JP2005315417A - Metal gasket - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal gasket free of setting of its foaming rubber layer at a high temperature and with high pressure, free of contraction of the foaming rubber layer at a low temperature, and capable of sealing a cylinder block in good performance even if it involves blowhole(s) or asperity on the surface. <P>SOLUTION: The metal gasket to be interposed between a cylinder head and the cylinder block for sealing the two surfaces in between is composed of a pair of resilient base boards of metal where beads are formed at the peripheral edges of a plurality of openings for cylinder and a metal sheet having openings mating with the cylinder openings, wherein a foaming rubber layer whose thickness before foaming is 15-50 μm and foaming magnification is 2-4 times as large, is formed on each surface of at least one of the resilient base boards which is located on the cylinder block side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an improvement in a metal gasket interposed between a cylinder block and a cylinder head of an internal combustion engine.

  In an internal combustion engine, a sealing function is imparted by tightening a joint surface between a cylinder block and a cylinder head with a metal gasket interposed therebetween. In particular, the seal in the region surrounding the cylinder opening is important. If the seal in this portion is insufficient, the pressure in the combustion chamber is reduced and overheating appears. Therefore, as a metal gasket, a bead that is concentric with the cylinder opening is provided on an elastic metal substrate, and the peripheral edge surrounding the cylinder opening is made by utilizing the repulsive force of the bead generated when the metal gasket is tightened with a bolt. Gaskets configured to enhance the sealing function of the part are often used.

  In addition, the surface of the cylinder block or the cylinder head is often formed with a cast hole (a fine concave portion of the surface based on bubbles at the time of casting). In order to prevent leakage through these, foamed rubber is formed on the elastic metal substrate. A metal gasket having a layer is also known (see, for example, Patent Document 1 and Patent Document 2).

Japanese Utility Model Publication No. 5-86070 Japanese Utility Model Publication No. 6-32836

  However, in an elastic metal substrate having a foamed rubber layer, it is generally difficult to foam (particularly, the foaming ratio is twice or more) unless the rubber layer before foaming (unfoamed rubber layer) has a thickness of about 70 μm or more. Become. Further, since the rubber layer before foaming is thick, the foamed rubber layer sags under high temperature and high pressure, and the axial force of the bolt decreases. The expansion ratio is the ratio of the thickness of the rubber layer after foaming to the thickness of the rubber layer before foaming. Furthermore, in order to obtain a foamed rubber layer, there are generally a microcapsule method and a thermal decomposition method using a chemical foaming agent. However, since the foamed rubber layer obtained by the microcapsule method has a low foaming ratio, The effect is small, and most of the foamed rubber layer is closed-celled (bubbles with independent foamed cells), so the closed-cell shrinkage occurs at low temperature (under minus temperature), causing a decrease in the axial force of the bolt, and sealing. When the surface pressure is low, the foamed rubber layer is not completely immersed, so that there is a problem that the foamed rubber layer falls during use and the bolts relieve stress.

  Also, conventional foam rubber layers are generally excellent when there is a cast hole of φ1.5 mm or less on the seal surface or when the surface roughness is 12.5 Ra (10-point average roughness according to JIS B0601-1994) or less. However, it may not be possible to secure sufficient sealing performance.

  The present invention has been made in view of the above problems, and there is no settling of the foamed rubber layer under high temperature and high pressure, and there is no shrinkage of the foamed rubber layer at low temperature, and the cast block and the cylinder block with rough surface roughness are provided. However, an object is to provide a metal gasket that can seal well.

