US3631918A

US3631918A - Vent for core boxes and the like

Info

Publication number: US3631918A
Application number: US48935A
Authority: US
Inventors: Charles W Barrett
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-06-19
Filing date: 1970-06-19
Publication date: 1972-01-04
Anticipated expiration: 1989-01-04

Abstract

A vent comprising elongated flow passageways through a thin sheet having thin fingers forming at least one of the two opposite side edges of the flow passageway with the top surface of the fingers being generally parallel with the top surface of the sheet. The width of the flow passageways is less than the particle size of the material to be screened from the passing gas, and the fingers are cantilevered, preferably from adjacent one end for maximum flexibility of the fingers. The flexing of the fingers provides a self-cleaning action which may be produced by the passage of gases through the passageways or may be produced by a change in temperature. The sheet material preferably has a thickness that is approximately no greater than the particle size of the material being screened, and in the preferred embodiment, the fingers are made integral with the sheet. This is accomplished by forming an irregular opening through the sheet material, which opening has a width that is less than the particle size of the material to be retained. This opening in some instances will be tapered to provide greater width adjacent the bottom side of the sheet than adjacent the top side of the sheet, and the vents are preferably made by etching out the irregular opening with an acid.

Description

Unite States Patent [7 2] Inventor Charles W. Barrett 2401 S. Wayne Road, Westland, Mich. 48185 [21] Appl. No. 48,935 [22] Filed June 19, 1970 [45] Patented Jan.4,1972

Continuation of application Ser. No. 744,143, July 11, 1968, now abandoned. This application June 19, 1970, Ser. No. 48,935

[54] VENT FOR CORE BOXES AND THE LIKE 22 Claims, 9 Drawing Figs.

[52] US. Cl 164/410 [51] 1nt.Cl B22c 23/00 [50] Field of Search 164/410, 234

[56] References Cited UNITED STATES PATENTS 2,238,506 4/1941 Rienacker 164/410 2,482,330 9/ 1949 Dudzinski.... 164/410 3,188,701 6/1965 Mc1ntyre.. 164/410 3,214,803 11/1965 Amt 164/410 3,529,656 9/1970 Levy 164/410 X u q I I a I,

Primary ExaminerRobert D. Baldwin Assistant Examiner.lohn S. Brown Attorney-William P. Hickey ABSTRACT: A vent comprising elongated flow passageways through a thin sheet having thin fingers forming at least one of the two opposite side edges of the flow passageway with the top surface of the fingers being generally parallel with the top surface of the sheet. The width of the flow passageways is less than the particle size of the material to be screened from the passing gas, and the fingers are cantilevered, preferably from adjacent one end for maximum flexibility of the fingers. The flexing of the fingers provides a self-cleaning action which may be produced by the passage of gases through the passageways or may be produced by a change in temperature. The sheet material preferably has a thickness that is approximately no greater than the particle size of the material being screened, and in the preferred embodiment, the fingers are made integral with the sheet. This is accomplished by forming an irregular opening through the sheet material, which opening has a width that is less than the particle size of the material to be retained. This opening in some instances will be tapered to provide greater width adjacent the bottom side of the sheet than adjacent the top side of the sheet, and the vents are preferably made by etching out the irregular opening with an acid.

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SHEET 1 OF 2 IN VENTUR. Ear/e L 6 PATENIED JAN. 4 B72 SHEET 2 OF 2 VENT FOR CORE BOXES AND THE LIKE This application is a continuation of Ser. No. 744,l43, filed July I l, 1968, now abandoned.

BACKGROUND OF THE INVENTION In the founding art, cavities are produced in cast metals by means of sand temporarily held together by a binder to produce what is known as a core. The molten metal is poured around the core and is allowed to solidify. The binders used are temporary and can be decomposed, usually by prolonged treatment and oxidation. The solidified metal having the core therein is subjected to conditions which decompose the binder, usually prolonged heating in air, following which the sand is shaken out of the cast metal body through one or more small openings.

