INSULATED SPRUE BUSHING IN PLASTIC MOLDING APPARATUS

Abstract: The insulation (3) for the sprue bushing comprises a thermoset molding to insulate or break the heat flow between the sprue bushing shoulder (5) and neck section of the stem (1) of the sprue bushing.

Description: INSULATED SPRUE BUSHING IN PLASTIC MOLDING APPARATUS Apparatus for molding of plastics, particularly injection molding, comprises dies mounted on die blocks which blocks in turn are mounted on the platens of a press. Molten or plasticized material is forced by pressure out of a nozzle through a sprue bushing which sprue bushing serves to transmit or conduct the plasticized material from the nozzle to the runners which feed the plasticized material to the various cavities. There is, however, a problem in molding thermoplastics as outlined above, in that due to the temperature difference between the nozzle and the sprue bushing, it is necessary to heat the material at the nozzle to an excessively high temperature in order to be sure the plasticized material or compound will feed into the die. The high temperature required as indicated above can cause break down of the plasticized material, while without adequate heating, cold spots develop on passage from the nozzle through the sprue bushing into the runners, then to the cavities. As for injection molding of thermoset compounds, it is important that the sprue bushing be insulated from the heated die to prevent premature curing or "setting" of the plasticized material or compound prior to filling of the molding cavities. In view of above then, an insulated sprue bushing is useful in thermoplastic and thermoset molding. Several U.S. patents have been issued pertaining to various sprue bushings, as follows. Patent 2,227,966 to E sley for "Injection Type Mold", which states: An object of the invention is to substantially retard cooling of the thermoplastic composition in the gate and/or runners, until after the article in the mold cavity is hardened, which is done with a dead air chamber around the gate bushing. Patent #2,828,509 to S ucker, et al . for "Plastic Molding Machines": This covers a plastic molding machine, with the nozzle extending to the molding cavity. The nozzle is merely guided to the seat of the bushing for filling of the die. Patent #3,537,139 to Seg ' uller for "Injection Nozzle for Hot Channel - Injection Molding Device". This patent covers a heat conducting core located internally of each delivery channel. This is to heat the material going or flowing from the nozzle to the molding dies or cavities. Patent #3,698,849 to Czerski for "Injection Molding Assembly". This patent covers a molding assembly which is suitable for use in the manufactu of cellular plastics particles, wherein the injection nozzle is insulated from the sprue bush by a thermally insulating element between the outlet end of the nozzle and the sprue bush. Patent #3,945,535 to Leiste et al . for "Injection Molding Apparatus". This patent covers apparatus for injecting plasticized material containing a foaming agent into a mold from an extruder, and a heating element to maintain the nozzle needle at high temperature. Patent #4,069,003 to Cecchi for "Injection Molding Apparatus", which describes a sprue bushing provided with a plurality of grooves in its bore. Patent #4,260,348 to Graham, for "Sprue Bushing For Injection Molding Machine". This patent describes a sprue bushing, the temperature of which is controlled by water flowing through channels in the bushing. Patent #4,273,525 to Reitan for "Injection Mold Bushing", which describes a sprue bushing having heating and cooling means. Patent #4,279,588 to Gellert for "Hot Tip Seal". This describes a heating coil in the nozzle section. Patent #4,345,892 to Schulte et al . for "Injection Molding Die With Heavy-Duty Sprue Bush". This patent covers a heated sprue bush along with air gaps, and injection molding gates are perpendicular to the longitudinal axis of the sprue bush. Rees Patent #4,173,448 -- for Actuating Mechanism For Gate Valve of Injection Nozzle. This patent covers a "nozzle body" which is entirely different from a sprue bushing described in this Shaw invention. Rees Patent 4,268,241 for Heated Injection Nozzle. This patent is for a heated nozzle and a sheath of resinous material around the nozzle — nozz O PI is highly heat conductive. This patent is not concerned with a "sprue «, bushing" as described in this Shaw