ELECTRICALLY FUSION-BONDED JOINT

Abstract: An electrically fusion-bonded joint includes a body proper and is provided with a heater including a magnetic alloy piece having a fixed degree of Curie temperature at a portion in the vicinity of the body proper surface to be bonded so that the surface of the heater is exposed outside from the body proper surface to be bonded. When the body proper surface to be bonded is brought into contact with the surface of a member to be bonded and high frequency current is supplied to the magnetic alloy piece by electric induction, the magnetic alloy piece generates heat and the temperature thereof is kept at a fixed degree of Curie temperature by temperature self-control function thereof. Accordingly, when a Curie temperature is set at a degree for fusion-bonding, the body proper surface and the member to be bonded are fusion-bonded.

Description: This invention pertains to an electric fusion coupling. More specifically, it pertains to an electric fusion coupling which is utilised to connect synthetic resin pipes etc. An example of prior electric fusion couplings used to connect pipes made of polyethylene, polybutene and other synthetic resins is disclosed in US-A-4, 117,311 and US-A-4 486,650. As indicated in Fig. 12, an electric fusion coupling 1 of the prior art includes a body 2 which is a hollow cylindrical pipe made of synthetic resin. Buried in the inner section of the body 2 is the electric hearing wire 3, while both ends of the electric heating wire 3 are attached to the terminals 4 which project from the body 2. In such an electric fusion coupling 1 of the prior art, there were problems in manufacturing since terminals 4 have to be shaped in both end sections of the electric heating wire 3. Moreover, since the heating was accomplished by the electric heating wire 3, the temperature control was difficult, and there easily emerged a temperature unevenness, which constituted another problem. EP-A-0458957 (relevant under Article 54(3) EPC) describes a structure for joining plastics members in the form of a sleeve positionable around part of a member, the sleeve including high mu material heating means embedded therein for causing fusion of the sleeve and the member. The heating means may comprise one or more bands, a plurality of rings or corrugated strips. WO-A-80/02124 describes a method of joining two pipes in which ferromagnetic material is located in a region of the joint to be formed. The surrounding pipe material is melted to produce the joint. The ferromagnetic material may be in the form of a band of conductive material in the form of either a polymer with metal powder therethrough or a perforated ferromagnetic alloy. In any event, the heating element so-formed is embedded (at least in one embodiment thereof) in a surface of the coupling. In all embodiments a surface of the heating element is exposed. A main purpose of this invention is to offer a new electric fusion coupling. Another purpose of this invention is to offer an electric fusion coupling which would be simple in manufacturing. Another purpose of this invention is to offer an electric fusion coupling that does not generate temperature unevenness. Still another purpose of this invention is to offer an electric fusion coupling which uses a magnetic alloy body as a heater. An electric fusion coupling for connecting plastic members formed from a first plastics material with a first fusion temperature and having a first connecting surface comprises a connecting body formed from a second plastics material with a second fusion temperature and having a second connecting surface similarly curved to the first connecting surface whereby the second connecting surface of the connecting body can be positioned closely adjacent the first contacting surface of a member to which it is to be joined to provide a length of overlap therebetween and a temperature self-regulating heating means fully embedded in the connecting body adjacent the second connecting surface for heating the body and the member to which it is to be joined to their fusion temperatures whereby an extensive region of the length of overlap of the connecting body and the member are fused to one another, the heating means including a magnetic alloy body with a high Curie temperature equal to or above the first and second fusion temperatures and being in the form of either a punched sheet or a mesh. The invention is therefore distinguished from WO-A-80/02124 by virtue of the total embedding of the heating element in the body of the coupling and the extensive amount of the overlap between the coupling and member which is covered by the heating element. An electric fusion coupling according to this invention connects members to be connected made from the first synthetic resin, and is equipped with the following: the main body which is made of the second synthetic resin and has the second joining surface which has practically the same curve as the first joining surface, while the above-mentioned first and second synthetic resins have their respective first and second melting temperatures; a heater which