EP0089317A2 - Method and device for making moulded articles - Google Patents

Abstract

To produce a ceramic part, two molded bodies (14/15) made of porous plastic are used, which are arranged between two pressure plates (4a / 4b). There are parallel channels (2) in the shaped bodies (14/15), which are fed by a channel network (3a / 3b) of the pressure plates (4a / 4b) and which, in the form of blind holes, reach just below the shape space used for the formation of cullets. After filling the slip, it is kept under pressure to accelerate the filtration. After the back and cavity slip has expired, i.e. after the formation of the body (13), the remaining cavity is placed under pneumatic pressure to prevent it from running on and to achieve further solidification. The filtration water (W) which has penetrated into the shaped bodies (14, 15) is kept in the boundary region of the body (13), if appropriate by a targeted interaction of the pneumatic cavity pressure and a counter pressure applied from the outside to the shaped bodies (14, 15). As a result, the filtration water (W) is available for the detachment process. Use for the manufacture of dishes and sanitary ware, but also for processing other substances, e.g. Asbestos slip, to moldings.

Description

The invention relates to a process for the serial processing of an inorganic and / or organic material, which contains a liquid content of between 3 and 90% by weight, into a molding by means of core casting and / or hollow casting, the material being located in at least two porous moldings Cavity is introduced and dehumidified in contact with the adjacent moldings.

The invention further relates to a device for performing this method.

It is known to the person skilled in the art that moldings from liquid or pasty masses, the moisture content of which can be between 3 and 90% by weight, can be produced in porous molds by removing moisture. A particular area of application of this technology is in the mass production of dishes and sanitary ware, but the application of the method according to the invention should in no way be restricted to this area. All possible inorganic and / or organic starting materials, which can be made to flow with or without the application of pressure and can be processed with water or another liquid, are definitely within the scope of the invention. The grain spectrum of the solid base substance can vary between 0.5 µ and 5 mm. In addition to the present In connection with preferably described production of ceramic parts, reference is made as an example to the processing of asbestos slip, ie an asbestos suspension prepared with the addition of cement.

The plaster molds commonly used in the manufacture of tableware and sanitary ware are known to have the disadvantage that on the one hand they can only be used for a limited number of castings, while on the other hand the filtration process, i.e. the consolidation of the body by dehydration requires a great deal of time and therefore also cost. It is generally assumed today that the formation of a body with a thickness of 10 to 11 mm takes about 1 1/4 hours and that after a further hour the body is released from the plaster mold by the shrinkage. If the usual plaster molds are used, the next casting can only take place after a time-consuming and energy-consuming drying or dewatering process. Such waiting times are of course a considerable obstacle in mass production (see. Handbook of Ceramics, Verlag Schmid GmbH, 1970, page 9).

In order to counter these disadvantages, efforts have been made for some time to replace the gypsum with a more durable material which, in addition to the longer service life, should also have a smooth surface and a uniform pore structure in the micro range. Attempts have been made with various porous materials, such as sintered metal and plastics, but this has shown that the mere replacement of the mold material has not been able to solve the problem to a satisfactory extent.

One of the problems that has so far remained unsolved, for example, is to specifically control the moisture distribution that necessarily fluctuates within the porous shape during the entire manufacturing process in such a way that not only is the water removed from the slurry introduced, as uniformly and quickly as possible, but that the shape in the border area of the body still has enough water for problem-free removal of the body and this "release water" does not remain in the porous molding material at the moment of removal, but emerges in the above-mentioned limit area and thus forms an ideal release pad. It is important here that the release water mentioned is not only available in the form of a thin film of moisture, but that a plentiful, even water cushion is available on all sides.

What is particularly important here is the fact that such a release pad must be free of air inclusions, since if the uniform release pad is destroyed by larger air inclusions, localized bonding occurs between the body and the mold surface, which must lead to damage to the damp body.

Since the cullet solidified within the mold shows a certain tendency to form cracks when the mold is opened or the mold is detached, despite its still high moisture content, the opening process or the careful preparation of an exact detachment is of the utmost importance. Due to the complexity and complexity of this detachment problem, the attempts that have previously been carried out with porous plastic molds have failed.

