REDUCTION OF REQUIRED MOLD-CAVITY CLAMPING FORCE AND CONTROL OF INJECTION-MOLDED PRODUCT WALL-THICKNESS

Abstract: In a system and method for injection molding a hollow, plastic product having an end wall and a cylindrical side wall (30), a protractable and retractable contact element (20) of a core section (12) of the mold cavity (24) is protracted to a forward position so that its contact surface (22) contacts at least a significant part of the fringe region of the end-wall-defining portion of the cavity section (10), to thereby reduce the mold cavity area as projected on a plane perpendicular to the mold opening direction, and thus reduce the clamping force required. The dimensions of a plastic product are controlled during injection of a first quantity of plastic material by means of contact between a non-perpendicular contact surface and during an injection of a second quantity of plastic material by means of at-least-partly-solidified wall sections.

Description: (1) REDUCTION OF REQUIRED MOLD-CAVITY CLAMPING FORCE AND CONTROL OF INJECTION-MOLDED PRODUCT WALL-THICKNESS CROSS REFERENCE TO RELATED APPLICATION This is a continuation-in-part of United States Patent Application No 07/347,472 filed May 4, 1989, which is a continuation-in-part of United States Patent Application No. 07/201,690 filed June 2, 1988 BACKGROUND OF THE INVENTION The present invention generally pertains to injection molding of plastic products and is particularly directed to improvement in systems and methods for reducing the required mold-cavity clamping force and in methods of controlling the wall thickness of a plastic product while injection molding the product in a mold cavity of a mold comprising a core section and a cavity section, separated by a parting line and defining the mold cavity. Prior art methods for controlling the wall thickness of injection molded plastic products are described in U S. Patent No. 4,508,676 to Sorensen, U.S. Patent No. 3,737,272 to Segmuller, U.S Patent No 3,305,892 to Heider, U.S. Patent No 4,128,381 to Bonis, Australian Patent Specification No. 17,577/70 (Ryles), and French Patent No. 962,726 to Mazzoni. SUMMARY OF THE INVENTION The present invention provides an improved injection molding system which may be used for performing a method of injection molding a hollow, plastic product having an end wall and a cylindrical or approximately cylindrical side wall, wherein the end wall includes fringe region bordering the side wall, wherein the mold clamping force required during the injection of plastic material into the mold is reduced. The injection molding system of the present invention includes a mold- cavity-forming combination of a core section for forming the inside surface of the product with a cavity section for forming the outside surface of the product, with the axis of the cylindrical or approximately cylindrical side-wall defining portion of SUBSTITUTE SHEE the mold cavity being the same as the moid-opening direction, wherein the core section includes a protractable and retractable contact element, with the end of the contact element that faces the mold cavity including a contact surface; means for protracting the contact element to a forward position so that the contact surface contacts the cavity section or core section of the mold cavity; means for injecting a first quantity of plastic material into the mold cavity while the contact element is in the forward position; means for retracting the contact element to a rear position where the contact surface ceases to contact the cavity section or core section of the mold cavity; and means for injecting a second quantity of plastic material into the moid cavity while the contact element is in the rear position; wherein the contact element has a contact surface that is able to contact at least a significant part of the fringe region of the end-wall-defining portion of the cavity section, so that when the contact element is protracted to a forward position the contact surface contacts at least a significant part of the fringe region of the end-wall-defining portion of the cavity section of the mold cavity, to thereby reduce the mold cavity area as projected on a plane perpendicular to the mold opening direction, and thus reduce the clamping force required when the first quantity of plastic material is injected into the mold cavity; and wherein both the end-wall defining portion and the side-wail defining portion of the core section consist of the contact element. This system may be used to perform a method of injection molding such a hollow, plastic product, wherein the mold clamping force required during the injection of plastic material into the mold is reduced. Such method includes the steps of (a) forming a mold cavity by combining a core section for forming the inside surface of the product with a cavity section for forming the outside surface of the product, with the axis of the cylindrical or approximately cylindrical side- wall defining portion of the mold cavity being the same as the mold-opening direction, wherein the core section includes a protractable and retractable ram- shaped contact element, with the end of the contact element that faces the mold cavity including a contact surface; (b) protracting the contact element to a forward position so that the contact surface contacts the cavity section of the mold cavity; (c) injecting a first quantity of plastic material into the mold cavity while the contact element is in the forward position; (d) retracting the contact element to a rear position where the contact surface ceases to contact the cavity section of the mold cavity; and (e) injecting a second quantity of plastic material into the mold cavity while the contact element is in the rear position; wherein step (a) comprises the step of (f) forming the mold cavity with a contact element having a contact surface that is able to contact at least a significant part of the fringe region of the end-wall-defining portion of the cavity section; wherein step (b) comprises the step of (g) protracting the contact element to a forward position so that the contact surface contacts at least a significant part of the fringe region of the end- wall-defining portion of the cavity section of the mold cavity, to thereby reduce the mold cavity area as projected on a plane perpendicular to the mold opening direction and thus reduce the clamping force required when the first quantity of plastic material is injected into the mold cavity; and wherein step (a) further comprises the step of (h) forming the mold cavity by combining the cavity section with a core section in which both the end-wall defining portion and the side-wall-defining portion of the core section consist of the contact element. in an embodiment of the present invention, wherein the method is used to control the wall thickness of the product, step (b) comprises the step of (i) protracting the contract element to a forward position so that the contact surface contacts the cavity section of the mold cavity to secure the core section in position in relation to the cavity section in order to impede movement SUBSTITUTE SHEET of the core section in relation to the cavity section; step (c) comprises the step of (j) injecting a first quantity of plastic material into the mold cavity while the contact element is in the forward position, whereby the wall thickness of the mold cavity is controlled because relative movement between the core section and the cavity section is impeded; and step (d) comprises the step of (k) retracting the contact element to a rear position where the contact surface ceases to contact the cavity section of the mold cavity, while the injected first quantity of plastic materiaf at least partly solidifies to impede movement of the core section in relation to the cavity section and thus control the wall thickness of the cavity during further injection of plastic material into the mold cavity. As used herein, the terms "solidify" and "at least partly solidify" and their variations mean at least solid enough to provide support. In a separate aspect of the present invention directed to controlling the wall thickness of a molded product, a method of injection molding a hollow, plastic product having an end wall and a cylindrical or approximately cylindrical side wall, wherein the end wall includes a fringe region bordering the side wall, includes the steps of (a) forming a mold cavity by combining a core section with a cavity section for forming said product, wherein the core section includes a protractable and retractable contact element, with the end of the contact element that faces the mold cavity including a contact surface; (b) protracting the contact element along a longitudinal axis of the cavity section to a forward position so that the contact surface contacts the cavity section; (c) injecting a first quantity of plastic material into the mold cavity while the contact element is in the forward position; (d) retracting the contact element to a rear position where the contact surface ceases to contact the cavity section of the mold cavity; and (e) injecting a second quantity of plastic material into the mold cavity while the contact element is in the rear position; wherein step (a) comprises the step of (f) forming the mold cavity by combining the cavity section with a core section in which both the end-wail defining portion and the side-wall-defining portion of the core section consist of the contact element; wherein step (a) further comprises the step of (g) forming the moid cavity with a contact element having a contact surface, at least part of which contact surface is non-perpendicular to the longitudinal axis of the cavity section, and which non-perpendicular part of the contact surface is able to contact at least part of the fringe region of the end- wall-defining portion of the cavity section when the contact element is protracted; and wherein step (b) comprises the step of (h) protracting the contact element to a forward position so that the non- perpendicular part of the contact surface contacts at least part of the fringe region of the end-wall-defining portion of the cavity section to secure the core section in position in relation to the cavity section in order to impede lateral movement of the core section in relation to the longitudinal axis of the cavity section. The present invention further provides a system for practising such a method. In still another aspect, the present invention provides an injection molding method, in which the mold cavity dimensions are controlled during an injection of a first quantity of plastic material by locking the core section to impede lateral movement thereof by means of contact between a non- perpendicular contact surface of a protracted contact element of one mold section and an associated non-perpendicular contact surface of the other mold section, SUBSTITUTE SHEET and is further controlled during an injection of a second quantity of plastic material, which occurs a predetermined period after discontinuing the flow of plastic material into the mold cavity and after the contact element has been retracted, by locking the core section to impede lateral movement thereof by means of at-least-partly-solidified wall sections having a controlled thickness formed during the injection of the first quantity of plastic material. The method of the present invention includes the steps of (a) forming a mold cavity by combining the core section with the cavity section, wherein at (east one section includes a protractable and retractable contact element, with the end of