NZ228924A

NZ228924A - Vibration damper containing slightly crosslinked rubber

Info

Publication number: NZ228924A
Application number: NZ228924A
Authority: NZ
Inventors: Akihiko Ogino; Mitsuaki Maeda; Yoshihide Fukahori
Original assignee: Bridgestone Corp
Priority date: 1988-05-02
Filing date: 1989-04-28
Publication date: 1990-12-21
Also published as: JPH02113138A; JP2832983B2; FR2630796A1; FR2630796B1

Description

<div class="application article clearfix" id="description"> 22 8 9 2 4 Priority Date(s): . *. ........ Complete Specification Filedf^-s?1. Class: 1 ■ iii«»* g,???. . .?. MJm.- Publication Date: ... 2.1.PKW9Q P.O. Journal, No: ... 1332 Patents Form No. 5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION DAMPER AND DAMPER STRUCTURE f/We, BRIDGESTONE CORPORATION/ A corporation organized under the laws of Japan, of 10-1/ Kyobashi 1-Chome/ Chuo-Ku/ Tokyo/ JAPAN hereby declare the invention, for which ^/we pray that a patent may be granted to fffe/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - 1 - (followed by page la) 228924 r DAMPER AND DAMPER STRUCTURE o FIELD OF THE INVENTION AND RELATED ART STATEMENT The present invention relates to a damper which absorbs the vibration and earthquake motion (collectively (O referred to as vibration hereinafter) transmitted to machines and structures. More particularly, it is concerned with a damper and damper structure which utilize the viscoelastic properties of very slightly crosslinked rubber having a very low degree of crosslinking to produce the damping effect. Dampers have long been known as a means to reduce vibration applied to machines and structures by an earthquake. Their ability to absorb vibrational energy is derived from the material of which they are constructed. They fall into two main groups; those which utilize the plastic effect of a metal (such as lead) and other materials, and those which utilize the viscous effect orf oil. A disadvantage of the conventional damper utilizing the plastic effect is that it produces very little damping effect when the deformation is small, in which case the deformation is elastic deformation. On the other hand, a disadvantage of the conventional damper utilizing the viscous effect of oil is that it has to be large in size if it is to produce a considerable r - la- (followed by page 2) 22 8 9 2 4 damping effect. An additional disadvantage is that the handling of oil needs care, the fabrication is difficult, and the complex maintenance work is required for use over a long period of time. OBJECT AND SUMMARY OF THE INVENTION It is an object of the present invention to provide an ideal viscoelastic damper and damper structure which are free of the above-mentioned disadvantages and characterized by the following. (1) They are constructed of a material which retains its maximum viscous effect. (2) They are so constructed as to permit the constituent material to fully exhibit its viscous effect (damping effect) . (3) They can be produced by easy molding and fabrication. (4) They can be handled with ease. . " (5) They can be produced at a very low cost. The damper of the present invention is constructed, at least partly, of very slightly crosslinked rubber formed by crosslinking a rubber compound incorporated with a crosslinking agent in an amount corresponding to 1-7 0 wt% of the minimum amount of crosslinking agent in common practice, the very slightly crosslinked rubber having a hysteresis ratio (h50) of 0.25 and above measured at the 50% tensile deformation at 25"C. 22 8 9 24 The damper structure of the present invention is made up of the above-mentioned damper and a damping device in which the former is enclosed. In order to eliminate the disadvantages of the conventional viscous damper and to obtain the ideal viscous damper having the above-mentioned characteristics (1) to (5), the present inventors carried out comprehensive studies on the durability, production cost, and maintenance of the damper. As the result, it was found that the damper produces an extremely high damping effect when it utilizes the high damping performance (high hysteresis loss performance) of very slightly crosslinked rubber having a very low degree of crosslinking. The present invention was completed on the basis of this finding. Needless to say, rubber materials are used in the completely crosslinked state except some special thermoplastic elastomers. Only when crosslinked, rubber materials come to have their elastic properties of restoring their original form after large deformation. Therefore, rubber materials with incomplete crosslinking are expected to have a low elastic modulus and strength and poor durability and adhesion and to cause troubles such as foaming during processing. For this reason, no one has ever ' ' ! ' *\< -v V ' *■- : " "• fT' ^ / 22 8 9 24 thought of using a rubber product in the very slightly crosslinked state for a long period of time, as in the case of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing