Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Producing multilayer work or article
Reexamination Certificate
2002-11-14
2004-11-09
McDowell, Suzanne E. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Producing multilayer work or article
C264S516000, C264S152000, C264S161000
Reexamination Certificate
active
06814921
ABSTRACT:
The present invention relates to a process for manufacturing a plastic fuel tank.
Plastic fuel tanks on board vehicles of various kinds must generally meet sealing and permeability standards in relation to the type of usage for which they are designed and the environmental requirements that they must respect. At the present time, both in Europe and in the world, there is a substantial tightening of the requirements relating to the limitation of pollutant emissions into the atmosphere and the environment in general. As a consequence, the design of fuel tanks is moving rapidly toward techniques capable of providing a better guarantee of sealing and of safety under various operating conditions. Moreover, manufacturers are also striving to reduce as far as possible the losses caused by various pipes and accessories connected to the tanks. One means sometimes used has been to incorporate certain accessories and pipes inside the tanks, thus eliminating their interface with the external environment.
Patent application GB-1 136 613 discloses a process for molding articles from a sheet of thermoplastic resin, comprising the extrusion of the sheet followed by its molding in a two-part mold, the peripheral outlines of which can press the peripheral parts of the sheet, producing a join capable of maintaining a pressure difference on either side of the sheet so as to form the central part.
This known process is, however, applied to the manufacture of open articles having around their periphery a flat edge, which is optionally recessed by a groove. The articles, of quite small size, are suitable as containers. They are manufactured with blowing pressures of at most 10 kg/cm2. In addition, no device or accessory is introduced before molding or found in the articles obtained.
Patent U.S. Pat. No. 5,129,544 is known, which discloses a plastic fuel tank comprising two hollow shells made of a multilayer material, said shells being joined together in an impervious manner over their entire perimeter by fastening together their flat peripheral rim. In this tank, the shells may be formed by stamping or by vacuum-forming.
German patent application DE-OS-1 801 966 discloses the manufacture of hollow bodies made of thermoplastic from two shells which are formed by molding and joined together by mirror welding. The molding of each of the shells is performed by compression-molding a portion of a thermoplastic sheet and by blow-molding the remaining portion of the sheet in the region not compression molded.
The aim of the invention is to provide a process for producing a plastic fuel tank with excellent control of the reproducibility and accuracy of the dimensions, which may have a large volume of up to about 100 to 150 liters and which is well suited to the incorporation of accessories before the molding phase.
For this purpose, the subject of the invention is a process for manufacturing a plastic fuel tank from two shells formed by molding, which are joined together, at least one shell being produced by compression-molding a portion of a plastic sheet between a mold and a punch and by the remaining portion of the sheet being blow-molded in the region not compression-molded.
The term “fuel tank” is understood to denote a sealed tank capable of storing fuel under diverse and varied operating and environmental conditions. An example of this tank is that with which automobiles are equipped.
The fuel tank produced in the process according to the invention is made of plastic, that is to say of material comprising at least one polymer in the form of a synthetic resin.
All types of plastic may be suitable. Plastics which are very suitable belong to the thermoplastics category.
The term “thermoplastic” denotes any thermoplastic polymer, including thermoplastic elastomers, and blends thereof. The term “polymer” denotes both homopolymers and copolymers (especially binary or ternary copolymers). Examples of such copolymers are, in a non-limiting manner: random copolymers, alternating copolymers, block copolymers and graft copolymers.
Any type of thermoplastic polymer or copolymer whose melting point is below the decomposition temperature is suitable. Synthetic thermoplastics which have a melting range spread over at least 10 degrees Celsius are particularly suitable. Examples of such materials include those which exhibit polydispersity in their molecular weight.
In particular, polyolefins, thermoplastic polyesters, polyketones, polyamides and copolymers thereof may be used. A blend of polymers or copolymers may also be used, as may a blend of polymeric materials with inorganic, organic and/or natural fillers such as, for example, but non-limitingly, carbon, salts and other inorganic derivatives, natural or polymeric fibers. It is also possible to use multilayer structures consisting of stacked layers bonded together, comprising at least one of the polymers or copolymers described above.
A polymer often employed is polyethylene. Excellent results have been obtained with high-density polyethylene (HDPE).
According to the invention, the tank is manufactured from two shells. The term “shell” denotes a non-closed partial envelope in the form of an open hollow body, with a surface shape having at least one concave portion.
The two shells are joined together in order to obtain the tank. Any type of impervious joint is suitable. However, it is preferred to join the shells together by welding.
Each shell used has been formed by molding a plastic sheet. A sheet intended for molding may consist of a single plastic composition. It may also be in the form of a structure resulting from stacking several layers of different plastic compositions. A layer often used to advantage in such a structure is a layer comprising at least one material acting as a barrier to liquids and gases, in particular to hydrocarbons.
According to the invention, the molding of at least one shell comprises the compression-molding of a portion of the sheet and the blow-molding of the portion not compression-molded. These two operations are performed in the same mold.
The compression-molding is carried out by bringing together and clamping, on each side of the sheet, at least one region of a mold portion and of a punch which is fastened to the other mold portion.
The blow-molding is carried out by introducing, on one side of the sheet, into the region not compression-molded, a pressurized fluid. This fluid may be a gas, a liquid or a dispersion of at least one liquid in a gas. When the fluid comprises a liquid, it advantageously ensures better heat transfer between the sheet and the fluid. Preferably, the pressurized fluid is introduced on that side of the sheet where the punch is located. As pressurized fluid, compressed air has given good results. It is also possible to use a pressurized purging fluid containing a reactive gas. Such a reactive gas may be fluorine. It is also possible to use an inert gas, such as nitrogen. A mixture of various gases may also be used, in particular a mixture containing at least two of the abovementioned gases. Among liquids, it may be advantageous to use water. A fluid that has led particularly to excellent results is a dispersion (a spray) of water in compressed air.
In the process according to the invention, the molding is well suited to the treatment of a sheet placed vertically. One example is that of a sheet produced by extrusion, in an extruder placed vertically, the extrusion head which includes the die being located at the lowest point and the sheet produced flowing rectilinearly owing to the effect of its own weight.
According to the invention, the sheet is obtained in the same manufacturing line as the shell which will be produced from this sheet, by cutting and opening an extruded parison of closed cross section. One of the shells may have been independently manufactured beforehand in a manufacturing unit other than for the tank. For example, the shell may have been manufactured in a molding installation different from that used to manufacture the tank.
However, at least one of the shells used is preferably mold
Dupont Serge
Gerard Yannick
Leonard Stéphane
Van Schaftingen Jules-Joseph
Hunt, Jr. Ross F.
McDowell Suzanne E.
Solvay ( Societe Anonyme)
Stites & Harbison PLLC
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