Background of the Invention

The present invention relates to methods and apparatus for making fluid conduits, particularly multilayer (metal and plastic) conduits suitable for use in fire sprinkler and nozzle systems.

Sprinkler system installers typically use metal conduit, either copper or more commonly iron or steel pipe, as supply lines in automatic sprinkler systems. Such metal lines obviously resist fire and temperature damage better than other structural materials that might be used. Each metal has relative cost advantages and disadvantages. Typically, piping is provided in fixed lengths and must be cut to size prior to installation. Ferrous pipe was then typically threaded in the field and mated with a threaded coupling. The use of threaded couplings in ferrous piping adds significantly to the labor costs of installing such systems. Copper tubing installs more quickly than ferrous pipe as the cut lengths of copper can simply be slip-mated with appropriate fittings and then soldered. However, copper is quite expensive in material cost compared to ferrous pipe.

Other types of non-threaded mating systems have been developed for metal, particularly steel pipe. Crimpable fittings can be used to join small diameters of the lightest Schedule 5 steel piping. Other types of

mechanical, compression type fittings are known which sealingly mate with the exterior ends of grooved piping. Still other types of mechanical joining systems employ a tubular insert positioned in each open end of a pair of adjoining piping members and an external compression fitting which is applied over the ends and the insert to compress the ends against the insert . Such systems require either the mechanical shaping and disruption of the smooth, cylindrical ends of the piping by the addition of grooves, flanges or the like and/or the use of unique and typically expensive compression fittings. Chlorinated polyvinyl chloride (CPVC) plastic piping and fittings have been listed by Underwriters Laboratories for certain fire sprinkler systems. One listed CPVC compound is BLAZEMASTER ^® brand CPVC of The

B.F.Goodrich Co., Cleveland, Ohio. BLAZEMASTER ^® is a registered trademark of The B.F.Goodrich Co. Underwriters Laboratories also lists certain polybutylene sprinkler pipe and fittings for such use. Piping made from plastic has proved to be less expensive in material cost than copper while installation costs have been comparable to copper. Similar steps are involved in joining together both types of plastic and copper pipe. However, plastic piping is more flexible than metal piping. Support must be provided more frequently with plastic piping than with metal piping and more frequently with polybutylene than with CPVC. This can add sufficiently to both the material and labor costs

to raise the total costs of such plastic systems above the costs of metal systems in some cases.

Hybrid plastic/metal piping and couplings have been proposed for fluid conduit systems for many years. For example, U.S. Patent 5,143,407 to Cokeh refers to copper tubing coated with polyvinyl chloride (PVC) for protection against denting and discloses a variety of copper fittings partially coated with PVC for the formation of joints. Cokeh does not indicate how such composite tubing is or could be made or if it has been made. U.S. Patent No. 3,502,492 discloses the electrostatic deposition of a light dusting of an epoxy resin upon the surface of a metal substrate like the outer surface of a metal pipe, the electrostatic deposition of PVC resin particles upon the surface in a heavier layer and the heating of the substrate to coalesce the PVC and epoxy resins to form a PVC layer adhered to the surface of the substrate. U.S. Patent No. 4,481,239 discloses coating metallic substrates such as iron pipe with one or more crosslinking resins which are applied to the pipe surface and heated sufficiently to crosslink, and an olefin polymer applied to the heated, coated substrate as an outer layer.

Summary of the Invention

In one aspect, the invention is a method of fabricating plastic covered metal conduit comprising the steps of: applying a heat activated adhesive material to an outer surface of a tubular metal pipe, completely

around the outer surface; heating the material on the outer surface to at least a predetermined elevated temperature above ambient effective to render the material adhesive; and extruding a thermoplastic material selected from the group consisting essentially of chlorinated polyvinyl chloride, polyvinyl chloride, acrylonitrile-butadiene-styrene, polyurethane and combinations thereof onto the heat activated adhesive material and entirely along and around the tubular outer surface of the heat activated adhesive covered metal pipe, seamlessly covering the entire outer surface of the tubular metal pipe.

