GB2141374A - Foam filter production - Google Patents

Abstract

A process for foam filter production comprises the steps of forming a preliminary plastics sealing element in a rotary mould and applying thereto a foam filter material for fusion bonding therewith as the sealing plastics material cools, and reorientating the resultant foam and plastics assembly to present a fresh portion of the foam to a mould in which a further quantity of sealing material has been deposited for fusion bonding therewith, to form a complete operational seal for the foam body. The resultant filter may be an automobile air filter.

Description

SPECIFICATION Apparatus and process for the production of foam filters This invention relates to the production of foam filters and is particularly concerned with the production of a foam filter according to my co-pending UK patent application number 8222402, which finds particular application in the automobile field, as an in internal (fuel/air) combustion engine air intake filter.

It is a general requirement that a foam filter be produced in a manner which ensures the possibility of effecting a secure seal between the filter body and housing therefore, and in particular a seal around the periphery of the filter where installed. Preferably the seal is one which is integrally formed as a unitary assembly with the foam filter body itself.

The filter body may incorporate one or more reinforcing elements, for example plastics or metal wire mesh grid or spaced strands or rods of wire or plastic, conveniently as a reinforcing layer and it is also convenient to use a synthetic plastics material as the peripheral seal, in which case bonding of the peripheral seal to both the filter body and the reinforcement is desirable. In this way the reinforcement may effectively act as a seal stiffener.

For economy in manufacture, the process should be as straightforward and reliable as possible, with minimal discrete process steps and intermediate handling of the part-finished prodcut.

It is also desirable to keep the positioning tolerances of the individual filter components prior to assembly as uncritical as possible in order to achieve a generally satisfactory overall manufacturing tolerance, and thus to allow some of the process steps to be effected manually - for example component positioning and repositioning. However, robotic techniques may also be used for this and indeed to control the overall assembly process.

For foam filter construction to be comparable and indeed competitive in terms of cost and efficiency to other known and more conventional filter constructions in which an impregnated or coated, for example with wax, paper is employed in corrugated form, both the inherent design and the manner of component fittings and assembly must be simple, straightforward, secure and capable of consistent and high volume mass production, particularly taking into account the existing heavy investment in other filter production capability, such as paper air filter construction machines.

In terms of operational performance or efficacy, a foam air filter offers the prospect of a more consistent, long term performance, and in particular one not necessarily deteriorating markedly with time for a very considerable period when compared with known, eg paper, filter construction.

For such improvements in performance to be achieved the filter sealing with respect to the filter housing or casing must be of a high standard and the inter-assembly of component parts of the foam filter must be such as to avoid unwanted leakage of unfiltered (gas) medium.

Since the ingredient materials for plastics foam filter construction are expensive, in particular the granules of synthetic plastics materials used for injection moulding, and similarly pre-formed foam sheet itself is expensive, particularly in multi-layer form with layers of different porosity and when intermediate reinforcing layers are provided, the process of producting of a foam filter must necessarily be economical in ingredient or constituent materials, with minimal wastage during the production assembly.

According to the invention, a process for foam filter production comprising the steps of forming a preliminary sealing element in a mould and applying thereto a molten foam filter material for fusion bonding therewith as the sealing plastics material cools and forms an expanded internal pore structure, and reorientating the resultant foam and plastics seal assembly to present a fresh portion of the foam to a mould in which a further quantity of sealing material is injected for fusion bonding therewith, to form a complete operational seal for the foam body.

According to another aspect of the invention, there is provided a foam filter produced by the method or process of the immediately preceding paragraph.

Conveniently, the mould for the plastic seal is mounted on a turntable for rotation adjacent to a moulding nozzle of an injecting moulding station, whereby to fill the mould recesses or channels as the turntable rotates, rotation and injection being synchronized so as to just fill the mould without excess.

Desirably, the mould is slightly warmed, for example by temporary exposure to a heated air oven environment, before injection in order to promote the curing of injected synthetic plastics material and the formation of the seal.

Conveniently, the turntable mounting of the mould incorporates elevator means for raising and lowering the mould relative to the injection moulding station.

