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Title:
IMPROVED SEALING FOR VERTICALLY MOUNTED AIR FILTER ELEMENT
Document Type and Number:
WIPO Patent Application WO/2017/212498
Kind Code:
A1
Abstract:
This invention comprises an Air filter element frame for the internal combustion engine of seal comprising a compressible seal or compressible gasket; illustrated by a polyurethane foam seal/gasket; and a process of making the illustrative seal/gasket wherein two parts of a mould provide a channel around the four margins of the air filter elements that have Guide Slots and molten polyurethane mixture is filled up, entrained with air bubbles and the compressible seal is formed around the margins. The Air filter element frame made of thermoplastic material combined with additives comprises an air filter element frame holding feature, filter paper media, a Guide Slot provided on all the four margins holding the polyurethane foam seal/gasket that facilitates assembly by press fitting. The filter paper media used are insert molded into the air filter element frame.

Inventors:
MADDINENI AJAY KUMAR (IN)
SONONE SAGAR DINESH (IN)
GARKHEDKAR GANESH GANGADHAR (IN)
SHEJWAL RAMCHANDRA PURUSHOTTAM (IN)
CHAKOTE SUBHASHCHANDRA MAHADEVRAO (IN)
JOSHI SUNIL LAXMANRAO (IN)
Application Number:
PCT/IN2017/050215
Publication Date:
December 14, 2017
Filing Date:
May 31, 2017
Export Citation:
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Assignee:
VARROC POLYMERS PVT LTD (IN)
International Classes:
F02M35/024; B01D46/00; F16J15/00
Domestic Patent References:
WO1999067517A11999-12-29
Foreign References:
US20110197556A12011-08-18
Attorney, Agent or Firm:
SAVANGIKAR, Vasant Anantrao (IN)
Download PDF:
Claims:
C L AI M S :

Air filter element frame for the internal combustion engine of seal comprising a compressible seal or compressible gasket.

Air filter element frame of claim 1 wherein the compressible seal or compressible gasket comprises a polyurethane foam seal or a polyurethane foam gasket.

The Air filter element frame of claim 2 further comprising an air filter element frame holding feature and filter paper media,

T he A i r f i Iter el ement frame of clai m 3 wherei n:

a. the air filter element frame is made of thermoplastic material, preferably Polypropylene with combined additives in proportion up to 30% comprisi ng at least talc or glass,

b. the air filter element frame holding feature comprises an outwardly projecting/arching-out extension of the filter element frame for the proper gripping and insertion into the air filter assembly and the filter paper media,

c. a guide slot is provided on all the four margins of the element frame as a part of its structure, further carrying ribs for reinforcement,

d. the filter paper media used are insert molded into the air filter element frame, comprise oil impregnated or dry type, that is reinforced into the element frame positioned into the mould into the pre-determined location,

The Air filter element frame of claim 2 wherein: a. the densities used for gasket of this invention vary from 100 grams per liters to 300 grams per liters,

b. the 'Compression Set_ of the polyurethane foam seal, defined as the inability to regain its original dimensions after compression expressed in terms of percentage of the original dimensions, varies from 1 % to 3% with a recovery up to 99%,

c. the gui de si ot has transverse di mensi on i n a range of 2mm to 3mm d. the hardness of the foam material on specimen with the skin on both the surfaces for dwell period of 15 seconds varies from 10e3 on Shore A scale.

A process of making an Air filter element frame comprising a polyurethane foam seal or a polyurethane foam gasket comprising steps of: a. applying release agent to a mold in the beginning of the process to achieve easy release of the seal from the mould after setting of polyurethane,

b. heati ng the mol d up to 40°C ,

c. placing the air filter element on the 'Cavity, to create a channel shaped space one side of which is provided by the longitudinal Guiding Slot present on the four outer sides of the air filter frame and two other sides being provided by two surfaces of the surface of 'Cavity _,

d. mixing polyol and isocyanate in a Polyurethane Dispensing Machine,

e. pouri ng the mixture i n a channel, f. placing the ore_ on the 'Cavity _ to enclose the channel on the fourth side,

g. keeping the poured mix for partial curing in atmospheric temperature for 8-10 mi nutes,

h. openi ng the moul d after curi ng,

i . recoveri ng the A i r F i Iter el ement frame with the polyurethane seal formed on the same,

j. curing the same for a further period of 24 hours..

