GB1589667A

GB1589667A - Manufacture of shaped articles of plastics material foams such as pipe insulators

Info

Publication number: GB1589667A
Application number: GB3559077A
Authority: GB
Original assignee: Dynamit Nobel AG
Current assignee: Dynamit Nobel AG
Priority date: 1976-08-26
Filing date: 1977-08-24
Publication date: 1981-05-20
Also published as: IE45573B1; DK377177A; NL7709402A; SE7709561L; DE2638447B2; FR2362712A1; DE2638447C3; IE45573L; CH625994A5; DE2638447A1; BE858089A; FR2362712B1; IT1115771B

Abstract

The mouldings (3) are obtained by pushing a pipe in the cold state over a correspondingly shaped inner mould (2) and fixing the pipe ends (3a, 3b). Subsequently, the structure obtained is conditioned at an elevated temperature at which the foam is flexible to plastic, then cooled and the pipe is stripped off the inner mould. A vacuum is advantageously applied to the inner mould which is pierced for this purpose. <IMAGE>

Description

(54) MANUFACTURE OF SHAPED ARTICLES OF PLASTICS MATERIAL FOAMS, SUCH AS PIPE INSULATORS (71) We, DYNAMIT NOBEL AKTIENGE- SELLSCHAFT, a German company of 521 Troisdorf, near Cologne, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the manufacture of shaped articles of plastics material foams deformable upon heating, particularly bent tubes of thermoplastic foam for use as pipe insulators.

Foam is widely used for the insulation of pipes for cold and hot water, Straight pipes are encased either by slotted foam tubes or by foam tubes, The problem of insulating pipe bends, elbows and the like still remains, It'is desirable to encase these pipe bends in a foam tube, thereby to insulate them. Taking the existing foam tubes as a basis, the object of the invention is to remould these and shape them into moulded tubes with which pipe bends and elbows, for example, can be encased, It is known to heat tubes of thermoplastic plastics materials, to insert into these heated tubes bending hoses or bending spirals, and to bend the tubes whilst in the heated state. Also it is known to deform thermoplastic plastics materials in the heated state using an outer and/or inner mould.

According to the present invention, there is provided a method of making a shaped article of a plastics material foam deformable upon heating, which method comprises positioning a tube of the plastics material foam whilst cold or whilst slightly hot over a hollow, perforated inner mould of the desired shape, which shape is different from that of the tube; heating the tube in this position at a temperature corresponding to the thermoplastic state or up to the thermoplastic state of the plastics material foam so that it becomes deformable; applying a vacuum to the inner mould so that the tube is drawn onto the inner mould by suction; allowing the tube to cool thereby to form a tube having the shape of the inner mould; and removing the shaped tube from the inner mould.

According to a modification of this method, the inner mould is at least partly flexible, and the inner mould is deformed to the desired shape during the method.

The invention thus takes advantage of the properties of foams of elastic plastics materials, namely that they are deformable at normal temperature. The tube is permanently fixed in its deformed state by heating and cooling.

Foams of, for example, polyethylene and cross-linked polyethylene are particularly suitable for use in the method of the invention.

When manufacturing from a foam tube a bent tube for insulating a pipe line, there may be used, as the inner mould, metal pipe bends and pipes of dimensions the same as those of the pipe lines to by insulated by the shaped tubes. Accurately sized casings can thus be produced by this method.

The vacuum may be used both during heating of the foam tube drawn onto the inner mould and possibly at least for a time during cooling, but it is also possible to apply the vacuum only after heating and at least for a time during cooling, Iri order that the vacuum can draw the foam tube onto the inner mould, the inner mould is provided with holes, slots or other perforations, these perforations being disposed particularly in strongly deformed regions of the tube. The inner mould is otherwise sealed tight, particularly at its ends, in order for the desired vacuum to be maintained even over a fairly long period of time. The ends of the tube drawn onto the inner mould may be sealed off, for instance, by means of rubber plates held in position by the applied vacuum.

The magnitude of the vacuum is such as to avoid collapse of the foam due to destruction of the foam cells, taking into account the heating temperature, the heating time, the foam thickness and the type of foam.