the first embodiment of the damper of the present invention. Fig. 2 is a perspective view showing the second embodiment of the damper of the present invention. Fig. 3 is a perspective view showing the third embodiment of the damper of the present invention. Fig. 4 is a perspective view showing the fourth embodiment of the damper of the present invention. Fig. 5 is a perspective view showing the fifth embodiment of the damper of the present invention. Fig. 6 is a perspective view showing the sixth embodiment of the damper of the present invention. Fig. 7 is a perspective view showing the seventh embodiment of the damper of the present invention. Fig. 8 is a perspective view showing the eighth embodiment of the damper of the present invention. Fig. 9 is a perspective view showing the ninth embodiment of the damper of the present invention. Fig. 10 is a perspective view showing the tenth embodiment of the damper of the present invention. - 4 - .. -1^ \ - ■ - ■ 22 89 24 Fig. 11 is a perspective view showing the eleventh embodiment of the damper of the present invention. Fig. 12 is a perspective view showing the twelfth embodiment of the damper of the present invention. Fig. 13 is a sectional view showing the thirteenth embodiment of the damper of the present invention. Fig. 14 is a sectional view showing an embodiment of the damper structure of the present invention. Fig. 15is a perspective view showing another embodiment of the damper structure of the present invention. Fig. 16 is a graph showing the stress-strain curve of uncrosslinked rubber. Fig. 17 is a graph showing the stress-strain curve of the material. Fig. 18 is a sectional view showing another embodiment of the damper structure of the present invention. Fig. 19 is a sectional view showing further another embodiment of the damper structure of the present invention . DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is a detailed description of the present invention. At first, the rubber material used for the damper of the present invention will be explained. - 5 - ^2 8 9 2 4 The rubber material used in the present invention basically embraces all rubber materials which can be crosslinked with a crosslinking agent. Preferred rubber materials include ethylene-propylene rubber (EPR, EPDM), nitrile rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (CIR), chloroprene rubber (CR), natural rubber (NR), isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), acrylic rubber (AR), ethylene-vinyl acetate rubber (EVA), polyurethane (UR), silicone rubber (SiR), fluororubber (FR), chlorosulfonated rubber (CSM), and chlorinated polyethylene (CPE). According to the present invention, special rubber is used which is very slightly crosslinked so that it has a sufficiently low crosslink density. This special rubber is formed by crosslinking a rubber compound with a very small amount of crosslinking agent which is equivalent to 1-70% of the minimum amount of crosslinking agent used in common practice. The very slight crosslinking is achieved by incorporating a rubber compound with a controlled amount of crosslinking agent as explained in the following. In general, the optimum amount of crosslinking agent (or the optimum crosslink density) is limited with some allowance for individual rubber compounds, so that the resulting rubber product has the necessary performance such as 22 8 9 24 elastic modulus, strength, fatigue resistance, adhesion, and restoring force. On the other hand, the crosslink density of rubber is determined by the total amount of sulfur (or organic peroxide) and crosslinking accelerator (which are collectively referred to as "crosslinking agent" hereinafter), because crosslinking is usually accomplished by using (1) sulfur as a major ingredient in combination with a crosslinking accelerator, (2) a small amount of sulfur and a large amount of crosslinking accelerator, or (3) an organic peroxide. Rubber materials vary in physical properties depending on the crosslinking (or vulcanizing) conditions. Commercial crosslinking agents for a large variety of rubber compounds are shown in "Kogyo Zairyo" Vol. 29, No. 11 (1981), pp. 37-136 (published in Japan). According to this literature, individual rubber compounds are cross-linked with an average amount and minimum amount of cross-linking agent as shown in Table 1. The amount is expressed in phr (parts by weight for 100 parts by weight of rubber). Table 1 22 8 9 Rubber Average amount of crosslinking agent (phr) Minimum amount of crosslinking agent (phr) IR 3.0 2.75 SBR 2.75 2.70 BR 2.4 1.30 NR 3.1 3.0 NBR 3.5 1.75 CR 1.0 0.8 IIR 3.0 2.75 EPR 3.5 2.72 EPDM 3.0 2.1 AR 1.5 1.0 SiR 0.75 0.55 FR 3.0 1.5 CSM 2.5 2.5 CIR 1.0 1.0 CPE 4.0 4.0 UR 8.0 3.0 CIR : halogenated butyl rubber For a rubber compound to be made into a rubber product having a balanced performance, it should be incorporated with an optimum amount of crosslinking agent, as mentioned above. This optimum amount