CA2419500C

CA2419500C - Method and apparatus for analyzing separation between spaced surfaces using magnetic field intensity measurements

Info

Publication number: CA2419500C
Application number: CA002419500A
Authority: CA
Inventors: Stefan A. Lupke; Manfred A. A. Lupke
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-02-21
Filing date: 2003-02-21
Publication date: 2006-08-15
Anticipated expiration: 2023-02-21
Also published as: CN1262813C; CN2632628Y; CN1523321A; CA2419500A1

Abstract

A method of analyzing spacing between two separated surfaces which has particular applicability for use in centering of die tooling within a mold tunnel of a plastic pipe molding apparatus is achieved by setting up a magnetic force which spans both surfaces between the spacing and then measuring intensity of the magnetic force to indicate extensive separation between the surfaces.

Description

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 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.

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;

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.

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.

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 _ 7 _ 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 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.

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 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.

Claims

1. A method of determining positioning of correspondingly shaped first and second bodies of a plastic pipe molding apparatus where the first body comprises a circular member of die tooling and said second body comprises a circular mold outwardly around said circular member with a spacing between the bodies defining a pipe wall passage;
said method comprising setting up a plurality of magnetic forces at a plurality of different test sites, the magnetic forces at the different test sites spanning exterior surface regions of the first body and interior surface regions of the second body at different locations in the spacing between the bodies and providing a measure of the pipe wall passage at the different locations.

2. A method as claimed in Claim 1 including moving one of the bodies until the magnetic forces at the different test sites are in equilibrium with one another to provide a centered positioning of the circular member within the circular mold.

3. A method as claimed in Claim 2 comprising moving the circular member until the magnetic forces at the different test sites are in equilibrium with one another.

4. A method as claimed in Claim 2 comprising moving the circular mold until the magnetic forces at the different test sites are in equilibrium with one another to provide a centered positioning of the circular member within the circular mold.

5. A method as claimed in Claim 1 wherein the magnetic forces at each of the test sites is set up by locating a first measuring member at an interior surface region of the mold and by locating a second measuring member at the circular member, one of the first and second measuring members being a magnetic member which produces a magnetic field providing said magnetic force and the other one of the first and second measuring members being a metallic member which is influenced by the magnetic field produced by the magnetic member.

6. A method as claimed in Claim 5 including a load cell at each test site and wherein the second measuring member is a movable member which is moved by the magnetic field to place a load on the load cell which indicates extent of separation between the exterior surface of the circular member and the interior surface of the mold at each of the test sites.

7. A method as claimed in Claim 6 wherein the load cell is placed between the first and second measuring member and wherein the second measuring member is pulled at the load cell by the magnetic field to place the load on the load cell at each test site.

8. A method as claimed in Claim 6 wherein the second measuring member is placed between the load cell and the first measuring member and is drawn by the field at the first measuring member to pull and place the load on the load cell at each test site.

9. A method of analyzing a pipe wall of a plastic pipe while being formed in a pipe extrusion molding apparatus having die tooling spaced from a surrounding mold tunnel by a pipe wall passage, said method comprising setting up 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, measuring intensity of each magnetic force to produce a passage width measurement at each test site and comparing the passage with measurements of the different test sites to determine consistency of wall thickness around the pipe wall.