Method For Coating Tubular Objects

Abstract

A relatively high speed, continuous method and novel apparatus, especially adapted to large diameter steel pipe, for applying external thin-mill coatings, such as thermal setting epoxy and epoxy resins, wherein the pipe sections are successively advanced in a train and continuously rotated through numerous operating stations, and embodying a change-over from an external roller drive line to an internal conveyor system. The pipe overhead suspension system permits even mill coating over the complete surface of the pipe and precludes damage to the coating during curing and while it is in the critical fluid state.

Parent Case Text

This is a division of our copending application Ser. No. 689,646, filed Dec. 11, 1967 now U.S. Pat. No. 3,581,922 and entitled Method and Apparatus for Coating Tubular Objects.

Description

It is an important object of the present invention to provide a simple, rapid and inexpensive, continuous pipe coating system, involving six separate, automated operations of preheating, cleaning, heating to a desired temperature, powder coating, fast curing, and quenching, wherein the bare pipe enters at one end of the assembly, proceeds without interruption in a straight line while it is continuously rotated, and emerges fully coated and ready for loadout, at a relatively high rate of approximately 22 feet per minute, for example, all with the assurance that the coating has been uniformly applied throughout the outer surface of the pipe and has not been damaged in any manner during the process by the novel equipment employed in the assembly, or otherwise.

Another important object of the instant invention is the provision of unique internal support means for the pipe, placed in the system at the zones of coating and curing, and operable to continue the linear advancement and rotation without interruption, coupled with the outstanding advantages of even coating and absolute protection against damage until the coating is capable of withstanding external support of the pipe.

In the drawings:

FIG. 1a is a schematic plan view showing a portion of a system or assembly embodying the apparatus for coating tubular objects of the present invention and illustrating the method employed through use of such apparatus;

FIG. 1b is a continuation of FIG. 1a;

FIG. 2 is a side elevational view, partially schematic, showing a portion of the apparatus, including the overhead suspension system;

FIG. 3 is an enlarged, fragmentary view similar to FIG. 2, partially in section, showing one of the pipe suspension units;

FIG. 4 is a cross-sectional view taken on line 4--4 of FIG. 3;

FIG. 5 is a detailed cross-sectional view of a portion of FIG. 3, still further enlarged;

FIG. 6 is an elevational view of the coating unit;

FIG. 7 is a plan view of one of the external pipe-supporting and rotating sections;

FIG. 8 is a side elevational view of the structure shown in FIG. 7; and

FIGS. 9 and 10 are cross-sectional views taken on lines 9--9 and 10--10 respectively of FIG. 8.

A number of identical units 1-17 inclusive, shown in FIGS. 1a and 1b, are each adapted to support the pipe 18 from therebeneath in contact with its outer surface through use of longitudinally spaced pairs of peripherally beveled rollers 21 that are laterally spaced and relatively offset (see FIGS. 7-10 showing unit 12 by way of example). One roller of each pair is driven by a motor such as motor E (preferably hydraulic) through belt and pulley means 20, jack shaft 22, intermeshing gears 24, stub shafts 26, chain and sprocket wheel means 28 and coupling shafts 30 provided with universal joints 32. Accordingly, the unit 12 not only rotates the pipe 18g continuously about its horizontal, longitudinal axis but advances the pipe 18g without interruption along a linear path of travel that is parallel with such axis. Some of the motors are of the variable speed type, as will be subsequently explained.

The system embodies, as aforesaid, an aligned series of 17 such units, so designated 1-17 inclusive in FIGS. 1a and 1b, driven by six motors, marked A-E inclusive. Motor A drives units 1-4 inclusive through a common jack shaft 22. In a similar manner, motor B drives units 5-7; motor C drives units 8-10; motor D drives unit 11; motor E drives units 12 and 13; and motor F drives units 14-17.

The incoming bare pipe sections 18 of various sizes (for example, 6-42 inches inside diameters) and of various lengths (FIG. 1a shows, for example, three pipe sections 18a, 18b and 18c that are 20, 40 and 60 feet long, respectively) are loaded on rack 34 for transfer to a first station 35 (units 1-4). The coated pipe sections 18d, 18e and 18f are shown in FIG. 1b transferred from units 15, 16 and 17 to another rack 36 ready for loadout.

The tandem roller units 1-4 continuously rotate the sections 18, and advance the same one at a time without interruption at a variable rate of speed, but generally at about 60 feet per minute (i.e., an increment of advancement per revolution, controlled by the location of the support rollers 21, which may be adjusted by the rotation of disc mounting means 19 shown partially in FIGS. 7 and 8) to a preheat furnace 38 to raise the temperature of the pipe to approximately 100.degree. F. to remove moisture, all, of course, depending also upon humidity conditions at the time of operation.

