Patent Application
20110227335
The invention relates to piping. More particularly, the invention relates to pipe electrofusion.
One aspect of the invention involves an electrofusion pipe fitting. The fitting has a body having a pipe-receiving aperture. An electric heating element surrounds the aperture. The fitting has a thermochromic indicator at an axial end.
In various implementations, the thermochromic indicator may be thermally communicated with terminal portions of the electric heating element. The fitting may be a collar for coupling first and second members.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference numbers and designations in the various drawings indicate like elements.
In operation, the collar is used to secure respective first and second mating members. An exemplary first member is a fitting having an annular end portion which is inserted into the channel 48. A clamp (not shown) may be placed around the outer wall 42 and closed, contracting the slots 44 and compressing the outer wall into engagement with the associated first member. The clamp may be positioned via ribs 80 (
As so far described, the collar and its operation may correspond to the exemplary prior art collar and process. However, other variations are possible.
It is desirable to verify that sufficient heating has occurred to form an effective fusion joint. To provide an indication of such sufficient heating, a thermochromic indicator 100 is provided on the body. The exemplary thermochromic indicator is provided along the outboard face 102 of the tab/boss 36. In an exemplary sequence of manufacture, the coil is prefabricated (wound from wire and contacts attached). The coil is then inserted into a molding tool and the body is molded thereover. The coil may be pre-encapsulated in material which forms the inner wall or the inner wall may be formed during a single molding process with the rest of the body. Exemplary molding of the body forms a low wall 104 along the face 102. The wall 104 bounds a pad portion of the surface 102 to which the thermochromic indicator may be applied (e.g., as a liquid in a brushing or spraying operation). The liquid may then dry (through evaporation which may be fan/hot air-assisted) or cure to harden.
The composition of the thermochromic indicator is selected in view of its proximity to the coil so that it changes color at a temperature where sufficient fusion has taken place. In particular, the location along the face 102 may provide a beneficial combination of visibility and proximity to the terminal legs of the conductor (which allows heat transfer from the terminal legs to the indicator). The exemplary location has the indicator coating starting within 4.0 mm of the interface of the pipe entering the fitting (e.g., 2.0-4.0 mm).The particular temperature of the indicator at which the indicator changes color will be appropriate to the plastic materials being fused. For example for a typical George Fischer Fuseal polypropylene fitting, an exemplary temperature is 60+/−1 C. For a polypropylene schedule 80 fusion system an exemplary temperature is 65+/−1 C and for a PVDF system an exemplary temperature is 71+/−1 C. Even a much lower temperature threshold allows the indicator to provide an indication that a joint has been energized (e.g., not missed by the technician who uses the electrofusion power source; although not then indicating quality of fusion).
The exemplary color change is permanent/irreversible. An exemplary indicator comprises a cholesteric thermochromic liquid crystal base (e.g., forming in excess of 50% by weight of the coating wet). An exemplary such base material is commercially available from LCR Hallcrest, LLC as Chromax. Such a base material tends to be very unstable when subjected to UV light and will change color over time with exposure. This would be disadvantageous because of a desire to store the finished product for some time and a desire to be able to install the product outside where it would be exposed to sunlight. To increase stability, a UV absorber may be added. An exemplary absorber is titanium dioxide (TiO2) which may be compounded into the coating to serve as a UV stabilizer and viscosity modifier (e.g., at least 2% of the coating by weight wet). Because the commercial thermochromic coatings have some variability to their UV stability, with each batch, one may make up a series of samples at different loadings and choose the lowest amount that works with the particular batch. Additionally, adding the TiO2 increases the viscosity of the coating, making it easier to apply and also shortening the drying time. Exemplary TiO2 is available as TiONA® from Millenium Inorganic Chemicals, Ltd./Cristal Global.
In addition to the TiO2 or other absorber, a hindered amine light stabilizer (HALS) may be used. An exemplary HALS is Lowinox® CPL Phenolic Antioxidant from Chemtura Corporation (e.g., at least 6% of the coating by weight wet). In the post heated condition the thermochromic indicator will turn (from the initial white) an intense red or black color in the area nearest to the highest fusion temperature and may turn gray or pink as the distance from this location increases. The presence of the red or black area (or other color if a different indicator is used) will indicate the fusion.
A specific example involves, by weight: 85% Chromax Magenta K60; 5% TiONA RCL4 (RMS 1049); and 10% Lowinox CPL 50D UV. A nominal broader specification would be 83-87% such base material, 3-6% such TiO2 material, and 8-12% such HALS by weight wet.
One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, different particular end uses (e.g., materials, pipe sizes, and purposes) may influence particular implementations. Furthermore, when implemented as a redesign of an existing electrofusion component, details of the existing component may influence details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.
Benefit is claimed of U.S. Patent Applications Ser. No. 61/316,229, Filed Mar. 22, 2010, and Ser. No. 61/362,470, Filed Jul. 8, 2010, both entitled “Electrofusion Fitting”, the disclosures of which are incorporated by reference herein as if set forth at length.
| Number | Date | Country | |
|---|---|---|---|
| 61316229 | Mar 2010 | US | |
| 61362470 | Jul 2010 | US |
