WO2010111774A1

WO2010111774A1 - Method and device for concentrated heating of shrink sleeves

Info

Publication number: WO2010111774A1
Application number: PCT/CA2010/000446
Authority: WO
Inventors: Dilip Kumar Tailor; Emerson John Tacoma; Robert James Brown; Mark Phillip Brandon; Ishwarlall Seepersaud
Original assignee: Shawcor Ltd.
Priority date: 2009-04-03
Filing date: 2010-03-31
Publication date: 2010-10-07

Abstract

A method for installing a heat shrinkable sleeve in a cylindrical configuration on an elongate tubular article using a high velocity gas burning heat gun to heat and shrink the sleeve. The gun has a nozzle through which combustion gases exit and has structure that accelerates air and gas toward the nozzle. The gun may be modified to provide greater efficiency of sleeve installation.

Description

METHOD AND DEVICE FOR CONCENTRATED HEATING OF SHRINK SLEEVES

U.S. patents Nos . 6,010,329 and 6,227,846 in the name Zagoroff describe high velocity heat guns that accelerate air and combustible gas to high speed and provide gas flames that exit at high speed through a fantail combustion nozzle. In the past, these guns have been used on generally planar surfaces, for example for paint stripping walls and for shrinking plastic bags on the generally planar sides of pallet loads.

It has now been found that similar high velocity guns can be used surprisingly advantageously for heat shrinking of shrinkable sleeves in a cylindrical configuration on elongate tubular articles, for example on welded pipeline joints. Such sleeves may be in the form of a continuous cylindrical sleeve or may be a conventional wrap-around sleeve wherein a rectangular member is wrapped around the article to form a sleeve.

In one aspect, the present invention provides a method of installing a heat shrinkable sleeve in cylindrical configuration on an elongate tubular article comprising applying a high velocity gas burning heat gun to heat and shrink said sleeve, said gun having a nozzle through which combustion gases exit and comprising structure that accelerates gas and air toward the nozzle.

In preferred embodiments, the method of the invention provides a number of surprising and unexpected advantages. The preferred guns provide tightly focused heating, that facilitates a preferred heating sequence in which the centre of the sleeve is heated selectively first, and then the heating is applied progressively outwards, in order to eliminate air entrapment under the sleeve. The focused high velocity heating also allows the flame to be kept focused on desired portions of the sleeve even under windy conditions, and the sleeve can be efficiently heated even during cold and inclement weather.

Further, it has been found that the preferred guns allow sleeves to be heated and shrunk relatively quickly, even in the case of sleeves that have relatively high shrink temperatures, such as polypropylene and polyamide sleeves, with considerably reduced tendency for the sleeve burning or catching fire in comparison to shrinkage operations with conventional torches. Without wishing to be bound by any theory, it is believed that the preferred guns have a more strongly chemically reducing character than conventional torches, allowing very high intensity heating without oxidation and burning of the sleeve.

Moreover, it has been found that the preferred heat guns use less gas than conventional torches under comparable conditions. Not only does this result in economy of gas usage but avoids problems encountered with conventional torches of high rates of evaporation of gas from the tank resulting in excessive cooling of the liquid in the tank. This problem is particularly acute in cold weather conditions in the field and results in reduced vapour pressure in the tank, reducing the flow of gas available to reach the torch, and resulting in impaired efficiency of sleeve shrinking. The preferred heat guns have an igniting on-off trigger that allows the torch to be started when desired and to shut off instantly when the trigger is released. This allows for faster ignition of the torch, and for faster shut off and re- ignition as necessary during the shrinking procedure. This may often be advantageous to maintain proper sleeve shrinking and conformance to the substrate .

With the preferred heat guns, the flame length is short and the heating extremely intense, as compared with conventional torches. This allows close control of the heating by only relatively short movements of the gun toward or away from the sleeve. Movement away from the sleeve rapidly reduces the intensity of the heat while movement toward the sleeve rapidly increases the heating intensity and this allows the sleeve to be shrunk very fast without burning the sleeve surface. Further, in the field, sleeve shrinking is often done in chaotic, cramped and windy conditions with the operators working in close proximity. The reduced length of the flame as compared with the flame from conventional torches may tend to reduce risk of injury to operators by inadvertent misdirection of the flame.

