FR2468034A1 - VIBRATION ISOLATORS AND PROCESS FOR PRODUCTION BY CO-INJECTION MOLDING - Google Patents

Abstract

The invention relates to a vibration isolator. According to the invention, it comprises first and second concentric and substantially spaced parts 2, 4, made of a stiff thermoplastic polymer; and a third part 6 between the first and second parts, in an organic thermoplastic elastomer, glued or fixed to the first and second parts by direct bonding of the organic thermoplastic polymer. The invention applies in particular to insulators of the tubular type or of the plate type.

Description

The present invention relates to improvements

  to vibration isolator technology and more particularly to a new form of

  vibration and a new manufacturing process.

  A number of different types of vibration isolators are known. The present invention relates primarily to plate-type and tubular-type insulators, so-called because the first type has a small ratio of length to diameter and is thus relatively flat. while the last type has a

  relatively large ratio of length to diameter.

  Before the present invention, such insulators are

  usually have internal and external metal parts and a molded part made of an elastomer extending between the two metal parts and glued to them. While this well-known form of construction has enabled the manufacture of insulators with different dimensions and load ranges the manufacturing process involves a number of steps that add to the price of the product and must

  be carried out with care for the reliability of the product.

  Among these steps, there are the important steps of cleaning the metal components, from applying a bonding conditioner or adhesive to the metal parts

  so that they stick to the elastomer part and then to

  troductindes components in the mold for the manufacture of the elastomer part. The molded product must also be heated to effect and complete the vulcanization of the elastomer. Third, shear bond strength in the range of 27.58 to 34.47 bar is desirable, to prevent separation of the elastomer and metal parts and to allow the insulator to meet the requirements. and withstand prolonged use. This resistance threshold of shear bonding can only be obtained by good design and strict agreement with manufacturing requirements, including temperature control and temperature control.

molding pressures.

  The present invention has as its main object an improved method of manufacturing vibratiom / oke insulators of the plate type and of the tubular type, as well as the

  new and improved forms of such insulators.

  The second object of the present invention is to allow the manufacture of insulators of the type described in a way that avoids or substantially reduces the problems and limitations associated with the manufacturing method according to the prior art. Another subject of the present invention is a method of manufacturing insulators against vibrations and shocks, which is substantially faster and cheaper than processes having a similar object, already employed.

in the art.

  These objects are achieved by forming a vibration and shock isolator made of two different synthetic plastics using a co-injection molding process. A plastics material is a rigid hermoplastic material; the other is a thermoplastic elastomer. The latter is injected after the rigid thermoplastic material. This injection order is initiated

  in order to obtain a good collage of the two materials.

  The invention will be better understood and other purposes, features, details and advantages thereof

  will become clearer during the description

  explanatory text which will follow with reference to the accompanying schematic drawings given solely by way of example illustrating several embodiments of the invention and in which: - Figure 1 is a sectional side elevation of a plate type vibration isolator; according to a preferred embodiment of the invention; FIGS. 2A-2C are sections illustrating

  different positions of a set of a mold by injecting

  the insulator of Figure 1, and - Figures 3 and 4 are similar views of two

  other embodiments of the invention.

  Referring now to Figure 1, the article shown therein is a plate type vibration isolator, which consists of inner and outer parts 2 and 4 and an intermediate part 6. The inner and outer parts are made in a substantially rigid thermoplastic material, while the intermediate piece is made of a thermoplastic elastomer. In this

  description, the term "thermoplastic material substantially

  rigid "means a rigid and substantially solid material having the property of melting (softening to the point of becoming liquid) when heated to an appropriate temperature and hardening and becoming a substantially rigid solid again when cooled to temperature ambient, ie 21 0C, and the term "thermoplastic elastomer" means a solid material having the property of melting when it is heated to an appropriate temperature and harden and become an elastic solid and behaving like a elastomer when he

  is cooled to room temperature. These thermo

  plastics can be separated from a single thermoplastic polymeric substance or a mixture of these substances, with or without additives such as coloring agents, plasticizers, antioxidants, stabilizers and other functional ingredients advantageously modifying one or more of the properties

  physical or thermoplastic substances.

  In addition, according to the invention, the parts 2, 4 and 6 are formed by injection molding. Therefore, the substantially rigid thermoplastic material and the thermoplastic elastomer must be made of

  molding materials capable of being injection molded.

