METHOD AND APPARATUS OF COOLING PRODUCT WITHIN A MOLD

Abstract: A method of forming a plastic product (P) comprises extruding molten plastic into a mold (3, 4) having a mold wall with product shaping interior face. After shaping the product (P) in the mold (3, 4), the method includes introducing gas via a gas inlet (11) through the mold wall (3) onto the product (P) to cool both the product (P) and the mold (3, 4) and then discharging the gas from the mold at a location (19) remote from the gas inlet (11).

Description: TITLE: METHOD AND APPARATUS OF COOLING PRODUCT WITHIN A MOLD FIELD OF THE INVENTION The present invention relates to a method of molding a product including the step of cooling the product while the product is in the mold while at the same time cooling the mold. The invention is particularly used for the formation of molded plastic pipe. BACKGROUND OF THE INVENTION Plastic pipe is generally formed by extruding plastic into a mold tunnel. The pipe is formed by either vacuum forming or blow molding. After the pipe has been shaped, it is typically cooled by cooling of the mold blocks . As the pipe continues down the mold tunnel the cooling becomes less and less efficient because the pipe shrinks producing an air gas between the mold blocks and the pipe. Accordingly, the pipe is insulated from and has difficulty in giving heat off to the mold blocks as the pipe continues down the mold tunnel . SUMMARY OF THE INVENTION The present invention provides a method and apparatus for molding a plastic product with novel means for cooling of both the mold and the product. The invention is particularly applicable to the molding of a plastic pipe. According to the method molten plastic is extruded into a mold having an interior face which shapes the product. After the product has been shaped, gas is introduced through an inlet at the interior face of the mold onto the product and cools both the outer surface of the product and the mold. The gas is then discharged out of the mold through an outlet at a location remote from the inlet . In the case of a plastic pipe, which is formed in a rounded mold tunnel, the cooling gas is introduced through mold block sections on one side of the mold tunnel and is moved circumferentially around the pipe. The method of the present invention can be used in combination with interior cooling to further increase the cooling effect on the product. BRIEF DESCRIPTION OF THE DRAWINGS The above as well as other advantages and features of the present invention will be described in greater detail according to the preferred embodiments of the present invention in which; Figure 1 is a side view of a plastic pipe molding apparatus according to a preferred embodiment of the present invention; Figure 2 is a top perspective view looking down on a pair of mold block sections from the apparatus of Figure 1; Figure 3 is a sectional view through the mold tunnel of the apparatus of Figure 1 showing pipe being vacuum formed according to one preferred embodiment of the present invention; Figure 3a is a sectional view through the mold tunnel of the apparatus of Figure 1 with the pipe being blow formed according to another preferred embodiment of the present invention; Figure 4 is a sectional view through the mold tunnel of the apparatus of Figure 1 showing initial cooling of the pipe; Figure 5 is a sectional view through the mold tunnel of the apparatus of Figure 1 showing final cooling of the pipe; Figure 6 is a sectional view through a mold tunnel of a further preferred mold apparatus. DETAILED DESCRIPTION ACCORDING TO THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION Figure 1 shows a pipe molding apparatus generally indicated at 1. In this apparatus, molten plastic is fed from an extruder 2 to a mold tunnel downstream of the extruder. Pipe indicated at P emerges from the downstream end of the mold tunnel . The mold tunnel is formed by an upper track of mold block sections 3 and a lower track of mold block sections 4. The mold block sections meet with one another to define the mold tunnel generally indicated at 5. Figure 2 shows a pair of side by side mold block sections 4 from the lower track of mold block sections. As will be seen, these mold block sections have an interior face generally indicated at 7 which defines the external shape of the pipe P. In this particular embodiment, the interior face of the mold block sections has alternating lands and grooves to produce a ribbed shaping of the pipe . Mold block sections 4 are particularly designed for vacuum forming of the pipe in that they are provided with small vacuum slits 9 at each trough in the mold block face. For vacuum forming of the pipe, suction is drawn through these vacuum slits which pulls the molten plastic onto the faces of the mold block sections. These vacuum slits may be intermittent or they may be continuous around the semicircular face of each mold block section. Figure 2 shows two slits in each trough of each mold block section, however