Plastic and nonmetallic article shaping or treating: processes – Forming continuous or indefinite length work – Layered – stratified traversely of length – or multiphase...
Reexamination Certificate
1998-09-25
2001-01-16
Pyon, Harold (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Forming continuous or indefinite length work
Layered, stratified traversely of length, or multiphase...
C264S173120, C264S173160, C425S133100, C425S464000
Reexamination Certificate
active
06174478
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to triple-wall pipe extruders and particularly to a method and apparatus for simultaneously extruding two triple-wall pipes.
Single-wall plastic pipes made of solid PVC are in widespread use throughout the world. PVC pipe is lightweight, inexpensive and strong. PVC pipe has become a standard for many uses, such as, for example, for drains. In some cases, one single-wall pipe is extruded through a single die, while in other cases two single-wall pipes are simultaneously extruded by connecting a two channel Y-block between the extruder and a pair of dies.
For many applications, single-wall PVC pipe is somewhat over-designed, resulting in a waste of materials. In order to reduce waste, so-called triple-wall PVC pipes are used for many applications. A cross-sectional view of a typical triple-wall pipe
10
is shown in FIG.
4
. Pipe
10
includes an inner wall
12
which is made of solid PVC plastic, a middle wall
14
which is made of PVC foam, and an outer wall
16
which is made of solid PVC plastic. Triple-wall PVC pipe is much lighter in weight than a single-wall pipe of the same thickness and, in addition, substantially less material is used. In some instances, a weight reduction as high as 29% has been achieved while still consistently passing the impact and strength requirements of ASTM-F-891.
The prior art includes many devices which are directed to extruding a triple-wall pipe, or more particularly, to dies which are designed to direct the output from a plurality of extruders into a format which will solidify into a triple-wall pipe. For example, U.S. Pat. No. 5,620,714 issued to Veen, discloses a distributor head for forming a tubular profile from one or more streams of extruded thermoplastic material. Veen discloses a die which includes one or more input channels for connection to one or more extruders and these channels divide one or more times before connecting to three concentric circular output channels at the opposite side of the die. Veen discloses use of three extruders, as shown in
FIG. 1
, including a first extruder
18
which provides thermoplastic material which forms the outer wall of a pipe, a second extruder
20
which provides thermoplastic material to form the middle or foam core wall of a pipe, and a third extruder
22
which provides thermoplastic material which forms the outer wall of a pipe. These extruders feed a die
24
which extrudes the thermoplastic material into concentric cylindrical walls which are then cooled within a cooling device
26
with the completed triple-wall pipe exiting the output opening
27
of cooling device
26
.
A further prior art disclosure related to a die for shaping the output from a dual extruder system into a triple-walled pipe is shown in FIG.
2
. This drawing is found in U.S. Pat. No. 4,846,648 issued to Spence et al., and entitled “Triple-wall Foam Co-Extrusion Apparatus.” As shown in
FIG. 2
, Spence discloses a die apparatus
24
which includes a first extruder connection channel
28
and a second extruder connection channel
30
. The first extruder connection channel
28
is designed for connection to a first extruder (not shown) in order to receive thermoplastic material, such as PVC, which is used to form the solid inner and solid outer wall of a triple-wall pipe, and the second extruder connection channel
30
is used to receive foam thermoplastic material from a second extruder (not shown) which is then fed through the die in order to form the middle wall or foam core of the triple-wall pipe.
In order to properly operate a single or a dual extruder system to form a triple-wall pipe it is desirable to create a die which does not constrict the flow of thermoplastic material, which delivers thermoplastic material at the proper rate to form an inner and outer wall and foam core of uniform thickness, and finally, a die which is well suited to the particular output capacity of the extruders to which it is connected. Experience has shown that extruders used to form the middle or foam core wall of a triple-wall pipe are typically not used to their full capacity due to the smaller amounts of thermoplastic material which is required to form the middle or foam core wall. This is particularly true with respect to the formation of smaller diameter pipes. Therefore it would be preferable to devise a method and apparatus for utilizing the full capacity of the extruders used to produce the foam thermoplastic material for the middle wall of a triple-wall pipe.
As previously discussed, the Spence die shown in
FIG. 2
requires two extruders to produce one triple-wall pipe. Accordingly, four extruders are required to produce two triple-wall pipes at the same time. Providing a means to produce a greater amount of pipe in the same time frame with fewer extruders would increase the energy efficiency and lower the energy cost of the production line. The foam extruder would operate within a higher range of its capacity and there would be no heat loss from the additional tooling required for the four-extruder process. The invention would also save on floor space and require lower maintenance costs versus the four-extruder method.
OBJECTS OF THE INVENTION
It is therefore one object of the invention to provide an apparatus and method to more fully utilize the output of an extruder used to form the middle or foam core wall of a triple-wall pipe.
It is another object of the invention to provide an apparatus and method for increasing the output capacity and production efficiency of a three extruder system for producing triple-wall pipe.
It is yet another object of the invention to provide a method and apparatus for producing two triple-wall pipes with three extruders in the same amount of time that prior art systems produce two triple-wall pipes with at least four extruders.
SUMMARY OF THE INVENTION
In accordance with one form of the invention, there is provided an apparatus and method for producing simultaneous extrusions of two triple-wall pipes with three extruders. A first extruder is connected to a first die in order to form the inner and outer wall of a first pipe and a second extruder is connected to a second die in order to form the inner and outer walls of a second pipe. A connector is connected to a third extruder and to the first and second dies for providing material for the middle walls for both the first and second pipes. Preferably, the connector is a Y-block.
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International Search Report, mailed Jan. 26, 2000, for PCT/US 99/22136, which was filed Sep. 23, 1999.
Carter & Schnedler, P.A.
Del Sole Joseph S.
Pyon Harold
Silver-Line Plastics Corporation
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