CA2508062A1

CA2508062A1 - Pipe forming apparatus for double walled pipe

Info

Publication number: CA2508062A1
Application number: CA002508062A
Authority: CA
Inventors: Manfred A. A. Lupke; Stefan A. Lupke
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-05-20
Filing date: 2005-05-20
Publication date: 2006-11-20

Abstract

The pipe forming apparatus provides for pressurizing of the closed cavities defined between the pipe corrugations and an inner wall of the pipe. Each pipe corrugation is pierced by a piercing member while the corrugation is being molded. A pressure media is introduced into the cavity to force the forming corrugation against the molding surface of the mold block and the inner wall against the cooling plug. This apparatus have particular application for the large diameter pipe.

Description

PIPE FORMING APPARATUS FOR DOUBLE WALLED PIPE
FIELD OF THE INVENTION
The present invention relates to pipe mold equipment and in particular to pipe molding equipment for double-walled pipe where the walls of the pipe cooperate to form generally closed cavities along the length of the pipe. Equipment of this type is used for forming double-wall corrugated pipe.
BACKGROUND OF THE INVENTION
In pipe molding apparatus plastic is provided through passages and die-tooling to outlets for forming of the pipe where the exterior of the pipe is defined by exterior mold blocks. Typically the mold blocks cycle along the die-tooling as part of a continuous conveyer type arrangement or as a reciprocating mold block arrangement.
The forming of double-walled pipe where the pipe has a series of essentially closed cavities along the length thereof, it is particularly advantageous and provides additional pipe strength in a cost effective manner. The outer corrugations cooperate with an inner wall to reinforce the pipe and improve the properties thereof. The inner wall basically provides a smooth surface for the passage of fluid along the length of the pipe. In forming of the pipe, it is important to provide good definition to the outer corrugations and various arrangements have been provided for applying a vacuum force to the mold blocks urging the outer wall into contact with the molding surfaces of the mold blocks. In addition to drawing the plastic against the molding surface, it is important to effectively cool the plastic in an efficient manner. Rapid cooling o.f the plastic can lead to thermal stresses and cracking of the plastic, _ 2 -slower cooling of the plastic allows more time for reduction of thermal stresses, however typically the length of the pipe molding equipment must be extended or slower speeds are required. Therefore it is important to attempt to cool the plastic in a effective manner without unduly effecting the properties of the functional product.
It is known to provide cooling to both the mold blocks as well as to the interior plug of the extrusion tooling.
The present invention provides certain improvements with respect to pipe molding apparatus for Z5 forming of double-walled pipe having generally closed cavities.
SUMMARY OF THE PRESENT INVENTION
In an apparatus for molding plastic pipe having an inner wall forming a series of closed cavities with an undulating outer wall, the apparatus includes a series of mold blocks with a molding surface that collectively defines the outer wall of the plastic pipe. The improvement comprises at least some of the mold blocks including a piercing member moveable between a retracted position generally exterior to the molding surface to a piercing position extending through the molding surface into an associated closed cavity of the plastic pipe.
The apparatus includes means for introducing a pressurized media into the associated closed cavity to force the outer wall into contact with the molding surface .
According to an aspect to the invention the piercing member includes a hollow cavity and at least one vent through which the pressurized media is introduced r CA 02508062 2005-05-20 into the closed cavity.
In a further aspect of the invention the piercing member includes an elongated tube with a piercing tip at one end thereof.
In a different aspect of the invention the at least one vent is provided in a side the tube adjacent to the piercing tip.
l0 In a further aspect of the invention each piercing member includes a pneumatic actuator for controlling the movement thereof. With this arrangement the piercing member is initially positioned in a 25 retractable position and is subsequently moved to a piercing position and then maved to a retracted position prior to discharge of the pipe from the mold blocks. The timing of the actuator can be based on the mold block position.
In a different aspect of the invention at least some of the piercing members have an associated pierce/venting member through which the introduced pressurized media is vented. This arrangement is advantageous in using the pressurized media as a flow through cooling media.
In a further aspect of the invention the flow of pressurized media is controlled to vary the cooling of the plastic pipe.
In yet a further aspect of the invention the pressurizing media is air.
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 i.n which;
Figure 1 is a schematic view of a pipe molding apparatus;
Figure 2 is a schematic view of a series of mold blocks with associated die-tooling for extrusion of double-wall corrugated pipe;
Figure 3 is a sectional view through two mold blocks each mold block having a piercing member; and Figure 4 is a sectional through corrugated pipe illustrating various ports for introducing the pressurizing media and a series of ports for removing of the pressurized media from a pipe configuration.
DETAILED DESCRIPTION ACCORDING TO THE PREFERRED
EMBODIMENTS OF THE PRESENT INVENTION IN WHICH:
Figure 1 schematically illustrates a pipe forming apparatus commonly used for forming corrugated pipe. The apparatus includes an extruder 3 that feeds molten plastic 5 between moving opposed mold blocks 7 and 9.
The moving mold blocks 7 and 9 Passover the die-tooling 14 generally shown in Figure 2. This die-tooling has a first die passage 16 and a second die passage 18 that provide molten plastic to the passage outlets 17 and 19 respectively.
The type of tooling shown in Figure 2 allows forming of the corrugated plastic pipe generally shown ac 20. This corrugated pipe includes an inner wall 22 an undulating 24 with a series of generally closed cavities 26 defined between the inner wall and the outer wall.

