Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/16—Sealings between relatively-moving surfaces
  • F16J15/166—Sealings between relatively-moving surfaces with means to prevent the extrusion of the packing
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/16—Sealings between relatively-moving surfaces
  • F16J15/32—Sealings between relatively-moving surfaces with elastic sealings, e.g. O-rings
  • F16J15/3204—Sealings between relatively-moving surfaces with elastic sealings, e.g. O-rings with at least one lip
  • F16J15/3208—Sealings between relatively-moving surfaces with elastic sealings, e.g. O-rings with at least one lip provided with tension elements, e.g. elastic rings
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/56—Other sealings for reciprocating rods

Definitions

• This invention relates to sealing rings, especially the kind suitable for use between reciprocating components including pistons and cylinders and also piston rods, cylinder heads and the like.
• a known type of sealing ring is that of the lip seal in which a sealing member has a contact surface of minimum axial extent that is pressed radially into engagement with a moving surface to be sealed.
• the narrow contact surface of this type of seal makes it an effective high contact pressure, low friction seal, but it is vulnerable to the intrusion of solid contaminants that can damage the sealing lip and cause leakage.
• sealing ring is that of the broad band, face contact type which may be rectangular in cross-section and has a broad annular face pressed radially into engagement with the moving surface, to be sealed.
• This type of sealing ring is less vulnerable to damage by solid contaminants because of its broader contact surface, but the contact pressure is lower and leakage can be produced by hydrodynamic effects between the contact surface and moving surface.
• British Patent No. 1438619 discloses a lip type seal comprising a polytetrafluoroethylene (PTFE) sealing member in which the lip is formed, and an elastomeric energising member that presses radially on the sealing member to urge the lip into contact with the moving surface to be sealed.
• PTFE polytetrafluoroethylene
• a recess is formed in the axial face of the seal at the high pressure end, and a wedge-like gap is provided between the sealing lip and the low pressure end of the seal so as to improve sealing and reduce leakage.
• the sealing member and energising member are shown as separate components or in one instance as an integral one-piece structure.
• An object of the present invention is to provide ah improved sealing ring of the broad band, face contact type.
• a sealing ring comprising a sealing member having a contact surface for engagement with a surface to be sealed and extending over at least 50 per cent of the axial extent of the sealing ring, and an elastomeric energising member for radially pressing the contact surface into engagement with the surface to be sealed, characterised in that the sealing member comprises a polymeric material possessing good wear resistance and a higher modulus of elasticity than the energising member at the operating temperature of the sealing ring, and in that the sealing member is bonded to the energising member over the area of contact therebetween.
• the presence of a bond between the sealing member and the energising member is essential and this is preferably effected across the whole of the area of contact between the members.
• the effect of the bond is to vary the stress distribution within the body of the sealing ring so that a peak contact pressure is produced between the sealing member and surface to be sealed at the low pressure end of the sealing ring.
• the manner in which the bond is achieved between the sealing member and energising member will vary depending on the respective materials of the members. It is envisaged that the bond may be formed either physically and/or chemically by methods known in the art.
• the cross-section of the sealing ring may vary depending on the use to which it is to be put in practice.
• the overall cross section is rectangular or square and advantageously the sealing and energising members are rectangular or square also, thereby providing a flat sealing surface to contact the body being sealed and with the bond being parallel to that surface.
• the sealing member is generally arranged in a coaxial configuration with respect to the energising member with the sealing member on the inner diameter in the case of an internal seal and on the outer diameter in the case of an external seal.
• the respective radial thicknesses of sealing member and energising member may vary depending on a number of parameters. However, it is preferred that the sealing member has a radial thickness of at least 10%, but no more than 70% of that of the energising member; most preferably this figure does not exceed 50%, for example from 20 to 35%.
• the sealing member and energising member for any 6 particular seal it is essential that the former has both good wear resistance and a higher modulus of elasticity than the latter at the operating temperature; it is preferred that the difference in modulus between the members is substantial.
• good wear resistance of the sealing member is also important.
• the preferred material for the energising member is natural or synthetic rubber in general; nitrile rubber such as nitrile butadiene rubber having been found to be especially useful.
• Preferred materials for the sealing member include polyurethanes.
• Figure 1 is a schematic axial section of a sealing ring according to one embodiment of the invention
• Figure 2 is a similar section to Figure 1 showing a sealing ring according to a second embodiment of the invention
• Figure 3 is a similar section to Figure 1 showing a sealing according to a third embodiment of the invention.
• Figure 4 is a graph of load (L) against deformation produced from a modulus test to select materials for a sealing ring according to the invention.
• Figure 5 is a graph showing the load distribution across the axial width of the sealing ring of Figure 1.
• FIG. 1 there is shown an internal sealing ring of the invention positioned in an annular groove 1 of a housing 2 and positioned about a rod 3 of circular cross section which in use reciprocates within the housing.
• the sealing ring 4 is of overall rectangular cross section and comprises two components, a sealing member 5 and an energising member 6, both also of rectangular cross section.
• the sealing member is made of polyether urethane and the energising member is made of nitrile butadiene rubber.
• the sealing and energising members have a good bond formed across the whole of the area of contact 7 therebetween, this bond being formed in situ during the manufacturing process.
