Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
107799V
DEVICE FOR SEALING BETWEEN MEMBERS MOVABLE
; RELATIVE TO EACH OTHER
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This invention relates to a device for sealing between
members, which are movable relative to each other, preferably
:; between a piston rod and a surface surrounding the same in a
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piston rod passageway of a hydraulic cylinder, and which is
intended to be arranged in a groove in either member so as with
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a sealing portion to abut and seal against the other member.
In the field of hydraulics, the development shows a general
trend to increasingly higher working pressures in hydraulic
cylinders and similar means. Accordingly, the sealings to be
used in such means must meet high requirements. Working
pressures of approx. 170 kp/cm2 are usual to-day and may in
many machines amount to 200-300 kp/cm2. The conventional rubber
sealings of U-shape or in the form of O-rings, therefore,
meet the requirements only with ever increasing difficulty. ~`
In hydraulic cylinders and other means where high hydraulic
pressures are involved, therefore, preferably U-sealings of
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polyurethane or so-called compact sealings of different types
~' 20 are used both as piston sealing and piston rod sealing. The
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known compact sealings, ~hich are of single-acting as well as
double-acting design and made in one piece or, for simpler
mounting, in two pieces, usually comprise a sealing portion
- of a relatively soft material, preferably nitrile rubber, a
displacement guard in the form of a ring of a hard material,
preferably polyacetal plastic, which primarily has to prevent
displacement in the gap between the sealing groove and the
; sealing portion, and a fabric-reinforced layer for preventing
the softer material from being squeezed out between said
displacement-protective plastic ring and the member to be
sealed. Compact sealings of fabric-reinforced rubber have as
main disadvantages poor wear properties and high sensitivity
, to damages on the piston rod. At the sealing types, which
often are of great length, excess temperatures may easily
occur and cause damages on the sealing. The advantages of
these sealings lie in the possibility of dividing them and in
their good sealing effect even at low pressures and low tem-
peratures.
U-sealings of polyurethane show as main disadvantages,
20 that they seal poorly at low pressures and low temperatures,
and that it is probably impossible to divide such a sealing.
The polyurethane sealings, however, can be made tight at
normal pressures and temperatures, and their wear properties
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~` are distinctly better than those of compact sealings.
Compact sealings are to-day applied to a large extent
as piston rod sealings, because they have a short installation
length and provide an acceptable sealing effect.
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1C3 77990
The disadvantage of the piston rod sealing of com-
pact type of to-day is its service life, which is considerably
shorter than that of the corresponding piston sealing. The
piston rod sealing, therefore, must be exchanged at shorter
intervals, and in connection therewith the equipment mounted
thereon must be dismantled.
Such dismantling, which in most cases is very
troublesome and expensive, can be avoided by the alternative
- design of a two-piece sealing. Two-piece piston rod sealings
10 as they are constructed to-day, particularly those with
short installation dimensions, are weak and do not satisfac-
- torily meet the requirements. It is, therefore, one of the
most important objects desired in the field of hydraulics to
; solve this problem and at the same time eliminate the other
said shortcomings of the different sealing types.
The object of the present invention is, therefore,
' to solve the aforesaid problems and thereby bring about a
sealing, particularly for piston rods and the like, which
simultaneously satisfies all requirements on an effective
piston rod sealing, which can be manufactured in two pieces
as well as in one piece, which has a short installation
- length, provides with sufficient safety a slight leakage, has
a long service life and causes less friction losses than
known piston rod sealings of the two-piece type. The sealing,
furthermore, should be easy to mount, seal effectively at high
and low temperatures and high pressures and thereby also
eliminate displacement damages.