  The molding materials can consist or be formed, in the majority, of one or more polymers and / or one or more copolymers. In addition, the material used to make parts 2 and 4 and the material used to form part 6 must be compatible in the sense that they are capable of bonding or bonding to one another by fusion, that is to say by contact of the materials

2468034

  when at least one of them is in the fluid state and then cooling the material to the fluid state until it has solidified and forms a bond with the other material. While parts 2 and 4 may be formed of different mutually compatible materials that melt and solidify at the same or near the same temperatures, it is preferable that they be made of the same material. Preferably, the parts 2 and 4 have a modulus of flexion greater than 27580 bar while the part 6 is a soft thermoplastic elastomer with a low modulus, having a Shore durometer value with the scale A between 35 and 85. For example , but without limitation, the parts 2 and 4 can be made of polystyrene having a flexural modulus of the order of 32060 bars and the part 6 is made of a styrene-butadiene compound having a

  Shore durometer value at A scale of 55.

  Parts 2, 4 and 6 are illustrated in the drawings as having clearly defined limits because, as will be explained hereinafter in more detail, the interfaces between these parts are substantially devoid of any

  mixing or interdiffusion of thermoplastics.

  Referring again to FIG. 1, the inner part 2 has flat and annular upper and lower surfaces 8 and 10, an inner cylindrical surface 12 defining an axial bore 17 and an outer limit represented by a surface of revolution comprising extrusion sections. cylindrical 16 and 18 and an intermediate section 20 with double curvature. The outer member 4 serves as a flange for the insulator unit and has an outer cylindrical surface 22 and an inner boundary 24 represented by a cylindrical surface, and mutually parallel upper and lower surfaces 26 and 28, which are parallel to the corresponding surfaces of the the inner part 2 and which extend at right angles to the axis of the inner part. The outer part 4 also has a number of mounting holes 5. The intermediate part 6 has inner and outer sections and 32 which are respectively adhered to the inner part 2 by its limit section 18 and the piece 4 by its limit internal 24, plus a convoluted intermediate section 34 which extends between the inner part 2 and the outer part4. Intermediate section 34 is linked

  or glued to the inner part 2 at the limit section 20.

  The intermediate section 34 serves as a spring for elastically locating the inner part 4 with respect to the part

external 2.

  When the device of Fig. 1 is formed by the molding method described hereinafter, there is substantially no diffusion or mixing of material in or with each other. In addition, there are only minor deformations or not at all, from one material to another, along the boundary regions. It has been determined, by inspecting the cross-sections of insulators such as those of FIG. 1 according to the invention, with a scanning electron microscope at a magnification of 20000, that the boundaries between the styrene thermoplastic elastomer parts

  butadiene and polystyrene had a region of inter-

  face (the region of diffusion or mixing of a material in or with the other) of a thickness which. reached only about 25.4 X 10-6 mm. Nevertheless, the link between

  elastomer and non-elastomer parts are sufficiently

  strong enough for the device to work

satisfactory as an insulator.

  Referring now to FIGS. 2A-2C, the device of FIG. 1 is produced according to a preferred embodiment of the invention, by means of a coinjection mold which consists essentially of three relatively movable members. 36, 38 and 40, and a central portion or core 42 fixed to the member 36 of the mold. As can be seen in FIG. 2A, the member 36 has an internal contoured end surface which comprises four distinct parts 44, 46, 48 and 50 while the member 38 has a first flat inner end surface 52 and an inner surface The member 40 has an outer contoured inner surface including sections 56 and 58 and a cylindrical outer surface 60 forming a precise sliding fit with the surface 54. The mold members are arranged so that when in position closed, the surfaces 50 and 52 correspond to one another while the surfaces 44 and 58 and the upright 42 form a first cavity 62 and the surfaces 48, 52 and the upper portion of the surface 60 form a second cavity 64 The member 40 has a central orifice 66 o fits very precisely sliding the central upright 42. A number of pins 68 fixed in the member 36 adjust very precisely and The pins 68 serve as a core for forming the mounting holes 5. The members 36, 38 and 40 are adapted (by conventional means not shown but known to those skilled in the art. the material) to move relative to each other along the axis of the post 42, thus, as described above,

  the members 38 and 40 are movable separately and selectively

  at different positions along that axis, relative to

to the body 36.

  The vibration isolator of FIG. 1 is manufactured using the molding assembly of FIGS. 2A-2C according to the following method. First, the members 36, 38 and are placed in the fully closed position shown in FIG. 2A (first injection position), and a suitable thermoplastic injection molding material capable of solidifying into a rigid or nearly rigid solid (like polystyrene) is injected into the cavities 62 and 64 through the injection ports

  74 and 76 to form parts 2 and 4 of the insulator.

  Then, the member 40 is removed until the outer edge of its surface 56 is flush with the surface 52, to form a third cavity 78 as is

  illustrated in Figure 2B (second injection position).

