FR3080046A3 - AUTOMATIC SELF-CLEANING FILTER FOR PLASTIC MATERIAL - Google Patents

Abstract

It is an automatic and self-cleaning device for filtering melted plastic, equipped with special filters.

Description

Description

FIELD OF THE INVENTION: AUTOMATIC SELF CLEANING FILTER FOR PLASTIC MATERIALS Technical Field [0001] The object of the present invention relates to a device for filtering molten plastic.

[0002] Characteristics of the Prior Art [0002] The need to recover the plastic for reuse for a new use, as a material for melting for a new molding, is well known.

The component inside the filtering device that fulfills this function is a filter capable of more or less effectively separating the impurities from the material to be recycled, by retaining them and allowing the molten plastic to pass through.

This separation function is achieved through the different types of filters through different modalities, but the main criterion of evaluation of these devices essentially takes into account the costs and the degree of effectiveness.

A known device comprises a hollow cylindrical body inside which the material to be filtered is pushed by an extruder and is heated until it becomes plastic and fluid. It must pass through a pierced plate (similar to a section of limited height, obtained from a circle endowed with a central hole and pierced with a large number of small holes on its flat walls).

Dirt and impurities of this material stop in front of the plate, after back of the plate is obtained the recycled material "clean".

This system has many disadvantages: it must be stopped during the production of clean plastic to be able to remove the dirty material that has accumulated on the front part of this plate.

In addition, the plate, having to withstand very high pressures and temperatures, must be obtained from a very thick round, then perforated.

Although the costs for preparing this plate are very high, the cylindrical holes close quickly, so that it will replace the plate after a stop of the machine.

A solution to delay the replacement of the plate, as a filter element, is to adopt two rotating blades which by touching the surface of the plate, the one that faces the entrance, lift and move the part Dirty melting backwards with respect to the flow direction from the inlet to the outlet, reintroducing the dirty material raised in the melt, contained in the inlet of the cavity of the cylindrical body.

However, after the rotating blades have performed a few turns of rotation, the material in the cavity of the cylindrical body must be wide apart.

It is therefore expected to close the output of the clean material and open another output conduit directly connected to the hollow part of the device to be able, with the input of other material through the extruder that feeds the flow of the molten material that must be filtered, remove a good part of the dirty material, replacing it with the input material.

The main drawbacks of this mode concern the downtime of the machine, the large waste of material and the only partial replacement of the material to be filtered inside the cavity.

To ensure that the plate does not become irreversibly clogged, stopping operations of the aforementioned machine must be fairly close and frequent when treating the material, even slightly dirty.

However, this contrasts with the high cost of the perforated plate, so it tends to delay too much cleaning activities, with a compromise between the downtime of the machine, the amount of dirty material thrown and the costs. for the replacement of said grid.

It must be said that all the operations are not at all simple, since each opening of the cavity of the cylindrical body must be performed at the operating temperature or operating temperature of the filtration device, that is to say with a temperature between 180 and 260 degrees centigrade, depending on the type of plastic material filtered, when it is still soft or fluid.

Finally, it should be added that the high costs of the perforated plate are due to the manner in which it is manufactured, that is to say by drilling and not by perforation by means of a matrix and a punch .

OBJECT OF THE INVENTION [0019] The object of the present invention is to overcome the disadvantages of the known technique.

In particular, the objective of the present invention is to provide a self-cleaning automatic filter for plastics, which overcomes the disadvantages of the perforated plate.

An interesting object of the present invention is to provide a self-cleaning automatic filter whose stop and filter replacement steps are not expensive.

An important object of the present invention is to provide a self-cleaning automatic filter capable of overcoming the limits of the filtration capacity relating to current production processes.

An essential objective of the present invention is to provide a self-cleaning automatic filter with a filter that can not generally clog.

Finally, and this is not the least important purpose, the present invention provides a self-cleaning automatic filter whose filter can be replaced quickly and cheaply.

All the aforementioned objectives and others, which will appear better from the following description, are obtained through the invention characterized by all the aspects highlighted in the claims.

Exposure of the invention In particular, it is a self-cleaning automatic filter for plastics, which is equipped with a hollow cylindrical body with at least one inlet for the molten plastic material to be filtered. and provided with at least one outlet for the filtered molten plastic to exit, within said hollow cylindrical body is a perforated support disc integral with the hollow body, and characterized by the fact that above this support perforated a support filter is associated in support, on the surface of which are rotated one or more scraping blades, the holes of the support filter having a mean diameter of between 800 and 50 microns and the thickness of the filter being included between 0.5 and 2mm.

The advantages of the invention.

The advantage is that at least one scraper is associated with a conveyor, the scraper being inclined relative to the filter surface to lift the dirt and transport it, pushed by the pressure of the inlet flow to the outside, thus reducing the rate of waste to a few percentage points more compared to the amount of contamination existing in the material.

The advantage is that the filter has a thickness equal to the diameter of the holes of the molten plastic passage, with a range from 800 to 400 microns, so it is very economical, it can be changed frequently, it is appropriate for the production of recycled plastic and it can be used in injection molding.