• the size of the groove cross section is such that the sealing ring as a whole fills substantially the whole of the groove in a radial direction but leaves gaps 8, 9 on either side of the sealing ring in the longitudinal direction. Such a gap on at least one side of the sealing ring is generally necessary to cause the seals to operate at their optimum manner.
• the inner surface of the sealing member Prior to insertion of the rod 3, the inner surface of the sealing member is slightly proud of the groove so that some deformation and thus loading of the sealing ring occurs on insertion. After insertion, the inner contact surface 17 of the sealing member 5 is loaded into sealing engagement with the rod 3.
• a specimen in the form of a cylinder is used having a diameter of 16mm (with no positive variance allowed but a 0.2mm negative variance possible) and a height of 11mm (+ 0.2mm) and in increasing load applied to the top end of the cylinder to produce a strain at a rate of lmm/minute.
• results of such tests, and in particular plots of the applied load (L) versus strain (percentage deformation) (H) have shown that it is preferred for the results for the sealing member material to fall mainly above a line drawn between a point of 25 Kilograms Force (kgf) load, 5% deformation and a point of 120 kgf load, 30% deformation, as shown by X and Y in Figure 4; and that the results for the energising member should fall mainly beneath this line.
• the results for the sealing member and energising member are wholly above and below the line respectively, at least over the operating temperature range of the sealing ring.
• Typical modulus test results for the polyether urethane of the sealing member 5 are shown plotted as line A in Figure 4, and typical modulus test results for the nitrile butadiene rubber of the energising member 6, are shown plotted as line B in Figure 4, these results being obtained at room temperature.
• the test results for the same sample of polyether urethane as measured at 50 degrees C and 100 degrees C are also shown in Figure 4 as lines A' and A' ' . From this it is clear that the modulus approaches the standard line X - Y with increasing temperature but that it still lies above this line.
• elastomeric materials that is important in the context of the present invention, is that of stress relaxation or compression set.
• Stress relaxation is dependent on material, deformation, time, temperature, and fluid environment, and has to be allowed for in selecting the material of the sealing member so as to ensure that in the aforesaid modulus tests, the results fall above said load - deformation line X - Y.
• stress relaxation is less of a problem because of the lower modulus of elasticity of this member.
• the stress relaxation for the polyether urethane used in the modulus tests of Figure 4 is shown in Figure 4 as measured for 10 per cent deformation and 25 per cent deformation at both 50 degrees C and 100 degrees C.
• the specimen was compressed by 10 per cent or 25 per cent of its height and held compressed for three days, after which time the compression was removed and the height measured.
• the decrease in height as a percentage of the initial compressed height is a measure of compression set, which, assuming compression set is proportional to load, is taken as a measure of stress relaxation.
• good wear resistance of the sealing member 5 is also important. In addition to the determination of a preferred modulus of elasticity as described above, it is also preferred to determine good wear resistance of the sealing member material in accordance with a standard test and equate this with the load (L) of the modulus test above.
• the particular wear resistance test is that of DIN Standard 53516 which determines the weight loss of a given sample when moved in contact with a predetermined surface; hence a percentage volume loss (Wf) for this sample can be calculated to provide a load to wear ratio (L/Wf).
• the load to wear ratio (L/Wf) and the percentage strain should be in accordance with one or more and most preferably all the following equations for the sealing member:
• the load to wear ratio (L/Wf) and the percentage strain are as follows:
• a typical sealing ring such as illustrated in Figure 1 has a cross-section 8.05mm by 8.10mm, has the radial thickness of the sealing member 5 as 34 per cent of that of the energising member 6, has an internal bore adapted to fit a rod 3 of 60mm diameter, and has the sealing member 5 composed of the polyether urethane and the energising member 6 composed of the nitrile butadiene rubber for which test results are quoted above.
• This sealing ring was installed as a gland seal in a hydraulic piston employing the mineral hydraulic oil DT26 and was subject to an endurance test involving repeated operation of the piston rod in a cycle with pressures from 0 to 206 bar and an operating temperature of 59 degrees C.
• Figure 2 shows an external sealing ring of the invention positioned in an annular groove 10 on the outside surface of a piston 11 and in contact with the internal surface of a cylinder 12.
• the sealing member 13 and energising member 14, are made of the same materials as the sealing ring shown in Figure 1 and its mode of operation is largely identical.
• Figure 3 shows a sealing ring similar to that of
• FIG. 1 (the same reference numerals being used for equivalent components) except that a recess 15 is formed in the axial end face of the sealing ring 4 at the low pressure end and accommodates an anti-extrusion ring 16.
• sealing rings according to the invention can also be used as static seals between two relatively fixed members.
• polyurethane can be used for the sealing member in sealing rings according to the invention, including those prepared by the reaction of a polyol and an isocyanate together with a chain extender, and those prepared from prepolymers or by a "one shot” manufacture.
• typical polyols are polyethers, polyesters, polycaprolactones, polybutadienes and polycarbonates of various molecular weights.
• isocyanates are well known in the art and include toluene diisocyanate (TDI), diphenyl ethane diisocyanate (MDI), naphthalene diisocyanate (NDI), xylylene diisocyanate (XDI), dicyclohexylmethane diisocyanate (H MDI), hexa ethylene diisocyanate (HDI), cyclohexyl diisocyanate (CHDI) , para-phenylene diisocyanate
• TDI toluene diisocyanate
• MDI diphenyl ethane diisocyanate
• NDI naphthalene diisocyanate
• XDI xylylene diisocyanate
• H MDI dicyclohexylmethane diisocyanate
• HDI hexa ethylene diisocyanate
• CHDI cyclohexyl diisocyanate
• chain extenders are 1, 4 butane diol and trimethylol propane. Mixtures of any of the above substances may be employed when appropriate in the manner known in the art. Also the polyol isocyanate, and the chain extender, can be of varying functionality.
• compositions for the sealing member especially those suitable for higher operating temperatures are polyureas and acrylic monomer reinforced hydrocarbon elastomers.

