SE426785B - DISPERSIBLE DEVICE FOR PLASTIC OR FERGOR MATERIAL - Google Patents

Description

15 20 25 30 35 40 7907120-5 In an injection molding machine you can apply the back pressure hydraulically, but in an extruder this possibility does not exist. Instead, a so-called screen plate is placed in front of the end of the plasticizing screw, whereby this screen plate is provided with fine-mesh screen cloths, which are capable of raising the back pressure backwards in the plasticizing screw. The sieve package thus obtained affects the homogenization.

A so-called displacement insert can also be inserted in an extruder, which restricts the flow of material to the extruder nozzle while increasing the pressure backwards in the screw due to the throttling thus achieved.

However, these methods are not satisfactory solutions to the homogenization problem, especially with low-compression plasticizing screws, for example plasticizing screws with openings in the screw thread.

In an injection molding machine, a non-return valve is usually used at the end of the plasticizing screw to prevent the material from flowing back into the screw thread during the actual injection process. An injection molding machine also has a self-closing nozzle to prevent the material from being sprayed out of the machine during the plasticization process itself, during which the plasticizing screw returns to the position of producing a new injection stroke, during which the plasticizing screw is pushed forward like a piston. The self-closing nozzle may consist, for example, of a movable valve nozzle or a resilient piston inside the spray nozzle, and it may also consist of a ball valve or a hydraulically operated piston. However, none of these constructions are intended to provide an increased dispersion and homogenization of the material, nor can they be used for this purpose. Furthermore, they are not of such a nature that they can be modified for use in an extruder.

In order to replace sieve plates, throttling nozzles, self-closing nozzles and non-return valves of the conventional type in extruders or injection molding machines, arranged in the manner described above, according to the invention a device of the type indicated in the preamble is provided with the features of claim In order to clarify the invention, this will be described in more detail with reference to the accompanying drawings, in which FIG. 1 is an axial sectional view of the front part of an extruder with a dispersing valve according to the invention, FIG. 2 is a schematic view illustrating the flow of material at an open dispersion valve, FIG. 3 is a view corresponding to FIG. 1 with dispersion valves1 of modified design, FIG. 4 is an axial sectional view of the front part of an injection molding machine with dispersing valves according to the invention, FIG. 5 is a fragmentary axial sectional view of a spray cylinder with a plasticizing screw, provided with a dispersing valve according to the invention at its front end, FIG. 6 is an axial sectional view of an adapter, intended to be mounted in a spray head for an injection molding machine and provided with a dispersing valve according to the invention, FIG. 7 is an axial sectional view of a spring-loaded dispersion valve with a modified design, and FIG. 8 is an axial sectional view of a dispersing valve mounted in an extrusion tool.

In FIG. 1, the front part of an extruder is shown, which comprises a syringe barrel 10 with a rotating plastic screw 11 arranged therein, preferably of the above type with openings in the screw thread for backflowing the material being plasticized. A conventional spray head 12 for extruding tubes or sieve is mounted on the machine.

The displacement screw 11 and the spray head 12 are fitted with a constriction sleeve 13, between which the end of the plasticization screw faces the cylinder and the cylinder 10 is clamped with a dispersing valve according to the invention at the location where a conventional cylinder is mounted in the usual manner. This valve comprises a seat 14 with a genome opening, which in this case is smaller than the screw diameter itself but can also be made larger than the screw diameter. 10 15 20 25 30 40 7907120-5 4 the opening may be conical to facilitate the flow. Furthermore, the valve comprises a sieve washer 15, which lacks a hole in the center and instead is formed here with two small torpedoes 16 and 17. These torpedoes are pointed and are directed axially. A truncated conical spring washer 18 is arranged on the torpedo facing the screw 11, this spring washer - with a certain pretension abutting against the seat 14. The bias is then adapted to the force desired for a sufficiently specific pressure to arise in the plasticizing screw resp. a peace-dispersing dispersion in the valve itself must be achieved.

