Abstract:
Apparatus usable in combination with means for extruding a waterproof plastic sheath on foam coating on the exterior of pipe, for reducing the diameter of the plastic sheath adjacent the pipe section ends to conform to the beveled end surfaces of the foam coating and adjacent protruding marginal portions of the pipe surface and thereby form a water stop excluding moisture from the foam thus enclosed by the plastic sheath.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to apparatus and method of coating pipe and consists particularly in means for applying a moisture seal to the transverse end surfaces of foam coatings on pipes. 
     2. The Prior Art 
     On pipe coated with polyurethane foam for thermal insulation purposes and having an external moisture-proof coating or sheath of extruded plastic, the foam coating is normally cut back from the ends of the pipe sections and its end surfaces are beveled. To prevent the intrusion of moisture through exposed end surfaces, accepted practice has been to apply a heat-shrinkable sleeve to this region and shrink it into a close fit over the bevel, the end marginal portion of the plastic sheath and the protruding surface of the pipe. 
     SUMMARY OF THE INVENTION 
     The invention provides means for extending an extruded plastic sheath integrally over the beveled end surface of foam insulation on a pipe and the protruding surface of foam coated pipe in close conformity with the beveled surface and the protruding pipe surface in the same operation as the application of the plastic sheath to the cylindrical body of the foam insulation so as to provide a water stop on the beveled end of the insulation integral with the body of the sheath. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of apparatus constructed according to the invention. 
     FIG. 2 is an enlarged longitudinal diametral sectional view taken along line 2--2 of FIG. 5 showing the pipe coating in longitudinal cross section. 
     FIG. 3 is a longitudinal diametral sectional view corresponding to FIG. 2 but showing the exterior of the pipe. 
     FIGS. 4 and 5 are transverse vertical sectional views taken respectively along lines 4--4 and 5--5 of FIG. 3. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The numeral 1 denotes an extrusion die having an annular passage 2 for the extrusion therefrom of molten plastic material M and a central cylindrical passageway 3 of sufficient diameter to permit the passage of aligned metal pipe sections P coated with polyurethane foam insulation F except at their abutting ends where insulation F is cut back on a bevel B, leaving several inches of the end of each pipe surface exposed as at S. 
     Anterior to extrusion die 1 with respect to the direction of pipe travel therethrough, a first cylindrical wall section 5 is attached to the inlet face 7 of die 1 by an annular flange 9 and a similar flange 11 at the remote end of wall section 5 mounts an inwardly positioned annular flap 13 of elastomeric material, preferably gum rubber having a central circular aperture of sufficient diameter to permit passage of the pipe with foam coating F through it while sealingly engaging the outer surface of foam coating F so as to define, with cylindrical wall 5 and the passageway 3 in die 1, a generally annular primary vacuum chamber, the forward end of which is closed by the inner surface of plastic sheath or outer coating C as it is extruded from die 1 on the outer surface of foam coating F. 
     A conduit 15 connects the chamber surrounded by cylindrical wall section 5 to a vacuum source, to provide a sufficient depression in the chamber to draw plastic coating C radially inwardly toward pipe P in the beveled region B and cut-away end sections S which, along with the outer surface of foam F, have been previously covered with mastic A, except for a margin preferably of about four inches at the abutting pipe ends, which are covered with tape T to prevent the adherence of the plastic coating to the pipe end and facilitate the removal of the plastic coating from the end portion of the pipe surface. A vacuum gauge 16 is mounted on wall section 5 to facilitate determination of the amount of depression in the primary vacuum chamber. 
     To ensure the maintenance of a vacuum in the primary vacuum chamber, a secondary vacuum chamber is formed anterior to sealing flap 13 and comprises a cylindrical wall 17 slightly longer than the cut-away portions of the foam F on adjacent pipe sections P joined to cylindrical wall 15 by an annular flange 19 secured by bolts 21, passing through the outer peripheral margin of flap 13, to annular flange 11. The entry end of the secondary vacuum chamber is formed by an annular flange 23 on wall 15 to which is clamped, by means of a back-up ring 25, a second sealing flap 27 of the same form and construction as flap 13. The secondary vacuum chamber surrounded by wall 17 is connected by a conduit 29 to a source of vacuum, and is also provided with a vacuum gauge 30. 
     Operation of the device to apply integral water stops to pipe sections P which have been coated with foam insulation F beveled as at B at its ends and with the outer surface of insulation F including beveled portions B, along with the protruding ends of the pipe surface coated with mastic A, is as follows: As the line of pipe sections P approaches extrusion die 7 for application of plastic coating C, it passes through secondary and primary vacuum chambers surrounded respectively by cylindrical walls 17 and 5, the preservation of vacuum in the primary chamber being ensured by the vacuum provided in the secondary chamber. As the molten plastic coating being extruded onto the outer mastic-coated surface of foam insulation C approaches the beveled portion B, the vacuum in the primary vacuum chamber draws the coating radially inwardly onto the mastic-coated beveled surface B as at W, over the exposed mastic-coated parts S of the pipe end sections and over the taped ends T of the adjacent pipe section. 
     The resultant plastic coating forms highly effective water stops W at each end of the pipe which are integral with the exterior plastic coating C on the outer cylindrical surface of the foam insulation, thus eliminating the inconvenience, time and expense of applying separate water stops. 
     Satisfactory results can be obtained without the use of a secondary chamber if length of the reduced diameter portions of the work are less than the length of the primary chamber or if the diameter of the die passageway is only slightly greater than the outside diameter of the insulating material. 
     The details of the apparatus may be varied substantially without departing from the spirit of the invention and the exclusive use of such modifications as come within the scope of the appended claims is contemplated.