U.S. patent application number 10/221561 was filed with the patent office on 2005-10-13 for gasket, method of manufacturing and apparatus for manufacturing same.
Invention is credited to Botrie, Alexander, Hampel, Stefan, Schubert, Elvira, Ulman, Dorota.
Application Number | 20050223536 10/221561 |
Document ID | / |
Family ID | 26006656 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050223536 |
Kind Code |
A1 |
Botrie, Alexander ; et
al. |
October 13, 2005 |
Gasket, method of manufacturing and apparatus for manufacturing
same
Abstract
A gasket (1) has a gasket core (2) and an outer gasket layer (4)
covering the gasket core (2). At least one of the two sealing
materials that make up the gasket has two reactive components
before they are extruded, with said components chemically reatcting
with one another as they are combined and/or extruded. The extruded
core may be formed of a two-component resin which is at least one
of an elastomer and a foam. The flexible outer layer may be a
synthetic resin which is at least one of an elastomer and a foam.
The outer layer may be electrically conductive, ultra-violet
resistant, or resistant to the environment in which the gasket is
to operate. Also taught are methods of apparatus for the
manufacture of such gaskets
Inventors: |
Botrie, Alexander; (Toronto
Ontario, CA) ; Ulman, Dorota; (Mississauga Ontario,
CA) ; Schubert, Elvira; (Tennenbronn, DE) ;
Hampel, Stefan; (Aichalden, DE) |
Correspondence
Address: |
BANNER & WITCOFF
1001 G STREET N W
SUITE 1100
WASHINGTON
DC
20001
US
|
Family ID: |
26006656 |
Appl. No.: |
10/221561 |
Filed: |
November 24, 2003 |
PCT Filed: |
March 26, 2001 |
PCT NO: |
PCT/CA01/00399 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10221561 |
Nov 24, 2003 |
|
|
|
09534473 |
Mar 24, 2000 |
|
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Current U.S.
Class: |
29/527.2 ;
264/240; 264/45.1; 425/133.1 |
Current CPC
Class: |
F16J 15/14 20130101;
F16J 15/022 20130101; F16J 15/064 20130101; B29K 2301/10 20130101;
B29C 44/22 20130101; Y10T 29/49982 20150115; B29K 2075/00 20130101;
B29C 48/05 20190201; B29L 2031/265 20130101; F16J 15/104 20130101;
B29C 48/06 20190201; B29C 48/022 20190201; B29K 2083/005 20130101;
B29K 2995/0005 20130101; B29C 48/304 20190201; B29K 2083/00
20130101; F16J 15/108 20130101 |
Class at
Publication: |
029/527.2 ;
264/240; 264/045.1; 425/133.1 |
International
Class: |
B21B 001/46 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2000 |
DE |
100 39 068.4 |
Claims
1-44. (canceled)
45. An apparatus for the manufacture of a seal comprising: a nozzle
head having a feeding side and an outgoing side; an inner nozzle
arranged within the nozzle head for feeding a first sealing
material; an outer nozzle arranged within the nozzle head for
feeding a second sealing material, wherein the outer nozzle at
least partially, coaxially encloses the inner nozzle.
46. The apparatus according to claim 45 wherein the nozzle head
further comprises a first borehole, wherein the inner nozzle is
coaxially inserted into the first borehole, wherein the inner
diameter of the first borehole is larger than the outer diameter of
the inner nozzle, and the outer nozzle is inserted into the first
borehole.
47. The apparatus according to claim 46 further comprising a second
borehole connected to the side of the first borehole.
48. The apparatus according to claim 45 further comprising a
detachable first insert connected to the inner nozzle, wherein the
inner nozzle and the detachable first insert can be detachably
inserted from the feeding side of the nozzle head into the first
borehole.
49. An apparatus according to claim 48 wherein the inner nozzle is
interchangeable.
50. An apparatus according to claim 45 further comprising a
detachable second insert connected to the outer nozzle, wherein the
outer nozzle and the detachable second insert can be detachably
inserted from the outgoing side of the nozzle head into the first
borehole.
