Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR EXTRUDING AN EDGING SECTION ONTO A WORK PIECE
AND THE PRODUCTS PRODUCED TEIEREBY
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The invention relates to a method for -the manufacture
of a work piece having an extruded plastic edging section
running along one or more of its edges, to a work piece
manufactured by said method, and to a heat exchanger in
particular.
The bonding, for instance with an adhesive, of a
separate ex-truded section of thermoplastic resin onto -the
edge of a body like a sheet of pressboard or plastic having
a cross-section that is uniform along i-ts edge is generally
known. The adhesive is usually applied by hand. The
separa~ely manufac-tured edging section is also usually cut
into lengths and applied by hand.
There are in many cases disadvantages to the use
of adhesives because solvents can seep into the plastic
edging section and, if the edging section is to be applied
to a plastic body, into -the la-t-ter as well, which can cause
stress corrosion. The strength of adhesive seams also often
leaves much to be desired.
The present inven-tion provides a method oE
~0 manufac-turing work pieces having attached eclgin~ sec-tions,
or example plastic heat exchangers, and especially a
method that avoids steps in -the operation -tha-t mus-t be
carried out by hand. This method also permi-ts -the formation
of a strong bond between the work piece and -the edging section
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without the use of an adhesive. Such method comprises
applyi.ng a molten strip of thermoplastic resin, having the
cross-section of the edg:ing section to be produced, to
the edge region of the work piece by inserting the edge
regi.on of the work piece into a suitab~.e forming die.
The forming die has a molding channel for receiving the
edge region and sealing edge portions adjacent the channel
in contact with the edge region at a selected distance
from the edge of the work piece. The strip of -thermoplastic
resin is supplied to the channel. Relative movement between
the forming die and the edge region of the work piece is
arranged to occur at the rate at which the molten thermoplas-tic
resin emerges from the forming die to form the edging section.
If the work piece is made of a thermoplastic
resin, it is suitable for the edging section to be made of
the same or of a similar plastic. The plastics can be
considered similar if the edging section, while in a
thermoplastic state, can be welded to the edge of the body
to form a single piece and if the resulting bond is
permanent.
A core rod may be positioned in the molding
channel of the die parallel -to -the exit dixection o~ the
edging section thereby to produce a cavi-ty running through
the edging section.
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The invention further comprises a work piece having
an extruded edging section, manufacturecl by the process
according to the invention. Such work piece may comprise
a plastic heat exchanger including a plastic body in -the
form of a panel having two parallel, flat ou-ter walls. A
number of webs extending between the walls and connecting
the walls to define a plurality of parallel flowthrough
channels. A pair of plastic collector elements coopera-te
to define a conduit in the edge section. This conduit is
connected to the body of the heat exchanger in communication
with the flowthrough channels.
A better understanding of the present invention
and of its many advantages will be had by referring to the
accompanying drawings, in which
Fig. 1 is a perspective view of a planar work
piece having an edging section along an edge thereof;
Fig. lA is a side view, in section, through an
extrusion die employed to produce the edging section showing
a work piece inserted into the die;
Fig. 2 is a similar side view, in section, of an
extrusion die suited for the production of an edging section
having a cavity running through it;
E'ig. 3 is a plan vi~w, in s~c-tion a:long line 3-3
of E'ig. 2 of the apparatus shown in Fig. 2;
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Fig. 4 is an exploded side view, in section,
of a heat exchanger according to the present invention,
said exchanger comprising a body containing flow-through
channels and collector conduits in communication therewi-th;
Fig. ~A is a side view, in section, of the same
heat exchanger after assembly and attachment thereto of
an edging section;
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Fig. 5 is an exploded slde view, in section, of a
further embodiment of a heat exchanger according to the
present invention again comprising a body having flowthrough
channels and collector conduits in communication therewith;
Fig. 5A is a side view of the heat exchanger of
Fig. 5 after assembly and at~achment thereto of an edging
section; and
Fig. 6 is a plan view, in section, of part of the
heat exchanger shown in Fig. ~.
Referring in particular to Fig. 1 of the drawings,
work piece or panel 11 that is to be provided in accordance
with the invention with edging section 12 running along an
edge thereof may consist of any desired solid material that is
dimensionally stable under the conditions under which the
edging section :is extruded. Suitable materials are such metals
as aluminum, iron, or copper, plastics like polymethyl
methacrylate, polycarbonate, polyvinyl chloride, polystyrene,
polyolefin9,phell01ic resins or aminoplast resins, materials
like wood, chipboard, cardboard, laminates, and even foam if
its resistance to pressure and heat is h:Lgh enough. The work
piece may be composed of several diferent materials or parts
which may, indeed, first be firmly fastened together only
after the edging section is applied.
It is assumed in any case that the work piece will
have a uniform cross-section longitudinally along the edge to
which the edging section is to be bonded. Rough places or
small irregularities in the edge region to be covered by the
edging section are not significant so long as the surface of the
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work piece immediately adjacent to the edging section is
uniform. The most desirable type of work piece is a plate
or sheet with plane parallel surfaces and at least one
straight edge.
