US3394207A - Method of casting foam insulation for an elongated member - Google Patents

Description

E. ANDERSEN July 23, 1968 METHOD OF CASTING FOAM INSULATION FOR AN ELONGATED MEMBER Filed June 15, 1964 INVENTOR. Es E A N o E RSE N BY ATTORNEY United States Patent 3,394,207 METHOD OF CASTING FOAM INSULATION FOR AN ELONGATED MEMBER Ege Andersen, Logstor, Denmark Filed June 15, 1964, Ser. No. 375,274 8 (Ilaims. (Cl. 264-45) ABSTRACT OF THE DISCLOSURE A method of forming a thermally-insulated pipe by casting an insulating foam substance about pipe sections prior to lowering said sections to a horizontal position in which they become part of an underground pipeline. Each pipe section is inserted into a tubular casing section of appreciably larger diameter and maintained in substantially upright position, with the shield resting upon a surface and closed off thereby at its bottom. At least one of said sections is coated with a lubricant, and a charge of foaming plastic is introduced into the space between the pipe section and the casing section and allowed to rise and set to completely fill said space with foam insulation. The pipe section, casing section and foam insulation are then lowered as an integral unit to a horizontal position, with the lubricant serving as a slipping agent to allow for thermal expansion or contraction of the unit parts.

This invention relates to a novel and improved method for casting a thermal insulating foam substance between an elongated body such as a metal pipe and an outer protective shield such as a plastic tube. The invention is particularly applied to the insulation of heating and cooling pipes which are laid underground beneath the street.

It is known to insulate district heating pipes, for example, by laying them in street excavations within a jacket consisting of the upper and lower sections of a split concrete shell, and then pouring porous or cellular concrete into the space between the district heating pipe and the concrete shells.

Since such casting is performed after the pipes are laid in the street, the pipes and the concrete jackets necessarily are substantially horizontal at the time of casting. In order to avoid such inherent disadvantages as the formation of cavities due to improper filling between the district heating pipe and the outer shell, the cellular concrete must be poured through inlets at mimimum intervals, for example, six feet or less, which makes the operation extremely time-consuming.

In the aforementioned conventional method of casting insulation, the cellular concrete becomes firmly coherent with the surrounding concrete shell, and if the cellular concrete also becomes coherent with the inner heating pipe it tends to become crushed due to the thermal expansion or contraction of the heating pipe. In order to avoid this crushing, the heating pipe is wrapped in corrugated paper, thus establishing in the high temperature region, an uninsulated longitudinally-extending heat transmission path, which causes, in combination with unavoidable radial cracks and other unavoidable insulation defects in the cellular concrete, appreciable heat losses to the surrounding soil.

In the German patent application DAS No. 1,016,992, there is taught a method of casting an insulating foam substance around heating pipes at the time of. laying the latter. In this method, a wide mesh hose is used as a mould, the hose being stretched out around the heating pipe by spacing means. This hose, being woven of jute, fibre glass or wire, offered no protection against impact, and therefore, it was often necessary to resort to the cumbersome procedure of covering the hose with a jacket of concrete, tin plate, asphalt, impregnated paper etc., which, of course, further increased the costs of the already expensive method of casting on site.

In addition, it has recently been suggested to insulate cooling pipes by casting around them a polyurethane foam substance enclosed in a jacket of galvanized sheet metal formed in the usual manner employed for making such metal sheaths. This again is an instance of casting at the site of laying the pipe, with all of its attendant disadvantages. Further, it proved disadvantageous to use a protective jacket of sheet metal, which, in the course of time, would rust away and then he incapable of protecting the shock-vulnerable foam insulation.

Where polyurethane was used as a. foam substance, it has been found that excellent adhesion to the cooling pipe was attained, which is considered an advantage insofar as the insulating of cooling pipes is concerned. On the other hand, where heating pipes are to be insulated, a free mobility of longitudinal movement between the heating pipe and the insulating material, and between the insulating material and the surrounding protective jacket or casing must be sought for in order to avoid transverse cracks in the insulating layer.