invention. • * \ It is an object of this invention to describe a sprue bushing insulated from the die so that the plasticized material maintains its 5 temperature for more efficient molding operation. Another object of this invention is to disclose means to insulate the sprue bushing from the die in molding of plastic materials. Another object of this invention is to reduce the temperature difference which exists between the nozzle and sprue bushing in injection 10 molding. This invention is to disclose means for insulating the sprue bushing from the die, so that the plasticized or melted material will maintain more closely its temperature coming out of the nozzle and through the sprue bushing. Another object of this invention is to prevent excessive temperature 15 variance of the plasticized compound or material on being fed into and through the sprue bushing. Another object of this invention is to disclose in a plastic molding apparatus comprising a die mounted in a press, the improvement consisting of an insulated sprue bushing mounted in said die, said sprue bushing 20 insulated from the die block at the shoulder and stem section of said sprue bushing. Another object of this invention is to prevent nozzle "freeze off" by means of an insulated sprue bushing. Another object of this invention is to disclose a sprue bushing with 25 an insulating collar molded thereon. Another object of this invention is to disclose an insulating collar for a sprue bushing mounting, said insulating collar to be removable from said sprue bushing. Another object of this invention is to reduce the temperature 30 difference between the nozzle and sprue bushing in plastic molding, by ^ means of an insulated sprue bushing, between said sprue bushing and the die. O PI Brief Description of the Drawings Fi g. 1 - Si de View of sprue bushing with insul ating section , wherein : 1 . - Stem of sprue bushing 2. - Passage way through sprue bushing 3. - Insulating section 4. - Seat for press nozzle 5. - Head of sprue bushing 6. - Die section Fig. 2 - End View of sprue bushing and insulating section wherein: 1. - Stem of sprue bushing 2. - Passage way through sprue bushing 3. - Insulating section 4. - Seat for press nozzle 5. - Head of sprue bushing Fig. 3 - Side View of insulating section ring wherein: 7. - Insulating section 8. - Shoulder section of insulating section Fig. 4 - Side View of sprue bushing mounted in die with insulating section in position at the shoulder of said sprue bushing wherein: 1. - Stem of sprue bushing 2. - Passage way through sprue bushing 3. - Insulating ring section 4. - Seat for press nozzle 5. - Head of sprue bushing 6. - Die section 7. - Sprue bushing insulator 8. - Shoulder section of insulator Fig. 1 shows the plastic insulating material molded onto the sprue bushing which had been machined "out" so that the plastic insulating material is molded onto the sprue bushing in the machined out section. Fig. 4 shows the plastic insulating material as a separate ring and shoulder section to be inserted into the machined out die block. The sprue bushing is then inserted in the die block holding the insulating section between said die block and the sprue bushing section. Description of Invention This invention discloses means to insulate a sprue bushing from the die in plastic molding. In particular, the sprue bushing is insulated at its shoulder and stem section from the die so that as plastic compound is forced from the press nozzle to and through the sprue bushing that the temperature of the compound is not adversely affected to cause problems in molding. For example, in molding of thermoplastic compounds the die temperature is below the congealing or freezing temperature of the plastic material. In this conventional molding the sprue bushing is at or near the die temperature, thus when melted plastic compound is injected from the nozzle into and through the sprue bushing that the temperature of the melted plastic is reduced causing flow problems from the sprue bushing into the runners through the die gates and into the cavities of the dies. In thermoset molding, the die is at a high temperature for cure of the compound such as phenolic melamine or alkyd compound. The temperature of the die in thermoset molding is in the vicinity of 162.8 - 183°C, thus in conventional molding the sprue bushing is at or near this temperature. Thus when plasticized thermoset material is forced from the nozzle