NL8005796A - VIBRATION INSULATOR AND METHOD OF MANUFACTURE THEREOF. - Google Patents

Description

* i_— "N.O. 29.503 1

Vibration isolator, as well as a method for its manufacture.

The present invention relates to improvements in vibration isolator technology and more particularly to a new form of vibration isolators and a new method of manufacturing such a device.

A number of different types of vibration isolators are known. The present invention primarily relates to plate and tubular insulators, so called because the former type has a small length to diameter ratio and thus is relatively flat, while the latter type has a relatively long length to diameter ratio. For the present invention, such insulators usually consist of internal and external metal parts and a molded elastomer part which extends between and is bonded to the two metal parts. While this known form of construction has allowed the manufacture of insulators of different sizes and load ranges, the manufacturing process involves a number of steps, which add to the cost of the product and must be performed carefully due to product reliability. suitability. Among these steps are the important steps of cleaning the metal components, applying a bonding conditioner or adhesive to the metal parts so that they will adhere to the elastomeric part and then loading the molded components for the fabrication of the elastomeric part. The molded product also needs to be heated to effect and complete vulcanization of the elastomer. Third, a shear bond strength of about 2800 to 3500 kPa is desired to prevent separation of the elastomer from the metal parts and allow the insulator to meet technical requirements and withstand continued use. This level of shear bond strength can only be achieved through appropriate design and strict adherence to manufacturing requirements, including appropriate control of molding temperatures and pressures.

The main object of the present invention is to provide a new and improved method for the manufacture of plate and house type vibration shock insulators and new and improved forms of such insulators.

A second important object is to enable the manufacture of insulators of the type described in a manner which avoids the problems and limitations of the known manufacturing method or practically reduces δ Π Π ^ 7 Q 8 2.

Yet another object is to provide a method of manufacturing vibration and shock isolation insulators which is considerably faster and less expensive than methods of a similar purpose already in use.

These objectives are achieved by making the vibration and shock isolators of two different synthetic plastics using a co-injection molding process. One plastic is a rigid thermoplastic material; the other is a thermoplastic elastomer. The latter is injected after the rigid thermoplastic material. This order of injection is initiated to achieve an appropriate bonding of the two materials. Other features and many accompanying advantages of the present invention are described in detail or made clear by the following detailed description of preferred embodiments and other embodiments of the invention and the accompanying figures, in which Figure 1 is a side cross-sectional view of a vibration isolator. plate type tor, which is a preferred embodiment of the invention; Figures 2A-2C are cross-sectional views illustrating different positions of an injection molding device for use in the manufacture of the insulator of Figure 1, and Figures 3 and 4 are like cross-sections of two other embodiments of the invention.

According to Fig. 1, the article being illustrated is a plate type vibration insulator consisting of internal and external parts 2 and 4 and an intermediate part 6. Both internal and external parts are made of a practically rigid thermoplastic material, while the intermediate part is made of a thermoplastic elastomer. As used herein, the term "practically rigid thermoplastic material" refers to a solid practically rigid material, which has the property of melting (softening to the point of becoming a liquid) when heated to a suitable temperature and of curing and a solid dust and practically re-stiffening when cooled to room temperature, ie 21 ° C, and the term "thermoplastic elastomer" means a solid material which has the property of melting when heated to a suitable temperature of curing and becoming a solid which is resilient and behaves like an elastomer when cooled to room temperature. These 40 thermoplastic materials may consist of a single thermoplastic polymer product or a mixture of such products with or without additives such as dyes, plasticizers, antioxidants, stabilizers and other functional ingredients, which are suitably one or more modify more of the physical properties of the thermoplastic product (the thermoplastic products).

A further requirement of the present invention is that parts 2, 4 and 6 are formed by injection molding. As a result, the substantially rigid thermoplastic material and the thermoplastic elastomer must be made of molding materials which can be injection molded. The molding materials can largely consist of or be made of one or more polymers and / or one or more copolymers. In addition, the material used to manufacture parts 2 and 4 and the material used to form part 6 should be compatible in that they are able to bond together by melting, ie by contacting the materials when at least one is in a flowable state and then cooling the material in a flowable state until it has solidified and bonded with the other material. While parts 2 and 4 can be made from different mutually compatible materials that melt and solidify at the same or substantially the same temperatures, it is preferred that they be made from the same material. Preferably, parts 2 and 4 have a flexural modulus greater than 2,758,000 kPa, while part 6 is a low modulus soft thermoplastic elastomer with a durometer value on the Shore A scale between 35 and 85. For example, however, no limitation, parts 2 and 4 are made of polystyrene with a flexural modulus of about 3,206,000 kPa and part 4 is made of a butadiene-styrene compound having a durometer value on the 30 Shore A scale of 55.

