GB2032331A - Shaping a length of tubing - Google Patents

Abstract

A method of manufacturing an article having a pre-determined shape from heat mouldable material characterised by the steps of heating a tubular blank of the material to a temperature, below its softening point, at which it is mouldable, by flowing heated liquid through the blank and thereafter cooling the heated tubular blank while maintaining it in the predetermined shape in a constrained state such that on release of the constraint after cooling, it assumes the predetermined shape. The blank may be cooled by flowing cooling liquid through it after the flow of heating liquid is terminated. The blank may comprise a substantial length of tubing which is sufficiently flexible to permit it to be set to the required shape, e.g. a coil, either at room temperature or at a raised temperature on a jig, former, cradle or other support structure.

Description

SPECIFICATION Thermoforming articles The invention relates to thermoforming articles and is more particularly concerned with methods of manufacturing articles having a predetermined shape or form and manufactured from heat mouldable material.

In general there have been two principal ways of manufacturing predetermined shaped articles from material that can be thermoformed. The first ofthese methods comprises conventional moulding in which the article is formed in an openable mould. For a hollow article the mould comprises a casing and a core, the mould being designed so that the core can be removed from the moulded article. At some stage in such moulding, the mould is heated. In the other way of manufacture, the article is shaped from material while the material is in a plastic or pliable state and then the shaped article is baked or at least heated in an autocleave or oven.

Each of the conventional ways of manufacture have substantial dis-advantages. Thus, the cost of moulding apparatus, for example injection moulding apparatus, is sufficiently high to justify such expenditure only when very large volumes of articles are to be manufactured. Further it is really only economical and practical to mould relatively small articles. This is equally relevant to a manufacturer using an autocleave since the cost of a large volume autocleave can only be justified either for large volumes or for high value large articles.

Neither of the conventional manufactures is particularly suitable for low volume production of relatively large awkward shaped articles. The present invention addresses this difficulty.

Accordingly the invention provides a method of manufacturing an article having a predetermined shape or form from heat mouldable material characterised by the steps of heating a tubular blank of the material to a temperature, below its softening point, at which it is mouldable by flowing heated liquid through the blank and thereafter cooling the heated tubular blank while maintaining it in the predetermined shape or form or in a constrained state such that on release of the constraint after cooling, it assumes the predetermined shape or form.

Preferably the blank is cooled by flowing cooling liquid through the blank after the flow of heating liquid is terminated.

Suitable heat mouldable orthermoformable materials are polyethylene, vinyl polymers, vinyl chloride, vinyl acetates polymers or polyamides.

The tubular blank can, for example, comprise a tube and can be shaped either by winding it onto a former to form a coil or by threading it onto or fixing it to a jig or like support structure.

Two examples of ways of performing the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic drawing of apparatus for carrying out the first way of performing the invention, and Figure iis a diagrammatic'drawing .ofthe article manufactured in the second example.

The manufacture to be described with reference to the drawing is usable to form a coil of tubular plastics material e.g. a polymer. Such coils are usable for coupling vacuum from a motortractorto its trailer.

The initial tube is straight and flexible and is wound Into a coil 11 on a rigid, in this example wooden, cylindrical former 12. The tube is formed of Nylon Hose has an internal diameter of about 1cm and a wall thickness of about0.1cms. The former is about 12to 15 cms. in diameter and about 60-75 cms long. The former is detachably and rotatably mounted in a suitable frame (not shown). The tube is wound as a coil onto the former either while the former is detached from its mounting frame or by rotating the former in its frame and feeding the tube onto the rotating former. The former may be helically grooved to receive the tube; The rigidity of the wall of the tube is such that the bore remains substantially constant and the tube does not flatten.