In another aspect the invention is an apparatus for fabricating plastic covered metal conduit comprising: means for applying a heat activated adhesive material to an outer surface of a tubular metal pipe, completely around the outer surface; means for heating the adhesive on the outer surface to at least a predetermined elevated temperature above ambient effective to render the material adhesive; and means for extruding a thermoplastic material selected from the group consisting essentially of chlorinated polyvinyl chloride, polyvinyl chloride, acrylonitrile-butadiene-styrene, polyurethane and combinations thereof onto the heat activated adhesive material and entirely along and around the tubular outer surface of the heat activated adhesive covered metal pipe, seamlessly covering the entire outer surface of the tubular metal pipe.

299 PO7US96/17608

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Detailed Description of the Drawings

The foregoing summary as well as the following detailed description of preferred embodiments will be better understood when made in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown diagrammatically in the drawings, embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the specific embodiments, elements and methodε disclosed in the drawings. In the drawings:

Fig. 1 is a partially broken away length of multilayer conduit according to the present invention;

Fig. 2 is a cross-section of an exemplary plastic pipe fitting; Fig. 3 is a side elevation of part of an automatic ceiling sprinkler system utilizing multilayer conduits and fittings of Figs. 1 and 2;

Fig. 4 is a cross-sectional view taken along the lines of 4-4 of Fig. 3; Fig. 5 is a cross-sectional view taken along the lines 5-5 of Fig. 4;

Fig. 6 is a quarter-section side elevation view of a multilayer metal/plastic, tee-shaped threaded adaptor fitting of the present invention for mating a conventional threaded fire sprinkler or nozzle in a multilayer conduit system like that of Fig. 3;

Fig. 7 depicts in quarter-section side elevation view, another exemplary fitting of the present

invention with an alternate form of securement to the forms depicted in Fig. 6;

Fig. 8 depicts in end view yet another exemplary fitting of the present invention with an alternate form of securement to those depicted in Figs. 6 and 7;

Fig. 9 is a schematic view of a process for manufacturing multilayer pipe according to the present invention; Fig. 10 depicts schematically, in cross- section, an extrusion head for applying a layer of CPVC resin to the adhesive covered outer surface of a ferrous pipe;

Fig. 11 depicts schematically an end view of the extrusion pin of the extrusion head of Fig. 10.

Fig. 12 depicts schematically the interior of an air sizing collar on the extrusion head.

Detailed Description of Preferred Embodiments Certain terminology is used in the following description for convenience only and is not intended to be limiting. The words "right", "left", "lower" and "upper" designate directions in the drawings to which reference is made. The words "radial" and "axial" refer to directions perpendicular to and along the central axis of an object, element or structure referred to or other designated axis. The words "inwardly" and "outwardly" refer to directions towards and away from, respectively, the geometric center of the object, element or structure.

The terminology includes the words above specifically mentioned, derivatives thereof and words of similar import. Moreover, throughout the drawings, like numerals are used to indicate like elements. Fig. 1 depicts diagrammatically an exemplary multilayer fluid conduit of the present invention indicated generally at 10. Conduit 10 is formed by a length of hollow metal pipe 12 having a completely closed, tubular outer surface 13 and an opposing closed tubular inner surface 14. The multilayer fluid conduit 10 further includes a preferably uniformly thick thermoplastic layer 20 which preferably at least essentially completely covers the closed, tubular outer surface 13 of the ferrous metal pipe 12 from one end 15 to an opposing end 16 of the pipe 12. An adhesive layer 22 is provided between the metal pipe 12 and the thermoplastic layer 20, bonding the thermoplastic layer with the outer tubular surface 13 of the metal pipe 12. The tubular inner and outer surfaces 14 and 13 of the metal pipe 12 are, in this embodiment, uniformly smooth (within manufacturing tolerances) from end 15 to end 16 and provide uniform inner and uniform outer diameters to the ferrous metal pipe 12 from one end of the pipe 15 to the other end 16. Fig. 2 depicts diagrammatically one fitting 30 of a variety of fittings which may be used with the multilayer fluid conduit 10 to assemble multilayer fluid conduit systems of the present invention like the fire sprinkler system indicated generally at 40 m Fig. 3.

