Process for producing a convex sail or a tensile structure

A process for modelling a sail with a sandwich configuration and a three-dimensional convex shape, wherein the "mould" is formed by a semirigid film material which has a shape identical to that of the sail to be produced. On this kind of "parent sail", a cloth is prepared by adhering, by means of a removable adhesive, synthetic weft (1) and warp (2) filaments onto the "parent sail". This cloth will form the inner layer of the final "sandwich". Two thin external plastic laminates are applied on the cloth, one on each side, after removal of the cloth from the "parent sail". The thin external plastic laminates are applied in individual pieces adapted to follow the convexity of the cloth. The application of the external laminates is performed on a plane support.

TECHNICAL FIELD
 The present invention relates to a triangular or trapezoidal sheet which
 can be utilized as a sail for sailboats. As already known, modern sheets
 used as sails for sailboats, are preferably produced in the form of a
 sandwich structure, in which two external plastic laminates are joined by
 an appropriate adhesive material or in another way, enclosing therebetween
 reinforcement filaments made of Kevlar, Spectra, Polyester or some other
 kind of resistant synthetic material.
 BACKGROUND ART
 According to the the prior art, plastic filaments are laid in thread
 groups, using an automated mechanism, onto a plastic film previously put
 on a convex and rigid mould, and subsequently they are covered by a second
 film having the same features as the first one. A considerable drawback of
 known production processes lies in the complexity of the automated plant,
 comprising the rigid adjustable mould and the robot which puts the
 reinforcement filaments on the first plastic laminate laid onto the rigid
 convex mould. In order to allow the adjustment of the mould, the latter
 must be provided with a plurality of flexible fillets or strips, which are
 nevertheless substantially rigid and which are provided with associated
 pneumatic cylinders to be adjusted individually depending on the value of
 the sail's camber.
 Further problems must be faced when a different mould must be constructed
 for a sail of different size.
 DISCLOSURE OF THE INVENTION
 An object of the present invention is to realize a sail production process,
 which is less expensive than the traditional process, by replacing the
 known rigid mould, with a mould which in the following description will be
 called the "parent sail" ("loom").
 This definition is useful to emphasize--not only in terms of costs--the
 difference with respect to the traditional rigid and adjustable mould.
 Another most important object of the present invention is that of realizing
 a "cloth" on said parent sail. In fact, the "parent sail" is a "fictitious
 sail" made of thermoplastic material, for instance a polyester film, which
 is much thicker than a plastic laminate used in practice to make sails.
 The parent sail is only used for the purpose of modelling, according to
 the desired camber and dimensions, a cloth made of reinforcement filaments
 (Kevlar, Spectra, polyester, etc.), which is to be introduced between the
 plastic laminates of the sail, in order to form a "sandwich".
 Since the parent sail has a negligible cost with respect to known
 adjustable rigid moulds, it may be realized according to different shapes
 (cambers) and different dimensions corresponding to those of known sails
 for sailboats. Preferably, a polyester film of 250 micron of thickness (10
 mils) will be used, which forms a common extrusion material of a
 commercial kind.
 Once the cloth has been realized, which is very different from the ensemble
 of reinforcement filaments arranged between the plastic laminates in a
 traditional sail--as will be explained afterwards--conventional (vacuum)
 techniques will be used for applying the thin external plastic laminates.

BEST MODE OF CARRYING OUT THE INVENTION
 In the present process, the "parent sail" is realized in the same way as a
 sail made of a very thin plastic laminate, according to the traditional
 process.
 The camber of the parent sail and its dimensions will obviously be
 identical with those of the sail to be obtained.
 Once the parent sail has been realized, the cloth is formed on the same,
 and this cloth will constitute the inner layer of the sandwich forming the
 sail to be realized.
 The cloth is made to adhere to the parent sail by means of a quick setting
 removable adhesive, so that it remains "welded" thereon, and so that each
 thread will have the desired length according to the arc whereon it lies.
 Once this operation is terminated, and after having obtained the desired
 triangular cloth, which is shown in FIG. 1, the cloth will be removed from
 the parent sail and the vacuum lamination will start according to known
 techniques.
 The cloth (FIG. 1) is much thicker (more closely woven) than the net of
 reinforcement filaments of the known processes. The cloth includes a warp
 2 and a weft 1. FIG. 1 shows a homogeneous-type cloth having the same size
 as the sail and including a weft 1 and a warp 2, wherein two close
 parallel filaments of the warp and the weft, are preferably arranged at a
 distance less than 1 cm.
 Each lateral plastic laminate of the sandwich, which is not shown in FIG.
 1, is not made of a single piece. Actually, each laminate is applied on
 the perfectly pliable cloth (FIG. 1), in pieces of about 1 meter of height
 and variable length.
 The cloth will be arranged onto a plane support, and since the cloth has a
 convex shape, the respective piece of plastic laminate will have a length
 varying according to where the piece of plastic laminate must be applied,
 on condition that it can follow the local convexity of the cloth. It is
 obvious that pieces having the greatest possible length and ensuring at
 the same time perfect adherence of the individual piece of plastic
 laminate to the cloth will be used in the production process.
 Industrial Applicability
 The advantage of the present invetion is that once the cloth has been
 prepared, the latter forms a valid three-dimensional support, which is
 perfeclty pliable and made of close filaments, whereon it is possible to
 apply, one at a time, on a plane, the two external plastic laminates.
 The process of the present invention is not limited to the specific
 configuration of the cloth which is shown in FIG. 1.
 It is obvious that the plastic laminates are those normally used in this
 field, e.g. with the required elasticity, reduced weight, high mechanical
 resistance, resistance to heat, UV rays and optimum imperviousness. In
 this case and in the case of the cloth, many different materials known to
 those skilled in the art may be employed, so that it is worthless to
 mention them explicitly.
 It is also evident that in the above description nothing has been said
 about other already known operations, like e.g. the application of
 suitable reinforcements at the sail's corners A,B,C, or the like.