CA1077990A

CA1077990A - Device for sealing between members movable relative to each other

Info

Publication number: CA1077990A
Application number: CA206,653A
Authority: CA
Inventors: Stig Stenlund
Original assignee: Skega AB
Current assignee: Skega AB
Priority date: 1973-08-28
Filing date: 1974-08-09
Publication date: 1980-05-20
Also published as: IT1016889B; ZA745180B; ATA681274A; SE7311651L; FI249974A; BR7406838D0; YU230974A; SE375591B; AU7237974A; FR2245888A1; GB1464452A; PL110748B1; DK144197C; CS178825B2; NO146613B; DE2440124A1; JPS5645026B2; BE818971A; DD115189A5; DK144197B

Abstract

ABSTRACT OF THE DISCLOSURE
A sealing ring for sealing between relatively movable outer and inner members, and particularly around the piston rod of a hydraulic cylinder, and which is effective at high pressures while having a long service life and causing relatively low friction. The sealing ring which is usually mounted in a groove in the piston rod passageway of a cylinder, has a sealing portion with an inwardly facing surface having ridges making line contact in at least two separate radial planes with the piston rod,the ridges being formed with a comparatively steep flank facing in a forward axial direction and decreasing in height in the rearward axial direction at an acute angle. The sealing portion is pressed against the piston rod by an elastic pressure member (for example an O-ring), and the sealing portion at one of its edges is provided with a radial flange extending perpendicularly to the ridged surface of the sealing portion and which contacts a fixed supporting ring forming one side of the groove. The sealing ring is divided by a dividing cut extending through the sealing portion and the radial flange and consisting of two axial partial cuts having a staggered relationship and communicating with opposite ends of the sealing ring, and a third circumferentially extending partial cut connects the axial cuts and is located between two sealing ridges and closer to the forward one than the rearward one of the sealing ridges.

Description

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 . .,:, piston rod passageway of a hydraulic cylinder, and which is intended to be arranged in a groove in either member so as with ....
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 ,,.
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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, 1077~90 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 :
~` 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.

- 2 -,' 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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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 ,. . .
' 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 :
, have a relatively steep flank 12 at the forward side i.e. toward ,:, 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 1'' i ~;

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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 . . .
support ring is a thermoplastic polyester, ~, .

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',,' ~' m77sso 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, .. . _ _ _ _, ., , . _ .. . .... .. . . .
as shown in Figs. 4 and 5. It will also be clear from referring _ . .. . . . .
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 ,"
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 :.,; .
- 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 , .
in a groove it is to b~-observed that the dividing cutting of the support ring is located offset in relation to the dividing .,~, .
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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.' 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 .~
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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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A seal assembly for sealing a space between an inner and an outer member movable relative to each other of which said outer member has a groove to receive the assembly, comprising an annular sealing element having a sealing portion which is provided with at least two inwardly facing sealing ridges arranged in mutually separated radial planes,said sealing ridges being formed with a comparatively steep flank facing in a forward axial direction of the sealing element and decreasing in height in the rearward axial direction at an acute angle, and a radial supporting portion integral with and situated at one end of said sealing portion, and annular pressure means of elastic material placed, in use, between the sealing portion and the bottom of the groove in one member to surround the sealing portion and to urge said sealing ridges of the sealing portion into sealing relationship with said other member, and a support ring, which, in use, abuts the supporting portion of the sealing element to prevent axial displacement of said element, wherein at least the sealing element of the assembly is divided by a dividing cut extending through the sealing portion and the supporting portion of the sealing element and consisting of two axial partial cuts having a staggered relationship and communicating with opposite ends of the sealing element, and a third circumferentially extending partial cut connecting said axial cuts and located between two sealing ridges,approaching the peak of and closer to the forward one than the rearward one of said sealing ridges.

2. A seal assembly according to claim 1, wherein said third partial cut is closer to the uppermost point of a sealing ridge than its lowermost point.

3. A seal assembly according to claim 1, comprising three sealing ridges, characterized in that said third partial cut connecting the two axial partial cuts is located close to the uppermost point of the intermediate sealing ridge.

4. A seal assembly according to any of claims 1 to 3, characterized in that the third partial cut connecting the two axial partial cuts extends in parallel with the outer edges of the sealing and supporting portions.

5. A seal assembly according to any of claims 1 to 3, char-acterized in that the axial partial cuts are arranged at right angles in relation to the outer edges of the sealing and supporting portions.

6. A seal assembly according to any of claims 1 to 3, characterized in that the third partial cut connecting the two axial partial cuts is arranged approximately in the middle of the sealing portion.