Returning back to Fig. 2, fitting 30 is a conventional, "tee" shaped sprinkler head adaptor. Fitting 30 includes an integral, thermoplastic body with first and second opposing tubular open ends 32 and 33. The tubular open ends 32, 33 are connected by a central tubular branch section 34 having a third tubular open end 35. A metallic insert 36, internally threaded to receive the threaded end of a fire sprinkler or nozzle or other complementary threaded member, is preferably molded into the fitting body to form the internally threaded opening of the third open end 35. The exposed, innermost tubular surfaces of the tubular open ends 32 and 33 are thermoplastic and again preferably uniformly smooth and of a constant inner diameter. Fig. 3 depicts diagrammatically a portion of a fire protection system 40 utilizing multilayer fluid conduits 10 of the present invention. The portion of the multilayer fluid conduit system depicted in Fig. 3 iε provided by a plurality of the multilayer fluid conduits 10, connected together, end to end, by a plurality of the tee fittings 30. Hollow ends of adjoining lengths of the multilayer conduits 10 are received in each of the opposing first and second open ends 32 and 33 of each tee fitting 30. The tubular opening 35 of each tee fitting 30 receives the threaded end of a conventional fire sprinkler 38 or nozzle 39. A fire sprinkler 38 would have a plug and triggering mechanism holding the plug in place until released. A fire nozzle would be similar to a sprinkler but would lack a plug and triggering

mechanism. It may even lack a deflector and achieve a water distribution pattern by special shaping of its orifice.

As is best seen in Figs. 4 and 5, the outer thermoplastic layer 20 of each conduit 10 is bonded at 46 to the exposed innermost tubular surface of one of the tubular open ends 32 or 33 of the thermoplastic fitting 30 (or another suitable fitting) to form a sealed joint between the conduit 10 and fitting 30. It should be noted that the central branch section 34 defines an exposed, thermoplastic inner tubular surface section of the conduit system 40.

In addition to being joined by thermoplastic fittings like the fitting 30, it will be appreciated that according to the present invention, the multilayer conduit 10 can be connected or otherwise combined using other fittings of standard configuration which are currently used with all-CPVC piping for fire protection systems and with other plastic conduit systems for other uses. These include but are not limited to other forms of sprinkler adapters, straight couplings, elbows, bushings, crosses, caps, plugs, flanges, grooved coupling adapters, and unions, each with slip, spigot or slip and spigot style ends and reduction or uniform internal diameters.

In the preferred embodiment of system 40 configured for fire protection, metal pipe 12 of conduit is of ferrous material, preferably steel. The thermoplastic layer 20 is preferably of a fire protection

rated chlorinated polyvinyl chloride (CPVC) such as BLAZEMASTER ^® brand CPVC of The B.F.Goodrich Co. The adhesive layer 22 permanently bonds the CPVC layer 20 to the outer surface 13 of the ferrous metal pipe 12 and can adapt to the different coefficients of thermal expansion of the steel and the CPVC to maintain the bond. The fittings 30 and like fittings for fire protection systems are preferably of a fire protection rated CPVC such as BLAZEMASTER ^® brand CPVC with brass threaded inserts 36 and are currently available today from various commercial sources including Central Sprinkler Co. of Lansdale, PA.

The use of CPVC, in particular, is an important aspect of the preferred embodiment of the invention in several respects. In terms of fire protection systems, only CPVC and polybutylene have passed industry standards for fire safety and thus are the only plastics that can be used currently for fire protection conduit systems in virtually all locals which permit the use of plastic in such systems. However, polybutylene systems have lower maximum ambient operating temperatures (120°F versus

150°F for CPVC) , are more flexible than CPVC and require the provision of heat bonded mechanically crimped joints. Polybutylene heat bonded joints have been proven to be prone to failure after extended thermal cycling. CPVC can be bonded directly to CPVC to form leakproof joints at ambient temperatures of from about 0°F to 100°F or more with known, solvent based bonding agents. CPVC can be installed with fewer support hangers and in locations with higher ambient temperatures and with less structural

protection than can polybutylene. Among plastics commonly molded or extruded, CPVC is one of the most difficult to work with. Extrusion temperatures for CPVC polymers range generally from between about 400° to about 450°F. However, extrusion temperature for particular extrusion equipment and CPVC formulations may have much narrower ranges, i.e. only about 10°-20°F. For example, the BLAZEMASTER ^® brand CPVC compound has a preferred extrusion temperature range of only between about 415° to 430°F. in the extrusion layout to be described. The CPVC preferred for extrusion is the conduit outer layer 22 is The B.F.Goodrich Co. BLAZEMASTER ^® No. 88745 compound. Further information about CPVC resins used in BLAZEMASTER ^® No. 88745 CPVC compound is provided in U.S. Patent 4,412,898 which is incorporated herein in its entirety.

