Method of fabricating a tank and method of fabricating a tank connector therefor

Abstract: The method of fabricating a tank connector assembly comprising the steps of first providing a metal spud member (24) having an internally threaded portion (26) and a cylindrical wall portion (28). Mounting an insert member (14) of polymer material inside the cylindrical wall portion of the spud member, the insert member having a cylindrical wall portion. Positioning a bonding member (12) between the cylindrical wall of the spud and the cylindrical wall of the insert member. Applying heat to the spud insert member and bonding member to cause the material of the bonding member to become bonded to the spud wall and the insert wall. In a preferred embodiment, the polymer material of the bonding member is maleated olefin. The metal spud member is welded in an opening in the wall of a steel tank. A polymer material is introduced into the interior of the steel tank and the tank is then subjected to a rotational casting movement in the presence of heat to cause the polymer material in the tank to be uniformly distributed over the internal surface of the tank. The heat applied during the rotational casting step serves to cause the bonding member to become bonded to the spud and insert member.

Description: A conventional method of fabricating a tank connector for a tank is described in US-A-5,158,200. This method provides a metal spud member with an internally threaded portion and a cylindrical wall portion. A sleeve which is made of polymer material has a cylindrical body portion and a radially extending flange portion and is positioned inside the cylindrical wall portion of the spud member. After this, a plug member is threaded into the spud member and an inner shell of polymer material is formed by a rotational casting procedure within the tank. It is the object of the present invention to eliminate or at least reduce the likelihood of water leakage into contact with metal parts of the connector and/or the metal outer tank shell. According to the invention, this object is attained by the method according to claim 1. Advantageous features and embodiments are cited in the dependent claims. The method of fabricating a tank connector assembly comprising the steps of first providing a metal spud member having an internally threaded portion and a cylindrical wall portion. Mounting an insert member of polymer material inside a cylindrical wall portion of the spud member, the insert member having a cylindrical wall portion. Positioning a bonding member between the cylindrical wall of the spud and the cylindrical wall of the insert member. Applying heat to the spud member, insert member and bonding member to cause the material of the bonding member to become bonded to the spud wall and the insert wall. In a preferred embodiment, the polymer material of the bonding member is maleated olefin. Brief Description of the Drawings Fig. 1 is a sectional view of a connector assembly made in accordance with the present invention with the assembly positioned in an opening in a tank wall; Fig. 2 is a section view of the connector assembly of Fig. 1 after the assembly has been welded in the opening in the tank wall; Fig. 3 is a sectional view of the connector assembly of Fig. 2 after an inner shell of polymer material has been formed inside the outer tank wall; Fig. 3a is a sectional view of the connector assembly of Fig. 3 after the plug member has been removed from the spud; Fig. 4 is a sectional view of the spud member used in the connector assembly; Fig. 5 is a top plan view of the spud member shown in Fig. 4; Fig. 6 is a side elevation view of the insert member used in the connector assembly; Fig. 7 is a top plan view of the insert member shown in Fig. 6; Fig. 8 is a sectional view of the bonding member used in the connector assembly; Fig. 9 is a bottom plan view of the bonding member shown in Fig. 8; Fig. 10 is a sectional view of the core member used in the connector assembly; Fig. 11 is a top plan view of the core member shown in Fig. 10; and Fig. 12 is a sectional view of a second embodiment of a connector assembly made in accordance with the present invention. Figs. 13a-13d show a prior art tank connector reproduced from U.S. Patent No. 5,158,200. Figs. 14, 15, 16, 17 and 18 correspond to Figs. 2, 3, 4, 5, and 6 in U.S. Patent No. 5,217,140. Description of the Preferred Embodiment The tank connector fitting construction of the present invention is specifically designed for use in a tank comprised of an outer shell of metal material and an inner shell of non-corrosive and non-metallic polymer material. More specifically, the preferred embodiment of the present invention is designed for installation in a tank construction shown and described in U.S. Patent No. 5,217,140 issued June 8, 1993 and assigned to the assignee of this application. Description of the Prior Art Prior tank connector fittings for use in the tank construction shown in U.S. Patent No. 5,217,140 are shown and described in U.S. Patent No. 5,158,200 dated October 27, 1992 and assigned to the assignee of this application. An example of such a prior art tank connector construction is as follows. Referring to Figs. 13a-13d, Fig. 13a shows a tank connection comprised of an outer tank shell 370 of metal and a metal connector fitting 372 welded to shell 370 at weld areas 374. Fitting 372 has an internal threaded body portion 376 and an internal groove 378. A sleeve 380 having a cylindrical body portion 382 and a radially