7. The process of claim 6 for making an Air filter element frame comprising a polyurethane foam seal or a polyurethane foam gasket, wherei n:

a. polyol, and isocyanate are stored in machine tank at temperature of 20°C to 30°C and used in proportions selected between a range of polyol: isocyanate of 100:20 to 100:30,

b. nucleating them before use by entraining air or gases by mechanical mixers or frothing devices,

8. The process of claim 7 for making an Air filter element frame comprising a polyurethane foam seal or a polyurethane foam gasket, wherein the nucleation is preferably done in the range of 55% to 65%.

9. Mould for making polyurethane foam seal or a polyurethane foam gasket f or ai r f i I ter el ement frame for the i nternal combusti on engi ne.

10. The mould of claim 9 comprising:

a. one part, called as 'Cavity _ in which the air filter element with its paper pack assembly (3) have been placed for the purpose of making the polyurethane seal around the filter paper element; the 'Cavity _ having a channel shaped space that is formed between the outer margin of the Filter Paper E lement and the surface of the 'Cavity _ of the mould, in which the mixture of polyol and isocyanate is intended to be poured for making the polyurethane seal,

and a ore_, which is complementary part of the mould which covers the 'Cavity, from above when the assembly is made for making the polyurethane foam seal and provides the fourth side for the channel in which the mixture of polyol and isocyanate for making PU is poured for making the PU seal/gasket.

Description:
IMPROV E D SEA LING FOR V E RTICA L LY MOU NTE D AIR FILT E R

E L E ME NT

F ield of Invention

The present invention is directed towards improved seal construction of vertically mounting automotive air filter element for proper sealing using polyurethane gasket i n ai r f i Iter assembly.

BAC K G ROU ND O F T H E INV E NT ION:

Air filter element is required in automobiles to ensure that the air provided to the internal ignition engine for combustion of the fuel is dust free. Air filter elements are i nstal I ed i n one of the two ways: horizontal and verti cal .

Generally the choice of method of installation of air filter element has to be made taking into account the space constraint in the vehicle for filter housing and inlet duct position. Often, horizontally installed panel air filter element encounters servicing difficulties due to limited space. In case of 2 wheeler applications, air filter element is installed horizontally under the driver seat. The servicing of the air filter element, in such a case needs removal of the seat assembly first for accessing the air filter during servicing. Similarly, in case of passenger cars, low and heavy duty commercial vehicles, the air filters are engine mounted under the hood that restricts the air filter accessibility due to ever increasing components to meet the environmental regulations (emissions & noise) and passenger comfort. V ertical installation of air filter element serves as a viable alternative to such space limitations.

A customary practice for the horizontal installations of air filter element is the use of the O-rings of material such as Neoprene and E PDM for the sealing of the two pressure zone; i.e. the clean side and the dirty side. But for the vertical case, the application of 0- rings are prone to fail under combined shear and compression forces. Hence, adhesive seal tapes are utilized in vertical installations. In current practice, use of seal materials such as Polyurethane, ethylene propylene diene terpolymer [E PDM] and poly-vinyl chloride [PV C] with one sided adhesive strip for the air sealing purpose of vertically installed air filter element is widely used. The functional requirement of the adhesive seal is that the adhesion strength of seal with plastic frame of filter element should be greater than the pull and push force of the filter element during servicing. Furthermore, the seal should possess good compression set property. But with the current practice of the adhesive seal tapes, there can be a chance of tampering, peeling of the adhesive seal ends and hence there exist a chance of seal failure which causes particle penetration from raw side to clean side of filter element. Thus, there is a need of a technologically better alternative to present practice.

