COMPRESSION MOLDING HOLLOW STRUCTURE

Abstract

A process for molding a hollow structure comprising the steps of: a. Forming a mandrel in a shape of a proposed cavity from a water-soluble substance capable of withstanding temperatures and pressures from a predetermined compression molding process; b. Positioning the mandrel in a suitable mold for forming an article which includes the mandrel within the article; and, c. Removing the mandrel by loosening and dissolving the mandrel with a water solution, thereby creating a cavity in the article.

Claims

1. A process for molding a hollow structure comprising the steps of: a. Forming a mandrel in a shape of a proposed cavity from a water-soluble substance capable of withstanding temperatures and pressures from a predetermined compression molding process; b. Positioning the mandrel in a suitable mold for forming an article which includes the mandrel within the article; and, c. Removing the mandrel by loosening and dissolving the mandrel with a water solution, thereby creating a cavity in the article.

2. The process of claim 1 wherein the mandrel is formed from a mixture of salt and sugar and shaped to the desired shape of the cavity.

3. The process of claim 2 wherein the mandrel is formed from a mixture of from about 3% to about 25% by weight sugar selected from the group of saccharose maltose, trehalose, starch and mixtures there of mixed with from about 97% to about 75% by weight of a salt comprising a Group 1A metal and a Group 7A halogen element.

4. The process of claim 2 wherein the mandrel is comprised of variable sections, a combination of a re-usable mandrel and water-soluble mandrel.

5. The process of claim 1 wherein sheet molding composition is used for the compression moldable sheets.

6. The process of claim 1 wherein a thermoplastic sheet is used for the compression moldable sheets.

7. The process of claim 1 wherein the molding process is selected from the group of RTM, filament winding, pultrusion, wet press molding and thermoplastic injection molding.

8. The process of claim 1 wherein the molding process is a compression molding process and the mandrel is positioned between two thermoformable or thermosetting sheets of material for forming a final cavity in the article.

9. The process of claim 2 wherein during molding of the part and mandrel withstands molding pressures of up to about 1300 psi and temperatures up to about 150° C.

10. The process of claim 1 wherein the mandrel core is molded to form the structure and is processed in a compression mold at a temperature up to 180° C. and 1400 psi pressure for hardening of the mandrel.

11. The process of claim 1 wherein hot water and/or pressurized water and/or an ultrasonic bath is used for removing of the mandrel core.

12. The process of claim 2 wherein the mandrel core is painted to provide an improved surface porosity for providing a smooth inner part surface after molding.

13. The process of claim 12 wherein the paint remains within the part after the manufacturing process.

14. The process of claim 2 wherein the mandrel core is manufactured in thin sections of greater than or equal to ¼ inch.

15. The process of claim 2 wherein the mandrel core is manufactured with variable cross-section of any predetermined shape.

16. The process of claim 2 wherein said predetermined shape is selected from the group consisting of rectangle, omega, trapezoidal and combinations thereof.

17. The process of claim 2 wherein the mandrel core is manufactured with predetermined variable thickness cross-sections to enable variable cavity thickness.

18. The process of claim 2 wherein the mandrel core is manufactured with local core thickness reductions to enable locally thickened parts in the final part to provide a thickened portion which is used for mechanical fastening purposes.

19. The process of claim 1 wherein the salt is selected from the group consisting of sodium chloride, potassium chloride, sodium bromide, potassium bromide and mixtures thereof.

20. A process for compression molding of a hollow structure comprising the steps of: a. Forming a mandrel in a shape for forming a predetermined cavity a water-soluble substance comprising a mixture of sugar selected from the group of saccharose maltose, trehalose, starch and mixtures thereof and a group 1A metal and group 7A halogen containing salt material which is capable of withstanding temperatures of up to about 150° C. and pressures of up to about 3000 PSI compression molding process of from about; b. Positioning the mandrel between layers of thermoformable or thermosetable material in a suitable mold for forming an article which includes the mandrel within the article and compression molding the part including the mandrel; and, c. Removing the mandrel by loosening and dissolving the mandrel with a water solution, thereby creating a cavity in the article.

21. An article formed by the process of claim 20.

22. The process of claim 20 wherein the salt is selected from the group consisting of sodium chloride, potassium chloride, sodium bromide, potassium bromide and mixtures thereof

23. The process of claim 22 wherein the salt is Sodium Chloride.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0017] FIG. 1A-1H are illustrative views of the process of the present invention;

[0018] FIG. 2 is a perspective view showing the mandrel core molded into shape in a mold;

[0019] FIG. 3 is a perspective view of the core of FIG. 2 out of the mold;

[0020] FIG. 4 is a perspective view of the core being placed on a first sheet of sheet molding composition in preparation for compression molding;

[0021] FIG. 5 is a side view of the mandrel core and SMC assembly ready for compression molding;

[0022] FIG. 6 is a perspective view of the mandrel core and SMC assembly being placed in a compression mold;

[0023] FIG. 7 is a view of the completed molded part with mandrel core before removing the core with water; and,

[0024] FIG. 8 is a sectional view of the part of FIG. 7 which is cut for inspection.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0026] Referring now to the drawings and specifically to FIG. 1, the present invention includes a process for molding a hollow structure 10 using a removable mandrel core 12. In the process of the present invention, a mandrel is formed in a shape of a predesigned cavity 14 from a water-soluble substance 16 (in the present embodiment a salt and sugar mix) capable of withstanding temperatures and pressures from a predetermined molding process 18. The mandrel 12 is then positioned in a suitable mold 18 for forming an article 20 which includes the mandrel 12 within the article 20. Thereafter, the cavity 14 is formed by removing the mandrel by loosening and dissolving the mandrel with a water solution 22, which creates a cavity 14 in the article 20.