extending flange portion 384 is mounted in groove 378 of fitting 372. Body portion 382 and flange 384 have a continuous smooth tapered internal surface 385. Sleeve 380 is made of a polymer material. The body portion 382 of sleeve 380 extends through an opening 386 in shell 370. A plug member 388 is threaded into fitting 372 and extends through sleeve 380 as shown in Fig. 13a. Plug member 388 is preferably made of a material having a low thermal conductivity such as fluoroplastics. Plug member 388 is comprised of an externally threaded body portion 390 and an end portion 392 having a smooth external tapered surface 394. With the plug 388 installed as shown in Fig. 13a, the threaded portion 390 extends only to the groove 378 in fitting 372 and the tapered surface 394 on the plug fits snugly in the tapered internal surface 385 of sleeve 380. Fig. 13b shows the assembly of Fig. 13a after an inner shell 396 has been formed in the metal outer shell 370. Inner shell 396 is preferably made of a polymer material and is formed by a rotational casting procedure. The inner shell 396 will become fused to the exposed surface of sleeve 380. Fig. 13d shows the assembly of Fig. 13c with a threaded pipe nipple 398 installed in fitting 372. In a water heater tank, the threaded nipple 398 may be a part of a temperature and pressure relief valve or a part of a drain valve. It will be appreciated that as a threaded pipe nipple 398 is threaded into fitting 372, the lead threads 400 thereon will cut into the polymer material of tapered surface 385 of sleeve 380 to thereby cut a length of threads into surface 385 as shown in Fig. 13d. The present invention constitutes an improvement to the tank connection shown in Figs. 13a-13d. As explained hereinafter, an object of the present invention is to eliminate or at least reduce the likelihood of water leakage into contact with metal parts of the connector and/or the metal outer tank shell. One embodiment of the present invention is described as follows. The description will be made in the form of an explanation of the method of fabrication of the tank connector and the tank in which the connector is mounted. Referring to the drawings in detail, Figs. 1, 2, 3 and 3a show one embodiment of a tank connector assembly identified by reference numeral 10. The first step in the assembly of connector 10 is to assemble bonding member 12 (Figs. 8 and 9) with insert member 14 (Figs. 6 and 7). Member 12 is preferably of polymer material and has an inverted cup-shape comprised of a top ring portion 16 and a depending cylindrical wall portion 18. Member 14 is also preferably of a polymer material and has a cylindrical shape comprised of an upper section 20 and a lower section 22 of a smaller diameter than the upper section 20. A shoulder 21 is formed between sections 20 and 22. Parts 12 and 14 can be assembled to form a sub-assembly by simply forcing cup-shaped member 12 over the top section 20 of member 14. An alternate method would be a co-injection molding process wherein bonding member 12 would be molded and inserted into a suitable mold and then insert member 14 would be injection molded into the bonding member 12 to produce a single part. A second alternative co-injection molding process could be employed wherein insert member 14 would be molded and inserted into a suitable mold and then bonding member 12 would be injection molded onto the insert member 14 to produce a single part. The co-injection molding processes described above could be performed by an automated molding apparatus. The next step in the assembly of connector 10 is to assemble the sub-assembly of parts 12 and 14 into a spud member 24. Spud member 24 (Figs. 4 and 5) is made of metal (preferably steel) and is comprised of an internally threaded upper portion 26 and a cylindrical depending wall portion 28 having a weld projection 30 formed at the end of wall 28. The sub-assembly of parts 12 and 14 is forced upwardly into the space inside the spud member defined by depending wall portion 28. The final step in the assembly of connector 10 is to install a plug member 32 into the spud 24. Plug member 32 (Figs. 10 and 11) is preferably of a polymer material such as 15% glass filled fluoroplastics and is comprised of an externally threaded top portion 34 and a closed nose portion 36. Plug member 32 is threaded into spud member 24 to complete the connector assembly 10 as shown in Fig. 1. The upper interior 38 of plug member 32 is splined to facilitate its installation into and removal from spud member 24 by a suitable tool (not shown). The particular polymer materials used in making bonding member 12 and insert member 14 and the characteristics of such materials are important features of the present invention and will be described in detail hereinafter. The next step in the fabrication of a finished tank connector is to securely fasten the assembly 10 in the steel wall 11 of a tank. This is accomplished by positioning the assembly 10 in an opening 13 in the wall 11 of a tank and then welding the projection 30 on spud wall 28 to the surface of the tank wall as shown in Fig. 2. The welding step will cause welding projection ring 30 to be fused to tank wall 11 as indicated by reference numeral 13 in Fig. 2. With the spud 24 welded in place, the shoulder 21 on insert member 14 will fit snugly against the outer surface of tank wall 11. After the required number of assemblies have been welded to the tank wall, the fabrication of the completed tank is accomplished as described as follows. To