corresponds to the average amount given in Table 1. On the other hand, "the - 8 - L 2 8 9 24 minimum amount" in Table 1 applies to a special case in which the crosslinking agent is used in a small amount purposely. According to the present invention, the rubber shown in Table 1 should be incorporated with a crosslinking agent in an amount equal to 1-70 wt%, preferably 5-60 wt%, and more preferably 10-50 wt% of the minimum amount. Such a small amount of crosslinking agent gives rise to the very slightly crosslinked rubber for the damper of the present invention, which has the characteristic properties defined by (i) below. (i) The hysteresis ratio (h50) at the 50% tensile deformation at 25*C is greater than 0.25, preferably greater than 0.30, more preferably greater than 0.4. The hysteresis ratio (hso) is the ratio of area "OABCO" to area "OABHCT in the stress-strain curve (at a pull speed of 200 mm/min) shown in Fig. 17. In addition, the damper of the present invention should preferably have the characteristic properties defined by (ii) below. (ii) The glass transition temperature (Tg) is outside the range of -10'C to 30"C and the storage modulus (E) at -10'C and 30"C for repeated deformation of 0.01% at 5 Hz are such that their ratio (E at -10'C to E at 22 8 9 2 4 30 °C) is lower than 10, preferably lower than 7, and more preferably lower than 5, and most desirably lower than 3. The above-mentioned rubber materials may be used alone or in combination with one another in the present invention. In addition, they may be incorporated with additives such as filler, tackifier, slip agent, antioxidant, plasticizer, softening agent, low-molecular weight polymer, and oil which are commonly used for rubber processing to impart desired hardness, loss characteristics, and durability according to the object of use. Where the rubber materials are required to maintain the desired performance over a long period of time, they should be stabilized by adding a proper antioxidant, polymerization inhibitor, anti-scorching agent, etc. and/or by modifying the polymer itself by hydrogenation, etc. Examples of the additives are give below. (a) Filler: Flaky inorganic fillers such as clay, diato-maceous earth, carbon black, silica, talc, barium sulfate, calcium carbonate, magnesium carbonate, metal oxide, mica, graphite, and aluminum hydroxide; granular or powdery fillers such as metal powder, wood chips, glass powder, ceramics powder, and - 10 - 22 8 9 24 n O polymer powder or granules; and natural and artificial short fibers and long fibers (such as straw, wool, glass fiber, metal fiber, and polymer fiber), which are intended for rubbers and resins. (b) Softening agent: Aromatic, naphthenic, and paraf-finic softening agents for rubbers and resins. (c) Plasticizer: Ester-type plasticizers such as phthalic ester, mixed phthalic ester, ester of dibasic aliphatic acid, glycol ester, ester of fatty acid, phosphoric ester, and stearic ester; epoxy-type plasticizers; and other plasticizers for plastics. Phthalate-, adipate-, sebacate-, phosphate-, polyester-, and polyester-type plasticizers for NBR. (d) Tackifier: Coumarone resin, coumarone-indene resin, phenol-terpene resin, petroleum hydrocarbon, and rosin derivative. (e) Oligomer: Crown ether, fluorine-containing oligomer, polybutene, xylene resin, chlorinated rubber, polyethylene wax, petroleum resin, rosin ester rubber, polyalkylene glycol diacrylate, liquid rubber (such as polybutadiene, styrene-butadiene rubber, butadiene-acrylonitrile rubber, and polychloroprene), silicone oligomer, and poly-a-olefins. - 11 - 22 8 9 24 (f) Slip agent: Hydrocarbon-type slip agents such as paraffin and wax; fatty acid-type slip agents such as higher fatty acid and hydroxy fatty acid; fatty acid amide-type slip agents such as alkylene bisfatty acid amide; ester-type slip agents such as lower alcohol ester of fatty acid, polyhydric alcohol ester of fatty acid, and polyglycol ester of fatty acid; alcohol-type slip agents such as aliphatic alcohol, polyhydric alcohol, polyglycol, and polyglycerol; and metal soap; and mixtures thereof. As known well, a rubber material in the uncrosslinked state is a viscous organic polymer and hence exhibits a marked damping effect. The present inventors filed Japanese Patent Applications (183196/1986, 234897/1986, and 157191/1987) for the anti-seismic device incorporated with a damper that utilizes the high damping capacity of uncrosslinked rubber. A disadvantage of uncrosslinked rubber is that it has a considerably high modulus as long as it is deformed slightly but it sharply decreases in modulus when it is greatly deformed (strained), as shown in Fig. 16. Therefore, it does not provide strength necessary for rubber products. - 12 - 11 8 9 2 4 On the other hand, a rubber material comes to have a high elastic modulus and strength (which lead to a high restoring force) when it is sufficiently crosslinked (or given a large number of crosslink