includes a magnetic alloy body, the aforesaid magnetic alloy body having a high Curie temperature equal to or higher than the melting temperatures of the first and second synthetic resins. The heater is buried, eg in the vicinity of the second joining surface of the body. The Curie temperature of the magnetic alloy that makes up the heater is established (as an optimal temperature) slightly higher than the melting temperatures of the first and second synthetic resins. The second joining surface of the body follows one of the joining surfaces of the heater joining member. In this situation, when a high frequency current is applied by magnetic induction to the magnetic alloy which makes up the heater, the magnetic layer is heated by the skin effect, the temperature of the magnetic alloy body and hence of the heater is increased. Thereupon, if the temperature of the heater reaches the Curie temperature, the magnetic permeability of the magnetic alloy body rapidly decreases, the current is almost entirely discontinued, and the temperature of the magnetic alloy body, ie the heater, no longer increases. If the temperature of the heater is reduced by heat conduction, then the magnetic permeability of the magnetic alloy body is increased, and an electric current again flows in the magnetic alloy body. Since such actions are recurrent, the temperature of the magnetic alloy body, ie the heater, is maintained actually at a constant level, that of the Curie temperature. Consequently, the first and the second joining surfaces are heated to the Curie temperature or to a value close to it, ie to the optimal temperature, the members to be connected and the first and the second joining surfaces of the body as well as its surroundings are melted, and the member to be connected and the body are fused. The above-mentioned purposes of this invention, as well as its other purposes, characteristic features, aspects and advantages will become clearer from the following detailed explanation of a practical example which is provided in conjunction with the attached drawings, in which: Fig. 1 is a cross-section which shows a practical example of a coupling; Fig. 2 is a cross-section which shows the situation of the coupling of the Practical Example of Fig. 1; Fig. 3 - Fig. 8 are cross-sections which show different modified examples of heaters, Fig. 6 - Fig 8 being in accordance with the present invention; Fig. 9 is an oblique view which shows another practical example; Fig. 10 A and 10 B serve to explain another practical example, Fig. 10 A being a cross-section, while Fig. 10 B shows the bottom surface; Fig. 11 is a cross-section which shows another practical example; and Fig. 12 is a cross-section which shows prior art. Referring to Fig. 1, the electric fusion coupling 10 of this practical example includes a hollow cylindrical body 10 made of polyethylene and other synthetic resins. The hollow inside of the body 12 acts as a socket 16 which accepts the pipe 14 mentioned below. Close to the inner surface of the socket 16, ie the joining surface (the second joining surface) there is buried a cylindrical magnetic alloy body 18. The magnetic alloy body 18 acts as a heater; it has a fixed Curie temperature. Such a magnetic alloy body 18 can be the magnetic alloy body disclosed in US-A-4, 256, 945. The Curie temperature of the magnetic alloy body 18 can be adjusted by varying the composition ratio of the components which constitute the alloy. The Curie temperature is established at the optimal temperature of the coupling. Of course, this optimal temperature varies according to the particular kind of the first synthetic resin used in the pipe 14 to be connected and of the second synthetic resin used in the body 12. Referring to Fig. 2, the pipe 14 made of polyethylene, polybutene and/or other synthetic resin is inserted into socket 16 on the right and left of the electric fusion coupling, and then a high frequency electric current is applied by electric inductance to the magnetic alloy body 18 buried inside the coupling 10 using a high frequency power source. Then, the magnetic alloy body 18 is heated rapidly, since due to the skin effect, the electric current is only concentrated in the skin section. When the temperature of the magnetic alloy body 18 is increased and reaches the Curie temperature, its magnetic permeability diminishes rapidly so that the skin current is discontinued, thus the heating of the magnetic alloy body 18 becomes exceedingly small. When the heat of the magnetic alloy body 18 propagates to the body 12 and the pipe 14, reducing the temperature of the magnetic alloy body 18, the magnetic alloy body 18 is again heated by the skin current. Consequently, the magnetic alloy body 18, ie, the heater, maintains an almost constant temperature which is the Curie temperature or close to it. Thus, the joining surfaces of the body 12 and pipe 14 as well as the synthetic resin in their vicinity are melted and the two become fused. The high frequency power source that can be used can be, eg, the high frequency power source disclosed in US-A-4, 769, 519. According to this practical example, a