The cores are produced in molds comprising two or more pieces usually two which can be disassembled to remove the core once the binder has hardened. The cores are produced by assembling the portions of the mold to provide an enclosure whose cavity corresponds in shape to the shape of the core desired. The cavity is filled with sand and binder, the binder is hardened, and the mold is disassembled to remove the finished core. In some instances the binder is a powder that is mixed with the sand that is forced into the mold cavity. In other instances, the sand is coated with the binder and the coated sand is forced into the mold cavity. The sand and binder may be tamped into the mold cavity, but in the process with which we are concerned, the sand is blown into the mold cavity by means of compressed air. The air displaced by the sand as well as any compressed air reaching the cavity must be vented therefrom in order to be sure that no air pockets or soft spots exist in the finished cores. The air is vented through screening devices commonly called vents which retain the sand and binder while allowing the escape of the air. These vents are subject to sand abrasion, which can be quite severe in those instances where some of the sand particles are forced through the openings of the vent. In all prior art vents with which I am concerned, sand and binder tends to accumulate in the air passages of the vent. Sand particles just slightly larger than the openings through the vent become wedged in the opening, and this wedging process continues until substantially all of the openings through the vent become plugged. Most molds are designed with only sufiicient venting capacity to make satisfactory molds when the vents are in an unplugged condition, and consequently the quality of the cores deteriorate when the vents start to become plugged. In many instances the core-producing process is carried on in automatic machinery and the plugged condition of the vents is not ascertained until a sizable production of nonusable cores has been produced.

Air blown cores are made by a number of different processes. In one commonly used process, an oil such as linseed oil is used to coat the sand which is air blown into the molds. The unhardened cores made with oxidizing oil is removed and placed in dryers which allows air circulation therethrough. The dryers conmining the cores are put in ovens where oxidization of the binder takes place to set the binder to a rigid condition. This is sometimes called a green-sand-molding P ocess.

Another type of process commonly used is called the hot bo'x process. In the hot box process, sand either coated with or mixed with a thermosetting resin, usually a phenol-formaldehyde is air blown into the cavity of the mold. The mold is heated, and after the resin and sand has become stationary against the mold cavity surface for a few seconds, the resin is transformed into its therrnoset condition, and thereafter the mold is split and the core removed form the mold cavity. Other types of thermosetting resins can be used, as for example phenol-furfural resins, etc.

Air blown cores can also be made by several cold processes wherein a gas is caused to pass through the core to set up the binder after the sand and binder are blown into the mold cavity. In one such process, sand is coated with sodium silicate binder and this binder coated sand is then blown into the mold cavity. Thereafter, carbon dioxide is caused to flow through the core to gel the sodium silicate. In order that properly uniform hard cores is made, the carbon dioxide must reach all parts of the core and must displace the air in the pores between the sand particles. In this process it is particularly necessary that the vents remain open and in an unplugged condition, otherwise the air in some portions of the core is not displaced with the carbon dioxide, and a soft core results.

In another type of cold core-making process, sand and an oil containing a polyalcohol, such as a glycol, is air blown into the mold cavity. Thereafter a diisocyanate, as for example methylene bis (phenylene isocyanate) or 2,4-toluenediisocyanate is blown through the pores of the core to set the binder oil into a cross'linked condition. Here again the openings of the vents must be kept open if soft cores are to be avoided.

Still other cold methods of making cores involving blowing gases through the sand and binder have been, and will be developed, and in all of these processes it is critical that the passages through the vents remain open.

The prior art in a few instances has attempted to make a self-cleaning core vent. The self-cleaning core vents with which I am familiar involve openings in plates which are appreciably thicker than the particle size of the sand that is to be retained. In a few instances, these prior art attempts have utilized yieldable members, but while the members have been yieldable, they have been so stiff and heavy that the frequency of vibration has been too low to be set into vibration by air escaping through the vent. What is more, the movement of the thick members has usually only resulted in the repositioning of the sand particles to further embed them between the side edges of the relatively moving parts. In the Dudzinski U.S. Pat. No. 2,482,330 for example, each coil of the spring has limited movement relative to the adjacent coil because of the substantial nature of the structure, and relative movement of these coils merely allows the sand to be repositioned and in some instances only further embedded between the deep side edges of each of the adjacent coils. Furthermore, the long length of spring that is provided has a natural frequency that can never be in tune with the natural pulses which are created by the passage of air through the vent.