Also schematically illustrated in Figure 2 is the introduction 31 of a pressure media to one of the corrugations 13 and preferably a means 33 for exhausting the pressurized media. Basically, each mold block is provided with a mechanism for piercing the outer wall of each corrugation of the pipe as it is being formed to pressurize the cavity 25 and improve the definition o.f~
the corrugation of the pipe as it is forced against the interior molding surface 11 of the mold block.
Figure 3 shows two mold blocks 38 each with a cavity piercing arrangement schematically shown as 39.
Each mold block 38 includes an interior molding surface 11 which effectively forms the corrugating outer wall 24 of the pipe. The inner wall 22 cooperates with the outer wall 24 and forms the generally closed cavities 26.
The piercing arrangement 39 includes a pneumatic actuator generally shown as 60 which is used to move the piercing member 40 from the retracted position generally indicated as 62 to the extended position generally shown as 64. Prior to the pipe being discharged from the mold blocks the piercing member will be returned to the retracted position. Timing of the actuator is typically a function of the mold block position within the apparatus.
A pressurizing media such as air is introduced through inlet 54 provided at one end of the actuator 60.
Basically, the actuator includes a hollow feed tube arrangement for allowing the pressurizing media to pass through the actuator to the piercing member 44. The piercing member includes an elongate passage 42 within the tube member 44. Thus, the pressurizing media is introduced through the center of the piercing member 40 and is free to pass out the ports 48 provided in the sides of the tube. Piercing end 46 is provided at one end of the tube and is used for piercing of the outer wall 24 of the pipe.
As shown in Figure 3 the pressurizing media is introduced into the cavity 26 and effectively applies pressure to the cavity urging the outer wall 24 into contact with molding surface 11 and the inner wall is forced against the cooling plug. Typically, the pressurizing media is air and 1 to 2 Psi pressure is provided for effectively blow molding of the outer wall of the corrugations to the molding surface. This pressure can be varied with the particular molding operation, the extent that the outer wall has cooled prior to the introduction of the pressurizing media etc.
It can be appreciated that pressure is also being applied to the inner wall 22 but this wall remains supported by the interior plug 35 of the die-tooling.
Figure 4 is a section through a pipe illustrating how a series of inlets can be provided about each corrugation and additionally outlets can. be provided for venting of the cavity 26. In this way, the pressurizing media is effectively circulated through the cavity 26 and effective cooling of the plastic of both the outer wall and the inner wall can be provided. As can be appreciated, each inlet and outlet normally requires a separate piercing member. The number of inlets and outlets will vary with each application and the size of the pipe being formed and the forming equipment.
Depending upon the particular arrangement for the pipe forming apparatus different locations for the inlets and outlets will be mare convenient. Typically, the outlets may be slightly smaller than the inlets to provide some resistance to the venting. The venting can _ 7 _ also be controlled by a valuing arrangement.
For some applications the inlet and outlet ports provided in the corrugations are not detrimental to the final use of the pipe and can remain open. In other cases it may be desirable to provide plugs for these ports which can be provided after the piercing members have been removed. It can also be appreciated that sealing layers could be tact welded or otherwise secured to the corrugations 26 to seal the inlets and outlets.
Preferably, this is carried out as part of the molding process or adjacent the discharge of the pipe from the mold blocks.
Z5 Another approach for sealing of the ports involves adapting the piercing member to inject a material into the corrugation that seals the port as the piercing member is withdrawn. A plug type member could also be inserted by the piercing member and plugs the port as the piercing member is withdrawn.
It has been found that this particular apparatus allows the controlled pressurizing of the cavities 26 and improves the definition of the corrugations. In addition, this apparatus can be used to control shrinkage or reduce thermal stresses that may occur during cooling of double-walled corrugation pipe. In addition, by providing venting to the corrugations the pressurized media can be controlled and cycled through the cavity to provide the desired cooling. Therefore in addition to good definition of the corrugations improvements are also realized with respect to the effective cooling of the pipe to maintain desired properties of the double-walled pipe. The more pressurizing of a cavity with the media can allow improvements with respect to cooling of the pipe.

