outside a reinforced point
2. Through the tempering process, a bonding of both the internal
coating 6 to the wall 5 and of the individual layers made of fiber-reinforced
PEEK in the wall 5 itself has occurred. A test measurement using
water flowing through the measuring tube 1 finally results in a
natural frequency for the first mode of the measuring tube 1 at
approximately 192 Hz, so that the measuring tube manufactured in
this way is quite suitable for use in a Coriolis mass flow meter. |