In prior art U.S. Pat. No. 3,214,803, air passages through the vent are provided between a disk and the sidewalls of the vent. Downward movement of the disk is prevented by engagement of ears or projections on the lid with the sidewalls. Vibration, therefore, is prevented or at the best greatly restrained.

An object of the present invention is the provision of a new and improved self-cleaning vent wherein the air passages through the vent have a depth no greater than the particle size of the sand that is to be retained.

Another object of the invention is the provision of a new and improved vent of the above described type wherein the air passages are provided between fingers cantilevered in openings through a plate structure.

A further object of the invention is the provision of a new and improved vent of the above described type wherein the side walls of the fingers and the slot in which they are positioned diverge from each other in the direction of air flow.

A still further object of the invention is the provision of a new and improved vent wherein the fingers are made of a bimetallic material which is flexed upon a change in temperature.

A still further object of the invention is the provision of a new and improved method of making a core vent and the like in which the fingers are made integrally with the material in which the openings are formed by etching an irregularly shaped opening through the metal surrounding the fingers.

Further objects and advantages of the invention will become apparent to those skilled in the art to which the invention relates form the following description of several preferred embodiments described with reference to the accompanying drawing forming a part of this specification.

SUMMARY OF THE INVENTION The gas passages through the vents of the present invention are formed by elongated openings through sheet material with at least one side edge of the elongated opening being defined by a flexible finger. The elongated opening has a width less than the particle size of the material to be retained, and the sheet preferably has a thickness that is approximately equal to or less than the particle size of the material to be retained. The fingers are cantilevered in a flexible manner to permit relative movement with respect to the opposite sidewall of the passageway through the sheet, and the cantilevered support is preferably provided at one end of the fingers. The fingers preferably act like a reed and are vibrated by the passage of air through the passageways bordered by the fingers. In some instances the sidewalls of the passageways including the side edges of the fingers diverge toward the downstream end of the air passages, and in some instances the fingers are made of a bimetallic material so that changes in temperature will provide relative movement between the fingers and the sidewalls of the openings to free the particles which may become lodged between the side walls of the passageways.

The fingers are preferably an integral part of the sheet and are formed by an opening or slit which zigzags back and forth to form fingers alternate ones of which project in opposite directions. The vents are preferably made by acid etching one or more zigzag openings through a thin metal plate. The etching may be accomplished from both sides of the plate, but is preferably accomplished fon'n one side only, to provide the above referred to tapered opening.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic sectional view through an assembled core box and depicts the process of blowing cores;

FIG. 2 is a plan view of a vent plate embodying the present invention;

FIG. 3 is a plan view of another embodiment of vent plate;

FIG. 4 is a sectional view taken approximately on the line 4-4 of FIG. 2;

FIG. 5 is a schematic sectional view showing the acidetching process which is used to produce the vents of the present invention.

FIG. 6 is a fragmentary view of another embodiment;

FIG. 7 is a plan view on another embodiment of vent;

