Note: Descriptions are shown in the official language in which they were submitted.
8S313
This invention relates to travelling mold tunnels
for the molding of rigid and semi-rigid plastics material
profiled tube. The tube may be, for example, corrugated
or ribbed tube. The invention also relates to mold blocks
for use in such travelling mold tunnels and to liners for
such mold blocks.
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Mold blocks utilizable in travelling mold tunnels
are often located in two endless loops of mold blocks
which bring co-operating pairs of mold blocks together on
forward runs of each loop to form the mold tunnel.
However single loops of mold blocks which are closed to
form a tunnel on one run and open on a related run are
also possible. Inner surfaces of the mold blocks are
machined or otherwise provided with mold surfaces to form
the tube.
In practice, a parison of molded thermoplastics
material is introduced to the mold tunnel to be molded
against the mold surface. The formed tube cools and sets
as the tunnel moves along the forward runs of the loops of
mold blocks. When the tube is formed and self supporting,
the mold blocks move away towards a return run thus ending
the tunnel and releasing the tube. The inner surface of
the tube may be formed by an inner forming plug which is
usually a cooling plug. Whien the tube is corrugated tube,
the single or outer corrugated tube may be forced against
a corrugated mold and any inner wall may be formed on this
plug .
It is not necessary that the mold blocks be
brought together to form the tunnel by means of the
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endless loops of mold blocks. Other means of forming the
tunnel are possible as, for e~ample, described in PCT
Patent Application No. Ca 90/00372 to the same inventor.
The mold blocks themselve~ are bulky and
expensive in both materials and in the labour necessary in
machining their mold faces. Each set of mold blocks may
be utilized for only one specific profile of tube even if
the general diameter of the tube is similar.
This problem is well recognized and attempts have
been made to reduce the very high investment necessary for
providing the various sets of mold blocks for a
corresponding variety of tube profiles. One such attempt
has involved the provision of a set of mold block carriers
which may be used with different sets of mold blocks.
This solution has somewhat alleviated the problem
since the mold blocks themselves may be of relatively
simple construction as regards their external fittings.
It is, however, up to this time necessary to have a
separate set of sturdy mold blocks for each tube profile.
Not only is the expense of such sets of mold
blocks appreciable but their maintenance is also
considerable. In operation, the movements of the mold
blocks and their opening and closing to form the mold
tunnel subjects them to considerable general wear and to
breakage.
Breakage is especially prone at points in travel
o the mold blocks where they may knock against other
eguipment such as the die, the cooling plug or even each
other~ As the mold blocks turn into their forward runs to
form the tunnel they are prone to hîtting each other or
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203853~3
other apparatus parts. Repair or replacement of worn or
broken mold blocks is costly.
The problem is possibly emphasized in the
production of ribbed tube. The process for the production
of such tube is much more akin to injection molding than
the blow molding technique which may be used in the
production of corrugated tube and is, therefore, subject
to the greater pressures and equipment stresses which are
present in injection molding.
The above-mentioned problems have now been
addressed by the present inventor, who has addressed the
specific problem of providing a mold block which is
capable of adaptation for forming different tube profiles.
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According to the invention there is provided a
travelling mold tunnel for continuously molding profiled
tube surface, e.g. an annularly or helically ribbed outer
surface or corrugated tube, and comprising mold blocks
having interchangable mold liners acting together to form ;
the mold tunnel, each mold block comprising a mold block
base and a removable mold liner, the mold block base
having an inner surface forming a seat for the mold liner; ~ -
and the mold liner being removably seated through an outer
surface conforming in shape to the seat of the mold block
base, and having an inner surface configured to form at
least part of a mold surface for tube. The travelling
mold tunnel may be of the type in which the mold blocks
are arranged in one or two endlesæ loops coming together
to form a tunnel in a forward run of each loop. It may,
however, be of other types.
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The present invention may be useful in the
production of ribbed tube having circumferentially
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extending upstanding ribs spaced generally smooth surface
bands. "Generally smooth surface" is intended to mean
generally smooth in comparison with the upstanding ribs.