In order to achieve the above object, the present invention provides the following metal gasket.
(1) A metal gasket that is interposed between a cylinder head and a cylinder block and seals between both surfaces, and a pair of elastic metal substrates each having a bead formed at a peripheral edge of a plurality of cylinder openings, and the pair of elastic metals In a metal gasket composed of a thin metal plate sandwiched by a substrate via the bead and having an opening corresponding to the cylinder opening,
Foam foamed with a rubber layer thickness of 15 to 50 μm before foaming at a foaming ratio of 2 to 4 times on at least both surfaces of the elastic metal substrate disposed on the cylinder block side among the pair of elastic metal substrates. A metal gasket characterized in that a rubber layer is formed.
(2) A metal gasket that is interposed between the cylinder head and the cylinder block and seals between both surfaces, and a pair of elastic metal substrates each having a bead formed on a plurality of opening peripheral edges of the cylinder, and the pair of elastic metals In a metal gasket composed of a thin metal plate sandwiched by a substrate via the bead and having an opening corresponding to the cylinder opening,
Of the pair of elastic metal substrates, at least the surface of the elastic metal substrate disposed on the cylinder block side that contacts the cylinder block has a rubber layer thickness of 15 to 50 μm before foaming and is 2 to 4 times larger A metal gasket, wherein a foamed rubber layer foamed at a foaming ratio is formed, and a layer made of unfoamed rubber is formed on a surface in contact with the metal thin plate.
(3) The foamed rubber layer foams a rubber compound containing 20 to 70% by mass of a polymer having a Mooney value of 10 to 70 at a ratio of 20 to 70% by mass of a total amount of the rubber compound and 20 to 60% by mass of a thermal decomposition type chemical foaming agent. The metal gasket according to (1) or (2), wherein 80% or more of the foamed rubber layer is open-celled. The open cell is a bubble in which foam cells are continuously connected.

  The metal gasket of the present invention does not have a foamed rubber layer settling under high temperature and high pressure, does not shrink the foamed rubber layer at low temperature, and can be well sealed even in a cast block or a cylinder block with rough surface roughness.

  Hereinafter, the present invention will be described in detail.

  The metal gasket of the present invention includes a pair of elastic metal substrates each having a bead formed at a peripheral edge of a plurality of cylinder openings, and the pair of elastic metal substrates sandwiched by the beads to form an opening corresponding to the cylinder opening. And a thin metal plate. Specific examples are shown in FIG. 1 and FIG. 2 (XX sectional view of FIG. 1). The metal gasket is provided with a convex bead 2 formed along the peripheral edge of each cylinder opening 1 of a multi-cylinder engine. Each of the elastic metal substrates A1 and A2 and an annular portion that surrounds the peripheral edge of each cylinder opening 1 with a required width and is opposed to the bead convex side of the elastic metal substrates A1 and A2. It consists of a thin metal plate B. In addition, the metal thin plate B is preferably made of stainless steel, and the thickness is preferably 0.05 to 0.15 mm.

  The metal thin plate B is configured to be integrally connected at adjacent portions, and at that time, one of the elastic portions at a plurality of metal portions (symbol 6 in the figure; four places in the example in the figure) of the peripheral edge of the cylinder opening. It is fixed to the metal substrate A2.

  In the metal gasket of the present invention, the foamed rubber layer 10 is formed on the elastic metal substrate A2 at least on the cylinder head side (the lower side in FIG. 2) of the pair of elastic metal substrates A1 and A2. The rubber compound forming the foamed rubber layer 10 is preferably blended with a polymer having a Mooney value of 10 to 70 in a proportion of 20 to 70 mass% of the total amount of the rubber compound. More preferably, the Mooney value is 20 to 60, and the blending amount is 20 to 60% by mass of the total amount of the rubber compound. By blending such a polymer, it is possible to effectively suppress the sag of the foamed rubber layer 10.

  Although not shown in the drawings, the bends of the elastic metal substrates A1 and A2 may be formed starting from a bent portion having a radius of curvature (R) of 0.5 mm or more. A cast hole is often formed on the surface of the cylinder head or cylinder block (see FIG. 4), and a large cast hole exceeding φ1.5 mm exists therein. If the bent part of the bead is bent in a straight line to form a corner, the sealing performance is reduced due to the gap between the corner and the cast hole. The seal is secured by elastic deformation so that the curved starting point covers the casting cavity. Such a curved portion is effective in that the contact width with the cylinder head or the cylinder block surface obtained under the same tightening conditions can be increased by 1.5 to 2.0 times or more as compared with the conventional gasket. Here, the general elastic metal substrates A1 and A2 are made of stainless steel plates having a thickness of 0.2 to 0.3 mm, and in order to reliably cover a cast hole exceeding φ1.5 mm by elastic deformation, The curvature radius (R) of the curved starting point is set to 0.5 mm or more, preferably 1.5 mm or more. Such a bent portion can be easily formed by bending while applying R. By forming curved portions on the elastic metal substrates A1 and A2, in combination with the foamed rubber layer 10, compared to the case where only the foamed rubber layer 10 is used for a cylinder block or a cylinder head having a larger cast hole or surface density. This further increases the sealing effect.

