CA1076041A

CA1076041A - Filters for liquids or gases

Info

Publication number: CA1076041A
Application number: CA275,513A
Authority: CA
Inventors: George S. Hunter; Brian Walker; Susanne P. Hunter
Original assignee: Process Scientific Innovations Ltd
Current assignee: Process Scientific Innovations Ltd
Priority date: 1976-04-05
Filing date: 1977-04-04
Publication date: 1980-04-22
Also published as: NL7703681A; DK149577A; JPS5626452B2; CH619152A5; FR2347081B1; DK148952B; JPS52144868A; NL183871C; DE2715204C2; SE7703897L; ATA232877A; AU2395577A; SE432201B; AU510129B2; BR7702120A; DE2715204A1; FR2347081A1; AT368401B; ES457536A1; DK148952C

Abstract

ABSTRACT

Filter elements are described in which a pleated cylindrical sheet of non-woven microporous glass fibre filter material impregnated with a binder, which may be silicone, polyurethane, phenolic resin or epoxy resin, is mounted in contact with a cylindrical supporting sheet of, for example, expanded metal for maintaining the filter material against shock pressure loads. To protect the filter material during assembly a porous layer of protective material may be interposed between the filter material and the supporting cylinder. The supporting cylinder may be a simple cylinder or pleated so as to fit the filter material. An activated carbon layer for removing odours during air filtration may be added to the filter material.
When the air contains oil mist, a layer containing dye that will be taken up by the oil and discolour the filter element as a warning indication that the filter has become saturated, may be interposed between the filter material and the activated carbon layer. The filter material may comprise an organic binder holding together borosilicate glass fibres, this amorphous mass being further impregnated by a synthetic resin binder. The filter material may consist of a glass fibre filter paper with a further layer of non-woven material secured thereto by a synthetic resin binder.

Description

, .
~his invention relates to filters ~or gas or l~quid wher~in a high efficiency filter medium iY
used. Such a filter medium is glass fibre paper, This is a very h~gh efficiency medium wllich, when tested to B.S. 3~28 tsodium flame test), will be ~ubstantially 100% efricie~t. D.O.P. teæts with 0.3 micron particles would give similar results.
A filter element when made from at least - one layer of glass fibre paper, even when pleated, is weak when subjected to shoc~ preæsure loads, asæuming that an excess of bonding agent for the fibres, which would impair the filtering properties of the medium, is avoided. One object of the present invention is to provide a filter having an adequately supported high efficiency filter medium.
According to the present invention, a rilter element for iluids comprises at least one cylindrical pleated sheet of non-woven microporous fibrous material impregnated with a binder carried against a perforate supporting cylinder so that the filter material is retained against the cyl~der when subjected to pressure.
Where one supporting cylinder is used this is located so as to give maximum support to the filter sheet baving regard to the direction Or flow, i.e. irom inside to outside or cutside to inside Or the cylinder.
Alternatively, of course, the cylindrical sheet of pleated-riltering material may be located betwecn two comparatively stiif supporting cylinders to provide a very strong structure. rhe microporous non-woven material may be borosilicate glass fibre held together ' P

.

