Method for manufacturing an air filter and apparatus to carry out such method

Abstract: The method for manufacturing an air filter consists of building in two times, around a paper filtering element (9) previously prepared, an edge (3⊘) made of flexible foam, first injecting resin into a separate space (27) from the filtering element (9), and then letting it expand till it anchors to it. An apparatus to carry out such method substantially consists of a die (1, 2) in which the filtering element (9) is inserted, around which a channel (25) is formed where a mobile frame (1⊘) is sinked, whose shape corresponds to the filtering element (9) one, in such a way as to define an injection recess (27) separated fron the filtering element, and an expansion recess (28) adjacent to the filtering element (9), connected by the mobile frame (1⊘) lift, so that the resin can expand and anchor to the filtering element (9).

Description: The present invention refers to a method for manufacturing an air filter and to the apparatus to carry out such method. An air filter, particularly for vehicle engines, is usually composed of a filtering element made of pleated paper, shaped as a parallelepiped or a cylinder, to which a perimetral edge is sticked, made of foamed resin, usually polyurethane (PU) or polyvinylchloride (PVC). The foamed resin is generally in the form of flexible foam that fixes shape and dimensions of the filtering element, and simultaneously works as seal gasket when the filter is assembled in its vessel, on board of the vehicle. The foamed resin edge is usually obtained by placing the paper, adequately pleated, into a die, and then injecting or casting the resin into a die recess running all around the paper. The resin at plastic state sticks to the paper generating an edge that copies the die recess shape. The employmeny of this technique, however, provides different kinds of problems. One of these problems is created by the possible not uniform distribution of the resin along the die recess, particularly in the part that is far away from the injection point. Another problem can be the excessive penetration of the resin into the filtering paper, due to the low resistance opposed by it to the melted resin flow that enters the above-said recess under pressure, during injection. In the German Patent nr. 2.162.355, a die equipped with side plates is proposed to be used, where such plates limit the contact area between paper element and injected resin, to avoid that the latter migrates on the paper and impregnates its pores. However, though the contact area is reduced, a direct interface is always present between filtering paper and injected resin, so that the chance of migration of the resin through the paper cannot be excluded. The present invention aims to eliminate or reduce the above-said inconveniences of the known manufacturing methods for paper filters with resin edges, providing a method that allows to make the resin distribution regular into the die recess and to prevent its migration into the filtering paper. Another purpose of the invention is to provide an apparatus to automatically carry out the above-said method, in order to allow a high productivity in the manufacture of air filters for vehicle engines. The above-said and other purposes and advantages of the invention, such as the ones resulting from the following description, are reached with a method for manufacturing an air filter, including a preparation stage for a filtering element in pleated paper and a stage to form an edge made of synthetic resin around said filtering element, characterized in that said stage to form said edge made of synthetic resin is obtained in two times, first inserting the resin at plastic state into a restrained space outside contact with said filtering element but next to it, till said space is regularly filled, and then connecting said space with the paper filtering element and letting the resin expand till the contact with it and the anchorage to it. Another object of the invention is to provide an apparatus to manufacture an air filter, including a die in which a perimetral edge made of synthetic resin is formed by injection on a paper filtering element placed inside said die, characterized in that a mobile frame with parallel walls that are contiguous to the paper filtering element sides is contained in said die, said frame being prone to assume a contact position against the bottom of said die, in which an injection recess is defined for said synthetic resin, spaced and separated from said filtering element, and an expansion recess, internally delimited by said filtering element; and a disconnection position from the bottom of said die, whereby said injection and expansion recesses are a single recess that extends up to said paper filtering element, so that the resin injected into it can reach by expansion said paper filtering element and anchor to it. A preferred embodiment of the invention will now be described, given as an illustrating and not limiting example, with reference to the accompanying drawings, in which: Fig. 1 is a partially sectional view of the apparatus according to the invention with open die; Fig. 2 is a partially sectional view of the apparatus in Fig. 1, with closed die, in the injection position; Fig. 2a is an enlarged sectional view of a part in Fig. 2, during injection; Fig. 2b is a view corresponding to the one in Fig. 2a, during expansion; Fig. 3 is a sectional view along line III-III in Fig. 2, in another operative position; Fig. 3a is an enlarged sectional view of a part in Fig. 3; and Fig. 4 is a schematic plan view of a machine to manufacture filters including the apparatus according to the invention. With reference to Fig. 1, the apparatus according to the invention includes a die composed of a lower die 1 and an upper die 2, equipped with a gasket 3 on its lower side aimed to press closed against the lower die 1. The two dies 1 and 2 are rotatingly constrained one another through their respective arms 4 and 5 with fulcrum on the pin 6. Fig. 1 shows the open die, while Fig. 2 shows the closed die. The central plan 8 of the lower die 1 is realizeed of such shape and dimension as to be able to house a paper filtering element 9, produced apart in a known way. In case of air filters for vehicle engines, the