there may only be one slit or more than the two slits shown for each trough. Mold block sections 3 in the upper track of mold block sections have an identical construction. Figure 3 shows the vacuum forming of the pipe as it occurs in an upstream region of mold tunnel 5. Here it will be seen that the mold block sections 3 and 4, both of which are mounted to mold block carriers 2, are closed tightly with one another in the mold tunnel . A source of vacuum 11 which as shown in Figure 3 is located externally of the mold block section is in direct communication with the small slits 9 in the upper mold block section at discrete locations 16, 17 and 18 through passages 13, 14 and 15 respectively. These passages, as shown, go directly through the wall of the upper mold block section. A similar arrangement is found in the lower mold block section 4 where a source of vacuum 19 again outside of the mold tunnel is in connection with the vacuum slits 9 opening at the face of the lower mold block section through passages 21, 22 and 23 having separate access regions 25, 26 and 27 respectively with the vacuum slits. Figure 3 shows that when vacuum is applied through both the upper and the lower vacuum source, the plastic is pulled onto the interior surfaces of the two mated mold block sections to shape the pipe P. Figure 3a, while using the same mold block sections 3 and 4 shows that the pipe can also be blow molded from air pressure applied internally of the pipe as shown by the arrows in Figure 3a. This air pressure pushes the molten plastic outwardly onto the mold block faces . Regardless of the method of forming the pipe, i.e. either by vacuum forming or by blow molding of the pipe, the pipe is cooled using openings in the mold block faces and in this case by using the vacuum slits 9 through the mold block sections. After the pipe has been shaped and as it continues down the mold tunnel where the plastic starts to set to hold the shape of the pipe, a cooling gas is introduced from one of the mold block sections into the mold tunnel and onto the pipe. Eventually, this cooling gas is drawn out of the mold tunnel through an outlet remote from the location where the gas is introduced to the mold tunnel . More particularly, as indicated by the arrows in Figure 4, cooling gas is introduced to the upper mold block section 3. In the event that the pipe has been vacuum formed, the vacuum while being continued in the upstream region of the mold tunnel is replaced by a flow of cooling gas into the mold tunnel in the more downstream region of the tunnel after the pipe has been shaped and sufficiently set to hold its shape. Passage 11 which now becomes a pathway for the cooling gas. This cooling gas, which may be in a number of different forms including outside ambient air or air which is passed through a cooling device, is forced along the passages 13, 14 and 15 and in this case through the vacuum slits 9 in the upper mold block section. These slits now become inlets into the mold tunnel for directing the cooling gas onto the exterior surface of the pipe P . Figure 5 shows that the pipe, with some initial cooling, shrinks away from the interior surface of the mold sections creating a gap G between the outside surface of the pipe and the interior face of mold tunnel. This allows the cooling gas to be forced circumferentially around the pipe as indicated by the arrows in gap G to the vacuum slits in the lower mold block section where the gas is then drawn out of the mold tunnel. Therefore, the slits in the lower mold block section which continue to be subjected to vacuum, now become gas outlets from the mold tunnel. It is not necessary to introduce cooling gas to the mold tunnel in order to produce some initial shrinkage of the pipe away from the mold tunnel wall. This occurs naturally as a result of normal cooling of the pipe. Therefore, the cooling gas can be introduced after the natural pipe shrinkage which still produces the gap G allowing the cooling gas to be fed into the mold tunnel from one of the mold block sections and around the pipe to the other mold block section. The cooling gas has two benefits. Firstly, it provides faster cooling and setting up of the pipe. Secondly, it reduces the temperature of the mold blocks which results in greater ability of the mold blocks to absorb heat from the pipe which again allows the pipe to cool and set faster than normal. One of the advantages of using the vacuum slits for both the introduction and the discharge of the cooling gas, preferably cooling air, is that the vacuum slits whether they be continuous or intermittent form paths for the cooling air completely through the main body of the mold block sections. Therefore, the cooling air not only runs around and along the interior surfaces of but additionally penetrates into the mold block sections. This substantially enhances cooling the mold block sections. This in turn increases the ability of the mold blocks to cool the pipe particularly after the