  The type of polymer is not limited as long as the Mooney value is in the above range, and NBR, HNBR, fluororubber, EPDM, acrylic rubber, etc. that have been used for gaskets laminated with rubber layers can be used. NBR, HNBR Fluorine rubber is preferably used. Moreover, in order to give oil resistance to NBR, it is preferable to use an AN value (content of acrylonitrile group in NBR) of 39 to 52, more preferably 40 to 48.

  The rubber compound is blended with a heat decomposable chemical foaming agent. The kind of the heat decomposable foaming agent is not limited, but a foaming temperature of 120 ° C. or higher is preferable. Furthermore, the thing of 150-210 degreeC is the best. Moreover, it is preferable to mix | blend the compounding quantity in the ratio of 20-60 mass% of rubber compound whole quantity, More preferably, it is 15-35 mass%.

  Moreover, a vulcanizing agent and a vulcanization accelerator are added to the rubber compound. The vulcanizing agent is preferably blended in a large amount so as to increase the vulcanization density. In the case of sulfur vulcanization, it is preferably used at 1.5 to 4.5 phr. As the vulcanization accelerator, it is preferable to use a high-speed vulcanization accelerator that rises within 4 minutes until T50 in the curast data (150 ° C.). The time to T50 in the curast data (150 ° C.) is the time required for the degree of rubber vulcanization to reach T50 when vulcanized at 150 ° C. using a curast tester.

  The above rubber compound is dissolved in an organic solvent to form a coating solution, which is applied to the elastic metal substrate A2. The organic solvent is not limited as long as it can dissolve the above rubber compound, but 10 to 90% by mass of the ester solvent with respect to 10 to 90% by mass of an aromatic hydrocarbon solvent (such as ketone) such as toluene. What mixed in the ratio of -90 mass% can be illustrated. And said rubber compound is melt | dissolved in this organic solvent so that it may become solid content concentration 10-60 mass%.

  Although there is no restriction | limiting in the application | coating method of the coating liquid containing a rubber compound, The method which can control application | coating thickness is preferable and a skimmer coater, a roll coater, etc. are suitable. The coating thickness is 15 to 50 μm, and then the foaming agent is foamed by heat treatment at about 150 to 240 ° C. for 5 to 15 minutes to form a foamed rubber layer. At this time, the foaming ratio of the foamed rubber layer to be obtained is 2 to 4 times, and the foaming conditions such as the vulcanizing agent, the foaming agent, and the heating time to be used are adjusted so that 80% or more is open-celled. In order to freely change the expansion ratio to 2 to 4 times, it can be achieved by blending the polymer having the Mooney value described above, the vulcanizing agent and the foaming agent described above, and in particular, This expansion ratio depends on the Mooney value of the polymer and the vulcanization rate. This is because when the Mooney value of the polymer is low, the deformation of the polymer due to the foaming gas increases, and conversely, when the Mooney value is high, the deformation of the polymer due to the foaming gas decreases. With regard to the vulcanization speed, if the speed is high, vulcanization proceeds before the polymer expands and deforms by the foaming gas, so that the expansion ratio can be suppressed. Conversely, if the vulcanization rate is low, the foaming ratio increases because the deformation of the polymer by the foaming gas has priority over the curing rate of the rubber by vulcanization. For example, a polymer having a Mooney value of 20 to 40, a slow vulcanization accelerator (curast data: rise time to T50 by vulcanization at 150 ° C. of about 5 to 6 minutes), a foaming agent having a low foaming decomposition temperature, When combined, the expansion ratio becomes large, and conversely, a polymer having a Mooney value of 40 to 60 and a vulcanization accelerator with a fast vulcanization rate (curast data: rise time to T50 with vulcanization at 150 ° C. is about 1 to 3 minutes. ) And a foaming agent having a high foaming decomposition temperature, the foaming ratio is reduced. Thus, the expansion ratio can be freely controlled by the combination of the polymer, the vulcanization accelerator and the foaming agent.