51. An apparatus according to claim 50 wherein the outer nozzle is
interchangeable.
52. An apparatus according to claim 45 further comprising a first
feeding passage connected to the inner nozzle to supply the first
sealing material to the inner nozzle and a second feeding passage
connected to the outer nozzle to supply the second sealing material
to the outer nozzle.
53. An apparatus according to claim 52 further comprising a shutoff
device inserted into the first feeding passage, into the second
feeding passage, or both.
54. An apparatus according to claim 52 further comprising two
reservoirs connected to the first feeding passage, wherein the two
reservoirs hold components of the first sealing material.
55. An apparatus according to claim 52 further comprising two other
reservoirs connected to the second feeding passage, wherein the two
other reservoirs hold components of the second sealing
material.
56. An apparatus according to claim 54 further comprising a first
mixer connected between the first passage and the two reservoirs,
wherein the components of the first material are mixed in the first
mixer.
57. An apparatus according to claim 55 further comprising a second
mixer connected between the second passage and the two other
reservoirs, wherein the components of the second material are mixed
in the second mixer.
Description
FIELD OF THE INVENTION
[0001] This invention relates to gaskets, their manufacture and
apparatus for manufacturing same.
BACKGROUND OF INVENTION
[0002] There are many applications in which outer surface layers of
a gasket and an inner core of the gasket require different and
possibly mutually inconsistent properties, and thus proposals have
been made for gaskets formed with an outer layer and an inner core
of different materials.
[0003] For example, the prior art describes the production of
prefabricated gaskets for electromagnetic shielding consisting of
an inner core and an outer layer. The inner core provides the
gasket with physical properties such as compression deflection,
tensile strength and elongation. The outer layer provides the
surface with properties such as electrical conductivity. Both the
inner core and the outer layer are elastomeric. The two layers can
be co-dispensed (U.S. Pat. No. 4,968,854) or the inner core can be
formed first with the outer layer applied afterwards (U.S. Pat. No.
5,141,770). The inner core usually consists of a one-component
thermoplastic resin or a one-component, heat-cured extruded rubber.
The outer layer is also a one-component thermoplastic resin or a
one-component, heat-cured extruded rubber. The outer component can
also be made from a low-viscosity coating dispersion containing an
elastomeric binder, a metallic material, a curing agent and a
diluent, such as an organic solvent. The solvent is used to
substantially reduce the viscosity of the coating, the inner core
being in this case extruded and solidified prior to the application
of the coating.
[0004] Gaskets may be used for electromagnetic shielding of
electronic casings, and in the course of increasing miniaturization
of casings, are placed in a free-flowing state from a nozzle
directly onto a casing section to be sealed, where they harden. For
the electromagnetic shielding of casings, the outer gasket layer
usually consists of a sealing material that is a good conductor of
electricity, while the inner layer, or an inner gasket core, is
usually made of a sealing material that is a poor conductor of
electricity or does not conduct electricity at all. Such a seal
combines the good electrical properties of the outer layer with the
good mechanical properties of the inner core, with the outer layer
normally exhibiting worse mechanical properties, i.e., as regards
compressibility, due to the addition of metal articles.
[0005] Such a gasket is known, for example, from the unexamined
European application EP 0 895 49 A2. This publication describes an
electrically conductive seal that is produced through coextrusion
of a silicon polymer and a silicon polymer with silver components
to form a sealing material cord and a conductive medium cord
enclosed by the sealing material cord. The outer, electrically
conductive cord through the silver components serves to connect
electrically conductive casing halves, in whose opening the seal is
designed, in order to shield electromagnetic radiation from the
casing interior or into the casing interior.
[0006] The use of a silicon polymer involves some disadvantages.
Silicon is not very compressible, thus, when reducing the size of
the casing to be shielded with the consequent corresponding
reduction in size of the gasket diameter, good compressibility of
the sealing material is required in order to compensate for
unevenness on the surfaces of the casing and to ensure that the
gasket rests against all the surfaces to be sealed. Furthermore,
silicon, which is applied in a viscous state, dries when exposed to
air, and continues to harden in the process, is relatively
difficult to process and comparatively expensive.