Landscapes

• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Sealing Material Composition (AREA)
• Gasket Seals (AREA)
• Sealing Devices (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10638429

Family Applications (1)

Country Status (13)

Families Citing this family (18)

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• 1988
  • 1988-06-10 GB GB888813784A patent/GB8813784D0/en active Pending
• 1989
  • 1989-05-30 IL IL90455A patent/IL90455A0/xx unknown
  • 1989-06-01 GR GR890100363A patent/GR890100363A/el unknown
  • 1989-06-06 YU YU01164/89A patent/YU116489A/xx unknown
  • 1989-06-07 PT PT90781A patent/PT90781A/pt not_active Application Discontinuation
  • 1989-06-07 ES ES8901986A patent/ES2020811A6/es not_active Expired - Lifetime
  • 1989-06-07 ZA ZA894312A patent/ZA894312B/xx unknown
  • 1989-06-08 GB GB8913255A patent/GB2219636B/en not_active Expired - Fee Related
  • 1989-06-08 EP EP89906408A patent/EP0379536A1/en not_active Withdrawn
  • 1989-06-08 JP JP1506178A patent/JPH02504665A/ja active Pending
  • 1989-06-08 AU AU37473/89A patent/AU3747389A/en not_active Abandoned
  • 1989-06-08 PL PL27985289A patent/PL279852A1/xx unknown
  • 1989-06-08 WO PCT/GB1989/000639 patent/WO1989012191A1/en not_active Application Discontinuation
  • 1989-06-10 CN CN89104989A patent/CN1040667A/zh active Pending

Non-Patent Citations (1)

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