The worlc piece may contai.n one or more cavities
therein. Its outer walls must be sufficiently resistant to
temperature and pressure not to be damaged by the hot molding
material ~mder pressure.
The 'ledge region" of the work piece in the sense of
the present invention is one of its outer, bounding edges
together with the adjacent surface areas; in plate-type pieces
these are the top and bottom surface areas. The extent of an
edge region that is to be provided with an edging section can
differ from case to case, from a few millimeters to several
centimeters for example. As a rule, the edging section will
cover the edge and the adjacent top and bottom edge regions to
about 5 mm to S0 mm from the edge. In the extreme case, the
area covered by the edging section may be larger than the area
left uncovered on the work piece. As the eclging section is
being manufactured, the edge re.gion to be covered will be
bounded by the seali.ng lips of the forming tool or die, which
lips will be in contact with the edge region at a distance from
the outside edge.
An extrudable molding material, such as polymethyl
methacrylate, polystyrene, polycarbonate, polyvinyl chloride,
or polyolefins,is appropriate for manufacture of the edging
section. These materials may be dyed or pigmented in the
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usual way. If the edgin~ section is to serve as a sealing
strip, soft-elastic plastics such as soft polyvinyl chloride
or high-pressure polyethylene are preferred.
Referring now to Fig. lA, the figure shows forming
tool or die 13 according to the invention. Its design
resembles that of known tools for sheathing cable or the like
with an extruded plastic layer. But whereas the cross-section
of the molding channel in a sheathing tool is a closed curve,
molding channel 14 of the present invention is shaped like a
horseshoe, with edge region 15 of work piece 11 to be provided
with edging section 12 extending into channel 14 at the open
side thereof. Die 13 comprises two jaws 16, 17 joined at the
base to enclose laterally open intake channel 18 in communication
in the direction o~ extrusion with molding channel 14, also
laterally open. Jaws 16, 17 close securely over the surface
of the body piece and terminate in sealing lips 19, 20 in the
vicinity of molding channel 14. Sealing lips 19, 20 are
separated by a distance equal to the thickness oE edge re~ion 15
of work piece 11 and are in close contact with said region
~hen the machine is in operation. Inside the cross-section
bounded by the lips, molding channel 14 is separated from the
inserted edge region 15 of work piece 11 by a distance equal
to the thickness of edging section 12.
Edging section 12 can be of many different shapes.
It may completely enclose edge region 15 or be limited to
edge 21 or to one or more areas inside the adjacent edge region.
* A d ~t _ ct of the sealin~ lips with the b~dy piece is not
necessary. Rather, if there is a ~ap between the lips and the
surface of the body piece or the ~aid surface is not quite uniform
in cross section the sealin~ lips should close only ti~htly enough
to prevent considerable leaka~e of liquidlr,oldin~ ~aterial.
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It may also consis-t of several separate strips. Its thickness
may be uni~orm or be different at different locations along i~s
length, ranging, for example, from 0.5 Tnm to 10 mm.
As is more particularly shown in Figs. 2 and 3, an
edging section having one or more cavities therein can be
produced using a die 13 provided with at least one core rod 23.
Rod 23 may be in contact with edge 21 of work piece 11, as
shown in Figs. 2 and 3, or may be completely surrounded by
molding material 24. In practice, a core rod mounted in a
fixed position in the tool can cause problems. These can be
avoided by positioning a freely moving rod against the edge
o a work piece, ~eeding the rod into the tool together with
the edge region of the work piece, and removing the rod after
the edging section is formed.
In carrying out the method according to the present
invention, edge region 15 of work piece 11 is introduced into
work piece feed channel 25 and is transported toward molding
channel 14. As the work piece enters the molding channel,
edging section 12 is applied. I'he feed rate oE work pi~ce 11
is adjusted to the rate at which edging section 12 can be
applied. The production rate can be controlled ln a known way
by means of the output of the extruder (not shown in the
drawings), with thermoplastic molding material 24 being supplied
from the extruder through intake channel 18 into molding
channel 14.
As a rule, an îT~movably mounted tool or die connected
to an immovably mounted extruder is employed. The edge region
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of the work piece in such a case is conveyed in an appropriate
feed direction into the Eeed channel and hence into the molding
channel. In continuous operation it is practical to convey
the work pieces to be provided with edging sections in an
uninterrupted sequence through the tool. This produces a
continuous edging section that can be cut up at appropriate
points between the individual work pieces as it emerges Erom
the tool. The feed system may be equipped with stop 26
(cf. Fig. 1~) to prevent body piece 11 from being forced out
of tool 13 by the pressure of the molding material. Such a
stop 26 can be omitted if two edging sections are produced
at the same time on parallel and opposite edges of one work
piece.
If the work piece to be provided with an edging
section is large, unwieldy, or immovable, it may be simpler to
employ a movable tool that can be moved along the edge regi.on
of the stationary piece.