SUMMARY OF THE INVENTION
[0007] The present invention provides a gasket which combines
sealing materials with various mechanical, chemical, and/or
electrical properties that can be produced in a simple manner, and
which preferably have good compressibility.
[0008] In an embodiment, at least one of the sealing materials has,
before it is dispensed, at least two reactive components that react
chemically with one another after they are combined and/or the
components are dispensed. Polyurethane may be used as a sealing
material, consisting of two components that react with one another
after they are combined or after being dispensed into the air, and
form a sealing foam. The result of the chemical reaction after the
curing is a foam gasket that has good compressibility. The two
components forming the polyurethane can be easily processed. Thus,
these two components, which are suitable for the manufacture of the
inner gasket core as well as the outer gasket layer, can be
dispensed or processed in liquid state--and therefore a state that
lends itself well to processing--onto the surface to be sealed,
while forming a cord, where the two components react with one
another and cure. Moreover, polyurethane is reasonably priced.
[0009] An advantage of a sealing material that has at least two
initial components to be used for at least one of the sealing
layers is that the gasket assumes its desired characteristics and
cures only after it is put in place through the reaction of at
least two components, while the components that have already been
mixed but have not yet reacted with one another can be easily
worked with and can be dispensed or processed by means of a nozzle.
The length of time that the components remain workable without
reacting with one another depends on the material. In an
embodiment, one can use initial components that react with each
other only after they are dispensed into a reaction-promoting
atmosphere in a mixed state.
[0010] The invention thus provides a versatile co-dispensed gasket
and a method for its manufacture, based on the use of a
two-component core material setting to an elastomer or foam, to
which is applied an outer layer which may be a further
two-component material, setting to an elastomer or foam, or a
solvent-based coating, either co-dispensed with the core material
or applied to the latter subsequently. In this context,
"two-component" as applied to the core material, should be
construed broadly. The core material must be able to cure or set to
a stable final material within the outer layer. This can be
achieved with materials not traditionally considered to be
two-component materials, as described further below. The core
material should have a consistency such that it can be dispensed
but will remain in situ after dispensing and during curing.
[0011] This enables the core and/or the outer layer to be foams as
well as elastomers. With a suitable choice of two component
compositions or solvent-based coatings, the entire process can be
carried out at ambient temperatures. The co-dispensing process can
be used to provide form (and foam) in place gaskets, which is not
practicable with any known process for two-component gaskets of the
types concerned. Rather than forming the gasket in situ, it may be
co-dispensed into a mould and then cured to provide a desired
profile. If low density co-dispensed foams are used, the process is
highly cost-effective, while the ability to use foams and/or
elastomers with widely different properties makes it very
versatile. The use of a mould also means that relatively low
viscosity materials may be used, whereas in situ formation usually
requires the materials to be highly viscous or thixotropic in order
that they may remain in situ while curing or setting. The core and
outer layers may be formed of different density foams, or the outer
layer may be of a material selected to provide a thin, tough
flexible skin.
[0012] Accordingly, the invention provides a gasket comprising a
core formed by a two-component resin which, when set, is at least
one of an elastomer and a foam, over which is applied a flexible
outer layer of a synthetic resin which, when set, is at least one
of an elastomer and a foam.
[0013] The invention also includes a method for the manufacture of
a gasket according to the invention and an apparatus for the
manufacture of a gasket according to the invention.
[0014] The apparatus includes two coaxial nozzles, an inner nozzle
for the material of the gasket core and an outer nozzle enclosing
this inner nozzle for the material of the outer gasket layer. In an
embodiment, these nozzles or at least one of these nozzles can be
used interchangeably in the nozzle head, as a result of which the
diameter and/or the sheathing thickness of the gasket can be varied
in a simple manner.
[0015] Further features of the invention will be apparent from the
following description and examples of embodiments of the
invention.