Parts 2, 4 and 6 are indicated in the figures with sharply delineated boundaries since, as will be explained in more detail below, the interfaces between these parts are substantially free from any intermixing or diffusing of the thermoplastic materials.

According to Fig. 1, the internal part 2 has planar annular top and bottom surfaces 8 and 10, a cylindrical internal surface 12 defining an axial bore 17 and an external boundary represented as a surface of revolution, which cylindrical end sections 16 and 18 and includes a double curved intermediate section 20. The external 8 η n ^ 7 qr 4 part 4 serves as a flange for the insulator unit and has a cylindrical external surface 22 and an internal interface 24 represented as a cylindrical surface and parallel top and bottom surfaces 26 and 28, which are parallel are on the corresponding surfaces of the part 2 and extend at right angles to the centerline of the internal part. The external part 4 also has a plurality of mounting openings 5. The intermediate part 6 has internal and external sections 30 and 32, which are respectively bonded to the internal part 2 at its boundary section 18 and the internal part 4 at the internal boundary 24. , plus a twisted intermediate section 34, which extends between the internal part 2 and the external part 4. The intermediate section 34 is bonded to the internal part 2 at the boundary section 20. The intermediate section 34 acts as a spring to resiliently the internal part 2 to be placed in relation to the external part 4.

When the device of FIG. 1 is manufactured by the molding method described below, substantially no diffusion or mixing of one material into or with the other material will occur.

Moreover, there will be no or only minor deformations of one material by the other along the boundary areas. It has been determined by cross-sectional inspection of insulators such as those of Fig. 1 made in accordance with the present invention, with a scanning electron microscope with a magnification of 20,000, that the interfaces between the butadiene-styrene thermoplastic elastomer and the polystyrene parts have an interface area (the area of diffusion or intermixing of one material in or with the other) with a thickness in the order of magnitude of only 2.5 x 10 "cm. Nevertheless, the bond between the elastomer and the non-elastomer parts is sufficiently strong for the device to behave satisfactorily as an insulator.

With reference to Figs. 2A-2C, the device of Fig. 1 is manufactured according to a preferred embodiment of the invention by means of a co-injection mold, comprising essentially three relatively movable mold members 36, 38 and 40 and a central part or core 42 bonded to the molding member 36.

As shown in Fig. 2A, the molding member 36 has a profiled inner end surface, which includes four different parts 44, 46, 48 and 50, while the molding member 38 has a flat inner surface 52 and a cylindrical inner surface 54. Molding member 40 has a profiled inner end surface, containing sections 56 and 58, and a cylindrical outer surface 60, which makes a precise sliding fit with the surface 54. The molding members are arranged such that when the molding members are in the closed position, the surfaces 50 and 5 52 fit together, while the surfaces 44 and 58 and column 42 form a first cavity 62 and the surfaces 48, 52 and the upper part of the surface 60 will form a second cavity 64. The molding member 40 has a central opening 66 in which the central column 42 makes a precise slip fit. A plurality of pins 68 mounted in the molding member 36 make precise sliding fits in the openings 70 in the molding member 38. The pins 68 serve as cores for forming the mounting openings 5. The molding members 36, 38 and 40 are adapted (by means not shown , however, known to those skilled in the art of injection molding) to move relative to each other along the axis of column 42 so that, as described below, the mold members 38 and 40 are separated and selectively movable to different positions along the axis relative to the molding member 36.

The vibration isolator, shown in Figure 1, is fabricated using the molding assembly of Figures 2A-2C by the following method. First, the molders 36, 38 and 40 are placed in the totally closed position shown in Fig. 2A (the first injection position) and a suitable liquid thermoplastic injection molding material, which can solidify to a rigid or nearly rigid solid (for example, poly-25 styrene) is injected into the mold cavities 62 and 64 through injection openings 74 and 76 to form the insulator parts 2 and 4. Then, the mold member 40 is retracted until the outer edge of its surface 56 is flush with one another with the surface 52 to form a third cavity 78 as shown in Fig. 2B (the second injection position). Then, a suitable liquid thermoplastic injection molding material, which can solidify to a solid material having the properties of elastomer (e.g., butadiene-styrene), is injected into the cavity 78 through one or more injection ports 80 to form the insulator part 6.

