GB1581170A - Shaped body and process for its manufacturer - Google Patents

Description

(54) SHAPED BODY AND PROCESS FOR ITS MANUFACTURE (71) We, HOECHST AKTIENGESELLSCH AFT, a Body Corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Germany, and ERNST KEUTNER, of Josef-Schlicht-Strasse 6, 8 Munchen 60, Federal Republic of Germany, a German citizen, 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 a process for tlle manufacture of a pipe bend, and pipe bends produced thereby.

In our co-pending Application No. 45382/ 74, Serial No. 1,491,041, there is described and claimed a one piece plastics pipe bend, which is an article for covering an elbow in a pipe, that is inherently dimensionally stable both in the form of a pipe bend-a portion of a hollow ring open along an inner arcand also in the form of a shell-type body having no re-entrant curves, which can also be regarded as an open and open-ended trough, the depth of the central portion of the trough being greater than that at the ends. The disclosure of the above-mentioned application is incorporated by reference herein.

The above-mentioned application also describes and claims a process for the manufacture of the pipe bend in which the article is heat-treated in the pipe bend conformation to render it dimensionally stable in that conformation.

The present invention provides an improvement in the process for the manufacture of a pipe bend, especially in the heat-treatment step.

The present invention accordingly provides a process for the manufacture of a shaped body of a thermoplastic material, which body is dimensionally stable both in the form of a portion of a hollow ring open along an inner arc and also in the form of a shelltype body havin no re-entrant curves, which comprises bending the dimensionally stable shell-type body having no re-entrant curves into the hollow ring portion conformation, maintaining it in that conformation by external mechanical forces while subjecting it for a period of from 6 to 12 minutes to a temperature above the second order transition temperature Tg of the thermoplastic material, e.g., by exposure to a gas at a temperature within the range of from 80"C to 90"C, cooling it to below the second order transition temperature and then removing the external mechanical forces.

The material is advantageously a synthetic polymer in the form of a flexible sheet having at least the toughness of one of rigid polyvinyl chloride, and preferably is rigid (or unplasticized) polyvinyl chloride.

Preferably, the process comprises the steps of a) producing a shell-type body of plastics material of the shape of a shell having no reentrant curves and provided, on opposite sides of its opening, with two spout-like tongues which are narrower than the centre piece of the shell, by thermoforming a section of plastics film by means of a dee-drawing tool of appropriate shape; b) allowing the thermoformed film section, while still on the surface of the deep- drawing tool, to cool; c) separating the shell-type body from the deep-drawing tool; d) converting the shell-type body, by a bending operation, into a body of the shape of a quarter torus slit along its innermost circular arc; e) causing external mechanical forces to act upon the torus sector to enforce a stabilization of its shape; f) exposing the whole of the shaped body for a period from 6 to 12 minutes to the action of a gas current heated to a temperature within the range from 80 to 900C; g) cooling the pipe bend stabilized in its shape to a temperature below the second order transition temperature of the polymer from which the film is made; and h) withdrawing the mechanical forces which exert the form stabilizing influence upon the shaped body.

If the pipe bend is to cover a bend in a pipe of other than 90 , the torus sector is chosen accordingly.

The invention also provides a shaped body (in either conformation) produced by the process. It will be understood that although the body is preferably manufactured in the shell conformation, the invention also includes a body, and a process for its manufacture, in which the shell has been formed from a dimensionally unstable torus sector.

Advantageously, in the process, a sheet of film consisting of synthetic thermoplastic polymer, the film being flexible and advantageously having at least the toughness of one consisting of rigid polyvinyl chloride, of appropriate size and thickness, e.g., a thickness in the range between 300 and 700 ,u, advantageously between 350 and 600 Il, preferbly 400 11 and as indicated above, preferably a section of rigid polyvinyl chloride film, is first thermoformed (deep-drawn) and by means of known thermoforming tools (deep-drawing tools), so that the resulting three-dimensional plastics body assumes the shape of a shell having no re-entrant curves and provided, on opposite sides of its opening, with two spoutlike tongues which are narrower than the centre piece of the shell. The shape of this shell-type body corresponds to that of the three-dimensional body notionally formed by opening a hollow torus, preferably a quarter torus for covering a 90" bend, along its innermost circular arc and bending the opened torus sector outwardly.

Thermoforming of the plastics film may be effected, for example, by horizontally clamping the film in a frame adapted for vertical displacement and fastening it in this position.

The flat film fixed in the frame is first transformed into the deep-drawable condition by the action of adequate heat, for example by the action of heat within a temperature range from 100 to 1800C, preferably from 120 to 140"C, if rigid polyvinyl choride film having a thickness of 400 y is used. For example, the film clamped in the frame may be exposed to the influence of infrared radiators for this thermal treatment.