  Such a foamed rubber layer 10 is prevented from sagging even under high temperature and high pressure, and maintains a good sealing property over a long period of time. In addition, sufficient sealing performance can be maintained even when there is a cast hole exceeding φ1.5 mm on the surface of the cylinder block or the surface roughness exceeds 12.5 Ra.

  On the other hand, an unfoamed rubber layer 11 is formed on the elastic metal substrate 1A on the cylinder head side (upper side in FIG. 2). Since the cylinder head is at a lower temperature than the cylinder block, it is not easily affected by heat, and a sufficient sealing property can be obtained even with the unfoamed rubber layer 11. However, since the cylinder head is also produced by casting in the same manner as the cylinder block, there is a possibility that a casting hole or a rough surface exists and the sealing performance is deteriorated. Therefore, in the metal gasket of the present invention, although not shown, it is preferable to form a foamed rubber layer similar to the above on the elastic metal substrate 1A on the cylinder head side.

  Further, as described above, the foamed rubber layer 10 is particularly effective for sealing performance against a cast hole or a rough surface of a cylinder block or a cylinder head, but sag occurs due to pressure contact with the metal thin plate B, and the sealing performance gradually increases. It is feared that it will drop. Therefore, as shown in FIG. 3, an unfoamed rubber layer 11 may be formed on the surface of the elastic metal substrate A2 on the metal thin plate B side instead of the foamed rubber layer. In the case where the foamed rubber layer is also formed on the elastic metal substrate 1A on the cylinder head side, similarly, the unfoamed rubber layer 11 is formed on the surface of the elastic metal substrate 1A on the metal thin plate B side.

  Examples The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited thereto.

(Examples 1-3, Comparative Examples 1-7)
[Preparation of sample]
As shown in Table 1, a rubber compound containing a polymer and a foaming agent was dissolved in a mixed organic solvent of toluene and ethyl acetate so as to have a solid concentration of 40% by mass to prepare a coating solution. And the primer process was given to the stainless steel plate which carried out the chromium-free process, and after apply | coating a coating liquid with a roll coater (application thickness is as Table 1), it heat-processed for 10 minutes at 210 degreeC, and obtained the sample.
Each sample was evaluated as follows.

[Evaluation methods]
1. Foaming ratio The foaming ratio was measured by measuring the thickness of the rubber layer before foaming and the thickness of the rubber layer after foaming with a micrometer, and calculating the foaming ratio from the following formula.

2. Measurement of open cell ratio A sample is immersed in water and vacuum degassed to replace water in the foam rubber layer cell. The test was conducted until the weight after substitution in water was constant, and the open cell ratio was calculated from the following formula.

3. Heat-resistant flow property The sample was allowed to stand under conditions of a surface pressure of 100 MPa and 150 ° C. × 22 Hr, and the appearance of the sample after the test was observed with a microscope and evaluated according to the following criteria.
Evaluation criteria ○: No rubber flow ×: With rubber flow

4). Torque down rate Each sample was subjected to the following test to evaluate the torque down rate.
(1) The sample was set on the flange, the bolt was tightened with a torque wrench, and the torque value (initial torque value) when tightened was measured.
(2) The sample was cooled to −35 ° C. in the state of (1). In that state, markings were made on the contact surfaces of the bolt and flange, and the bolt was removed.
(3) The bolt was tightened to the marking part again using a torque wrench, and the torque value at that time (torque value when cooled to -35 ° C.) was measured.
Further, the initial torque value (normal temperature) of the sample was compared with the torque value when cooled to -35 ° C., and the torque down rate was calculated from the following equation.