filtering element has the shape of a cylinder or a parallelepiped. In the shown case, the filtering element 9 is a parallelepiped in shape. Inside the die 2 a structure is contained, essentially composed of a quadrangular frame 1⊘, whose hollow interior has shape and dimensions corresponding to those of the filtering element 9, and is therefore such as to surround and keep in position on the plane 8 the filtering element during working, as will be said afterwards. With reference also to figures 2 and 3, the frame 1⊘ consists of four orthogonal walls 12, 12a, 13, 13a, rigidly connected one another, and connected at the upper side to four columns 15, 15a, 17, 17a, that are suitable to slide in holes 11 provided in a driving plate 16 of the upper die, and are then secured to plate 18, parallel to plate 16. The plate 18 is in turn connected to the piston 19 of an actuator cylinder 2⊘, only partially shown. In the retracted position of the piston in the cylinder, shown in Figures 1, 2b, 3, 3a, the frame 1⊘ is lifted as regards the lower die 1, but, with closed die, sorrounds the filtering element 9 and keeps it centered on the bearing plane (8) of the lower die 1. In the extended position of the piston 19, shown in Figure 2, the frame 1⊘ is sinked against the die 1, and in this position the plate 18 beats against the driving plate 16. The piston 19 stroke is adjusted in such a way as to realize this bedding and disconnection movement of the frame 1⊘ against the die 1. For this purpose, the frame 1⊘ is formed with a continuous shoulder 22 suitable to beat against the stop surface 23 of the upper die 2. Around the bearing plane 8 of the lower die 1, a channel 25 is defined whose profile generates the section of the edge 3⊘ made of flexible foam of foamed resin that must be formed around the filtering element 9. The frame 1⊘ beats, while closing, inside such very channel, defining, in the radially external part of the channel 25, an injection recess 27, separated and insulated from the filtering element 9, and, in the radially internal side of the channel 25, an expansion recess 28, internally delimited by the filtering element 9 (Fig. 2). This latter one preferably extends till below a part of the filtering element, in order to allow a better anchorage of the resin. This is shown in detail in the part of Fig. 2a. The recess 27, more external, communicates with an injection channel 24, through which the melted resin is injected into the die. The operation of the described apparatus is the following one. With open die (Fig. 1), a filtering element 9, previously prepared, is placed on plane 8 of the lower die. After that, the die is closed and the frame 1⊘ is sinked against the lower die 1. The walls 12, 12a, 13, 13a settle in a radially intermediate position inside channel 25, so that the injection recess 27 and the expansion recess 28 (Fig. 2) are defined. The melted resin 29 is injected into the recess 27, as indicated by arrow I in Fig. 2a. The resin 29 is regularly and homogeneously distributed along the whole recess, completely filling it. After a time varying depending on the properties of the used resin, on the recess geometry and on other operating factors, the frame 1⊘ is lifted and the resin is allowed to expand through the expansion recess 28, now communicating with the recess 27, till the filtering element 9 is reached, to which the resin adheres and anchors. The expansion of resin 29 towards the filtering element 9 is shown in the part of Fig. 2b. It is evident that the resin anchorage to the filter paper only occurs under the thrust determined by the expansion, and not owing to the much stronger thrust generated by the injection pressure, as well known in the technique. Therefore, a deep penetration of the melted resin does not occur into the paper filtering element, that would produce an excessive impregnation of it, with following decrease of the filtering surface and capacity. After having ended the expansion and cooled the resin, the filter complete with an edge 3⊘ is produced with flexible foam of foamed resin, like in Fig. 3 and in the part in Fig. 3a. At that time, the die is opened, the filter is removed, another paper filtering element is placed into the die and the described cycle is repeated. Fig. 4 shows a machine for the volume production of the filter using the above described apparatus. The machine consists of a carrousel carrying 18 work stations progressively numbered from 41 to 58, each comprising two molding apparatus of the above described type, for a total of 36 apparatus. Every apparatus is marked by numbers 41.1 and 41.2, 42.1 and 42.2, 43.1 and 43.2 ... 58.1 and 58.2. Each one of the single molding apparatus can produce only one filter, like in the embodiment described by the previous Figures, or can produce more filters, for example when their dimensions are small. In this case, the lower die will be formed with a channel that sorrounds every bearing plane of every filtering element, and all the channels will communicate with the injection channel. Also the mobile frame that limits the injection recess will be a multiple one, with such shape and dimensions as to allow the production of more filters within a single molding operation. Next to the carrousel 4⊘, a double injection unit is placed, composed of two injectors 6⊘ and 61, aligned from time to time with each device in each work station 41 ... 58 of the carrousel 4⊘. The injection unit is sided by the stocking tanks for raw materials and additives, in a known way, and therefore not shown. For every carrousel 4⊘ turn of a 2⊘° angle, the injection unit is aligned with a work station. In this alignment condition, the injectors are pushed against the apparatus of each work station - with an automatism known to any experienced person in the field - and at the same time the resin injection occurs into each one of the two apparatus composing every single work station. In the meantime, the finished filter is unloaded from the previous stations and the paper filtering element is loaded into the following ones, realizing a volume production with high productivity. The described method and apparatus are particularly advantageous to produce air filters for vehicle engines, though their use is possible also to produce air filters suitable for other uses.