The advantage is the filter has a thickness greater than the diameter of the passage holes of the molten plastic, with a range from 400 to 50 microns, achieving filtration qualities previously considered impossible to obtain, which makes it Recycled plastic can be used in very high quality applications, such as filming.

The advantage is that the support filter, with holes of average diameter between 400 and 50 microns, can be obtained by means of an electron beam and / or a laser beam, which allows to exceed the limits imposed by the punching technique.

The advantage is that the thickness of the support filter can be 2 to 20 times greater than the average diameter of the relative holes present on the support filter, obtained by means of an electron beam and / or 'a laser beam, realizing filters a lot

Claims (1)

more durable compared to the corresponding filters that could be obtained with the punching technique. The advantage is that the section of the holes can increase gradually from the entrance to the exit, so it is possible to obtain a little filter subject to clogging because of the obstruction of the holes caused by the dirt present. in the material to be cleaned. The advantage is that the increase of the section of the holes can be verified from a few tenths of degrees centigrade to 15 degrees centigrade, being able already with the extreme lower of the range to check that the dirt, once past the inlet section, manages to pass without being restrained in the filter thickness section, whereas when section increases occur from more than 15 degrees, it has been verified that no obvious benefit is not obtained. The filtration mechanism, with its diameter holes of between 800 and 400 microns, can be obtained by means of the punching technique. The advantage is that the filtering mechanism can be subject to a curing process, such as chromium plating, and the material contribution to the thickness does not cause clogging of the holes, so these treated filters are less prone to wear caused by scraping blades and last much longer before replacement is necessary. At least one conveyor may be equipped with a collection and conveying channel for transporting the impurities raised by the scraper to the exit route, outside. The advantage is that the path of the exit and the removal of impurities raised by the scrapers secured conveyors, coaxially traverses the motor shaft for the start of the same conveyors, or an extension thereof. , making the construction of the device much more simplified, that is to say without the need that there is need for a further opening in the hollow cylindrical body for the dirt to come out, and also limiting the percentage waste only to the dirt present in the material to be cleaned. BRIEF DESCRIPTION OF THE DRAWINGS [0041] The technical characteristics of the invention, according to the above-mentioned objectives, can be clearly ascertained from the content of the above-mentioned claims and they will be evident in the detailed description which follows and which refers to the drawings illustrating an embodiment which serves a purely exemplary and non-limiting example, in which: [0042] [fig.l] represents a filtering device of the prior art, seen in section. [Fig. 2] shows the device of the invention in a perspective view. [Fig. 3] represents the device of the invention in a perspective view partially in section, leaving a glimpse of the structuring of the front part. [0045] [fig.4] represents a vertical plan view of the device of the invention in a vertical plane passing through the axis of the inlet duct of the melt to be cleaned; [0046] [fig.5] is a sectional view of the device of the invention according to a horizontal plane ho passing through the axis of the motor shaft which rotates the scraping blades attached to the conveyors; [0047] [fig.6] shows a sectional view of the device of the invention in a vertical plane passing through the axis of the motor shaft. Detailed description of a preferred embodiment [0049] Referring to the drawing of FIG. 1, an example of filtration device 1 of the prior art, it can be seen that it illustrates a filter 2 (as filtration unit included in the same device 1), composed of a hollow cylindrical body 3 and fed to the before by an extruder 4 that pushes the molten plastic that needs to be cleaned. In the hollow cylindrical body 3 is the expensive perforated plate 5 provided with holes 7 which connect the opposed flat surfaces 8 and scraped by the rotating blades 9 which lift the dirt of the cleaning material which rests on the flat surface 8 input. This plate 5 can be made with thicknesses greater than 1 cm and with holes, made using a drill, with a diameter equal to or greater than 1 mm. Given the height extension of the cylindrical holes 7, this plate 5 is easily clogged because of the obstruction of the holes 7, caused by the dirt present in the molten plastic to be cleaned. Figures 2 to 6 show the self-cleaning automatic filter object of the invention. The automatic self-cleaning filter 12 comprises a hollow cylindrical body 13, which is in the filtration unit and encloses it. The filtration unit consists of a perforated support disc 16 which has a considerable thickness and which is housed integrally and removably inside a stop provided for this purpose of the hollow body 13 and is provided with a central hole for the passage of the motor shaft. On this support disk 16 perforated, which serves as a support, a support filter is associated in support, the holes 20 retain the impurities of the material to be filtered. On said filter 17, at least one scraper 18 is rotated by the drive shaft 21 to lift the accumulated dirt on the surface of the filter 17 and transport it through a coaxial hole 22 present in the motor shaft. 