through the sprue bushing into runners through gates and into the dies, there is often a problem of filling the dies due to pre-cure of the compound on going through the sprue bushing. Attempts have been made to eliminate the above problems, and surprisingly it has been found that insulating the sprue bushing shoulder and a section of the stem from the die, that fill of the dies are readily accomplished, and the problem of "freeze off" is eliminated. IPO On insulating the sprue bushing from the die as mentioned above, the nozzle temperature of thermoplastic compounds can b reduced, and other advantages obtained as indicated in the fiv examples listed as follows: Case 1. Adaptor of 6/6 40% GF Nylon a. reduced nozzle temperature from 329.4 to 271.1° C b. eliminate small bent cores from cold flow resin. c. improved flatness & surface appearance. d. eliminated gas trapping. e. eliminated sprue sticking. f. eliminated nozzle freeze-off. Case 2. Fuse Holder of 30% Glass filled PBT a. reduced nozzle temperature from 260 to 232.2 C. b. eliminated nozzle freeze-off. c eliminated sprue sticking. d. eliminated voids in thick section. e. eliminated critical knit line of cored hole. f. improved resin reprocessability. Case 3. Handle of high impact ABS a. eliminated sticking sprue. b. reduced splay and lamination. c. eliminated subgate plugging. d. improved overall part appearance. e. reduced nozzle temperature from 248.9 to 215.6 Case 4. Cover 30% Glass filled PBT SEO a. reduced nozzle temperature from 254.4° to 221.1° b. eliminated sticking sprue. c. eliminated splay and streaking. d. improved part flatness. * Case 5. Cover SEO Polycarbonate a. reduced nozzle temperature from 310 to 276.7 C. b. eliminated sprue sticking. c. eliminated splay and streaking. * SEO - Self extinguishing, zero burning There are two ways to insulate the bushing shoulder and section of the stem; one method is to machine out a section of the sprue bushing and form the insulating section by injec molding phenolic compound to fill the machined out segment of the shoulder and section of the stem. The molded segment wil be of the same diameter as the sprue bushing stem. The thick of the molded section is of the order of 2.54 to 5.08 mm. Another method of insulating the shoulder and section of stem of the sprue bushing is to insert a molded cylindrical section called insulation section ring to be mounted between the shoulder and stem section of the sprue bushing and the die as shown in Fig. 4. With this second method of insulating the sprue bushing section from the die block requires a machined step on the die block to allow fitting of the insulating ring in the die block to then allow mounting of the sprue bushing therein. This insulated section ring as shown in Fig. 3 can be molded of pheno'lic compound and have a wall thickness of 2.54 to 5.08 mm. The insulating section as outlined above to have a heat transfer value of about 4 to 22 x 10 -4 σal-cm/sec-σm2 - oC. Suitable materials for the sprue bushing insulating segment or ring are phenolic compounds or polyi ide thermoset compounds.

Claims: Having described my invention, I claim: 1.) Insulated sprue bushing in plastic molding apparatus, said apparatus comprising a die mounted in a press, the improvement consisting of an insulated sprue bushing mounted in said die, said sprue bushing insulated from the die block at the shoulder and stem section of said sprue bushing. 2.) An insulated sprue bushing of Claim 1, wherein the insulation comprises a molded thermoset section to be positioned between the sprue bushing and the die mount. 3.) An insulated sprue bushing of claim 1, the insulation consisting of a molded phenolic compound. 4.) An insulated sprue bushing of claim 1, the insulation consisting of a molded heat resistant phenolic compound. 5.) An insulated sprue bushing for plastic injection molding apparatus, the said insulated sprue bushing comprising a molded segment on the shoulder and stem of the bushing, and said molded stem end section having an outer diameter the same as the stem of the bushing. 6.) A sprue bushing insulation ring molded of plastic material comprising said plastic material comprising a thermoset material from the group consisting of phenolic compound and polyiraide thermoset compound. f O PI

Inventors: SHAW RICHARD J, SHAW, RICHARD, J.
Applicants: SHAW RICHARD J, SHAW, RICHARD, J.
Application year: 1983
Main classification: B29F1
IPC codes: B29C45