mold block sections are returned along their endless loops in a much cooler state than normal to the upstream end of the mold tunnel where they are in direct contact with and have the greatest cooling effect on the plastic as it is extruded into the mold tunnel . Figure 6 shows a slightly different mold tunnel design comprising a pair of mold block sections 21 and 25 provided with passages 23 and 27 respectively. These passages first provide vacuum paths during formation of the pipe P and later act as cooling gas inlet and outlet passages. They feed into the interior of the mold tunnel along the parting faces of the mold block sections where they meet as indicated at 29 rather than through holes provided directly in the walls of the mold block sections. If desired, for faster cooling of the pipe in the mold tunnel, a cooling medium such as a cooling plug or even cooling gas can be introduced interiorly of the pipe simultaneously with the exterior cooling of the pipe. In another embodiment of the invention a cooling gas is introduced at the interior face of the mold tunnel, e.g. through the slits in the mold blocks, along the parting faces of the mold block sections, or through other inlets provided in the mold block faces. After cooling both the product and the mold blocks the gas is discharged through the downstream end of the mold tunnel which is open for releasing the pipe from the mold tunnel as earlier described with respect to Figure 1 of the drawings. Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art, that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.

Claims: THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS: 1. Apparatus for forming a plastic product, said apparatus comprising an extruder, a mold region which receives molten plastic from said extruder, said mold region having a mold wall with a product shaping interior surface, a gas inlet through said mold wall and through which gas is introduced to said mold region onto and cooling both the product and the mold wall and a gas outlet which is remote from the gas inlet and through which the gas is discharged from the mold region. 2. Pipe molding apparatus comprising an extruder and a mold tunnel which receives molten plastic from said extruder to shape the pipe, said mold tunnel having a downstream open end for releasing the pipe from the mold tunnel, said mold tunnel being formed by first and second mold block sections, all of said mold block sections having interior faces which define shape of the pipe, said first mold block sections having first wall openings through the interior faces thereof, means for passing a gas into said mold tunnel through said first wall openings of said first mold block sections onto and cooling both the pipe and the interior faces of the mold block sections and then out of the mold tunnel through gas outlet means remote from said first wall openings. 3. Pipe molding apparatus as claimed in Claim 2 , wherein said second mold block sections have second wall openings therethrough to form said gas outlet means . 4. Pipe molding apparatus as claimed in Claim 2, wherein said downstream end of said mold tunnel provides said gas outlet means. 5. Pipe molding apparatus as claimed in Claim 3, wherein all of said wall openings are connected to a vacuum source for vacuum forming the pipe in an upstream region of the mold tunnel prior to cooling the pipe. 6. Pipe forming apparatus as claimed in Claim 2, including an air cooling device which cools the gas before entering the mold tunnel . 7. Pipe forming apparatus as claimed in Claim 2 including a pressure source providing positive gas pressure internally of the pipe for blow molding thereof. 8. A method of forming a plastic product, said method comprising extruding molten plastic into a mold region having a mold wall with a product shaping interior face, shaping the product on the interior face of the mold wall and then passing gas through gas inlet means through the mold wall and opening at the interior face of the mold wall onto and cooling the product and the mold wall in the mold region and then discharging the gas out of the mold region through gas outlet means remote from the gas inlet means . 9. A method as claimed in Claim 8, wherein said gas outlet means is provided through the mold wall opening at the interior face of the mold wall. 10. A method as claimed in Claim 6, wherein the gas is air taken from a cooling device. 11. A method as claimed in Claim 6, wherein the gas is ambient air taken from externally of said mold region. 12. A method as claimed in Claim 8, wherein the gas flows into said mold region following shrinkage of the product away from the interior face of the mold wall to produce a gap therebetween, and wherein the gas also flows into the gap between the product and the interior face of the mold wall . 