.
with an or~anic binder, the glass fibres having 0.1 to 0.9 microns (inclusive) mean diamcter an~l a leIIgth of between 1 and 2 mm (inclusive) and containin~ coarse fibres of up to 6 m~ len~th and the glass material being impregnated by a synthetic resin binder to enable it to withstand shock pressure loads.
For larger sizes of filter element, an apertured cylinder of stiff material may be pleated so a~
precisely to fit the pleated filter sheet or sheets in overall contact with the filter sheet or one of the filter sheets. Alternatively the apertured cylinder may be a simple cylinder. The sti~f material may very conveniently be expanded metal or metal gauze.
The microprous filter material may consist o~
fibre filter paper bonded to a non-woven filter material which may be roughly classified as paper by means of a binder and comprises ceramic fibre, metal fibre, asbestos, mineral wool, organic fibre, further glass ~ibre or a membrane.
While the aforesaid filter elements can be ma-le exceptionally efficient in their capacity to remove contaminating suspensions such as dust, dirt, oil or water droplets or vapour from an air stream, in some - cases it is highly desirable also to remove odours, that car find their way through the filter element.
A further object of the present invention is, th~rerore, to provide for e~fective odour removal.
Therefore, at least one activated carbon layer may be included in the pleated wall of the filter element.
Alternatively at le&st one activated carbon layer ~076041 may be included in a filter element having a pleated wall which may or may not be formed in accordance with ths invention but is mounted in series with such a filter ele~ent~ In this case, the pleated wall oi the filter element may comprise two layers, namely a layer containing activa~ed carbon immediately adjacent to a layer of filter paper. ~owever, more than one such layer may be used; for example, two layers - containing activated car~on immediately adjacent to a layer of filter paper.
In order that the ~nvention may be clearly under-- stood and readily carried into effect filter elements and filters in accordance therewith will now be - described, by way of example, with reference to the accompanying drawings, in which:-Figure 1 is a side elevation of a filter element;
Figure 2 is a cross-section on an enlarged portion of the filter element of Figure l;
Figure 3 is a diagrammatic side elevation of the filter assembly;
Figure 4 is a side elevation of a filter element with an outer cylinder cf stiff material shown partially removed;
Figure 5 is an end elevation of the filter element of Figure 4; and Figure 6 shows a c oss-section, on an enlarged scale~ of a portion of a ~ilter element similar to that of Figures 4 and 5 ~eferring to Figures 1 and 2, the filter element of this example comprises two pleated sheets 1 of .

