Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR ANALYZING SEPARATION BETNIEEN
SPACED SURFACES USING MAGNETIC FIELD MEASUREMENTS
FIELD OF THE INVENTION
The present invention provides a method of
measuring separation between two surfaces and is
particularly applicable to measuring width of a pipe wall
passage internally of a plastic pipe extrusion mold
apparatus to determine consistency of wall thickness
around a pipe while the pipe is being formed in the
apparatus.
BACKGROUND OF THE INVENTION
It can be very difficult to measure the separation
or spacing between two surfaces when access is blocked to
either one of the surfaces. For example, it is difficult
to measure the separation between the exterior surface of
a first body and the interior surface of a second body
where the second body completely surrounds and blocks
access to the first body.
By way of example, a plastic pipe extrusion
molding apparatus includes internal die tooling separated
from a surrounding moving mold tunnel by a spacing that
forms a pipe wall passage. The moving mold tunnel which
is substantially longer than the die tooling blocks easy
access for taking a measurement of the spacing between
the die tooling and the mold tunnel around the pipe wall
passage. Such a measurement if it could be taken is
extremely beneficial for determining alignment of the die
tooling within the mold tunnel. This alignment sets
thickness around a pipe wall of a plastic pipe formed
within the apparatus.
In view of the difficulties encountered in taking
an internal measurement of a plastic pipe extrusion
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molding apparatus, consistency of wall thickness around a
pipe wall is presently determined by cutting the pipe
after it has been released from the mold tunnel to take
actual measurements of pipe wall thickness around the
pipe wall. If the measurements taken shows that the
consistency of wall thickness around the pipe wall is not
acceptable then adjustments are made to better center the
die tooling within the mold tunnel with the results of
these adjustments again being determined by cutting and
measuring the pipe wall. This is a very time consuming
and therefore costly testing method.
SUN~IARY OF THE PRESENT INVENTION
The present invention provides a method of
assessing or analyzing spacing between two separated
surfaces and is particularly applicable to a method of
assessing consistency of wall thickness around a pipe
wall formed in a plastic pipe extrusion molding apparatus
without having to physically cut through the pipe wall.
On a very broad basis, the method of assessing
spacing between two separated surfaces according to the
present invention comprises setting up a magnetic force
which spans the two surfaces and then measuring intensity
of the magnetic force which indicates extent of
separation between the surfaces.
According to an aspect of the present invention
the method is used for analyzing a pipe wall of a plastic
pipe while the pipe is being formed in a pipe extrusion
molding apparatus having die tooling spaced from a
surrounding mold tunnel by a pipe wall passage. The
method comprises establishing a plurality of magnetic
forces between exterior surface regions of the die
tooling and interior surface regions of the mold tunnel
at different test sites around the pipe wall passage.
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Measurements are then taken to determine intensity of
each of the magnetic forces to produce a passage width
measurement at each test site. The passage width
measurements for the different test sites are then
compared with one another to determine consistency of
wall thickness around the pipe wall.
If it is desirable to produce a pipe with uniform
thickness around the pipe wall adjustments are made to
the apparatus until the passage width measurements are
the same at all of the different test sites.
It is also possible to analyze positioning of the
die within the mold tunnel when the apparatus is not in
use. In this case tests are made around the plastic flow
passage when it is empty i.e., when there is no pipe
being formed. However the analysis will still provide an
indicator as to whether or not any pipe formed in the
apparatus will have consistent wall thickness.
BRIEF DESCRIPTION OF THE DRAWINGS
The above as well as other advantages and features
of the present invention will be described in greater
detail according to the preferred embodiments of the
present invention in which;
Figure 1 is a perspective view of a plastic pipe
extrusion molding apparatus incorporating pipe wall
passage width measuring means according to a preferred
embodiment of the present invention;
Figure 2 is a sectional view through the apparatus
of Figure 1;
Figure 3 is an enlarged sectional view through the
molding region of the apparatus of Figure 1;
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Figure 4 shows an individual measuring site for
measuring separation between the die tooling and the mold
tunnel walls of the apparatus of Figure 1 to provide an
assessment of wall thickness of a pipe wall formed at the
test site;
Figure 5 is a perspective view of a component of
the measuring site from Figure 4;
Figure 6 is a side view of the measuring component
shown in Figure 5;
Figure 7 is a side view of a measuring site
according to further preferred embodiment of the present
invention;
Figure 8 is an enlargement of the measuring site
shown in Figure 7;
Figure 9 is a sectional view through the mold
tunnel of Figure 3 incorporating a plurality of test
sites and with the die tooling out of alignments with the
mold tunnel;
Figure 10 is a view similar to Figure 9 after
adjustments made to the apparatus using the test sites to
align the die tooling with the mold tunnel through use of
the different test sites.