[0027] As examples and as set forth above, the mandrel/core 12 is formed from a salt and sugar solution in the form of the final cavity desired in the part. In a preferred embodiment, the mandrel 12 is formed from a solution of salt and sugar. In a preferred embodiment mixture of from about 3% to about 25% by weight sugar is mixed with from about 97% to about 75% by weight salt (containing a periodic table Group 1A metal, such as sodium combined with a Group 7A halogen such as chloride, with preferred salts being sodium chloride, potassium chloride, sodium bromide, potassium bromide and mixtures thereof). The sugars used can be saccharose, maltose, trehalose or starch or a mixture of them. As shown in the drawings the mandrel is formed in the shape of the cavity 14 by way of a mold 24 which has a forming cavity 26 in a lower platen 28 and an upper platen 30 with a mold insert 32. Thereafter a compression mold is used to form a hardened mandrel core 12 by heating the mold containing the salt and sugar mixture at a temperature between 120 and 180° C. and a pressure between generally about 200 to about 5000 psi, typically from about 600 to about 3400 psi and preferably from about 1200 to about 2400 psi until cured. Typical curing times are between 1 and 30 minutes depending on the mixture pressures and temperatures used. Suitable cavities are found to be formed in molded parts.

[0028] It will be readily appreciated by those skilled in the art that the process for molding a part of the present invention can be used and is readily adaptable with RTM, filament winding, pultrusion, wet press molding and thermoplastic injection and compression molding. For purposes of illustration, the process disclosed herein as an example is sheet molding compound compression molding. After a suitable mandrel/core is formed from the salt and sugar mixture, it is placed between at least a lower SMC sheet 32 and an upper sheet 34. As shown in FIG. 4, several layers of SC are typically used to form a proper sandwiched layered construction for forming of the part via compression molding.

[0029] A compression molding machine 18 with upper 36 and lower 38 platens for forming the final part under heat and compression. It has been found that the part and mandrel assembly of the present invention can withstand heat of up to about 150° C. and up to a pressure of 1300 psi (pounds per square inch) during this molding process. It is to be appreciated that different resin systems used for molding of parts may withstand higher pressures. The Mandrel itself can withstand higher pressure, therefore, typically the material used for compression molding limits the amount of pressure used. Thus, parts with a different resin system may allow higher compression and temperature. The sandwiched structure is heated under pressure for forming a one-piece part shown in FIGS. 7 and 8.

[0030] Thereafter, the part is cooled and hot water and/or pressurized water and/or an ultrasonic bath is used for removal of the mandrel/core 12. And the part is completed by machining, drilling or shaping and the like.

[0031] In some applications if the part geometry allows it a reusable core portion (such as made of a Teflon (PTFE) material) mandrel may be used in combination with the mandrel described above. In such situations the Teflon portion of the mandrel must be situated at a portion of the mold which allows removability of the Teflon core prior to removal by water or the like of the water soluble portion of the core. In such a case the Teflon core is removed and reused with a new water soluble core if desired in a particular application.

[0032] The water-soluble core can be easily removed after molding and provides the possibilities of complex geometries for cavity formation. The process of the present invention provides fast cycle times which facilitates use in large scale manufacturing operations. The mandrel core is low cost and environmentally friendly and provides an incompressible core that does not require external plungers or other fixtures to exert pressure to maintain its shape during molding.

Example

[0033] As examples and as set forth above, the mandrel/core 12 is formed from a salt and sugar solution in the form of the final cavity desired in the part. The mandrel 12 is formed from a solution of salt and sugar in mixtures of embodiment mixture of from about 3% to about 25% by weight sugar is mixed with from about 97% to about 75% by weight of salts (containing a periodic table Group 1A metal, such as sodium combined with a Group 7A halogen such as chloride, with preferred salts being sodium chloride, potassium chloride, sodium bromide, potassium bromide and mixtures thereof). The sugars used can be saccharose, maltose, trehalose or starch or a mixture of them. As shown in the drawings the mandrel is formed in the shape of the cavity 14 by way of a mold 24 which has a forming cavity 26 in a lower platen 28 and an upper platen 30 with a mold insert 32. Thereafter a compression mold is used to form a hardened mandrel 12 by heating the mold containing the salt and sugar mixture at a temperature between 120 and 180° C. and a pressure between generally about 200 to about 5000 psi, typically from about 600 to about 3400 psi and preferably from about 1200 to about 2400 psi until cured. Typical curing times are between 1 and 30 minutes depending on the mixture pressures and temperatures used. Suitable cavities are found to be formed in molded parts at temperatures up to 150 degrees centigrade and 1300 PSI.

[0034] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the essence of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.