points). Crosslinking, however, brings about a sharp decrease in damping performance (hysteresis loss). The damper of the present invention has both the high hysteresis of rubber in the uncrosslinked state and the outstanding mechanical properties of rubber in the cross-linked state, because it is made of special rubber having specific characteristic properties attributable to the low crosslink density resulting from the use of a small amount of crosslinking agent. Therefore, the damper of the present invention has the following advantages over the conventional viscous damper which employs oil. (1) It is possible to select the temperature dependence and rate dependence of the hysteresis loss characteristics according to the properties of the individual rubber materials. (2) Easy molding. (3) Easy handling and easy execution. (4) Easy maintenance. (5) Low cost. (6) High damping effect and small size. - 13 - 22 8 9 In addition, the damper of the present invention is free of the disadvantages involved in the plastic damper ana has much better characteristic properties than the conventional plastic damper. Moreover, it is free of the disadvantage involved in uncrosslinked rubber that the elastic modulus sharply decreases as the deformation increases. In other words, the present invention provides a new outstanding damper which exhibits both the high hysteresis of rubber in the uncrosslinked state and the superior mechanical properties of rubber in the crosslinked state. The damper of the present invention is used as a core member of the damper structure of the present invention. The damper structure finds use as an anti-seismic bearing, vibration isolator, fender, etc. The damper and damper structure of the present invention will be effectively used in broad application areas such as building, construction, mechanical engineering, office machines, household machines, automobiles, bicycles, aircraft, vessels, sporting goods (shoes), etc. which need vibration isolation and noise reduction. The damper and damper structure of the present invention will be applied to the anti-seismic device and damping device for buildings which are now in the limelight . - 14 - 22 89 24 The invention will be explained in more detail with reference to the experiment examples and working examples which follow. Experiment Example Two kinds of very slightly crosslinked rubbers were prepared according to the formulation shown in Table 2. They were tested for hysteresis ratio (h50) at the 50% tensile deformation at 25 "C, tensile strength (breaking strength), storage modulus E, and elongation (%) at break. The results are shown in Table 2. It should be noted that the rubber specimens Nos. 1 and 2 are suitable for use as the damper of the present invention because they have a hysteresis ratio (h50) higher than 0.25. Table 2 No. 1 2 Composition (parts by weight) NR 50 BR 50 Carbon black 85 DCPD * 60 Phenolic resin 30 Sulfur 0.45 EPDM 100 Graphite 150 Aromatic oil 20 Sulfur 0.45 hM 0.55 0.48 E (kg/cm2) 1020 250 Elongation at break (%) 100 and up 100 and up * DCPD: dicyclopentadiene - 15 - 22 8 9 2 4 The damper of the present invention can be constructed in various ways as shown in the drawings. The dampers are broadly divided into three classes according to their construction. (A) Dampers of simple construction made of the very slightly crosslinked rubber as the major constituent. (B) Dampers of composite construction made of the very slightly crosslinked rubber and a hard material. (C) Dampers of composite construction in which the damper (A) and/or (B) is combined with hard plates. The dampers (A) are further divided into the following four subclasses. (A-l) Dampers of monolithic construction of desired shape which are made of the very slightly crosslinked rubber alone. They may be a rectangular prism (as shown in Fig. 1) or cylinder (as shown in Fig. 2). Their shape may be properly selected according to the object of use. (A-2) Dampers of multilayered construction which are made of the very slightly crosslinked rubber of different kinds (in rubber type, compounding, and degree of cross-linking) . The multiple layers may be arranged vertically, horizontally, or coaxially. The multilayered construction also includes the macroscopic uneven dispersion of rubber components of different kinds. With this construction, the dampers can exhibit any desired performance (such as - 16 - 22 8 9 24 elastic modulus, failure characteristics, and hysteresis). Examples of this construction are shown in Figs. 3, 4, and 5. The dampers 3, 4, and 5 shown in these figures are made up of layers a2, a2, ... a„ arranged horizontally, vertically, or coaxially. The individual layers are made of the very slightly crosslinked rubber which varies in type of rubber, compounding, and degree of crosslinking. (A-3) Dampers of composite construction which are made of the very slightly crosslinked rubber and ordinary rubber. In this construction, the outside or inside of ' the