SHORT DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a cross-section of a gasket according to the
invention, the gasket placed on a section of casing;
[0017] FIG. 2 is a cross-section of a gasket according to the
invention, with the gasket compressed in a closed casing;
[0018] FIG. 3 is a cross-section of a gasket formed in a groove of
a casing;
[0019] FIG. 4 is a section of an apparatus for the manufacture of a
gasket according to the invention;
[0020] FIG. 5 is an enlarged section from FIG. 4;
[0021] FIG. 6 is a schematic diagram of an apparatus for producing
gaskets of the invention;
[0022] FIG. 7 is a fragmentary cross-sectional view of two machine
parts, one with a groove to be gasketed with a foam-in-place
co-dispensed gasket;
[0023] FIG. 8 is a cross-sectional view of a mould used to form
prefabricated gaskets of the invention;
[0024] FIG. 9 is a fragmentary cross-sectional view showing an
overlap of ends of an extrusion forming a co-dispensed gasket.
[0025] FIG. 10A to 10D are end views of some different nozzle
arrangements that can be utilized in performing the method of the
invention.
DESCRIPTION OF EMBODIMENTS
[0026] FIG. 1 shows a cross-section of a gasket 1 according to the
invention, with the gasket placed on a surface 5 of a casing part
6A. The gasket has an inner gasket core 2 and an outer gasket layer
4 that completely encloses the inner gasket core 2 in the
embodiment shown. To manufacture the gasket 1, the first,
free-flowing sealing material for the gasket core 2, and the second
free-flowing sealing material for the outer gasket layer 4, are
placed on surface 5 where the sealing materials can cure.
[0027] At least one of the two sealing materials has, before being
dispensed, at least two components that chemically react with one
another after they are combined and/or dispensed into a
reaction-promoting atmosphere. Air is a particular example of a
reaction-promoting atmosphere, while polyurethane is an example of
a sealing material that has at least two components. The components
of polyurethane cure after the reaction, while forming a foam that
has good compressibility and therefore adjusts well to the contours
of the casing to be sealed.
[0028] The outer gasket layer 4, which can also consist of a
sealing material that has at least two initial components, may be
electrically conductive so that it can connect conductively two
conductive halves of the casing, 6A, 6B in a closed casing as shown
in FIG. 2, and consequently so that it can electromagnetically
shield the electronic components found in the casing. The material
of the outer gasket layer 4 can also be chosen in such a way that
it is UV- and/or acid-resistant or has this property in addition to
the electric conductivity. The gasket 1 is compressible so that it
can fit closed casing 6A, 6B all over the casing halves 6A, 6B and
level out unevenness on the sealing surfaces of the casing halves
6A, 6B.
[0029] The outer gasket layer 4 may consist of a material that has
a closed surface. Sealing foams, such as polyurethane, have pores
that liquid can penetrate, and thus may allow the liquid to
penetrate the casing to be sealed. In a gasket core 2 having pores,
the outer gasket layer 4 therefore may comprise a sealing material
that has no pores, for example, silicon. For the outer gasket
layer, a sealing material that has at least two initial components
that react with one another after they are combined and/or are
dispensed while forming an outer gasket layer 4 with a closed
surface is also taught.
[0030] FIG. 3 shows a gasket 1 of the invention, which is formed in
a groove 9 of a casing part 7. The groove 9 supports the
positioning of the gasket core that is dispensed, with the core
being still soft. The disadvantage in placing the sealing materials
in a groove 9 is that there can be insufficient ventilation for
drying the sealing in the groove 9. As a result, in some sealing
materials used for the outer gasket layer 4, no integral skin
impermeable to liquid forms on the surface of the outer gasket
layer 4 in the area of the groove 9. The risk is that moisture gets
through the seal in the area of the groove 9, and in this manner,
the moisture penetrates the interior of the casing. To avoid these
disadvantages, the outer gasket layer 4 may consist of material
which forms an integral skin on the surface even when ventilation
is bad during the curing. Such a sealing material can have at least
two initial components that react with each other after they are
combined or after they are dispensed.
[0031] The thickness of the outer gasket layer 4 may be less than
the diameter of the gasket core 2. In a seal for electromagnetic
shielding of a casing, in which only the outer gasket layer 4 needs
to be electrically conductive, one can save on resources such as
silver as conductive material.