Claims: Method for manufacturing an air filter for vehicle engines, including a preparation stage for a filtering element in pleated paper and a stage to form an edge made of synthetic resin around said filtering element, characterized in that said stage to form said edge made of synthetic resin is obtained in two times, first injecting the resin at plastic state into a restrained space outside contact with said filtering element but next to it, till said space is regularly filled, and then connecting said space with the paper filtering element and letting the resin expand till the contact with it and the anchorage to it. Apparatus to manufacture an air filter for vehicle engines, including a die (1, 2) in which a perimetral edge (3⊘) made of synthetic resin is formed by injection on a paper filtering element (9) placed inside said die, characterized in that a mobile frame (1⊘) with parallel walls (12, 12a, 13, 13a) that are contiguous to the paper filtering element (9) sides is contained in said die (1, 2), said frame being prone to assume a contact position against the bottom of said die, in which an injection recess (27) is defined for said synthetic resin, spaced and separated from said filtering element (9), and an expansion recess (28), internally delimited by said filtering element; and a disconnection position from the bottom of said die, whereby said injection (27) and expansion (28) recesses are a single recess that extends up to said paper filtering element (9), so that the resin injected into it can reach by expansion said paper filtering element and anchor to it. Apparatus according to claim 2, characterized in that said single recess (27, 28) that extends up to said filtering element (9) is limited in its lower side by a channel (25) obtained all around the perimeter of the bearing plane (8) of the filtering element (9). Apparatus according to claim 3, characterized in that, in said contact position with the bottom of said die, said mobile frame (1⊘) is placed with its walls (12, 12a, 13, 13a) against the bottom of said channel (25), in an about radially intermediate position. Apparatus according to claim 2, where said filtering element (9) has the shape of a parallelepiped, characterized in that said mobile frame (1⊘) has a quadrangular shape with walls (12, 12a, 13, 13a) that are parallel to the filtering element (9) ones. Apparatus according to claim 5, characterized in that said mobile frame (1⊘) is connected through columns (15, 15a, 17, 17a) to a plate (18) in turn connected to an actuator (2⊘), said columns (15, 15a, 17, 17a) being sliding into holes (11) drilled into a driving plate (16) that is part of the structure of said die (2). Machine to produce air filters for vehicle engines, characterized in that it includes a carrousel (4⊘) carrying a plurality of apparatus (41 ... 58) according to any of the claims from 3 to 6, and in that it includes also an injection unit (6⊘, 61) for synthetic resin, sided to said carrousel (4⊘), each one of said apparatus (41 ... 58) being able to be aligned with said injection unit (6⊘, 61) owing to the rotation of said carrousel (4⊘). Machine according to claim 7, characterized in that said apparatus (41.1, 41.2 ... 58.1, 58.2) are paired in couples and said injection unit is composed of a couple of injectors (6⊘, 61) suitable to inject the resin into each couple of apparatus.

Inventors: BARACCHI FABRIZIO, CASALICCHIO SILVANO, GALLINO MAURO, TARDITI LUIGI, BARACCHI, FABRIZIO, CASALICCHIO, SILVANO, GALLINO, MAURO, TARDITI, LUIGI
Applicants: GILARDINI SPA, GILARDINI S.P.A.
Application year: 1991
Main classification: F02M35
IPC codes: B29C45, B29C70, B29C44, B29C33, B01D39, B01D46, F02M35