summarize, as shown in Figs. 2, 3, 4, 5 and 6 of U.S. Patent No. 5,217,140 (corresponding to Figs. 14, 15, 16, 17, 18 herein), the outer shell 26a of the completed tank 28a is comprised of two parts; namely, an upper half member 30a and a lower half member 32a, each of which is formed by a deep drawing process. After the required number of connector assemblies 10 are welded to the tank half members, the half members are fastened together in a secure manner to form a completed outer shell. Preferably such fastening step is performed by laser welding. After the completed outer shell is fabricated, an inner shell 44 of non-corrosive polymer material is formed inside the outer shell adjacent the internal surface of the outer shell. In one preferred embodiment, the non-corrosive polymer material is polybutelene. The polybutelene material is introduced into the outer shell in powder form. This can be accomplished before the two halves are welded together or the powder material can be introduced through an opening in the tank wall after the two halves are welded together. After the outer shell is charged with a polymer material, it is then subjected to rotational casting operation while heat is applied to the outer shell. A suitable rotational casting operation is described in detail in U.S. Patent No. 5,217,140. Such a rotational casting operation will cause the powder material to melt and be distributed uniformly over the internal surface of the outer shell to thereby form an inner shell 44. Referring to Fig. 3 of the present invention, the material of the inner shell will cover the tank wall and each connector fitting as shown in Fig. 3. The portion of the inner shell 44 which comes in contact with portion 22 of insert member 14 will be bonded to such member. The polymer material of inner shell 44 will puddle up in the area of the bond as indicated by reference numeral 45 in Fig. 3. After the formation of the inner shell 44, the plug members 32 will be removed by a suitable tool to produce a finished connector assembly as shown in Fig. 3a. As indicated above, members 12 and 14 are made of a polymer material. The particular characteristics of the materials of these two members is important. Referring first to the material of insert 14, it is important that the tensile strength of the material be sufficiently great to prevent rupture at certain critical areas. A critical area is indicated by the dotted circle 23 on Fig. 2. The polymer material of member 14 must also be capable of providing a strong bond between the lower section 22 of member 14 and inner shell 44 in the area indicated by reference numeral 45 in Fig. 3. Polymer materials suitable for use in making insert member 14 may be from the olefin family. More specifically, such materials can be polypropylene, polyethylene and polybutylene. Referring now to the polymer material of bonding member 12, it is important that the material of member 12 is capable of bonding to both insert member 14 and the steel spud 24. In one preferred embodiment, material of member 12 is an olefin that has been maleated. For best results, the maleated olefin material has a resin component having a high melt index, i.e., an index of 4 or greater. The maleated olefin bonding member will bond to spud member 24 over its external surface and will bond to insert member 14 over its internal surface. Such bonding will occur in the presence of heat. In a preferred embodiment,the bonding will occur during the rotational casting operation as described above wherein the inner tank shell 44 of polymer material is formed inside the outer shell. Such bonding of member 12 to both insert member 14 and spud member 24 will prevent, or at least substantially reduce any tendency of the water in the tank to leak past the outer surface of insert member 14 which, in turn, prevents water from coming in contact with the wall 11 of the steel tank. Such contact, if allowed to occur, could cause corrosion of the steel tank. The bond between the outer surface of wall 18 of bonding member 12 and spud 24 prevents water from coming in contact with wall 28 of spud 24 to thus prevent corrosion of the spud. It will be appreciated that because of the sandwich position of member 12 in the assembly 10, the tensile strength of bonding member 12 need not be as great as that of insert member 14. The important characteristic of bonding member 12 is its capability of becoming bonded to both insert member 14 and spud 24 as explained above. The fact that in obtaining the desired bonding characteristic there is some loss of tensile strength does not pose a problem. On the other hand, as indicated above, it is important that insert member 14 have a sufficient tensile strength to prevent a possible rupture in the area indicated by the dotted circle 21 in Fig. 2. By maintaining sufficient tensile strength in insert member 14, its capability of bonding to spud 24 is reduced. This again does not pose a problem because of the bonding function of bonding member 12 as explained above. The particular configuration of the connector assembly 10 described above is for connection of hot and cold water connections to the tank and for installation of a drain valve and a temperature/pressure valve to a water heater tank. The configuration of the connector assembly 10a shown in Fig. 12 is designed for mounting an electrical heating element to the tank of an electric water heater. The parts of Fig. 12 corresponding to the parts of Fig. 1 are designated with an identical number with a suffix "a".