21, outside. The advantage is that the connecting element between the scraper 18 and the motor shaft 21 is a dirt conveyor raised by the scraper 18 to the outlet channel of the impurities of the hollow cylindrical body 13, in fact, it has a preferred channel 23 for collecting and conveying impurities to the coaxial cavity 22 of the drive shaft 21. The advantage is that the conveyors 19, which are associated with the relative scrapers 18, are two arranged in a diametrically opposed position relative to the axis of the motor shaft, achieving a symmetry of the construction and efforts that are verified during operations. We can verify that the dirt that approaches the filter 17 can not plug any hole 20 of the filter 17 because the relative holes 20 are flared downstream, so that the various dirt particles, once overcome the section d 20, go downstream when their dimensions are tolerable with the quality required by the degree of cleaning or (if they are larger than the filter holes) stop before, or at each hole 20, in order to being raised by the scraping blades 18 which rotate by touching, rotated by the conveyors 19 driven in rotation by the motor shaft 21. The discriminant distinction which concerns the size of the holes of the filters 17 of the invention has both a technological meaning to which a qualitative result corresponds. The world of recycled plastic applies to two categories: the category of injection molding and the category of filming. For example, injection molding allows "to print" the backrest of plastic chairs. All small inclusions are tolerated and are insignificant compared to the object obtained as a whole. Of course, for products that require hygiene and non-toxicity, as in the case of products that come into contact with food, such as forks and glasses, it is necessary to use plastic virgin, but for anything that can be reused, such as plastic pallets or garden furniture, recycled plastic is used. For these types of applications, fine filtration is not necessary because they usually have a dark color that hides the impurities that remain inside the plastic. While, if we take the packaging as an example, the plastic to be reused must be filtered finely because inclusions visible to the naked eye are not accepted. For these applications, which are increasingly in demand worldwide, that is to say a recycled plastic of high quality, this invention is particularly appropriate. With this invention, it has been possible to obtain economic filters with diameters that can reach 800 mm in diameter. In addition, it was possible to exceed the limits of the punching technique (the filtering mechanism is linked to the limit defined as "same diameter same thickness"), thanks to an electron beam technology and / or laser drilling less than 400 microns. With the new technology, the filters 17 can have a considerably greater thickness compared to that of the filters that can be obtained correspondingly through the punching technique. For example, with a 1 mm thick filter, it is possible to obtain both 400 micron holes and 200 micron holes, or even 80 micron holes, reaching a limit for 50 holes. microns. The increase of this thickness, with respect to the diameter of the holes, makes it possible to have a filter 17 perforated with an electron beam and / or a laser technology whose duration is even four times longer compared to that of the respective filters, made through the punching technique. Finally, thanks to the new technology, it has been possible to obtain flared holes diverging in the flow direction, which do not become plugged because of the materials having the same diameter as the holes 10, as it is produced in the punching technique. Claims [Claim 1] Automatic self-cleaning filter for plastics, equipped with a hollow cylindrical body (13) with at least one inlet (15) of molten plastic material to be filtered and provided with at least one outlet for the filtered molten plastic so, inside this hollow cylindrical body (13) is a perforated support disk (16) integral with the hollow body (13), and characterized by the fact that above this support ( 16) perforated a support filter (17) is associated in support, on the surface of which are rotated one or more scraping blades (18), the holes (20) of the support filter (17) having a mean diameter between 800 and 50 microns and the thickness of the filter (17) being between 0.5 and 2 mm. [Claim 2] Automatic self-cleaning filter for plastics according to claim 1, characterized in that the support filter (17) with holes (20) having a mean diameter of between 400 and 50 microns is obtained by means of an electron beam and / or a laser beam. [Claim 3] Automatic self-cleaning filter for plastics according to claim 2, characterized by a thickness of the filter (17) which is 2 to 20 times greater than the average diameter of the relative holes (20) present on the support filter (17). [Claim 4] Automatic self-cleaning filter for plastics according to any one of claims 1 to 3, characterized by progressively increasing the section of the holes (20) from the inlet to the outlet. [Claim 5] Automatic self-cleaning filter for plastics according to claim 4, characterized in that the aforementioned increase in the cross-section of the holes (20) takes place from a few tenths of a degree centigrade up to 15 degrees centigrade . [Claim 6] Automatic self-cleaning filter for plastics according to claim 1, characterized in that the filtration mechanism (17), with its holes (20) having a diameter of between 800 and 400 microns, is obtained by means of the punching technique. [Claim 7] Automatic self-cleaning filter for plastics according to one of claims 1 to 6, characterized in that the filter mechanism (17) is subjected to a curing process, such as chromium plating, and the material contribution to the thickness does not cause the plugging of the holes (20) themselves. [Claim 8] Automatic self-cleaning filter for plastics, according to claim 1, characterized in that at least one scraper (18) is associated with at least one conveyor (19), the scraper (18) being inclined relative to on the surface of the filter (17) for lifting the dirt and transporting it, pushed by the pressure of the flow from the inlet to the outside. [Claim 9] Automatic self-cleaning filter for plastics according to claim 1, characterized in that at least one conveyor (19) is equipped with a collection (23) and conveying channel for conveying impurities raised by the scraper (18) to the exit route, outside. [Claim 10] Self-cleaning automatic filter for plastics, according to claim 1, characterized in that the path of the outlet and the removal of impurities raised by the scrapers (18) integral with the conveyors (19), crosses coaxially the motor shaft (21) for starting the conveyors (19) themselves, or an extension thereof.