13. A method as claimed in Claim 8, wherein the air causes shrinkage of the product away from the interior face of the mold wall to produce a gap therebetween, and wherein the gas flows into the gap between the product and the interior face of the mold wall. 14. A method as claimed in Claim 8, wherein the gas is discharged through an open downstream end of the mold region . 15. A method of forming a pipe, said method comprising extruding molten plastic into an elongated mold tunnel surrounded by a tunnel wall, shaping the pipe against a circular interior surface of the mold tunnel, flowing gas through first openings in the tunnel wall from one side of the mold tunnel onto and around both the pipe and the interior surface of the mold tunnel to provide cooling thereof and then drawing the gas out of the mold tunnel through the second openings in the tunnel wall at the other side of the mold tunnel. 16. A method as claimed in Claim 15, wherein said mold tunnel is formed by mating first and second mold block sections which are moved through said mold tunnel and wherein the gas flows into said mold tunnel through said first mold block sections on the one side of the mold tunnel and is drawn out of the mold tunnel through said second mold block sections on the other side of the mold tunnel . 17. A method as claimed in Claim 15, comprising first using all of said wall openings as vacuum passages to vacuum form the pipe within a first upstream region of the mold tunnel and then using said first wall openings as air inlets to the mold tunnel and said second wall openings as air outlets from the mold tunnel in a second region downstream of the first region of the mold tunnel . 18. A method as claimed in Claim 15, wherein the pipe is blow molded in the mold tunnel . 19. A method as claimed in Claim 15, wherein the gas flows into the mold tunnel following initial cooling and shrinkage of the pipe away from the interior wall surface to produce a gap therebetween and wherein the gas then flows into the gap circumferentially around the pipe and along the interior surface in the mold tunnel . 20. A method as claimed in Claim 15, wherein the gas causes shrinkage of the pipe away from the interior surface of the mold tunnel to produce a gap therebetween and wherein the gas flows through the gap circumferentially around the pipe on the interior surface in the mold tunnel . 21. A method as claimed in Claim 15, including additional cooling of the pipe from the interior thereof. 22. A method of forming pipe, said method comprising extruding molten plastic into an elongated mold tunnel surrounded by a tunnel wall having a circular interior surface defining shape of the pipe and an open downstream end from which the pipe is released from the mold tunnel, shaping the pipe against the interior surface of the mold tunnel, passing air through air openings through the tunnel wall onto and cooling both the pipe and the interior surface of the mold tunnel and discharging the air through the downstream end of the mold tunnel. 23. A method of forming pipe comprising extruding molten plastic into a elongated mold tunnel surrounded by a tunnel wall having an interior pipe shaping face, producing a vacuum by drawing air out of the mold tunnel through openings in the tunnel wall in a first upstream region of the mold tunnel to pull the plastic onto and to shape the pipe against the interior face of the mold tunnel, moving the pipe to a second region downstream of the first region of the mold tunnel and flowing a gas into the mold tunnel through said wall openings to cool both the tunnel wall and the pipe within the second region of the mold tunnel . 24. A method as claimed in Claim 23, wherein said mold tunnel has an open downstream end and wherein the gas after cooling the pipe and the tunnel wall is discharged through the downstream end of the mold tunnel. 25. A method of forming pipe comprising extruding molten plastic into an elongated mold tunnel surrounded by a tunnel wall formed by first and second mold block sections which mate with one another from opposite sides of the mold tunnel, said mold block sections having interior surfaces which define shape of the pipe, producing a vacuum through openings in the first and second mold bloςk sections in a first upstream region of the mold tunnel to pull the plastic onto and to shape the pipe against the interior surfaces of the mold block sections, moving the pipe to a second region downstream of the first region in the mold tunnel, flowing a gas into the mold tunnel through the openings in the first mold block sections around the pipe to the second mold block sections and drawing the gas out of the mold tunnel through the openings in the second mold block sections while the pipe is in the second region of the mold tunnel to cool both the mold block sections and the pipe within the mold tunnel.

Inventors: LUPKE MANFRED A A, LUPKE STEFAN A, LUPKE, MANFRED, A., A., LUPKE, STEFAN, A.
Applicants: LUPKE MANFRED ARNO ALFRED, LUPKE STEFAN A, LUPKE, MANFRED, A., A., LUPKE, STEFAN, A.
Application year: 1998
Main classification: B29C47
IPC codes: B29C33, B29C35, B29C47, B29C49