In one preferred form of the present invention, there is employed a heat gun as described in the above mentioned U.S. patents Nos . 6,010,329 and 6,227,846, to which reference should be made for further details, and the disclosures of which are incorporated herein by reference. Other similar heat guns that accelerate combustible gas and air mixtures to higher velocities may also be employed.

In further preferred forms of the present invention, modifications are made to the gun generally as described in the above mentioned U.S. patents Nos. 6,010,329 and 6,227,846 in order to provide highly advantageous adaptations that better allow the gun to be used efficiently in heating and shrinking a cylindrical sleeve. In one of such adaptations in accordance with a preferred form of the present invention, the gun has an elongate gas and air mixing section having a handle on one side, and a connector section between the mixing section and the nozzle, this connector section having a length 7.5 to 30 cm., more preferably 10 to 15 cm. With this arrangement, manipulation of the gun around the circumference of the pipe joint is made significantly easier.

In a further preferred embodiment, a connector section of the gun includes a portion inclining at an angle of 5 to 40°, preferably 10 to 20° with respect to a longitudinal axis of a mixing section of the gun. With this arrangement, the directing of the flame on a cylindrical sleeve through manipulation of the gun, especially when shrinking bottom sections of the sleeve has been found to be made significantly easier, with the result that the ergonomics of use of the gun and the shrinking efficiency of the sleeve are dramatically improved.

In a still further modification in accordance with the present invention, the gun has an opening of its nozzle when viewed axially with a length to width aspect ratio of from 1:1 to 10:1, more preferably 1:1 to 4:1. It has been found that when this aspect ratio is greater than 10:1, the focus of the flame is too extreme in one direction, with the result that, in order to obtain full coverage of the sleeve, the orientation of the gun relative to the pipe axis has to be constantly changed. This manipulation makes the shrinking process inefficient, and also imparts strain to the operator's arms and wrists. With the above aspect ratios in accordance with the above mentioned preferred form of the present invention, the ergonomics of operation of the torch are improved significantly, and manipulation of the torch becomes easier to control and the covering of the sleeve surface becomes much faster. This greatly increases the efficiency of the shrinking process and tends to improve the quality of the resultant shrunk sleeve product.

In a still further preferred form of the present invention, the gun includes a manually operable valve in a gas supply line to the gun, the valve allowing continuously variable adjustment of the gas flow. In a still further preferred form, the gun includes a second manually operable valve in said gas supply line, the second valve snapping between a fully closed and a fully open position. Known guns have only a valve of the second type mentioned above, which snaps between fully open and fully closed positions, with the result that the gun has only a single heat output rate resulting in one fixed flame intensity. It is found that this is inefficient for shrinking of cylindrical sleeves, since shrinking of the sleeve requires adjustment of the heat intensity during different stages of the shrinking operation. For example, for initial pre-warming of the adhesive side of the sleeve underlap and during application of a closure patch on a wrap-around sleeve, reduced heat intensity is required. During the shrinking stage, the highest heat intensity can advantageously be used and, subsequently during post -heating following shrinkage of the sleeve, medium heat output may advantageously be used. With the above noted modifications, the continuously variable valve allows variation of the heating intensity during different stages of sleeve shrinking.

Preferred embodiments of the invention will be described by way of example only with reference to the accompanying drawings . Figure 1 shows somewhat schematically a side view of a heating gun in operation.

Figure 2 shows somewhat schematically a top plan view of the gun.

Figure 3 shows somewhat schematically a side view of a modified form of the gun.

Figure 4 is an end view of the opening of the nozzle viewed axially in the direction of the arrow A in Fig. 3.

Figures 5 and 6 show schematic side views of two further modified forms of gun in accordance with the invention, respectively.