the contact element that faces the mold cavity including a contact surface; (b) protracting the contact element to a forward position so that the contact surface of the contact element contacts an associated contact surface of the other moid section; ■ (c) injecting a first quantity of plastic material < to cause said first quantity of plastic material to flow into the moid cavity while the contact element is in the forward position to form at least one first-piastic-material wall section of the product; (d) cooling the injected first quantity of plastic material in the mold cavity while discontinuing the fiow of plastic material into the mold cavity for a predetermined period; (e) retracting the contact element to a rear position where the contact surface of the contact element ceases to contact the associated contact surface of the other mold section; (f) injecting a second quantity of plastic material into the mold cavity after the injected first quantity of plastic material has at least partly solidified and while the contact element is in the rear position, wherein any lateral movement of the core section in relation to the cavity section that might be caused by injection of the second quantity of plastic material is impeded by the at-least-partlγ- solidified first-plastic-material wall section(s); wherein step (a) includes the step of (g) forming the mold cavity with said mold sections in which at least part of said contact element contact surface is non-perpendicular to the longitudinal axis of the cavity section, and at least part of said associated contact surface is non-perpendicular to the longitudinal axis of the cavity section, wherein step (b) includes the step of (h) protracting the contact element to a forward position so that the non- perpendicular contact surface of the contact element contacts and is locked by the associated non-perpendicular contact surface of the other mold section to impede lateral movement of the core section in relation to the cavity section while the contact element is protracted, wherein step (c) includes the step of (i) injecting the first quantity of plastic material into the mold cavity while the non-perpendicular contact surface of the contact element contacts and is locked by the associated non-perpendicular contact surface in the other moid section in order to form first-plastic-mateπal wail sectιon(s) having a controlled thickness as a result of the lateral movement of the core section in relation to the cavity section being impeded by said contact of the non-perpendicular contact surfaces, wherein step (d) includes the step of (j) at least partly solidifying the wall sectιon(s) having a controlled thickness to impede lateral movement of the core section in relation to the cavity section; and wherein step (f) includes the step of (k) injecting a second quantity of plastic material into the mold cavity while movement of the core section in relation to the cavity section is impeded by the at-least-partly-solidified wall sectιon(s) having a controlled thickness In a separate aspect, the present invention provides an injection molding method, in which the mold cavity dimensions are controlled during an injection of SUBSTITUTE SHEET a first quantity of plastic material, which does not completely cover the parting line of the mold, by locking the core section to impede lateral movement thereof by means of contact between a non-perpendicular contact surface of a protracted contact element of one mold section and an associated non-perpendicular contact surface of the other mold section, and is further controlled during an injection of a second quantity of plastic material, which occurs after the contact element has been retracted, by locking the core section to impede lateral movement thereof by means of at-least-partlγ-soiidified wall sections having a controlled thickness formed during the injection of the first quantity of plastic material. The method according to this separate aspect of the present invention includes the steps of (a) forming a mold cavity by combining the core section with the cavity section, wherein at least one section includes a protractable and retractable contact element, with the end of the contact element that faces the mold cavity including a contact surface; (b) protracting the contact element to a forward position so that the contact surface of the contact element contacts an associated contact surface of the other mold section; (c) injecting a first quantity of plastic material into the mold cavity while the contact element is in the forward position so that the injected first quantity of plastic material does not completely cover the parting line to form at least one fϊrst-plastic-material wall section of the product; (d) cooling the injected first plastic material in the mold cavity; (e) retracting the contact element to a rear position where the contact surface of the contact element ceases to contact the associated contact surface of the other moid section; (f) injecting a second quantity of plastic material into the mold cavity after the injected first quantity of plastic material has at least partly solidified and while the contact element is in the rear position, wherein any lateral movement of the core section in relation to the cavity section that might be caused by injection of the second quantity of plastic material is impeded by the at-least-partly- soiidified first-plastic-material wall section(s); wherein step (a) includes the step of (g) forming the mold cavity with said mold sections in which at least part of said contact element contact surface is non-perpendicular to the longitudinal axis of the cavity section, and at least part of said associated contact surface is non-perpendicular to the longitudinal axis of the cavity section; wherein step (b) includes the step of (h) protracting the contact element to a forward position so that the non- perpendicular contact surface of the contact element contacts and is locked by the associated non-perpendicular contact surface of the other mold section to impede lateral movement of the core section in relation to the cavity section while the contact element is protracted; wherein step (c) includes the step of (i) injecting the first quantity of plastic material into the mold cavity while the non-perpendicular contact surface of the contact element contacts and is locked by the associated non-perpendicular contact surface in the other mold section in order to form first-plastic-material wall section(s) having a controlled thickness as a result of the lateral movement of the core section in relation to the cavity section being impeded by said contact of the non-perpendicular contact surfaces; wherein step (d) includes the step of (j) at least partly solidifying the wall section(s) having a controlled thickness to impede lateral movement of the core section in relation to the cavity section; and wherein step (f) includes the step of (k) injecting a second quantity of plastic material into the mold cavity while movement of the core section in relation to the cavity section is impeded by the at-least-partly-solidified wall section(s) having a controlled thickness. SUBSTITUTE SHEET In an additional aspect the present invention provides a method of cyclic injection molding a hollow, plastic product having laminated walls, utilizing a first mold cavity and a second mold cavity, the first moid cavity being defined by a first common moid part and a first complimentary mold part, and the second mold cavity being defined by said first common moid part and a second complimentary moid part. The method includes the steps of (a) combining the first common mold part with the first complementary mold part to assemble the first mold cavity; (b) injecting a primary plastic material into the first mold cavity; (c) solidifying the injected primary plastic material to form a first plastic wall; (d) combining the first common mold part with the second complementary moid part to assemble the second moid cavity with the. first plastic wail attached to the first common mold part so that when the second mold cavity is assembled the first plastic wail is contained within the second mold cavity; (e) infecting a secondary plastic material into the second mold cavity while the first plastic wall is contained therein; and (f) solidifying the injected secondary plastic material so as to form a second plastic wall that fuses with the first plastic wall to produce a hollow plastic product having laminated wails; wherein step (b) comprises the steps of (g) injecting a first portion of the primary plastic material into the first moid cavity; (h) cooling the injected first portion of the primary plastic material in the first mold cavity; (ϊ) injecting subsequent to injecting the first portion of the primary plastic material a second portion of the primary plastic material into the first mold cavity so that the cooled injected first portion of the primary plastic material in the first moid cavity stabilizes the dimensions of the first mold cavity by impeding movement of the first common mold part in relation to the first complementary mold part caused by injecting the second portion of the primary plastic material, whereby the second portion of the primary plastic material fuses with the cooled previously injected first portion of the primary plastic material. Additional features of the present invention are described in relation to the description of the preferred embodiments. BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a sectional view of one system for performing certain preferred embodiments of the method of the present invention, with the contact element in a protracted position. Figure 2 is a sectional view of the system of Figure 1, with the contact element in a retracted position. Figure 3 is a sectional view of the system of Figures 1 and 2 taken along line 3-3 in Figure 1. Figure 4 is a sectional view of the system of Figures 1 and 2 taken along line 4-4 in Figure 2. Figure 5 is view of the mold cavity in the system of Figures 1 -4 with the injected first quantity of plastic material not covering the parting line of the mold. Figure 6 is view of the mold cavity in the system of Figures 1 -4 with the injected first quantity of plastic material covering the parting line of the mold. Figure 7 is a sectional view of an alternative system for performing certain preferred embodiments of the method of the present invention, with the contact element in a protracted position. Figure 8 is a sectional view of the system of Figure 7, with the contact element in a retracted position. Figures 9A through 9D illustrate a series of steps in the performance of preferred embodiments of the methods of the present invention su r^ C! ViTi W ϊ • ■ = mm ' W C >Ui* ' •S_— il. (12) DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figures 1-6, a system for performing certain preferred embodiments of the method of the present invention includes a cavity section 10, a core section 12, a gate 13, a stationary base member 14, a siidable wedge- shaped member 17 and spacing bars 17. The core section 12 includes a mating element 18 and a protractable and retractable ram-shaped contact element 20. The end of the contact element 20 that faces the cavity section 10 has a contact surface 22. The cavity section 10 has an associated contact surface 23, which coincides with the contact surface 22 of the contact element 20. The cavity section 10 and the core section 12 are combined to define a mold cavity 24. When combined, the cavity section 10 and the core section 12 have