IMPROVEMENTS RELATING TO THE MANUFACTURE OF TOILETS

Abstract: A bowl unit or a holding tank for a portable toilet is formed from first and second mouldings (28, 30) in a thermoplastic material which are adapted to fit together in a joint plane to form an enclosure. The mouldings define respectively a con­ tinuous channel (64) and a continuous tongue (66) capable of being received in the channel for forming a joint between the mouldings. A sealing strip (68) which is substantially co-exten­ sive with the channel and comprises a thermoplastic material capable of fusing with the material from which the mouldings are formed and having magnetically excitable particles dis­ persed therein, is positioned in the channel and the mouldings are assembled with the tongue engaged in the channel of the other. The sealing strip is then subjected to a high-frequency magnetic field to an extent sufficient to cause the strip to fuse with the channel and tongue and form a liquid-tight seal be­ tween the mouldings.

Description: Improvements relating to the manufacture of toilets This invention relates generally to the manufacture of toilets and is concerned more particularly (but not exclusively) with the manufacture of a component such as a bowl unit or waste holding tank for a portable toilet. A portable toilet typically comprises a bowl unit which includes a toilet bowl having a discharge opening, and a holding tank which is normally disposed below the bowl unit and is detachably coupled thereto. Valve means are provided for controlling flushing of liquid and waste from the bowl into the holding tank. The bowl unit often incorporates a reservoir for flushing liquid and an example of this type of toilet is disclosed in our U.S. Patent No. 4,091,475. Another example is disclosed in our Canadian Patent Application Serial No. 380,039 filed June 17, 1981. The bowl unit and holding tank of a portable toilet are normally made of plastic material. In some cases, at least the holding tank is made in one piece by blow moulding. However, in other cases, the holding tank is a composite structure made of upper and lower tank sections secured together around the periphery of the tank. Similar construction techniques have been used for making the bowl unit. Obviously, in either case, the joint between the two sections must be secure and liquidtight. As disclosed in our Canadian Patent application identified above, joining of the two tank sections is effected by providing a continuous, downwardly facing channel around the periphery of the upper tank section for receiving the corresponding peripheral margin at the top of the lower tank section. The two sections are then secured together by adhesive. While this method works well with certain types of plastic material, with others, it is difficult to obtain a reliable joint using adhesives An object of the present invention is to provide an improved method of manufacturing a component such as a bowl unit or holding tank for a toilet. The method involves forming first and second mouldings in a thermoplastic material, the mouldings being adapted to fit together in a joint plane to form an enclosure having a hollow internal space for receiving liquid, the mouldings defining respectively, a continuous channel and a continuous tongue capable of being received in said channel for forming a joint between the mouldings. A sealing strip is provided and is adapted to be received in the channel. The strip is substantially co-extensive with the channel and comprises a thermoplastic material capable of fusing with the termoplastic material from which the mouldings are formed and having magnetically excitable particles dispersed therein. The strip is positioned in the channel and the mouldings are assembled to form the enclosure with the tongue of one moulding engaged in the channel of the other. The sealing strip is then subjected to the effect of a high-frequency magnetic field having characteristics selected to excite the particles in the sealing strip to an extent sufficient to cause the strip to fuse with the channel and tongue and form a liquid-tight seal between the mouldings. The method provided by the invention may be employed to manufacture various components for a toilet. For example, in the case of a portable toilet, the method may be used to manufacture one or both of the holding tank and bowl unit. In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention by way of example, and in which: Fig. 1 is a partially exploded perspective view of a two-piece portable toilet manufactured in accordance with the present invention; Fig. 2 is a partial longitudinal sectional view illustrating a step in the manufacture of the toilet of Fig. 1; Figs. 3 and 4 are enlarged sectional views showing respectively a part of the joint between the two sections of the holding tank as shown in Fig. 1, before and after the sealing operation is performed; and, Figs. 5, 6 and 7 are views similar to Fig. 3 showing respective alternative forms of joint. Referring first to Fig. 1, a portable two-piece toilet is shown to include a bowl unit generally denoted 20 and a holding tank 22. The bowl unit is shown separate from and raised above the holding tank for clarity of illustration but, in use, the bowl unit will of course fit onto and be supported by the holding tank. Clasp-type fasteners, one of which is visible at 24 are provided at both sides of the holding tank for releasably coupling the bowl unit and holding tank together. A keeper formation on the bowl unit for co-operation with latch 24 is shown at 26. In this embodiment, the bowl unit and holding tank are both manufactured by the same method. Thus, each of these components comprises upper and lower sections which are sealed together around the periphery of the component to form a hollow internal space for receiving liquid. In the case of the holding tank, the upper and lower sections are denoted respectively 28 and 30 and the joint between the two sections is visible at 32. The upper section incorporates an integral housing 34 for a valve mechanism, parts of which are visible in Fig. 2. The valve mechanism is essentially the same as that disclosed in our Canadian Patent application