very slightly crosslinked rubber is partly covered or combined with the ordinary rubber (referred to as "highly crosslinked rubber") which is formed according to the average formulation shown in Table 1. In the example shown in Fig. 6, the damper 6 is made up of the very slightly crosslinked rubber a (forming a core) and the highly crosslinked rubber b (forming a cover thereon). In the example shown in Fig. 7, the damper 7 is made up of the highly crosslinked rubber b (forming a lattice frame) and the very slightly crosslinked rubber a (filling the space of the lattice frame). In another example, the very slightly crosslinked rubber may contain the highly crosslinked rubber dispersed therein. - 17 - 22 8 9 2 4 The highly crosslinked rubber used for this construction may be incorporated with additives such as filler, tackifier, slip agent, antioxidant, plasticizer, softener, low-molecular weight polymer, and oil which are commonly used for rubber processing. Furthermore, the highly crosslinked rubber may be used in combination with hard materials (mentioned in (B) later) to form a laminate. (A-4) Dampers of composite construction which are made of the very slightly crosslinked rubber and uncrosslinked rubber. In this invention, the uncrosslinked rubber can be partly used as supplement although it cannot be used as the principal constituent as mentioned above. An embodiment of this construction may be made up of the very slightly crosslinked rubber and uncrosslinked rubber dispersed therein. In the example shown in Fig. 8, the damper 8 is made up of the very slightly crosslinked rubber a and the uncrosslinked rubber c enclosed therein. (In this case, the uncrosslinked rubber may be replaced by the above-mentioned plasticizer, softener, tackifier, oligomer, or slip agent.) The dampers of composite construction (B) includes those which are formed by combining the damper (A-l), (A-2), (A-3), or (A-4) with a hard material. In the dampers 9, 10, and 11 of composite construction shown in Figs. 9, 10, and 11, the layers of the very slightly - 18 - 22 89 crosslinked rubber a and the layers of hard material d are laminated horizontally or vertically on top of the other or arranged alternately coaxially. The hard material, which is not specifically limited, includes, for example, metal, ceramics, glass, FRP, plastics, polyurethane, hard rubber, wood, rock, sand, and leather. The hard material may be in the plate, reticulated, corrugated, honeycomb, or woven form. The damper of composite construction (C) is shown in Fig. 12. The damper 12 is made up the body e of construction (A) or (B) and the hard plates f bonded to the top and bottom thereof. In actual application, one or more units of the damper 12 are arranged horizontally or vertically. Where two or more units are used, they may be of the same or different type and construction. The hard plates used in this construction include those of metal, ceramics, FRP, plastics, glass, wood, paper, polyurethane, and hard rubber. In the case of the construction containing hard plates f, the damper 13 shown in Fig. 13 is provided with a layer of highly crosslinked rubber b (of the same of different kind) to increase the bond strength between the very slightly crosslinked rubber and the hard plate. This layer may be replaced by a proper adhesive. - 19 - 22 8 9 2 4 The damper of the present invention is used in the following manner. (I) The damper of the above-mentioned construction (A), (B), or (C) is placed between the source of vibration and the body subjected to vibration. (II) The damper of the above-mentioned construction (A), (B), or (C) is enclosed in the other product. The latter case applies to the damper structure of the present invention. In this case, the damper is enclosed in an anti-seismic rubber bearing, rubber vibration isolator, fender, and any other product intended for damping. The damper structure thus constructed has multiple functions. An embodiment of the damper structure is shown in Fig. 14. In this embodiment, the damper 30 of the present invention is placed in the center of the anti-seismic rubber bearing composed of hard layers 21 and soft layers 22, and the entire structure is held between the upper and lower flanges 23. Another embodiment of the damper structure is shown in Fig. 15. In this embodiment, the damper 30 of the present invention is placed in the center of the rubber vibration isolator or fender 40. Other related embodiments are shown in Figs. 18 and 19. In the embodiment shown in Fig. 18, a through hole is made at the center of the damper 30 and it is filled with - 20 - 22 89 an elastoplastic body 31 which is preferably lead. In the (~*"N embodiment shown in Fig. 19, the core elastoplastic body is held between the fasteners 32 and 33 attached to the flanges 22 and 23. The fastener 32 is open downward and the fastener 33 is open upward, so that they hold the O upper and lower ends of the elastoplastic body 31. O - 21 - </div>