Thus a generally smooth surface may be a surface which
includes various surface m~rkings such as annular or
helical ridges or grooves, the height or depth of which is
not great as compared with that of the upstanding ribs.
Each mold block base may be provided with mold grooves
configured to mold the ribs and each mold block liner may
have a mold surface configured to mold at least one of the
bands, the mold block liner being seated on a respective
mold block and located to mold said one of the bands. The
liner may be removably atached to the mold block so that
it may be replaceable by a different liner, e.g. one
having a different thickness to produce tube of different
diameter.
Alternatively or additionally, each mold block
base may be provided with mold grooves configured to mold
rib side walls but having a depth greater than necessary
for molding the tips of ribs of a desired height, and each
mold block liner may comprise a rib tip forming an insert
for the rib forming grooves. The inserts may be
replaceable by different inserts for molding ribs of
grater or lesser height or of different profile to mold
ribs of different profile.
It is possible to provide a single mold block
liner which seats in seating grooves of the mold block
base. The seating grooves generally correspond to desired
locations for the provision of ribs in resulting molded
tubes. The liner has surfaces configured to mold the
bands and has mold grooves extending into each seating
groove configured to mold a rib.
203~3538
It may be possible by way of mold block linPrs to
provide tube of varying diameter and varying rib height or
profile. Thus, if one rib tip forming liner is used in
one groove of a mold block a rib tip forming liner of
greater or lesser depth may be used in another groove to
produce a different height of rib. Similarly, different
band diameters may be obtained by different band liners.
If the tube to be molded is corrugated tube,
through the use of suitably profiled liners, it is
possible to change the inner or outer diameter of the
tube. Thus mold block liners may rest in the inner
corrugations of a mold block to define the depth of the
resulting corrugation.
The liner may be formed ~rom various materials -
such as stainless steel, steel, aluminum, brass, bronze,
etc.
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The invention includes the lined mold blocks and
the liners themselves.
Embodiments of the invention will now be
described by way of e~ample with reference to the
drawings, in which:
Figure 1 is a longitudinal cross-section of
a mold block for the production of ribbed tube in a
travelling mold tunnel and having liners according to ~;
the present invention; and
Figure 2 is a similar section of another
mold block for ribbed tube having another embodiment
of a liner according to the invention;
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Figure 3 is a longitudinal cross-section of
mold blocks in a travelling mold tunnel for molding
corrugated tube, having liners according to the
present invention.
Referring first to Figure 1, mold block 10 are part of
a travelling mold tunnel 12. Each mold block 10 is
configured for molding ribbed tube 14 having ribs 16 and
bands 18 between the ribs 16.
Each mold block 10 comprises a mold block bsse 22
and rmovable, interchangable, band liners 24 and rib tip
liners 26. It will be appreciated that the band ljners 24
may be used without the rib tip liners 28 or vice versa.
The mold block base 22 corresponds roughly in
shape to a conventional mold block but it will have
sufficient diameter to accomodate band liners 24a, 24b of
different thickness. Grooves 30 wh;ch in a conventional
mold block would be configured to exactly mold tube ribs
16, are deeper than would be necessary for that purpose.
The increased depth is to act as a seating for rib tip
liners 26a, 28b which, as shown, line the grooves 30 at
the e~treme tip and have different depths according to the
height of the required ribs. The rib tip liners 26 may
have walls merging into the tip to partially, or even
wholly, line the depth of the grooves 30.
As illustrated, a single mold block base 22 is
provided along its length with band liners 24a, 24b of
different thicknesses and rib tip liners 26a, 28b of
different depths. While such longitudinal variation is
possible, it is more likely that for any one tube, the
bands and ribs will be of constant thickness and height.
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Fixing means may be separately provided for each rib tip
liner 26a, 26b but, within the depth of groove 30,
provision of specific attachment might be labour intensive
and provide problems in roughness at the rib tip. It is :
considered that a friction fit of rib tip liner 26 into
groove 30 is normally satisfactory.