  Next, a suitable thermoplastic injection molding liquid material capable of solidifying into a solid material having the properties of an elastomer (such as butadiene-styrene) is injected into the cavity 78 through one or more injection ports 80 in order to This injection step is carried out after the material injected into the cavities 62 and 64 has solidified or become sufficiently viscous not to be displaced or expanded by the material injected through the orifice, but soft enough to stick

  or bind to the elastomer. Thus, the second stage of injection

  yours is done while the material in the cavities 62 and 64 is still hot but after it is taken as a solid. By a suitable choice of materials, it is possible for the cavity 78 to be filled in as little as one to three seconds after filling the cavities 62 and 64, while obtaining a satisfactory connection between the elastomer and non-elastomer parts. . Finally, when the piece 6 has taken a solid in the cavity 78, the members 38 and 40 are separated from the member 36 as ox + could see it in Figure 2C, and then the insulator

  finished can be removed from the mold and set aside to cool.

  Then, the mold members are returned to the position shown in Figure 2A for the next molding cycle. In the preferred embodiment of the invention, parts 2 and 4 of the insulator are molded of polystyrene which solidifies in order to have a flexural modulus of the order of 32060 bars, and the workpiece

  6 of the insulator is formed of a styrene copolymer

  butadiene which solidifies in order to have a Shore A hardness of between 35 and 85 (depending on the desired elasticity rate for the insulator), the polystyrene preferably being a material sold by Shell under the trade name ShelU DP-203 and styrene-butadiene being the material sold by Shell under the trade name Kraton 3000 series thermoplastic rubber. Temperatures and

  appropriate pressures are determined by the characteristics

  In fact, the polystyrene is injected at around 344.73 bar and the styrene-butadiene is injected into the chamber 78 at about 413.68 bar, all at 1990C. The last injection step should occur about one to three seconds after completing the injection of the polystyrene molding compound into the cavities 62 and 64. The injection materials are maintained at a temperature of the order of 1990C for both injection steps, but the mold is maintained at a temperature of the order of 38 to about 661C during the molding process. The mold is open and the finished part is removed

  about one minute after the end of the second injection step.

  The molded part is then set aside and allowed to cool to room temperature before labeling, examination and packaging. The finished products exhibit shear bond strength between part 6 and parts 2 and 4 of at least 27.58 to 34.47 bar and usually in the range of 41.37 to 55.16 bar compared at the typical bond strength of 34.47 bar between metal and elastomer parts

  traditional metal / elastomer insulators.

  It will be noted that the injection of the elastomer after injection of the rigid material is critical. It has been determined that if the elastomer is injected at the same time or before the rigid material, a satisfactory insulator can not be obtained because the elastomer was unable to resist the deformation in the cavity 78 under the pressures to be used to inject the material. rigid plastic material

  cavities 62 and 64. This is true even if the elasto-

  mother fully hardened before the non-elastomer material

  mother is injected. Only if the injection of -

  the elastomer is retarded until after the rigid plastic has taken enough to withstand deformation under the pressures required to inject the elastomer, it is possible to obtain a sufficiently strong bond between the elastomeric and non-elastomeric parts , and also that the elastomer parts are

  conform exactly to the shape of the three cavities of the mold.

  The present invention has another distinct advantage, in fact the elasticity of the insulator can be modified by modifying the compositicaet therefore the durometer of the material used to form the intermediate part 6. Thus, for example, the material of Kraton molding is sold by Shell under the name of Kraton 3226 for a durometer of 35 at A scale, of Kraton 3202 for a durometer of 55 at A scale and of Kraton 3204 for a durometer of 85 at A scale. Other values can be obtained by a suitable mixture of 2 or 3 of the

  Kraton materials above or by addition or substitution

  other thermoplastic elastomers. The stiffness of parts 2 and 3 can be modified by mixing a portion of the elastomer as a polystyrene molding material as a molding material. It should be noted that parts 2 and 4 must not be absolutely rigid; for some

  applications of insulators, it may be sufficient or desirable

  that these parts are simply straight, that is to say

semi-rigid.

  The above described process according to the invention has another advantageous characteristic, in fact the molding materials are injected coaxially rather than by the bi-axial process disclosed by I. Martin Spier in US Pat. No. 3,950,483. found that coaxial injection molding was simpler to perform

  and thus led to a more reliable product.

  Another advantage of the present invention is that insulators of various shapes can be formed.

  dimensions and having different characteristics of isolation

  vibrations. Thus, for example, the shape and / or the dimension of the intermediate part 6 can be modified simply by modifying the various parts of the mold. In addition, for example, by suitably molding the entire mold, it is possible to form a flat insulator 90 (FIG. 3) consisting of a cylindrical inner part 2A, a cylindrical outer part 4A with a flange flat circular 92, and

  of the cylindrical intermediate piece 6A having surfaces

  Similarly, for example also, the present invention can adapt to the formation of an axially elongate insulator 96 (Figure 4) o the three parts 2B, 4B and 6B are all cylindrical and o the length of the part 6B exceeds substantially its inner radius as well as its outer radius. These two other forms of insulators have different vibration isolation characteristics than the unit of FIG. 1, even if they are made of the same material. The present invention has other advantages, in fact it can be implemented. practical with a wide variety of thermoplastic injection molding materials. Thus, the thermoplastic injection molding elastomer constituting part 6 may consist of or consist of a material other than styrene-butadiene known to those skilled in the art. It will be appreciated that the term "thermoplastic elastomer" is a term already known to those skilled in the art, as evidenced by Tobolsky et al., Polymer Science and Materials, page 277, Wiley-Interscience (1971); and that there is a wide variety of these materials as revealed by A.A. Walker, Handbook

of Thermoplastic Elastomers (1979).

