Abstract:
A method of joining a thermoplastic tube to another tube includes orienting a thermoplastic tube within an outer tube, positioning a malleable band within the thermoplastic tube, and expanding the malleable band radially until a seal is formed between the thermoplastic tube and the outer tube. The invention may also be considered an apparatus including a first tube a second tube and a malleable band. The first tube contains a portion of the second tube. The malleable band is expanded radially, forming a seal between the first and second tube.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates generally to a method of joining a plastic tube to another tube, and, in a particular embodiment, to a method of joining a baffle comprising a plastic tube to a tank also having a tube. 
     (2) Description of the Prior Art 
     Joining a pair of concentric metallic tubes to form a seal between the tubes is known. One method of joining such tubes includes inserting an elastomeric sleeve within the inner tube and compressing it axially. The elastomeric sleeve expands radially against the inner tube and, if enough compressive force is applied, the sleeve deforms the inner tube so it engages the outer tube. An annularly enlarged portion of the tubes results from a resulting radial force having been applied from within the tubes. This annularly enlarged portion forms a joint between the tubes. 
     The ends of tubes such as polyvinyl chloride (PVC) pipes are also often joined in male/female fashion. However, PVC pipes are often joined with PVC glue or cement, a composition including PVC resin. Other thermoplastic materials such as polyethylene and polyurethane are not as susceptible to gluing or cementing. Thus, where it is desirable to join a polyethylene or polyurethane tubular member to another tube, welding the parts together is often necessary. This process may be labor intensive and time consuming. 
     Thus, there remains a need for a new method of joining a thermoplastic tube to another tube. Specifically, where the thermoplastic tube is a polyethylene or polyurethane part of a grease separator tank baffle, a new method of joining the baffle to the tank is needed. 
     SUMMARY OF THE INVENTION 
     The present invention solves one or more of these needs in the art by providing a method of joining a thermoplastic tube to another tube comprising: orienting a thermoplastic tube within an outer tube; positioning a malleable band within the thermoplastic tube; and expanding the malleable band radially until a seal is formed between the thermoplastic tube and the outer tube. 
     One aspect of the present invention is to provide a method of joining an interior baffle to a tank for a grease separator including: configuring a housing having a plastic tube extending outwardly from a side of the housing. A baffle is inserted into the tank so that a plastic tube of the baffle is disposed within a tube of the tank, and a malleable band is inserted in the plastic tube of the baffle. A tool having an elastomeric sleeve is inserted into the plastic tube of the baffle such that the elastomeric sleeve is within the malleable band in the plastic tube. The tool is operated to compress the elastomeric sleeve axially to expand the elastomeric sleeve radially and force the malleable band radially outward until the plastic tube of the baffle contacts the tube of the housing and forms a watertight seal between the tubes. 
     Another aspect of the present invention is to provide a method of joining substantially concentrically disposed plastic tubes comprising expanding a malleable band within an inner tube to form a seal between it and an outer tube. 
     In one embodiment, the present invention provides a tank having a tank housing and a rotomolded, thermoplastic baffle, the baffle comprising a tube and a malleable band positioned within the tube, the baffle positioned in relation to the tank housing to form a watertight seal between a the tube of the baffle and a tubular portion of the tank housing. 
     Yet another aspect is to provide a substantially dog bone shaped assembly comprising first and second rotomolded, polyethylene or polyurethane parts, each part having a tubular portion, the tubular portion of the first part extending within the tubular portion of the second part, the assembly further comprising a malleable band disposed within and deforming the tubular portion of the first part to form a joint with the tubular portion of the second part. 
     These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side perspective view of a pair of cylindrical tubes wherein the inner tube is disposed within the outer tube according to an embodiment of the invention. 
         FIG. 2  is a side perspective exploded view of a tool for joining a thermoplastic tube to another tube. 
         FIG. 3  is a side perspective view of the tool of  FIG. 2  with the parts assembled for joining a thermoplastic tube to another tube. 
         FIG. 4  is a top view of the tool and a malleable band within a pair of cylindrical tubes. 
         FIG. 5  is a side cross sectional view of a baffle and tank housing constructed according to an embodiment of the invention. 
         FIG. 6  is a side cross sectional view of a dog bone shaped assembly according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The illustrations and descriptions are for the purpose of describing an embodiment of the invention. Those of ordinary skill in the art will recognize that the invention defined by the claims is capable of various and numerous embodiments. 