The spring washer is replaceable. It does not itself have to be frustoconical in itself, but can initially be flat and obtain the frusto-conical shape by clamping the washer during mounting on the supporting torpedo. Depending on how the diameter of the spring washer, the thickness, the cup, the travel path and the preload are selected, different pressures can be achieved. It is also possible to increase the pressure by arranging a package of two or more spring washers. The conventional screen, which is to be regarded as a commonly used low-pressure equipment for extrusion, has already been replaced with a modern high-pressure equipment.

The screen tray 15 may be provided with one or more screen cloths 19 in a conventional manner.

When the plasticized material leaves the plasticizing screw 11, it passes through the opening in the seat 14 but can then not pass freely out through the filter washer 15, because the prestressed spring washer (or the spring washers are arranged) 18 is closed against the seat 14. The plasticizing screw 11 must thus work up or "pump up" a pressure corresponding to the spring load, before the material is allowed to pass. However, this is not the case when applying conventional plasticizing principles.

The pressure thus worked up by the screw can vary from a few atoms to several hundred atoms and can be adapted to the maximum overpressure which the screw is able to produce by its application force.

When the plasticizing screw has worked up the internal pressure corresponding to the load of the biased spring washer 15 against the seat, the spring washer opens by suspension and leaves a thin gap between the seat and the abutment edge of the spring washer, the plasticized material flowing through this gap as a thin film with a high flow rate and then passes through the screen cloths 19, the screen washer 15 and the constriction sleeve 13 to the spray head 12.

FIG. 2 schematically shows the material flow through the dispersion valve through arrows F. It can be seen that the material flows approximately radially outwards through the gap.

Since the material plasticized by the plasticizing screw 11 must spread to a thin film in the manner indicated above, an excellent dispersion is obtained from thick layer with low flow rate to thin layer with high flow rate, after which during the continued flow of the material there is a return to thick layer with low flow rate, when the material has passed the dispersing valve. This switching between thicker and thinner layers gives an excellent homogenization of the material.

The larger the diameter of the spring washer 18, the thinner the gap between the washer and its seat 14 at constant material flow. In principle, it also applies that the larger the diameter and thickness of the dispersion washer, the higher the applied pressure.

The dispersing valve can be designed such that the screen tray 15 with the screen cloths 19 lies on the other side of the spring washer than shown here, or the dispersing valve can be provided with a screen washer and associated screen cloths on either side of the spring washer.

It should be mentioned that the constriction sleeve 13 can have a different design and can also be completely omitted, for example when a profile tool is to be mounted instead of the pipe head shown, without the dispersion thereby becoming worse.

According to FIG. 1, the spring washer 18 is so placed that it has the large end, i.e. the concave side, facing the screw, ie. in the direction from which pressure is exerted. However, it can also be turned half a turn, so that the concave surface faces the pressureless outlet and the convex surface of the spring washer faces the pressure side, thus towards the plasticizing screw 11. This out behavior is shown in FIG. 3, which otherwise corresponds to the embodiment according to FIG. 1. In that the spring washer is positioned as shown in FIG. 3, a seal is obtained by means of the spring washer acting as a non-return valve, e.g. when it is desired that propellants in an expansion process should not penetrate into the plasticizing screw 11 and there interfere with the plasticizing and cool down the melt. This guarantees that the expansion process takes place first on the pressureless side of the dispersion valve.

Both in the case of chemically reacting solid propellants and in the case of liquid and gaseous propellants, it must be possible to control the internal pressure in the plasticizing screw so that the gas does not escape until the material passes out of the cylinder.

In the case of extrusion of expanded thermoplastics, it has therefore not hitherto been possible to incorporate sufficient gas into the raw material inside the plasticizing screw, and this also applies to the injection molding process.

When extruding expanded thermopiasters, it is common for the gas to "spit out" at a density of 0.7 g / cm 3 or at an even lower density. It is therefore not possible to deliver a lighter product from the machine.

The dispersion valve according to the invention, on the other hand, retains the gas at a high internal pressure, and if the valve is combined with a plasticizing screw of the type having openings in the screw thread, a better mixing and homogenization of gas and melt is achieved at the same time.