FIG. 8 is a sectional view taken approximately on the line 8-8 of FIG. 7; and

FIG. 9 is a plan view similar to FIG. 7 but showing another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS One of the principal uses of the vents of the present invention will be the venting of air blown core molds and the like as depicted in FIG. 1 of the drawing. In the process of air-blowing cores, a mixture of sand and binder I0 is blown from a pressure reservoir 12 through an orifice 14 in a blow plate 16 into the cavity 18 of a core mold 20. The air that is displaced form the cavity 18 by the sand and binder exits through the self-cleaning vents 22 of the present invention. The vents 22 are positioned in openings 24 which communicate the cavity 18 to the atmosphere. The vents 22 are usually positioned to vent the portions of the cavity 18 which are the last to be filled by the sand and binder blown into the cavity, to prevent air from being trapped in the cavity and the cavity, therefore, not being completely filled with sand and binder. If the cavity is not completely filled, soft spots" in the cores are produced, and cores having soft spots" cannot be used in the metalcasting operation. During the final stages of compaction of sand and binder into the cavity 18, the sand and binder is compacted against the surface of the vents 22. The vents 22 of the present invention have a smooth end surface and do not leave an imprint in the finished core.

One embodiment of the present invention is shown in FIGS. 2 and 4 of the drawing. The vent 22 generally comprises a tubular body portion 26 having a shoulder 28 formed in its upper end by means of an internal counterbore 30. A thin sheet or reed plate 32 is positioned against shoulder 28 and the thin sidewall section 36 opposite the counterbore 30 is rolled over into a stepped portion 34 of the reed plate 32, so that the top edge 38 of the rolled over portion is flush with the outer surface of the reed plate 32. The tubular body portion 26 is retained in its opening 24 by a slight interference therewith.

The fluid flow passage of the vent 22 shown in FIG. 2 is made by one or more zigzag openings 40 two shown in the drawing through the thin disk or reed plate 32. The zigzag openings 40 have a width which is less than the particle size of the sand to be retained by the vent. Each zigzag opening 40 has generally parallel portions 42 which separate side edges of fingers 44, and connecting generally right angle portions 46 at the free ends of the fingers 44. The opposite end of the fingers 44 is unsevered from the main portion of the reed plate 32 and provides a cantilevered support for the fingers 44. In the embodiment shown in FIG. 2, one zigzag opening 40 starts adjacent one side of the reed plate and zigzags back and forth between a median strip 48, which extends across the major diameter of the plate 32, and a circumferential strip 50. The openings 40 may be opposite hand to each other, but in the embodiment shown in FIG. 2 have their generally right angle portions 46 staggered so that opposite fingers face generally in the same direction. This arrangement causes a finger on one side the median strip 48 to be free of the median strip while the fingers on the opposite side of the median is supported by the median strip 48. This arrangement produces a twisting action in the median strip 48 opposite the free end of the opposed finger which is helpful in some instances in providing an additional freeing action for particles which become lodged adjacent the median strip 48. The preferred form of reed plate 32 will have a thickness that does not appreciably exceed the thickness of the particle size of solids to be retained by the vent. In the embodiment shown in FIG. 2, the vent has a diameter of one half inch and the reed plate has a thickness of 0.015 inch. The opening has a width that is 0.015 inch and the sand which is to be retained by the vent has an average particle size of 0.020 inch. This vent has adequate strength to withstand blowing pressures up to approximately 500 pounds per square inch.

The embodiment shown in FIG. 3 is generally similar to that shown in FIGS. 2 and 4, but dilfers principally therefrom in the configuration of the openings 40 that are provided. Those portions of the embodiment shown in FIG. 3 which correspond to portions shown in FIGS. 2 and 4 are designated by a like reference numeral characterized further in that a suffix a" is affixed thereto. In the embodiment shown in FIG. 3, the zigzag openings 40 extend radially to cover generally pieshaped sections that are separated by radially extending median strips 52. ,The embodiment shown in FIG. 3 has six openings 40 which are separated by six radial median strips 52 which join at the center. The median strips 52 in effect fonnthree diametrically extending reinforcing members, and the vents so formed withstand pressures up to approximately 750 pounds per square inch.

The vents of the present invention are preferably made by the acid-etching process depicted in FIG. 5. The reed plate 32 can be made of any suitable metal, and because stainless steel is strong and resistant to corrosion, it is a preferred material. A stainless sheet of a desired thickness is coated with a photographic resist" material 54. A photographic negative is laid over the surface of this material, and a light is passed through the light-transmitting portions of the negative to strike the photographic resist material. The photographic negative has light-transmitting portions corresponding with the openings 40, and the light struck portions of the resist" layer 54.