Figures 7 to 10 are side views of a welded pipeline joint in successive stages of installation of a heat shrinkable sleeve thereon. Referring to the drawings, Figs. 1 and 2 show one form of gun 11 usable in the method of the invention. Although various types of high velocity heat gun are available, in one preferred form the heat gun 11 is a SHRINKFAST (trademark) 998 gun, available from Shrinkfast Corporation of Newport, New Hampshire, United States of America, as described in more detail in the above mentioned U.S. patents Nos. 6,010,329 and 6,227,846, to which reference should be made for further details.

In the example shown, the gun 11 comprises an elongate cylindrical combustible gas and air mixing section 12 wherein combustible gas is mixed with air, and the combustible gas air mixture is passed toward a connector section 13 and nozzle 14, for example of fantail form as shown in Figs. 1 to 4. On one side of the section 12 is a handle 16, including a trigger 17 and a gas inlet supply line 18.

One preferred form of gun described in the above- mentioned patents, and as preferably employed in the present invention, comprises structure that accelerates air and gas toward nozzle 14, this structure comprising a venturi tube into which the gas is introduced. In one form the gas is introduced through narrow tubes adjacent the narrowest portion of the venturi tube.

In one known form of the gun, depression of the trigger

17 operates a snap action on-off gas control valve and actuates the valve from a fully closed to a fully open position, allowing gas to flow from the supply line 18 to the interior of the mixing section 12. Further, depression of the trigger 17 actuates an electrical spark plug located in the connector section 13 that ignites the combustible gas air mixture .

In one preferred form, the combustible gas is propane, but other combustible gases may be employed, for example butane and natural gas. The combustible gas may be supplied from a conventional gas tank or supply line that preferably supplies gas to the gun at its connection to the inlet line

18 at a gauge pressure of 100 to 350 KPa, more preferably 150 to 250 KPa or still more preferably approximately 200 KPa. The mixing section 12 operates to accelerate the gas and entrained air to a velocity such that an ignited gas flame exiting the nozzle 14, indicated at 21 in Fig. 1, provides a high heat intensity flame. This flame 21 includes a crisply defined luminous blue inner portion 22 and a more diffused lighter blue outer flame portion 23. Without wishing to be bound by any theory, it is considered the flame has a chemically reducing character, offering the advantages of high intensity heating without causing excessive oxidation of the sleeve, as discussed in more detail above.

As seen in Figs. 2 and 4, the nozzle 14 is in one preferred form of generally fantail burner configuration, and converges toward its exit opening, tending to produce a high heat intensity relatively short flame 21, with the advantages noted in more detail above.

In one preferred form, as seen in Fig. 3, the connector section 13 of the known gun is modified, as seen in Fig. 3 to provide a section 13a having a length 7.5 to 30 cm., more preferably 10 to 15 cm. , providing the advantages of ease of manipulation of the gun 11 when shrinking a cylindrical shrink sleeve, as discussed in more detail above.

In a further preferred modified form of the gun 11 in accordance with one preferred form of the invention, the opening 24 of the nozzle 14 when viewed axially, as seen in Fig. 4 has a ratio of its length 1 to width w, as indicated in Fig. 4 from 1:1 to 10:1, more preferably 1:1 to 4:1, providing the advantages of improved flame focus providing for significantly improved efficiency and quality of sleeve shrinkage, as described in more detail above. The opening 24 of the nozzle may be of rectangular or oval shape.

In one further preferred form of the gun of the invention, the connector section 13 includes a portion 13b inclining at an angle of 5 to 40°, preferably 10 to 20°, with respect to a longitudinal axis of the mixing section 12, providing for significantly improved ease of manipulation of the gun, particularly when shrinking bottom sections of the sleeve, as discussed in more detail above.

In still one further preferred form of the gun of the invention, the combustible gas supply line 18 is provided with a manually operable valve 26 that provides for continuously variable adjustment of the gas flow passing through the supply line 18 to the mixing section 12. The advantages of the provision of such valve in allowing for variation of the intensity of the flame 21 are described in more detail above.

The valve 26 may be, for example, a ball valve with a rotating handle, a regulator with pressure adjustment, a needle valve, a variable switch valve, and like continuously variable valves.