The dispersing valve thus prevents expansion inside the plasticizing screw itself. Only when the material passes the gap between the spring washer 18 and the seat 14, i.e. at atmospheric pressure on the pressureless side, the gas escapes. A11a types of propellants1 are gaseous at atmospheric pressure and room temperature. The expansion of the gas inside the plasticizing screw is thus held back by an internal overpressure corresponding to the plasticizing temperature.

This is especially important when it is desired to obtain an expansion down to a weight of 10 kg / m 3. Here one must use propellants1, which are mainly completely gaseous at room temperature and atmospheric pressure. These propellants should not leave any residual products behind when transitioning to gaseous form; however, any residual products that arise during gas formation after the dispersion passage can be redispersed in a second dispersion valve. In this case, an internal pressure in the plasticization screw of 150 - 200 kp / cm2 must be taken into account, but in principle, the higher the internal pressure, the better the expansion is obtained. The dispersing valve according to the invention enables a high pressure in the screw to be maintained.

What has been said above regarding the extrusion process also applies in applicable parts to the injection molding process. This is illustrated in FIG. 5, which shows the front part of an injection molding machine with a spray head 20 and a spray nozzle 21l fixed therein. The plasticizing screw 11 is provided with a conventional non-return valve 22 at its front end. The plasticizing non-return valve 22 can be replaced with a dispersing valve according to the invention in the manner shown in FIG. 5, wherein this dispersing valve may be present in combination with a conventional spray head or in combination with a spray head with dispersing valve according to FIG. 4. If the dispersing valve of FIG. 5 is combined with the dispersing valve according to FIG. 4, two dispersion processes arise, separated from each other, which in many cases can be an advantage. Two different dispersing processes can also be arranged in an extruder by placing a dispersing valve according to FIG. l in front of the screw and a dispersing valve is placed in the tool itself or in connection with the spray head. In that case both dispersion valves are stationary, whereas in the injection molding process one is stationary according to FIG. 4, while the other is movable together with the plasticizing screw according to FIG. 5.

The dispersing valve according to FIG. 5 comprises a pin 23, which is screwed into the plasticizing screw 11 and supports the spring washer 18 with its large end, i.e. with the concave side facing the plasticizing screw.

The spring washer 18 bears against a ring 24 slidably arranged in the cylinder 10 at one end edge thereof, while the other end edge of the ring 24 abuts against the seat 14 fixed by means of the pin 10 on the plasticizing screw 11. Under the pressure of the plasticized material, a gap is thus created partly between the spring washer 18 and the ring 24 and partly between the ring 24 and the seat 14, whereby two thin films of the plasticized material are formed.

These thin films can be adapted in the manner described above by suitable selection of the spring washer 18 and by combining two or more spring washers.

Thanks to the fact that two films are obtained, the flow rate becomes very high and a dispersion is achieved which far exceeds what has previously been possible to achieve.

In an injection molding machine, it is common to establish a hydraulic back pressure in the plasticizing screw by throttling the backward movement which the screw automatically wants to perform in connection with the plasticizing process which precedes the next injection stroke. The pressure then rises in the plasticizing screw to the same extent as this natural, backward movement is stopped and counteracted.

The disadvantage of applying a hydraulic back pressure to the plasticizing screw is that this back pressure affects the melt in front of the screw and propagates backwards through the melt in the finished zone without causing any actual dispersion. Semi-molten or undispersed material particles or particles of dye or filler can thereby, even under high pressure, penetrate the finished zone, which results in poor plasticization, non-homogenized mixture and poor dispersion of the material. In other words, a hydraulically applied back pressure, which acts from the front, will only reverse the screw under the set pressure while unmelted particles, unmixed paint and unmixed fillers are let through.

The advantage of the dispersing valve provided according to the invention, when it is arranged according to FIG. 4, is that it partly creates a back pressure inwards in the screw and partly produces a simultaneous dispersion in the manner described here, thereby preventing half-melted or poorly dispersed particles from penetrating the non-return valve, since the narrow gap does not allow this. The high internal pressure and the narrow gap in combination force the undigested particles to disperse with the rest of the melt. The undigested particles, which incidentally reach the dispersing valve, are thus forced to enter a plastic state in order to be able to pass through the narrow gap in the dispersing valve.