5). Seal Test Using Examples 1 to 10, gaskets of Examples 1 to 3 and Comparative Examples 1 to 7 having the shapes shown in Table 2 below were created. Each gasket was incorporated in the flange shown in Table 2 and evaluated as follows.
Cast hole seal test (1) As shown in FIG. 4, the sample was processed into a half bead shape having a height of 0.2 mm × width of 1.5 mm and a half bead having a center diameter of φ51.5 mm to form a gasket. It is assembled to a flange provided with a nest (φ2.5 mm × depth 2.5 mm) so that the cast hole is positioned at the half bead center, and tightened under the condition of a bead linear pressure of 10 N / mm.
(2) In the state of (1), air (200 KPa) was sent from the nozzle at the center of the flange, and the amount of leakage was measured.
・ Surface roughness seal test (1) The sample was processed into a half bead shape with a height of 0.2 mm × width of 1.5 mm and a half bead center diameter of φ51.5 mm to form a gasket, which was used as a flange with a surface roughness of 50 Ra. Then, the cast hole is assembled so that the position of the casting hole is φ51.5 mm and tightened under the condition of a bead linear pressure of 10 N / mm.
(2) In the state of (1), air (200 KPa) was sent from the nozzle at the center of the flange, and the amount of leakage was measured.

  The results of the above measurements and tests are summarized in Table 3. In the evaluation of each seal test, “◯” indicates that there is no air leak, and “X” indicates that there is an air leak.

  From Table 3, it can be seen that the sample of the example having the foamed rubber layer according to the present invention gives good results for any of heat-resistant flow, torque down rate, and seal test. On the other hand, the sample of Comparative Example 1 in which the rubber layer thickness before foaming is excessive has poor heat resistance flow properties, and the torque down rate is slightly inferior. Since the sample of Comparative Example 2 used a microcapsule-type foaming agent, the open cell rate was low and the torque down rate was also inferior. The sample of Comparative Example 3 having an excessive Mooney value has a low expansion ratio and inferior sealing performance. The sample of Comparative Example 4 having an excessively small amount of foaming agent also has a low foaming ratio and is inferior in sea performance. The sample of Comparative Example 5 having an excessively small amount of polymer has a low open cell ratio, inferior heat-resistant flow properties, and the largest torque-down rate. Since the sample of Comparative Example 6 uses a microcapsule type foaming agent and the rubber layer before foaming is excessive, the foaming ratio and the open cell ratio are the lowest and the sealing performance is poor. Since the sample of Comparative Example 7 does not use a foaming agent, it has poor sealing properties.

It is a top view which shows one Embodiment of the metal gasket of this invention. It is XX sectional drawing of FIG. It is a figure which shows other embodiment of the metal gasket of this invention along the XX cross section of FIG. It is a schematic diagram for demonstrating the test method of the cast hole seal test implemented in the Example.

Explanation of symbols

A1, A2 Elastic metal substrate B Metal thin plate 1 Cylinder opening 2 Bead 3 Opening 6 Fixing part 10 Foamed rubber layer 11 Unfoamed rubber layer

Claims (3)

A metal gasket that is interposed between a cylinder head and a cylinder block and seals between both surfaces, wherein a pair of elastic metal substrates each having a bead formed at a peripheral edge of a plurality of cylinder openings, and the pair of elastic metal substrates In a metal gasket composed of a thin metal plate sandwiched between beads and having an opening corresponding to the cylinder opening,
Foam foamed with a rubber layer thickness of 15 to 50 μm before foaming at a foaming ratio of 2 to 4 times on at least both surfaces of the elastic metal substrate disposed on the cylinder block side among the pair of elastic metal substrates. A metal gasket characterized in that a rubber layer is formed. A metal gasket that is interposed between a cylinder head and a cylinder block and seals between both surfaces, wherein a pair of elastic metal substrates each having a bead formed at a peripheral edge of a plurality of cylinder openings, and the pair of elastic metal substrates In a metal gasket composed of a thin metal plate sandwiched between beads and having an opening corresponding to the cylinder opening,
Of the pair of elastic metal substrates, at least the surface of the elastic metal substrate disposed on the cylinder block side that contacts the cylinder block has a rubber layer thickness of 15 to 50 μm before foaming and is 2 to 4 times larger A metal gasket, wherein a foamed rubber layer foamed at a foaming ratio is formed, and a layer made of unfoamed rubber is formed on a surface in contact with the metal thin plate.   The foamed rubber layer is obtained by foaming a rubber compound containing a polymer having a Mooney value of 10 to 70 in a proportion of 20 to 70% by mass of the total amount of the rubber compound and a thermal decomposition type chemical foaming agent in a proportion of 20 to 60% by mass. 3. The metal gasket according to claim 1, wherein 80% or more of the foamed rubber layer is open-celled.

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