Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-08-24
2003-02-18
Crispino, Richard (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S159000, C156S211000, C156S296000
Reexamination Certificate
active
06521072
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the electrofusion welding of profile wall pipes made from thermoplastic materials including polyethylene, polyvinyl chloride, nylons, polybutylene, polypropylene, and the like. Specifically, this invention relates to electrofusion welding of such pipes to obtain a joint which has substantially flush interior and exterior surfaces and provides constant inside and outside diameters, without the need for a coupler.
BACKGROUND OF THE INVENTION
This invention pertains to the joining of profile wall thermoplastic pipes including polyolefin, polyethylene, polyvinyl chloride, nylon, polybutylene, polypropylene, and the like. These types of pipes are gaining popularity in water, sewer, culverts, and industrial piping because of their characteristics of being lightweight, corrosion resistance, strong, and durable.
“Trenchless” rehabilitation of culverts, storm sewers, sanitary sewers, and other underground pipes by “slip lining” or “insert renewal” using thermoplastic pipes is gaining popularity and growing rapidly throughout the United States and other countries. In this process, a thermoplastic pipe or liner is inserted into an existing pipe or culvert without removal of the deteriorated pipe. The replacement pipe is pushed into or pulled through the existing culvert. In many cases, an existing pipeline can be rehabilitated for a fraction of the cost of replacement and with minimal inconvenience to the public.
Thermoplastic pipes, including polyethylene, are the preferred pipe material for many rehabilitation projects because of the price and the above-noted characteristics of such pipe. Generally, thermoplastic pipe is manufactured in lengths which are sufficiently short to permit transportation and handling. In the field where the pipe is to be installed, the short pipe sections must be connected to form a continuous pipe of a predetermined length appropriate for the application.
The joining or connecting of thermoplastic pipes can present many problems because of the variety of field conditions encountered and because of the chemical resistance of the thermoplastic pipes which, in many cases, makes such pipes impervious to glues or cements. Additionally, some thermoplastic pipes have a tendency to “creep,” or move, when subjected to changing temperatures. Because most applications include exposure to such temperature changes, such movement or “creeping” limits the ability to use mechanical type joints such as threads.
In general, several methods exist to join thermoplastic pipe in the field. A first method, known in the art as “butt fusion,” involves the use of a heat fusion machine which includes line up equipment and a heat plate. The ends of two pipes to be joined are inserted into the line up equipment which aligns and advances the pipe ends toward one another as necessary. The two pipe ends are pressed against the heat plate which heats and softens the two pipe ends. The heat plate is then removed and the line up equipment advances the two pipes toward one another at a predetermined rate (depending on the size and thickness of the pipe walls) in order to fuse the pipe ends together. This type of butt fusion requires special fusion equipment that is expensive, is not always available in the field, and cannot be used with certain types of pipe.
Another method known in the art is the use of electrofusion collars or inserts. One type of electrofusion collar is shown in U.S. Pat. No. 4,530,521 to Nyffeler, et al. and one type of electrofusion insert is shown in U.S. Pat. No. 3,768,841 to Byrne at al. These devices, as shown in the references, use a sleeve, collar, or insert made of thermoplastic material which either fits over or into the two pipes being joined. The pipes, and the collar or insert are first heated to soften the thermoplastic material. If using a collar, the pipe ends are inserted into the collar and are thereby joined. If using an insert, the insert is inserted into each pipe end, thereby joining the pipes. The heating can be performed with fusion equipment or, alternatively the collar or insert can contain an electrical resistance element to provide the necessary heat to cause electrofusion welding between the pipes and the collar or insert.
These devices have various disadvantages, including the creation of interior obstructions or exterior protrusions which are not acceptable in many applications. For example, because the collar must be large enough to accept insertion of the pipe ends, the resulting joint does not have a flush exterior. Additionally, because the insert reduces the inside diameter of the pipes at the joint, the insert acts as an obstruction to flow through the pipe. This is unacceptable in most applications, including most trenchless rehabilitation projects, because interior flow obstruction is not acceptable. Furthermore, exterior collars impede insertion of the replacement pipe during slip lining, as known in the art, thereby requiring the use of smaller diameter replacement pipes so that the collar can fit over the pipe and the entire coupling can still fit inside the existing pipe or culvert.
Another method of joining thermoplastic pipes utilizes electrofusion rods or mesh as shown in U.S. Pat. No. 5,410,131 to Brunet et al. Although this method requires no collar or insert, the application requires substantial end pressure to join the two pipe ends. Due to the weight of the pipes, such pressure is usually supplied by special line up equipment and this equipment is expensive and not always available or practical for use in field conditions.
Another method, hot air gun welding, uses a welding rod of thermoplastic material fed through the nozzle of a hot air gun. The hot air gun applies heat to the ends of the pipes being welded and melts the welding rod which is applied to a bevel cut between the two ends of the pipes to be joined. As with the butt fusion methods, line up equipment must be used and this method has not proven satisfactory in field conditions due to a lack of uniformity in the weld.
As thermoplastic resin prices increase, plastic pipe manufacturers are constantly looking for manufacturing methods to make pipe lighter without reducing physical strength. One type of thermoplastic pipe that has been developed to address these concerns, and that is gaining popularity, is “profile wall pipe” as it is known in the art. An example of this type of pipe is shown in U.S. Pat. 5,362,114 to Levingston. Profile wall pipe is thermoplastic pipe formed by extrusion to have an inner cylindrical wall, a generally concentric outer cylindrical wall, and a helical rib between and connecting the inner wall and outer wall.
Profile wall pipe is lighter than solid pipe and is created with less material, thereby reducing resin costs, but maintains a high degree of strength. Because of its light weight, profile wall pipe generally has a competitive advantage over solid wall plastic pipe. For these and other reasons, profile wall pipe is popular in the industry. Unfortunately, conventional methods of fusing solid wall thermoplastic pipe are unacceptable and will not work on profile wall pipe. This is due, in part, to the configuration of the end wall of the profile wall pipe which does not provide a solid annular surface due to the presence of the helical rib.
For example, butt fusion is very difficult on profile wall pipe because the pipe ends of profile wall pipe are not solid. The profile wall pipe ends have a thin inner wall, a thin outer wall, and a “profile space” between the inner and outer walls, the axial depth of which is equal to the distance between the end of the pipe and the helical rib which connects the inner and outer walls. The same problems that exist in joining solid wall thermoplastic pipes are multiplied in profile wall pipes because of their relatively thin inner and outer walls and large profile space between the walls.
For example, one manufacturer produces a polyethylene 10″ inside diameter profile wall pipe that has inner and outer wall thicknesses of 0.065″
C&S Intellectual Properties, LLC
Crispino Richard
Koch, III George R.
Thompson & Coburn LLP
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