Note: Descriptions are shown in the official language in which they were submitted.
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A device for reception of a tEat and a method for its
manufacture.
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a device for reception
of a teat, comprising a thin flexible wall surrounding a
channel for reception of said teat, wherein said wall in
a direction towards the channel has an inner side and in
a direction from the channel an outer side.
The invention also relates to a method for the manu-
facture of a device of this kind.
BACKGROUND OF THE INVENTION
A device of the above described kind is previously known
from US-A-1 285 079, which device constitutes a part of
a teat liner which is usually made of nitrile rubber.
During manufacture of a rubber product, there always
arise, in the material, discontinuities, which may
consist of e.g. air or foreign particles. When load is
put on the rubber product cracks may arise, which in
that case firstly occurs in connection with the dis-
continuities.
It is commonly known that surface cracks are more
dangerous for the strength of the rubber product than
cracks inside the rubber product. It is accordingly
especially important to hamper growth of cracks in the
surface layer of the rubber product.
When a rubber product ages micro cracks also arise in
its surface layer because of reduced elasticity of the
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rubber. These cracks propagate i.e. get larger,
especially during loading of the rubber product. One
reason for reduced elasticity of rubber in course of
time is that this material is hygroscopic.
A newly produced teat liner made of nitrile rubber
contains less than 0,3 % water. A teat liner is during
use contacted by milk during milking and detergent
solution during subsequent cleaning. The milk as well as
the detergent solution contains water, which is absorbed
by the rubber material of the teat liner. The more water
that is absorbed by the rubber material the more the
teat liner loses its elasticity. Furthermore the tension
of the rubber material is increased owing to this. When
a known teat liner made of nitrile rubber is worn out,
it contains about 3 % water.
At this stage surface cracks have already arisen in the
teat liner because of the reduced elasticity in combina-
tion with the movement that the teat liner has been
forced to perform during milking. The movement has
caused tensions in the teat liner that have promoted the
growth of the cracks.
OBJECT OF THE INVENTION
The object of the present invention is to accomplish a
device for reception of a teat, which device has a
longer life than previously known such devices.
SUMMARY OF THE INVENTION
This object is obtained by a device of the initially
defined kind, which is characterized in that at least a
part of the outer side of the wall is provided with a
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large number of surface enlargements, which have such a
form, size and distribution that they form obstructions
to propagation of cracks on the outer side of the wall.
Hereby is obtained a reduced risk for fatigue of the
material in the wall.
The said surface enlargements are formed on the outer
side of the wall in order to create intentional
discontinuities with small mutual interspaces, which
discontinuities are not limited by sharp edges such as
normal surface cracks but form gentle transitions
between recesses and protrusions of the outer side of
the wall.
The intentional discontinuities provide a substantially
less risk for crack growth than sharp naturally arisen
cracks; the tension at the sharp crack edge is con-
siderably larger than the tension at a rounded off crack
edge at the same load level and is therefore more likely
to result in fatigue of the material.
If a crack in spite of these intentional discontinuities
would arise in the surface layer, the crack must turn at
the surface enlargements, disregarding whether these are
constituted by recesses or protrusions. Such a turn
requires energy and the crack growth can in this way be
hampered.
It fs thus realized that the more surface enlargements
that are arranged per unit area, the better the protec-
tion against crack growth.
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It should however be noted that intentional dis-
continuities in the form of ribs, as disclosed in
US-A-1 285 079 cannot hamper crack growth, since the
size of such ribs is much larger than the thickness of
the surface layer of the teat liner.
According to a first embodiment of the invention the
outer side of the wall has a surface with an area, which
is at least 10 % larger than the area of the surface of
the inner side. According to a second embodiment of the
invention the area is at least 50 % larger than the area
of the surface of the inner side. According to a third
embodiment of the invention the area is at least 200 %
larger than the area of the surface of the inner side.
Preferably, the extension of the surface enlargements
substantially across said channel is insignificant in
comparison with the thickness of the wall.
Preferably, the inner side of the wall substantially
lacks surface enlargements, obtaining that the surface
of the device that is contacted by milk can easily be
washed.
Suitably, the surface enlargements comprise protrusions
on the outer side of the wall. Alternatively the surface
enlargements comprise recesses on the outer side of the
wall.
The number of surface enlargements per unit area is at
least 100 pieces per square centimetre. According to a
second embodiment the number of surface enlargements per
unit area is at least 1 000 pieces per square centi-
metre.
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Hereby is achieved surface enlargements that are rela-
tively small and are substantially evenly distributed
over the outer side of the flexible wall.
5 Preferably said device constitutes a part of a teat
liner.
In addition to the fact that the surface enlargements
provide an improved strength against crack growth, it
has been established that they provide a larger
evaporation of water from the outer side of the wall.
This evaporation contributes to a slower accumulation of
water in the rubber, i.e. the rubber is more slowly
saturated by water, which in turn contributes to an
elongated life of the device.
The invention also comprises a method for the manufac
ture of a device of the above indicated kind, wherein a
moulding is produced with an inner side, which has
irregularities adapted to form said surface enlarge-
ments, and the moulding is used for moulding of the
device. Hereby is achieved a simple and inexpensive way
of manufacturing a device according to the invention.
The manufacture is suitably performed by injection
moulding, transfer moulding, compression moulding or
casting.
Advantageously, the interior of the moulding is provided
with irregularities by mechanical treatment. Alterna-
tively, the interior of the moulding is provided with
irregularities by chemical treatment.
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Examples of mechanical treatment are spark machining,
brushing, blasting, grinding, turning, hammering and
glazing.