[0032] Of course, the inner gasket core 2 as well as the outer
gasket layer 4 can consist of a sealing material that has at least
two components that chemically react with one another and cure
after they are combined and/or dispensed into a reaction-promoting
atmosphere. In the process, electrically conductive particles can
be added to the components for the outer layer 4.
[0033] The final properties of the gasket 1 will be exhibited only
after the reaction of the initial components of the respective
gasket layers 2, 4, i.e., the sealing material arises only as a
result of the initial components reacting with one another after
they are combined and/or dispensed. Depending on the application,
there are desired properties of the sealing material that can be
influenced by the selection of the initial components, such as the
foaming of the components during the chemical reaction, the
formation of a sealing layer with a closed surface, or the curing
while an integral skin is formed even when ventilation is not good.
Preferred as initial components are liquid components that are easy
to work with and can be easily dispensed onto the surface to be
sealed before the chemical reaction occurs. Depending on the choice
of the initial components, the chemical reaction may take a certain
duration after the initial components are combined, and/or it may
occur only after the initial components are dispensed into a
reaction-promoting atmosphere. The start time of the reaction, or
the time period after the time the components to react after they
are combined, can be adjusted by selecting the components in such a
way that sufficient time remains for dosing the gasket core onto
the sealing surface after the initial components react with one
another.
[0034] One embodiment of the invention provides for the sealing
layer to completely enclose the gasket core and to have
electrically conductive particles. This embodiment ensures that two
conducting halves of the casing are always connected in an
electrically conductive manner through the seal, independent of
which part of the surface of the seal the casing halves lie
against.
[0035] A further embodiment provides that the outer gasket layer
consists of a material that has a closed surface after the
curing.
[0036] Silicon is an example of such a material. Sealing materials
that have two initial components that chemically react with each
other after they are combined and/or dispensed into a
reaction-promoting atmosphere in order to form a gasket with a
closed surface can also be used. The use of such material prevents
moisture from penetrating the pores of the seal, and consequently,
the interior of the casing.
[0037] Furthermore, it is possible to use for the outer gasket
layer a material that exhibits a better resistance against various
environmental influences, e.g., the outer gasket layer may have a
material resistant to UV-light or acid, in order to adapt the seal
to the respective conditions for use.
[0038] Sealing materials may be extruded in a viscous state into
the grooves of the casings in which they cure in order to form the
seal. However, some materials may cure in the groove, particularly
in the groove base, where there is poor ventilation, without
forming a so-called integral skin on the scaling surface. The risk
is that moisture will penetrate the gasket, and from there, the
interior of the casing. The material forming the outer gasket layer
is therefore preferably a sealing material that cures even in the
grooves, i.e., even when ventilation is not good, while forming an
integral skin on the surface. A sealing material that has at least
two initial components comes into consideration as sealing
material, in which the two components, after being combined or
after being dispensed onto the surface to be sealed react with one
another and cure, even when ventilation is not good, while forming
an integral skin.
[0039] FIG. 7 is a cross-sectional view of a part 128 with a groove
126 to be gasketed, illustrating one way in which a co-dispensed
gasket can be formed-in-place. The cover 130 can be applied after
the gasket is formed. The surface of the groove and the composition
used for the outer layer will determine whether the outer layer
bonds to the surface. The co-dispensed gasket can also be applied
on a flat surface rather than in a groove.
[0040] FIG. 8 is a cross-sectional view of a mould used to shape
prefabricated gaskets in accordance with the invention. The gasket
is dispensed into the bottom of the mould 132. The cover 134 is
applied before the gasket sets. In this case, the outer layer and
the mould surface are selected so that the cured gasket will
release from the mould surface.
[0041] FIG. 9 is a longitudinal cross-sectional view of a portion
of a co-dispensed gasket in which the beginning and end of the
extrusion overlap. This type of overlap is created by starting the
dispensing of the outer layer material 136 before starting
dispensing of the core material 138, and continuing dispensing of
the outer layer material after dispensing of the core material has
been stopped. This may be conveniently achieved by using valves 111
and 113 in FIG. 6. A continuous, closed-loop gasket is formed if
the ends 140 and 142 of the dispensed material are overlapped. An
open-ended gasket is formed without the overlap. Gaskets of many
sizes and shapes can be made by mounting the nozzle 118 of FIG. 6
on a programmable robot.
