Flexible hose

Details Flexible hose Flexible hose

2000-11-08

2002-05-28

Brinson, Patrick (Department: 3752)

Pipes and tubular conduits

Flexible

Corrugated

C138S122000, C138S177000, C138SDIG001

Reexamination Certificate

active

06394143

ABSTRACT:

This invention relates to a flexible corrugated hose according to the preamble of the first claim.
Such flexible corrugated hoses find numerous applications, for instance in vacuum cleaners and other industrial applications. This and other types of hoses are often produced by blow-moulding a thermoplastic material, as this provides lightweight, flexible and inexpensive hoses. The wall of these hoses is provided with convolutions or corrugations, which results in added flexibility and crush and kink resistance. The corrugated shape makes the hose return to its original shape after being bent, compressed or stretched. Moreover, the corrugated shape prevents the hose from collapsing when the pressure inside the hose is reduced.
The corrugated shape of such a hose results in an internal surface with projections and recesses. It was found that the hose produces an annoying whistle when an air stream passes through its interior, especially at high rates of air flow. The whistle occurs when the hose is in stretched condition, but particularly when the hose is bent. The whistle is caused by resonance of audible harmonics which are created when the air, which is blown or sucked through the hose, strikes the corrugations of its internal surface.
From U.S. Pat. No. 4,756,045 a flexible hose of a plastic material is known which is produced by an extrusion blow-moulding process. The flexible hose disclosed in U.S. Pat. No. 4,756,045 has an internal surface comprising alternating projections and recesses, recesses of a greater depth and/or width alternating with recesses of a smaller depth and/or width. These alternating corrugations provide the hose with a roughened internal surface which reduces whistle by breaking up the flow of the passing air: the resonance caused by the harmonics created at the larger recesses is counteracted by the resonance caused by the harmonics created at the smaller recesses, which have a different frequency. This solution to the problem of unwanted whistle however has the disadvantage that the rougher internal surface amounts to a higher internal air resistance, giving rise to a loss of air pressure along the corrugations of the internal surface and thus to a loss of capacity of the hose.
There is thus a need for a flexible corrugated hose with which the problem of whistle can be solved without however increasing the internal air resistance of the hose. It is the object of this invention to provide a flexible corrugated hose which shows a reduced internal air resistance.
This is achieved according to the invention with the technical features of the characterising part of the first claim.
According to the invention each internal projection of the hose has a substantially flat and smooth top face. These flat top faces can prevent pressure loss on the internal protrusions and give the whole of the internal surface of the hose a smoother appearance, so that the air resistance of the interior of the hose can be reduced. By limiting pressure loss to the recesses and preventing pressure loss on the protrusions, the overall pressure loss over the entire length of the hose can be reduced.
As an air stream passes through the interior of the hose and the air strikes the side walls of the recesses, harmonics are created. Because of their substantially flat shape, the top faces form dampers for the harmonics which are created when air strikes the side walls of the internal recesses of the hose. The result is that a vibration created at one recess can be damped before the air reaches the next recess. This damping effect is supplied by the top face of the projection in between the two successive recesses. This damping effect has the advantage that less air resistance and less loss of air pressure occurs in the hose of the invention compared to the hose described in U.S. Pat. No. 4,756,045 in which the harmonics are counteracted by other harmonics of a different frequency. The damping effect in the hose of the invention reduces the amount of air vibrations created in the hose, whereas the counteracting effect in the hose described in U.S. Pat. No. 4,756,045 increases the amount of air vibrations created in the hose and causes comparatively more loss of air pressure.
An advantage of the smoother appearance of the internal surface of the hose is that less dust ends up in the internal recesses of the hose when it is used as a vacuum cleaner hose.
The ratio between the width of the top faces W
1
and the width of the recesses W
2
is preferably larger than or equal to 2.2, preferably W
1
/W
2
≧3.5, in order to obtain that the damping effect exerted by the top faces can last long enough to sufficiently damp a vibration created at one recess before the air reaches the next recess. In this way interference of harmonics and a resulting production of whistle can be prevented. The first width W
1
is the distance between a first intersection A of a first tangent line T
1
with a second tangent line T
2
and a second intersection B of a third tangent line T
3
with the second tangent line T
2
. The second width W
2
is the distance between the second intersection B and a third intersection C of a fourth tangent line T
4
with a fifth tangent line T
5
. The first tangent line T
1
touches a side wall of a first recess. The second tangent line T
2
touches the top face of a first projection which is adjacent to the side wall of the first recess. The third tangent line T
3
touches a first side wall of a second recess, this first side wall being adjacent to the first projection. The fourth tangent line T
4
touches the second side wall of the second recess, this second side wall opposing the first side wall of this second recess. The fifth tangent line T
5
touches the top face of a second projection which is adjacent to the second side wall of the second recess.
The inventor has also noted that the hose described in U.S. Pat. No. 4,756,045 and other existing hoses of a similar type are only substantially whistle-free at rates of air flow which do not exceed 115 m
3
/h. By providing a hose with a ratio W
1
/W
2
≧2.2 according to the invention, preferably W
1
/W
2
≧3.5, a hose is obtained which is still substantially whistle-free at higher rates of air flow, for example at 130 m
3
/h or higher. This is important because the rate of air flow of vacuum cleaners has risen from 90 m
3
/h in the past to 130 m
3
/h nowadays, so that the existing hoses are no longer applicable as they produce whistle at a rate of air flow of 130 m
3
/h. This feature of the hose of the invention can also be advantageous in other industrial appliances which involve a flexible hose with an air stream passing through its interior.
In order to obtain a hose with recesses which are as narrow as possible to prevent whistle especially at high flow rates, it is preferred that these recesses have substantially straight side walls which extend almost perpendicular to the longitudinal direction of the hose. In particular side walls are preferred of which the tangent line forms an angle of approximately 90 to 100° with the plane formed by top faces of the internal projections.
According to another preferred embodiment of the invention the external surface of the hose comprises projections and recesses, higher projections alternating with lower projections and these lower external projections corresponding to the substantially flat top faces of the internal projections. These lower external projections are provided to collect an excess of plastic material and to prevent that plastic material piles up onto the projections in between two internal recesses of the internal surface of the hose during the moulding process. In other words, these lower external projections permit the plastic material to take such a shape that the internal projections have a substantially flat top face.
It is also preferred that along the internal recesses of the hose the wall has a substantially uniform material thickness T. Furthermore it is preferred that the transition between the top face of each internal projection and the side wall of ea

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