a parting line 25 therebetween. The mating element 18 and the stationary base member 14 are maintained in a fixed position in relation to each other by the spacing bars 17. The wedge-shaped member 16 has a dove-tail-shaped lateral cross section, as shown in Figure 3; and the contact element 20 and the stationary base member 14 have corresponding dove-tail-shaped slots for receiving the wedge- shaped member 16 so that the wedge-shaped member 16 is siidably and retentatϊvely coupled to both the contact element 20 and the stationary base member 14. Accordingly, protraction of the wedge-shaped member 16 causes the contact element 20 to be protracted to a forward position; and retraction of the wedge-shaped member 16 causes the contact element 20 to be retracted to a rear position. At least part of the contact surface 22 of the contact element 20 is non- perpendicular to the longitudinal axis 32 of the cavity section 10. At least part of the associated contact surface 23 of the cavity section 10 also is non- perpendicular to the longitudinal axis 32 of the cavity section 10. Referring to Figure 4, the contact surface 22 of the contact element 20 has a generally conical shape and includes a plurality of flow channels 26, which extend radially from the apex of the cone. Each contact surface may include several disconnected portions, such as the separate portions 33 shown in Figure 4. The contact element 20 forms the entire mold-cavity-defining portion of the core section 12. Referring to Figures 1 -4, the mold cavity 24 defines a hollow, plastic product 27, having a generally conical end wall 28 and a cylindrical or approximately cylindrical side-wall 30. The longitudinal axis 32 of cavity section 10 is also the axis of the cylindrical or approximately cylindrical side-wall defining portion of the mold cavity 24, and is the same as the mold opening direction. The system illustrated in Figures 1 -4 is used to perform certain preferred embodiments of the methods of the present invention in the following manner. Referring to Figure 2, the mold cavity 24 is formed by combining the core section 12 with the cavity section 10. The core section 12 forms the inside surface of the product 27 defined by the mold cavity 24 and the cavity section 10 forms the outside surface of the product. The slidable wedge-shaped member 16 is protracted between the contact element 20 and the stationary base member 14 to forcefully protract the contact element 20 along the longitudinal axis of the cavity section 10 to a forward position so that the non-perpendicular portion of the contact surface 22 of the contact element 20 contacts the coincident non-perpendicuiar portion of the associated contact surface 23 of the cavity section 10. Such contact is effected between the fringe region of the contact element contact surface 22 and the the fringe region of the associated contact surface 23. The fringe region of the contact surface 22, 23 is the portion thereof that borders the side-wall-defining portion of the respective contact element 22 or cavity section 10. In an alternative preferred embodiment (not shown) the cavity section includes a protractable and retractable contact element. Whether the contact element is included in the core section as shown in Figures 1 and 2 or the cavity section (not shown) it may or may not be protractable along a longitudinal axis of the cavity section, as shown in Figures 1 and 2. Protracting the contact element 20 to a forward position causes the non- SUBSTITUTE SHEET perpendicular portion of the contact surface 22 to contact and be locked by the non-perpendicuiar portion of the associated contact surface 23 of the cavity section 10 to thereby impede lateral movement of the core section 10 in relation to the longitudinal axis 32 of the cavity section 10. A first quantity of plastic material is injected through the gate 13 and caused to flow into the mold cavity 24 and through the flow channels 26 in the contact surface 22 of the contact element 20 while the contact element is held in the forward position by the wedge-shaped member 16 to form at least one first- piastϊc-material section 34, 35 of the product 27. In one embodiment the injected first quantity of plastic material 34 does not completely cover the parting line 25, as shown in Figure 5. In an alternative embodiment, the injected first quantity of plastic material 35 completely covers the parting line 25, as shown in Figure 6. The wall thickness of the mold cavity 24 is controlled during injection of the first quantity of plastic material because lateral movement of the core section 12 in relation to the cavity section 10 is impeded by the non-perpendicular portion of the contact surface 22 of the contact element 20 contacting and locking the coincident non-perpendicuiar portion of the associated contact surface 23 of the cavity section 10, as described above. Effecting such locking contact between the fringe regions of the contact element contact surface 22 and the fringe region of the associated contact surface 23 spreads such contact over a more far-reaching area and thereby better impedes any such lateral movement. In one preferred embodiment, the injected first quantity of plastic material 34, 35 cools in the moid cavity 24 while flow of plastic material is discontinued for a predetermined period. The slidable wedge-shaped member 16 is then retracted to cause the contact element 20 to be retracted to a rear position, as shown in Figure 2, where the contact surface 22 ceases to contact the cavity section 10; while the injected first quantity of plastic material 34, 35 at least partly solidifies. The at-least-partlγ-solϊdified plastic material wall sectioπ(s) 34, 35 have a controlled wall thickness as a result of the lateral movement of the core section 12 being impeded by the locking contact of the non-perpendicuiar wall surfaces 22, 23 during the injection of the first quantity of plastic material 34, 35. A second quantity of plastic material is injected into the mold cavity 24 while the contact element 20 is held in the rear position by the wedge-shaped member 16 to form the remainder of the plastic product 27. In the embodiment of Figure 5, the injected second quantity of plastic material flows to the parting line 25 to complete the formation of the side wall 30 of the plastic product 27 and also forms the end-wall 28 of the plastic product 27. In this embodiment, the at-least- partly-solidified plastic material wall section(s) 34 define flow channels 37 for directing the injected second quantity of plastic material into the remainder of the mold cavity 24. In the embodiment of Figure 6, the injected second quantity of plastic material forms the end-wall 28 of the plastic product 27. The at-least-partly-soiidified plastic material wall section(s) 34, 35 impede any lateral movement of the core section 12 in relation to the longitudinal axis 32 of the cavity section 10 while the second quantity of plastic material is being injected, and thus control the wall thickness of the mold cavity 24 during the injection of the second quantity of plastic material into the mold cavity 24. Because lateral movement of the core section 12 is thus impeded during injection of the second quantity of plastic material, the second quantity of plastic material may be injected at the same or a higher pressure than the pressure at which the first quantity of plastic material was injected. In the embodiment of Figure 5, in which the injected first quantity of plastic material does not completely cover the parting line 25, the second quantity of plastic material typically is injected at a higher pressure. In the embodiment of Figure 6, in which the injected first quantity of piastic material completely covers the parting line 25, the second quantity of plastic material is injected at a higher pressure, at the same pressure or at a lower pressure in relation to the pressure at which the first piastic material was injected. Injecting the the second quantity of plastic material at a higher pressure enhances bonding between the first and second quantities of plastic material. The second quantity of piastic material may be injected into the mold cavity 24 at a lower pressure than the first quantity of plastic material in order to further reduce the required clamping force. SUBSTITUTE SHEET This completes formation of the plastic product 27 having a controlled wall thickness in accordance with the above-described embodiments of the present invention. After the product 27 is solidified, the mold is opened and the product 27 is ejected. The above-described cycle is then repeated. In an alternative preferred embodiment, the steps of the method are the same as described above, except that flow of the plastic material in the mold cavity is not interrupted between the injection of the first quantity of plastic material and the infection of the second quantity of plastic material. In this alternative embodiment, however, the first quantity of plastic material does not flow to completely cover the parting line. Such limited flow of the first quantity of plastic material is shown in Figure 5, wherein the first quantity of plastic material at least partly solidifies to form the wall sections 34. Protracting the contact element 20 to a forward position to causes the non-perpendicular portion of the contact surface 22 to contact the associated contact surface 23 of the cavity section 10 also reduces the area of the mold cavity 24 as projected on a plane perpendicular to the moid opening direction and thus reduces the clamping force required during the injection of piastic material into the mold cavity 24. When the contact element 20 is protracted to the forward position, as shown in Figures 1 and 3, the contact surface 22 covers approximately the complete eπd-wall-defining portion of the cavity section 10 to thereby reduce the mold cavity area as projected on a plane perpendicular to the mold opening direction to approximately the cross-sectional area of the side-wall-defining portion of the mold cavity, which is relatively small because the product 27 has a cylindrical or approximately cylindrical side wall 30. Additional preferred embodiments of the method of the invention are practised by using the system of Figures 7 and 8. The system of Figures 7 and 8 includes a cavity section 40, a core section 42, and a gate 43. The core section 42 includes a protractable and retractable ram-shaped contact element 50. The end of the contact element 50 that faces the cavity section 40 has a contact surface 52. The cavity section 40 has an associated contact surface 53, which coincides with the contact surface 52 of the contact element 50. The cavity section 40 and the core section 42 are combined to define a mold cavity 54. When combined, the cavity section 40 and the core section 42 have a parting line 60 therebetween. At least part of the contact surface 52 of the contact element 50 is non- 5 perpendicular to the longitudinal axis 62 of the cavity section 40. At least part of the associated contact surface 53 of the cavity section 40 also is non- perpendicular to the longitudinal axis 62 of the cavity section 40. The contact surface 52 of the contact element 50 has a generally conical shape and includes a plurality of fiow channels 56, which extend radially from the apex of the cone. 10 Each contact surface may include several disconnected portions. The mold cavity 54 further defines an end region 55, a side region 56 adjacent the end region 55 and a cyiindrical or approximately cylindrical side-wall- defining region 57 adjacent the side