By the method according to the invention, it is not only possible to form shaped articles from foam tubes having internal diameters corresponding to the interior diameter of the subsequent shaped articles such as pipe bends, but also to form foam tubes with measurements differing therefrom, particularly tubes with larger dimensions.

In a preferred embodiment of the invention in order to hasten cooling after heating, the inner mould and shaped article is cooled from the exterior, for example, by means of air sprays or spray coolings. Furthermore, to accelerate cooling still further, water can be introduced into the interior of the inner mould. This water may possibly evaporate when the vacuum is applied.

In the case of extensively curved shaped articles, it is preferred that the shaped article be cut, particularly in concave curve areas, before it is stripped off the inner mould. Since shaped articles of this type, when used as a casing for a pipe bend, have later to be drawn onto a corresponding pipe bend, there is no injurious effect.

The apparatus for manufacturing shaped articles, particularly bent tubes, uses as the inner mould metal pipe bends and pipes whose external dimensions correspond to the desired inner dimensions of the shaped articles to be manufactured. In order to fix the ends of the tube after the tube has been slipped over the inner mould, cylindrical sleeves whose inner diameter corresponds roughly to the outer diameter of the foam tube, funnel-shaped receptacles, tightening strips, collets or the like are used. Furthermore, the inner mould may be such that on the outside it has bulges corresponding to cavities desired in the shaped article. Such cavities are necessary in the case of, for example, tubes which are to be drawn onto pipe lines provided externally with welded joints or sockets.

In the case of shaped articles with a sharp curve, it is preferred that at least the curved region of the inner mould be flexible. This means that it is possible both to insert the inner mould into the cold tube more easily and later to remove the inner mould from the finished shaped tube perfectly. To prevent the foam tube from buckling when it is slipped onto the inner mould, it is preferred that one free end of the inner mould have a conical extension. To prevent the foam tube from adhereing to the inner mould during the heat treatment, it is preferred that the inner mould be coated with lacquers or such like which do not adhere to the foam or that the inner mould be manufactured from a material which does not adhere to the foam. To make removal of the finished tube from the inner mould easier and to guide the incision to be made in the tube, the inner mould preferably has a guide slot. This guide slot is preferably provided in the area of the sharpest concaved curve.

Furthermore, this guide slot serves to allow the foam tube to be drawn onto the inner mould by suction when the vacuum is applied.

However, the inner mould may have additional perforations.

To accelerate cooling of the shaped tube, the inner mould may be provided with a water line having a nozzle at its discharge end.

In order to draw the foam tube onto the inner mould by suction, the inner mould is connected to a device for producing a vacuum.

For this purpose, when the inner mould is tubular, for instance, the ends of the mould are closed and the suction device is connected to one end. The discharge end of the water line in the inner mould is then preferably arranged at the other end of the inner mould.

The method and the apparatus according to the invention permit shaped articles, particularly pipe bends and the like, of a constant and accurately sized shape, to be manufactured quickly from foam tubes.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a foam tube; Figure 2 shows an inner mould with the foam tube shown in Figure 1 positioned on it; Figure 3 shows a shaped foam tube in a plan view; Figures 4, 5, 6 show different views and constructions of the inner mould; Figure 7 shows in cross-section an inner mould provided with a vacuum device; Figure 8 shows in cross-section an inner mould provided with cooling devices; and Figure 9 is a lateral view of an inner mould provided with a flexible centre part.

Referring to the drawings, Figure 1 shows a tube 1 made of foam, for example, crosslinked polyethulene foam, for use as a pipe insulator. The object is to form from this tube 1 a bent tube 3 as shown in Figure 3 for use as an insulator for a bent pipe. To do this, the tube, which is made of an elastic thermoplastic foam material, is drawn or slipped in the cold state over a perforated inner mould. The tube is then subjected to a heat treatment to change the foam into or as far as the thermoplastic/ thermoplastic state. A vacuum is applied to the inner mould, and the tube is then cooled.

This procedure will now be more fully described.