The edging sections produced in accordance with the
invention may serve different purposes, for example a.s an
edge protector for fragile pieces, or to Eorm a smooth edge on
a piece with lrregular or rough edges, or as a frame for various
types of installation or mounting systems, or as an elastic
seal.
Figs. 4-6 refer to a preferred embodiment of the
invention pertinent to the manufacture of a plastic heat
exchanger 30 consisting o an extruded plastic body in the
form of a plate having two parallel, flat outer walls 31
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connected by a large number of webs 32 to form a large
number of parallel flowthrough channels 33 running be~ween
outer walls 31 and webs 32 to edges 34 of the body of the
heat exchanger, and of two plastic collectors 35 each
connected to an edge 34 of the body of the heat exchanger
and in communication with flowthrough channels 33.
Collector 35 can be prefabricated and provided with a large
number of smaller, lateral connecting tubes 36. The pre-
fabricated collectors are then attached to edge 34 of the
heat-exchanger body in such a way that connecting tubes 36
project into throughflow channels 33 and, according to the
present invention, are connected to the heat exchanger body
by extruding thereover edging section 37 which extends over
the collector onto the planar body of the heat exchanger.
The collectors preferably consist of at least two separate
longitudinal segments and of a layer that surrounds them and
that grips the body of the heat exchanger.
Separate segments can be made by injection molding
more simply and cheaply than a one-piece tube. Referring to
Fi.gs 4 and ~A, collector segments 38, 39 are joined together
beEore final assembly o~ the heat exchanger and are attached
to edge 3~ of heat exchanger 30 in a way such that the
interior of collec-tor 35 is in communication through tubes 36
with flowthrough channels 33. After the various parts have
been so assembled, surrounding edging section 37 which holds
collector segments 38, 39 together and at the same time
constitutes the connection between collector 35 and the body
of heat exchanger 30 is extruded over the assembled parts.
Edglng section 37 avoids the need for an adhesive connection
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of segments 38, 39 to each other or to the body of the piece
so that gluing or welding the individual parts together can
be eliminated.
Extruded edging section 37 must be made thick enough
to accept the pressure o~ the fluid flowing through
collector 35 when the heat exchanger is in operation. It
must be connected to the body of the exchanger firmly enough
to ensure against separation of the collector.
The inner portions of collector 35 can be sepa.rated
into segments along various planes parallel to its longitudinal
axis. It is not necessary to divide it into more than two
parts. In the embodlment shown in Figs 4 and 4A, the plane
of division runs parallel to edge 3~ of the heat exchanger and
passes through the a~is of the collector. Segment 3g
immediately adjacent to edge 34 is provided with openings 40
into flowthrou~sh channels 33. These openings can be formed
in lateral connecting tubes 36.
In the embodiment in Figs. 5 and 5~, the plane
dividing collector 35 into segments 38', 39' is in the median
plane oE the body of heat exchanger 30. Lateral connecting
tubes 36' are also made in two parts in this embodiment.
Tubes 36' serves as supports which project into flowthrough
channels 33 and not only serve temporarily to fasten segments 38',
39' to the heat exchanger but also to reinforce edge 34 in the
region where edging section 37 is fastened to the exterior. While
this edging section is being extruded, the molding material
exerts considerable pressure in the region of edge 34. The
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body of the heat exchanger is usually not large enough to
resist this pressure by itself. Tubular supports 36 and 36'
must be designed thick enough so that their total cross-
section does not get warmer than the glass transition
temperature while edging section 37 is being extruded and
so that they can support the body of the heat exchanger
against the pressure of the molding material.
According to a preferred embodiment of the invention
shown in Fig. 6, one end of collector 35 comprises two plugs 41, 42
without openings. When extruded edging section 37 is formed,
the molding material forces itself between them and forms a
tight bond with the collector at the outer edge region of
the heat-exchanger plate as well.
In another preferred embodiment, collector 35 projects
on at least one end thereof beyond side 43 of the heat exchanger.
Projecting portion 4~ serves as a support and connection for
intake or release of the heat-exchanger fluid.
Especially suitable materials for -the manufacture of
the heat exchanger are the polyolefins, and polypropylene in
particular. These plastics may be dyed or pigmented. IE use
as a solar collector -ls contemplated, a plastic with a heat-
absorbent color should be employed. Carbon black is especially
effective.
Heat exchangers in accordance with the invention may
have gaseous or liquid heat-exchange media flowing through them
that are inert with respect to the particular plastic employed.
The operating temperature of the heat exchanger must be lower
than the softening temperature of the plastic. In operation,
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the heat exchanger may be surrounded by another liquid or
gaseous heat-absorbing or heat-emitting medium, or the
heat exchange may occur with incident heat rays, especially
sunlight.
The ratio of the thickness of the walls of the
collector to its largest inside dimension is preferably no
more than twice the ratio of the outer walls of the body of
the heat exchanger to its inside dimension. These ratios
are determined only by specified strength requirements and by
the pressure of the heat-exchange medium flowing through the
collector.
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