~076041 laminated filter media including ~lass fibre paper reillforced e~ternally by a pleated sheet 2 of exl~nded matal that e~actly fits the layers of glass fibre paper. An inner simple support cylinder ~ of e~,allded meta] bears on the peaks of the filter sheets ~.
The thickness of the fi]ter sheets 1 according to the nl~ber of sheets may be between 40 thousandths of an inch and half an inch according to the size of the filter. The fibre diameters may vary between 0.1 and 20 microns according to the mini~um size of particle that has to be separated from the fluid.
The composite filter element is impregnated and bonded with a phenolic,silicone, or other synthetic resin that will withstand water, mineral, vegetable and synthetic oils, acids, alkalis and such contaminants as are usually found in air, compressed air, vapours and gases.
The filter sheet 1 or each iilter sheet, comprises laminated filter media consisting of a glass fibre filter paper bonded to a non-woven or woven fil~er aterial, which may be roughly classified as papcr, by means o~ a plastics material such as polythene or polypropylene or other suitable synthetic resin, which may, for example, be thermosetting or cold curing by the addition of a liquid chemical or heat setting, ; - 5 -The laminated filter material~ may be ~ormcd by first spra~ing the non-wo~ren or wo~en material filt~r medium with a thermoplastic material The paper thus treated is then brought into contact with the g~ass fibre paper under pressure and heat, so that th~
thermoplastic material melts and forms a bond on curing. Then this material is pleated and formed into a cylinder, but this may be done subsequently to the addition o~ another layer of non-laminated filter mediu~o which is bonded by thermoplastic other material or / synthetic re~in dispersed in a suitable solvent to the laminated filter media, thus forming two layers in which the bonding material gives the fibrous material some structural rigidity. The pleated paper sheet is then located in the pleated apertured sheet 2 o~ expanded metal. The composite pleated element may also be supported on its internal peaks by a simple cylinder of expanded metal~ Finally as is usual with pleated ~ilters, the ends of the element are dip sealed into end caps by means of ~
synthetic resin or other sealing medium that penetrates through the edge regions of the filter element and prevents leakage o~ the fluid round these edges. This synthetic resin may advantageously be o~ the ~ind that can be moulded while being applicd to the filter elemant to ~orm a ring or cap having the properties o~ a gas~et.
These end caps are, o~ course, for the purpose of ensuring the passage o~ the fluid throu~h the filter material when the element is mounted in a filter housing.
In a modi~ication o~ the a~oresaid ~ilter element, ~ 1~76041 applicable to smaller elements, for example two inches diameter and two to three inches high, the pleated apertured sheet ~ of expanded metal, is replaced by a simple cylinder of sucb material that merely touches the external or the internal peak~ of the pleated medium. Alternatively two such simple cylinders touching the external and internal peaks may be provided.
An advantage of the aforesaid laminated media including glass fibre ~ilter paper is that it gives the media more inherent streng~h in the direction of ilow through the media. This means that less synthetic plastics material can be used to reinforce the filter media, thus allowing a greater flow of air, or other fluid to be filtered, ~or a smaller pressure drop across the filter. Moreover, the filter element containing the laminated media can withstand higher shock pressures and higher pressure drops across the filter as the iilter becomes blocked with particulate matter during use.
~n example cf a iilter element having the cylindrical pleated laminated media between simple cylinders Or expanded metal has substantially the - rollowing dimensions: o~erall outside diameter 4.4 cms, length 6.0 cms, distance between outside peaks 0.4 cms, radial distance between the inside and outside cylinders 0.6 cms.
The assembly oi Figure 3 comprises a delivery pipe 11 ~or supplying compressed air to a primary filter 12 containing a iilter element 13 constructed according to the invention. This filter removes any oil or water mist or dirt from ~he air stream whieil then flows through a pipe 14 t~ a secondary filter 15 containing a filter element 16 as shown in Figures 4 to 6. After passing through the filt~r e~ement 16~ the cleaned air is discharged through a pipe 17.
The filter element 16 comprises a pleated layer 18 of activated carbon and paper filter media supported between internal and external cylinders 19, 20 of expanded metal. The ends of the ~ilter elements 13, 16 are sealed to end caps, the upper one wi~h a ~- central aperture, as is usual in the case of pleated, cylindrical ~ilter elements.
As shown by the arrow A in Figure 6, the air to be cleaned flows from outside to inside the filter element 16 so that the activated carbon layer 21 is outside the layer 22 of filter paper. For flow in the opposite direction, the carbon would be inside.
The activated carbon layer may be approximately 1 mm thick with an activated carbon content of 50%
by weight, the balance being made up by fibres.
Such material is obtainable from C.H.Dexter and Sons Company of Windsor Locks, Connecticut, U.S.A. .~
alternative is a charcoal cloth manufactured by the Chemical Defence Establishments Porton Down, Salisbury, Wiltshire. This is a strong highly absorbent charcoal, the activity of which can be varied to suit vary-ng requirements. The activated carbon layer 21 remo~es, for example, hydrocarbon gas from the air by adsorption, and any particulate matter, shed from the activated ~07604~

carbon layer, is removed W~ the downsteam adjac~nt filter layer which is at lea~t 96~ erficient ~ainst 0.3 micron particles.
Th~ paper filter layer 12 may be constituted by a sheet as aforesaid of laminated filter media conisting of a glass fibre filter paper bonded to a ron-wo~en or woven filter material that may be roughly classified as paper. In this and in the other examples de~cribed above, the woven or non-woven filter material that may be roughly classified as paper may comprise ceramic fibre, metal fibre, asbestos, mineral wool, organic fibre or further glass fibre, or even a membrane.
In fact, where a pleated supporting sheet of perforate stiff material is used, any of these materials can be used in a single or multiple sheet. The pleated support sheet enables these materials to withstand shock pressure loads even although they are weak, assuming that an e~cess of bonding for kinding the fibres together is avoided. Such an excess would impair the iiltering properties of the medium.
'rhe apertured pleated sheet which, as an alternative to expanded metal may be of gauze or of a stiff non-metallic material, is shown in Figure 2 as fitted outside the pleated layer or layers of filter medium. ~owevcr, in some cases, the filter needs higher mechanical ~trength i~ the main direction of flow than in the reverse direction~ Thus, where the fluid to be ~iltered passes ~rom outside the cylinder to the inside, the support layer is preferably on the inside. ~owever, in an alterr.ative arrangements, two or three layers of filter medium are addcd to the corrugateA inside or outside surface of the pleated c~ylinder, over the support sheet.
Very advantageously~ further to impart high mechanical strength to prevent rupture of the fragile filter medium when subjected tc. shock pressure loads, the filter clement, comprising the composite pleated filter medium and support, is resin reinforced. This may be done by forcing a liquid carrier of a phenolic or silicone resin for example, into the medium, but only to such an extent as substantially to avoid impairing the ~ilter qualities of the medium.
~he force may be generated by a centri~uge, a vacuum technique or compression technique. Alternatively the filter element can simply be immersed for a period in a resin solutionO
To hold the filter medium in place during this process and during operation, a simple cylinder of perforated support material may be added so as to touch only the peaks of the pleated filter medium on the opposite face to the pleated support sheet. After the impregnation the filter is ~ut into an oven so as to cure the resin at the requisite temperature. Alternatively the medium may be impregnated prior to pleating with a resin that subsequently cures with heat.
A further example of the invention comprises one or more cylindrical pleated sheets consisting of micro-poro~ls non-woven borosilica'e glass fibres, the fibres being held together witn an organic binder, the glass fibres having 0.5 to 9.0 microns (inclusive) mean diameter and a length of between ~ and 2 mm (inclusive) and coarse f.hrcs up to 6 mm length, and the borosilicate glass matcrial being further impregnated by a synthetic resin -- 10 _ 107604~