Special problems arise with so-called hollow casting, for example in the manufacture of sani ceramic, but is also practically unavoidable with certain types of dishes. Cavities are created within the body, for example when casting a ceramic washbasin, through water removal, in which the achievement of stable walls and the avoidance of running on of liquid slip adhering to the walls are particularly delicate.

Finally, a further disadvantage of the conventional hollow casting process is that the residual or hollow casting slip has to be checked, cleaned and reprocessed after leaving the mold, which requires additional lines, apparatus, means of transport and thus increased costs.

It is therefore the object of the present invention to propose a method and a device for the series production of moldings, in particular dishes and sanitary ware, which allows the aforementioned disadvantages to be remedied. The method according to the invention is accordingly based in particular on the task, using porous plastic molds, to control the liquid distribution fluctuating within the molds in the course of the manufacturing process in a targeted manner and in dependence on the respective production phase in such a way that not only is there a significant reduction in the filtration process, but also an optimal one Detachment of the body results. At the same time, the aim is to solidify the damp body while, to a certain extent, the reusability of the backcasting or hollow casting slip results as a secondary effect without any control or cleaning. Furthermore, the moldings are said to be able to withstand the strength requirements set in the company.

This object is achieved by the combinations of features defined in the two independent patent claims. Preferred embodiments result from the dependent patent claims.

An exemplary embodiment of the method according to the invention is described below with reference to the accompanying drawing.

• 1 is a simplified sectional view of a device for producing sanitary ware, for example a ceramic washstand,
• 2 is a simplified perspective view of a plate used to hold the moldings and to supply and remove gas and moisture,
• 3 shows, on the basis of a sectional illustration, an enlarged detail from a mold,
• 4 to 6 illustrate various phases of the manufacturing process on the basis of sectional representations,
• 7 is a diagram used to explain the relief or detachment process of moldings consisting largely of hollow castings,
• Fig. 8 is a plan view of a part of a reinforced molded body and
• Fig. 9 is a sectional view of the same molded body.

1, the device has two mutually opposite molded bodies la and lb, which consist of a porous plastic and are shaped on their mutually facing surfaces so that they are one in the retracted state (see FIG. 4) for receiving the slip and Limit the formation of the ceramic body serving cavity shape F. Both molded bodies la / lb are provided with parallel bores 2 which protrude inwards from the rear end face of each molded body and end shortly before the front end faces Sa / Sb. It is therefore blind holes that can be fed in each molded body through a common network of channels 3a, 3b. The channels 3a / 3b are worked into the surface of pressure plates 4a / 4b, which are provided with an inlet and outlet channel 5a / 5b.

The pressure plates 4a / 4b, which are preferably made of metal, for example aluminum, have a grid of channels 3a / 3b on their end faces facing the shaped bodies (see FIG. 2) and are fastened to the shaped bodies by means of screws 6. By means of a drive device (not shown), for example a corresponding hydraulic energy store, the two pressure plates 4a / 4b can be moved against one another for the purpose of closing the mold and can be kept under pressure for the final sealing of the interface between the moldings. For example, piston rods 7, which rest with end flanges 8 on the respective pressure plates 4a / 4b, are used for power transmission.

At the beginning of the manufacturing process, the two-part form according to FIG. 1 is open. Both molded bodies la / lb are connected to a vacuum source via the duct networks 3a / 3b. The over the grid system of the press plate (Fig. 2) on the channels 3a / 3b continuing negative pressure exerts a suction effect thanks to the porosity of the moldings, which extends practically into the end faces Sa / Sb. This results in a careful drainage of the free surfaces of the moldings, which can be controlled in a targeted manner by means of the negative pressure.

As soon as the two shaped bodies are moved together in the direction of the arrow (FIG. 1) and their sealing surfaces D come to lie on one another, the negative pressure applied drops and a vent valve opens, which ventilates the entire channel system of the shaped bodies. A locking pressure which is above the internal surface pressure of the casting is then applied via the hydraulic pressure-maintaining system and the piston rods 7. The mold is now ready to accept the slip.

The slip which forms the prepared starting material of the manufacturing process can consist of an inorganic and / or organic material with a liquid content between 3 and 90% by weight. The grain spectrum of the solid basic substance can be within wide limits, i.e. are between 0.5 p and 5 mm.