region 56. The side region 56 has a negative slope. In addition, the mold cavity 54 defines a flow region 58 between the gate 15 43 and the end region 55. The longitudinal axis 62 of cavity section 40 is also the axis of the cyiindrical or approximately cylindrical side-wall defining portion of the mold cavity 54, and is the same as the mold opening direction. The system illustrated in Figures 7 and 8 is used to perform certain 20 preferred embodiments of the methods of the present invention in the following manner. The moid cavity 54 is formed by combining the core section 42 with the cavity section 40. The core section 42 forms the inside surface of the product defined by the mold cavity 54 and the cavity section 40 forms the outside surface 25 of the product. The contact element 50 is protracted by means such as the wedge- shaped member 16 of the embodiment of Figures 1 -6 along the longitudinal axis 62 of the cavity section 50 to a forward position so that the non-perpendicular portion of the contact surface 52 of the contact element 50 contacts the -30 coincident non-perpendicular portion of the associated contact surface 53 of the SUBSTITUTE S cavity section 40. Such contact is effected between the fringe region of the contact element contact surface 52 and the the fringe region of the associated contact surface 53. The fringe region of the contact surface 52, 53 is the portion thereof that borders the side-wall-defining portion of the respective contact element 52 or cavity section 40. Protracting the contact element 50 to a forward position causes the non- perpendicular portion of the contact surface 52 to contact and be locked by the non-perpendicular portion of the associated contact surface 53 of the cavity section 40 to thereby impede lateral movement of the core section 40 in relation to the longitudinal axis 62 of the cavity section 40. A first quantity of plastic material is injected through the gate 43 and caused to flow into the moid cavity 54 through the flow region 58 and through the flow channels 56 in the contact surface 52 of the contact element 50 to completely cover the parting line 60 while the contact element 50 is held in the forward position to form at least one first-plastic-material section of the product. The wall thickness of the mold cavity 54 is controlled during injection of the first quantity of plastic material because lateral movement of the core section 42 in relation to the cavity section 40 is impeded by the non-perpendicular portion of the contact surface 52 of the contact element 50 contacting and locking the coincident non-perpendicular portion of the associated contact surface 53 of the cavity section 40, as described above. Effecting such locking contact between the fringe regions of the contact element contact surface 52 and the fringe region of the associated contact surface 53 spreads such contact over a more far-reaching area and thereby better impedes any such lateral movement. The injected first quantity of plastic material cools in the mold cavity 54 while fiow of piastic material is discontinued for a predetermined period. The contact element 20 is then retracted to a rear position, as shown in Figure 8, where the contact surface 52 ceases to contact the cavity section 40; while the injected first quantity of plastic material at least partly solidifies. The at-least-partiy-solidifϊed plastic material wall section(s) have a (19) controlled wall thickness as a result of the lateral movement of the core section 42 being impeded by the locking contact of the non-perpendicular wall surfaces 52, 53 during the injection of the first quantity of plastic material. Because the side region 56 has a negative slope, the first-plastic-material wall section(s) are compressed when the contact element 50 is retracted to the rear position, and thereby seals the moid cavity 54 in the side region 56 to prevent the flow of subsequently injected plastic material beyond the side region 56. A second quantity of plastic material is subsequently injected into the moid cavity 54 while the contact element 50 is held in the rear position. The injected second quantity of plastic material forms the end-wall of the plastic product. The flow region 58 is of such dimension and/or temperature that some of the first quantity of piastic material residing in the flow region 58 while the first quantity of plastic material is cooling does not solidify during the predetermined period that flow of plastic material into the mold cavity 54 is interrupted, and is forced further into the mold cavity 54 by the subsequently injected second quantity of plastic material. Such a flow region may also be used in embodiments of the invention wherein the injected first quantity of plastic material does not completely cover the parting line, such as the embodiment described above with reference to Figures 1-5. The at-least-partly-solidified piastic material wall section(s) formed by the first quantity of plastic material impede any lateral movement of the core section 42 in relation to the longitudinal axis 62 of the cavity section 40 while the second quantity of piastic material is being injected, and thus control the wall thickness of the mold cavity 54 during the injection of the second quantity of plastic material into the mold cavity 54. Because lateral movement of the core section 42 is thus impeded during injection of the second quantity of plastic material, the second quantity of plastic material is injected at a higher pressure, at the same pressure or at a lower pressure in relation to the pressure at which the first piastic material was injected. Injecting the the second quantity of plastic material at a higher pressure enhances (20) bonding between the first and second quantities of plastic material This completes formation of the plastic product having a controlled wall thickness in accordance with the embodiments of the present invention described with reference to Figure 7 and 8. After the product is solidified, the mold is opened and the product is ejected. The above-described cycle is then repeated. In practising the various embodiments of the methods of the invention described herein, there may be injections of piastic material in addition to those so described; and such additional injections may take place, before, after and/or between the respective injections of first and second plastic materials described herein, such as for example, during the production of laminated products. Also, the second quantity of plastic material may be of a different composition and/or color than the first quantity of plastic material, and may be injected into the mold cavity by a different gate (or gates) than that used to inject the first quantity of plastic material. A preferred embodiment of a method of cyclic injection molding hollow, piastic products having laminated walls, according to the present invention is described with reference to Figures 9A through 9D. This method utilizes a first common mold part 140, a second common mold part 1 10, a first complementary mold part 112, and a second complementary mold part 126. Referring to Figure 9A, the first common moid part 140 is combined with the first complementary mold part 112 to assemble a first mold cavity 142. A primary plastic material 144 is injected through a runner system 124 and a gate 122 into the first moid cavity 142. The injected primary plastic material 144 solidifies to form a first plastic wall 144. The first common moid part 140 is then separated from the first complementary mold part 1 12, as shown in Figure 9B, and combined with the second complementary mold part 126, as shown in Figure 9C to assemble a second mold cavity 148 with the first plastic wall 144 attached to the first common mold part 140 so that when the second mold cavity 148 is assembled the first piastic wall 144 is contained within the second mold cavity 148. A secondary plastic material 150 is injected through a runner system 136 and a gate 134 (see Figure 9A for identification of these components) into the second mold cavity 148, as shown in Figure 9C. The injected secondary plastic material 150 solidifies so as to form a second plastic wall 150 that fuses with the first plastic wall 144 to produce a first hollow plastic product 152 having laminated walls. The first common mold part 140 is then separated from the second complementary mold part 126, as shown in Figure 9D, and the plastic product 152 is ejected. In accordance with the wall-thickness-control aspect of the present invention, the process of injecting the primary plastic material 144 into the first mold cavity 142 may include the steps of: (a) injecting a first portion of the primary plastic material 144 into the first mold cavity 142, such as the first portion of plastic material 34 shown in Figure 5; (b) cooling the injected first portion of the primary plastic material 144 in the first mold cavity 142; and (c) injecting subsequent to injecting the first portion of the primary plastic material 144 a second portion of the primary plastic material 144 into the first mold cavity 142 so that the cooled injected first portion of the primary plastic material in the first mold cavity stabilizes the dimensions of the first mold cavity 142 by impeding movement of the first common mold part 140 in relation to the first complementary mold part 1 12 caused by injecting the second portion of the primary plastic material, whereby the second portion of the primary plastic material 144 fuses with the cooled previously injected first portion of the primary plastic material 144. Also in accordance with the wall-thickness-control aspect of the present invention, the process of injecting the secondary plastic material 150 into the second mold cavity 148 may include the steps of: UBSTITUTE SHEET (a) infecting a first portion of the secondary plastic material 150 into the second mold cavity 148; (b) cooling the injected first portion of the secondary piastic material 150 in the second mold cavity 148; and (c) injecting subsequent to injecting the first portion of the secondary piastic material 150 a second portion of the secondary plastic material 150 into the second mold cavity 148 so that the cooled injected first portion of the secondary plastic material 150 in the second mold cavity 148 stabilizes the dimensions of the second mold cavity 148 by impeding movement of the first common mold part 140 in relation to the second complementary mold part 126 caused by injecting the second portion of the secondary plastic material 150 , whereby the second portion of the secondary piastic material 150 fuses with the cooled previously injected first portion of the secondary plastic material 150. The simultaneous production of a plurality of plastic products 138, 152 with the system of Figures 9A through 9D is further described as follows. Referring again to Figure 9C, the second common mold part 1 10 is combined with the first complementary mold part 112 to assemble a third mold cavity 1 14. A tertiary plastic material 120 is injected through the runner system 124 and the gate 122 into the third mold cavity 1 14 while the secondary piastic material 150 is being injected the runner system 136 and the gate 134 into the second mold cavity 148. The injected tertiary plastic material 120 solidifies in the third mold cavity 114 to form a first plastic wall 120 while the injected secondary plastic material 150 is solidifying in the second mold cavity 148 to form the second plastic wall of the laminated piastic product 52. The second common mold part 110 is then separated from the