_ g This arrangement is particularly sL~itable for large diameter pipe tin excess of two feet). In addition to better definition and improved cooling some S improvements in farming time can be realized. The actual size of the parts in the corrugations caused by the piercing member may be 1/8 of an inch to 1/4 of an inch.
Other size ports can be used. This process is particularly advantageous as the thickness of the plastic wall of the corrugation and the inner wall increases.
Better definition and in redirection corrugation deformation is realized.
Although various preferred embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that variations may be made without departing from the spirit of the invention or the scope of the appended claims.

Claims

1. In an apparatus for molding plastic pipe having an inner wall forming a series of closed cavities with an undulating outer wall where said inner wall joins with said undulating outer wall at spaced points along the length of said plastic pipe, said apparatus including a series of mold blacks with a molding surface that collectively define the outer wall, the improvement comprising at least some of said mold blocks including a piercing member movable between a retracted position generally exterior to said molding surface to a piercing position extending through said molding surface into an associated closed cavity of said plastic pipe, said apparatus including means for introducing a pressurized media into said associated closed cavity to force the outer wall into contact with said molding surface and force the inner wall against a cooling plug.

2. In an apparatus as claimed in claim 1 wherein said piercing member includes a hollow cavity and at least one port through which said pressurized media is introduced into said closed cavity.

3. In an apparatus as claimed in claim 2 wherein said piercing member includes an elongate tube with a piercing tip at one end thereof.

4. In an apparatus as claimed in claim 3 wherein said at least one part is provided in a side of said tube adjacent said piercing tip.

5. In an apparatus as claimed in claim 1 wherein each piercing member includes a pneumatic actuator for controlling the movement thereof.

6. In an apparatus as claimed in claim 1 wherein at least some of said piercing members have an associated piercing/venting member through which the introduced pressurizing media is vented.

7. In an apparatus as claimed in claim 1 wherein said pressurizing media also provides cooling of the plastic pipe.

8. In an apparatus as claimed in claim 7 wherein said pressurizing media is air.

9. In an apparatus as claimed in claim 8 wherein at least some of said piercing members have an associated piercing/venting member through which the introduced pressurizing media is vented.

10. In an apparatus as claimed in claim 9 wherein said piercing/venting members are provided in said mold blocks.

11. In an apparatus as claimed in claim 1 wherein two or more piercing members are associated with each molding surface partially defining a closed cavity of the pipe.

12. In an apparatus as claimed in claim 1 or 11 including a sealing arrangement for sealing of each port resulting from withdrawal of one of said piecing members.

13. In an apparatus as claimed in claim 12 including each piercing member including means for providing a seal closing the cavity as the piercing member is withdrawn.

14. In an apparatus as claimed in claim 1, 11, 12 or 13 wherein each piercing member has an associated piercing vent member for withdrawing pressurizing media introduced through the associated piercing member.