In the first phase of the mold filling, the casting slip is used to avoid turbulence under low pressure, i.e. at about 0.1 to 3 bar. The inflowing slip mass displaces the volume air of the casting, which escapes through an appropriately arranged opening (hollow casting opening). Even a small amount of water, be it residual water from the previous manufacturing process or water separated from the newly filled slip, can already escape in this initial phase through the pores of the moldings and the still unpressurized channel system.

After the hollow mold denoted by F in FIG. 4 is filled with slip, an overpressure of about 10 to 50 bar is applied to the slip, the casting solidifying in the mold with dehydration. Under the applied overpressure, the water absorption on the part of the shaped bodies accelerates considerably, so that approximately 50% or more of the water contained in the slip escapes within a few minutes. This water, which exits the slurry under pressure, the so-called filtration water, is now not pressed out through the shaped bodies, but remains for the most part in the capillaries of the shaped bodies directly behind the shaped body surface facing the casting. Since the filtration water displaces the air contained in the capillaries of the molded body and can escape it unhindered to the outside, an air-free water cushion is formed in the border area of the molded body adjacent to the casting, which is of great importance for the subsequent detachment of the casting.

The pressure on the tableware slip in the mold is hydraulic, for example with the aid of membranes. As FIG. 1 shows, two channels 9 and 10, which are provided with shut-off valves 11 and 12, open into the hollow mold F. When filling and then pressurizing the slip, the filling valve 12 is opened, the emptying valve 11, on the other hand, is closed. The air contained in the cavity 5 escapes through the porous shape and the channel system. In this phase of dehydration and solidification under pressure, the channels 3a, 3b, 5a, 5b are open.

As long as the pouring slurry is kept under pressure for water removal and solidification, the channels are le 3a / 3b / 5a / 5b thus vented. Depending on the composition and viscosity of the slip and depending on the material of the porous moldings, it may also be expedient to apply a pneumatic or hydraulic counterpressure during this phase via the supply channels 5a / 5b in order to selectively increase the moisture absorption and distribution within the moldings Taxes. This back pressure, which is applied from the outside, can have the task, inter alia, of keeping the water which has entered the moldings from the slip within the moldings, so that it is still available during the final detachment process.

According to a further embodiment of the method, however, the formation of the uniform water cushion which is absolutely necessary for a problem-free detachment process and which is not interrupted (e.g. due to larger air pockets) can take place completely independently of any counter pressure exerted on the channel system of the mold. The moisture absorption and distribution in the mold are thus not controlled by any kind of back pressure in this phase, but are exclusively a function of the pressure from the slip side and the very special properties of the microporous structure and the structure of the mold, i.e. Sealing to the outside, formation of the sealing surface D etc.

• - undichte Formenoberfläche im Bereich D
• - undichte Formenaussenwände
• - im Vergleich zum Schlickerdruck überhöhter Unterdruck von der Formenseite her oder
• - zu hoher und zu langer angesetzter Gasdruck nach dem Hohlgiessen, d.h. in der Phase der Verfestigung des Formlings.

According to this variant, the water that has entered the mold from the slip does not have to be kept in the cullet / mold surface border area by an "external pressure" applied from the outside, rather the water remains! upholstery there if it is not transported or changed due to errors or incorrect measures. Errors or wrong measures in this sense can be, for example:

• - leaky mold surface in area D
• - leaky mold outer walls
• - In comparison to the slip pressure, excessive vacuum from the mold side or
• - Gas pressure applied too high and too long after the hollow casting, ie in the phase of solidification of the molding.

In the course of the filtration process, the slip mass solidifies as a result of the removal of water, and the shaped body of the ceramic shards shown in FIG. 5 and designated 13 is formed on the end faces Sa / Sb. Once the body formation is complete, i.e. when the cullet has reached the desired contour and a desired thickness, the valve 11 is opened and the residual or cavity slip runs off. This emptying process can be supported by compressed air, which can be introduced through the valve 12.

