Method and Apparatus for Molding Plastic Products With Flash Removed

This invention relates to the field of plastics molding, and more particularly to a method and apparatus for molding plastic in which flash may be removed from the plastic product during the molding process.

Conventional plastic molding systems often produce a residue, called flash, which is extruded between the mold sections during the molding process and then must be removed from the plastic product. The removal of flash is typically done manually, and is a very labor intensive task, which of course results in higher production costs for the product. Also, many cases of Carpal Tunnel Syndrome have developed from the repetitive trimming of molded plastic parts, resulting in lost work and expensive Workmans' Compensation claims.

The present invention teaches an improved method and apparatus for molding plastic products which results in the removal of flash from the products during the molding process itself. The invention teaches that the flash may be secured to a mold section during the molding process by means of retainers situated within the mold and into which the plastic flash is forced while in a fluid state. The flash is then retained upon that mold section when the mold is opened and is detached from the product when the product is retained within the opposite mold section or as the product is ejected from the mold. The flash is then removed from the mold by means of ejector pins which are inserted to within the retainers, forcing the flash from the retainers and thereby freeing the flash from the mold.

These and other attributes of the invention will become more clear upon a thorough study of the following description of the best mode for carrying out the invention, particularly when reviewed in conjunction with the drawings, wherein:

FIG. 1 through FIG. 6 depict side elevation views of a representative blow molding operation utilizing the teachings of the present invention;

FIG. 7 through FIG. 9 depict partial cross-sectional views of a representative blow molding operation utilizing the teachings of the present invention;

FIG. 10 shows another embodiment of the present invention shown with the parison dropping down between the two mold halves;

FIG. 11 is a view taken along line 11--11 of FIG. 10;

FIG. 12 is a cross sectional view like FIG. 10, but showing the mold halves closed to blow mold a product;

FIG. 13 is an enlarged cross sectional view of the lower part of FIG. 12;

FIG. 14 is a cross sectional view like FIG. 10, but showing how the flash is removed around the exterior periphery of the plastic product formed;

FIG. 15 is a cross sectional view like FIG. 10, but showing the mold starting to open again after the flash has been separated from the molded product;

FIG. 16 is a view like FIG. 10, but showing the mold opened and the flash being ejected;

FIG. 17 is a view like FIG. 16 after the flash has been ejected and showing the plastic product being ejected from the mold; and

FIG. 18 is a view like FIG. 17 showing the part ejected and in readiness to receive another parison so the process can be repeated.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, FIG. 1 through FIG. 6 depict a representative blow molding operation with an extruder 12 positioned above a mold 14. The mold 14 is initially in the open position (FIG. 1), at which time a parison 7 is extruded to a position between the mold sections 14a, 14b (FIG. 2). The mold sections 14a, 14b then close upon the parison and the mold is blown to expand the parison upon the internal surface of the mold (FIG. 3). After the plastic has hardened sufficiently, the mold is opened (FIG. 4) and the product 5 is ejected from the mold section 14b within which it has been retained (FIG. 5), at the same time separating the product 5 from the flash 9 which is retained upon that mold section 14b. Finally, the flash 9 is ejected from the mold section 14b and the mold is ready to repeat the molding operation. FIG. 7 is an enlarged depiction of the mold 14 after it has closed upon the parison 7 (as depicted in FIG. 3), but more clearly shows the present invention. A plurality of flash pins 20 are mounted in one of the mold sections 14a such that they protrude from the mold face a sufficient distance so as to engage a like number of flash retainers 30 mounted in the opposite mold section 14b. The flash pins 20 are fitted to within apertures 22 formed into the mold section 14a, and are held in place with set screws 24 threaded into the outer portion of the aperture 22. The flash pins 20 have an enlarged head so that they will be firmly held in place within the mold section 14a when the set screws 24 are screwed into place. The number of flash pins is of course a function of the size of the mold and of the type of plastic being molded. The pins would typically be spaced at approximately two inch intervals around the edge of the mold.

The flash retainers 30 are cylindrical (but can also be other shapes), housings which are secured into the face of a mold section 14b so as to receive a flash pin 20 from the opposing mold section 14a when the mold is closed. The flash retainers 30 have a hollow core with a curved inlet 32, an internal chamber 34, and a cylindrical aperture 36. The diameter of the throat of inlet 32 must be somewhat larger than the diameter of flash pin 20, preferably approximately 1.2 times the flash pin diameter. The diameter of the chamber 34 at its largest point must be somewhat larger than the inlet throat diameter, preferably 1.5 times the diameter of the flash pin 20. This configuration allows flash to be forced by the flash pin 20 to within the flash retainer 30 where, due to the larger diameter of the chamber 34, the flash is held after the flash pin 20 is withdrawn as the mold is opened. The mold section 14b has threaded apertures 40 for receiving the flash retainers 30, and unthreaded apertures 42, coaxial with the threaded apertures 40, through which slide flash ejector rods 50. The flash ejector rods 50 are slidably mounted within the unthreaded apertures 42 and serve to force the flash from within the chamber 34 and inlet 32, thereby releasing the flash from the face of the mold section 14b (FIG. 6 and 9).