Very thin, cold rolled steel, for example SAE C1010 twenty gauge steel, is presently preferred for the ferrous metal pipe 12 of the multilayer conduit 10 of the present invention as it offers cost benefits not found in other metals. Other ferrous metals that might be used include galvanized steel, stainless steel or a steel with higher carbon values than C1010 to minimize wall thickness through increased strength. Adhesion of the preferred CPVC material with the ferrous pipe 12 is necessary as CPVC will not directly bond to metal even when extruded in a melted form onto the metal. Adhesive layer 22 is provided to prevent the likelihood of water wicking between the metal

pipe 12 and the CPVC outer layer 20 covering the pipe 12 when the conduits 10 are connected together into a fluid conduit system. The adhesive layer 22 further is also sufficiently elastic to accommodate the different thermal expansion coefficients of the metal pipe 12 (about 6 to 7xl0 ^"6 /F°) and CPVC outer layer 20 (about 3.4xlO- ⁵ /F°) to prevent failure of the bond between the CPVC and the ferrous pipe in use. If the conduit 10 is to be capable of being cut to any length for use, the adhesive layer must extend entirely around and entirely along the pipe 12 from end to end. A series of separate, individual adhesive rings might be provided along the pipe but a continuous adhesive layer running the entire length of the pipe completely around the pipe is preferred for versatility and reliability. If the conduit 10 is to be used without further cutting, it is only necessary to provide an adhesive layer around either end of the pipe 12 extending away from the pipe end a distance sufficient to create an enduring waterproof seal between the pipe 12 and CPVC layer 20 around each of the ends of the pipe 12.

Preferred bonding materials for the aforesaid steel pipe and BLAZEMASTER ^® brand CPVC compound are The B.F. Goodrich Co. Adhesive No. A1718B and a two part system, Chemlok ^® 485 and Curative 44, of the Lord Corporation, Elastomer Products of Erie, Pennsylvania.

Each is preferably sprayed on the outer surface 13 of the pipe 12 without dilution in an amount sufficient to yield a thickness of about two to three mils when dry.

If the outer diameter of the multilayer conduit 10 is fixed by the inner diameter of the conventional fittings with which it is used, the outer diameters of the metal pipe 12 will depend upon the thicknesses of the thermoplastic and adhesive layers 20 and 22. As a result, the metal pipe of the present invention generally typically will be of non-standard outer and inner diameters.

The multilayer conduit 10 of the present invention has all of the fabrication advantages of all plastic piping. Multilayer conduit 10 of the present invention can be cut to any length in the field using common wheel cutters. The cut end is preferably deburred and the CPVC layer may be chamfered for ease of assembly. No threading or grooving or other disruption of the conduit ends or of the metal pipe in particular is required for joint formation. An ambient temperature acting bonding agent is simply applied around the end of the conduit 10 on the exposed thermoplastic layer 20 and/or on the exposed innermost surface of the fitting, which is formed by the exposed thermoplastic layer, receiving the end of the conduit. The pieces are joined by inserting the conduit end in the fitting open end and twisting to distribute the bonding agent. The resulting bonded joint will cure and be pressure supportive within minutes using the indicated preferred bonding agents. The thermoplastic outer layer 20 has the further advantage of protecting the outside of the metal pipe 12 from corrosion.

One step solvent cements produced by the IPS Corp. of Gardena, CA, and the Oatey Company, Cleveland, OH, are the preferred ambient temperature acting bonding agents to join the above described CPVC coated conduits 10 and CPVC fittings 30 and provide joints which remain leak-proof and integral at pressures of at least 875 psi or more. The IPS formulation is known as Central Sprinkler CSC-300 Solvent Cement. It is also known as WELD-ON 723 (Modified for BLAZEMASTER ^® CPVC Pipe) . The Oatey formulation is called "Oatey Medium Red