In cooling applications, there is particular interest in providing a firm and unbroken connection between the cooling pipe and the waterproof insulating medium, since otherwise sweating or condensation will inevitably destroy the thermal insulating capacity of the insulating material, possibly throw off the material, and in the course of the time cause the pipe to rust. However, since foam insulation material tends to adhere even more firmly to the outer jacket or casing, adverse radial expansion cracks very soon develop in the insulation.

An object of the present invention, is to provide a method of casting a thermal insulating foam substance between a pipe to be insulated and an outer sheath, preferably a plastic tube, which method avoids the aforementioned difiiculties inherent in conventional methods.

It is another object of the invention to provide a process for the industrial casting in quantity of tight and durable insulation around elongated bodies such as pipes of uniform length, in such a manner as to avoid the tendency for the development of insulating defects incurred either during the casting operation, or following extensive use, or by reason of large fluctuations in temperature.

The method of casting foam insulation in accordance with the present invention, is characterized in that the casting is performad with the elongated pipe and easing disposed in a rather steep position, preferably vertically upright. The pipe, which is preferably metal, is disposed within the casing and spaced from the walls thereof. The bottom end of the casing is closed off either by a metal plate, or by a plug formed by pouring a small amount of foaming insulation material into the tube and allowing it to set at the bottom thereof. Into the space between the inner pipe and outer tube there is then poured a measured amount of plastic containing a foaming agent and setting agent, and the plastic is allowed to foam and rise until it completely fills the tube and hardens to provide a filler of foam insulation between the tube and the pipe.

A lubricating coating is applied to the outer surface of the inner pipe and/or to the inner surface of the outer tube to provide longitudinal slippage between these parts and the cast foam insulation. If the pipe is used for cooling or refrigeration, the lubricating coating is applied only to the outer tube. The casting may be performed in a fractory or other site remote from the street excavation into which the insulated pipe is subsequently to be laid.

Another object of the invention is to provide a casting method of the character described which may be performed by industrial or workshop techniques, eliminating the formation of cavities even though pipes and casings of considerable lengths are cast in a single operation. This novel process also avoids the formation of radial cracks in the insulating material during the casting operation, since the body weight of the insulating material in the vertically-disposed casing will produce a slight compressive stress during the setting or hardening of the insulation.

Additional objects and advantages of the invention will become apparent during the course of the following specification when taken in connection with the accompanying drawing which is a vertical sectional view showing the manner in which polyurethane foam insulation is cast between a metal pipe and its outer sheath or casing.

Referring ni detail to the drawing, the numeral designates a pipe such as a district heating pipe of the usual type, which is conventionally made of metal such as steel. Surrounding the pipe 10 is a jacket or casing in the form of a tube 12 preferably made of polyvinyl chloride (PVC), and of substantially the same length as the pipe 10. The pipe 10 is of substantially smaller diameter than the outer tube 12, and is concentric therewith. Both the pipe 10 and tube 12 are shown in a vertical position which is preferable for the casting operation, although it is not essential in that the members be vertically disposed. Any upright angle sufficiently steep to enable the foam material poured therein to fill the outer tube 12 by action of gravity, would suffice. The outer tube 12 rests and is covered over at its bottom end by a base plate 14.

With the tube or casing 12 disposed in upstanding position and the pipe 10 centered therein and spaced from the walls thereof, the insulation is cast about pipe 10 by pouring into the space between the pipe and the casing, a foam plastic mixture consisting of a plastic such as polyurethane, a foaming agent or propellant therefore, and a setting agent, so that the plastic charge foams and rises within the tube.

To eliminate the necessity for cumbersome trimming and plugging operations before the casting of the insulation, which operations require the purchase and use of expensive precision tools, the casting process described herein makes it possible to first cast a short length of the insulation material to serve as a tight bottom plug. The drawing shows such a bottom plug 16 which is formed by pouring a small amount of foam plastic casting mixture into the top of casing 12 and allowing the mixture to foam and set providing a seal at the bottom of casing 12. Thereafter, the main charge of plastic foaming mixture is poured into the casing, and the foam insulation is cast in lengths (heights) as large as possible without forfeiting uniform specific density of the foam material along the entire extent of the casting. Careful plugging at the bottom of the pipe assembly is desirable for economy where long pipe lengths are to be packed in a single operation, although where the casing end surface rests snugly upon the plate, the latter may serve as a seal and the formation of the bottom plug may be omitted.