As experience has now shown, after draining the back and cavity slip from the cavity H (FIG. 5) there is a risk that on the one hand the still wet slip "runs on" the cavity walls and thereby leads to the formation of streaks; on the other hand, it has been shown that the cullet often has insufficient strength with a short exposure time. In order to counter these disadvantages, a pneumatic pressure is built up within the cavity H after the back or cavity slip has expired and is held for a certain period of time which is dependent on the molding and slip material. For example, when manufacturing a ceramic vanity, a pneumatic pressure of 15 bar was maintained for 10 to 15 seconds. This prevents the run-on, with part of the water in on the walls of the formed product penetrates the molding. The cullet treated in this way with compressed air accordingly has a drier inner surface and is demonstrably more solidified than a non-pressure-treated ceramic part, which can be of crucial importance in particular in hollow casting.

The process of pneumatic pressure application can be repeated several times, whereby the remaining slip material that has meanwhile gathered can be drained by temporarily opening the drain valve.

The application of a pneumatic pressure in the cavity H thus serves to prevent overrun and to achieve increased strength of the molding. In addition, the filtrate extracted from the slurry during the formation of the cullet penetrates into the boundary layer of the shaped body adjacent to the cullet, where it forms the coherent water cushion which is essential for the detachment process. It is imperative to prevent air from passing through the cullet during the cohesion hardening process that is too long or too strong and to displace or interrupt the interrelated water cushion (false air) and therefore the problematic detachment of the cullet from the mold surface is no longer guaranteed.

As soon as the direct contact between the molding and the water cushion in the mold is interrupted by larger air pockets or a large amount of smaller air bubbles, adequately even back pressure cannot be built up over the entire body of the cullet or mold become, which leads to tension and compression in the cullet and thus to defects due to irregular pressure on the piece.

If necessary, the moisture distribution within the moldings can be additionally controlled by a balanced coordination of the air pressure applied in the cavity H and a pneumatic or hydraulic counter pressure applied from the outside via the channels 5a / 5b.

6, a vacuum is first applied to the one molded body 1b via the channel 5b, while a pneumatic release pressure acts on the molded body 1a via the channel 5a. As a result, the body 13 is pressed out of the shaped body 1 a and held in place by the shaped body 1 b by vacuum. The process taking place here is best seen in FIG. 3.

FIG. 3 shows, on the basis of a simplified sectional illustration, two molded bodies 14 and 15 consisting of porous plastic, which in turn are clamped between two plates 4a / 4b. The plates are anchored in the moldings by screws 18. The cavity H enclosed by the two molded bodies 14 and 15 serves to form a hollow casting which is ready for the detachment process in the phase shown. Accordingly, part of the filtration water was displaced into the adjacent area W of the shaped bodies by the slip pressure, the capillary action of the porous material and the pneumatic pressure applied in the cavity H. W in FIG. 3 thus designates a water cushion that completely encompasses the fragments. Of course, this cushion of water must not escape through channels 2 to the outside. This is ensured by keeping the water in the cullet / mold surface border area by preventing air from entering.

This measure is supported by the capillary forces of the open pores that act on the water. In order to be able to control the position of the water cushion W in each phase in a targeted manner, a pneumatic pressure can be exerted on the cavity H on the one hand, and on the outside on the molded body on the other. A hydraulic or pneumatic back pressure is applied via channels 2. By mutually coordinating these pressures, the water cushion can be held in the position shown in FIG. 3 until the demolding process.

If, as described with reference to FIGS. 3 and 6, an overpressure is applied to the molded body 14 and an underpressure is applied to the molded body 15, the stored filtration water W is pressed back against the cavity H until it reaches the interface between Shaped body 14 and cullet 13 emerges and thus promotes the detachment of the cullet.

In a similar manner, the body 13 is then detached from the remaining molded body 1b (FIG. 6) or 15 (FIG. 3).

4 and 5, the tightness in the sealing gap D between the two molded bodies is ensured by the hydraulic pressure which is applied via the piston rods 7 and the press flanges 8. It has now been found through tests that this contact pressure must not be chosen too high.

wobei der Faktor h, der die Dichthaltung im Grenzbereich D gewährleistet, zwischen 1,05 und 1,2 liegen sollte.Taking into account that when relieving in With regard to the detachment of the compressible molded bodies, the cullet and the slip pressure, the locking or contact pressure in the limit area D must not be significantly above the sum of these elastic restoring pressures. If one designates the elastic restoring force of the molded body with FF, that of the ceramic body with FK, the slip pressure with FS, the following applies for the locking pressure FZ:

the factor h, which ensures tightness in the border area D, should be between 1.05 and 1.2.