When regenerating and recycling plastic scrap, it is advantageous to use a plasticizing screw with openings in the screw thread, since the low compression of this type of plasticizing screw purely geometrically allows a deeper thread in the finished zone. Pebbles, metal particles and other indigestible contaminants can be collected in front of the valve, which in that case is designed with a special pocket for the purpose. When regenerating mixed plastic scrap, consisting of many different plastics with many different melting intervals and flow or temperature intervals, the homogenization of the melt can be controlled by means of the dispersing valve according to the invention, which is not possible with hitherto known constructions.

In the embodiments of FIG. 1 - 5, the dispersing valve is arranged as an insert in the extruder or injection molding machine itself. However, it can also be arranged as an adapter according to FIG. In the embodiment according to this figure, the dispersing valve is arranged in a nipple 25, the seat being formed by a conical surface 26 in the nipple. This has a threaded nozzle 27 to be screwed into the spray head, while the spray nozzle Z1 is screwed into the nipple.

The nozzle then serves to hold the screen washer 15 within the nipple 25, and it is thus possible to remove the screen washer with the spring washer 18 for cleaning or inspection only by unscrewing the nozzle 21. An electric heating band 28 is arranged on the outside of the nipple 25.

The spring washer in FIG. 7 is more streamlined and provides a larger abutment surface against the seat than the previously described spring washers. Streamline formation can be important for materials that do not tolerate so-called floating pockets arise, e.g. PVC, and the advantage of a larger contact surface is that a wider gap is obtained. The tray in FIG. 7 is generally denoted by 29 and is made of spring steel.

It consists of a conical portion 30, which has the tip facing and projecting into the opening in the seat 14, while the outer surface of the portion abuts sealingly against the seat. The conical portion 30 joins at the large end with soft rounding to the large end of a truncated conical annular portion 31, with which the washer is stepped on the torpedo 16. A washer of this design basically functions as two mutually opposed conical spring washers.

In addition, it can be mentioned that the dispersing valve can also be arranged in the tool itself, either in the case of an extruder or an injection molding machine, and can also be designed as a groove bushing for a mold tool.

Thus, FIG. 8 a tool, which in principle can be used as a film blowing head or alternatively a pipe head for the manufacture of plastic foil resp. plastic pipe, but the tool according to FIG. 8 can also represent a bottle blowing tool.

A tool of the type shown in FIG. 8 always has a central mandrel holder 32, to which mandrels of different diameters can be exchangeably attached to the hose or pipe to be manufactured. Arranged in the mandrel holder are either a number of bores 33, as shown in the lower part of FIG. 8, or a number of supporting webs 34, as shown in the upper part of FIG. 8. The bores 33 resp. the spaces between the webs 34 allow the material to flow through with the central portion of the mandrel holder located in the middle of the material flow. This portion carries a mandrel 35 releasably attached thereto, which is surrounded by a sleeve 36 and together with it defines the nozzle gap through which the material is to be dispensed.

However, both the goods between the bores 33 and the webs 34 can deposit undesirable floating stripes (slips) on the finished product. To eliminate this, it occurs that, for example during film blowing, the tool is allowed to rotate slowly, for which a complicated drive device is required, which makes the tool complicated. It also happens that threaded grooves are accommodated on both the mandrel 35 and on the sleeve 36, so that the material flow is divided both radially and axially in the direction of flow, for elimination of floating stripes or other marks from the mandrel holder.

A dispersing valve according to the invention with a spring washer 18, which cooperates with a seat 14, is arranged on the mandrel holder 32 in FIG. 8 by being attached to the mandrel holder by means of a screwed-on torpedo 37. The spring washer 18 is a high-pressure washer and is intended to produce the high pressure backwards in the screw in the plasticizer. In the lower part of FIG. 8, however, an additional spring washer 18 'is also shown, which cooperates with a seat 14' formed by the sleeve 36 and which is fixed to the mandrel holder 32 by being clamped therebetween and the mandrel 35 screwed thereto. The spring washer 18 'is smaller than the spring washer 18 and serves to eliminate flow edges and other marks after the mandrel holder, whereby the above-mentioned complicated and less satisfactory devices for eliminating such flow edges and marks can be dispensed with.