In the embodiment shown in FIG. 5, the metal is 0.015-inch thick, and the openings 56 in the resist layer 54 are approximately 0.008 inches. In the embodiment shown in FIG. 6,

openings 56 are positioned on both sides of the plate 32 opposite each other, and the acid-etching processing is performed form both sides of the plate. In the embodiment shown in FIG. 5, however, the openings 56 are provided in only the bottom layer of the resist material 54 and the acid etching proceeds from the bottom only. Using this technique and stock 0.015-inch thick, the openings 40 are 0.0l6-inch wide adjacent the holes 56 and are 0.0l2-inch wide at the opposite side of the plate. The plates etched form the bottom side only are installed in the vents with the widest portion of the openings 40 facing inwardly of the vent, and with the narrow portions of the openings 40 facing outwardly where they are engaged by the sand particles to be retained. In the resist layers 54 are positioned directly opposite each other and the shoulder 34 is formed by removing a circumferential strip 58 of the resist material 54 around the plate 32 on its top surface only. A proper groove is therefore provided for receiving the turned over edge 38 as shown in FIG. 4.

Plates having openings of various widths can be made using the same photographic plate by varying the duration of the acid etching. Similarly, vents of various strengths can be made using the same photographic plate by varying the thickness of the plate that is etched.

A preferred embodiment is produced by using a strip material for the reed plate 32 which is a laminated or bimetallic material whose bottom layer has a coefficient of expansion which is greater than that of its top layer. Preferably the two layers of the bimetallic sheet material are stainless steels of different composition arranged so that the bottom layer has the greatest coefficient of expansion. These materials can be etched satisfactorily and will provide fingers which flex upwardly against the flow of sand and air when the reed plate 32 is heated.

In the preferred method of use of the vents of the present invention, the bimetallic embodiments are positioned as above described and are heated to around 200 F. temperature prior to the time that the mold cavity 18 is filled with the sand. The lengths of the fingers are such that they will be deflected upwardly form the upper surface of the plate 32 by approximately 0.002 inch at a temperature of approximately 200 F. In the embodiment shown in FIG. 2, 90 p.s.i. air pressure on the fingers deflects the fingers downwardly by approximately the same amount, so that they are substantially parallel with the top surface of the plate 32 when the core material is compacted thereagainst at the elevated temperature. The cold sand and resin which engages the vent reduces the temperature of the vent to approximately 200 F. The vent is then heated to a temperature of between 400600 F. to cure the binder. When the finished core is removed form the mold 20, the fingers flex outwardly approximately 0.005 inch and thereafter the temperature of the vent again decreases to approximately 200 F. This flexing of the fingers dislodges any sand that has been embedded in the upper end of the openings 40. It will be seen that the embodiment shown in FIG. 2 has fingers with free ends adjacent supported sections of the plate so that maximum relative movement is provided in these areas. It will also be seen in FIGS. 2 and 3 that the fingers are arranged adjacent to each other so that a free end on one finger is always adjacent the cantilevered end of an adjacent finger. This provides maximum relative movement therebetween for dislodging sand particles.

A further advantage of the invention is had by the reed effect which is produced when high-pressure air is blown through the passages 40. The lengths of the fingers are such as to have sufficient flexibility to vibrate when air or other gas escapes through the opening 40. The reed effect causes what would be small static deflections to build up into large oscillations which remove sand particles from the openings.