binder to enable it to withstand shock pressure loads ~hen mounted bet-~een t~o simple perforate metal supporting cylinders. The synthetic resln binder is preferably silicone but alternative materials such as polyurethane, phenolic resin or epoxy resin may be used.
In assembling the filter elements described above wherein an internal and an external, or both ~n internal and external, simple cylinder of perforate supporting material is used, it is sometimes desirable to interpose a cylindrical layer of protective ma-terial between thepleated filter sheet and the cylinder, or - each cylinder, the protective material being such ~s to protect the pleated filter material during assembly.
The layer, or each layer, of protective material ~ must be sufficiently porous to permit the passage through it of the gas or liquid being filtered. Non-woven - nylon has been found to be particularly suitable but non-woven polyester, rayon or acrylic materials can be used as alternative.s as also can woven materials such as woven glass fibre.
In æuch an example, each layer in the filter material may advantageously be 0.73 mm thick and the ba~ic fibre may be manufactured from pure borosilicate glass micro fibre of 0.5 micron mean diameter. The plcats are preferably pac~ed ~uite closely together.
As in the examples prevlously described, the filter element may be bonded into end caps as is usual with pleated cylindrical filter elements.
Very advantageously means are provided for providing ~07604~

warning indication when a filter element is saturated with oil, in particular a filter Wit]l a layer 0~
carbon material as shown in ~igure 8~ 'rhis may be achieved by applyin~ a layer containin~ an oil soluble dye which changes the colour of the filtcr element to red in the presence of oil. This may be applied in the form of chips or grinules or may consist of a .; !
mixture of oil soluble wax and dye stuff. ~he dye stuff may be that known under the ~egistered Trade 1~ h~ark "Waxoline Red O.S." manufactured by I,C.I. Ltd.
In the case of a filter element such as that of Figure 8, the dye may be retained between the activated carbon layer 21 and the layer 22 of filter paper by dipping, prior to assembly of the filter element, the inner cylinder 22 into a molten wax containing dye dispersed in it but leaving the inner cylinder porous. The dye turns oil passing through the filter element to a reddened colour which appears on the outside of the filter element as a warning.
In a further example the dy~ is dissolved in a aolvent such as trichlo~ethylene or toluene and one layer of the filter material can be impregnated with this. The layer can be the aforesaid activated carbon layer or a third layer may be impregnated with the solution 25- and located between the activated carbon layer and the sheet of non-woven microporous fibrous material impregnated with a binder.

~ ' .