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`~ - 1077990
In accordance with the present invention, a sealing
assembly for sealing space between an inner and an outer
member movable relative to each other, the outer member of
which has a groove to receive the assembly, comprises a sealing
element having a sealing portion which is provided with at
least two inwardly facing sealing ridges arranged in mutually
separated radial planes, and a radial supporting portion integral
with and situated at one end of said sealing portion. The seal-
ing ridges are formed with a comparatively steep flank facing in
one axial direction of the sealing element and decreasing in
height in the other axial direction at an acute angle. An
annular pressure means of elastic material is placed, in use,
between the sealing portion and the bottom of the groove to
urge the sealing ridges of the sealing portion into sealing
relationship with the other member. Also, a support ring abuts
the ~upporting portion of the sealing element to prevent axial
displacement of said element. The sealing element of the assembly
is divided by a dividing cut extending through the sealing portion
and the supporting portion, and consisting of two axial partial
j~ 20 cuts having a staggered relationship and communicating with
opposite ends of the sealing element, and a third partial cut
connecting inner ends of the axial cuts and located at one of said
sealing ridges approaching the peak of and closer to the forward
one than the rearward one of said sealing ridges.
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1077990
The in~ention is described in ~reater detail in
the following, with reference to the accompanying drawings, in
which
Fig. 1 is a section through a piston-cylinder means
provided with a piston rod sealing according
to an embodiment of the invention selected
by way of example,
Fig. 2 is a section on an enlarged scale through the
sealing proper,
Fig. 3 is a section through a sealing ring comprised
in the sealing according to the invention and
slightly modified in relation to the sealing ~ -
ring shown in Fig. 2, and
Figs. 4 and 5 show how the sealing ring is to be
divided.
In Fig. 1, the designation 1 refers to a cylinder with
an associated piston, and 2 designates a piston rod, for which
a passage is included in the rear portion 3 of the cylinder
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' which is provided with a cover 4 consisting, for example, of
two halves and maintained in place by means of screws (not
shown). In a groove 5 in said rear portion 3 a sealing with
: the general designation 6 according to the invention is
arranged. At the embodiment shown, thus, the sealing acts as
a piston rod sealing. It is, however, not restricted thereto,
but may be modified so as to be applicable also in other con-
nections, for example when pressure prevails on both sides, as
will appear from the following.
The embodiment of the invention shown as a piston
rod sealing comprises a sealing ring 7, which consists of a
sealing portion
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- 8 with axial extension and a ~upporting portion 9 with radial
extension, corresponding substantially to the depth of the groove
5. The sealing portion 8 has a sealing surface lO so deslgned
that it makes only line contact with the piston rod 2 in more
than one radial plane. This line contact is established thereby
~ that the sealing portion 8 is provided with several ridges ll,
,' edges or the like extending all about said portion. Said ridges
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, have a relatively steep flank 12 at the forward side i.e. toward
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the pressure side and decrease in height toward the rearward side,
~o which is more or less pressure~free, at an acute angle, so that
- a space is formed between the ridges ll of the sealing portion.
In Fig. 2 the angle between the flank of the ridges and the
piston rod is shown to be approx. 90, but at other embodiments
, this angle may be made smaller, as shown in Fig. 3 where said
~, angle is approx. 70, or greater, i.e. the flank is made undercut.
` The angle should be chosen between l and 15, preferably about
; 7. The number of ridges can be varied and is not restricted
to the number shown in the Figures. The distance between the
ridges may be varied, too.
The sealing ring 7, of which the sealing portion 8 and
supporting portion 9 preferably are made integral, consists of a
rubber material or a relatively soft plastic material and prefer-
ably polyurethane, which renders an optimum combination of freedom
from settling and wear resistance in the sealing portion and
thereby malntains the edges sharp.
, Polyurethane, however, is unsuitable at low temperatures,
becau5e
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1(~779~
it then looses its desirable properties. In order to compen-
sate for this deficiency, the sealing according to the inven-
tion is provided with a pressure member 13, which is shown in
the form of an O-ring of elastic material, preferably nitrile
rubber, pre-stressed between the sealing portion 8 and the
bottom of the groove 5. This ring solves the low temperature
problems and at the same time provides very good low pressure
properties, because it was very surprisingly found, that the
O-ring even at very low pressures shows very little leakage,
due to its prestressing-compression together with the oil-film
breaking sealing edges 11 on the sealing portion 8. It was
hereby to a pretty large extent succeeded to combine the pro-
perty of the known O-ring of adjusting to large movements
; and heavy wear with the capacity of the known compression -
sealings of sealing at low pressures, thick oil and low tem-
peratures.