After the plug 16 has hardened so that it adheres to both the outer surface of pipe 10 and the inner surfaceof casing 12, and thus seals off the bottom of the latter, the polyurethane casting mixture is poured into the space between the pipe and tube and allowed to rise until the entire tube is filled with foam insulation. After the insula- .4 tion is completely set, the unit is brought to a horizontal position and is ready for use.

An important feature of the invention is that the process is capable of being performed at a factory or other location remote from the excavation site. The pipe with its foam insulation and outer casing is subsequently brought as a unit to the excavation site where it is laid into the excavation. The process of the invention thus not only enables long pipe sections to be insulated in a single operation, but it avoids the current difficulties of applying insulation of the pipes at the excavation site and after they have been laid'in horizontal position.

The casting mixture employed for the formation of both the plug and the main foam insulation comprises a flowable plastic such as polyurethane mixed with a propellant and foaming agent therefore as well as a setting agent. The foaming and setting agents are well known and commercially available.

In order to avoid undesirable longitudinal stresses in the foam insulation (radial stresses being of minorsignificance), a slipping agent or lubricant should be applied to the outer wall of the pipe 10 and/or the inner wall of the casing 12. This slipping agent may be introduced either before or during the casting of the foam insulation to prevent the latter from sticking to the casing 12 and/or to the pipe 10. Of course, where a cast plug 14 is provided, the slipping agent is omitted from the bottom portion of the pipe and easing at which the bottom plug is to be formed.

By the use of such slipping agent or lubricant, the cast foam insulating material is prevented from following the longitudinal expansion and contraction of the pipe and its casing at varying temperatures, and accordingly the formation of cracks in the insulation due to such movement, is eliminated. Since the slipping agent is applied in the form of a very thin film adhering to the pipe or casing, no harmful air gap will result between the pipe and the insulation, and no loss of heat will be caused by such a gap.

Where insulating material is cast about cooling pipes by the process of the present invention, it is desirable that the insulating material adhere firmly to the cooling pipe, and therefore the slipping agent or lubricant is applied only to the inner surface of the outer casing. For the insualtion of refrigeration pipes, for example, it may in certain instances prove labor saving if the slipping agent or lubricant is selected from the type which will adhere or dress better to the plastic material of the outer casing than to the metal surface of the pipe. In this way, time-consuming care need not be devoted to preventing traces of the lubricant from coating the inner pipe which is to be insulated against loss of cold. Where the pipe is made of plastic, such selected lubricants can be easily determined and are readily avail able commercially. For example, if, according to the method herein, the lubricant is applied at the time of casting the foam insulation, a lubricant containing a substance which acts as a plasticizer for the plastic material of the casing will be found to adhere much more readily to the inner wall of the casing than to the outer wall of the metal pipe, and consequently will coat the former rather than the latter. Where the casing is madein its preferred form from PVC polyvinyl chloride, any of the well-known plasticizers for the same may be employed as the slipping agent. Plasticizers for other plastics will be evident in the literature, and are well-known to those skilled in the art.

In addition, to its function in providing selective application of a lubricant, the use of molded plastic as the constituent material for the outer casing effects a number of other advantages. These include high tensile strength, corrosion resistance, contribution to. thermal insulation, minimum weight and bulk, electrical insulation as protection against stray currents, etc. 7 1

ln accordance with the invention, the process contemplates the preferred use of a lubricant or slipping agent containing stearates, for example, a mixture of calcium and magnesium stearates mixed with oil and alcohol.

The oil may be of any of the standard inert oils which will evaporate so slowly that vapor bubbles or steam pockets are avoided. The oil acts partly as a lubricating medium, but also, and perhaps principally, as a suspension and distributing agent for the stearates which will cause the latter to form a film upon the wall of the outer casing. The alcohol may be any volatile type which provides an effective mixing by stirring of the stearates in the oil. The alcohol is volatile so that it will evaporate completely before the casting around the pipe is commenced, eliminating risk of formation of air pockets dur ing casting.