SU M MA RY

This invention comprises an Air filter element frame for the internal combustion engine of seal comprising a compressible seal or compressible gasket. In one embodiment of this invention, the compressible seal or compressible gasket comprises a polyurethane foam seal or a polyurethane foam gasket.

The Air filter element frame of this invention further comprises an air filter element frame holding feature and filter paper media. The air filter element frame is made of thermoplastic material, preferably Polypropylene with combined additives in proportion up to 30% comprising at least talc or glass. The air filter element frame holding feature comprises an outwardly projecting/arching-out extension of the filter element frame for the proper gripping and insertion into the air filter assembly and the filter paper media. A guide slot is provided on all the four margins of the element frame as a part of its structure, further carrying ribs for reinforcement. The filter paper media used are insert molded into the air filter element frame, comprise oil impregnated or dry type, that is reinforced into the element frame positioned into the mould into the pre- determined location, In one embodiment of this invention, the densities used for gasket of this invention vary from 100 grams per liters to 300 grams per liters. The ' Compression Set_ of the polyurethane foam seal, defined as the inability to regain its original dimensions after compression expressed in terms of percentage of the original dimensions, varies from 1 % to 3% with a recovery up to 99%. The Guide Slot is one embodiment of the air filter element of this invention which has transverse dimension in a range of 2mm to 3mm. The hardness of the foam material on specimen with the skin on both the surfaces for dwell period of 15 seconds varies from 10e3 on Shore A scale.

a. This invention also comprises a process of making an Air filter element frame comprising a polyurethane foam seal or a polyurethane foam gasket comprising steps of: (a) applying release agent to a mold in the beginning of the process to achieve easy release of the seal from the mould after setting of polyurethane, (b) heating the mold up to 40°C, (c) placing the air filter element on the ' Cavity , to create a channel shaped space one side of which is provided by the longitudinal Guiding Slot present on the four outer sides of the air filter frame and two other sides being provided by two surfaces of the surface of ' Cavity , , (d) mixing polyol and isocyanate in a Polyurethane Dispensing Machine, (e) pouring the mixture in a channel, (f) placing the ore_ on the ' Cavity , to enclose the channel on the fourth side, (i) keeping the poured mix for partial curing in atmospheric temperature for 8-10 minutes, (j) opening the mould after curing, (k) recovering the Air Filter element frame with the polyurethane seal formed on the same, (I) curing the same for a further period of 24 hours.

The polyol, and isocyanate are stored in machine tank at temperature of 20°C to

30°C and used in proportions selected between a range of polyol: isocyanate of 100:20 to 100:30, nucleating them before use by entraining air or gases by mechanical mixers or frothing devices, The nucleation is preferably done in the range of 55% to 65%.

This invention also comprises a Mould for making polyurethane foam seal or a polyurethane foam gasket for air filter element frame for the internal combustion engine. The mould comprises one part, called as ' Cavity , in which the air filter element with its paper pack assembly (3) have been placed for the purpose of making the polyurethane seal around the filter paper element; the ' Cavity , having a channel that is formed between the outer margin of the Filter Paper E lement and the surface of the ' Cavity , of the mould, in which the mixture of polyol and isocyanate is intended to be poured for making the polyurethane seal, and a ' Core , , which is complementary part of the mould which covers this ' Cavity , from above when the assembly is made for making the polyurethane foam seal and provides the fourth side for the channel in which the mixture of polyol and isocyanate for making PU is poured for making the PU seal/gasket. DE TAIL E D DE SC RIPTION OF T H E INV E NT ION

Brief description of figures and legends

F igure 1A: (i) Horizontal installation of air filter element; (ii) V ertical installation of air filter element.

F igure 1 : (1) Air filter element frame, (2) Air filter element holding feature, (3) filter paper media, (4) insert molding of the paper reinforced into the element frame.

F igure 2: Shows air filer element frame with polyurethane foam gasket of this i nventi on: ( 1 ) A i r f i I ter el ement frame, (2) A i r f i I ter el ement hoi di ng feature, ( 3) filter paper media, (4) insert molding of the paper reinforced into the element frame, (5) Polyurethane foam seal/gasket (7) ribs for reinforcement, (A -A) Transverse axis of the air filter element.