When the coil has been wound on theformer is connected by a feed conduit 13 to a liquid pump 14 connected via a three-way valve V1 to a hot oil reservoir 16. The oil in the reservoir is Shell Clams 25. An immersion heater is used in this example to heat the oil to a temperature of 1 50 c. Oil is returned to the reservoir 16 by a return conduit 17 including a second three-way~valve V2. A second inlet of the supply valve V1 is connected to the outlet of a cold oil reservoir 21 and a second outlet of the return valve V2 is connected to the in let of the reservoir21.

The cold oil is at room temperature but can be cooled to a lower temperature.

After winding the coil and connecting up the conduits, the pump is switched on and hot oil flowed through the coil. The flow is maintained for about four minutes with the reservoir oil temperature at about 1 500C. The valves V1 and V2 are then adjusted to change the oil flow from hot oil to cold oil. The cold oil is allowed to flow for about four minutes The oil is then vented from the coil by setting the valve 14 to its third setting in which air is pumped into the coil. Finally and if required, the oil in the cold can be scavenged, for example by admitting a blast of nitrogen from a high pressure source into the coil.

After cooling and, if done, scavaging the former is removed from its mounting frame and taken out from the coil. The coil retains its helical form. The helical coil can be extended and compressed in the manner of a concertina. Suitable fitting can be swaged or otherwise secured to the ends of the coil tube to permit it to be connected in a fluid or vacuum circuit.

In the second example an article of relatively large size is thermo-formed. The article is usable in the air conditioning system of a vehicle and replaces a similar article which, of necessity, has to be assembled from discrete parts, at least some of which were metal. The article is formed from what is commercially identified as "high pressure nylon hose". Such hose is flexible in that it can be wound into relatively large diameter coils of, say for a 1.25cm bore hose, 75-1 00cms diameter. However cold, or at room temperature the hose cannot be taken around small radius curves e.g. curves of say 5 to 1 Ocms radius.

As illustrated in Figure 2, the article comprises five consecutive sections 31 to 35 and is between 1 and 2 meters in length. The sections are not all in the same plane and, in fact, in this example only sections 31,32 are in the same plane. The article is formed using a jig structure which provides a grooved path into which the hose can be fitted. This is done by first laying out the hose along side the jig path and then flowing hot oil (temperature 1 00 C) through the hose for two minutes. By this time the hose has reached a temperature at which the nylon wall is sufficiently flexible to permit the tube to be fitted into and secured in the jig path. The oil temperature is then raised (e.g. to 1 50 C) and caused to flow for a further four minutes.The hose is connected in an oil flow circuit similar to that illustrated in Figure 1. Thereafter, the oil flow is changed from hot oil to cold (room temperature) oil and then vented and, if required, scavenged.

Many changes may be made to the two ways described hereinafter of performing the invention.

For example, a liquid other than oil may be used to heat and/or cool the tubular blank. The article can be moulded to have substantially any reasonable, re quired shape or form. The two described articles retain the full bore through their length since collapse of the tube is prevented by the internal liquid pressure. However, if it is required to intro duce a constriction this can be done during the thermoforming. Again, if an exterior fixing flat is required this can be moulded into the tube wall. In both the examples the ambient medium was atmos pheric air. However there could be circumstances where a different medium, for example a liquid, is required.

Claims (3)

1. A method of manufacturing an article having a predetermined shape or form from heat mouldable material characterised by the steps of heating a tubular blank of the material to a temperture, below its softening point, at which it is mouldable by flowing heated liquid through the blank and thereaf ter cooling the heated tubular blank while maintain ing it in the predetermined shape or form or in a constrained state such that on release of the con straint after cooling, it assumes the predetermined shape orform.

2. A method as claimed in claim 1, further characterised in that the blank is cooled by flowing cooling liquid through the blank after the flow of heating liquid is terminated.

3. A method as claimed in claim 1 or 2, further characterised in thatthe initial blank comprises a substantial length of tubing which is sufficiently flexible to permit it to be set to the required predetermined shape or form at room temperature and in that the tubing is set to the required shape or form by shaping it on a jig, former, cradle or other support structure.