Pipe joints or couplings – With assembly means or feature – Molded joint facilitator
Patent
1995-08-28
1998-05-19
Arola, Dave W.
Pipe joints or couplings
With assembly means or feature
Molded joint facilitator
2852881, 2853344, 285423, 285906, 228 23, 228 1, 2281145, F16L 1302
Patent
active
057527253
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and apparatus for joining together two or more lengths of a continuous section such as a pipe or a shaft or a rod, each having a substantially circular cross-section and particularly but not exclusively to a method or apparatus for joining sections formed from a material which softens or melts on heating such as thermoplastics, and metals such as steel or copper.
The invention is applicable to both solid and hollow sections and is particularly applicable to extruded plastics hollow pipe sections.
It is known to join two pipe sections by means of a friction welding process. Friction welding relies on generating heat at an interface between components to be welded by causing relative motion between them and applying suitable pressure on the interface to sustain the friction force. This motion could be linear or rotary and also could be oscillatory or continuous.
Conventionally, one of the components to be joined is moved towards or vibrated against the other. The heat generated at an appropriate rate by friction causes a layer of the surfaces of each component to melt at the interface. A degree of mixing of these layers due to the continuation of relative motion exists and the interface is gradually diffused forming a continuation of the material across the original interface.
The motion is then stopped and cooling is allowed to occur. The interfacial melt layer solidifies and forms a solid joint.
A disadvantage of this known process is that it is severely hampered in cases where one or both of the members of the joint is too large, heavy or already fixed in a structure, which makes the process of rotation and creating relative frictional motion too difficult or impossible.
In addition, in the case of axi-symmetric parts, such as solid round shafts, tubes or pipes, the welding process is restricted to forming joints having a coaxial configuration.
In a case where the material has a molecular or crystalline structure which can be controlled during the manufacturing stage of a pipe or a shaft by means of rotating dies, for example, an additional disadvantage of known welding operations which rely on heat by friction or any other means is observed. In some cases the structure of the material is given a particular pattern of orientation which is frozen in the material. This pattern may be lost, decreased or distorted during welding by conventional means.
It is known to join two hollow pipes formed by extrusion or any other method by means of a hot plate welding operation. In this method the ends of the pipes to be welded are placed in contact with a metal plate, which is electrically heated, one pipe at each side. The contact is sustained by applying a suitable axial force to the pipes against the plate sides. After a relatively short while (a few seconds), the heat from the plate causes a certain amount of the pipe material to melt. The plate is then removed and the pipes are pushed against each other. Contact takes place at the interface which is wetted by melt and suitable axial pressure is applied. The two molten layers at each of the pipe ends achieve contact and a bond takes place. Some of the melt material is squeezed out radially forming what is known as a welding bead. Upon cooling the joint becomes permanent and the bead is removed later by mechanical means.
Another known process for welding pipes together is a process known as electro-fusion. In this process the ends of the pipes are inserted into a specially designed cylindrical sleeve of suitable internal diameter. The sleeve contains a coil of electrically resistant wire incorporated in its body near the internal surface and with electrical contacts which are connected to an external source of electric current. With the pipes in position, the wire coil heats up upon passing a suitable current through it for a given length of time. This heat melts a sufficient amount of material from the pipes and the internal surface of the sleeve which fuse together forming a joint upon cooling. The sleeve remains in position and
REFERENCES:
patent: 3351512 (1967-11-01), Zelewsky et al.
patent: 3874067 (1975-04-01), Toyooka et al.
patent: 3888521 (1975-06-01), O'Sickey
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