first complementary mold part 1 12, as shown in Figure 9D, and combined the second complementary mold part 126 to assemble a fourth mold cavity 128, as shown in Figure 9A, with the first plastic wall 120 attached to the second common mold part 1 10 so that when the fourth mold cavity 128 is assembled the first plastic wall 120 is contained within the fourth mold cavity 128. A quaternary plastic material 132 is injected through the runner system 136 and the gate 134 into the fourth mold cavity 128 while the first plastic wall 120 is contained therein, and while the primary plastic material 144 is being injected into the first mold cavity 142. While the injected primary plastic material is solidifying in the first mold cavity 142, the injected quaternary plastic material 132 solidifies in the fourth mold cavity 128 so as to form a second plastic wall 128 that fuses with the first plastic wall 120 to produce a second hollow plastic product 138 having laminated walls. The second common mold part 1 10 is then separated from the first complementary mold part 126, as shown in Figure 9B, and the piastic product 138 is ejected. In accordance with the wall-thickπess-control aspect of the present invention, the process of injecting the tertiary piastic material 120 into the third moid cavity 1 14 and of injecting the quaternary plastic material 132 into the fourth moid cavity 128 include the above-described steps (a), (b) and (c) of injecting the primary plastic material 144 into the first mold cavity 142 and injecting the secondary plastic material 150 into the second mold cavity 148. This method is particularly advantageous when the primary plastic material 144 is different from the secondary material 150 and the tertiary plastic material 120 is different from the quaternary plastic material 132. For example, the present invention is ideally suited for molding a hollow, thin-walled plastic product in which the side wail must provide both a moisture barier and a gas (such as Oxygen) barrier. To mold such a product, a plastic material having a desirable mositure-barrier characteristic is selected as one of the injected plastic materials; and a plastic material having a desirable gas-barrier characteristic is selected as the other injected plastic material. When the plastic products 138 are to be of the same composition as the plastic products 152, the primary plastic material 144 is the same as the tertiary plastic material 120 and the secondary plastic material 150 is the same as the quaternary plastic material 132. Preferably at least one of the mold parts defining each mold cavity 1 14, 128, 142, 148 includes a protractable and retractable ram-shaped element with one end of the ram-shaped element facing the moid cavity, such as described above with reference to Figures 1-6. Accordingly, during step (a) of the injection process described above, the ram-shaped element is protracted to a forward position; and the first portion of the plastic material is injected into the mold cavity while the ram-shaped element is in the forward position; and during step (c) of the injection process described above, the ram-shaped element is retracted to a rear position; and the second portion of the piastic material is injected into the mold cavity while the ram-shaped element is in the rear position.

Claims: CLAIMS 1. A method of controlling the wall thickness of a plastic product while 2 injection molding the product in a mold cavity of a mold comprising a core section and a cavity section, separated by a parting line and defining the mold cavity therebetween, the method comprising the steps of 6 (a) forming a mold cavity by combining the core section with the cavity section, wherein at least one section includes a protractable and retractable 8 contact element, with the end of the contact element that faces the mold cavity including a contact surface, 10 (b) protracting the contact element to a forward position so that the contact surface of the contact element contacts an associated contact surface of 12 the other mold section, (c) injecting a first quantity of plastic material to cause said first quantity 14 of plastic material to flow into the mold cavity while the contact element is in the forward position to form at least one first-plastic-mateπal wall section of the 16 product; (d) cooling the injected first quantity of plastic material in the mold cavity 18 while discontinuing the flow of plastic material into the mold cavity for a predetermined period, 20 (e) retracting the contact element to a rear position where the contact surface of the contact element ceases to contact the associated contact surface of 22 the other moid section, (f) injecting a second quantity of plastic material into the mold cavity 24 after the injected first quantity of piastic material has at least partly solidified and while the contact element is in the rear position wherein any lateral movement oτ " 26 the core section in relation to the cavity section that might be caused by injection of the second quantity of plastic material is impeded by the at-least-partly- 28 solidified first-piastic-matenal wall sectιon(s), wherein step (a) comprises the step of 30 (g) forming the moid cavity with said mold sections in which at least part of said contact element contact surface is non-perpendicular to the longitudinal 32 axis of the cavity section, and at least part of said associated contact surface is non-perpendicular to the longitudinal axis of the cavity section; 34 wherein step (b) comprises the step of (h) protracting the contact element to a forward position so that the non- 36 perpendicular contact surface of the contact element contacts and is locked by the associated non-perpendicular contact surface of the other moid section to impede 38 lateral movement of the core section in relation to the cavity section while the contact element is protracted; 40 wherein step (c) comprises the step of (i) infecting the first quantity of plastic material into the mold cavity while 42 the non-perpendicuiar contact surface of the contact element contacts and is locked by the associated non-perpendicular contact surface in the other mold * 44 section in order to form fϊrst-plastic-material wall section(s) having a controlled thickness as a result of the lateral movement of the core section in relation to the 6 cavity section being impeded by said non-perpendicuiar contact surfaces being locked; * 8 wherein step (d) comprises the step of (j) at least partly solidifying the wall section(s) having a controlled 50 thickness to impede lateral movement of the core section in relation to the cavity section; and 52 wherein step (f) comprises the step of (k) infecting a second quantity of plastic material into the mold cavity 4 while movement of the core section in relation to the cavity section is impeded by the at-least-partly-solidified wall section(s) having a controlled thickness. 2. A method according to Claim 1, wherein step (a) comprises the step of (27) (I) forming the mold cavity with mold sections in which the non- perpendicuiar contact surface of the contact element coincides with the non- perpendicular associated contact surface of the other mold section. 3. A method according to Claim 1, wherein step (a) comprises the step of (I) forming the mold cavity with a core section that includes said contact element. 4. A method according to Claim 3, wherein step (a) comprises the step of (I) forming the mold cavity with a core section in which said contact element forms the entire mold-cavity-side-wall-defining portion of the core section. 5. A method according to Claim 3, wherein step (a) comprises the step of (I) forming the mold cavity with mold sections that define a gate, an end region adjacent the gate, and a cylindrical region adjacent the end region so that the first-plastic-material wall section(s) contact both the core section and the cavity section when the contact element is retracted to the rear position during step (e) to impede movement of the core section in relation to the cavity section when the second quantity of plastic material is injected during step (f). 6. A method according to Claim 3, wherein step (a) comprises the step of (I) forming the mold cavity with mold sections that define a gate, an end region adjacent the gate, and a cylindrical region adjacent the end region so that the first-plastic-material wall section(s) contact both the core section and the cavity section when the contact element is retracted to the rear position during step (e) to prevent lamination of the first-piastic-material wall section(s) when the second quantity of plastic material is injected during step (f). 7. A method according to Claim 3, wherein step (a) comprises the step of (I) forming the mold cavity with mold sections that define a gate, an end region adjacent the gate, and a side region adjacent the end region, wherein the side region has a negative slope so that when the contact element is retracted to the rear position during step (e) the first-piastic-material wall sectioπ(s) formed during step (c) are compressed. 8. A method according to Claim 7, wherein step (c) comprises the step of (1) infecting the first quantity of plastic material into the mold cavity while the contact element is in the forward position so that the injected first plastic material completely covers the parting line. 9. A method according to Claim 1, wherein step (c) comprises the step of (I) infecting the first quantity of plastic material at a first injection pressure; and wherein step (f) comprises the step of (m) injecting the second quantity of plastic material at a second injection pressure that is not less than the first injection pressure. 10. A method according to Claim 1, wherein step (a) comprises the step of (I) forming the mold cavity with mold sections that define at least one flow channel after the contact element is retracted pursuant to step (e) for directing the injected second quantity of plastic material into predetermined regions of the mold cavity during step (f). 1 1. A method according to Claim 1, wherein step (a) comprises the step of (I) forming the mold cavity with mold sections that define a flow region when the contact element is protracted to the forward position, wherein the flow region is of such dimension and/or temperature that some of the first quantity of plastic material residing in the flow region during step (d) does not solidify during the predetermined period and is forced further into the mold cavity by the second quantity of plastic material injected during step (f). 12. A method according to Claim 1, wherein step (c) comprises the step of (I) injecting the first quantity of plastic material from a given gate; and wherein step (f) comprises the step of (m) injecting the second quantity of piastic material from the given gate. 13. A method according to Claim 12, wherein step (c) comprises the step of (I) injecting the first quantity of plastic material from only one given gate; and wherein step (f) comprises the step of (m) injecting the second quantity of plastic material from the one given gate. 14. A method according to Claim 1, further comprising the step of (I) protracting the contact element to hold pressurize the infected plastic material. 