The use of paste-like lubricants in the instant process is undesirable and should be avoided, since the precise application of such lubricants in a fine uniform film on the inner surface of the casing would involve considerable manual work. In addition, such a film of paste would be easily damaged when the inner pipe is inserted. into the casing, and contact would cause unintentional coating of the inner pipe, which, as previously indicated, is disadvantageous in the case of cooling pipes. To facilitate the process, therefore, it is possible to use a lubricant or slipping agent, in powder form, which powder is poured on top of the rising foam plastic and kept in a state of agitation within the outer casing by swirling or vibrating the same directly above the surface of the rising foam material. The powder may be a mixture of calcium and magnesium stearates, as previously described. A reliable manner of spreading a thin lubricant film of such powder on the inner wall of the casing and outer wall of the pipe, is by maintaining the lubricating powder in continuous motion by agitating means, for example, by an air jet emitted by a nozzle held slightly above the rising level of the foaming plastic. The pressure of the air jet need only be sufficient to swirl the powder about above the level of the rising foam, so that, as the foam rises, the powder forms a uniform thin coating on the walls of the pipe and casing.

The lubricating powder is added immediately after the plastic foam mixture is poured into the casing and before it begins to rise appreciably, by pouring a quantity of the powder onto the top surface of the plastic charge. The powder does not mix with the rapidly-expanding viscous foam, but if it were not agitated as described, there would be a tendency for the pile of powder to be entrapped in irregular thicknesses between the rising foam materials and the walls of the pipe and casing. Such enclosed amounts of powder would be lost as a lubricant and would cause irregular defects in the insulating material.

The lubricating of the casing and/or pipe walls will, as previously indicated, serve to avoid longitudinal stressing of the insulating material as the pipe or casing expands or contracts under temperature variations. The lubrication is further advantageous in avoiding undesirable residual stresses in the insulating material incurred during the casting operation.

For a better understanding of the process contemplated by the present invention, reference is now made to the following examples constituting specific illustrations of the process as employed for heating and cooling pipes.

Example I.Thermal insulating of a district heating line The steel heating pipes employed are commercially supplied pressure tested and in lengths of twenty feet. The tubular casings for these pipes are made in lengths of nineteen feet and four inches and are in the form of molded polyvinyl chloride pipes without pipe sockets.

Each steel pipe may be first lubricated on its exterior surface using an oil-stearate mixture, as previously described, and is inserted within a casing 12. Both the casing and contained pipe are hoisted to a vertical position and supported in such a manner that the steel pipe 10 is centered within the casing 12, as shown in the drawing with the steel pipe projecting from both ends of the casing by approximately four inches. The bottom end of the casing 12 rests upon the sealing base plate 14, which, where only minor static head. pressures are involved, can itself create a sufficient seal to prevent the plastic insulation material from leaking out of the bottom of casing 12.

The organic foam casting mixture is now poured into the space between the pipes. The mixture consists of polyurethane to which the foaming agent. and setting agent have been added immediately before pouring. The quantity of the mixture initially poured out has been exactly proportioned by weighing or measuring so that it will expand and harden to form a base plug 16 of suflicient height to provide an effective seal, but low enough to render negligable the static or head pressure at the 'bottom of the casing 12, and also low enough so that friction against the walls of the pipe and casing will not be sufficient to cause appreciable downward foaming pressure.

As previously indicated, if the base plate and the bottom end of casing 12 are finished with such precision as to make a snug fit, the surface-to-surface contact therebetween provides a sufficient seal and the step of preliminarily forming the plug may be omitted.

After a short time, approximately one minute, the plug becomes well-hardened, and a measured charge of casting mixture is poured down into the space between the pipe 10 and casing 12. This measured mixture of polyurethane and its propellant and setting agents, has been carefully weighed and is in the amount determined by experience to completely fill up the space between the pipe and easing at the prevailing temperature.

The drawing shows a charge of polyurethane mixture 18 after it has been poured and as it is starting to foam and rise within the casing 12.