high frequency current is applied to the magnetic alloy body 18 by means of electromagnetic induction. Therefore the electric fusion coupling 10 can be manufactured easily without any need to shape welding terminals. In the practical example indicated in Fig. 3, the heater 11 is used which connects in series the left and right magnetic alloy bodies 18 in the practical example of Fig. 1 by means of a connecting section 24. In order for the connecting section 24 to prevent the central part 22 of the body 12 from melting as efficiently as possible, it is shaped partly around the body 12. By connecting the two magnetic alloy bodies 18 by means of such a connecting section 24, it is ensured that the positions of both magnetic alloy bodies 18 are not dislocated along the diameter of the body 12, therefore the fusion is accomplished with more reliability. The heater 13 shown in Fig. 4 includes the magnetic alloy body 28, cylindrical (or planar) in shape. On the external surface of (or internal surface of) the magnetic alloy body 28, there are a number of projecting lines 26 extending along the circumference. These projecting lines 26 have a double function, ie, preventing separation between a magnetic alloy body 28 and the body 12, and expanding the heating area. The heater 15 shown in Fig. 5 includes a cylindrical magnetic alloy body 30 shaped by a wave plate. The reason why this magnetic alloy body 30 is constituted by a wave plate is the same as in the practical example of Fig. 4. In the practical example indicated in Fig. 6 which is in accordance with the invention, the heater 17 is constituted by a magnetic alloy body 34 shaped by punching metal; ie, there are a number of pierced holes 32 on the lateral surface of the magnetic alloy body 34. These pierced holes 32 are efficient to prevent separation between the magnetic alloy body 34 and the body 12. That is, since the synthetic resin of the body 12 involves the magnetic alloy body 34 via the pierced holes 32, separation between the two of them can be prevented. If a sufficient aperture ratio is not obtained in the punched metal shown in Fig. 6, in another embodiment of the invention a heater 19 can be used which is constituted by the mesh-shaped magnetic alloy body 36 indicated in Fig. 7. Thus the introduction of the synthetic resin of the body 12 is promoted via these apertures, while separation between the mesh magnetic alloy body 36 and the body itself can be further prevented. The practical examples shown in Figs. 6 and 7 are advantageous in that they enable one to reduce the amount of magnetic alloy. Fig. 8 shows the use of a heater 21 made of a coil-shaped magnetic alloy body 38. In the practical examples indicated in Figs. 1 - 8, the electric fusion coupling 10 was obtained by injection molding of the body so as to mold the magnetic alloy body inside the body. But the shape of the magnetic alloy body can be further modified. This invention can be applied to the joining of a variety of pipe members: a socket 44 divided in two pieces as indicate in Fig. 9, a saddle 31 as indicated in Fig. 10 A and 10 B, or an elbow 33 as indicated in Fig. 11, and other tees, reducers, etc., not shown in the accompanying drawings. The two-section socket 44 indicated in Fig. 9 consists of the top section 46 and bottom section 48. In the case shown, and outside the scope of the invention, magnetic alloy powder is kneaded into the sections close to their respective inner surfaces. During the joining, the pipe 50 is held on both sides by the top and bottom pieces of the two-piece socket 44 in such a way as to bring the extremities of the two pipes 50 to be connected butt to butt and place the confronting sections 52 in vacuum. The top and bottom pieces are fixed by a clamp tool, and a high frequency current is applied to the magnetic alloy powder 40. In this way, the magnetic alloy powder 40 is heated and the top and bottom pieces of the two-piece socket 44 become fused, while the pipe 50 can be connected at the same time. If this two-piece socket 44 is used, the time required to insert the pipe 50 into the coupling socket is reduced, therefore the manufacturing efficiency can be increased, which is especially advantageous for large diameter pipes which are becoming increasingly important. In this practical example, too, any of the heaters of the practical examples of Figs. 1 - 8 can be used. The saddle 31 shown in Fig. 10 A and 10 B includes a seating section 35. On the inside surface of the seating section 35, ie, in the vicinity of the joining surface, in a position indicated by a two-dash line in Fig. 10 B, a heater 37 is shaped according to any of the previous practical examples. In the centre of the seating section 35 there is shaped a branch pipe 39. In this practical example, too, the heater 37 can be heated by an induced high frequency current. The elbow 33 shown in Fig. 11 includes a body 41, in the vicinity of the inner surface of the socket 43, there is shaped a heater 45 according to any of the previous examples. In this Practical Example, as well, the heater 45 can be heated by an induced high frequency current.