BLAZEMASTER ^® Cement CPVC-Low VOC." These bonding agents are applied directly, without dilution and are suitable for use at ambient temperatures, i.e. at some temperature (s) between about 0° and 120°F. Each is described as a mixture of CPVC resin and organic solvents including tetrahydrofuran, methyl ethyl ketone, cyclohexanane and acetone. Each is applied without dilution and cures at room temperature (e.g. about 0 - about 120° F) . Fig. 6 depicts a multi-layer metal/plastic threaded sprinkler tee shaped fitting 130, that can be used for increased thermal protection in higher challenge fire locations. The fitting 130 includes an inner, conventional CPVC fitting 30, like fitting 30 of Fig. 2, and a surrounding metal shell 132. Metal shell 132 can be stamped, shaped and folded around the fitting 30 and secured by brazing indicated generally at 134 or banding indicated by band 136. Other forms of securement are shown in Figs. 7 and 8. In Fig. 7, pairs of facing

flanges (one being depicted at 138) are provided on a modified metal shell 132' of another embodiment 130' with opening(s) 140 to receive a conventional fastener 142. Fig. 8 is another fitting embodiment 130'' in which outwardly turned and inwardly turned opposing flanges

138'', 139'' of metal shell 132'' overlap one another and lock around the fitting 30. Each of shells 132, 132' and 132'' provides a metal layer at least substantially entirely covering the otherwise outer surface of fitting 30.

Fig. 9 depicts in block diagram form, suggested steps for fabricating the multilayer conduit 10. Preferably, the thin-walled steel pipe 12 is provided preformed in individual, cut standard lengths. The steel pipe is cleaned of any residual scale and other contaminant (s) and degreased at step 60 and then cleaned of degreaser, for example, by forced air evaporation at step 62. Next, an appropriate adhesive material 24 is applied to the completely closed tubular outer surface 13 by any suitable means in an adhesive applying step 64.

Spraying the entire outer surface of the metal pipe 12 is preferred but the adhesive material 24 may be brushed or rolled onto the pipe 12 or the pipe 12 may be dipped. The adhesive material 24 is then dried in a drying step 66. For the disclosed preferred adhesives, drying is preferably accomplished by heating at a temperature below the activation temperature, for example, about 150°F., to sufficiently eliminate solvent carriers from the adhesive to permit the pipe with adhesive coating or layer to be

handled. The adhesive coated pipe will hereinafter be identified by reference numeral 12' . The pipe with adhesive material layer 12' can be dried by heating to a temperature as hot as the adhesive will permit without activating. This is about 340°-350°F. for The

B.F.Goodrich adhesive but only about 250°F. for the Lord Co. system.

The pipe with adhesive coating 12' is passed through an extrusion head 88 as shown in Fig. 10. The preferred adhesive material layer 24 is preheated by a set of preheaters 85a, 85b, 85c and by the tooling of the head 88 to an activation temperature above the drying temperature, desirably above 350°F., in a heat activating step 68 just prior to application of the melted CPVC. The indicated adhesives are heated to about 360°F. or more for activation. The adhesive 24 is preferably heat activated before physically entering the extrusion head 88 but could be heat activated within the head as well. By preheating the surface of the pipe 12' at the entrance to the head 88, the pipe 12' can still be handled from outside the head to advance it through the preheaters and the head. Preheating the pipe 12' helps to maintain the temperature of the extruded plastic. CPVC 21 or other extrudable thermoplastic is applied in a tubular layer 20 in an extruding step 70.

The multilayer conduit 10 can be moved through the extrusion head 88 in a variety of ways including pushing, pulling or, preferably, a combination of

initially pushing and subsequently pulling, for example, using pinch wheels (not depicted) .

The conduit 10 may be treated in a sizing step 72 in which the outside surface is finished to achieve a more exact and uniform sizing of the outer diameter of the CPVC layer 20 and conduit 10. The outer diameter of the conduit 10 is believed to be sizable in a number of ways which are standard for sizing plastic tubing including but not limited to mechanical rolling, vacuum sizing or a combination of such processes, as well as by positive air pressure as will be described with respect to Fig. 12.

If mechanically cut lengths of steel pipe 12 are fed sequentially into the extrusion head 88, the ends of such pipe would be slightly inwardly rolled or

"dimpled" from the manufacturing process. This slight reduction in pipe diameter at the pipe ends is within normal manufacturing tolerances for such pipe. Although slight, the variation in dimension should be detectable by a proximity detector or the like with the pipes 12 butted end to end. Also, it would be possible to track the location of the pipe ends by providing an encoder or encoders on one or more servos controlling wheels feeding pipe through the extrusion head with a sensor or sensors which can detect the beginning and end of the pipe.