15. A method according to Claim 1, wherein step (c) comprises the step of (I) injecting the first quantity of plastic material into the mold cavity while the contact element is in the forward position so that the injected first plastic material completely covers the parting line. 16. A method of controlling the wall thickness of a plastic product whiie injection molding the product in a mold cavity of a mold comprising a core section and a cavity section, separated by a parting line and defining the mold cavity therebetween, the method comprising the steps of (a) forming a mold cavity by combining the core section with the cavity section, wherein at least one section includes a protractable and retractable contact element, with the end of the contact element that faces the mold cavity including a contact surface; 0- (b) protracting the contact element to a forward position so that the contact surface of the contact element contacts an associated contact surface of Z the other mold section; (c) injecting a first quantity of plastic material into the mold cavity while - the contact element is in the forward position so that the injected first quantity of piastic material does not completely cover the parting line to form at least one 6 first-piastic-material wall section of the product; (d) cooling the injected first plastic material in the mold cavity; 18 (e) retracting the contact element to a rear position where the contact surface of the contact element ceases to contact the associated contact surface of 20 the other moid section; (f) injecting a second quantity of plastic material into the mold cavity '22 after the injected first quantity of plastic material has at least partly solidified and while the contact element is in the rear position, wherein any lateral movement of 24 the core section in relation to the cavity section that might be caused by injection of the second quantity of plastic material is impeded by the at-least-partly- 26 solidified first-plastic-materiai wall section(s); wherein step (a) comprises the step of 28 (g) forming the mold cavity with said mold sections in which at least part of said contact element contact surface is non-perpendicular to the longitudinal 30 axis of the cavity section, and at least part of said associated contact surface is non-perpendicular to the longitudinal axis of the cavity section; 32 wherein step (b) comprises the step of *■ (h) protracting the contact element to a forward position so that the non- 34 perpendicular contact surface of the contact element contacts and is locked by the associated non-perpendicular contact surface of the other moid section to impede 36 lateral movement of the core section in relation to the cavity section while the contact element is protracted; 38 wherein step (c) comprises the step of (i) injecting the first quantity of plastic material into the mold cavity while G the non-perpendicuiar contact surface of the contact element contacts and is locked by the associated non-perpendicular contact surface in the other mold 42 section in order to form first-plastic-material wall section(s) having a controlled thickness as a result of the lateral movement of the core section in relation to the 44 cavity section being impeded by said contact of the non-perpendicular contact surfaces; 46 wherein step (d) comprises the step of (j) at least partly solidifying the wall section(s) having a controlled thickness to impede lateral movement of the core section in relation to the cavity section; and wherein step (f) comprises the step of (k) injecting a second quantity of plastic material into the mold cavity while movement of the core section in relation to the cavity section is impeded by the at-least-partly-solidified wall section(s) having a controlled thickness. 17. A method according to Claim 16, wherein step (a) comprises the step of (I) forming the mold cavity with mold sections in which the non- perpendicuiar contact surface of the contact element coincides with the non- perpendicular associated contact surface of the other mold section. 18. A method according to Claim 16, wherein step (a) comprises the step of (1) forming the mold cavity with a core section that includes said contact element. 19. A method according to Claim 18, wherein step (a) comprises the step of (I) forming the mold cavity with a core section in which said contact element forms the entire moid-cavity-defiπing portion of the core section. 20. A method according to Claim 16, wherein step (c) comprises the step of (I) infecting the first quantity of piastic material at a first injection pressure; and wherein step (f) comprises the step of (m) injecting the second quantity of piastic material at a second injection pressure that is not less than the first injection pressure. 21. A method according to Claim 16, wherein step (a) comprises the step of (I) forming the mold cavity with mold sections that define at least one flow channel after the contact element is retracted pursuant to step (e) for directing the injected second quantity of plastic material into predetermined regions of the mold cavity during step (f). 22. A method according to Claim 16, wherein step (a) comprises the step of (I) forming the moid cavity with mold sections that define a flow region when the contact element is protracted to the forward position, wherein the flow region is of such dimension and/or temperature that some of the first quantity of plastic material residing in the flow region during step (d) does not solidify and is forced further into the mold cavity by the second quantity of plastic material injected during step (f). 23. A method according to Claim 16, further comprising the step of (I) protracting the contact element to hold pressurize the injected plastic material. 24. A method according to Claim 16, wherein step (c) comprises the step of (I) injecting the first quantity of plastic material from a given gate; and wherein step (f) comprises the step of (m) injecting the second quantity of plastic material from the given gate. UBSTIT 25. A method according to Claim 24, wherein step (c) comprises the step of (I) injecting the first quantity of plastic material from only one given gate; and wherein step (f) comprises the step of (m) infecting the second quantity of plastic material from the one given gate. 26. A method of infection molding a hollow, plastic product having an end wall and a cylindrical or approximately cylindrical side wall, wherein the end wall includes a fringe region bordering the side wail, the method comprising the steps of (a) forming a mold cavity by combining a core section for forming the inside surface of the product with a cavity section for forming the outside surface of the product, with the axis of the cylindrical or approximately cylindrical side- wall defining portion of the moid cavity being the same as the mold-opening direction, wherein the core section includes a protractable and retractable contact element, with the end of the contact element that faces the mold cavity including a contact surface; (b) protracting the contact element to a forward position so that the contact surface contacts the cavity section or core section of the mold cavity; (c) injecting a first quantity of plastic material into the mold cavity while the contact element is in the forward position; (d) retracting the contact element to a rear position where the contact surface ceases to contact the cavity section of the mold cavity; and (e) injecting a second quantity of plastic material into the mold cavity while the contact element is in the rear position; 20 wherein step (a) comprises the step of (f) forming the mold cavity with a contact element having a contact 22 surface that is able to contact at least a significant part of the fringe region of the end-wall-defining portion of the cavity section; ' 24 wherein step (b) comprises the step of (g) protracting the contact element to a forward position so that the 26 contact surface contacts at least a significant part of the fringe region of the end- wall-defining portion of the cavity section of the mold cavity, to thereby reduce 28 the mold cavity area as projected on a plane perpendicular to the mold opening direction, and thus reduce the clamping force required when the first quantity of 30 plastic material is injected into the mold cavity; and wherein step (a) further comprises the step of 32 (h) forming the mold cavity by combining the cavity section with a core section in which both the end-wall defining portion and the side-wall-defining 34 portion of the core section consist of the contact element. 27. A method according to Claim 26, wherein step (e) comprises the step of (h) injecting the second quantity of plastic material at a lower pressure than the first quantity of plastic material in order to further reduce the required clamping force. 28. A method according to Claim 26, wherein the wall thickness of the product is controlled, wherein step (b) comprises the step of (i) protracting the contract element to a forward position so that the contact surface contacts the cavity section of the mold cavity to secure the core section in position in relation to the cavity section in order to impede movement of the core section in relation to the cavity section; wherein step (c) comprises the step of (J) infecting a first quantity of plastic materiaf into the mold cavity while the contact element is in the forward position, whereby the wail thickness of the mold cavity is controlled because relative movement between the core section and the cavity section is impeded; and wherein step (d) comprises the step of (k) retracting the contact element to a rear position where the contact surface ceases to contact the cavity section of the moid cavity, while the injected first quantity of plastic material at least partly solidifies to impede movement of the core section in relation to the cavity section and thus control the wall ' thickness of the cavity during further injection of plastic material into the mold cavity. 29. A method according to Claim 28, wherein step (i) comprises the step of (I) protracting a slidable wedge-shaped member between the contact - element and a stationary base member to forcefully protract the contact element to the forward position; and wherein step (k) comprises the step of (m) retracting the slidable wedge-shaped member so that the contact element may be retracted. 30. A method according to Claim 29, wherein steps (1) and (m) comprise protracting and retracting a said wedge-shaped member that is slidably and retentatively coupled to both the contact element and the stationary base member so that during step (g) the retraction of the wedge-shaped member causes the contact element to be retracted. 31. A system for injection molding a hollow, plastic product having an end wall and a cylindrical or approximately cylindrical side wall, wherein the end wall includes a fringe region bordering the end wall, the system comprising a mold-cavity-forming combination of a core section for forming the inside surface of the product with a cavity section for forming the outside surface of the product, with the axis of the cylindrical or approximately cylindrical side- wall defining portion of the mold cavity being the same as the mold-opening direction, wherein the core section includes a protractable and retractable contact element, with the end of the contact element that faces the mold cavity including a contact surface; means for protracting the contact element to a forward position so that the contact surface contacts the cavity section or core section of the mold cavity; means for injecting a first quantity of plastic material into the mold cavity while the contact element is in the forward position; means for retracting the contact element to a rear position where the contact surface ceases to contact the cavity section or core section of the mold cavity; and means for injecting a second quantity of plastic material into the mold cavity while the contact element is in the rear position; wherein the contact element has a contact surface that is able to contact at least a significant part of the fringe region of the end-wall-defining portion of the cavity section, so that when the contact element is protracted to a forward position the contact surface contacts at least a significant part of the fringe region of the end-wall-defining portion of the cavity section of the mold cavity, to thereby reduce the mold cavity area as projected on a plane perpendicular to the mold opening direction, and thus reduce the clamping force required when the first quantity of plastic material is injected into the mold cavity; and wherein both the end-wall defining portion and the side-wall defining (38) portion of the core section consist of the contact element. 