Still other designs of vent plates can be made having fingers of even greater flexibility. The embodiments shown in H68. 7 and 8 is generally similar to that shown in FIGS. 2 and 4, but differs principally therefrom in that there is no median strip, and that the fingers run across the width of the disk, so that they are approximately twice as long as those shown in FIGS. 2 and 4. Those portions of the embodiment shown in FIGS. 7 and 8 which are similar to corresponding portions of the embodiment in FIGS. 2 and 4 are designated by the same reference numeral characterized further in that a suffix b" is affixed thereto.

in the embodiment shown in FIGS. 7 and 8 the peripheral strip 50b is narrower than in the embodiment shown in FIGS. 2 and 4, so that the outer edges of the openings 40b are positioned over the sidewalls of the tubular body portion 26b. The tubular portion 26b is provided with a shoulder or abutment 60 on its inside walls beneath the disk 32b. The shoulder 60 projects radially inwardly by a distance greater than the width of the openings 40bto provide an abutment on which the fingers 44b may hear. The shoulder 60 is positioned beneath the disc 32b by a distance which permits normal vibration of the fingers Mbbut which prevents their being deflected by a distance which will produce permanent defonnation or damage to the fingers. The fingers 44b are cantilevered form the peripheral strip 50b and extend across the disk, then arcuately around the disk with their outer edges positioned over the top of the shoulder 60, and then back across the disk. A second finger starts at a position on the opposite side of the disk and proceeds similarly, with its back-tumed portion being positioned within the U of the other finger 44b. The fingers 4412 have a period of vibration that is approximately in tune with the frequency of the vibrations of air vented through the openings 40b. The configuration shown in FIG. 7 is preferably used in small size vents, as for example those having an outside diameter of one-quarter inch.

The embodiment shown in FIG. 9 is similar to the embodiment shown in FIGS. 7 and 8 in that it is provided with a shoulder 60c for limiting deflection of the fingers 44c. The embodiment shown in FIG. 9 differs from the embodiment shown in FIG. 7 principally in that the fingers are cantilevered from a median strip 480. Those portions of the embodiment shown in FIG. *9 which are similar to portions of the embodiments previously described are designated by a like reference numeral. characterized further in that a sufiix 0" is affixed thereto. The configuration shown in FIG. 9 is likewise preferably used for smaller size vents, as for example those having a diameter of approximately one-quarter inch.

The construction can also be thought of as comprising fin gers positioned in slots, or opening portions through a sheet structure, as would occur where the fingers are not made integral with the sheet structure containing the slots or opening portions.

While the invention has been described in considerable detail, I do not wish to be limited to the particular embodiments shown and described, and it is my intention to cover hereby all novel adaptations, modifications, and arrangements thereof which come within the practice of those skilled in the art to which the invention relates, including the use of the vents in the forming and or molding of plastic foams, beads etc.

I claim:

1. A vent and the like for confining particulate material of generally predetennined size, comprising: a support member, a thin sheet of flexible material secured to said support member, a plurality of generally parallel opening portions through said sheet, and a plurality of generally parallel fingers positioned in said opening portions to provide flow passages through said sheet which are bordered by said fingers and which flow passages have a width that is less than the predetermined size, and whereby flexure provides relative motion between the fingers and the sidewalls of said opening portions.

2. The vent of claim 1 wherein said flexure is provided by airflow through said flow passages.

3. The vent of claim 1 wherein said flexure is provided by thermal expansion.

4. The vent of claim 1 wherein said sheet is less than approximately 0.020-inch thick and said flow passage is wider ad jacent one side of said sheet than it is adjacent the other side of said sheet.

5. A vent and the like for confining particulate material of generally predetermined size, comprising: a support member, a thin sheet of flexible material secured to said support member, said sheet having at least one long narrow opening therethrough which repeatedly reverses direction to form a plurality of generally parallel spaced apart oppositely extending side by side fingers, and said opening having a width that is less than the predetermined size.

6. The vent of claim wherein adjacent ones of said fingers are cantilevered form opposite ends from each other.

7. The vent of claim 5 wherein said support has a shoulder positioned beneath at least one of said fingers, said shoulder having clearance with said finger in the undeflected condition of the finger and being adapted to limit deflection of said fingets.

8. The vent of claim 5 wherein said sheet has an integral portion extending across said support member, with integral fingers projecting generally perpendicularly form opposite sides of said integral portion.