F igure 3: Section through the axis A-A of filter element including gasket/polyurethane seal and paper pack. (6) The Guide slot (7) ribs for reinforcement.

F igure 3.1 (A): The section through the axis A-A consisting enlarged view of the air filter element with the Polyurethane foam seal/gasket (5), ribs for reinforcement (7), and the guide slot (6).

F igure 4: T he mould assembled with the air filter element and paper pack assembly for pouring the polyurethane: (3) paper pack assembly, (8) shows the area where the mixture of polyol and isocyanate for making polyurethane is poured, (9) location in aluminum mould where the ribs for reinforcement is aligned, (10) locating pin in the lower part of the mould (11) called as ' Cavity _, since it carries a channel shaped depression meant for pouring isocyanate and polyol in it, and it has a locating pin for engaging with the upper part of the mould [(12), shown in Figure 5)] is intended to be fitted to enclose the channel shaped depression.

F igure 4.1 (A): The section through axis B-B consists of view of (6) the Guiding Slot, channel (8) where the mixture of polyol and isocyanate for making polyurethane is dispensed, (3) paper pack assembly.

F igure 5: Assembly of the C ore and Cavity: This view shows the assembly of Core and Cavity wherein after making the assembly the filter paper pack of Air Filter E lement of Figure 4 is visible; thereafter on part no (11) the other half of the mould is placed so that the channel shaped space in which mixture of polyol and isocyanate for making polyurethane is poured [(8) in Figure 4)] is formed which is covered, after pouring the above mixture, from upper side by the other part of the mould (12). This assembly is completed after pouring the mixture of polyol and isocyanate for making polyurethane to make the Polyurethane Foam Seal gasket [(5) in figure 2)].

Figure 1 shows the general features/structure/design/parts of an air filter element. Air filter element for the intake air filter of internal combustion engines comprises: air filter element frame (1) which may be made of thermoplastic material such as Polypropylene with combined additives such as talc, glass etc. in proportion up to 30%; filter element holding feature (2), which is an outwardly projecting/arching-out extension of the filter element frame (1) for the proper gripping and insertion into the air filter assembly and the filter paper media (3). The filter paper media used may be oil impregnated, dry type or synthetic filter media. The part labeled as (4) shows the insert molding of the paper reinforced into the element frame. The paper is positioned into the mould into the predetermined location. The process used may be injection molding where the plastic material, resulting from the mixture of polyol and isocyanate, is dispensed into the heated barrel and is pressurized to fully fill up the channel that is formed on one side by the guiding slot channel of the air filter frame, on the other two sides by the parts of ' Cavity , and on the fourth side by the part of the ' Core_ of the mould that is placed over the ' Cavity _. This results in formation of a solid gasket of polyurethane foam around the f i Iter frame when it cools down.

Thus, this invention comprises an air filter element frame of an internal combustion engine comprising a compressible seal, which is also designated, alternatively in this specification, as a compressible gasket. As a result, the air filter frame can be assembled vertically by compressing in an air filer assembly and will, thus, overcome the problems arising in course of time from applying one side adhesive tape.