A conveyor may be used to transfer moulds to the moulding station and therefrom to subsequent process stages. For this purpose a robotic arm may conveniently be employed for transferring partcompleted filters from one stage of the apparatus to another. This avoids unnecessarily long and complex conveyor assemblies.

Oven chambers may be employed to achieve the desired mould temperature ready for injection of synthetic plastics material for subsequent curing; such moulds may incorporate thermostats to determine the oven chamber temperature. Optical sensors may also be employed to register the presence of moulds in the oven chamber. Such peripheral control devices may be linked with an overall process control system controlling the mould positioning injection moulding and robotic movement and positioning Conveniently, the filter body material is cut from a roll by a slicing or knife arrangement arranged to cut the unwound web from the roll into, say, slices by action of a vibratory knife with an elongate blade, or alternatively one or more rotating cutter wheels with a peripheral knife edge.

For some filter applications, in particular automobile air filters, it is desirable that the foam be impregnated with a special retentive oil, in order to promote the filtration characteristics required. This oil impregnation may be achieved by an oil bath and conveniently foam from a roll is fed by a roller guide system into a trough containing the prescribed oil at a slightly elevated temperature and thereafter out of the bath through guides and a series of squeezing, rotating rollers arranged to squeeze the foam therebetween to discharge excess oil, leaving only a predetermined quantity by weight or volume of weight of foam left impregnated in the foam.

The subsequent bonding of oil impregnated foam cut to the desired shape and size may be effected by the seal moulding apparatus and process described previously.

There now follows a descripton of a particular embodiment of the invention, by way of example only, with reference to the accompanying schematic drawings, in which: Figure 1 shows a filter seal moulding apparatus; Figure 2 shows a foam cutting station; and Figure 3 shows a foam oil impregnation station.

Referring to the drawings, a foam filter assembly apparatus comprises a moulding station 20, with a conveyor 16 arranged for feeding and unloading the moulding station 20.

The conveyor 16 is arranged to feed through a preliminary heating oven chamber 30 upstream of the moulding station 20 and subsequently into a reheating oven chamber 36; the conveyor having a recirculating return route 18 enabling part moulded articles, specifically foam filters, to be returned to the moulding station 20 after necessary preheating in the preliminary oven chamber 30.

A robotic arm 31 is provided for selectively moving part-formed filters from one stage of the process to another and this may be used to obviate unnecessarily long and tortuous conveyor routes possibly enabling the elimination of a return run of the conveyor altogether in some configuration.

The moulding station 20 incorporates an injection moulding machine 32 under the control of a control unit 33 with a digital display 34 for indicating the process stage.

The moulding machine 32 has an arm with a nozzle assembly at the end which may be rotated and articulated to position the nozzles over a mould 19, which is positioned on a turn-table 22 itself mounted for rotation and vertical movement upon a drive and positioning motor 23.

In order to accommodate for occasions when the injection machine may need clearing, a waste container 24 is provided adjacent the nozzle assembly for selective discharge and cleaning.

A typical process sequence is as follows: A series of moulds are preheated in the oven chamber 30 and are passed by the conveyor 16 onto the turn-table 2 which is elevated into the position shown intruding across the conveyor run. The conveyor is temporarily halted and the turn-table rotated as the injection moulding machine 32 is activated to inject from the nozzles at the end of the injection arm synthetic plastics material which will form the mould seal, in the form of a peripheral seal for the filter in use. The mould 19 has a peripheral annular channel or groove 17 as shown in Figure 4.

As the turn-table 22 is rotated, so successive portions of the mould channel are brought into alignment with the injection nozzle(s) and are filled with injected plastics material, which subsequently cures into an integral foam sealing ring with a skin and a spongy body. Curing is promoted by the preheating of the mould tray 19 in the preliminary oven chamber 30.

After one complete rotation of the turn-table 22 the drive unit 23 stops the rotation and lowers the turn-table into the passage of the conveyor 16, which may be restarted to take the filled mould from the conveyor and allow curing during subsequent cooling.

When the mould 19 is filled, a foam filter body material may be applied thereto so that, in the subsequent curing of the seal, it is bonded to the foam body material.

The bonded assembly described above may be provided with a further seal in a similar moulding step with the part formed filter and initial seal removed from the mould and repositioned in a fresh mould after subsequent preheating in the oven chamber 36 prior to return to the turn-table 22.