Alternatively the pipes could be fed into the extrusion head with gaps between each pipe. A space of about 1/32" or more could be developed between adjoining ends of adjoining lengths of pipe, depending upon the method of

feed. The space will be spanned by a continuous tube of the CPVC material, which should collapse between the pipes for lack of internal support to identify the pipe ends. Since these changes would be more pronounced than the rolled pipe ends, it is believed that other, different sensors (e.g. ultrasonic, magnetic, electric and/or optical means of detection) also can be used to locate the pipe ends exiting the extrusion head 88. The precut lengths of metal pipe 12 can thus be identified, separated from one another and the ends of the resulting multilayer conduits 10 cleaned of excess CPVC in a finishing εtep 74.

Fig. 10 depicts diagrammatically the major tooling components of a preferred extrusion head 88 for applying CPVC material to adhesive coated metal pipe 12' . A conventional extruder is partially depicted and indicated generally at 80. The extruder 80 includes a reservoir of CPVC which is heated and fed under pressure in a conventional manner through a coupling 82 into a feed conduit 86 of the head and into the extrusion head 88 itself. The CPVC passes through an opening 87a in a bushing 87 of the head 88 and into a compression chamber 96 defined between an inner tubular surface of bushing 87 and an outer surface of an extrusion pin 90. Extrusion pin 90 has a central bore 91 (in phantom) to receive and pass the adhesive coated metal pipe 12' and a feed channel 92 on its outer surface to receive CPVC from the feed conduit 86. The extrusion head 88 further includes a mandrel 94 supporting the pin 90 from its upstream end.

If desired, the downstream end of the pin 90 can supported by a knife edge spider extended between the pin 90 and the bushing 87 or between a die 98 attached to the bushing 87 and the pin 90. The bushing 87 surrounds the proximal end of the pin 90 and the die 98 surrounding the distal end of the pin 90.

Feed channel 92 has two symmetric halves, one of which is indicated at 92a and is seen in Fig. 10. The hidden half is a mirror image on the other side of the pin 90. Both halves 92a, 92b are seen in phantom in Fig. 11, an end view of the pin 90. Each feed channel portion 92a, 92b spirals helically from opening 87a to an opposing side of the pin 90, 180° around the pin 90 away from the opening 87a. Preferably, the feed axis of the extruder 80 and the central axes of the coupling 82 and feed conduit 86 are coplanar with one another and with feed channels 92a, 92b to minimize stagnation and shear. Each feed channel portion 92a, 92b smoothly and progressively diminishes in cross-sectional area from an essentially true semi-circle directly adjoining opening 87a to no cross-sectional area, where the feed channel 92a and its mirror 92b meet on the opposite side of the pin 90 from opening 87a. The pin 90 includes a generally cylindrical portion 90a supporting the channel 92. Pin 90 is thereafter inwardly tapered down in a cone-shaped portion 90b to a second, smaller diameter cylindrical portion 90c, having a wall thickness of less than 0.1 inch and an inner diameter only about 60 mils larger than the outer diameter of the steel pipe 12. If desired a

plurality of radially inwardly and longitudinally extending knife edges can be provided within the bore of pin 90 to help keep the pipe 12' centered as it feeds from the end of pin 90. The inner diameter of the bushing 87 below the channel 92 is about 0.3 inches greater than the diameter of the pin 90 immediately below the channel 92. This difference essentially defines the radial dimension of the annular compression chamber 96. The die 98 has a tapered portion 98a facing the tapered portion 90b of pin 90 and a uniform diameter bore 98b receiving the uniform diameter distal end 90c of pin 90. The uniform inner diameter bore 98b in die 98 might be, for example, about 0.09 to about 0.12 inches greater than the outer diameter of the extreme distal 90c of the pin 90 to extrude a tube of CPVC with a wall thickness of about 45 to 60 mils in order to apply about a forty mil thickness of CPVC or other thermoplastic to pipe 12'. The pipe 12' is passed through the extrusion head at a speed greater than the speed at which the CPVC compound is being extruded. Preferably, the speed is controlled to stretch the CPVC compound to approximately 40 mils, which is slightly less than the original extruded thickness.

