Electric heating – Heating devices – Combined with pressure application means
Reexamination Certificate
1999-01-05
2001-05-29
Leung, Philip H. (Department: 3742)
Electric heating
Heating devices
Combined with pressure application means
C156S499000
Reexamination Certificate
active
06239412
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to portable machines for fusing polyolefin pipe and more particularly concerns heaters used to bring the pipe surfaces to be joined to a molten state prior to fusion.
The end-to-end welding of polyolefin pipes is the subject of earlier U.S. Pat. No. 3,729,360 issued on Apr. 24, 1973 for a Portable Thermoplastic Pipe Fusion Apparatus, U.S. Pat. No. 4,352,708 issued on Oct. 5, 1982 for a Defined Force Fusion Machine for Joining Plastic Pipe and U.S. Pat. No. 5,814,182 issued Sep. 29, 1998 for a Self-Contained and Self-Propelled Machine for Heat Fusing Polyolefin Pipes. In all of these machines, the pipe surfaces to be joined are brought to a molten state using a heater which is substantially planar in nature. That is, since the pipes are being joined end-to-end at planar faces, the heater inserted between them to simultaneously bring the faces to a molten state is a relatively thin planar structure. The heater is, therefore, relatively lightweight and easy to handle and consequently is suitable for use in field operations.
In the aforementioned U.S. Pat. No. 4,352,708, fusion of a branch pipe saddle fitting to the side wall of a main pipe is also taught. Branch pipe is then fused to the saddle fitting. However, while the machine therein disclosed can be used for sidewall fusion, the heater required to bring the surfaces to be joined on larger diameter pipes to a molten state is comparatively large and unwieldy for use in the field. Since the surfaces to be joined are curved, the heater must have opposed faces with complementary curves. Since these curved surfaces are disposed on opposite sides of a planar thermal element, the heater is much thicker and, in the case of larger diameter pipes, also comparatively larger diameter, so as to require the use of a crane or other lifting device to manipulate the heater. Therefore, sidewall fusion on pipes greater than 8″ in diameter cannot be practically accomplished in the field using known heaters. The present practice for larger diameter pipes is to make a T-configuration in the plant using a lifting device such as a crane to manipulate the heater, to ship the T-configuration to the site, to cut the main pipeline and remove a section of the pipe and then to weld the T-configuration to the main pipeline using existing end-to-end fusion technology. Furthermore, the undesirable thickness of the heater results in longer heat-up times for the heater, perhaps as much as half an hour, and poor temperature distribution over the heater surface which in turn causes an undesirable uneven melt in the pipe surface.
It is, therefore, a primary object of this invention to provide a heater usable in the field to bring surfaces of larger diameter pipe to molten condition for sidewall fusion. It is also an object of this invention to provide a heater usable in the sidewall fusion of polyolefin pipes which is lightweight and easy to handle. A further object of this invention is to provide a heater usable in the sidewall fusion of polyolefin pipes which is a relatively thin laminar assembly of a heating element sandwiched between relatively thin surface-contacting plates. Another object of this invention is to provide a heater usable in the sidewall fusion of polyolefin pipes which is adapted to be easily separated from the molten surfaces of the main and branch pipes. It is also an object of this invention to provide a heater usable in the sidewall fusion of polyolefin pipes which is easily removed from its operating position between the molten surfaces of the main and branch pipes. A further object of this invention is to provide a heater usable in the sidewall fusion of polyolefin pipes which has a relatively short heat-up time, perhaps in the order of 12 minutes. Another object of this invention is to provide a heater usable in the sidewall fusion of polyolefin pipes which provides relatively even temperature distribution on the heater contact surfaces.
SUMMARY OF THE INVENTION
In accordance with the invention a heater for use in fusing the end of a branch polyolefin pipe to the side wall of a main polyolefin pipe of specified radius has a first plate with a convex outer surface definable as a surface generated by rotating a first straight line about a first parallel line of origin at a radius equal to the specified radius of the main pipe and a concave inner surface, a second plate with a concave outer surface definable as a surface generated by rotating a second straight line about a second parallel line of origin at a radius equal to the specified radius of the main pipe and a convex inner surface and a heating element of substantially constant thickness disposed in laminar relationship between the first and second plates, the inner surfaces of the plates being contoured so that, with the heating element in laminar relationship therebetween, the lines of origin of the outer surfaces of the plates lie a common plane. Preferably one of the plates, and most preferably the second plate with the concave outer surface, has a constant thickness. The plates can be welded or screwed together with the heating element therebetween. Preferably the outer surfaces of the plates are serrated and their radii extend from their lines of origin to their respective meridians between the zeniths and nadirs of their serrations with their zeniths and nadirs aligned on cross-sections transverse to their lines of origin, zenith-to-zenith and nadir-to-nadir. Preferably, the laminar arrangement has a weight reducing aperture therethrough defined by a circular cylinder of radius less than an inner radius of the branch pipe, the cylinder being centered on the common plane of and extending perpendicular to the lines of origin. A thermometer is provided for indicating the temperature of the heater and a temperature sensor such as a resistance temperature device is used to provide a control signal from the heater. A junction box is provided for connecting the temperature sensor to the machine control circuit and the heating element to an electrical power source.
Preferably the machine has a base for clamping the main pipe in alignment with the branch pipe and a carriage assembly for guiding motion of the branch pipe toward and away from the main pipe and the laminar arrangement is adapted to be cooperable with the carriage assembly for horizontally aligning the laminar arrangement with a saddle-cut end of the branch pipe. Most preferably, the carriage assembly has a pair of horizontal rods diametrically aligned outside of the branch pipe and a pair of rods fixed to and extending outwardly from the laminar arrangement along an axis parallel to the lines of origin and above the common plane for aligning the laminar arrangement with the branch pipe.
It is further preferred that the machine include a linkage pivotally connected at one end to the base of the machine and pivotally connected at another end to the carriage of the machine, the linkage being cooperable with one of the heater assembly aligning rods to disengage the laminar arrangement from the molten branch or main pipe from which the laminar arrangement does not first disengage as the molten branch pipe is moved away from the molten main pipe. In a preferred embodiment, the linkage has a branch link pivotally connected to the carriage of the machine, a main link of length substantially equal to the length of the branch link and pivotally connected to the vertical post of the machine and a drag link shorter than the branch and main links and pivotally connected therebetween The linkage is disposed in a cup-configuration around one of heater assembly rods when the laminar arrangement is abutted between the main and branch pipes. Either the branch or main link strikes the heater assembly rod after the branch or main pipe, respectively, is disengaged from the laminar arrangement as the molten branch pipe is moved away from the molten main pipe. Thereupon, the other of the branch and main links and the drag link rotate into alignment with each other and urge th
Perrault James R.
Thoman Timothy M.
Catalano Frank J.
Leung Philip H.
McElroy Manufacturing Inc.
Van Quang
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