IL98017A - Inflatable mandrel - Google Patents

Description

INFLATABLE MANDREL 1828/91 -1- INFLATABLE MANDREL The present invention relates to a mandrel for producing elongated bodies, and to a method for their production. More particularly, the invention relates to a collapsible, inflatable mandrel, and to a method of using the same.

It is well known in the art to produce elongated bodies made of fiber-reinforced plastic material. Such elongated bodies are normally of a tubular shape and may be, for instance, tanks used as containers for liquids in industry. The material employed for producing such elongated bodies is normally glass-reinforced polyester, commonly called "fiberglass". In order to produce the elongated body, a mandrel is provided, the envelope of which has the shape of the inner part of the elongated body to be produced, and the impregnated fibers are spooled thereon, left to solidify and then removed from the mandrel.

As will be apparent to the skilled person, in order to be able to remove the elongated body formed by this process it is necessary to detach it from the mandrel, and for this purpose it is necessary to provide mandrels which collapse easily. This is normally done by providing mandrels made of hard material and constructed into halves, which halves can be caused to move slightly, one towards the other, for instance by the action of an appropriate gear, thus leaving a gap between the surface and the produced body which is sufficient in order to remove the bodies so produced therefrom. 1828/91 -2- However, the mandrels available in the art present serious drawbacks, particularly when large elongated bodies are to be produced, because of cost, space requirements, difficulty of operation, and maintenance requirements. It should be understood that this is particularly so when large tubular bodies (e.g., having diameters of 0.5 m or higher) are to be produced. As will be apparent to a person skilled in the art, it is customary to produce, e.g., tanks for liquid storage having diameters of up to six meters, and lengths up to ten meters.

Another considerable drawback is that, by mandrels known in the art, it is extremely difficult to produce elongated bodies having shapes which substantially differ from tubular, because substantial collapse of the mandrel is difficult to achieve, while in tubular bodies a slight collapse is sufficient to enable to remove the body produced therefrom.

It is an object of the present invention to provide a mandrel which can be used for producing elongated bodies, which is not expensive, lightweight and easy to operate.

It is another object of the invention to provide a collapsible inflatable mandrel which can be used to produce elongated bodies of difficult shapes.

It is still another object of the invention to provide a method for producing elongated bodies which employs the mandrel of the invention. 1828/91 -3- The collapsible inflatable mandrel according to the invention, which is adapted to produce elongated bodies made of fiber-reinforced plastic materials, comprises an inner inflatable member connected or attached to a rotation shaft, and an outer jacket mounted on the said inflatable member and having the envelope shape and effective dimensions which are to be imparted to the inner surface of the elongated body produced thereon.

As said, the fiber-reinforced plastic material can be a variety of combinations, starting from the commonly employed glass fiber-reinforced polyester, but including other fibers, e.g., evlar or carbon fibers, impregnated with a variety of impregnation agents.

The inner inflatable member will normally be connected or attached to the rotation shaft which will pass through its axis, and will rotate when the rotation shaft is caused to rotate. Rotation of the inner member shall bring about a rotation of the outer jacket, and this will cause the spooling action on the outer jacket. The rotation of the rotation shaft may promote rotation of the inner inflatable member by a variety of methods, for instance, the shape of the shaft may be such that it fits into the shape of the inner part of the inflatable member. For instance, the shaft may be of square cross-section and the inner part of the inflatable member may be closely connected thereon. Alternatively, the shaft may be made of, or coated with, materials having high friction coefficient with the inner part of the inflatable member, and rotation of the latter may be caused by friction only. Similarly, the rotation of the outer jacket, which is brought about by the rotation of the inner inflatable member, can be 1828/91 -4- caused by friction between the two surfaces, but may also be caused by additional connections between the inner inflatable member and its outer jacket.

The method of producing an elongated body made of fiber-reinforced plastic material, according to the invention, comprises the steps of: (a) providing a mandrel comprising an inner inflatable member connected to a rotation shaft; (b) providing an outer jacket mounted on the said inner inflatable member, the said outer jacket having the envelope shape and effective dimensions which are to be imparted to the inner surface of the elongated body to be produced; (c) inflating the inner inflatable member to obtain full exposition of the envelope of the outer jacket; (d) rotating the rotation shaft and simultaneously spooling the impregnated fibers on the surface of the outer jacket; (e) allowing the elongated body generated by the spooling action of above to solidify; (f) deflating the inner inflatable member to cause the outer jacket to collapse inwards; and (g) removing the elongated body from the mandrel.

By "effective dimensions" is meant to indicate the portion of the jacket which is actually used for spooling the fibers and for creating the 1828/91 -5- elongated body, and does not include any dead areas not involved in such production.

All the above and other characteristics and advantages of the invention will be further understood from the following illustrative and non-limitative description of preferred embodiments, with reference to the appended drawings, wherein: - Fig. 1 illustrates a prior art mandrel; - Fig. 2 illustrates a mandrel according to a preferred embodiment of the invention; and - Fig. 3 shows a mandrel according to another preferred embodiment of the invention.