Claims: A method of fabricating a tank connector assembly comprising the following steps: (a) providing a metal spud member (24) having an internally threaded portion (26) and a cylindrical wall portion (28); (b) producing a sub-assembly comprised of a bonding member (12) and an insert member (14), said members (12) and (14) made from a polymer material; (c) assembling the sub-assembly of step (b) with the spud member of step (a), with the sub-assembly of step (b) positioned inside the cylindrical wall portion (28) of spud member (24); (d) applying heat to the assembly of parts (a), (b), and (c) to cause the material of the bonding member to become bonded to the spud member (24) and the insert member (14). The method according to Claim 1 in which the polymer material of the bonding member (12) is maleated olefin. The method according to Claim 1 in which the polymer material of the bonding member (12) is formulated using a resin having a high melt index. The method according to Claim 3 in which the resin in the bonding member has a melt index greater than 4. The method according to Claim 1 wherein the sub-assembly of step (b) is made by manually assembling bonding member (12) with insert member (14) with the bonding member fitted over the exterior surface of the insert member. The method according to Claim 1 wherein the sub-assembly of step (b) is made by a co-injection molding process wherein bonding member (12) is molded and then inserted into a suitable mold and then insert member (14) is injection molded into the bonding member (12) to produce a single part. The method according to Claim 1 wherein the sub-assembly of step (b) is made by a co-injection molding process wherein insert member (14) is molded and then inserted into a suitable mold and then bonding member (12) is injection molded onto the insert member (14) to produce a single part. The method of fabricating a tank connector assembly according to one of the claims 1 to 7 for mounting on a tank wherein the tank has an outer shell of metal material and an inner shell of polymer material inside the outer shell, said insert member having a cylindrical wall portion (20,22), and the material of the bonding member is caused to become bonded to the spud wall (28) in the insert wall (20,22) in step (d). The method of fabricating a tank and tank connector assembly therefor according to one of the claims 1 to 8 comprising the steps of (i) forming a pair of top and bottom members by a metal deformation procedure; (ii) welding at least one tank connector assembly in an opening in one of the members by welding; (iii) fastening the top and bottom half members together by welding to form an outer shell having an internal surface; (iv) charging one half member of the outer shell with the polymer material before said welding steps; (v) subjecting the tank to a rotational movement in the presence of heat to thus cause the polymer material of step (iv) to be uniformly distributed over the internal surface of the outer shell to thereby form an inner shell of non-corrosive material inside the outer shell wherein the inner shell provides a substantially leak-tight liner for the outer shell to thus prevent contact between the contents of the tank and the outer shell, said outer shell serving as a mold for the inner shell, wherein said mold becomes a permanent part of the completed tank. The method according to claim 9 in which the application of heat in step (d) of claim 1 occurs during step (v).

Inventors: FABER ROLF E, LINDAHL D KENT, SYLER RODNEY R, FABER, ROLF E., LINDAHL, D. KENT, SYLER, RODNEY R.
Applicants: STATE IND INC, STATE INDUSTRIES, INC.
Application year: 1995
Main classification: B29C65
IPC codes: B65D39, B29C65, B29C41, F16L47, B65D90