DETAILED DESCRIPTION ACCORDING TO THE PREFERRED
EMBODIMENTS OF THE PRESENT INVENTION IN WHICH:
Figure 1 shows a plastic pipe extrusion molding
apparatus generall~~ indicated at 1. This apparatus is
fitted with a plastic extruder 3 which feeds into a mold
tunnel generally indicated at 5. The mold tunnel is the
region in which the plastic pipe is shaped or molded.
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Figures 2 and 3 show die tooling generally
indicated at 15 which is used to carry plastic from
extruder 3 into the mold tunnel 5. The mold tunnel
itself is formed by moving mold blocks 19 which outwardly
surround die tooling 15. The die tooling is separated
from the mold blocks by a spacing 27 which during
production of a pipe in the apparatus forms a pipe wall
passage.
As seen in Figure 3 of the drawings the spacing 27
is not consistent around die tooling 15. Accordingly the
die tooling is not properly aligned i.e., centered within
the mold tunnel formed by the surrounding mold blocks.
The downstream end of the die tooling 15 includes
what is known in the industry as a cooling plug 17. The
plastic from extruder 3 runs over the external surface of
die tooling 15 against the internal surface of the mold
blocks 19 and is cooled by cooling plug 17 during the
extrusion process.
Cooling plug 17 is fitted with a plurality of
measuring devices used to assess the spacing between the
die tooling and the internal surface of the mold tunnel.
The measurements taken from these devices such as device
31 shown in Figure 4 of the drawings can be carried out
either when the apparatus is not in use i.e., when there
is no plastic material i.n passage 2,7 or when th.e
apparatus is in use and plastic is flowing through gap
27. In the latter situation, the measuring devices are
used to not only measure alignment of the die tooling in
the mold tunnel but to additionally assess wall thickness
of a pipe while the pipe is being formed within the
apparatus.
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Referring in more detail to Figures 4 through 6 of
the drawings it will be seen that each of the mold blocks
19 has a profiled inner face generally indicated at 21.
This face comprises a series of crests 25 separated by
troughs 23 on the mold block face. The separation
between the crests 25 and the die tooling determines the
wall thickness of a pipe wall formed between the die
tooling and the mold block faces.
Although Figure 4 shows the apparatus being set up
to manufacture a profiled wall pipe i.e., a ribbed or a
double wall corrugated pipe, the apparatus could equally
as well be set up to form a single flat wall pipe where
each of the mold blocks has a flat rather than a profiled
face.
It should be noted that cooling plug 17 which has
a circular configuration is centered on the circular die
tooling 15 which is located within the circular mold
tunnel formed by mold blocks 19. As such, the cooling
plug is subject to the same potential misalignment
conditions within the mold tunnel as the upstream part of
the die tooling and can be used as a mounting location
for test devices used to measure the alignment of the die
tooling within the mold tunnel.
Figures 4 through 6 of the drawings show an
individual test device generally indicated at 31 set up
at a specific test site on the end of cooling plug 17.
Test device 31 comprises a mounting bracket 33 which
supports a magnet 35 and a load cell 37. Magnet 35
produces a magnetic field which spans the gap or spacing
27 between the cooling plug and the interior surface of
the mold formed by mold blocks 19. These mold blocks and
specifically the crests 25 of the mold block are fitted
with metallic inserts such as the inserts shown in Figure
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8 of the drawings to be described later in detail. As
such the magnetic field produced by magnet 35 causes an
attraction between the magnetic and the metallic
relatively immovable inserts in the mold block faces.
Magnet 35 is however allowed a small amount of movement
which due to the attraction between the magnet and the
mold block faces causes the magnet to move against and
place a load on load cell 37. The load that the magnetic
does place on the load cell is directly dependent upon
the intensity of the magnetic field spanning gap or
spacing 27. Therefore is that gap widens the load on the
load cell decreases and as that gap narrows the load on
the load cell increases.