Referring now to Fig. 1(a), a mandrel is shown in operating position, in which it forms a substantially perfect circle. The mandrel, generally indicated at 1 , has a diameter d and is held in place by beams 2, mounted on central shaft 3. Fig. 1(b) shows the mandrel of Fig. 1(a) in its collapsed position. It can be seen that the two halves 1' and 1" have been moved one towards the other, by the action of an appropriate gear (not shown), so that the effective diameter d' of the mandrel of Fig. 1(b) is smaller than the diameter d of the mandrel in its operational position of Fig. 1(a). Therefore, it is possible to remove the elongated body which has been produced in the operational position of Fig. 1(a), and which has 1828/91 -6- an inner diameter of approximately d, from the mandrel when its collapsed diameter is d'.

Fig. 2(a) schematically shows a mandrel according to one embodiment of the invention, which is indicated by numeral 4. This mandrel comprises an inner inflatable member 5, mounted on shaft 6, which is inflated through air inlet/outlet 7. On this inner inflatable member there is mounted an outer jacket 8, on which spooling of the impregnated fiber is effected.

It should be noted that the combination of an inner "softer" inflatable member and of an outer "harder" jacket presents several advantages. First of all, it is possible to use relatively hard and strong material for the jacket, which is difficult to inflate, but which can be repeatedly used to produce elongated bodies, without undergoing substantial damage. On the other hand, when a "hard" material is used the end edges of the mandrel, where a curvature exists, which are schematically indicated by numeral 9, are reduced. This is important because these areas, where the mandrel does not have the actual diameter required, are lost and cannot be used in spooling.

While a variety of construction materials can be used to provide the inner member and the outer jacket, it is convenient to employ reinforced rubber, elastomers or PVC sheets that can be sewn together and welded for air tightness, e.g., for the inner inflatable member. Such welding and sewing operations are well known to the man of the art, and employ conventional technologies. 1828/91 -7- Looking now at Fig. 2(b), the mandrel of Fig. 2(a) is shown in its collapsed position, in which air has been allowed to exit from air inlet outlet 7. The inner member has been deflated, and the outer member has collapsed, leaving a substantial gap from the inner surface 10 of the elongated body which has been produced thereon, which elongated body can now be easily removed from the mandrel.

In Fig. 3 a mandrel is shown having the shape of a "numeral 8". Such a shape can be achieved by producing a jacket having a fully exposed outer envelope in the shape of an eight which rotates around its axis. Depending on the actual curvature of the surface, the inner inflatable member can be of an elongated shape, and can be allowed to inflate differently, according to the pressure it applies on the inner surface of the outer jacket. Alternatively, the inner inflatable member can also be produced in a predetermined shape, to inflate more easily at different locations along its axis.

By "fully exposed envelope of the outer jacket" is meant the entire surface of the jacket obtainable when the inner inflatable member is inflated and completely fills the inner cavity contained within the envelope. In this situation an inner pressure exists which prevents the outer jacket from collapsing inwards to an appreciable extent.

The above description has been given for the purpose of illustration, and is not intended to be limitative. Many different shapes of mandrels can be provided, many different construction materials, jackets and 1828/91 -8- additions can be devised, as well as different uses can be made of the method of the invention, all without exceeding its scope.

Claims (9)

1828/91 -9- WHAT WE CLAIM IS:

1. A collapsible inflatable mandrel for producing elongated bodies made of fiber-reinforced plastic material, comprising an inner inflatable member connected or attached to a rotation shaft, and an outer jacket mounted on the said inflatable member and having the envelope shape and effective dimensions which are to be imparted to the inner surface of the elongated body produced thereon.

2. A mandrel according to claim 1, wherein the outer jacket has an exposed envelope having a substantially tubular shape.

3. A mandrel according to claim 1, wherein the outer jacket has an exposed envelope having a diameter which varies at different locations along the shaft of the mandrel.

4. A mandrel according to claim 1, wherein the diameter of the exposed envelope of the outer jacket is 0.5 meter or more.

5. A method of producing an elongated body made of fiber-reinforced plastic material, comprising the steps of: (a) providing a mandrel comprising an inner inflatable member connected or attached to a rotation shaft; (b) providing an outer jacket mounted on the said inner inflatable member, the said outer jacket having the envelope shape and effective dimensions which are to be imparted to the inner surface of the elongated body to be produced; 1828/91 -10- (c) inflating the inner inflatable member to obtain full exposition of the envelope of the outer jacket; (d) rotating the rotation shaft and simultaneously spooling the impregnated fibers on the surface of the outer jacket; (e) allowing the elongated body, generated by the spooling action of above to solidify; (f) deflating the inner inflatable member to cause the outer jacket to collapse inwards; and (g) removing the elongated body from the mandrel.

6. A method according to claim 5, wherein the air pressure is utilized to support the members of the mandrel against the loads encountered in the manufacturing of elongated reinforced plastic bodies, including attachment to the rotating shaft, stretching of the applied reinforcements, contraction of the curing resins, rotational moments and the like.

7. An elongated body made of fiber-reinforced plastic material, whenever produced by the method of claim 5 or 6.

8. A collapsible inflatable mandrel for producing elongated bodies made of fiber-reinforced plastic material, essentially as described and illustrated.

9. A method of producing an elongated body made of fiber-reinforced plastic material, essentially as described and illustrated. LUZZATTOi & LUZZATTQ