The tube 1, cut to the required length, is slipped in the cold state over a perforated inner mould 2, i.e. a 90 pipe bend, as shown in Figure 2, and is deformed while cold to form a bent tube 3 (see Figure 2). Before heat treatment, it is expedient to fix the ends 3a and 3b of the tube to the inner mould 2, for example, by tightening strips 5 as shown in Figure 2. The inner mould 2 and the tube 1 are then introduced into, for instance, a hot air furnace. Heat radiators or other devices can also be used. The temperature and time of heating essentially depend on the type of foam material of which the tube 1 is made and the size of the tube l. A vacuum is applied to the inner mould 2, and the tube 1 is then allowed to cool, whilst still attached to the mould 2, to room temperature, either with or without additional cooling. The shape of the bent tube 3 is thereby "set" by the heat treatment.

Because of the elasticity of the foam material used, the tube 3 can be removed from the inner mould as a whole. Alternatively, it may be severed first and then removed. The ends 3a and 3b are cut off to form the finished bent tube 3 as shown in Figure 3.

The required inner mould 2 can be a standard commercial pipe line section used in pipe line construction, which section has been perforated.

This ensures that the bent tube manufactured by the method of the invention fits the pipe line section. Examples of inner moulds of this type, made of metal pipe sections, are shown in Figure 4 and in Figures 5 and 6, the latter Figure being a view of the mould shown in Figure 5 taken in the direction shown by arrow A Iri the case of steel pipes, a bent section 2a connected to pipes 4 of appropriate nominal width, is used as the inner mould 2. In the case of copper pipes, soldering fittings 4b connected to pipe bends 2a are together used as the inner mould 2. In all cases in which work is to be done at the connecting points between the tube 3 and the pipe to be insulated, for example, when welds or screw couplings for double sockets are to be provided, the inner mould 2 is provided with bulges 6 of suitable size and position. It is usual to slit open the tube 3. It is advantageous therefore for the tube 3 to be manufactured in pre-slotted form. Thus, the inner mould 2 may be provided with a guide slot or a slotted groove 8 at the required point, see Figure 6, which serves, inter alia, to guide an incising device such as a cutter. To make it easier to slide the tube onto the inner mould 2, the inner mould has a conical extension 2b at one end.

Referring to Figure 7, the inner mould 2 is so shaped that the vacuum acting on the moulded part can be retained in it, i.e. bne end is sealed with a closure 9 and at the other end a hose socket 10 for the vacuum connection is provided. By the application of the vacuum, the foam tube slipped onto the inner mould 2 is neatly drawn onto the inner mould 2 by suction via perforations 7 in the inner mould and is formed into the finished bent tube 3.

The vacuum may be applied at the beginning of the heat treatment, or during the heat treatment or after the heat treatment. It may be necessary to apply the vacuum at a particular time and to apply it for a particular length of time, depending on the properties of the material of which the tube is made and the design of the tube. To ensure an exact internal contour, the vacuum should be maintained at least for a time during the cooling process. To achieve good suction to the inner mould 2, the mould is perforated with, for example, bores or slots of suitable position and size. Figure 4 shows bores 7 on the inner radius of the mould. Also, the slot 8 shown in Figure 6, serving as a cutting guide, allows suction to take place.

By the use of a vacuum, pipes 1 made of foam with rough tolerances, differing from the later end measurements, can be used to form shaped articles of good appearance and fit.

The ends 3a and 3b slipped or drawn onto the inner mould 2, may be fixed by means of clamping or tightening elements which are easy to operate and quick to manipulate, for example, tongs, clamps or tightenining strips 5.

It is desirable to seal the tube ends 3a and 3b to the inner mould to maintain the vacuum.

This may be done by the use of clamping or tightening elements 5 mentioned above, but funnel-shaped receptacles 14 in which the end of the foam tube is held between the outer cone and the inner mould, can also be used (see Figures 5 and 8). Further, sleeves or sealing discs 15 made of elastic material, e.g.

rubber, can also be used. These discs are drawn by suction and thus automatically effect the sealing (see Figure 8). The sealing discs or sealing sleeves preferably have a smaller opening than the receiving diameter of the inner mould 2. This means, on the one hand, that a good seal is formed and, on the other hand, that any movement of the seals 15 towards one another as a result of the application of the vacuum, and consequent compression of the foam tube 1 , is avoided.