Examples of chemical treatment are chlorination and
etching.
Certainly the surface enlargements could alternatively
be produced by after treatment of the device, but such a
method would be more expensive than the above indicated
method.
The teat liner disclosed in the US patent specification
No. 1 285 079 is provided with longitudinally disposed
ribs, having the function of preventing bending or
wrinkling of the teat liner tranversely, which according
to the document, might tend to rub or constrict the
teat, causing a congestion of the blood therein and
further tending to cause breakage of the teat liner
wall. Any number of ribs may, according to the document,
be provided, while in the drawing only five are shown.
However, the number of ribs that could at all be used to
prevent bending or wrinkilng of the teat liner is
limited to a size of the ribs that would still reinforce
the liner such that bending or wrinkling may be pre-
vented. In contrast to the device according to the
invention, ribs of this size cannot form obstructions to
propagation of cracks, since a small crack in the
surface of the liner would propagate across the ribs,
due to the fact that the thickness of the surface layer
is much smaller than the size of each rib.
Other teat liners that on the outer side are provided
with irregularities which neither are of the same size
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nor have the same effect as the surface enlargements
according to the present invention, are described in
the Swedish patent specifications 63 885 and 404 286,
the German patent specifications 922 447, 922 742
and 936 724 and in the French patent specification
1 554 653.
DRAWING SUMMARY
The invention will now be closer described in the
following with reference to the accompanying drawings,
in which
Figure 1 shows a device according to the invention for
reception of a teat, comprising a wall with surface
enlargements,
Figure 2 shows schematically a first model of a surface
enlargement,
Figure 3 shows schematically a second model of the
surface enlargement,
Figure 4 shows schematically a third model of a surface
enlargement in cross-section,
Figure 5 shows an example of distribution of surface
enlargements on a surface,
Figure 6 is a photograph of a part of the device in
fig 1 in about 10 times enlargement, and
Figure 7 is a photograph of a part of the device in
fig 1 in about 200 times enlargement.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 shows a device 1 in the form of a teat liner
for reception of a teat of an animal to be milked, such
as a cow, a sheep, a goat or a horse.
The device 1 comprises a capsule formed element 2 with a
relatively thin wall. The outer side of the wall is
provided with surface enlargements 3, while the inner
side of the wall (not shown) fs even.
Figure 2 shows schematically a first model of a surface
enlargement for quantifying of the degree of surface
enlargement and the number of surface enlargements per
unit area. The surface enlargement is approximated with
a cross-section of an arc-formed slit with the depth of
half a radius.
The degree of surface enlargement is achieved in this
approximation by the ratio between the width of the slit
and the length of the arc that follows the slit in its
cross-direction, namely
nr / ( 4r/~ 2 )
i.e. about 10 %.
Of course this also relates to a protrusion formed in
corresponding manner on the relevant surface as well as
at a comparison of the areas of the inner side and outer
side of the wall, if the inner side is even and the
outer side is provided with surface enlargements 3.
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Figure 3 shows schematically a second model of a surface
enlargement. The surface enlargement is approximated by
an arc-formed slit having a depth of a radius.
The degree of surface enlargement is achieved in this
approximation of the ratio between the width of the slit
and the length of the half-circle that follows the slit
in its cross-direction,
2nr / 4r
i.e. about 50 %.
In order not to constitute indications of fracture, the
slits shown in the figures 2 and 3 should not be deep in
relation to the thickness of the wall and they should
also not be too long. It is accordingly preferable to
provide the slits in such a way that their respective
end ends where the next slit extends in another
direction in order to prevent crack growth along the
slit.
Figure 4 shows schematically a third model of a surface
enlargement. The surface enlargement is approximated by
a half spherical protrusion having the height of one
radius.
The degree of the surface enlargement is in this
approximation achieved by the ratio between the surface
of the semisphere and the surface of the circle that is
covered by the semisphere, namely
2arz / arz
i.e. about 200 %.
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Of course, this is also the case for a surface
enlargement in the form of a half spherical protrusion
in the surface having the depth of one radius.
5 Naturally, there should in reality be no sharp edges
between the wall and the surface enlargement, but the
surface enlargements shown in figures 2, 3 and 4 are
only represented in this way in order to achieve a
simple mathematical model.
Figure 5 shows a surface with a plurality of semispheres
according to figure 4 distributed over a surface. The
semispheres are placed against one another, which means
that the centres of two adjacent semispheres are at the
distance of two radii from one another. One embodiment
of the invention comprises such semispheres, the radius
of which is half a millimetre, which implies a density
of 100 semispheres, i.e. 100 surface enlargements per
square centimetre.
In order to even more minimize the risk for crack growth
it is however suitable to provide the exterior of the
wall with at least 1 000 surface enlargements per square
centimetre.
Figure 6 shows in about 10 times enlargement a part of
the outer side of the wall comprising a large number of
surface enlargements 3.
Figure 7 shows the surface enlargements of figure 6 in
about 200 times enlargement. The surface enlargements
are, as is obvious, very different in form and size.
The invention is not limited to the above indicated
embodiments, but also variations thereof are possible.
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Consequently, the device may be provided with more than
one element 2 with surface enlargements. Likewise the
surface enlargements may form a regular as well as a
stochastic pattern. Likewise several large or small
parts of the device may be provided with surface
enlargements, for example in a plurality of fields.
The number of surface enlargements per unit area is
also not limited to what is indicated above, but can
certainly be 10 000 pieces per square centimetre,
100 000 pieces per square centimetre or even more.
