Note: Descriptions are shown in the official language in which they were submitted.
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l~ Background of the Invention
~ I
il Flexible hoses made of elastomeric or flexible plastic
materials require reinforcement by material such as braided
I Rayon, Dacron, stainless steel wire, or the like when the hoses ~-
5 1l are to be used for high fluid pressures, such as hydraulic
service where working pressures may be over 1,000 PSI. For
small diameter hoses, such as 1/4" ID, one layer of reinforce-
I ment may be sufficient to give the hose a burst strength of as
~ much as 6,000 PSI, depending upon the hose diameter and the
10 ¦ particular reinforcement material used. For larger size hoses, `such as 1/2" ID and over, more than one layer, is frequently , ~
required to provide the necessary burst strength. , -
¦ When two or more layers of braided reinforcement are
¦ used, several problems arise. If the reinforcement is metal
¦ wire, the elastic elongation value is small, such as about
¦ .2%, and upon application of internal fluid pressure the first
¦ braid does not readily stretch within its elastic limit a
¦ sufficient amount to permit the braid to expand in diameter I -
to transfer a substantial part of the load to the second braid.
¦ Because the load transfer from one braid to the other is
~ difficult to calculate and to control by feasible manufacturing¦
! methods, it is common practice in the industry, based on I -`
empirical data, to rely on no more than a 50~ increase in burst
l strength by adding a second braid. Normally, it would be
expected that the burst strength would be doubled. The
~ comparative rigidity of the steel wire and resultant resistance
! to expansion of the hose under hydraulic shock pressures also
results in a failure to cushion or dissipate such shock pressurçs
with the result that they may have injurious effects on other
30 l parts of the system.
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l With synthetic fibers such as regular Nylon the
I elastic elongation value is much greater and may be in the
neighborhood of 4~. This results in a better distribution of
internal fluid pressure loading between the two braids.
However, the accompanying swell and volume increase of the hos~
may produce sluggish or spongy reaction of other units in the
hydraulic system.
As more layers of reinforcement are provided the wall~
l thickness of the hose increases and the flexibility decreases.
¦ Moreover, the use of the metal wire reinforcement makes the
hose relatively less flexible than when fibrous ~on-metallic ~ I
~ r~ ~a~
materials, such as Nylon, RayOn, cotton, Dacron, and the like,~
are used as the reinforcement. Also, the cost of making the
.~ ,;~,
hose increases and the problem of satisfactorily bonding the
layers to each other and the problem of gripping the hose with
a coupling becomes more difficult as more layers of reinforce-
ment and/or metal reinforcement are used.
Summary of the Invention
l In accordance with this invention, a high strength hosle -~
¦ is provided by use of a special fibrous aromatic polyamide
(Nylon) yarn as the reinforcement material, the yarn having a ~
section modulus of over 400 grams per denier (gpd) and a ', -
tenacity of more than 15 gpd at room temperature. Such yarn is
I¦ far stronger than non-metallic reinforcement materials hereto-
¦~ fore in use so that one layer of the special yarn may be used
I in lieu of a metallic reinforcement or in lieu of two or more
il layers of non-metallic materials heretofore used.
The elastic elongation of the special Nylon is about
~ and therefore the first braid will stretch under high
~ internal fluid pressures to transfer a significantly higher
i~ percentage of the pressure load to the second braid than is
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the case with stainless steel braid. Also, the hose volume
will increase to a greater extent than with stainless steel
braid to give more cushion to fluid pressure shock forces
than a hose having stainless steeI braid, but the volume
increase is less than with regular Nylon so as to reduce or
eliminate any sponginess in the hydraulic system.
Thus, according to the present invention there is
provided in a high strength flexible hose having a calculated
burst strength of over 10,000 psi. and comprising a core ~ube
of elastomeric material, and at least one layer of reinforce-
ment over the core tube, the improvement wherein said layer '
of reinforcement is of high strength nylon fibrous yarn
having, at room temperatures, a modulus of elasticity of at
least 400 gpd., a tenacity of over 15 gpd., an elastic elonga-
tion of about 1%, and an elongation less than 5% at maximum
stress.
Detailed Description
Figure 1 illustrates a well known construction for
a hose for high pressure hydraulic service.
Figure 2 illustrates a hose for hydraulic service in
accordance with the present invention.
As shown in figure 1, a prior weIl known type of
hose 10 for high pressure hydraulic service has a core tube 11
of synthetic rubber, a first layer of braided reinforcement 12
of cotton, a second layer of braided reinforcement 13 of
stainless steel wire, a third layer of braided reinforcement -
14 of cotton, and a protective sheath 15 of elastomeric material '-
such as synthetic rubber, which may also contain a fungicide.