At a second station 39 the units 5-7 move the sections 18 through a pair of blasters 40 and 42. These two blast machines clean the pipe, i.e., remove all rust and mill scale, leaving a surface which will form a high strength bond with the epoxy or plastic resin coating later to be applied. The relatively sharp grit used in blaster 40 to effectively clean the pipe leaves an anchor pattern that is normally too deep. Therefore, shot is employed in blaster 42 to peen or smooth out the exterior surface of the pipe.

In order to avoid loss of the abrasives through the pipe inlets and outlets of blasters 40 and 42, the ends of the pipe sections 18 are brought close together though not in abutment. Such close spacing (approximately one-sixteenth of an inch) is maintained by the operator who controls the variable speed of the motor A. Before the sections 18 leave the second station 39 they are subjected to the last cleaning operation, i.e., to high speed brushes 44 (about 1,800 r.p.m.) which remove all abrasive that has become embedded in the pipe.

While the sections 18 are on the rack 34 their ends are closed by removable plugs (not shown) to avoid collection of abrasive therewithin. These plugs are removed before the pipe sections 18 move to a third station 47 by slowing down the variable speed motors A and B to about 25 feet per minute for a sufficient period of time to present a gap of about 3 feet between the sections 18.

At the third station 47 the units 8-10 advance the sections 18 through an infra red preheat oven 45 which raises the metal temperature to about 350.degree. F. At this juncture there is a change-over to an internal support of the pipe sections 18, reference now being had to FIGS. 1b and 2-5.

A support in the nature of an oblong overhead track 46 (FIG. 1b), consisting of an H-beam (FIG. 4), having one of its longitudinal stretches spaced above and in alignment with the linear path of the sections 18, is adapted to receive a plurality of identical hangers or carriers in suspended relation thereto. Only two carriers, designated 48 and 50 respectively, have been shown in the drawings. Manifestly, sufficient carriers are provided to ensure uninterrupted advancement of the pipe sections. Five such carriers have been found adequate for an operation proceeding at the speeds described herein. Hanger 48 has a wheeled trolley structure 52 on track 46 from which depends apparatus 54, including a vertically extensible upright, for varying the height of a pair of rotatable devices 56 and 58 in the nature of rollers fixed to a shaft 60.

Shaft 60 is carried by bearings 62 within a horizontal tube 64 that is in turn secured rigidly to a crosshead 66 rigid to the lower end of a vertical tube 68. In addition to tube 68, apparatus 54 includes a rod 70 (telescoped in tube 68), a screw 72 and a nut 74. Crossbolts 76 pass through selected cross holes in tube 68 and rod 70 to permit vertical adjustment to accommodate pipes of any of a number of diameters. The upper end of rod 70 is tapped to receive screw 72, and lock nuts 78 and 80 on screw 72 bear against rod 70 and nut 74 respectively. A suitable tool passing through head 82 of screw 72 may be used to make fine adjustments of the distance between rod 70 and nut 74.

Nut 74 hangs from trolley 52 by means of a cross pin 84 and has a pair of opposed pulleys 86 which ride along guide strip 88 on track 46 so as to maintain shaft 60 horizontal as well as parallel with the longitudinal axes of pipe sections 18. If desired, track 46 may also be provided with risers 90 within the paths of the trolley wheels for purposes hereinafter explained.

Pipe sections 18 are normally provided with an external, circumferential 60.degree. chamfer 92 at each of their ends, each terminating in an outermost, annular feather edge 94 which must be protected because such edges 94 are held in abutment during welding of the sections 18 together in ultimate use. Such protection is afforded by use of a pair of roller retainers 96 and 98 on tube 64 set at an incline of about 55.degree. so as to abut chamfers 92 remote from and in spaced relation to edges 94 as best seen in FIG. 5.

Referring now again to FIGS. 1b and 2, the operator initially manipulates the carrier 48 to insert its roller 56 into the leading end of a pipe section 18 emanating from unit 11 at the fourth station 100. COntinued advancement of the pipe section by unit 11 moves the carrier along track 46 with the leading end of the pipe section supported on the track by the carrier. While the trailing end of the pipe section is supported on unit 11 and after the trailing end moves beneath track 46, another carrier 50 is manipulated around the track to a position where its roller 58 is inserted into the trailing end of the pipe section. The rate of advancement of the next succeeding pipe section 18 is then increased by increasing the speed of motor D to bring the leading end of this section into coupled relationship over roller 56 of carrier 50.

Noteworthy in FIG. 2 is the fact that such procedure has previously taken place with respect to section 18g. Thus, pipe section 18h is shown supported by rollers 56 and 58 of carriers 50 and 48 respectively. In FIG. 2 also, the section 18g is shown supported by roller 58 of carrier 50, as well as by units 12 and 13. Chamfers 92 of sections 18g and 18h bear against the rollers 98 and 96 respectively of carrier 50. Both rotation and advancement of section 18g by the units 12 and 13 are transmitted to section 18h through shaft 60 of carrier 50.