Before removal of the moulded parts from the inner mould, they must cool down. To accelerate this cooling process (which, due to the insulating effect of the material, is of relatively long duration), exterior cooling may be used. Figure 8 shows air sprays 12 with spray coolings mounted on the work table 11 on which the moulding apparatus is disposed.

To accelerate the cooling process further, internal cooling of the inner mould may be effected. For this purpose, water is introduced via inlet 13 and line 19 into the inner mould 2 under vacuum. The water evaporates because of the vacuum and thereby causes cooling. For uniform water distribution, the discharge end of the supply line 19 is provided with a nozzle 18 or constructed in the form of nozzle. The nozzle is preferably disposed at the opposite end of the suction point 10, so the cooling stream sweeps over the entire inner mould.

When the inner mould has sudden changes in shape and when the foam is relatively inelastic, problems may arise when the foam tube is drawn or slipped onto the inner mould.

In order to overcome this problem, there may be used an inner mould provided with a flexible, perforated, intermediate piece 16 forming at least its curved region and with rigid ends 2c, as shown in Figure 9. The intermediate pieces 16 may consist of, for instance, per- forated rubber hose, perforated metal hose or perforated bendable spirals. The tube 1 is placed over this inner mould and only then is it angled into the desired bent position and fixed in this state, e.g. by means of an abut ment 17.

Depending on its nature, slipping or drawing of the tube 1 onto the inner mould 2 can be made easier by slightly pre-heating the tube, particularly if made of a foam which is stiff at normal temperature.

Depending on the tube 1 and the nature of the foam of which it is made, relatively long heat treatment times may be necessary. Accordingly, the metal inner moulds, because of their heat conductivity, heat up during the heat treatment. The temperatures thereby arising may result in the foam tubes becoming struck or welded on to the inner mould. To avoid this, there are used inner moulds either made of materials with non-adhesive properties, e.g.

polytetrafluoroethylene or silicon or metal moulds with non-adhesive lacquers or coatings.

Non-adhesive properties may also be obtained by the application of release agents, e.g. by spraying polytetrafluoroethylene onto the inner mould or onto the inner surface of the foam tube. This process must be repeated during manufacture.

In order to save time and to take full advantage of the work cycle time, several inner moulds can be placed on one working table.

The inner moulds may also be in the form of multi-impression moulds.

WHAT WE CLAIM IS: 1. A method of making a shaped article of a plastics material foam deformable upon heating, which method comprises positioning a tube of the plastics material foam whilst cold or whilst slightly hot over a hollow, perforated inner mould of the desired shape, which shape is different from that of the tube; heating the tube in this position at a temperature corresponding to the thermoelastic state or up to the thermoplastic state of the plastics material foam so that it becomes deformable; applying a vacuum to the inner mould so that the tube is drawn onto the inner mould by suction; allowing the tube to cool thereby to form a tube having the shape of the inner mould; and removing the shaped tube from the inner mould.

2. A method according to Claim 1, wherein the ends of the tube are fixed to the inner mould prior to heating.

3. A method according to Claim 2, wherein a cylindrical sleeve, a cone, a tightening strip, a collet or the like is used to fix the ends of the tube to the inner mould.

4. A method according to any of Claims 1 to 3, wherein the vacuum is applied whilst the tube is hot and, if desired, at least for a time whilst the tube is being cooled.

5. A method according to any of Claims 1 to 3, wherein the vacuum is applied after heating and at least for a time during cooling.

6. A method according to any of Claims 1 to 5, wherein the ends of the tube are sealed by means of rubber plates, which plates are held in position by the applied vacuum.

7. A method according to any of Claims 1 to 6, wherein the magnitude of the applied vacuum is such that collapse of the foam due to destruction of the foam cells is avoided, taking into accout the temperature to which the tube is heated, the time for which the tube is heated, the thickness of the foam and the type of foam.

