Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Utility Patent
1998-12-29
2001-01-02
Davis, Robert (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Including application of internal fluid pressure to hollow...
C264S209300, C425S392000, C425S532000, C425S534000
Utility Patent
active
06168750
ABSTRACT:
The present invention relates to a system and a method for preforming an extruded parison by means of which it is possible to manufacture a moulded article of complex three-dimensional geometry.
Several moulding methods by means of which it is possible to manufacture moulded articles from polymer resin and having a complex three-dimensional geometry are known. Such articles may for example have a succession of segments each oriented in a different direction.
Such articles have many applications. Examples of these that may be mentioned, relating to the automotive industry in particular, are filling sleeves for fuel tanks and hoses for ventilation or for conveying various kinds of fluids, the positioning and routing of which can be dictated by the surrounding geometry.
The difficulties encountered during manufacture of such articles arise from their complex spatial structures. In particular, the parison must be introduced safely into the mould, taking particular care to avoid loss of material and excessive local stretching.
One solution is to deposit the parison directly in one of the mould sections whose opening is face uppermost. This method requires that either the said mould section or the extrusion head be made to follow a complex three-dimensional movement reproducing the shape of the article to be moulded. The weight of the equipment required is usually very great, so this method has few advantages, either in terms of engineering or economics.
In order to solve this problem, several methods involve preforming the parison before introducing it into the mould, i.e. giving it a shape adapted to the shape of the mould impression. This preforming process makes it unnecessary to employ a mobile mould or extrusion head. Only the relatively light equipment that carries out the preforming process is mobile.
Patent application WO-A1-9628295 discloses such a method. The parison, which is intended to produce a tubular article, is deposited on a horizontal planar conveyor belt travelling at approximately the extrusion speed. After closure at one end, preblowing, closure at the other end and stoppage of the belt, the parison is then deformed in the horizontal plane only, using a tool with two parts that work together to form it laterally. The parison thus acquires a shape corresponding to the projection in the horizontal plane of the shape of the article to be produced. After this step of preforming in two directions, the conveyor belt is moved away and the parison is brought by the preforming tool vertically over the lower section of the mould. The retraction of the two parts of the preforming tool causes the parison to drop into the mould, which is then closed.
The above method has the advantage of not requiring precise synchronization of the speed of extrusion with the movement of the preforming equipment and can be carried out equally satisfactorily with a vertical extrusion head or with a horizontal head. However, it still has certain disadvantages. One of the main problems is that the preforming is effected in only the two directions of the plane of the conveyor belt. As the mould impression usually includes segments whose orientation is outside this plane, these segments may, when the preform is placed in the mould, bring about large, non-uniform deformations of the material prior to moulding, and therefore, for example, bring about a lack of uniformity of wall thickness. Another problem is that the preform, which is necessarily contained in a plane prior to being placed in the mould, must be released from a certain height, a height which is greater and less uniform in proportion as the article to be produced possesses a large component outside this plane. This large dropping height inevitably results in a less precise positioning the preform in the mould, and therefore results in articles with less reproducible characteristics.
The subject of the present invention is therefore a system that makes preforming simple to carry out and that does not have the abovementioned disadvantages.
Consequently, the invention relates to a system for preforming an extruded plastics parison, which is characterized in that it comprises a nonplanar conveyor belt.
Within the context of the present invention, the term “preforming” means any operation or series of operations intended to modify the geometry of the parison, between the moment in which it is extruded and the moment in which it is introduced into a moulding tool.
Any plastics material can be used to make the parison used within the scope of the invention. It makes no difference whether it is a thermosetting resin or a thermoplastic resin. The parison preferably consists essentially of thermoplastic resin. The said thermoplastic resin may include one or more polymers. These polymers may include homopolymers, copolymers or mixtures of these. It is preferable for the polymer to be a polyolefin. It is more preferable for the polyolefin to be a polyethylene. Excellent results have been obtained with high-density polyethylene.
The plastics material may also contain any ordinary appropriate additive, such as fillers, reinforcing materials, stabilizers, lubricants or combinations of these additives.
It makes no difference whether the parison is single-layer or multilayer.
It may also be solid or possess a hollow core.
In the case of a multilayer parison with a hollow core, one of the layers may be composed of, for example, a resin that has a barrier action selected for the application envisaged.
The parison may be extruded by any technique known to those skilled in the art. Extrusion may e.g. be continuous, discontinuous, with use of an accumulator, or sequential. The extrusion head may be horizontal or vertical. Extrusion can also be carried out using constant parameters or parameters that are programmable in the course of time.
If the extrusion parameters are to be programmable, it is advantageous to be able to vary the section of the parison and/or, if appropriate, the thicknesses of the different layers.
Very good results have been obtained with continuous extrusion, with an approximately horizontal extrusion head, and, preferably, programming in the course of time of the parison wall thickness.
The conveyor belt used may adopt any configuration known to those skilled in the art, provided that at least a part of its surface intended to take the parison is not planar; i.e. the longitudinal profile of the conveyor belt, between its furthest upstream support and its furthest downstream support, is not approximately rectilinear.
In the present context the description “approximately rectilinear” is applied to a profile in which no point deviates from the straight line segment that tangentially joins the supports at the upstream and downstream extremities by more than 2% of the length of this segment, and preferably by not more than 1% (hence ignoring any curvature of the conveyor belt due to these supports).
The invention gives very good results when this deviation is more than 10% and in particular more than 20%. The profile may be of any possible geometry, but will preferably approach the corresponding profile of the mould impression. Such a profile may include, for example, two or more planes and/or one or more curves. This nonplanar arrangement makes it possible to minimize, when the parison is introduced into the mould, both the stretching imposed on the said parison and the height through which it has to drop.
Any technique known to those skilled in the art may be employed to create the desired longitudinal profile of the conveyor belt. The simplest technique is to run the conveyor belt, between its two ends, over one or more continuous or discontinuous intermediate transverse supports (rotary cylinders for example) lying outside the plane defined by the endmost supports. Other techniques use, e.g., series of rollers at the sides.
The material of the conveyor belt may be of any kind compatible with the material and temperature of the parison and will preferably be chosen, in a known manner, so as to limit the risk of adhesion of the pariso
Dupont Serge
Van Schaftingen Jules-Joseph
Davis Robert
Schneller Martin V.
Solvay S.A. (Societe Anonyme)
Venable
LandOfFree
System and method for preforming an extruded parison does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for preforming an extruded parison, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for preforming an extruded parison will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2508327