The injection stage is performed after the material injected into cavities 62 and 64 has solidified or is sufficiently viscous so that it will not be displaced or expanded by the material injected through port 18, yet is soft enough to bond elastomer material. Therefore, the second injection step is performed 40 while the material in the cavities 62 and 64 is still warm, however, after Q ft 7-Λ λ O j y y j 3 6 has started to solidify. By a suitable choice of materials, it is possible for the cavity 78 to be filled within one to three seconds after the cavities 62 and 64 have been filled and yet achieve a satisfactory bond between the elastomer and non-elastomer components. Finally, after the part 6 has solidified in the cavity 78, the molding members 38 and 40 are separated from the molding member 36 as shown in Fig. 2C, after which the finished insulator can be removed from the mold and set aside to be removed. to cool. Thereafter, the molding members are returned to their position as indicated in Figure 2A for the next molding cycle.

In the preferred embodiment of the invention, the insulator members 2 and 4 are formed from polystyrene, which solidifies with a flexural modulus of about 3,206,000 kPa and the insulator part 6 is made from a butadiene-styrene copolymer, which solidifies. with a durometer measured on the Shore A scale between 35 and 85 (depending on the spring ratio desired for the insulator), the polystyrene preferably being the material marketed by Shell under the trade name Shell DP-203 and the butadiene Styrene is the material marketed by Shell under the trade name Kraton 3000 series thermoplastic rubber. Suitable temperatures and pressures are determined by the properties of the materials used; i.e., the aforementioned polystyrene molding material is injected at a pressure of about 35,000 kPa at a temperature of about 200 ° C; the aforementioned butadiene-styrene mold-25 material is injected into the cavity 78 at a pressure of about 42,000 kPa and a temperature of about 200 ° C. The latter injection step should take place about 1 to 3 seconds after the injection of the polystyrene molding compound into cavities 62 and 64 has ended. The injection materials are maintained at a temperature of about 200 ° C during the two injection stages, but the mold is maintained at a temperature of about 38 to about 66 ° C during the molding process.

The mold is opened and the finished part is removed about one minute after the second injection step is completed. The shaped part is then set aside and cooled to room temperature before marking, testing and packaging. The finished products exhibit a shear bond strength between part 6 and parts 2 and 4 of at least 2800 to 3500 kPa and usually between about 4200 and 5600 kPa, compared to the usual bond strength of about 3500 kPa between the metal and 8005796 7 elastomer parts from conventional metal / elastomer insulators.

It should be noted that the injection of elastomeric material after the rigid material has been injected is critical. It has been determined that when the elastomer is injected simultaneously with or before the rigid material, a satisfactory insulator product cannot be obtained since the elastomer is unable to deform cavity 78 under the pressures to be used in the injection of withstand the rigid plastic material in the cavities 62 and 64. This is the case even when the elastomer is fully cured before the non-elastomer material is injected. Only when the elastomer injection is delayed until after the rigid plastic material has deposited enough or withstand compression under pressure to inject the elastomeric material, it is possible to obtain a sufficiently strong bond between the elastomeric and non-elastomeric components and also obtain the insulator parts exactly in accordance with the shape of the three mold cavities.

Another advantage of the invention is that the spring ratio of the insulator can be changed by modifying the composition and accordingly the durometer of the material used to form the intermediate part 6. Thus, for example, the Kraton molding material is available from Shell as Kraton 3226 for 35 durometer A scale, Kraton 3202 for 55 durometer A scale and Kraton 3204 for 85 durometer A scale. Other durometer values can be achieved by suitably mixing two or all three of the aforementioned Kraton materials or by adding or substituting other thermoplastic elastomers. The stiffness of parts 2 and 4 can be modified by mixing a small amount of elastomeric molding material with the polystyrene molding material. In this connection, it should be recognized that parts 2 and 4 need not be absolutely rigid; for some insulator applications, it may be sufficient or desirable that these parts be fairly rigid, i.e. partially rigid.

A further effective feature of the aforementioned preferred embodiment of the invention is that the molding materials are injected coaxially rather than biaxially as described in U.S. Pat. No. 3,950,483. It has been found that formation by coaxial injection is easier to perform and therefore results in a more reliable product.

Another advantage of the invention is that insulators of different shapes, sizes, and vibration isolating properties can be molded. Therefore, for example, the shape and / or the size of the intermediate part 6 can only be changed by modifying the different mold parts. Further, by way of example, by suitably forming the molding assembly, it is possible to form a flat insulator (Fig. 3) consisting of a cylindrical internal part 2A, a cylindrical external part 4A with a flat circular flange 92. and a cylindrical intermediate part 6A with flat end surfaces. Also, by way of example, the invention is adaptable to provide an axially stretched insulator 96 (Fig. 4), wherein the three parts 2B, 4B and 6B are all cylindrical and the length of part 6B is significantly greater than the internal radius. as well as its external radius. The two alternative forms of insulators have vibration isolation properties different from those of the unit of Fig. 1, even when made from the same materials as the latter.

