Liquid purification or separation – Filter – Within flow line or flow line connected close casing
Reexamination Certificate
1998-06-25
2001-01-30
Savage, Matthew O. (Department: 1723)
Liquid purification or separation
Filter
Within flow line or flow line connected close casing
C055S510000, C156S073100, C210S455000, C210S457000, C210S484000, C210S493200, C210S497010
Reexamination Certificate
active
06179131
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates assemblies of two or more thermoplastic components, and in particular, to a method for connecting two or more thermoplastic components together by an improved fusion-welding technique and to an improved fusion-welded assembly.
2. Description of the Related Art
One of the notable advantages of thermoplastic materials, such as, for example polyethylene, perfluoroalkoxy, hexafluoropropylene, polypropylene, and polyvinyldifluoride, in fabricating many industrial products is that, in many instances, components made of such materials can be welded together to form assemblies. There are many methods known in the plastic arts for welding thermoplastic components together. For example, the filter cartridge industry has used various welding techniques to fabricate filter cartridges, comprising thermoplastic housings and thermoplastic-encased filter elements, including spin-welding, contact-welding, injection-welding, and fusion-welding. In fusion welding, the mating surfaces of two or more thermoplastic components are heated to a molten state, or “wetted”, for example, by an infrared (IR) heating device, before the components are mated together. After heating the mating surfaces, but before the surfaces cool, the components are pressed together so that the wetted mating surfaces of the components contact one another. As the mating surfaces cool, they fuse together forming an intermingled thermoplastic interface, thus securing the components to one another.
Of the various thermoplastic welding techniques known, many skilled in the art prefer IR fusion-welding methods because of certain advantages provided by such methods. One known advantage of IR fusion-welding is that it produces a stronger bond between welded components than that produced by other thermoplastic welding techniques, because infrared radiation heats the thermoplastic materials internally and penetrates deeper into the thermoplastic materials. Accordingly, the resulting fusion bond between the welded components provides more than a mere adhesion of the component surfaces. Another appreciated advantage of IR fusion-welding over other thermoplastic welding techniques is that IR fusion-welding methods do not produce undesirable by-products or debris, which is especially important when a production environment is required to be clean. For example, many skilled in the art of filter cartridge manufacturing prefer IR fusion-welding over alternative welding techniques, such as spin-welding, in which debris is created while generating the necessary frictional heat through spinning of the thermoplastic components relative to one another. IR fusion-welding may also be preferred over contact-welding methods, because some contact-welding applications tend to melt the thermoplastic components excessively.
Despite its known and appreciated advantages, including, but not limited to the above, the inventors of the present invention have found the use of conventional IR fusion-welding techniques to be either impracticable or inefficient in certain situations. For instance, the inventors have found conventional IR fusion-welding methods to be unsuitable when the thermoplastic components to be welded have complex non-coplanar geometries which make it difficult, if not impossible, to apply plastic-melting radiation to only the mating surface of one or more of the thermoplastic components to be welded together without applying too much radiation to other surfaces of the component. This situation arises when the shape of a thermoplastic component to be welded is such that when the mating surface of the component is presented to the IR heating device for wetting the mating surface prior to welding, another surface of the component which forms no part of the mating surface is actually closer to the IR heating device than the mating surface. Thus, the closer surface is heated, and perhaps overheated and damaged, before the mating surface is sufficiently wetted.
FIG. 6
illustrates one such example. A first thermoplastic member shown in
FIG. 6
is a cylindrical member
22
having a sidewall
24
and radial endwall
26
with a bore
28
formed in its center. A second thermoplastic member is an insert
10
having a cylindrical body
12
, sized and shaped to fit within the bore
28
, with a peripheral, radially-extending flange
14
. The insert may have a closed bottom surface
30
as shown, or the insert may have an open end. A mating surface
16
of the insert is defined on the underside of the flange
14
. The mating surface
16
contacts and mates with a portion of the endwall
26
of cylindrical member
22
surrounding the bore
28
when the cylindrical body
12
of the insert
10
is inserted into the bore
28
of cylindrical member
22
.
To weld the insert
10
to the cylindrical member
22
by a conventional IR fusion-welding technique, the insert
10
would be first aligned coaxially with the bore
28
of the cylindrical member
22
in a spaced-apart relation with respect to the cylindrical member
22
, and the insert
10
would be oriented as it would be disposed within the cylindrical member
22
. An infrared heating device, such as an IR platen
20
, would be positioned between the insert
10
and the cylindrical member
22
, and the mating surface
16
and end wall
26
would be subjected to IR radiation until sufficiently wetted. Next, the IR platen
20
would be removed and the insert
10
would be inserted into the cylindrical member
22
until the mating surfaces
16
and
26
contact one another and fuse together as the thermoplastic cools.
Problems arise here, however, because of the non-coplanar geometry of the insert
10
. The mating surface
16
of the insert
10
, which needs to be heated, is recessed relative to a bottom surface
30
of the insert
10
, which is actually closer to platen
20
than the mating surface
16
. If the mating surfaces
26
,
16
of the cylindrical member
22
and the insert
10
were to be irradiated, the end surface
30
of the insert
10
would melt before the mating surface
16
is sufficiently heated and wetted, thus rendering the mating surface
16
essentially inaccessible to the radiation of the IR platen
20
. Therefore, IR fusion welding is not a practical option for welding such an insert into a cylindrical member. Thus, to attach the insert
10
into the cylindrical member
22
, one skilled in the art would heretofore have resorted to other, less desirable welding techniques, such as spin-welding.
Other problems attendant to conventional IR fusion welding techniques and other thermoplastic welding techniques, such as spin welding, arise when a welded thermoplastic assembly includes more than two components welded together. After the first two components of the assembly are welded together, structural and geometrical interferences created by the two connected components can make it difficult to weld subsequent components to the assembly.
Accordingly, while IR fusion welding provides certain advantages over other thermoplastic welding techniques, geometrical or other limitations can make it impracticable to employ IR fusion welding to connect two or more thermoplastic components to form a thermoplastic assembly.
SUMMARY OF THE INVENTION
An object of the present invention, therefore, is to overcome the disadvantages associated with conventional IR and other thermoplastic welding techniques by providing methods of IR fusion-welding thermoplastic members having complex, non-coplanar geometries and methods of IR fusion welding assemblies of more than two components in a single fusion welding step and to provide a thermoplastic assembly fabricated using such methods. Thus, this object is achieved in accordance with the principles of the present invention by providing a fusion-welded thermoplastic assembly which comprises a first thermoplastic element, a second thermoplastic element connected to the first thermoplastic element at an edge of the first thermoplastic element; and a thermoplastic fusion element disposed a
Knebel Kevin J.
Muzik Thomas A.
Fleming Michael
Pillsbury Madison & Sutro LLP
PTI Technologies, Inc.
Savage Matthew O.
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