In order to prevent displacement at very high pres-
sures and to facilitate the dividing, the sealing according
to the invention also comprises a support ring 14, which is
located on the same side as the supporting portion 9 of the
sealing ring and co-acts therewith. The support ring 14, which
has about the same radial extension as the supporting portion
9 of the sealing ring and a contact surface corresponding
` thereto, consists of a relatively hard and elastic material,
which also must be plastic for being able to compensate for
wear and defects of varying kind. The material used for the
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support ring is a thermoplastic polyester,
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for example the material which is registered with the trade mark
"Hytrel". This material performs in an extraordinary way the
disp]acement function in co-action with the sealing ring 7 of
polyurethane, which at the embodiment shown has L-shape.
In addition to the very low friction owing to the line
contact and in addition to the satisfactory sealing owing to the
support by the pressure member 13, the oil-film breaking sealing
edges 11 show the further advantage, that the sealing according
to the invention can be divided without thereby causing a greater
leakage than with an integral sealing. The dividing should be
carried out in such a manner, that the dividing cutting shows
two axial partial cuttings 15, 16 of opposedly directed spaced
relationship, and one radial partial cutting 17 uniting said
two axial partial cuttings and located between two ridges 11 so
as to lie closer to the forward ridge than to the rearward ridge,
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as shown in Figs. 4 and 5. It will also be clear from referring
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to Figures 4 and 5 that the axial partial cuts 15 and 16 are at
right angles to the outer edges of the sealing and supporting
' portions, which edges form the top and bottom of Figure 4, and
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that the third partial cut connecting these axial cuts extends
;~ circumferentially and parallel to these outer edges. Also, it
will be apparent that the third partial cut is located close to
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- the uppermost point of the intermediate sealing ridge, and closer
to this uppermost point than to its lowermost point. As regards
the dividing of the support ring, the dividing cutting may have
substantially any extension, but at the mounting of the sealing
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in a groove it is to b~-observed that the dividing cutting of
the support ring is located offset in relation to the dividing
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cutting of the sealing ring. For this purpose, the sealing ring
`'~ 30 according ~o th embodiment shown is provided at the surface of
; the supporting pcrtion 9 facing toward the support ring with a
~; bos3 18, and in the support ring a recess 19 is so placed in
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1077990
.' relation to the dividing cutting that at the mounting of the
- sealing, with the bo~s inserted into
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107~7990
the recess, the dividing cuttings of the sealing ring and
support ring are disposed offset with the necessary distance
from each other, and by means of the recess and boss a guid-
ance of the position of the rings relative to each other is
obtained. It is, however, possible at other embodiments to
abandon said boss and recess.
In the drawings, the sealing according to the in-
vention is shown in the form of a piston rod sealing, i.e. the
sealing is shown single-acting, but may also be made double-
acting, most simply by arranging two sealings mirror-inverted
relative to each other. This is possible because the sealing
j edges on one sealing half permit oil to pass in one direction
i to the next sealing half, but not in the opposite direction.
A double-acting sealing obtained in this manner, of course, has
a relatively long installation length which, however, can be
reduced by giving the sealing ring U-shape, with space for
;~ one or more pressure members in the form of O-rings, and with
sealing ridges of the aforedescribed design arranged on both
halves of the sealing portion, so that the ridges on one half
~ 20 are directed to the ridges on the other half. The present
`~ invention is not restricted to the embodiment described above
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and shown in the drawings, but may be modified in many different
ways within the scope of the invention as it is defined in
the claims.
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