Claims: An electric fusion coupling (10, 31, 33, 44) for connecting plastic members (14, 50) formed from a first plastics material with a first fusion temperature and having a first connecting surface, the coupling comprising a connecting body (12, 35, 41, 46/48) formed from a second plastics material with a second fusion temperature and having a second connecting surface similarly curved to the first connecting surface, whereby the second connecting surface of the connecting body can be positioned closely adjacent the first contacting surface of a member to which it is to be joined to provide a length of overlap therebetween and a temperature self-regulating heating means (11, 17, 18, 19, 21, 37, 45) fully embedded in the connecting body adjacent the second connecting surface for heating the body and the member to which it is to be joined to their fusion temperatures whereby an extensive region of the length of overlap of the connecting body and the member are fused to one another, the heating means including a magnetic alloy body with a high Curie temperature equal to or above the first and second fusion temperatures, and being in the form of either a punched sheet (17) or a mesh (19) or a coil (21). An electric fusion coupling as claimed in Claim 1, wherein the connecting body comprises an annular member (12, 33, 41, 44) which defines, at either end thereof, a socket (16, 43) for receiving a member to be connected (14,50), the second connecting surface comprising the inner surfaces of the annular member around the sockets. An electric fusion coupling as claimed in Claim 2, wherein the annular member comprises a straight cylindrical member (12,44). An electric fusion coupling as claimed in Claim 2, wherein the annular member comprises a cylindrical member (33, 41), one portion of which extends at an angle to the other. An electric fusion coupling as claimed in any one of Claims 2 to 4, wherein the thickness of the ends of the annular member (41) is less than the remainder thereof whereby to define the sockets (43). An electric fusion coupling as claimed in Claim 5, wherein the heating means comprises a pair of heaters (17, 18, 19), each positioned in the annular member and surrounding a respective socket and an intermediate heating section (11 to mutually connect the heaters. An electric fusion coupling as claimed in any one of Claims 2 to 6, wherein the sockets (16) are coextensive whereby the annular member (44) can be joined to a member (50) passing therethrough. An electric fusion coupling as claimed in any one of Claims 2 to 7, wherein the annular member (44) is formed from two separable sections (46, 48). An electric fusion coupling as claimed in Claim 1, wherein the connecting body comprises a saddle shaped member (31), the undersurface (37) of which comprises the second connecting surface.

Inventors: GOTO YUICHIRO, HARADA TAKATOMO, KASA HIDEKI, GOTO, YUICHIRO, HARADA, TAKATOMO, KASA, HIDEKI, GOTO, YUICHIRO, KUBOTA CORPORATION, HARADA, TAKATOMO, KUBOTO CORPORATION, KASA, HIDEKI, KUBOTA CORPORATION
Applicants: KUBOTA KK, UPONOR ALDYL COMPANY, KUBOTA CORPORATION
Application year: 1991
Main classification: F16L47
IPC codes: B29C65, F16L47