9. The vent of claim 8 in which said integral portion is unsupported except adjacent opposite sides of said support so that said integral portion acts as torsion member.

10. The vent of claim 9 wherein the fingers on opposite sides of said integral portion are alternately spaced.

1]. The vent of claim 6 wherein said sheet is circular, said sheet having at least two radial integral portions intersecting at the center of the circular sheet, each integral portion having integral fingers projecting towards the other integral portion with the fingers on one integral portion being positioned between the fingers of the other integral portion.

12. The vent of claim 11 having three evenly spaced integral portions each having oppositely projecting fingers positioned between fingers of the adjacent integral portions.

13. The vent of claim 12 wherein the fingers are arcuately shaped and are parallel to the periphery of said circular sheet.

14. The vent of claim 1 having upstream and downstream faces and wherein said sheet is a bimetallic laminate.

15. The vent of claim 14 wherein said opening is wider at the downstream face than at the upstream face.

16. The vent of claim 15 wherein the layer forming the downstream face has the greatest coefficient of expansion.

17. The vent of claim 16 wherein said sheet has an integral portion extending across said support member, with integral fingers projecting generally perpendicularly from opposite sides of said integral portion.

18. The vent of claim 17 wherein said sheet is circular and has at least two radial integral portions intersecting at the center of the circular sheet, each integral portion having integral fingers of one integral portion being positioned between the fingers of the other integral portion.

19. A vent and the like for confining particulate material of generally predetermined size, comprising: sheet material having upstream and downstream sides and spaced-apart elongated slots therethrough communicating said sides, and a plurality of cantilevered fingers respective ones of which are positioned in respective ones of said slots with their upstream surface generally parallel with the upstream surface of said sheet material around said slots and with the clearance between said fingers and sides of said slots being less than said predetermined size, said fingers being cantilevered in flexible fashion to provide relative movement with the side surfaces of said slots.

20. The vent of claim 19 wherein said fingers and sheet material are integrally connected.

21. The vent of claim 19 wherein said fingers are supported in cantilever fashion adjacent end portions of said slots.

22. The vent of claim 21 wherein said fingers have a thickness substantially no greater than said predetermined thickness.

Claims

1. A vent and the like for confining particulate material of generally predetermined size, comprising: a support member, a thin sheet of flexible material secured to said support member, a plurality of generally parallel opening portions through said sheet, and a plurality of generally parallel fingers positioned in said opening portions to provide flow passages through said sheet which are bordered by said fingers and which flow passages have a width that is less than the predetermined size, and whereby flexure provides relative motion between the fingers and the sidewalls of said opening portions.

3. The vent of claim 1 wherein said flexure is provided by thermal expansion.

4. The vent of claim 1 wherein said sheet is less than approximately 0.020-inch thick and said flow passage is wider adjacent one side of said sheet than it is adjacent the other side of said sheet.

6. The vent of claim 5 wherein adjacent ones of said fingers are cantilevered from opposite ends from each other.

7. The vent of claim 5 wherein said support has a shoulder positioned beneath at least one of said fingers, said shoulder having clearance with said finger in the undeflected condition of the finger and being adapted to limit deflection of said fingers.

8. The vent of claim 5 wherein said sheet has an integral portion extending across said support member, with integral fingers projecting generally perpendicularly from opposite sides of said integral portion.

9. The vent of claim 8 in which said integral portion is unsupported except adjacent opposite sides of said support so that said integral portion acts as a torsion member.

11. The vent of claim 6 wherein said sheet is circular, said sheet having at least two radial integral portions intersecting at the center of the circular sheet, each integral portion having integral fingers projecting towards the other integral portion with the fingers on one integral portion being positioned between the fingers of the other integral portion.

18. The vent of claim 17 wherein said sheet is circular and has at least two radial integral portions intersecting at the center of the circular sheet, each integral portion having integral figers projecting towards the other integral portion with the finger of one integral portion being positioned between the fingers of the other integral portion.