Figures 9 and 10 of the drawings show that a
plurality of testing devices 31 are set up at different
test cites around the pipe wall passage within the mold
apparatus. Each one of these test sites includes its own
magnetic field and the results of the measurement tests
for the different sites are fed from the individual sites
through wires 39 to a common center where the
measurements are all compared to one another. If the
field strength or intensity of one of the test sites is
greater than that of another of the test sites then there
is less gap between the die tooling and the mold tunnel
at the higher strength test site. This provides clear
indication that the die tooling is not centered within
the mold tunnel and that the pipe wall will not be of
uniform thickness around the pipe.
In Figure 9 it will be seen that the die tooling
is clearly off center relative to the mold tunnel formed
by the mold blocks, whereas in Figure 10 adjustments have
been made to center the die tooling relative to the mold
tunnel. As such the gap between the die tooling and the
mold blocks is uniform around. the gap in Figure 10. In
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order to produce the Figure 10 set up the adjustments are
made until the magnetic forces at each of the test sites
are in equilibrium witrn one another. After the
adjustments have been made to the Figure 10 position the
pipe wall formed in the wall passage is of consistent or
uniform thickness around the pipe wall.
As noted above, the measurements can be taken
either when there is no plastic running through the mold
tunnel or during formation of the pipe wall. If the
measurements are taken while the apparatus is in
operation the magnetic force at each test site penetrates
the pipe wall and the adjustments are made while the
apparatus is running.
Returning to Figure 1 of the drawings, it will be
seen that the main body of the apparatus which is
independent of the die tooling is mounted on adjustment
posts 9 which allow vertical adjustment of the apparatus
including the mold tunnel component relative to the die
tooling. In addition, the base 7 of the apparatus is
adjustable on bottom support members (not shown) to allow
adjustment of the apparatus in the direction of arrow 11
enabling full adjustment of the apparatus for the
centering of the apparatus relative to the die tooling.
It is also possible to adjust the die tooling
itself for the centering of the die tooling relative to
the mold tunnel.
In the description above, the magnet at each test
site is positioned on the cooling plug and the load cell
is placed between the magnet and the metallic insert of
the mold block faces. Figures 7 and 8 of the drawings
show a somewhat modified arrangement.
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More specifically, as seen in Figures 7 and 8 a
test site 51 for_ measuring a magnetic force comprises a
bracket 53 mounted on cooling plug 10. This bracket
supports a load cell 59 and a magnet 57. Note that
magnet 57 is located between the load cell and the gap to
be measured reversed to the earlier embodiment where the
load cell is positioned between the magnet and the gap to
be measured.
Figure 8 of the drawings shows that mold block 19
is fitted with inserts 61 in the crests of the mold
block. Figure 8 also shows the formation of a double
wall corrugated pipe filling the wall passage 27 between
the mold wall and the die tooling.
In this particular set up magnet 57 while being
drawn by the magnetic force or field at mold block
inserts 61 pulls rather than pushes on load cell 59.
Consistent with the earlier embodiment the load to which
the load cell is subjected by the magnetic force or pull
on magnet 57 provides a measurement indicative or
representative of the spacing between the die tooling and
the mold wall.
It should additionally be noted that further
changes to the set up can be made. For example, inserts
61 which are held by slide interlocks at the crests of
the mold blocks can be replaced with different inserts
such as for example, larger metallic inserts which would
be more strongly influenced by the magnetic force. As a
further alternative inserts 61 could themselves be
magnets and depending upon the polarity of the system
could be used to either attract or repel the magnets at
the different test devices. When using both a magnet at
the mold block face and the test device and with the two
magnets having common poles facing one another the load
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would be applied by pushing the magnet onto the load cell
in the Figure 8 set up. If the Figure 8 set up were
varied to place magnet 59 between inserts 61 and magnet
57 and if insert 61 were themselves magnets repelling
magnet 57 then magnet 57 would pull to place the load on
the load cell.
As a further alternative the inserts 61 in the
mold face can be the magnets while the test site is
fitted with nothing more than metallic inserts subjected
to the magnetic force produced by the inserts.
In the description above the testing devices have
been attached to the cooling plug. It is to be
understood they could also be positioned elsewhere on the
die tooling to take measurements. Furthermore, the
measurements taken do rot have to produce an actual
distance at each site for purposes of centering the die
tooling. Only comparative valves are required it the
different test sites to provide the centering of the die
tooling.
Although various preferred embodiments of the
present invention have been described in detail, it will
be appreciated by those skilled in the art that
variations may be made without departing from the spirit
of the invention or the scope of the appended claims.