[0042] FIGS. 10A to 10D are end views of some different nozzle
configurations for co-dispensing gaskets in accordance with this
invention. It will be noted that the nozzles are not necessarily
concentric or of a similar profile, and that the nozzle for the
outer layer material may not fully surround that for the core
material, providing a gasket in which the core material is not
fully enveloped by the outer layer. This may be necessary or
desirable in some applications.
[0043] As shown in FIGS. 10A and 10B, the relative thickness of the
outer layer relative to the core layer may vary. It will normally
be desirable that the outer layer and core are bonded securely
together, and this will be facilitated if both the core and the
outer layer are formed by resins of the same general type, e.g.,
polyurethane.
[0044] An apparatus whose nozzle head is shown in FIG. 4, and an
enlarged partial section of which is in FIG. 5, can be used to
manufacture a gasket according to the invention.
[0045] The nozzle head 10 has a first, continuous borehole 11
leading to a second borehole 12 inclined at an angle against the
axis of the first borehole 11. An inner nozzle 13 is inserted into
the first borehole 11, the nozzle having a diameter less than the
inner diameter of the first borehole 11, so that a ring-shaped
passage gap remains free between the exterior circumference of the
inner nozzle 13 and interior circumference of the first borehole
11. The inner nozzle 13 is pressed into a first insert 14, which is
inserted into the enlarged influx-side and (shown in the upper
portion in the figure) of the first borehole 11. The first insert
14 can be inserted in the seat in the nozzle head 10 or can be
screwed into it in a detachable manner so that the inner nozzle 13
fitted into the first insert 14 can be interchangeable. On the
influx-side end of the first insert 14 and the inner nozzle 13 is
inserted a first shutoff valve 15. A feed for the material to the
inner gasket core 2 is connected to an influx-side receptacle 16 of
the first shutoff nozzle 15. This feed can be formed in a known
manner. If the material is a two-component material, the feed
consists of a two-component mixing apparatus, in which the two
components are mixed and fed through the shutoff valve 15 and the
inner nozzle 13.
[0046] A second shutoff device, e.g., in the form of a second
shutoff valve 17, which can likewise be screwed into the nozzle
head 10, is fastened to the influx-side end of the second borehole
12. The second shutoff valve 17 also exhibits a receptacle 16, to
which a feed is connected, through which the material of the outer
feed is connected, through which the material of the outer gasket
layer 4 is fed. Here as well, the feed can be a one-component
dosing device or a two-component-mixture and dosing device, as
already known in the art. The first borehole 11 is enlarged in its
outlet end, shown in the lower portion of the figure. In this
enlarged end, a second insert 18 can be inserted, into which an
outer nozzle 19 is fit in. The second insert 18 exhibits a
continuous borehole into which the outer nozzle 19 has been
inserted. The inner diameter of the outer nozzle 19 or the borehole
of the second insert is larger than the outer diameter of the inner
nozzle 13, as a result of which the ring slot between the first
borehole 11 and the inner nozzle 13 in the second insert 18 and the
outer nozzle 19 continues. The second insert 18 may be inserted by
means of an outside screw into an inner screw of the end-side
enlargement of the first borehole 11 so that the second insert 18
can be interchanged with the outer nozzle 19.
[0047] For the manufacture of a gasket according to the invention,
the first sealing material or initial components of the first
sealing material are put in through the first shutoff valve 15 and
the second sealing material, or initial components of the second
sealing material, through the second shutoff valve 17 of the nozzle
head. At least one of the two sealing materials consists of at
least two free-flowing components that chemically react with each
other after they are combined and/or dispensed into a
reaction-promoting atmosphere. The chemical reaction may be, for
instance, a sealing foam that has good compressibility arising from
the free-flowing components, a sealing material with closed
surface, or a sealing material that also ventilates even when
ventilation is not good, while forming an integral skin.