       FIG. 1  illustrates an embodiment of a pair of cylindrical tubes  10  wherein the inner tube  12  is disposed within the outer tube  14 . The tubes  10  need not be cylindrical, nor does one need to be concentrically disposed within the other to practice embodiments of the invention. It is enough that the inner tube  12  or a portion thereof is within the outer tube  14 . In an embodiment of the invention, the inner tube  12  is a rotomolded polyethylene or polyurethane part. The outer tube  14  is not necessarily a rotomolded thermoplastic material, but may be. The ends of the tubes  13  and  15  may extend indefinitely, or may be shaped in any other desired manner. 
       FIGS. 2 and 3  illustrate an embodiment of a tool  50  useful for practicing an embodiment of the invention.  FIG. 2  is an exploded view of the tool  50 , while  FIG. 3  shows the tool  50  assembled. The tool  50  includes a metal collar  55  at one end through which a bolt  53  extends. Metal collars  51  are positioned at each opposing end of an elastomeric sleeve  54 . Within the elastomeric sleeve  54  is a threaded metal cylinder  52 . Two bolts  53  pass through each of the collars to the threaded metal cylinder  52 . When one or both of the bolts  53  are rotated into the threads in the metal cylinder  52 , the collars  51  are axially forced toward each other, axially compressing the elastomeric sleeve  54 . This axial compressive force distorts the elastomeric sleeve  54  to transfer a radial force to an object surrounding the sleeve  54  in a manner that is known. U.S. Pat. Nos. 2,748,463 to Mueller, 3,595,047 to Fanning et al., 4,075,755 to Bernatt et al., and 4,420,866 to Mueller disclose similar tools and this disclosure incorporates the entirety of those patent disclosures herein by reference. 
     While in the preferred embodiment of the invention, an elastomeric sleeve  54  is employed to expand the malleable band, any hand or power tool capable of exerting a radial force can be used. For example an expandable ring outside of a pneumatic or hydraulic chamber in communication with a pressurized gas or fluid source may be used to expand the malleable band. In the alternative, the gas or hydraulic chamber may flexibly constructed be to be inserted within the malleable band and expanded with pressurized gas or fluid. In addition, an electric motor or solenoids powering a radial expansion of a ring can also be used to expand the malleable band. Furthermore, a hand tool having a ratchet and lever mechanism for expanding the malleable ring can be used. Any tool producing an outward radial force on the band can be used to practice the invention. 
       FIG. 4  illustrates the tool positioned within a malleable band  70 , which, in a preferred embodiment of the invention, comprises copper. Other malleable metals and combinations thereof can be used. The malleable band  70  is positioned within the inner tube  12 . With the tool  50  and malleable band  70  positioned as shown in  FIG. 4 , one or both of the bolts  53  can be rotated into the metal cylinder shown in  FIG. 2  to expand the radius of the malleable band  70 . When the malleable band  70  expands outwardly into engagement the inner tube  12 , the inner tube  12  deforms and bulges outwardly towards and into contact with the outer tube  14 . At this point, any lack of concentricity of the tubes will be removed as the tubes conform to one another. Once the inner tube  12  is expanded sufficiently, a watertight seal is formed between the inner tube  12  and the outer tube  14 . The bolts can be reversed to allow the elastomeric sleeve  54  to return to its normal shape, releasing contact with the side of the malleable band  70 . The tool  50  may then be removed from within the malleable band  70 . The band  70  stays in place, permanently deformed, and permanently holding the inner tube  12  in engagement with the outer tube  14 . 
       FIG. 5  illustrates an application of an embodiment of the invention to the field of oil/grease separators for commercial kitchen sinks. A rotomolded polyethylene or polyurethane baffle  80  is positioned within a separator housing  90  so that a tube  81  of the baffle  80  is disposed within a tube  91  of the separator housing  90 . Within the tube of the baffle is a malleable band  70  that can be expanded radially with a tool to form a watertight seal between the baffle  80  and the separator housing  90 . U.S. Pat. No. 6,800,195 to Batten et al. discloses an oil/grease separator having a housing and an inner baffle that may be joined in this manner. The entirety of the disclosure of U.S. Pat. No. 6,800,195 to Batten et al. is incorporated herein by reference. 
       FIG. 6  illustrates a substantially dog bone shaped assembly  120 . The assembly  120  includes a rotomolded, polyethylene or polyurethane part  130  having a tubular portion  133  and a malleable band  140 . The tubular portion  133  of the part  130  is substantially disposed within and joined at a tubular portion  153  of another part  150  to form the dog bone shaped assembly  120 . The part  150  may be rotomolded. This technique enables low cost formation of rotomolded parts. Rotomolded parts having two larger ends connected by a narrow portion are difficult to rotomold, and this technique lets such shapes be made with low-cost rotomolded parts. Such shapes are referred to herein as “dog bone.” 
     Various modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. Such modifications and improvements, whether or not they are described herein, may certainly fall within the scope of the following claims.