To control the temperature of the CPVC compound, heating zones are maintained in or on the extrusion head tooling and elsewhere. Preferably separate, independently controlled heating zones are maintained on the coupling 82, the feed conduit 86, the head housing 84 above the bushing 87, and the bushing 87

itself below feed conduit 86. In addition, each of the preheaters 85a, 85b, 85c is preferably separately controlled upstream from the head 88 to preheat the pipe 12' and activate the adhesive coating 22 immediately prior to passing through the extrusion head 88. The extrusion head heat zones are preferably maintained at about 365°F. to permit some shear heating of the CPVC compound as it passes from the extruder 80 and through the head 88. The orientation and progressive reduction in cross-sectional area of the channel portions 92b, 92a are very important to the success of the CPVC extruding step. Portion 92a and its mirror image counterpart 92b move resin more quickly to the opposite side of the pin 90 than the resin would have arrived there without the channel 92 to prevent uneven cooling of the resin circumferentially around the pin 90. The channel halves 92a, 92b lie in a common plane with the centerline of the feed conduit 86 and bushing opening 87a. The depth of each channel half 92a, 92b is reduced linearly as each channel half extends from the bushing opening 87a (0° position on the pin 90) to the opposite side of pin 90 (180° position) . In addition, the cylindrical portion of the pin on the downstream side of the groove is further cut back from about halfway along each channel half 92a, 92b (i.e. about 90° and 270° positions) to the far side of the pin 90 (i.e. the 180° position) , again generally linearly beginning at about each halfway position (i.e. about 90° and 270° positions) to a depth of about 0.090

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inches at the opposite side (i.e. 180° position) of the pin 90. The generally uniform cooling of the melted CPVC is very important as it prevents the formation of a noticeable weld or knit line or a high stress concentration where such line might normally be located on the side of the pin 90 opposite opening 88a.

Preheating the adhesive coated pipe 12' to near the temperature of the extruded CPVC (e.g. within at least about 50°F. and preferably to within less than 50°F of the temperature of the applied CPVC) assists in maintaining temperature of the CPVC compound in the extrusion head 88, in a preferred temperature processing range. In the extrusion head 88, that range is only about 15°F (about 415° to about 430°F) . The preferred CPVC compound is resistive to being pulled to the preferred thinness due to its viscousness from chlorination. The preferred compound tends to tear if permitted to cool to 410°F. or below and tends to burn or gall if permitted to exceed about 450°F. If pulled too quickly through the tooling, the CPVC can be overheated by the friction and burn. The ideal temperature for discharging the CPVC would be just under or about 450°F. It is believed the above-described arrangement delivers CPVC compound to the pin 90 (or pipe 12') at about 430°F. One inch diameter pipe has been passed at a rate of up to about thirty to thirty-five feet per minute through the described tooling with the identified CPVC compound, steel pipe and heat activated adhesives.

Fig. 12 shows a proposed arrangement for sizing. A tubular sizing collar 100 is mounting in the exposed end of die 98. The collar includes an inner passageway 102 through which the plastic coated conduit 10 passes when exiting the die 98. An annular manifold 104 is provided within the collar coupled with a feed conduit 106 through which a pressurized source of air indicated by arrow 108 or other appropriate gas can be fed. A plurality of individual bores 110 extend radially inwardly from the manifold 104 into the inner passageway and define a ring of air jets which surround any conduit 10 passing through the extrusion head 88. Thickness of the thermoplastic layer 22 is controlled by a combination of operating parameters including feed rate of the pipe 10', feed rate and temperature of the CPVC compound or other extruded thermoplastic and pressure of the air or other gas blown through the bores 110.

While preferred embodiments of the invention have been disclosed and certain modifications thereto suggested, still other modifications and changes will occur to those of ordinary skill in the art. For example, while CPVC is preferred for the fittings and adhered CPVC is preferred for the conduits for sprinkler systems, other polymers might be used. Other extrudable, adherable, ambient temperature bondable polymers which might be used include, in addition to CPVC, polyvinyl chloride (PVC) , acrylonitrile-butadiene-styrene (ABS) , polyurethanes (both polyesters and polyethers) , and blends thereof with one another and with CPVC. All are

extrudable, adherable to metal and solvent bondable. In distinguishing between PVC and CPVC, any PVC polymer more than 57% by weight chlorine is considered a chlorinated ^■ PVC. The invention is not limited to the specific preferred embodiments and alternate embodiments disclosed, but is intended to cover all embodiments set forth in the appended claims .

U.S. Patent Application Nos. 08/552,298 and 08/552,295, both filed November 2, 1995, are incorporated by reference herein in their entireties.