32. A system according to Claim 31, wherein the means for injecting the second quantity of piastic material includes means for injecting the second quantity of plastic material at a lower pressure than the first quantity of piastic - material in order to further reduce the required clamping force. 33. A system according to Claim 31, comprising means for protracting the contract element to a forward position so that the contact surface contacts the cavity section of the mold cavity to secure the - core section in position in relation to the cavity section in order to impede movement of the core section in relation to the cavity section; -- means for injecting a first quantity of piastic material into the moid cavity while the contact element is in the forward position, whereby the wail thickness of the mold cavity is controlled because relative movement between the core section and the cavity section is impeded; and 0 ; means for retracting the contact element to a rear position where the contact surface ceases to contact the cavity section of the moid cavity, while the 2 infected first quantity of plastic material at least partly solidifies to impede movement of the core section in relation to the cavity section and thus control the 4- wall thickness of the cavity during further infection of plastic material into the mold cavity. 34. A system according to Claim 33, comprising a slidable wedge-shaped member; means for protracting the wedge-shaped member between the contact 4 element and the stationary base member to forcefully protract the contact element to the forward position; and 6 means for retracting the wedge-shaped member so that the contact element may be retracted. 35 A system according to Claim 34, wherein the wedge-shaped member is slidably and retentatively coupled to both the contact element and the stationary base member so that retraction of the wedge-shaped member causes the contact element to be retracted. 36. A method of injection molding a hollow, plastic product having an end wall and a cylindrical or approximately cylindrical side wall, wherein the end wall includes a fringe region bordering the side wall, the method comprising the steps of (a) forming a mold cavity by combining a core section with a cavity section for forming said product, wherein the core section includes a protractable and retractable contact element, with the end of the contact element that faces the mold cavity including a contact surface; (b) protracting the contact element along a longitudinal axis of the cavity section to a forward position so that the contact surface contacts the cavity section; (c) injecting a first quantity of plastic material into the mold cavity while the contact element is in the forward position; (d) retracting the contact element to a rear position where the contact surface ceases to contact the cavity section of the mold cavity; and (e) injecting a second quantity of plastic material into the mold cavity while the contact element is in the rear position; wherein step (a) comprises the step of (f) forming the mold cavity by combining the cavity section with a core section in which both the end-wall defining portion and the side-wall-definmg portion of the core section consist of the contact element; wherein step (a) further comprises the step of (40) (g) forming the mold cavity with a contact element having a contact 2.4- surface, at least part of which contact surface is non-perpendicular to the longitudinal axis of the cavity section, and which non-perpendicular part of the 2° contact surface is able to contact at least part of the fringe region of the end- wall-defining portion of the cavity section when the contact element is protracted; 28 and wherein step (b) comprises the step of 33X (h) protracting the contact element to a forward position so that the non- perpendicuiar part of the contact surface contacts at least part of the fringe region of the end-wall-defining portion of the cavity section to secure the core section in position in relation to the cavity section in order to impede lateral movement of 34 the core section in relation to the longitudinal axis of the cavity section while the first quantity of plastic material is being injected into the mold cavity. 37. A method according to Claim 36, wherein step (c) comprises the step of (i) injecting a first quantity of plastic material into the mold cavity while the contact element is in the forward position, whereby the wall thickness of the mold .cavity is controlled because lateral movement of the core section in relation to the cavity section is impeded by said contact between the non-perpendicuiar part of the contact surface and the fringe region of the end-wall-defining portion of the cavity section; and wherein step (d) comprises the step of 10 (j) retracting the contact element to a rear position where the contact surface ceases to contact the cavity section of the moid cavity, while the injected 12 first quantity of plastic material at least partly solidifies to impede lateral movement of the core section in relation to the longitudinal axis of cavity section 1 and thus control the wail thickness of the mold cavity during further injection of plastic material into the mold cavity. (Al) 38. A method according to Claim 36, wherein step (b) comprises the step of (i) protracting a slidable wedge-shaped member between the contact element and a stationary base member to forcefully protract the contact element to the forward position; and wherein step (d) comprises the step of (j) retracting the slidable wedge-shaped member so that the contact element may be retracted. 39. A method according to Claim 38, wherein steps (i) and (j) comprise protracting and retracting a said wedge-shaped member that is slidably and /etentatively coupled to both the contact element and the stationary base member so that during step (j) the retraction of the wedge-shaped member causes the contact element to be retracted. 40. A system for injection molding a hollow, plastic product having an end wail and a cylindrical or approximately cylindrical side wall, wherein the end wall includes a fringe region bordering the side wall, the system comprising - a mold-cavity-formiπg combination of a core section and a cavity section for forming a mold cavity by combining the core section with the cavity section for forming said product, wherein the core section includes a protractable and retractable contact element, with the end of the contact element that faces the mold cavity including a contact surface; means for protracting the contact element along a longitudinal axis of the 0 cavity section to a forward position so that the contact surface contacts the cavity section; 2 means for injecting a first quantity of plastic material into the mold cavity (42) while the contact element is in the forward position; means for retracting the contact element to a rear position where the contact surface ceases to contact the cavity section; and means for injecting a second quantity of plastic material into the mold cavity while the contact element is in the rear position; wherein both the end-wail defining portion and the side-wall defining portion of the core section consist of the contact element; wherein the contact element has a contact surface, at least part of which contact surface is non-perpendicular to the longitudinal axis of the cavity section, and which non-perpendicuiar part of the contact surface is able to contact at least part of the fringe region of the end-wall-defining portion of the cavity section when the contact element is protracted; and wherein the protracting means include means for protracting the contact element to a forward position so that the non-perpendicular part of the contact surface contacts at least part of the fringe region of the end-wall-defining portion of the cavity section to secure the core section in position in relation to the cavity section in order to impede lateral movement of the core section in relation to the longitudinal axis of the cavity section while the first quantity of plastic material is being infected into the mold cavity. 41. A system according to Claim 40, comprising wherein the means for infecting said first quantity of plastic material include means for injecting said first quantity of plastic material into the mold cavity while the contact element is in the forward position, whereby the wall thickness of the mold cavity is controlled because lateral movement of the core section in relation to the cavity section is impeded by said contact between the non-perpendicular part of the contact surface and the fringe region of the end- wall defining portion of the cavity section; and wherein the retracting means include means for retracting the contact element to a rear position where the contact surface ceases to contact the cavity section of the mold cavity, while the injected first quantity of plastic material at least partly solidifies to impede lateral movement of the core section in relation to the longitudinal axis of the cavity section and thus control the wall thickness of the mold cavity during further injection of plastic material into the mold cavity. 42. A system according to Claim 40, comprising a slidable wedge-shaped member; means for protracting the wedge-shaped member between the contact element and the stationary base member to forcefully protract the contact element to the forward position; and means for retracting the wedge-shaped member so that the contact element may be retracted. 43. A system according to Claim 42, wherein the wedge-shaped member is slidably and retentatively coupled to both the contact element and the stationary base member so that retraction of the wedge-shaped member causes the contact element to be retracted. 