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If it is desired to provide a tube with the same
general diameter but with a different configuration of
rib, the rib tip liners may be replaced by a set of liners
having the configuration to mold the desired rib shape~
Except for tube of very different diameter, it may not be
necessary to utilize a completely different set of mold
blocks 11 - only the liners need be changed.
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Somewhat similar considerations apply to the band
liners 24. Band liners 24 may be provided in different
thicknesses so that some adjustment of tube diameter
without the use of different mold bases 22 is possible.
The diameter of tube may be adjusted by band liners 24.
Band liners 22 seat against those portions of the mold
base 22 between rib forming grooves 30. However, unless
further grooves and complementary tongues are provided in
the respective mold bases 22 and outer surfaces of band
liners 24, a friction fit of the band liners 24 is not as
suitable as for the rib tip liners 26. Conveniently, band
liners 24 are attached to the mold bases 22 by screws 32.
When both rib tip liners 26 and band liners 24
are used, these may be integrally connected by a thin skin
lining the walls of rib forming groove 30.
It is, quite possible that liners for paired mold
blocks which cooperate one with the other to enclose a
tube section may vary in thickness or depth. Thus, if it
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is desired to form tube which will bend more easily in one
direc~ion, the rib height and/or band thickness may be
adjusted circumferentially so that the tube is thinner or
has shallower ribs on the side when greater flexion is
required.
When worn or chipped or otherwise broken, the
liners may be removed and replaced. They may also be
replaced by different configurations.
Figure 2 shows a slightly different embodiment
utilizing the concept of rib tip liners connected to or
separate from band liners. Reference numbers which are
also used in Figure 1 are used to denote similar parts.
As illustrated, the integrated liner 40 cover the whole of
the mold base seating surface 41. The integration of the
mold liners may be achieved by formina the liner in one
piece or by flush surfaces 43 between rib lip liners and
band liners. The mold base may be machined with seating
grooves 42. These seating grooves 42 are not intended to
carry out a molding function and need not be machined for
this purpose. The ease of construction may be somewhat
simplified iince the sealing grooves 42 ma~ be wider and
not so steeply contoured as those required for molding
ribs.
The integrated liner 40 has an outer surface
complementary to the seating surface 41 of the mold base
22, and an inner æurface accurately machined to provide
the required tube profile. The integrated liner 40 may
have sufficient structure to be self-supporting and
thickened walls 44 of the rib forming grooves 30 may
provide strength advantage. While such an integrated
liner 40 may be attachable to mold base 22 utilizing
screws i2 similar to those shown in Figure 1, such
attachment may not be necessary since it may be possible
to achieve a secure snap fitting of liner 40 into mold
base 22.
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A possible advantage of the arrangement of the
inventor, especially that of Figure 2, is that the mold
bases may be made of less e~pensive material then has been
possible for use as mold blocks in the past. The reason
for this is that the whole of the mold surface is provided
in liner 40 and thus it is only liner 40 which must be
made of a material suitable for providing such a mold face.
Figures 3 illustrates a mold base 22 for
producing corrugated tube. Where possible similar
reference numerals have been used to denote similar
parts. The mold bases 22 have liners 40a, 40b.
A further feature of the invention as applied to
corrugated tube molding, is that the inner diameter of the
tube may be varied in addition to the outer diameter.
Thus, the liners 40a, 40b which nest in the inwardly
projecting corrugations of mold bases 10, define the inner
diameter of corrugated tube 15. The liners 40a, 40b are
deeper than liners 40a, and the mold base 22 is shown
bro~en between liners 40a,40b in order to illustrate how
tubes 41a and 41b of different diameters may be molded.
It is, of course, possible to use separate liners for
altering only the mold troughs or ridges. Again screws
32 are illustrated to hold the mold liners 25 but a snap
fit may also be possible. In the case of a snap fit, the
corrugations of the mold blocks will hold the liners
securely during their tunnel turn.
Again, it should be noted that the variations
illustrated will not normally all be expected in a single
tube but are capable of being implemented alone or in
combination.
Other advantages and modifications will be
apparent to a man skilled in the art and are regarded as
within the scope of the appended claims.
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