The figure 2 shows the Air Filter E lement of this invention with the compressible seal illustrated by ' Polyurethane foam seal j also called as ' Polyurethane foam gasket , or also mentioned in this specification as Polyurethane foam seal/gasket (5). Polyurethane foam is used in this illustration as a material for making the compressible seal in the form of Polyurethane foam seal/gasket. The important variables in the process of making polyurethane foam seal/gasket for the seal comprise density, compression set and the hardness of the sealant. The densities used for gasket of this invention may vary from 100 grams per liters to 300 grams per liters. The compression recovery set for the polyurethane seal that shall be formed after molding plays a significant role as a parameter in general for the dimensional freezing of the thickness of the polyurethane seal which will be compressed into the air filter assembly for making the assembly. ' Compression Set_ of the material can be defined as the inability to regain its original dimensions after compression expressed in terms of percentage of the original dimensions. Compression Set of the seal depends on the composition of ingredients, temperature and other variables of making the polyurethane seal. C ompressi on S et of 0% woul d be a perfect case, but i s not possi bl e i n real practi ce. The polyurethane foam with compression set with a low value will yield superior foam quality in terms of compression recovery. The Compression Set used in current invention may vary from 1 % to 3% with a recovery up to 99% tested according to the Indian standard 7888. The hardness of the foam material is determi ned on speci men with the ski n on both the surfaces for dwel I peri od of 15 seconds as per AST M (American Society for Testing and Materials) D2240. The hardness of material may vary from 10e3 on Shore A scale. The process follows that the mixture of polyol and isocyanate for making polyurethane foam is dispensed with the polyurethane dispensing machine into the channel (8) into the pre-determined set co-ordinates. The aluminum mold is pre- heated into the oven up to 40°C. Wax is used as a mould release agent during operation. The mixture of polyol and isocyanate form polyurethane as soon as mixed, is heated up to 120°C. The polyurethane that is formed by mixing polyol and isocyanate is poured in molten state in the channel, which gets hardened at the room temperature in the channel (8). The time for cooling of the molten polyurethane foam formed by above process is around seven to ten minutes.

Figure 3 shows a section taken through the axis A-A of the Air Filter E lement through polyurethane foam gasket and paper pack. It is an embodiment of this invention that a Guide Slot (6) is provided as a part of air filter element frame, which enables even flow of the mixture of polyol and isocyanate poured for making the polyurethane foam seal/gasket in the channel (8). Guide Slot increases the surface area for better adhesion of the gasket material with plastic frame. This G ui de S I ot, ref erri ng to the figure 4.1 , has transverse di mensi on whi ch may vary from 2mm to 3mm depending on the compression provided for gasket. The molten polyurethane formed from mixture of polyol and isocyanate is poured at a high temperature above 100° C, which may cause warpage of the thermoplastic parts which adversely affects the part quality and fitment. Hence, the provision of the ribs for reinforcement (7) was introduced to bolster the strength of guiding slot and the f i I ter el ement frame.

A magnification of one end of the cut section A-A of the filter element with polyurethane seal is depicted in the figure 3.1 A. The seal may be compressed from 30% to 40% depending upon the sealing requirement in the assembly. The compression is selected such that there is optimum trade-off between the serviceability i.e. element push and pull force from the air filter assembly and the dust seal i ng. T here are three mai n consi derati ons whi I e sel ecti ng the seal material .

1. The seal should be oil compatible to avoid deterioration of its properties such as compression set, over a period of time on account of this oil contact; since the filter media may be the one which is treated with oil that comes i n contact with the seal,.

2. The material must yield low ' Compression Set_ at temperatures ranges from 20 G C " 70°C

3. Seal material must yield good serviceability i.e. the seal should resist teari ng duri ng the cl eani ng of the ai r f i Iter paper.

The above consideration is taken during the selection of the material for the seal. There are two types of PU [polyurethane] which are used widely in sealing purpose: Open pore skin and closed pore skin. The PU which is used in the current invention is the closed pore type.

An another embodiment of this invention comprises mould for making the polyurethane foam seal or a polyurethane foam gasket for ai r f i Iter el ement frame for the internal combustion engine. The mould comprises two parts, one called as ' Cavity , and the other called as ' Core_.

Figure 4 shows ' Cavity , of the mould (11) in which the air filter element with its paper pack assembly (3) have been placed for the purpose of making the polyurethane seal around the filter paper element. The ' Cavity _ has a channel that is formed between the outer margin of the Filter Paper E lement and the surface of the ' Cavity , of the mould in which the mixture of polyol and isocyanate is intended to be poured for making the polyurethane seal. ' Cavity , of the mould, thus, provides the outer side and bottom of the channel shaped space with the aluminum wall of the mould; and on the inner side the space of the channel is delimited by by the outermost margin of air filter element frame. The arrow labeled as (8) points to the channel in which the mixture of polyol and isocyanate for making polyurethane is poured. The numeral (9) shows the positi oni ng of the ri bs for rei nforcement i nto the al umi num moul d. N umeral ( 10) shows the locating pins in the ' Cavity , of the mould. During the design of the mould, the shrinkage allowance of 1.5% is taken into consideration for the polyurethane material.