44. A method of cyclic injection molding a hollow, piastic product having laminated walls, utilizing a first mold cavity and a second mold cavity, the first mold cavity being defined by a first common mold part and a first complimentary mold part, and the second mold cavity being defined by said first common mold part and a second complimentary mold part, the method comprising the steps of; (a) combining the first common mold part with the first complementary mold part to assemble the first mold cavity; (b) injecting a primary plastic material into the first mold cavity; (c) solidifying the injected primary plastic material to form a first plastic SU STITUTE SHEET wailr (d) combining the first common mold part with the second complementary mold part to assemble the second mold cavity with the first plastic wall attached to the first common mold part so that when the second mold cavity is assembled the first plastic wall is contained within the second mold cavity; (e) infecting a secondary plastic material into the second mold cavity while the first plastic wall is contained therein; and (f) solidifying the infected secondary plastic material so as to form a second plastic wall that fuses with the first plastic wall to produce a hollow plastic product having laminated walls; wherein step (b) comprises the steps of (g) injecting a first portion of the primary piastic material into the first mold cavity; (h) cooling the infected first portion of the primary plastic material in the first mold cavity; (ϊ) injecting subsequent to infecting the first portion of the primary plastic material a second portion of the primary piastic material into the first mold cavity so that the cooled injected first portion of the primary piastic material in the first ' mold cavity stabilizes the dimensions of the first moid cavity by impeding movement of the first common mold part in relation to the first complementary mold part caused by infecting the second portion of the primary piastic material, whereby the second portion of the primary plastic material fuses with the cooled previously injected first portion of the primary plastic material. 45. A method according to Claim 44, for cyclic injection molding a plurality of hollow, plastic products having laminated walls, further utilizing a third mold cavity and a fourth mold cavity, the third mold cavity being defined by a second common mold part and said first complimentary mold part, and the fourth mold cavity being defined by said second common moid part and said second complimentary mold part, the method comprising the steps of: (j) during step (d) combining the second common mold part with the first complementary mold part to assemble the third mold cavity; (k) during step (e) injecting a tertiary plastic material into the third mold cavity; (I) during step (f) solidifying the injected tertiary plastic material to form a third plastic wall; (m) during step (a) combining the second common mold part with the second complementary mold part to assemble the fourth mold cavity with the third plastic wall attached to the second common mold part so that when the fourth mold cavity is assembled the third plastic wall is contained within the fourth mold cavity; (n) during step (b) injecting a quaternary plastic material into the fourth mold cavity while the third plastic wall is contained therein; and (o) during step (c) solidifying the injected quaternary plastic material so as to form a fourth plastic wall that fuses with the third plastic wall to produce a second hollow plastic product having laminated walls; wherein step (k) comprises the steps of (p) injecting a first portion of the tertiary plastic material into the third mold cavity; (q) cooling the injected first portion of the tertiary plastic material in the third mold cavity; (r) injecting subsequent to injecting the first portion of the tertiary plastic material a second portion of the tertiary plastic material into the third mold cavity so that the cooled injected first portion of the tertiary piastic material in the third mold cavity stabilizes the dimensions of the tertiary mold cavity by impeding movement of the second common mold part in relation to the first complementary moid part caused by injecting the second portion of the tertiary plastic material, whereby the second portion of the tertiary plastic material fuses with the cooled previously infected first portion of the tertiary plastic material. 46. A method according to Claim 44, wherein the primary plastic material is different from the secondary material. 47. A method according to Claim 45, wherein the primary plastic material is the same as the tertiary plastic material and the secondary plastic material is the same as the quaternary plastic material. 48. A method according to Claim 45, wherein the primary plastic material is different from the secondary plastic material and the tertiary plastic material is different from the quaternary plastic material. 49. A method according to Claim 44, wherein at least one of the mold parts defining the first mold cavity includes a protractable and retractable ram- shaped element with one end of the ram-shaped element facing the first moid cavity, wherein step (g) comprises the steps of, (j) protracting the ram-shaped element to a forward position; and (k) infecting the first portion of the primary plastic material into the first mold cavity while the ram-shaped element is in the forward position; and wherein step (i) comprises the steps of, (1) retracting the ram-shaped element to a rear position; and (m) infecting the second portion of the primary plastic material into the first mold cavity while the ram-shaped element is in the rear position. 50. A method according to Claim 44, wherein step (e) comprises the 2 steps of (j) injecting a first portion of the secondary plastic material into the 4. second mold cavity; (k) cooling the injected first portion of the secondary plastic material in 6 the second mold cavity; and (I) injecting subsequent to injecting the first portion of the secondary 8 piastic material a second portion of the secondary plastic material into the second mold cavity so that the cooled injected first portion of the secondary plastic 10 ; material in the second mold cavity stabilizes the dimensions of the second mold cavity by impeding movement of the first common moid part in relation to the 12 second complementary mold part caused by injecting the second portion of the secondary plastic material, whereby the second portion of the secondary piastic 14 material fuses with the cooled previously injected first portion of the secondary plastic material. 51. A method of cyclic injection molding a hollow, piastic product having laminated walls, utilizing a first mold cavity and a second mold cavity, the first mold cavity being defined by a first common mold part and a first complimentary - mold part, and the second mold cavity being defined by said first common mold part and a second complimentary mold part, the method comprising the steps of; (a) combining the first common mold part with the first complementary mold part to assemble the first mold cavity; (b) injecting a primary piastic material into the first mold cavity; (c) solidifying the injected primary piastic material to form a first piastic IO! wall; (d) combining the first common mold part with the second 12- complementary mold part to assemble the second mold cavity with the first plastic wall attached to the first common mold part so that when the second mold cavity 14 * is assembled the first plastic wall is contained within the second mold cavity; (e) injecting a secondary piastic material into the second mold cavity 6 while the first piastic wall is contained therein; and (f) solidifying the infected secondary piastic material so as to form a § second plastic wall that fuses with the first plastic wall to produce a hollow plastic product having laminated walls; O wherein step (e) comprises the steps of (j) infecting a first portion of the secondary plastic material into the 2- second mold cavity; (k) cooling the infected first portion of the secondary plastic material in 4- the second mold cavity; (I) injecting subsequent to infecting the first portion of the secondary plastic material a second portion of the secondary plastic material into the second mold cavity so that the cooled infected first portion of the secondary plastic 8 material in the second mold cavity stabilizes the dimensions of the second mold cavity by impeding movement of the first common mold part in relation to the 0 second complementary mold part caused by injecting the second portion of the secondary plastic material, whereby the second portion of the secondary piastic 2 material fuses with the cooled previously injected first portion of the secondary plastic material. 52. A method according to Claim 51, for cyclic injection molding a plurality of hollow, plastic products having laminated walls, further utilizing a third mold cavity and a fourth mold cavity, the third mold cavity being defined by a - second common mold part and said first complimentary mold part, and the fourth mold cavity being defined by said second common mold part and said second 6 complimentary mold part, the method comprising the steps of: (j) during step (d) combining the second common moid part with the first 8 complementary mold part to assemble the third mold cavity; (k) during step (e) injecting a tertiary piastic material into the third mold cavity; (I) during step (f) solidifying the injected tertiary plastic material to form a third plastic wall; (m) during step (a) combining the second common mold part with the second complementary mold part to assemble the fourth mold cavity with the third plastic wall attached to the second common mold part so that when the fourth mold cavity is assembled the third plastic wall is contained within the fourth mold cavity; (n) during step (b) injecting a quaternary piastic material into the fourth mold cavity while the third plastic wall is contained therein; and (o) during step (c) solidifying the injected quaternary plastic material so as to form a fourth plastic wall that fuses with the third plastic wall to produce a second hollow plastic product having laminated walls; wherein step (n) comprises the steps of (p) injecting a first portion of the quaternary piastic material into the third moid cavity; (q) cooling the injected first portion of the quaternary plastic material in the fourth mold cavity; (r) injecting subsequent to injecting the first portion of the tertiary plastic material a second portion of the quaternary plastic material into the fourth mold cavity so that the cooled injected first portion of the tertiary plastic material in the fourth moid cavity stabilizes the dimensions of the fourth mold cavity by impeding movement of the second common mold part in relation to the second complementary mold part caused by injecting the second portion of the quaternary plastic material, whereby the second portion of the quaternary plastic material fuses with the cooled previously injected first portion of the quaternary plastic ^ material. 53. A method according to Claim 51 , wherein the primary piastic material is different from the secondary material. 54. A method according to Claim 52, wherein the primary plastic material is the same as the quaternary plastic material and the secondary plastic material is the same as the quaternary plastic material. 55. A method according to Claim 52, wherein the primary piastic material is different from the secondary piastic material and the quaternary plastic material is different from the quaternary plastic material. 56. A method according to Claim 51, wherein at least one of the mold parts includes a protractable and retractable ram-shaped element with one of the ram-shaped element facing the mold cavity, wherein step (g) comprises the steps of, (j) protracting the ram-shaped element to a forward position; and (k) injecting the first portion of the secondary plastic material into the second mold cavity while the ram-shaped element is in the forward position; and -- wherein step (i) comprises the steps of, (I) retracting the ram-shaped element to a rear position; and 0 (m) injecting the second portion of the secondary plastic material into the second moid cavity while the ram-shaped element is in the rear position;

Inventors: SORENSEN JENS OLE, SORENSEN, JENS, OLE
Applicants: SORENSEN JENS OLE, SORENSEN, JENS, OLE
Application year: 1989
Main classification: B29C45
IPC codes: B29C45