Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
2001-12-19
2004-07-06
Colaianni, Michael (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S261000, C264S271100, C264S277000, C264S328100
Reexamination Certificate
active
06759000
ABSTRACT:
FIELD OF INVENTION
This invention concerns screens for use as filters in vibratory filtration equipment such as shakers that are used in the oil drilling industry for separating solids from the liquid phase of oil and water based muds retrieved from drilling operations. In particular the invention is concerned with the construction and manufacture of supporting frames over which filtering material such as woven wire cloth is stretched and secured to form the screens and to the re-use of such frames.
BACKGROUND
Examples of filtering machines in which such screens are used are contained in UK 2237521 and UK 2229771.
One such screen is described in PCT/GB95/00411 (W095/23655).
The earlier design of screen extends the life of a screen by providing a sacrificial support cloth of woven wire below an upper woven wire cloth of harder wearing material than that of at least the surface of the wire from which the lower cloth is woven, so that wear due to rubbing and vibration during use occurs to a greater extent in the lower cloths than in the upper cloth. The specification also describes an improved design of frame across which woven wire cloths can be tensioned and bonded by adhesive, to form a sifting screen, in which the frame is proposed to be formed from glass reinforced gas blown polypropylene with elongate metal reinforcing elements or rods buried in the GRP. The improved frame construction is shown in
FIGS. 3
to
8
of the earlier specification.
It is an object of the present invention to provide an improved method of constructing such a frame and an improved frame for use as the support for layers of woven wire cloth, an improved screen formed-from such a frame, and a frame which can be reused under some circumstances.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a method of constructing a polymer support frame over which woven wire cloth is to be stretched and secured to form a sifting screen comprises the steps of locating in a mould tool a wire frame assembly comprising two parallel spaced apart arrays of reinforcing wires, closing the tool, injecting liquid polymer so as to wholly encapsulate the wire frame and to form an article having an open central region crisscrossed by intersecting orthogonal ribs bounded on all sides by a rigid flange, in which each of the ribs includes two parallel spaced apart wires of the said wire frame assembly, permitting the polymer to cure, and opening the tool, and removing the moulded article.
By arranging for two parallel spaced apart wires to extend through each of the ribs, one near one edge and the other neaer to the opposite edge of the rigs, each rib has the stiffness of a beam, and the resulting frame has high rigidity and resistance to bending, yet remains relatively lightweight.
Preferably the wire frame is selected so as to impart sufficient structural rigidity to the support frame as to prevent deflection thereof and consequent changes in the tension in the wire cloth when fitted thereto.
Additionally the wire frame is selected so as to impart sufficient strength to the support frame as to allow the latter to withstand shear stresses introduced as the frame is clamped into a vibratory screening machine.
Typically the wire frame is formed from high tensile straightened steel wire, bent as required, and in a preferred arrangement the wire is of 2.5 mm diameter.
The invention also provides a method of making a reinforcing wire frame for use in the above method of making a support frame, comprising the steps of:
equally spacing apart cut lengths of wire in a jig to form a first array,
locating thereover a second equally spaced array of cut lengths of wire at right angles to the first array,
resistance welding the wires of the two arrays at all the points of intersection so as to form a first rectilinear matrix
similarly positioning two similar arrays of similarly cut lengths of wire in a jig and resistance welding the points of intersection of the orthogonal wires so as to form a second, similar rectilinear matrix,
bending in a press break the protruding lengths of wire on at least two of the four sides of one of the rectilinear matrices, so as to bend each protruding section first in a generally upward sense and then at a point nearer to its end in a downward sense so that the end region of each protruding length extends parallel to the plane containing the matrix, but is displaced therefrom, and
and thereafter resistance welding the displaced ends of the protruding wires of the said one matrix to the protruding ends of the wires of the other matrix.
The welding may be in part effected through the intermediary of transversely extending filler wires, so that intersections are provided where welds are to be formed between parallel protruding ends of the reinforcing wires, and the filler wires facilitate the resistance welding of the parallel protruding ends.
Preferably the wire frame fabrication is assembled so that each matrix is bowed in an outward sense, opposite to the other.
During moulding it has been found that the pressure within the mould tool can distort the framework so that the outward bowing of the opposite faces of the framework can be replaced by significant inward bending—so destroying the alignment of the long rods within the upper and lower edges of the interstices of the moulded frame. To avoid this it is proposed that at least one spacer is located within the framework, so that if there is any tendency for the rod arrays to collapse inwards, the spacer will present this collapse occurring.
Preferably a plurality of spacers are located within the wire frame fabrication, each attached to one or other of the matrices so as to extend towards the other, whereby any tendency for the matrices to collapse inwards during moulding, is resisted by the spacers.
In one embodiment each spacer comprises a length of wire bent to form a shallow U with its two ends bent outwards to form two in-line lugs by which it can be welded to the underside of one of the wires which form one of the matrices, with the crest of the U section in close proximity to one of the wires of the other matrix, whereby the spacer will maintain a given dimension between the two matrices if the fabrication is subjected to a collapsing force during moulding, so causing the crest to engage the said wire of the other matrix.
The invention also provides a method of moulding a support frame in a mould tool as aforesaid around a wire frame fabrication as aforesaid wherein an inward force is exerted on opposite faces of the fabrication within the mould tool by fingers protruding inwardly from the inside faces of the tool, to externally engage the opposite matrices of the fabrication when the tooling closes.
In accordance with this method, the fingers sandwich the fabrication in position and produce just the required inward movement of the two oppositely bowed matrices to render them parallel and spaced apart by the desired distance.
Typically the fingers comprise inwardly projecting pegs which align with crossing points of wires in the upper and lower reinforcing matrices, to space the matrices from the corresponding upper and lower internal surfaces of the mould tool and ensure that the matrices are buried within the plastics material which is injected into the mould tool during the manufacturing process.
Preferably the ends of the peas taper to an edge, or a point.
After the mould tool is opened and the protruding pegs disengage from the struts, openings are left in the polymer. Preferably therefore the method further comprises plugging the openings with plastics material or filler.
Typically the wire frame fabrication is supported within the tooling by means of retractable pins which protrude through the tooling wall to engage the fabrication and accurately locate it within the tooling.
The pins may be retracted as the tooling opens after the moulding step has been completed.
Conveniently the pins align with protruding ends of wires making up the fabrication and are separably joined to the ends of the wires by means of sleeves of plastic
Bailey Arthur Robert
Cook Gordon James
Hartnup George Charles
Hughes Andrew
Stewart Dugald
Barnes & Thornburg
Colaianni Michael
Fontaine Monica
United Wire Ltd.
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