By vertically lowering the frame and evacuating the air entrapped between the film and the mold, the plastics film clamped in the frame-which by now is in the deep-drawable state-is drawn over the mold in such a manner that, if a male mold is used, the film fits the outer surface of the mold closely and practically without folds and assumes the shape of the mold.

Alternatively, the film may be deep-drawn by the female molding method, in which case, a female deep-drawing tool is used.

If a female deep-drawing tool is used for thermoforming the film, the tool is in the shape of a shell having no re-entrant curves and provided on opposite sides of the opening with two spout-like tongues which are narrower than the centre piece of the shell.

While it is still stretched over the surface of the mold and its edges are still clamped in the frame, the deep-drawn, deformed film is allowed to cool sufficiently, i.e., to a temperature below the second order transition tem perature (Tobolsky "Properties and Structure of Polymers", John Wiley and Sons; New York; 1960; pages 61 to 81) of the plastics film used, advantageously to room tempera ture (approx. 23"C). The shell-type shaped body formed from the film is then separated from the deep-drawing tool, without deforming it permanently, for example by lifting the frame with the film clamped in it from the mold. The deformed film is then taken from the frame and trimmed.

By a bending operation, which may be performed manually, the shell-type body thus produced is then deformed in a manner such that it assumes the shape of a hollow (quarter) torus slit along its innermost circular arc.

By the action of external mechanical forces the hollow torus section of plastics film slit along its innermost circular arc-in the following designated as "pipe bend"-is then secured in a position and under conditions which keep it from spontaneously reverting to its original shell-type shape.

The enforced form stabilization of the pipe bend may be effected, for example, by surrounding the areas near the ends of the pipe bend with rigid clamping rings, for example metal rings, in a manner such that the inner surfaces of the clamping rings are in mechanical, preferably close and direct mechanical, contact with the outer surface of the pipe bend. The clamping rings may be 3 to 6 cm wide. The clamping rings act as abutments for the pipe bend urged aginst them by their tension.

Advantageously, the clamping rings are provided on their outer sides with fasteners by means of which they can be fastened in a fixed position.

The resiliency inherent in the pipe bend (spring tension) is counteracted by the force which the inner surface of the clamping rings exerts upon the film.

After having its shape stabilized in this manner, the pipe bend is exposed for an adequate period of time, for example from 6 to 12 minutes, and virtually from all sides, to a current of gas, preferably air, of sufficiently high temperature, of 80 to 90"C.

The heat treatment may be effected, for example, by passing the pipe bend held in the clamping ring fasteners together with the fasteners and at constant speed, through a heating channel of sufficient length operated at an appropriate temperature; for example, the pipe bend made from polyvinyl chloride film of thickness 400 may be exposed in the heating channel for about 8 minutes, e.g. to the influence of air heated to a temperature within the range from 80 to 90"C.

After its thermal treatment, i.e., after the pipe bend has passed through the heating channel, it is cooled to a temperature below the second order transition temperature (glass transition temperature) of the polymer of which the film is made, preferably to room temperature (approx. 23"C), for example by causing a current of cooling gas, preferably air of room temperature, to act from virtually all sides upon the pipe bend for a period from 1 to 4 minutes, advantageously from 2 to 3 minutes. Advantageously, cooling (to below its glass transition temperature) of the pipe bend subjected to enforced form-stabilisation is effected immediately following the end of the heat treatment; for example, it may be effected, immediately after the pipe bend leaves the heating channel, by passing it into and through a cooling channel which may be operated with air of room temperature, for example. After cooling, the forces exerting the restraining influence upon the pipe bend are removed by separating the pipe bend from the clamping ring fasteners.

The product obtained by this process has the feature that it is stable in its pipe bend state, i.e., it has little or no tendency to change its shape without external influence, although the pipe bend may be reversibly converted, by a bending operation, into a shell-type body having no re-entrant curves in which form it is also stable and not inclined to change its shape spontaneously without external influences.

WHAT WE CLAIM IS: 1. A process for the manufacture of a shaped body ofa thermoplastic material, which body is dimensionally stable both in the form of a portion of a hollow ring open along an inner arc and also in the form of a shell-type body having no re-entrant curves, which comprises bending the dimensionally stable shell-type body having no re-entrant curves into the hollow ring portion conformation, maintaining it in that conformation by external mechanical forces while subjecting it for a period of from 6 to 12 minutes to a temperature above the second order transition temperature Tg of the thermoplastic material, cooling it to below the second order transition temperature and then removing the external mechanical forces.

2. A process as claimed in claim 1, wherein the body is subjected to a temperature above Tg by exposing it to a gas at a temperature of from 80"C to 90"C.

3. A process as claimed in claim 1 or claim 2, wherein the body is subjected to a temperature above Tg for about 8 minutes.