In FIG. 2, after insertion of roller 58 of carrier 48 into rotating section 18h, as shown, the motor D is speeded up to advance the pipe at about 60 feet per minute so as to thread the rotating section 18i onto the roller 56 of carrier 48. As soon as the chamfer 92 of section 18i abuts the roller 96 of carrier 48 (FIG. 3) both rotation and advancement of section 18h are transmitted through shaft 60 of carrier 48 from section 18i, the speed of the latter having been reduced to about 22 feet per minute. As soon as the trolley 52 of carrier 48 reaches riser 90 the rollers 58 and 56 of carrier 48 tighten against the sections 18h and 18i therewithin as shown in FIG. 3.

Before the hangers 48 and 50 traverse coater 101 the operator places a cutback asbestos shield 102 thereon which is so shaped as to cover the rollers 96 and 98 and the ends of the pipe sections 18h and 18i as shown in FIGS. 3 and 4. Rod support 104 for shield 102 has its upper ends hooked over tube 68 and is provided with a lateral extension 106 which bears against tube 64.

Within the coater 101 there is provided, as shown in FIG. 6, a manifold 108, carried by standards 110 which may be vertically adjusted by screw 112. Two rows of eight guns 114 each on manifold 108 direct the epoxy coating powder in one direction against the rotating pipe sections 18 as they pass through coater 101.

The temperature of the pipe sections 18 in the coater 101 is approximately 325.degree. F. which is sufficiently high to flow the epoxy or thermo setting plastic powder (such as vinyl) onto the pipe sections 18 and effect the electrostatic coating thereof. Such temperature is not high enough, however, to cure the coating, permitting adequate flow time to provide better coverage with a uniform coat of about 9 to 12 millimeters. The two banks of guns 114 and the spaced guns 114 themselves place successive layers of the powder onto the rotating pipe sections 18 as they pass along the manifold 108.

By the time the coating reaches post cure oven 120 it is relatively solid and at this point the temperature is raised by infra red heaters to roughly 450.degree. F. where curing takes place rather quickly. Many materials of the kind contemplated herein will not cure below 400.degree. F.

The shield 102 accomplishes the objectives of keeping the powder from entering the pipe ends as it passes the coating station 101, protecting the hangers 48 and 50 from being coated, and preventing contamination of the chamfers 92.

After the pipe leaves the post heat station 120 it passes to a seventh station 122 containing a quencher 124, wherein, through a water bath or otherwise, the temperature is quickly and appreciably lowered. Note the longitudinal slots 126 in the tops of coater 101, oven 120 and quencher 124 (FIG. 1b) which clear the hangers 48 and 50. As the pipe emerges from quencher 124, shield 102 is removed, the powder is stripped therefrom, and shield 102 returned to the front of the line for reuse.

Motor F is of the variable speed type so that the speed of advancement of the pipe sections may be increased when they reach station 128. The operator thereby causes a gap to occur between the ends of adjacent sections when the ends are located between units 13 and 14. An operation can then remove the carriers 48 or 50, previously intercoupling the ends, since the pipes are now supported on the external support rollers. The carrier is manually moved around the track to a ready position adjacent unit 11 for use in the sequence described above.

Finally, from station 128 the coated sections 18d, 18e and 18f are transferred to rack 36 ready for loadout.

Claims

Having thus described the invention, what is claimed as now and desired to be secured by Letters Patent is:

1. In a method of exteriorly coating a plurality of elongated pipe sections:

supporting the sections from therebeneath while advancing the same in succession along a horizontal path of travel parallel with the longitudinal axes of the sections;

applying suspending forces to each successive pipe section from therewithin while continuing the advancement of said sections and terminating the support from beneath the respective sections so that each section is successively suspended entirely from within;

rotating each respective section about its longitudinal axis while suspended from within and simultaneously continuing the advancement thereof; and

coating the exteriors of the internally suspended sections while said sections are rotated and advanced.

2. The invention of claim 1 wherein is included the step of curing of the coating following application thereof on the pipe; and maintaining the coating on the exterior of the sections exposed and free from supporting forces against the pipe exterior during continued rotation and advancement of the respective pipe sections while curing the coating.

3. The invention of claim 2, wherein is included the step of supporting the sections externally of the sections and terminating said internal suspension thereof while continuing the rotation and advancement thereof following curing of said coating.

4. The invention of claim 3, wherein rotative forces are applied to the sections both prior to and subsequent to suspending the same; and wherein is included the step of transmitting rotative motion from the sections being rotated by said applied forces to the section under suspension.

5. In a continuous method of exteriorly coating a plurality or elongated pipe sections:

supporting the sections from therebeneath while rotating the same continuously about their longitudinal axes and, at the same time, advancing the same continuously in succession along a horizontal path of travel parallel with said axes;

thereupon suspending the leading ends of the sections from therewithin while continuing to rotate the same about said axes and continuing to advance the same along said path;

then continuing said rotation while suspending the trailing ends of the sections from therewithin to expose the exteriors of the sections for coating;

coating said exteriors of the suspended sections while continuing said rotation of the latter; and

curing said coatings while the sections are suspended.