Patent Publication Number: US-2004045233-A1

Title: Sealing system and gasket therefor

Description:
[0001] The invention relates to a sealing system comprising an at least substantially cylindrical tube and at least two sealing collars at least partially made of an elastic material, which are arranged round the tube in spaced-apart relationship for sealing confinement by collaring of the tube in a bushing which is co-axial with said tube.  
       [0002] Such a sealing system is generally known. In the fitted position of the known system, an air space is present between the sealing collars, which air space is bounded by the bushing and, as already said before, the sealing collars. In the case of a fire, for example on one side of the bushing, the excellent thermal insulation properties of said air space prevent the other side of the bushing becoming (too) hot for some time. In practice it has become apparent, however, that the temperature in the air space can run up so high when there is a fire that the sealing collars are forced out owing to the increased pressure prevailing within the air space, with all its adverse consequences as regards fire safety. After all, if the known system is fitted in a ship&#39;s deck, for example, fire can freely propagate through the bushing and into the ship when the sealing collars are forced out and the sealing function is thus lost.  
       [0003] The object of the invention is to overcome the above-indicated drawback of the prior art, and in order to accomplish that objective, a sealing system of the kind referred to in the introduction is characterized in that the spacing between the sealing collars is less than 25 mm, with said sealing collars comprising an expandable material, in such an amount and of such a composition that the sealing collars will expand in the case of a fire, in such a manner that they will become wedged in the bushing. Preferably, the spacing between the sealing collars is less than 20 mm, in particular less than 15 mm, more in particular 10 mm or less. As a result, the thermal insulation properties of the air space will be retained in the case of a fire, whilst eliminating the risk of the pressure running up so high therein that the sealing collars are forced out, partially because of the fact that the sealing collars will swell as a result of the expansion reaction, thus fixing themselves in position in the bushing. At the very most, the sealing collars can be forced out over a distance of a few millimetres in the case of a fire, but they will remain substantially in position in such a case, as a result of which their sealing function is retained.  
       [0004] In one preferred embodiment of a sealing system according to the invention, the sealing collars comprise circular outer ribs and circular inner ribs, which outer ribs have an outside diameter which is larger than the inside diameter of the bushing, and wherein the inside diameter of the inner ribs is at most substantially equal to the outside diameter of the tube. In particular, the sealing collars each comprise at least two shell members, whose abutting boundary surfaces extend at least substantially in axial direction, wherein the rear flanks, seen in the direction of insertion, of the outer, serrated ribs extend in radial direction and the inner ribs are arranged in pairs in the radial area of the outwardly extending tips of the outer serrated ribs. The inner ribs of the sealing collars are preferably trapezoidal in shape, seen in the direction of the axial longitudinal section.  
       [0005] The advantages of the above aspects will be explained in more detail hereafter in the description of the figures.  
       [0006] The invention also relates to a sealing collar apparently suitable for use in a sealing system according to the invention. 
     
    
    
     [0007] The invention will now be explained in more detail with reference to a figure shown in a drawing, which schematically shows a sealing system according to the invention in perspective view.  
     [0008] The figure shows a sealing system  1 , comprising a metal (for example steel or copper) tube  2  of cylindrical cross-section, a bushing  3 , likewise made of a metal (for example aluminium or steel), which extends co-axially with the tube  2 , as well as two rubber sealing collars  4 . Said sealing collars  4  are fitted in spaced-apart relationship round the tube  2  in the annular space between the tube  2  and the bushing  3  for the purpose of retaining the tube  2  in the bushing  3  in a gastight and watertight manner. The bushing  3  is fitted in a steel ship&#39;s deck  6 , for example, or in any other wall, partition or the like.  
     [0009] Each sealing collar  4  of elastic rubber is preferably formed of two identical, shell-shaped collar halves  4 ′,  4 ″, whose abutting boundary surfaces extend in axial direction. The collar halves  4 ′,  4 ″ are provided with ribs  8  of right-angled triangular cross-section on the outer side and trapezoidal ribs  9  on the inner side. When the sealing collars  4  are forced into the annular space  5  and around the tube  2 , the ribs  8  thereof are compressed by the bushing  3 , as a result of which respective ribs  9  positioned opposite said ribs  8  will undergo a diameter reduction, so that they will press on the outer side of the tube  2  forcefully and sealingly. As a result of the pressures that are thus produced in the rubber, the abutting boundary surfaces of the collar halves  4 ′,  4 ″ of a sealing collar  4  are furthermore squeezed together sealingly, without external pressure means being required.  
     [0010] Extensive tests have shown that in the case of a fire, for example on one side of the ship&#39;s deck, the air space  7  that is present between the sealing collars  4  provides excellent thermal insulation, it is true, thus helping prevent excessive heating of the other side of the ship&#39;s deck  6 , but that the fire will cause the air temperature in the air space  7  to run up so high that the resulting increasing air pressure in the air space  7  will force the sealing collars  4  out of the annular space  5  in such a case. It stands to reason that the adverse effects will be incalculable in that case, since a seal is no longer provided as a consequence of the function of the sealing collars  4  being lost (after all, said sealing collars no longer surround the tube  2  in the annular space  5 ). It has become apparent that wrapping the bushing  3  in rock wool is not a suitable solution for keeping the temperature in the air space  7  within acceptable bounds in the case of a fire.  
     [0011] The invention is based on the hitherto unrealised insight that a solution for the phenomenon referred to above can be provided by selecting a spacing of less than  25  mm between the sealing collars  4 , and thus also a smaller length of the annular space  17 , and forming the sealing collars  4  of an expandable material, in such an amount and of such a composition that the sealing collars  4  will expand in such a manner that they will become wedged in the bushing  3  in the case of a fire. As a result, the thermal insulation provided by the air space  7  will not be lost when there is a fire, whilst the air pressure therein can at no time run up so high that the sealing collars are forced out of the annular space S. At the very most, the sealing collars  4  can be forced out over a width of one or more ribs  9  in the case of a fire, but the sealing collars  4  will remain substantially in position in such a case, as a result of which their sealing function is retained. The expandable rubber material of the sealing collars  4  comprises in particular expandable graphite. It has been proved by experiments that this graphite is extremely suitable for causing the sealing collars  4  to expand in the case of a fire.  
     [0012] Preferably, the spacing mm between the sealing collars  4  is less than 20 mm, in particular less than 15 mm, more in particular less than or equal to 10 mm.  
     [0013] The invention is not restricted to the above-described variant, but also other embodiments fall within the scope of the invention as defined in the appended claims.