8. A method according to any of Claims 1 to 7, wherein the cooling of the tube is accelerated by means of external cooling.

9. A method according to Claim 8, wherein the external cooling is effected by means of air sprays or spray ccoling.

10. A method according to any one of Claims 1 to 9, wherein the water is introduced into the inner mould, which water may evaporate when the vacuum is applied to the inner mould.

11. A method according to any of Claims 1 to 10, wherein the shaped tube is cut in its concave regions or elsewhere before being removed from the inner mould.

12. A method according to any of Claims 1 to 11, wherein the inner mould has a guide slot to aid in the cutting of the tube.

13. A modification of a method according to any of Claims 1 to 12, wherein the inner mould is at least partly flexible, and wherein the inner mould is deformed to the desired shape during the method 14. A method according to any of Claims 1 to 13, wherein the inner mould is a metal pipe bend and or a metal pipe.

15. A method according to Claim 14 when appendant to Claim 13, wherein the inner mould is a pipe bend at least the curved region of which is flexible.

16. A method according to any of Claims 1 to 15 wherein one or more bulges are provided on the outside of the inner mould whereby equivalent cavities are formed in the shaped article.

17. A method according to any of Claims 1 to 16, wherein one end of the inner mould is conical in construction at the end 18. A method according to any of Claims 1 to 17, wherein the inner mould is coated with a lacquer or such like which does not adhere to the foam, or consists of a material which does not adhere to the foam.

19. A method of making a shaped article of a plastics material foam deformable upon heating, substantially as hereinbefore described with reference to Figures 1, 2 and 3, Figures I, 2, 3 and 4, Figures 1,2, 3 and 5, Figures 1, 2, 3 and 6, Figure 7, Figure 8 or Figure 9 of the accompanying drawings.

20. A shaped article of a plastics material foam deformable upon heating, whenever made by the method claimed in any of Claims 1 to 19

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. it angled into the desired bent position and fixed in this state, e.g. by means of an abut ment 17. Depending on its nature, slipping or drawing of the tube 1 onto the inner mould 2 can be made easier by slightly pre-heating the tube, particularly if made of a foam which is stiff at normal temperature. Depending on the tube 1 and the nature of the foam of which it is made, relatively long heat treatment times may be necessary. Accordingly, the metal inner moulds, because of their heat conductivity, heat up during the heat treatment. The temperatures thereby arising may result in the foam tubes becoming struck or welded on to the inner mould. To avoid this, there are used inner moulds either made of materials with non-adhesive properties, e.g. polytetrafluoroethylene or silicon or metal moulds with non-adhesive lacquers or coatings. Non-adhesive properties may also be obtained by the application of release agents, e.g. by spraying polytetrafluoroethylene onto the inner mould or onto the inner surface of the foam tube. This process must be repeated during manufacture. In order to save time and to take full advantage of the work cycle time, several inner moulds can be placed on one working table. The inner moulds may also be in the form of multi-impression moulds. WHAT WE CLAIM IS:

1. A method of making a shaped article of a plastics material foam deformable upon heating, which method comprises positioning a tube of the plastics material foam whilst cold or whilst slightly hot over a hollow, perforated inner mould of the desired shape, which shape is different from that of the tube; heating the tube in this position at a temperature corresponding to the thermoelastic state or up to the thermoplastic state of the plastics material foam so that it becomes deformable; applying a vacuum to the inner mould so that the tube is drawn onto the inner mould by suction; allowing the tube to cool thereby to form a tube having the shape of the inner mould; and removing the shaped tube from the inner mould.

13. A modification of a method according to any of Claims 1 to 12, wherein the inner mould is at least partly flexible, and wherein the inner mould is deformed to the desired shape during the method

14. A method according to any of Claims 1 to 13, wherein the inner mould is a metal pipe bend and or a metal pipe.

17. A method according to any of Claims 1 to 16, wherein one end of the inner mould is conical in construction at the end

18. A method according to any of Claims 1 to 17, wherein the inner mould is coated with a lacquer or such like which does not adhere to the foam, or consists of a material which does not adhere to the foam.