Claims
- 1. A method for making a modular screen plate for use in a pulp pressure screening apparatus, said method comprising:
- forming undulations in relatively thin sheet material by bending;
- shaping said formed sheet material into a generally cylindrical shape;
- creating openings through said material;
- placing rigid support members at opposite ends of said cylindrically shaped material; and
- securing the position of said rigid support members relative to each other by fastening therebetween releasable tieing members.
- 2. The method for making a screen plate as defined in claim 1, in which said step of creating openings is performed by a punch.
- 3. The method for making a screen plate as defined in claim 1, in which said step of creating openings is performed by laser burning.
- 4. The method for making a screen plate as defined in claim 1, in which said step of forming undulations is performed by complimentary forming members operated on opposite sides of said sheet-like material, bending and forming said sheet-like material into desired undulations without stretching the sheet-like material.
- 5. A method for making a screen plate as defined in claim 1, in which said step of creating openings is performed before said step of forming undulations.
- 6. The method for making a screen plate as defined in claim 1, in which said step of creating openings is performed after said step of forming undulations.
- 7. The method for making a screen plate as defined in claim 1, in which said step of creating openings through said material is performed by punching holes therein, while forming undulations in the sheet material.
FEATURES OF THE INVENTION
This application is a division of application Ser. No. 07/206,151, filed June 10, 1988 now U.S. Pat. No. 4,954,249.
BACKGROUND OF THE INVENTION
The present invention relates to improvements in apparatus for processing wood pulp and other fibrous fluid suspensions, and methods for manufacturing the apparatus More particularly, the apparatus and methods relate to an improved screen for wood pulp, for removing foreign particles from a pulp slurry.
In processing wood pulp, screens are utilized to separate acceptable fiber from unacceptable constituents in a slurry. In a typical screen, the slurry flows through a perforate, cylindrical screen plate, which may be smooth, or which may present a contoured surface toward the stock flowing through the screen, to increase the effective screening area. The screen plate openings are formed in different hole or hole and slot combinations for optimizing screening performance To aid in passage of the acceptable pulp through the screen plate, and to avoid plugging, pulsations are generated in the slurry such as by passing a hydrofoil-shaped member past the screen plate In order to give the screen plate strength to withstand the pressure differential across the surface, and to increase the screening capacity by presenting increased screening area, it has generally been the practice to provide a thickly-walled screen plate which is machined to present the desired surface. Machining the desired contour has required a time consuming and expensive process Because of manufacturing restrictions in the machining process imposed at least in part by the machine tools themselves, total available open accepts flow area has been limited in known screen plates, and the final shape of the screen plate has been a compromise between the limitations of machining and the desired optimum screen shape.
In addition to the expensive costs of production and manufacturing, the type of screen described has been expensive to use and maintain in that, even if only a small area of screen is damaged, the entire screen plate, which includes the screening surface, mounting surfaces and support members must be replaced, thereby presenting a costly operating expense.
An additional problem encountered in operating screens using known screen plates is premature wear due to contaminants. In recycling waste paper, contaminants such as metals, sand, plastic, and glass are often present, and screen plates utilized to remove these contaminants experience rapid wear. In some instances, screen plates have been known to last less than seven days before failure has occurred When heretofore known screen plates are used in such screens, the cost and time required for screen plate replacement is significant.
It is, accordingly, an object of the present invention to provide a screening apparatus and a screen plate design wherein the necessity of an expensive machining manufacturing process is eliminated.
A further object of the present invention is to provide a screen plate structure wherein various modifications and alternatives of screen plate shape can be attained without prohibitive manufacturing costs, and wherein contours can be utilized which were heretofore not considered possible because of manufacturing limitations.
A further object of the present invention is to provide a screen plate structure wherein, for a given screen plate area, increased screening capacity is possible for increased throughput pulp screening rates, and wherein a variety of sizes and shapes are possible for the screen plate openings.
Another object of the present invention is to provide a screen plate forming process and a screen plate structure which can utilize relatively thin material to produce an aggressive profile for increasing the hydraulic capacity of the screen.
Yet another object of the present invention is to provide a modular screen plate structure which simplifies screen plate changing and which eliminates the need to change an entire screen plate when only a portion of the plate is damaged or worn.
A still further object of the present invention is to provide a screen plate structure and manufacturing process therefor which substantially reduce the manufacturing costs of a screen plate while improving the screening efficiency and throughput thereof.
Still another object of the present invention is to provide a screen plate structure and method of manufacturing which is more resistant to abrasive wear than heretofore known screen plates, thereby increasing the useful life of the screen plate when screening slurries containing highly abrasive contaminants.
In accordance with the concepts and objects of the invention, a screen plate is presented wherein relatively thin material is formed into a desired shape or contour, and the screen shape is formed in predetermined lengths and assembled into a modular type assembly. Forming the contours can be performed by stamping, pressing, or other bending techniques not requiring machining.
The various shapes or contours into which the material is formed provide mechanical strength and rigidity, which allow using thinner material than that previously used for screen plates. The thinner material allows for forming more aggressive contours, and makes possible the use of slot cutting techniques other than machining. Thus, thinner material properly formed with new and different slot openings can increase screening efficiency and capacity while retaining or even improving screen plate strength.
With the use of thin material, a laser beam may be utilized to cut openings or slots ranging from 0.004" to 0.020" wide. These openings may be formed in greater lengths than are presently available from currently used machining methods, and this increases the total available open accepts flow area and production rate for a given size screen plate.
The modular design employs a rigid, strengthening pilot back ring and a varying number of mid or support rings and flange rings, all connected by tie rods with the annular screen plates clamped between each ring. This permits various hole and slot combinations within the same assembly. The modular construction provides an inner contour permitting very close foil to plate gap settings. When a given section of the screen plate is damaged or worn out, only that section need to be replaced. The support rings, tie rods, and undamaged and unworn screen plate sections can be reused, thereby substantially reducing costs for repairing worn or damaged screens.
For highly abrasive applications, abrasive resistant inserts can be inserted in the screen plate and retained by the retaining rings of the modular construction. As wear occurs, the inserts can be replaced at much less cost than replacing entire screen plates
Other objects, advantages, and features will become more apparent with the teaching of the principles of the present invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims, and drawings, in which:
US Referenced Citations (11)
Foreign Referenced Citations (8)
| Number |
Date |
Country |
| 18957 |
Jun 1914 |
DKX |
| 25742 |
Jun 1883 |
DE2 |
| 39216 |
Nov 1886 |
DE2 |
| 561779 |
Sep 1932 |
DE2 |
| 148308 |
May 1981 |
DEX |
| 1360820 |
Dec 1987 |
SUX |
| 519680 |
Apr 1940 |
GBX |
| 2195911 |
Apr 1988 |
GBX |
Divisions (1)
|
Number |
Date |
Country |
| Parent |
206151 |
Jun 1988 |
|
Patent Grant
5023986