4. A process as claimed in any one of claims 1 to 3, wherein the body is formed of rigid polyvinyl chloride.

5. A process as claimed in any one of claims 1 to 4, wherein the body is cooled to below Tg immediately after the heat trcatment.

6. A process for the manufacture of a shaped body stable both in the shape of a shell having no re-entrant curves and in the shape of a hollow ring portion open along an inner arc, which comprises the steps of a) producing a shell-type body of plastics material of the shape of a shell having no re-entrant curves and provided, on opposite sides of its opening, with two spout-like tongues which are narrower than the centre piece of the shell, by thermoforming a section of plastics film by means of a deep-drawing tool of appropriate shape; b) allowing the thermoformed film section, while still on the surface of the deepdrawing tool, to cool; c) separating the shell-type body from the deep-drawing tool; d) converting the shell-type body, by a bending operation, into a body of the shape of a quarter torus slit along its innermost circular arc; e) causing external mechanical forces to act upon the torus sector to enforce a stabilization of its shape; f) exposing the whole of the shaped body for a period from 6 to 12 minutes to the action of a gas current heated to a temperature within the range from 80 to 90"C; g) cooling the pipe bend stabilised in its shape to a temperature below the second order transition temperature of the polymer from which the film is made; and h) withdrawing the mechanical forces which exert the form stabilizing influence upon the shaped body.

7. A process as claimed in claim 6, wherein the body is of rigid polyvinyl chloride.

8. A body, whenever produced by a process as claimed in any one of claims 1 to 7.

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

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. channel, it is cooled to a temperature below the second order transition temperature (glass transition temperature) of the polymer of which the film is made, preferably to room temperature (approx. 23"C), for example by causing a current of cooling gas, preferably air of room temperature, to act from virtually all sides upon the pipe bend for a period from 1 to 4 minutes, advantageously from 2 to 3 minutes. Advantageously, cooling (to below its glass transition temperature) of the pipe bend subjected to enforced form-stabilisation is effected immediately following the end of the heat treatment; for example, it may be effected, immediately after the pipe bend leaves the heating channel, by passing it into and through a cooling channel which may be operated with air of room temperature, for example. After cooling, the forces exerting the restraining influence upon the pipe bend are removed by separating the pipe bend from the clamping ring fasteners. The product obtained by this process has the feature that it is stable in its pipe bend state, i.e., it has little or no tendency to change its shape without external influence, although the pipe bend may be reversibly converted, by a bending operation, into a shell-type body having no re-entrant curves in which form it is also stable and not inclined to change its shape spontaneously without external influences. WHAT WE CLAIM IS:

1. A process for the manufacture of a shaped body ofa thermoplastic material, which body is dimensionally stable both in the form of a portion of a hollow ring open along an inner arc and also in the form of a shell-type body having no re-entrant curves, which comprises bending the dimensionally stable shell-type body having no re-entrant curves into the hollow ring portion conformation, maintaining it in that conformation by external mechanical forces while subjecting it for a period of from 6 to 12 minutes to a temperature above the second order transition temperature Tg of the thermoplastic material, cooling it to below the second order transition temperature and then removing the external mechanical forces.

2. A process as claimed in claim 1, wherein the body is subjected to a temperature above Tg by exposing it to a gas at a temperature of from 80"C to 90"C.

3. A process as claimed in claim 1 or claim 2, wherein the body is subjected to a temperature above Tg for about 8 minutes.

4. A process as claimed in any one of claims 1 to 3, wherein the body is formed of rigid polyvinyl chloride.

5. A process as claimed in any one of claims 1 to 4, wherein the body is cooled to below Tg immediately after the heat trcatment.

6. A process for the manufacture of a shaped body stable both in the shape of a shell having no re-entrant curves and in the shape of a hollow ring portion open along an inner arc, which comprises the steps of a) producing a shell-type body of plastics material of the shape of a shell having no re-entrant curves and provided, on opposite sides of its opening, with two spout-like tongues which are narrower than the centre piece of the shell, by thermoforming a section of plastics film by means of a deep-drawing tool of appropriate shape; b) allowing the thermoformed film section, while still on the surface of the deepdrawing tool, to cool; c) separating the shell-type body from the deep-drawing tool; d) converting the shell-type body, by a bending operation, into a body of the shape of a quarter torus slit along its innermost circular arc; e) causing external mechanical forces to act upon the torus sector to enforce a stabilization of its shape; f) exposing the whole of the shaped body for a period from 6 to 12 minutes to the action of a gas current heated to a temperature within the range from 80 to 90"C; g) cooling the pipe bend stabilised in its shape to a temperature below the second order transition temperature of the polymer from which the film is made; and h) withdrawing the mechanical forces which exert the form stabilizing influence upon the shaped body.

7. A process as claimed in claim 6, wherein the body is of rigid polyvinyl chloride.

8. A body, whenever produced by a process as claimed in any one of claims 1 to 7.