Where the pipe is not initially lubricated, an apportioned quantity of powdered lubricant (calcium and magnesium stearate) is poured down on the top surface of the foam mixture, and a pneumatic hose with a nozzle is lowered into the space between the pipe and casing to a point just above the powder. As the foam insulation rises within casing 12, the pneumatic hose is continually lifted so that the nozzle is always just above the surface of the foam, and the air flow is increased or decreased as desired. The swirling powder thus coats the surfaces of the pipe and easing just above the rising foam.

After the polyurethane foam has filled the casing 12 and has set, and only after setting, the casing and enclosed pipe are lowered to a horizontal position. Subsequently, a sharp knife is used to clean both ends of the casing of excess foam projecting from the casing, by radial cuts toward the center heating pipe.

The assembled insulated heating pipe is then brought to the site of the street excavation. A rubber ring is placed around each end of the casing 12 and a wide PVC collar, of a diameter to pass freely over the rubber ring, is slid onto one end of the casing. This PVC collar is made as a shrink collar, that is, it has in a heated state been stretched from a normally smaller diameter, and upon reheating will shrink toward its original size. One of the projecting four-inch lengths of the steel pipe 10 is now joined by welding to the projecting length of steel pipe of the preceding unit. When a sufficient length of conduit or pipeline has been welded together, the welded joints are pressure-tested.

Two eight inch half sections of polyurethane foam tubular shells are placed tightly around the steel pipe, and glued securely thereto. Any good synthetic resin glue of the abundant commercial types, which will adhere to polyurethane foam and to metal (without dissolving the polyurethane), may be used, or foaming polyurethane may be employed as the glue. The PVC collar is then pushed over the covered joint. until the collar is centered upon and covers the joint section, and the collar is reheated until it shrinks around the two rubber 7' rings, providing a tight seal and protection against damage.

The narrow ditch or trench surrounding the PVC casings may already be filled in before the welded pipe joints are pressure-tested, avoiding considerable nuisance in the street excavating operation. However, the ditch at the region of the welded pipe ends is not filled in with earth until the collars have been placed in proper position and secured by shrinking.

Shut-off valves and similar irregular fittings in the pipeline can be insulated by means of shrink collars in the same manner as described in connection with the pipe joints, these fittings being previously encased in cast polyurethane shells glued or otherwise secured around them, and having cylindrical outer surfaces. The shrink collars, for this purpose, must normally be slightly wider than the collars for the pipe joints, in order to provide for uniform thickness of insulation. Further, these collars may be provided with a radial aperture for passage of the valve stem, which, if desired, may be sealed watertight, for instance, by means of a synthetic rubber gasket.

Example 2.Insulating of cooling pipes The procedure is substantially the same as described above under Example 1, except that special care must be taken to insure that an unbroken and close-fitting insulation is provided around all pipes, fittings, valves and the like, and that the lubricant is applied only to the inner wall of the PVC casing, as previously explained.

In this instance, the lubricant is preferably a PVC plasticizer which will form a coating upon the inner surface 'of the PVC casing more readily than upon the metal pipe. This is applied to the interior of the casing before the foam insulation rises therein, and results in providing the necessary slippage between the insulation and the outer casing but not between the insulation and the inner metal pipe.

It may then be appropriate, in order to avoid even narrow paths of cold conductivity, when gluing the foam polyurethane shells onto the exposed welded pipe sections, as previously described, to use foaming polyurethane as the gluing agent. Immediately after the placement of these shells, which are first dipped in or coated with foaming polyurethane, the shells are carefully assembled, aligned and clamped together in order to preserve their correct assembled position after the setting and hardening of the polyurethane foam, which adheres to both the shell and the inner pipe.

In order to prevent considerable loss of the foaming polyurethane used as the gluing agent, the work should be so arranged that a number of gluing operations can be performed uninterruptedly in immediate sequence before the foam has time to set. Thus, a number of exposed welded pipe sections are made available for insulating, and the foaming polyurethane is stored in a vessel cooled sutficiently to reduce the foaming speed to a considerable extent. As soon as the cooled polyurethane mixture is applied to the shells nad the metallic pipe surfaces at ambient temperature, a normal foaming speed will again be restored.