  Furthermore, by way of example but without limitation, the thermoplastic parts 2 and 4 can be made of acrylonitrile-butadiene-styrene (ABS), poly methyl methacrylate (Plexiglas), a propylene polymer and other materials which are obvious to those which are competent in the field, as taught for example in US Patent Nos. 3,941,859, 3,962,154 and 4,006,116.

  exact choice of the materials used will depend on the characteristics

  desired and the compatibility of the elastomer and non-elastomer with respect to the bonding to each other. Naturally, the invention is not limited to the embodiments described and shown which have been given by way of example. In particular, it includes all the means constituting technical equivalents

  described means as well as their combinations if these

  These are executed according to his spirit and implemented

  as part of the protection as claimed.

Claims (18)

  1. Vibration isolator, characterized in that it comprises: concentric first and second parts and   substantially spaced (2, 4) made of a thermoset polymer   plastic and stiff; and a third piece (6) extending and fixed between said first and second pieces, said third piece being made of a thermoplastic organic elastomer and attached to said first and second pieces by bonding   direct of said thermoplastic organic polymer.   2. An insulator according to claim 1, characterized in that the third aforementioned part is bonded to the first and second aforementioned parts as a result of a direct melting of the aforementioned thermoplastic elastomer   and said thermoplastic polymer.   3. Isolator according to claim 1, characterized in that it has connection interfaces o the third piece above is glued to the first and second pIoesprécitées   at a depth of the order of 25.4 X 10-6 mm.   4. Insulator according to claim 1, characterized in that it has an outer flange portion formed by the aforesaid first portion (4) and a portion forming   internal sleeve formed of the second part (2) above.   5. Insulator according to claim 4, characterized in that the third piece (6) above is convoluted in radial cross section.   6. Insulator according to claim 4, characterized in that it has a central axis, and in that, in addition, the dimension of the aforesaid second piece measured parallel   axis is substantially greater than the corresponding dimension.   of the first piece mentioned above.   7. The insulator as claimed in claim 6, characterized in that said third piece has an outer portion (32) fixed to said first piece, an inner portion (30) attached to said second piece, and an intermediate portion (34). connecting said outer and inner portions, said outer portion being bonded or bonded and surrounded by said first piece and said inner portion being bonded or bonded and surrounding at least a portion of said second piece. 8. Insulator according to claim 7, characterized in that the aforementioned intermediate portion extends to a   angle acute with respect to the aforementioned axis.   9. Insulator according to claim 1, characterized in that the first and second aforementioned parts (2, 4) are made of polystyrene having a flexural modulus greater than 27580 bars.   10. Insulator according to claim 1, characterized in that the third piece (6) above is made of a soft material having a low modulus, having a hardness Shore A from 35 to 85.   11. Insulator according to claim 10, characterized in that the third piece (6) above is made   of a copolymer of styrene and butadiene.   12. Insulator according to claim 1, characterized in that the first and second aforementioned parts (2, 4). are tubular organs.   13. Insulator according to claim 12, characterized in that the first piece (4) above is composed of a tubular section surrounding and connected to the aforesaid third piece, and a forming section forming a flange with said tubular section.   14. Insulator according to claim 12, characterized in that the second piece (2) above is longer than the first piece (4) above, and in that a portion of said second piece is coextensive with said second   piece along the length of said second piece.   15. A method of producing a vibration isolator having (a) first and second concentric pieces   and spaced apart from each other in a non-elastomeric material   thermoplastic and substantially rigid mother, and (b) a trasième piece molded in a thermoplastic elastomer and extending and glued between said first and second parts, characterized in that it comprises the steps of (1) injection molding said first and second parts, second pieces (2, 4) simultaneously in first and second mold cavities (62, 64), respectively; and (2) injection molding said third piece (at 78) between said first and second pieces so that said thermoplastic elastomer from which said third piece is molded adheres directly to the thermoplastic non-elastomeric material of which said first and second pieces.   16. The method of claim 15, characterized in that the third aforementioned part is molded after curing of the aforementioned thermoplastic polymer before   that he has reached his maximum hardness.   17. Process according to claim 15, characterized in that the first and second parts mentioned above are polystyrene.   18. The method of claim 15, characterized in that the third piece above is a copolymer styrene and butadiene.