aforesaid and will not therefore be described in detail. For present purposes, it is sufficient to note that the mechanism is actuated by a handle 36 which can be pulled forwardly to the position shown in ghost outline in Fig. 1 to open the valve. The valve controls an inlet generally designated 38 fitted with a seal. The upper holding tank also incorporates a neck 40 through which the holding tank can be drained from time to time and which is normally closed by a cap 42. In the case of the bowl unit 20, reference numeral 44 indicates a joint between an upper bowl unit section 46 and a lower section 48. The upper section incorporates an integrally formed bowl, most of which is indicated in dotted lines at 50. An outlet from the bowl is indicated at 52. The hollow internal space surrounding the bowl forms a reservoir for flushing liquid and an inlet neck to the reservoir is shown at 54 and is formed as part of the upper bowl unit section 46. A cap is shown at 56. The upper section 46 also incorporates an integral pump cylinder (not shown) which receives a pump mechanism generally denoted 58 by which flushing liquid can be dispensed into the bowl at appropriate times. Again, the pump mechanism forms no part of the present invention and will not therefore be described in detail. A separate seat and lid assembly 60 is hinged to the upper bowl unit section 46 and the lid is shown raised in Fig. 1. In summary, each of the bowl units 20 and the holding tank 22 is made up of two plastic mouldings, one of which forms an upper section and the other a lower section. Each of these mouldings is separately manufactured by a conventional moulding technique (typically injection moulding) in a polypropylene plastic material. In each case, the two mouldings are then joined together by essentially the same technique which will now be described primarily by reference to the holding tank 22 although it is of course to be understood that similar steps would be followed to assemble the bowl unit 20. Referring now to Fig. 2, the holding tank 22 is shown in section and inverted as compared with the normal position of use in which it is shown in Fig. 1. In assembling the holding tank from the two plastic mouldings, the moulding which forms the upper tank section 28 is initially placed in this inverted position and supported in a suitable jig (not shown). At this time, the tank section will have been fitted with the valve mechanism, which is generally denoted by reference numeral 62 in Fig. 2, but the bottom holding tank section 30 will not be in place. In Fig. 2, that section is shown exploded above the upper section 28 prior to the lower section being fitted to the upper section. It will be seen that the moulding which forms the upper section includes a continuous channel 64 which is formed around the periphery of the moulding in a joint plane denoted P in Fig. 2. The moulding which forms the lower tank section is in turn formed with a corresponding continuous tongue 66 capable of being received in channel 64 for forming a joint between the two mouldings. Fig. 3 is a detail sectional view showing the channel and tongue fitted together prior to commencement of the sealing operation used to join the mouldings and Fig. 4 shows the channel and tongue after the sealing operation has been completed. However, before the two sections are brought together, a sealing strip which is generally indicated at 68 is placed within channel 64. The sealing strip is substantially co-extensive with channel 64 and is in the nature of a strand or filament of generally circular shape in cross-section. A length appropriate to the total length of channel 64 is prepared and placed in the channel so that the whole of the base of the channel is covered. Only then is the lower tank section fitted to the upper tank section with tongue 66 engaged in channel 64 as best shown in Fig. 3. Referring now to that view, the two mouldings (which form the two tank sections) are dimensioned so that tongue 66 is positioned in contact with the outer side wall 64a of channel 64; that is, the side of the channel which would be at the exterior of the completed holding tank. Ideally, the sealing strip 68 should be against the inner wall of the channel although in practice it may not be possible to position the sealing strip sufficiently precisely to ensure that this happens. In any event, if tongue 66 is at the outer side wall, the sealing strip 68 will tend to be confined at the inner side of the channel as shown in Fig. 3. A step 66a is formed immediately adjacent to tongue 66 so that the moulding at least partly covers the open mouth of channel 64 to further assist in confining the sealing strip within the channel during fusing of the strip with the channel and tongue. Fig. 3 also illustrates the fact that the portion of the moulding which forms channel 64 is shaped so that the channel is stepped outwardly from the remainder of the side wall of the moulding, indicated at 28a in Fig. 3. In this way, the portion of the moulding which forms the base of the channel (denoted 64b) protrudes outwardly from the wall of the moulding so that transmission heads indicated at 70 and 72 in Fig. 3 can be positioned close to the sealing strip 68 for exciting the particles therein. In this particular embodiment, the the sealing strip 68 is formed from the same material as the two mouldings to.be fused together (polypropylene) and has iron particles dispersed therein. The transmission heads 70 and 72 are in the form of rectangular section copper tubes which are hollow and through which cooling water is passed. The magnetic field is applied to the sealing Srip using a conventional radio frequency generator of the type used for induction welding. The generator is indicated generally by reference numeral 74 in Fig. 3 and includes an induction coil (not shown) in which a radio frequency magnetic field is induced. The magnetic field is applied to the sealing strip by way of the two transmission heads. The heads will be supported by the jig in which the mouldings are located. After the mouldings have been assembled with the tongue of tank section 30 engaged in the channel of section 28 sealing strip 68 is subjected to the effect of