Classifying – separating – and assorting solids – Sifting – Elements
Reexamination Certificate
1999-07-06
2001-10-23
Walsh, Donald P. (Department: 3653)
Classifying, separating, and assorting solids
Sifting
Elements
C209S401000, C209S405000, C209S044000
Reexamination Certificate
active
06305549
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibrating screen assembly composed of dissimilar materials which is used with a vibrating machine for separating solids and fluids.
2. Prior Art
Vibrating screen assemblies are used on vibrating machines or shakers to separate solid material from liquids and fine solid particles. A frame for the screen assembly may include opposed sides and ends and may include various cross-members and rods. The frame for the screen assembly is removably attached to the vibrating shaker and the screen assembly is vibrated at high frequency by a reciprocating motor.
The dynamic forces brought about by vibration separates the liquid and particles smaller than the pore size of the smallest screen layer. The screen assembly is subject to tremendous stress by virtue of the machinery vibrating it and is subject to stress from the weight of the material to be separated on the top layer of the screen.
While it is possible to replace a screen assembly, frequent replacement entails added cost and down-time for the machinery. Accordingly, extending the life of a screen assembly is highly desirable.
It is advantageous to retain the screen cloth or screen cloths in as tight a condition to the frame as possible. Slackness in the screen cloth or screen cloths may cause undesirable flapping of the screen cloth or cloths. Slackness also may permit the shute strands of the screen cloth to move in relation to the warp strands. This may influence the effectiveness of the screen cloth to filter. It is known that tensioning the screen or screens to the frame will enhance the life of the screen assembly. Indeed, screen tension is believed to be one of the greatest factors to determine the screen life. Accordingly, in some applications, the screen cloth or screen cloths are tensioned prior to being attached and bonded to the frame.
Vibrating screen assemblies may be used to screen materials which contain a heated slurry. In one such application, water is used as a slurry in order to screen calcium carbonate solids. The slurry mixture which is deposited on the top of the screen assembly may be approximately 190° F. and may range up to 250° F.
It is known that as the temperature of solid (and other) materials increases, the average separation of the molecules increases. Accordingly, the materials will expand when heated. The materials that comprise the vibrating screen assembly each have coefficients of thermal expansion. The coefficients of thermal expansion for some common materials are as follows:
CELSIUS SCALE
FAHRENHEIT SCALE
MATERIAL
m
m
°
C
.
×
10
-
6
in
in
°
F
.
×
10
-
6
Aluminum
23.9
13.3
Brass
18.7
10.4
Carbon Steel
10.8
6.0
Cast Iron
10.6
5.9
Magnesium
25.2
14.0
Stainless Steel
17.3
9.6
ABS
95
52
Glass-Filled Nylon
81
45
Glass-Filled Poly-
37
21
propylene
Each time the slurry and the materials to be separated are deposited on the screen assembly, heat is transferred to the frame and the screen cloths. The heat transfer causes the screen cloth and the frame to expand. If the frame is caused to expand greater than the screen cloth, the effect will be for the screen cloth or cloths to be tightened.
It is also believed that at the start-up of the screening operation, the heated slurry materials to be screened are deposited on the center of the screen assembly causing the cross-members and rods to be heated quicker than the sides and ends of the frame.
Accordingly, it is a principal object and purpose of the present invention to provide a screen assembly wherein the frame and screen cloth or cloths are composed of different materials and wherein the frame has a greater coefficient of thermal expansion than the screen cloth or screen cloths.
It is a further object and purpose of the present invention to provide a vibrating screen assembly which is self-tensioning when utilized to screen materials above the ambient temperature at which the screen assembly is fabricated.
SUMMARY OF THE INVENTION
The present invention provides a vibrating screen assembly composed of dissimilar materials for use with a vibrating machine or shaker. The screen assembly includes a frame which is removably held in the vibrating machine or shaker. In a preferred embodiment, the frame is composed of aluminum or aluminum alloy and includes tubular sides which are opposed and parallel to each other. The frame also includes a pair of tubular ends which are likewise opposed and parallel to each other. At each joint where the tubular sides meet the tubular ends, a corner gusset is provided. Extending between the tubular sides are a plurality of tubular cross members. Extending between the opposed tubular ends and extending through the cross members are a pair of solid aluminum rods. The solid aluminum rods are parallel to each other and parallel to the tubular sides.
In the present embodiment, two screen cloths are composed of stainless steel and are woven from a plurality of individual strands. A lower screen cloth is parallel to and adjacent an upper screen cloth. The screen cloths are bonded to the metal frame by high temperature adhesive, such as epoxy. Also, a bead of initially liquid urethane is placed on each of the cross members and is also placed on the frame sides and frame ends to help dampen the movement of the screen cloths during operation against the frame.
The ratio of coefficient of thermal expansion of the aluminum frame is greater than the coefficient of thermal expansion of the stainless steel screen cloths.
To assemble the vibrating screen assembly, the pair of tubular sides is welded to the pair of tubular ends with a corner gusset joining each side and end connection. The plurality of tubular cross members extend between the tubular sides and are welded thereto. The pair of solid rods extend between the tubular ends and pass through each of the cross members.
A high temperature adhesive, such as an initially liquid epoxy, is placed on one side of the frame, on each of the sides and each of the ends. Thereafter, a bead of initially liquid urethane or other dampening material may be placed adjacent the high temperature adhesive on the frame sides and ends and also covers each of the cross members.
The pair of screen cloths, having an outside dimension greater than the frame, are brought together and clamped or held in a jig which places the screen cloths under tension. The combined pair of screen cloths and accompanying jig are then lowered onto the epoxy and urethane. The screen cloths are held in the tensioned position on the frame until the adhesive has cured.
It has been found that the present invention will provide a self tensioning screen assembly when put in use to screen materials at temperatures above that at which it has been assembled.
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Baltzer Terry L.
Howard Bill
Riddle Russell Allen
Head Johnson & Kachigian
Schlak Daniel K.
Southwestern Wire Cloth, Inc.
Walsh Donald P.
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