Claims

<div class="application article clearfix printTableText" id="claims"> WHAT fy'A'E CLAIM PS- WHAT IS CLAIISD IS:

1. A damper which is constructed, at least partly, of very slightly crosslinked rubber formed by crosslinking a rubber compound incorporated with a crosslinking agent in an amount corresponding to 1-70 wt% of the minimum amount of crosslinking agent shown in Table 1, said very slightly crosslinked rubber having a hysteresis ratio (hso) of 0.25 and above measured at the 50% tensile deformation at 25 *C.

2. A damper as claimed in Claim 1, wherein the rubber compound contains a crosslinking agent in an amount corresponding to 5-60 wt% of the minimum amount of cross-linking agent shown in Table 1.

3. A damper as claimed in Claim 1, wherein the very slightly crosslinked rubber has a hysteresis ratio (h50) of 0.30 and above measured at the 50% tensile deformation at 25 ' C.

4. A damper as claimed in Claim 1, wherein the very slightly crosslinked rubber is characterized by that the glass transition temperature <Tg) is outside the range of -10"C to 30"C and the storage modulus (E) at -10°C and 30°C for repeated deformation of 0.01% at 5 Hz are such that their ratio (E at -10 *C to E at 30 *C) is lmASr-'Uhaii 10. 22 8 9 2 4

5. A damper as claimed in Claim 1 which is made of the very slightly crosslinked rubber as the major constituent .

6. A damper as claimed in Claim 5 which is constructed of two kinds of very slightly crosslinked rubbers.

7. A damper as claimed in Claim 5 which is of multi-layered construction made of two kinds or more of very slightly crosslinked rubbers.

8. A damper as claimed in Claim 5 which is of composite construction made of very slightly crosslinked rubber and ordinary crosslinked rubber.

9. A damper as claimed in Claim 5 which is of composite, construction made of very slightly crosslinked rubber and uncrosslinked rubber.

10. A damper as claimed in Claim 5 which is of composite construction made of very slightly crosslinked rubber and hard material.

11. A damper as claimed in Claim 10 which is of multilayered construction made of very slightly cross-linked rubber and hard material.

12. A damper as claimed in Claim 1 which is provided with upper and lower hard plates. - 23 - 228024

13. A damper structure which comprises a damper and a vibration damping device in which said damper is enclosed, said damper being constructed, at least partly, of very slightly crosslinked rubber formed by crosslinking a rubber compound incorporated with a crosslinking agent in an amount corresponding to 1-70 wt% of the minimum amount of crosslinking agent shown in Table 1, said very slightly crosslinked rubber having a hysteresis ratio (h50) of 0.25 and above measured at the 50% tensile deformation at 25*C.

14. A damper structure as claimed in Claim 13, wherein the vibration damping device is an anti-seismic rubber bearing, rubber vibration isolator, or fender.

15. A damper structure as claimed in Claim 14, wherein the damper is placed at the center of the anti-seismic rubber bearing composed of hard layers and soft layers and is provided with the upper and lower flanges.

16. A damper structure as claimed in Claim 14, wherein the damper is placed at the center of the rubber vibration isolator or fender.

17. A damper structure as claimed in Claim 15, wherein the damper has a central through hole which'—is... filled with an elastoplastic body. - 24 <4

18. A damper structure as claimed in Claim 17, wherein the elastoplastic body is held between an upper fastener and lower fastener attached to the upper and lower flanges, respectively,.said upper fastener being open downward and said lower fastener being open upward, so that they hold the upper and lower ends of the elastoplastic body. BRIDGESTONE CORPORATION - 25 - </div>