Because an open form of mould is used moulding costs are kept low; that is to say no elaborate precision metal machine or tooled moulds are required, rather straightforward vacuum or otherwise heat moulded sheets may be used as mould trays 19. The use of synthetic plastics material therefore enables the moulds to be essentially self-cleaning when the contents are discharged.

As further refinements of the process, optical on sensor 27 may be incorporated into the oven chamber 30 to check the positioning of moulds thereinto and to link in with the subsequent overall process control under the control unit 33. Similarly, the heat sensor 26 may be employed to control the oven chamber temperature.

A suitable form of conveyor is a multi-roller type in which a plurality of rollers 15 form the conveyor surface rather than necessarily a separate integral sheet, the rollers conveniently being inter-connected for example by chains and sprockets in a conventional manner.

Referring to Figure 2 a preliminary cutting of foam body material is performed in a cutting station in which a roll 42 of foam body material is fed under a guide roll 4 to a vibrated or oscillated linear cutting blade 43 mounted on spring/transducer 44 and the cut length or lengths 46 are fed to a take-up roller 48.

One or more rotating cutting wheels may be used instead of a linear cutting blade or edge.

Figure 3 shows a preliminary oiling stage in which the foam body material from the roll 59 is fed as a web 60 under guide rollers 61, an oil bath 50 containing a special preheated oil 51 and thereafter through a preliminary squeezing guide 56 into a series of spaced squeezing rollers 58 mounted over a catchment tray 52 arranged to catch residual discharged oil 53 and the overflow being transferred by a pipe 55 into the main oil bath 50, so that the residual oil in the squeezed foam is at the desired level, for example in terms of weight of oil against weight or volume of foam.

Figure 4 shows diagrammatically a section of a foam body material inserted in a mould tray 69 during the moulding step; and Figure 5 shows a plan view of a particular foam body material formed by the process stage of Figure 4.

Referring to Figures 4 and 5, a foam body material 76 comprises a dual density foam of which the outer layer 7 has a different porosity from the inner layer 78, an intermediate reinforcing or support layer 79 being provided and which may comprise individual wires or rods of metal or synthetic plastics material or a metal or synthetic plastics material web or grid.

Alternatively, a stiff porous paper or cardboard triple or multiple layer reinforcement sheet may be provided either internally or externally of the body.

The foam body material takes the form of an annular ring which is positioned either manually or by say the robotic arm previously referred to, squarely downwardly, indicated by arrow 80 into a channel 70 in the mould tray 60 into which synthetic plastics sealling material 75 is injected to an amount which will allow a seal to form to a level indicated by a dotted line as the sealing material cures and integrally bonds the peripheral end of the foam body material thereinto.

The mould tray 69 is mounted on a turn-table itself mounted on a shaft 82 for rotation and vertical movements indicated by the relevant arrows in the drawing.

Figure 5 shows how the enclosed ends of the annular foam body material 76 are joined by a staple 85, clamping spaced deflector plates 86 and 87 on opposite sides of the foam body material. In this way the butt join of the free ends of the foam body material 66 does not allow leakage in the subsequent use of the filter.

The mould 69 incorporates a further shallow annular recess or indent 71 which forms a peripheral lip seal for the main seal body material 75.

For a more detailed description of the filter construction, reference is made to my co-pending United Kingdom Patent Application number 8222402.

Claims (4)

1. A process for foam filter production comprising the steps of forming a preliminary sealing element in a mould and applying thereto a molten foam filter material for fusion bonding therewith as the sealing plastics material cools and forms an expanded internal pore structure, and reorientating the resultant foam and plastics seal assembly to present a fresh portion of the foam to a mould in which a further quantity of sealing material is injected for fusion bonding therewith, to form a complete operational seal for the foam body.

2. A process for foam filter construction, as claimed in Claim 1, wherein the mould for the plasticseal is mounted on a turntable for rotation adjacent to a moulding nozzle of an injecting moulding station, whereby to fill the mould recesses or channels as the turntable rotates, rotation and injection being so as to just fill the mould without excess.

3. A process for foam filter construction, as hereinbefore described with reference to, and as shown, in the accompanying drawings.

4. A foam filter produced by the method according to any of the preceding claims.