Figure 5 shows the assembly of the ' Cavity , and the ' Core , . The term ' Cavity , is used to designate one part of the mould labeled as (11) which carries the depression that provides half of the channel in which mixture of isocyanate and polyol is poured for making the polyurethane seal, and ' Core_ is the other part of the mould labeled as (12) which is placed over the ' Cavity , to cover this channel from above when the assembly shown in figure 5 is made. In this channel the mixture of polyol and isocyanate for making PU (poluurethane) is poured for making the PU seal/gasket. Once the mixture of polyol and isocyanate for making PU gets set as PU in the channel, the two parts of the mould (11 ) and (12) are separated from each other to get the air filter element lined on all the four sides with a continuous and compressible PU seal/ gasket that is held in position by the Guide Slot.

This vertical filter element design is a detachable installation with air filter housing comprising an insert molded filter media. In prior art seal of adhesive tape is open loop seal. In contrast, the feature of the Air Filter E lement design of this invention comprises the PU seal which is completely closed loop seal, which is formed directly in aluminum mould when mixture of polyol and isocyanate for making polyurethane is poured in the channel enclosed between two parts, the ' Cavity _ (11) and ' Core_ (12) of the mould. The polyurethane foam seal/gasket of this invention was made by steps of: (a) positioning the air filter element in the aluminum mould part (11), dispensing required quantity of the mixture of polyol and isocyanate for making polyurethane (PU) by PU dispensing machine in the channel shaped space enclosed by the surfaces provided by the assembly of the Cavity, and the Guide Slot of the outer sides of the air filter element , applying pri mer on the el ement surface to provi de the requi red adhesi on between the pi asti c and the PU seal surface. The air filter element Guide Slot (6) ensures proper dispensing of the PU in the pre-determined position.

M ethods of Analysis:

H ardness measurement: Test was conducted using hardness measuring apparatus such as durometer based on AST M D 2240. This test method allows for hardness measurement on rubber specimen using a specified standard indenter. It is used to evaluate the indentation hardness of materials such as elastomers, thermoplastic elastomers, vulcanized rubber, and plastics. The method consists of indenting the specimen using a hardened steel indenter with specific geometry and force, based on the chosen scale of measurements. The indenter tip displacement was measured for cal cul ati ng the hardness of the materi al . T est speci men shal I be at least 6.0mm in thickness with skin on the both surfaces. Five indentations were made for determination of hardness using durometer of Shore A at different position at least 6mm apart. The specimen was placed on the support table, five indentations were made for determination of hardness using durometer of Shore A at different position at least 6mm apart. C ompression Set measurement:

The test was conducted as per IS 7888 with specimen size of 50mm x 50mm x 25mm. The test was conducted at the specified environment of 27 e 2eC temperature and humidity: 65e 5%. A soft material dial thickness gauge was used for measuring the thickness of the specimen. In case of thin material the thickness of the foam is calculated by deducting the aggregate thickness of the glass slides from the measured total thickness of the assembly. The specimen was then put between the plates and with the help of spacers subjected to 50 percent deflection. The whole assembly is then stored under standard atmospheric conditions for 70 hours or at 70 e 2eC for 22 hours.