Electrically conductive particles may be added in the process to
the second sealing material or the components.
[0048] To extrude the sealing materials, the first sealing material
is put under pressure by the first shutoff valve 15 and the inner
nozzle 13. Accordingly, the second scaling material, under pressure
from the second shutoff valve 17 and the second borehole 12, is
pressed into the first borehole 11 and the outer nozzle 19, which
enclose the inner nozzle.
[0049] The first and second sealing materials are separated from
one another in the nozzles 13, 19. They meet each other only at the
common outlet end of the inner and outer nozzles 13, 19, where
gasket core 2 is formed by the first sealing material. The core
comes out of the inner nozzle 13 completely enclosed by an outer
gasket layer 4 out of the second sealing material, formed by the
outer nozzle 19 and the outer surface of the inner nozzle 13. The
sealing materials are chosen such that they do not mix, or mix very
little when they meet, but that they nevertheless adhere well to
each other.
[0050] The nozzle head 10 is fed through the casing part to be
sealed so that a viscous gasket core merging from the nozzles is
placed directly onto the casing part, and adheres and cures there
in order to form the gasket. The sealing strand may be dispensed
onto the casing under an atmosphere that promotes the chemical
reaction of at least two components, which comprise at least one of
the two sealing materials.
[0051] Through the shutoff valves 15 and 17, it is possible to
block the feed of the components into the nozzle head 10 at the end
of the dosing procedure so that no more component material enters
the nozzles and boreholes of the nozzle head 10, preventing a drip
of the sealing material at the end of the dosing procedure.
[0052] With the apparatus according to FIG. 4, a gasket for an
electromagnetic shielding can be produced completely out of
polyurethane, in which only the outer gasket layer is electrically
conductive. For this, the two initial components of polyurethane
are fed to the first hollow space and the two initial components
made of polyurethane and an electrically conductive material are
fed to the second hollow space. After the two sealing materials are
dispensed, the components of the polyurethane react, forming a
sealing foam in which the outer gasket layer is electrically
conductive.
[0053] The diameter of the inner gasket core 2 is largely
determined by the diameter of the inner nozzle 13 and the thickness
of the outer gasket layer 4 is largely determined by the difference
between the outer diameter of the inner nozzle 13 and the inner
diameter of the outer nozzle 19. By means of the first insert 14,
the inner nozzle 13 can be changed in order to vary the diameter of
the inner gasket core 2. By means of the second insert 18, the
outer nozzle 19 can be changed in order to vary the outer diameter
of the outer gasket layer 4, and consequently, the entire gasket.
The thickness of the outer gasket layer 4 can likewise be varied by
exchanging the nozzles 13 and 19.
[0054] FIG. 6 is a schematic of a dispensing apparatus for
producing gaskets using a two-component resin system for the inner
core and a two-component resin system for the outer layer. It
comprises reservoirs 102, 104, 106 and 108. Reservoirs 102 and 104
hold the two components of the inner core material. Reservoirs 106
and 108 hold the two components of the outer layer material.
Metering pumps 102A, 104A, 106A, and 108A dispense correct
quantities of each component. The components of the inner core and
outer layer are passed through mixers 110 and 112 and shut-off
valves 111 and 113 via tubes 142, and are then dispensed through
co-axial tubes 114 and 116 of nozzle 118 to form a co-dispensed
gasket 120, having a core 127 and an outer layer 124. The resulting
gasket will have an elastomeric or foam inner core 127 and an
elastomeric or foam outer layer 124.
[0055] Although the following examples make use of conventional
two-component thermosetting resin systems, the term two-component
in the context of the invention should be taken to include systems
in which the second component is a gas or simply moisture. A number
of moisture-curing foamable compositions are known, and these may
be used for the core material, as well as for the outer layer,
provided that the moisture required for curing may reach the core.