a high-frequency magnetic field by way of the transmission heads. The magnetic field has characteristics selected to excite the particles in the sealing strip to an extent sufficient to cause the strip to fuse with the mouldings in the region of the channel and tongue. While the magnetic field is being applied, slight downward pressure is exerted on tank section 30 so as to ensure that the tongue 66 is fully seated within channel 64 and is applied against the outer wall 64a of the channel. In this way, any excess material which might be exuded from the channel will tend to flow into the internal space within the holding tank rather than outwardly. Obviously, excess material at the exterior of the tank would be aesthetically undesirable. Fig. 4 shows the fused mass which results from this sealing operation. A fully secure and liquid-tight seal is produced in which the co-operating portions of tongue 66 and channel 64 have merged so as to be virtually indistinguishable. However, the particles which were within sealing strip 68 would generally be discernable in the fused mass. The magnetic field produced by generator 74 is applied to sealing strip 68 at a frequency and intensity and for a period of time sufficient to effect the required fusion of the mouldings. In one particular example, a frequency of 7,000 c.p.s. was found to be adequate. In any event, after a suitable period of time determined by experimentation generator 74 is switched off. Transmission heads 70 and 72 are, however, allowed to remain in contact with the channel 64 until the fused assembly has cooled to an extent sufficient to permit the holding tank to be handled. In an alternative embodiment (see Fig. 6), it would be possible to design the moulding which forms the lower tank section 30 so as to permit the transmission heads to be positioned vertically above and below the sealing strip 68 although this would involve some complication in jig design to allow the upper transmission head to be moved when the fused assembly is to be withdrawn from the jig. Fig. 5 illustrates a simplified form of the tongue and channel joint design shown in Figs. 3 and 4 in which a plain tongue 76 fits substantially closely within a channel 78 with the interposition of a sealing strip 80. A configuration such as this has the disadvantage that flow of the sealing strip is not controlled. However, it is believed that a practical and liquid-tight seal will be obtained with this design. Figs. 6 and 7 show further alternative forms of joint. As indicated previously, the moulding on which the tongue is formed (as tongue 66 in Fig. 3) may be shaped so that the tongue moulding at least partly covers the open mouth of the channel on the other moulding. In the embodiments shown in Figs. 6 and 7 the tongue moulding is designed to completely cover and close the open mouth of the channel so that the sealing strip is fully enclosed within the channel when the fusing operation is performed. In Fig. 6, the joint is also designed to permit the transmission heads (as heads 70 and 72 -- Fig. 3) to be positioned vertically respectively above and below the sealing strip as mentioned above. In this way, the lines of flux between the transmission heads are straight and pass directly through the sealing strip. It is believed that this may offer some advantage in terms of a faster cycle time for the induction welding operation. In Fig. 6, the transmission heads are denoted 70 and 72 as previously and are positioned respectively above and below the joint. The tongue and channel which form the joints are denoted respectively as 82 and 84. Tongue 82 is shaped to define a step 82a and has a width at the position of the step substantially equal to the width of the mouth of the channel so that when the tongue is inserted into the channel, its mouth is closed. The tongue then defines an enclosed space 86 within the channel for receiving the sealing strip; for clarity of illustration, the strip itself is not shown. In the Fig. 6 embodiment, the moulding from which the tongue is formed includes a portion denoted 82b immediately adjacent to the tongue itself, which portion extends substantially at right angles to the tongue across the outer edge 84a of the inner limb 84b of channel 84. The moulding is designed so that, when the tongue 82 is fully seated in channel 84, the lower surface of portion 82b as drawn bears against edge 84a and acts as a further barrier confining the sealing strip within the channel. Fig. 7 shows a still further form of joint in whcih the tongue and channel are denoted respectively 88 and 90. As drawn, tongue 88 is shown positioned within the channel but slightly above its fully seated position, for clarity of illustration. The channel and tongue are designed to define an enclosed space 92 for receiving the sealing strip (not shown). In both the embodiments of Figs. 6 and 7, the enclosed space (86 or 92) preferably has a cross-sectional area equal to the cross-sectional area of the sealing strip. It has been found that, by confining the sealing strip within the channel as described, flow of excess molten plastic from the joint can be avoided which, in turn, makes for reasonable certainty of a leak-free joint between the two mouldings. It will of course be appreciated that the preceding description relates to particular preferred embodiments of the invention only and that many modifications are possible within the broad scope of the invention. For example, the invention has been described specifically in the environment of portable toilets and more particularly for the manufacture of a bowl unit and/or waste holding tank. However, it is to be understood that the method provided by the invention may be applied to other components for a toilet. For example, it would probably be possible to employ the method of the invention for manufacturing a conventional toilet bowl and trap assembly from two plastic mouldings which meet in a horizontal joint plane passing through the trap. It should also be noted that a component to be manufactured by the method of the invention could be made from more than two parts. Each of the mouldings joined by the method of the invention could itself be a composite article.