E XA M PL E S:

E XA M PL E 1 : M aking the polyurethane Foam Seal/Gasket:

For making the Polyurethane Foam Seal/Gasket, various proportions of polyol, and isocyanate are used depending on the desired properties of the seal. Typically the proportions are selected between a range of polyohisocyanate of 100:20 to 100:30.T hese two chemi cals are stored i n machi ne tank at the temperature of 20°C to 30°C. The development of bubbles within a liquid is called nucleation. A ir or other gases may be purposely entrained into the system by mechanical mixers or frothing devices. The number and size of any entrained bubbles play an important part in foam performance, since gas from the above sources may preferentially diffuse into these sites. Nucleation to be given to machine is preferred in the range of 55% to 65%. The process of making polyurethane foam seal/gasket comprised following steps:

1. Release agent was applied to the mold in the beginning of the process to achieve easy release of the parts of the Air Filter E lement from the mold/mould i.e. for release of the seal from the mould after setting of polyurethane,

2. Mold is heated up to 40°C. The polyol and isocyanate were mixed in a Polyurethane Dispensing Machine,

3. The mixture was poured in the channel (8) enclosed between the ' Cavity _ and the ore_ of the mold/mould on three sides and the Air Filter E lement frame on the fourth side,

4. After pouring the poured mix, the :Core_ was placed on the ' Cavity _ to complete the assembly of the mould, which was kept for partial curing in atmospheric temperature for 8-10 minutes.

5. After curing the mould was opened and the Air Filter element was recovered with the polyurethane seal formed on the same. The Air Filter E lement with polyurethane foam seal was ready for testing of properties and for making assembly after full cure time of 24 hours . The total weight of the polyurethane utilized was 10 grams for an Air Filter E lement of di mension 135 mm * 115 mm.

E XA M PL E 2: Performance testing of the gasket/polyurethane seal:

The performance of the gasket / polyurethane seal was evaluated based on the Compression Set performance according to Indian Standard (IS) 7888 standard at elevated temperature i.e. 60°C. The Compression Set test was performed with the calculated quantity of oil, sprayed on the PU gasket to evaluate its oil compatibility; followed by the serviceability test on the filter element.

The ' Compression Set_ of a material is the permanent deformation remaining when a force that was applied to compress it is removed. The term is normally applied to soft materials such as elastomers. Compression set is defined as the percentage of original specimen thickness after the specimen has been left in normal conditions for half an hour after the same was subjected to 30% compression in the compression spacers for 24 hours. The compression set test is carried out at the elevated temperature of 60°C on the test slab button as per the IS 7888 standard. Also, the compression set is estimated in real time assembly condition at the same temperature and compression conditions. T he comparison of the two values shows that the gasket compression set in the real time assembly condition is 58.86% of the compression set in the compression spacer. Hence, this shows that compression set in assembly level is less than the Compression Set in the compression spacer. Hence the design is safe at elevated temperature for compression.

E XA M PL E 3: Oil compatibility test in two modes

The oil compatibility is tested in one mode, i.e. normal use mode, at the room temperature and on the other mode at the elevated temperatures 60°C i.e. at the accelerated ageing mode of the gasket. The dry air filter element with polyurethane foam seal is compressed in the air filter assembly at the room temperature and left in the assembly for the 24hours. The Compression Set is then determined after the stipulated time. The same procedure is followed for the oil impregnated element with the calculated amount of the oil. The Compression Set is then determined for oil impregnated PU gasket after 24 hours. The comparison of the results shows that the compression set of dry element is 1.19 times of the compression set of the oil impregnated element. Hence, the design is safe in compari son with oi I i mpregnati on at room temperature.

The same procedure described above for the room temperature is followed for the elevated temperature. This test is carried out to determine the deterioration of the performance of the gasket over a period of time i.e. accelerated testing. The air filter element, with and without oil, are compressed in air filter assembly and kept in oven for a period of 24 hours. The corresponding Compression Set is determined and compared. The results show 8.04% variation between the oil impregnated element and the dry element. Hence, there is no detrimental effect of the oil during accelerated testing at elevated temperature on polyurethane gasket. Hence, the design is safe in compression with oil impregnation at elevated temperature.

Serviceability of the element comprises the element push force of the air filer element when the same is assembled; and element pull force with which the air filters assembly is required to be pulled off from the automobile for servicing. The average force required for the element push is 27.5 N. Also, the element pull force is 29.62 N.