Thus the necessary moisture may be contained in the outer layer
material or be produced as a by-product of its curing or may
permeate through the outer layer, if the latter is an open cell
foam, or the inner core may be moisture-cured by direct application
of moisture, if the core is extruded using a nozzle which provides
an extrusion in which the core is not fully enveloped by the outer
layer. As a further alternative, a second component in the form of
a pressurised gas such as nitrogen may be added in the dispensing
system to a molten thermoplastic first component. On emerging from
the extrusion nozzle, the nitrogen expands to foam the first
component which rapidly sets to form a foam. The following examples
however make use of conventional two-component core materials.
EXAMPLE 1
[0056] A gasket of approximately a half-round cross-section, 8 mm
in diameter, and having an outer layer 0.5 mm thick was formed by
co-dispensing of two-component polyurethane foams as follows. An
inner core was a two-component, thixotropic material available from
Chemque Inc., Indianapolis, Ind., under the designation CHEM-CAST
624.TM., the mixing ratio of components A & B of that material
being 100 parts to 18.5 part by weight. It cures to a flexible,
polyurethane foam with the following properties when cured:
1 Shore OO Hardness: 45 Compression Deflection: 3.0 psi Foam
Density: 0.3 gm/cm.sup.3
[0057] The outer layer was an electrically-conductive thixotropic
material available from Chemque Inc. under the designation
CHEM-CAST 906.TM., the mixing ratio of components A & B of that
material being 100 to 3.1 parts by weight. The material cures to a
flexible polyurethane foam with the following properties:
2 Shore A Hardness: 10 Compression Deflection: 12.0 psi Foam
Density: 0.6 gm/cm.sup.3 DC Volume Resistivity: 0.10 ohm .multidot.
cm
[0058] The inner core constituted approximately 76% of the total
volume. The outer layer constituted approximately 24% of the total
volume. The inner core contributed to forming a very soft gasket
with good compression recovery, low density and low cost. The outer
layer contributed to providing a high electrical conductivity of
the finished gasket. The effects of high cost, high hardness and
poor compression recovery of the outer layer are minimized by
co-dispensing. The overall result was a soft flexible resilient
gasket with good conductivity at reasonable cost.
EXAMPLE 2
[0059] A gasket was formed of similar dimensions to that of FIG. 6,
except that the outer layer had a thickness of 0.25 mm. In this
case, the inner core was formed from CHEM-CAST 624.TM. mixed as
described in Example I to provide a flexible, MDI-based
polyurethane foam. This foam has poor UV resistance and outdoor
weathering properties:
[0060] The outer layer was a white-pigmented, two-component
low-viscosity material, available as CHEM-DEC ER96071.TM. from
Chemque Inc., with parts A & B mixed in the ratio of 100 to 110
parts by weight. This cures to a flexible polyurethane elastomer
incorporating an aliphatic isocyanate for good UV resistance, and
having a Shore A hardness of 50.
[0061] The two layers of this gasket were co-dispensed at the same
time. The inner core provides a very soft gasket with good
compression recovery, low density and low cost, while the outer
layer provides good UV and weather resistance and toughness to the
gasket.
EXAMPLE 3
[0062] A gasket was formed by co-dispensing, having similar
dimensions to those of Example 2. The core layer was a
two-component thixotropic material available from Chemque Inc.
under the designation CHEM-CAST 628-231.TM., with components A
& B mixed in the ratio of 87 to 100 by weight. It cures to a
flexible, silicone foam with the following properties:
3 Shore A Hardness: 15 Compression Deflection: 4.0 psi Foam
Density: 0.45 gm/cm.sup.3
[0063] The outer layer was a two-component, electrically
conductive, thixotropic material available from Chemque Inc. under
the designation CHEM-CAST ER 96088-3.TM. with components A & B
mixed in the ratio 100 to 4.6 by weight. It cures to an
electrically-conductive flexible silicone elastomer. It was found
that the addition of solvent reduced viscosity for ease of
application. As an alternative to co-dispensing, the outer layer
may be applied after curing of the inner core layer.
4 Shore A Hardness: 70 Elastomer Density: 2.9 gm/cm.sup.3 DC Volume
Resistivity: 0.15 ohm .multidot. cm
[0064] The elastomer of the outer skin adds electrical conductivity
and toughness to the soft resilient inner foam core.
* * * * *