All layers are preferably bonded to each other with a suitable '~
adhesive, such as Adiprene L 100, a urethane base material,
made by E. I. DuPont Company.
For the prior art hose of figure 1, in size 1/4" ID
for example, the core tube 11 may be of about .075" wall
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thickness, the layers of reinforcement a combined wall thick-
ness of about .158", and the sheath a wall thickness of about
.020", whereby the total wall thickness will be about .253".
With the cotton braids being of multiple ends of 8/3 or 8/4
ply yarn and the stainless steel wire being of .012", diameter
and about 320,000 PSI tensile strength the hose will have a
burst strength of about 10,000 PSI. However, the hose is
relatively stiff and not easily flexed.
In a hose illustrated in figure 2 made in accordance
with the present invention, a core tube 11 of synthetic rubber
identical in diameter, wall thickness and material as the tube
11 of figure 1 has over it first and second layers 18 and 19 ~- ;
of a braided fibrous aromatic Nylon yarn that is available
from E. I. DuPont Company under their trade name "Kevlar" and
known generically in the trade as "Fiber B Nylon". Kevlar
has a modulus of elasticity of between 400 and 500 gpd (grams
per denier) at room temperature and at least 300 gpd at 300F.
Its tenacity is between 15 and 25 gpd at room temperatures,
and over 10 gpd at 260F, the yarn further being of about
1,500 denier. At room temperature the varn has an elongation
of less than 5% at maximum stress and a loop tenacity of 9 -
gpd. The density of the yarn is between 1.40 and 1.50 and `
the tensile strength is about 405,000 PSI. ~ -
The hose as illustrated in figure 2 also has a
sheath 15 that may be of identical composition and wall thick-
ness as sheath 15 of figure 1, that is, of synthetic rubber
with a fungicide therein. The two braid layers 18 and 19 of
Kevlar may be bonded to each other and/or to the inner tube
11 and outer sheath 15, as for example by an adhesive such as
Adiprene L 100.
The two braid layers of the figure 2 hose in the
1/4" ID size when made of 1,500 denier Kevlar will have a
combined wall thickness of about .040" so that the total wall
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thickness is about .135", a significant amount smaller than
the .253" wall thickness of the hose of figure 1. Thus, in
the hose of figure 2 the combined thickness of the two braid
layers 18 and 19 is about 53% of the thickness of the core
tube 11. Moreover, this figure 2 hose as just described for
1/4" ID size will have an actual burst .....................
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strength of about 26,000 PSI and will be substantially more
~ flexible than the comparable hose of figure 1 construction.
i The 26,000 PSI actual burst strength is nearly twice the
I calculated burst strength of 14,044 PSI for a single braid hose
5 1 thus indicating that the burst pressure is shared substantially
i equally by the two braids. The calculated burst strength in
this instance is for the braid and does not include the burst
strengths of the cover and core tubes which are ignored in 'l ;
i arriving at the foregoing conclusion because they constitute a
10 1 relatively small portion of the total burst strength.
1The Kevlar yarn imparts greater radial and axial
dimensional stability to the hose when subjected to fluid
pressure or mechanical strain tha~n hoses with reinforcement
t~a~
~ I of regular Nylon, Dacron, Rayon, and other non-metallic fibrous~
¦ materials heretofore used because it has a substantially higher
¦ modulus and a smaller elastic elongation value than those other
¦ materials. Thus, regular Nylon, for example, has an elastic
elongation of about 4% at room temperature whereas that of
~ Kevlar is about 1%. The latter permits sufficient expansion
20 ~ of the first braid to permit substantial sharing of the load by
l the second braid but the expansion is less than that of the
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regular Nylon so that there is less chance of the hydraullc
system having a spongy feel.
I On the other hand, because the Kevlar elastic elonga-
~ tion value of about 1% is materially greater than the value for
! stainless steel, which is about .2%, the expansion in volume
! under fluid pressure of hose with Kevlar reinforcement is not as
restricted as with the stainless steel braid. Therefore, there
,, is more cushioning of the system against destructive hydraulic
3 0 1,1l shock.
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Although only one particular hose construction using
Kevlar reinforcement has been illustrated and thus far described
Kevlar yarn may be used in other hose constructions. Thus, the
¦ core tube 11 may be of any elastomeric material, examples of l ~
¦ which may be synthetic rubber or a flexible plastic such as j - :
Nylon, urethane, or the like. The reinforcement may be either ~ .
spirally wrapped or knitted instead of braided and may be of
one or more layers. The sheath 15 may be of any other flexible
plastic or synthetic materials, or it may be omitted. Likewise,
¦ the various layers need not be bonded for all purposes, or only
¦ se ected layer~ may be bonded.
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