The valve 26 may be provided in substitution for or in addition to the valve discussed above connecting to the trigger 17 that snaps the supply of gas to the mixing section 12 between fully on and fully off positions.

Referring to Figs. 7 and 8, these show pipeline sections 31 and 32 each comprising lengths of steel pipes 33 and 34, respectively, coated with mainline, usually plastic, pipe coatings 36 and 37 exposing the bare ends of the pipes 33 and 34, which are welded together at a girth weld 38 in the conventional manner.

In one preferred form of the method of the present invention, a continuous cylindrical sleeve or a wrap around cylindrical heat shrink sleeve 41, for example as described in Tailor et al U.S. Patent No. 4,472,468, is applied over the joint, as seen in Fig. 8 and, initially, a middle portion of the sleeve 41 is subjected to localized heating from a heating gun, such as a gun 11 as described above in more detail with reference to Figs. 1 to 6. The disclosures of U.S. Patent No. 4,472,468 are incorporated herein by reference. The above described guns 11 provide for focused application of the heating on the middle of the joint over the girth weld 38, so that this region is initially shrunk down selectively, as seen in Fig. 9. In order to avoid air entrapment beneath the sleeve the heating is applied progressively outwardly toward the ends of the sleeves in order to force air out from underneath the sleeve 41 as it shrinks. Once the middle portion of the sleeve 41 is fully shrunk down, heating may be applied from the gun 11 to end portions of the sleeve 41, as seen in Fig. 9. Once the sleeve 41 is fully shrunk down, as seen in Fig. 11, heating may be applied on the end portions using the gun 11, in order to cause bonding of the sleeve 41 to the mainline coatings 36 and 37.

The surprising advantages attained with the use of the gun 11 in the course of the shrinking and bonding operation have been described in more detail above.

Claims

CLAIMS :

1. Method of installing a heat shrinkable sleeve in a cylindrical configuration on an elongate tubular article comprising applying a high velocity gas burning heat gun to heat and shrink said sleeve, said gun having a nozzle through which combustion gases exit and comprising structure that accelerates air and gas toward the nozzle.

2. Method according to claim 1 wherein said structure comprises a venturi tube into which the gas is introduced.

3. Method according to claim 2 wherein the gas is introduced adjacent the narrowest portion of the venturi tube.

4. Method according to any one of claims 1 to 3 wherein said gun is supplied with gas at a gauge pressure of 100 to 350 KPa, preferably 150 to 250 KPa, more preferably 200 KPa.

5. Method according to any one of claims 1 to 4 wherein said nozzle is convergent.

6. Method according to any one of claims 1 to 5 wherein said gun provides a flame comprising a crisply defined luminous blue inner portion.

7. High velocity gas burning heat gun having a nozzle through which combustion gases exit and comprising structure that accelerates air and gas toward the nozzle, the gun having an elongate gas and air mixing section having a handle on one side and a connector section between the mixing section and the nozzle, said connector section having a length 7.5 to 30 cm, more preferably 10 to 15 cm.

8. High velocity gas burning heat gun having a nozzle through which combustion gases exit and comprising structure that accelerates air and gas toward the nozzle, the gun having an elongate gas and air mixing section having a handle on one side and a connector section between the mixing section and the nozzle, wherein the connector section includes a portion inclining at an angle of 5 to 40°, preferably 10 to 20° with respect to a longitudinal axis of the mixing section.

9. High velocity gas burning heat gun having a nozzle through which combustion gases exit and comprising structure that accelerates air and gas toward the nozzle, wherein the opening of the nozzle when viewed axially has a length to width aspect ratio of from 1:1 to 10:1.

10. Gun according to claim 9 wherein said aspect ratio is from 1:1 to 4:1.

11. High velocity gas burning heat gun having a nozzle through which combustion gases exit and comprising structure that accelerates air and gas toward the nozzle, and a manually operable valve in a gas supply line of the gun, said valve allowing continuously variable adjustment of the gas flow.

12. Gun according to claim 11 including a second manually operable valve in said gas supply line, said second valve snapping between a fully closed and a fully open position.