The mold section 14b upon which the flash is retained is also fitted with an aperture 60 leading into the molding compartment of the mold into which is slidably mounted a product ejection rod 62. After the mold is opened, the product ejection rod 62 is extended through aperture 60 so as to eject the plastic product from the mold section 14b (FIGS. 5 and 8).

The present invention is therefore intended to function as follows. A parison 7 is extruded between a pair of mold sections 14a, 14b, which then close upon the parison. As the mold closes, a series of flash pins 20 drive the plastic residue, deposited on the edges of the mold, to within the flash retainers After the plastic has hardened sufficiently, the mold is opened, thereby withdrawing the flash pins 20 from the flash retainers 30. As the mold is opened, or shortly thereafter, the product 5 is ejected from the mold section 14b by the action of product ejection rod 62. This action also tears the product 5 from the flash 9. Finally, the flash itself is removed from mold section 14b by the action of flash ejector rods as they slide within the flash retainers 30 and force the flash from the mold.

Referring to FIG. 10, a mold set up 100 has a first mold section 14a and a second mold section 14b. A cavity 115a is disposed in one mold section 14a and second mold cavity 115b is disposed in the cavity in the mold section 14b. A retainer recess 116a and 116b are disposed in mold half sections 14a and respectively. A first member 117a is disposed in the mold cavity 116a and a second member 117b is disposed in the other cavity 116b.

Pins 113a are connected by a member 121 so that when member 121 is moved to the right as shown in FIG. 10, the member 117 will be moved to the right and vice versa. Similarly, when member 113b and its associated connecting structure 122 is moved to the left, member 117b moves to the left, and vice versa.

Ejector pins 162 are moved by actuators 163 and ejector pins 150 are moved by ejector actuator 153. Internal chambers 134 in the flashing plate 117 are for the same purpose as recesses 34 in the aforementioned embodiment. Ejector pins 151 are shown in FIG. 11, along with a pinch-off section 118b, a crash pad 165 and a leader pin 166.

In operation, the nozzle 112 is operated to allow a plastic parison 107 to drop down between the mold sections 114a and 114b. The mold sections are then closed to the position shown in FIG. 12 whereupon air is blown inside of the plastic part member 105 as is conventional in this art. The lower part of the parison 107 is shown as flash portion 109 in FIG. 12.

Referring to FIG. 13, it is noted that a member 120 pushes part of the flash 132 into the enlarged opening 134 in member 117b. Consequently, the flash portion will be attached to member 117b in the manner that the flash is retained in chamber 34 in the aforementioned embodiment. After the FIG. 12 and 13 position of the mold parts, the flash is then removed by actuating or moving the member 121 from the position shown in FIG. 12 to the position shown in FIG. 14, which moves members 117a and 17b to the right as shown in FIG. 14. This tears the flash off of the outside of the part 105 completely on the outer periphery of the part 105.

The next step of the process is shown in FIG. 15 wherein the mold halves begin to open and although the flash is shown back in the position where it was torn off of the part 105, it is completely severed therefrom in the FIG. 15 position of the mold parts.

The next step of the process is shown in FIG. 16 wherein the mold is completely open and the pins 162 are actuated by actuators 163 to move from right to left to push the flash 109 out of the retainer openings 134 so that the flash can then drop down on a conveyor belt or the like.

The final step of the process is shown in FIG. 17 wherein pins 150 are moved from right to left so that pin 150 pushes the plastic product or part 105 out of the mold cavity 15b so that it can drop down onto a conveyor belt or the like to be removed.

FIG. 18 shows the mold in its open position in readiness to receive another parison 107 just like the process began in FIG. 10.

Advantages of the embodiment of FIGS. 10-18 are that it can be installed in most new and existing molds; the flash and part are ejected at different times, allowing both to fall to a conveyor at different times; it can improve molding efficiencies by reducing the amount of labor required to mold parts; and it can allow molding machines to run automatically.

It is to be understood that while the foregoing has described the use of the present invention in a blow molding operation, its teaching are equally applicable to thermoforming, both twin sheet and pressure form, and it is intended that this specification cover these devices and methods as well.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, many different configurations of the flash securement devices could be constructed. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.