What I claim is:

11. A method of forming, as an integral unit, a thermally insulated pipe to be laid in a horizontal position, comprising the steps of (a) enclosing an industrial length of pipe section in a hollow tubular casing section of substantially the same length as said pipe section and of appreciably larger diameter,

(b) placing said casing section and enclosed pipe section in a substantially upright position with the enclosed pipe section spaced from the interior surfaces of the casing section to provide an annular space therebetween,

(c) closing off the bottom end of said casing section,

(d) coating the surface of at least one of said sections with a thin film of lubricant,

(e) pouring into the space between the upright pipe and casing sections a charge of plastic foam comprising a mixture of plastic, and foaming and setting agents therefor, such that the composition will settle at the closed lower end of the casing section and foam and rise therein,

(f) allowing the composition to foam and rise until it fills the upright casing section and sets therein to provide permanent continuous foam insulation between the pipe and casing sections along the entire length of said casing section with the set foam insulation joining said pipe section to said casing section to provide said integral unit, and with said lubricant serving as a slipping agent providing limited longitudinal slippage between the set foam insulation and the coated surface to allow for expansion or contrac tion of the unit parts, and

(g) thereafter lowering the integral unit to a horizontal position for laying the same.

2. A method according to claim 1 in which the lubricant is applied only to the inner surface of the casing 'section and the foam insulation is permitted to adhere to the outer surface of said pipe section.

3. A method according to claim 1 in which said pipe section is made of metal and said casing section is made of plastic, and in whichsaid lubricant is of a typewhich will form a coating more readily upon the surface of the plastic casing section than upon said pipe section.

4. A method according to claim 3 in which said lubricant contains a plasticizer for the plastic material constituting said casing section.

5. A method according to claim 1 in which the lubricant contains a mixture of calcium and magnesium stearates in a carrier of oil and alcohol.

6. A method according to claim 1 which includes the steps of pouring a quantity of powdered lubricant onto the upper surface of said plastic foam composition immediately after said composition has been inserted at the lower end of said casing section and before said composition has begun to rise, and maintaining said powdered lubricant in a state of agitation as the lubricant is carried upward along the casing by the upper surface of the rising foam insulation.

7. A method according to claim 6 in which said powdered lubricant is maintained in a state of agitation by directing a stream of air thereon from a nozzle kept a slight distance above the surface of the rising foam insulation.

8. A method according to claim 1 which includes the steps of initially pouring into the space between the upright pipe and casing sections a relatively small amount of foam plastic composition, allowing the composition to foam and set to form a short plug of foam insulation at the bottom of the casing section such that the plug adheres to both the pipe section and casing section, thereafter placing said lubricant on a surface of one of said sections which faces the other section, and thereafter pouring onto the upper surface of said plug a charge of plastic foam composition sufiicient, upon rising, to fill the maximum extent of the upright casing section with foam insulation of substantially uniform density.

References Cited UNITED STATES PATENTS 536,184 3/1895 Case 26438 XR 1,003,730 9/1911 Freund 264338 XR 1,462,563 7/1923 Ohio 264-338 1,518,254 12/1924 Copeman 264338 XR 2,015,207 9/1935 Weller 264-338 2,081,867 5/1937 Gysling 26445 XR 2,865,868 12/1958 McKinley et a1.

(Other references on following page) UNITED STATES PATENTS OTHER REFERENCES 5/1960 Tillman 106*38-24 Wood, R. N.: IBM Technical Disclosure Bulletin, vol. 12/ 1960 Heroy et a1 264-54 XR 3, No. 10, March 1961, Foamecl Air Bearing Cylinder." 11/1961 Ammons 264-54 XR Rubber and Plastics Age article, Formed Core Panels 11/ 1961 Urban 26454 5 for Transport, vol. 44, N0. 5, pp. 499-500.

5/ 1962 HOlShOller 1 4 X Hoppe, Peter: Sandwich Laminates by In-Situ PU 1/1966 Helfner 26445 X Foaming. In Plastics, January 1965', pp. 71-77.

3/1966 Nicosia 26445 X FOREIGN PATENTS JULIUS FROME, Primary Examiner.

9/ 1955 Australia. 0 P. E. ANDERSON, Assistant Examiner.

9/ 1955 Australia. 11/ 1963 Australia.

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