10~604~
Generally, when a high efficiency filter is used as an oil removal filter, the flow is inside to out and the oil mist is transferred from an aerosol form into a bulk liquid form through the filter and drains away into the quiet zone of the filter housing where it can be drained at frequent intervals.
Due to the amount of air passing through the filter and the amount of oil draining away at the outer surface, to reduce the risk of reintrainment of oil a porous plastics stock is fitted to the outer surface of the filter and is sealed to the end caps to prevent leakage at these points.
Because the flow through the filters of the present invention can be substantially higher than through comparable previously known filters, it has been found that the most conven-ient material for the sock from a drainage point of view and to counteract reintrainment is urethane ester or ether foam having a minimum of 45 pores to the inch (2.54 cms) as supplied by:
Foam Engineers Limited, Dashwood Avenue, High Wycombe, Buckinghamshire, or Ranwall Limited, Chaulend Lane, Luton, Bedfordshire, or Declon Foam Plastics Limited, Humprys Road, Woodside Estate, Dunstable, Bedfordshire, England.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A filter element for fluids comprising at least one cylindrical sheet of nonwoven microporous fibrous filter material impregnated with a synthetic resin binder, said filter material consisting of an amorphous mass of borosilicate glass fibers, a substantial quantity of said borosilicate glass fibers each having a diameter of between 0.5 to 9.0 microns and a length of between 1 and 2mm, the remaining fibers having a length of up to 6mm, said sheet being at least about 0.03 inches thick and formed with pleats over its entire area, said pleats being substantially parallel to the axis of said cylindrical sheet and presenting peaks inter-nally and externally of said cylindrical sheet, the internal peaks being spaced from the external peaks by approximately 0.6 cm, and at least one perforate supporting cylinder of comparatively rigid material formed with perforations substantially over its whole area, said supporting cylinder being mounted closely adjacent to said cylindrical sheet to provide support for said sheet, said synthetic resin binder providing support for said borosilicate microporous fibrous material between said peaks.

2. A filter according to claim 1, in which two of said supporting cylinders are provided respectively adjacent the inside and outside of said cylindrical sheet.

3. A filter according to claim 1 in which said binder is silicone.

4. A filter according to claim 3 in which said impreg-nated filter material consists of borosilicate microporous material that has been impregnated with silicone prior to pleating and subsequently cured.

5. A filter according to claim 1 wherein said sheet of nonwoven borosilicate microfibrous filter material impregnated with a synthetic resin binder is bonded to a layer of porous paper.

6. A filter element according to claim 1 including a separate pleated layer of activated carbon covering one face of said pleated cylindrical sheet.

7. A filter element according to claim 6 including a further layer of material containing dye adapted to be taken up by oil when a gas containing oil mist is passed through the filter element, said further layer being interposed between said pleated cylindrical sheet and said pleated layer of activated carbon, whereby oil entering the filter element through said layer of activated carbon has its color changed on reaching said dye ultimately resulting in a color change of the outer surface of said filter element.

8. A filter element according to claim 2 including two layers of protective material pervious to the fluid being filtered and adapted to protect said pleated filter sheet during its assembly with said protective supporting cylinders, said layers of protective material being respectively interposed between said pleated filter sheet and said protective supporting cylinders.

9. A filter assembly comprising first and second filter elements and conduit means for passing a fluid to be filtered in succession through said filter elements; said first filter element comprising at least one cylindrical sheet of nonwoven microporous fibrous filter material impregnated with a synthetic resin binder, said filter material consisting of an amorphous

Claim 9 - Continued mass of borosilicate glass fibers, a substantial quantity of said borosilicate glass fibers each having a diameter of between 0.5 to 9.0 microns and a length of between 1 and 2 mm, the remaining fibers having a length of up to 6 mm, said sheet being at least about 0.03 inches thick and formed with pleats over its entire area, said pleats being substantially parallel to the axis of said cylindrical sheet and presenting peaks internally and externally of said cylindrical sheet, the internal peaks being spaced from the external peaks by approximately 0.6 cm, and at least one perforate supporting cylinder of comparatively rigid material formed with perforations substantially over its whole area, said supporting cylinder being mounted closely adjacent to said cylindrical sheet to provide support for said sheet, said synthetic resin binder providing support for said borosilicate microporous fibrous material between said peaks; and said second filter element comprising a cylindrical sheet of pleated filter paper coated with a layer of activated carbon.