Yet another advantage of the invention is that it can be carried out with a variety of thermoplastic injection molding materials. For example, the thermoplastic elastomeric injection molding material forming part 6 may contain or consist of a material other than butadiene styrene known to those skilled in the art. In this regard, it is noted that the term "thermoplastic elastomer" is one which is already known to those skilled in the art, as shown by Tobolsky et al., Polymer Science and Materials, p. 277, Wiley-Inter-science (1971); and that several such materials exist as described by A.A. Walker, Handbook of Thermoplastic Elastomers (1979).

Furthermore, by way of example, but not limited to, the rigid thermoplastic parts 2 and 4 may be made of acrylonitrile-butadiene styrene (ABS), polymethyl methacrylate (ple-30 xiglas), a polypropylene polymer and other materials readily available to those skilled in the art. as described, for example, in U.S. Patents 3,941,859, 3,962,154 and 4,006,116. The correct choice of materials will depend on the desired properties and compatibility of the elastomeric and non-elastomeric materials with regard to adhesion to each other.

Other modifications and advantages of the invention will be obvious to those skilled in the art.

8005796

Claims (18)

1. A vibration isolator, characterized by first and second concentric and substantially spaced parts, said first and second parts being made of a rigid thermoplastic polymer material and a third part extending between and attached to the first and second parts which third part is made of a thermoplastic organic elastomer material and is attached to the first and second parts by direct bonding of the thermoplastic organic polymer material. 2. Vibration isolator according to claim 1, characterized in that the third part is bound to the first and second parts as a result of a direct fusion of the thermoplastic elastomeric material and the thermoplastic polymeric material. Vibration isolator according to claim 1 or 2, characterized by bonded interfaces, wherein the third part is bound to the first and second parts with a thickness on the order of 2.5 x 10 6 cm. Vibration isolator according to claims 1 to 3, characterized by an external flange section formed by the first part and an internal slot section formed by the second part. Vibration isolator according to claims 1 to 4, characterized in that the third part is rotated in radial cross section. 6. A vibration isolator according to claim 4, characterized by a mid-center axis and wherein further the dimension of the second part measured parallel to the center line is considerably larger than the corresponding dimension of the first part. Vibration isolator according to claim 6, characterized in that the third part has an external part which is bonded to the first part, has an internal part which is bonded to the second part and has an intermediate part which connects the external and 30 bridges interior portions thereof, which exterior portion is bonded to and surrounded by the first member and which interior portion is bonded to and surrounds at least a portion of the second member. 8. Vibration isolator according to claim 7, characterized in that the intermediate section extends at an acute angle with respect to the center line. Vibration isolator according to claims 1 to 8, characterized in that the first and second parts are made of polystyrene with a flexural modulus greater than 2,758,000 kPa. 3005796 Vibration isolator according to claims 1 to 9, characterized in that the third part is made of a low modulus soft material with a durometer value on the Shore A scale between 35 and 85. Vibration isolator according to claim 10, characterized in that the third part is made of a copolymer of styrene and butadiene. Vibration isolator according to claims 1 to 11, characterized in that the first and second parts are tubular members. Vibration isolator according to claim 12, characterized in that the first part comprises a tubular section surrounding the third part and bound thereto and a flange section integrally formed with the tubular section. Vibration isolator according to claim 12, characterized in that the second part is longer than the first part and a part of the second part is the same size as the second part over the length of the second part. 15. A method of manufacturing a vibration insulator with (a) first and second concentric and reciprocally spaced parts formed from a substantially rigid thermoplastic non-elastomer material and (b) a third part formed from a thermoplastic elastomeric material and extending between and bonded to the first and second parts, characterized in that (1) the first and second parts are simultaneously injected into first and second mold cavities and (2) the third part between the first and second molds second parts injection molded, so that the thermoplastic elastomeric material from which the third part is formed will be directly bonded to the thermoplastic non-elastomeric material from which the first and second parts are made. Process according to claim 15, characterized in that the third part is formed after the thermoplastic polymer material has been deposited, but before it has reached its maximum hardness. Method according to claim 15 or 16, characterized in that the first and second parts are manufactured from polystyrene. 18. Process according to claim 15 or 16, characterized in that the third part is manufactured from a copolymer of styrene and butadiene. ssasss 8005796