Claims: CLAIMS: 1. A method of manufacturing a component for a toilet, the method comprising the steps of: forming first and second mouldings in a thermoplastic material, the mouldings being adapted to fit together in a joint plane to form an enclosure having a hollow internal space for receiving liquid, the mouldings defining respectively, a continuous channel and a continuous tongue capable of being received in said channel for forming a joint between the mouldings; providing a sealing strip which is adapted to be received in said channel and is substantially coextensive with said channel, the strip comprising a thermoplastic material capable of fusing with said thermoplastic material from which the mouldings are formed and having magnetically excitable particles dispersed therein; positioning said sealing strip in said channel; ; assembling said mouldings to form said enclosure, with the tongue of one moulding engaged in the channel of the other; and, subjecting the sealing strip to the effect of a high-frequency magnetic field having characteristics selected to excite said particles of the sealing strip to an extent sufficient to cause said strip to fuse with said channel and tongue and form a liquid-tight seal between said mouldings. 2. A method as claimed in claim 1, wherein said mouldings are shaped so that said tongue is positioned in contact with an outer side wall of said channel when said mouldings are assembled to form said enclosure, and wherein the mouldings are subjected to a compressive force tending to urge said tongue towards the base of said channel when the sealing strip is subjected to the effect of said high-frequency magnetic field, whereby the tongue is encouraged to seat fully in said channel and any excess plastic material which may tend to exude from the channel will tend to flow into said internal space. 3. A method as claimEd in claim 1 or claim 2, wherein said steps of positioning the sealing strip in the channel and assembling the mouldings are performed by initially positioning the first moulding with its said channel facing upwardly; inserting the sealing strip downwardly into said channel and engaging the tongue of the second moulding in said channel, and wherein the sealing strip is subjected to the effect of said high-frequency magnetic field with the mouldings located in said respective positions. 4. A method as claimed in claim 3, wherein said first moulding is shaped so that said channel is stepped outwardly from the remainder of the side wall of the moulding, and wherein said step of subjecting the sealing strip to the effect of a high-frequency magnetic field is performed by positioning respective transmission heads adjacent respective portions of said moulding defining the base and the outer wall of the channel, said heads being substantially co-extensive with the channel, and generating a high-frequency magnetic field between said heads. 5. A method as claimed in claim 4, wherein said second moulding is shaped so that said tongue is offset outwardly relative to the remainder of the wall of said moulding, wherein portions of said moulding adjacent said tongue tend to extend laterally across the open mouth of the channel and thereby assist in confining the sealing strip within said channel during fusing of the strip with the channel and tongue. 6. A method as claimed in any one of claims 1 to 5 wherein said component is a tank for a portable toilet and wherein said first and second mouldings form respective upper and lower sections of said tank. 7. A method as claimed in any of claims 1 to 5 wherein said component is a bowl unit for a portable toilet and wherein said first and second mouldings comprise respective upper and lower sections of said bowl unit. 8. A method as claimed in claim 7, wherein said first moulding defining the upper section of the bowl unit comprises an integral moulding defining an outer wall of the unit and a bowl. 9. A method as claimed in any one of claims 1 to 8, wherein said tongue is shaped to close the mouth of and define within the channel an enclosed space for receiving said sealing strip when the mouldings are assembled, whereby the strip is confined within said space during fusion of the strip with the tongue and channel. 10. A method as claimed in claim 9, wherein the cross-sectional area of said enclosed space is substantially equal to the cross-sectional area of the sealing strip. 11. A method as claimed in any one of claims 1 to 10, wherein the mouldings are shaped so that said tongue and channel are offset relative to walls of the respective mouldings in which they are formed to an extent sufficient to permit transmission heads for generating said high-frequency magnetic field to be positioned respectively above and below the assembled tongue and channel so that lines of magnetic flux between the heads will be substantially straight and extend through the sealing strip.

Inventors: HEWSON, CLIFFORD BRUCE, STEWART, JOHN M.
Applicants: SANITATION EQUIPMENT LIMITED
Application year: 1983
Main classification: B29C65
IPC codes: B29C65