By making the opening pressure of the washer 18 'lower than the opening pressure of the washer 18, a mein pressure chamber is obtained between the two washers. In the manufacture of expanded products, the expansion takes place in this pressure chamber. As mentioned above, an additional spring washer may be required for dispersing any residual products due to chemical reaction during gas evolution during the expansion, and the spring washer 18 'performs this function in the embodiment according to FIG. 8.

In summary, there are two things that effect homogenization and dispersion in the dispersion valve according to the invention: One is the thin gap which arises between the spring washer and its seat and which provides substantially radially directed material flow.

The second is the high specific pressure to which the material is subjected in the thin gap. This latter pressure is also propagated backwards in the plasticizing screw and thus contributes to a better circulation in the groove section and a better homogenization.

If the spring washer has a diameter of e.g. 50 mm, it alone can achieve an internal pressure of 100 kp / cmz depending on the bias voltage. Two washers on top of each other can cause twice as much pressure and so on. If the gap between this washer and the seat is 0.5 mm, this corresponds to a surface, through which the material flows, which is 7Txs> l0 l5 20 7907i2o-5 g i 12 This corresponds to a circular hole of 10 mmzs diameter.

Thus, if the washer by suspension opens a gap relative to the seat of 0.5 mm, this corresponds to the material flowing through a 10 mm hole. The difference, however, is that according to the invention it takes place under a high pressure in a thin film-like layer, which gives a hitherto unattainable, incomparably better dispersion than if the material were to flow without pressure through the corresponding 10 mm 2 hole.

The invention has been described with respect to the processing of plastic materials in extruders and injection molding machines, but is to the widest extent also useful in the paint industry for dispersing paint materials. In this case, color pigments can be dissolved in oil, varnish or water and pressed through the dispersing device according to the invention for homogenization and atomization of the color pigment.

It is not necessary that the means by which the material is fed under pressure be constituted by a screw, but this means can also be designed as a piston with reciprocating movement. It should also be mentioned that the spring washer can be made in one piece with the supporting torpedo.

Claims (10)

10 20 25 30 35 40 7907120-5 13 PATENT CLAIMS A dispersing device for plastic or paint materials, comprising means (11) for advancing the material under pressure, preferably a plasticizing screw of the type having openings in the screw thread for the return of the material, characterized in that in front of said means is arranged as a dispersing means a non-return valve with a seat (14; 14 '; 24; 26) and a spring washer (18; 18'; 29) abutting therefrom, arranged to expose by elastic yield under predetermined pressure from the fed plasticized material a substantially radial flow through the material allowing annular gap for spreading the material into a thin film and subsequent return of the material to a thicker layer with a low flow rate. Device according to claim 1, characterized in that the spring washer (l8; l8 ') has itself or through the mounting truncated conical shape. Device according to claim 2, characterized in that the spring washer (18; 18 ') is arranged with the large end against the feed feed member (11). 4. Device according to claim 1 or 2, characterized in that the spring washer (18) is arranged with the small end of the feed means (11). Device according to one of Claims 1 to 4, characterized in that the spring washer (18; 18 '; 29) has a central opening on a support member (16, 17) arranged in the passage for the plasticized material; 23; 32). t 6 Device according to one of Claims 1 to 5, characterized in that the non-return valve is arranged stationary between the feed means (11) and a screen plate (15) arranged in the passage for the material. t 6 Device according to one of Claims 1 to 5, characterized in that the non-return valve is arranged at the front end of a plasticizing screw (11) arranged as a feeding means. Device according to claim 7, characterized in that the spring washer (18) abuts against an axially movable ring (24) which can be pressed against the seat (14; 24; É 3 26). Device according to one of Claims 1 to 5, characterized in that the non-return valve is arranged in an adapter (25) screwed into the spray head with a socket for a spray nozzle (21). Device according to one of Claims 1 to 9, characterized in that two non-return valves (18, 18 ') are arranged one behind the other for delimiting an intermediate chamber, the valve (18) closest to the feed means (11) having a higher opening pressure than the second venti1en (18 '). k ä n n e -