Furthermore, not only the amount of the selected contact pressure plays an important role in the relief process, but also the timing of the mold opening. The feared cracking can only be avoided with certainty if the pressure reduction during the opening process is adapted to the special needs of the molded part, i.e. the pressure reduction is slow in all cases, the opening process also takes place slowly and in phases in the case of moldings consisting largely of hollow castings, but takes place rapidly for moldings largely consisting of core casting.

FIG. 7 shows the opening speed v, ie the speed at which the two sealing surfaces Sa and Sb move apart during the opening process, as a function of the time for molded articles which are largely produced using the hollow casting process. During a first phase, designated A, the body and the porous shaped bodies relax first until the end face of one shaped body begins to detach from the body. This replacement is now taking place extremely slow (separation phase B). After completion of this detachment phase, the molded body can be moved away from the shear den relatively quickly (rapid opening phase C).

The method described is characterized by the possibility of uniform moisture distribution, a perfectly manageable detaching process, and a body that is noticeably more solid than the prior art. Considerable time savings result from the fact that the slip is briefly kept under pressure after filling. However, as experience has shown, the slurry itself may only be filled with an initial pressure between 0.1 and 3 bar, otherwise turbulence may occur. Only afterwards, i.e. after at least a large part of the slip material has been introduced, the pressure can be increased to a multiple, for example to 10 to 50 bar.

It was also found and confirmed by tests that moldings made from warm material (e.g. slurry at 40 ° C) can be removed from the mold even better and can be processed more quickly and better after removal from the mold because they are quicker to set. It is therefore advantageous to preheat the material to 25 to 50 ° C before introducing it into the mold.

The shaped body denoted by lb in FIG. 1 has, as mentioned, an annular sealing surface D and a projection delimited by the end surface Sb (casting surface). These two surfaces D and Sb are loaded at the same time on the one hand and on the other hand with different pressures when carrying out the die-casting method described. The one made of porous plastic Molds, as tests have shown, cannot withstand this alternating stress in the long run. At the transition from the sealing surface D to the casting surface Sb, fine cracks soon appear under the influence of the notch effects that occur, which cause the molded body to break when it is used again.

The same applies in a similar way to the shaped body la.

In order to give the shaped bodies 1 a and 1 b the strength required for operation, they are preferably provided with a reinforcement which takes into account the special structure of the shaped bodies and their material. An embodiment of a shaped body reinforced in this way is described below with reference to FIGS. 8 and 9.

The reference numbers which have remained unchanged in relation to FIG. 1 have been retained on the shaped body which is also denoted by lb here.

To clarify the reinforced construction, the porous plastic mass, which has the main function of water absorption, is designated by K in FIGS. 8 and 9. This plastic mass K is penetrated by a coherent reinforcing grid A, which is guided around the holes 2 at a distance around them and also extends over a depth that corresponds to that of the holes 2. The lattice structure of the reinforcing lattice A thus encompasses all of the bores 2 over their entire length (FIG. 9) and gives the molded body considerable strength against the pressure loads that occur. The reinforcing material A penetrates the spaces between in the embodiment shown the individual holes 2 completely and thus forms a network of intersecting stiffening walls.

According to a preferred embodiment, the reinforcement grid A consists of the same plastic that forms the water-absorbing mass K, with the difference, however, that pore-forming substances were not added to this plastic during its production. This ensures that the base material K and the reinforcement A connect perfectly to one another, while on the other hand there is a considerable increase in strength due to the elimination of the pores.

Instead of this preferred material, other reinforcing materials can also be used.

As can further be seen from FIG. 9, the structure of the reinforcing mesh A in the variant shown is interspersed with metallic wire meshes G, three wire meshes D being arranged one above the other at a distance from one another. The division of the grids D corresponds exactly to the arrangement of the reinforcement grille A shown in FIG. 8.

There are various options for attaching the reinforcement grid A. According to a preferred variant, recesses are drilled or milled out on the cast molded body la or lb (as in FIG. 1), which are then poured out with the reinforcing material after the bores 2 have been closed by plugs. In principle, however, it is also possible to leave the recesses required for the reinforcement free at the first casting and then to pour them out.

The base material of the shaped bodies 1a, 1b is a wear-resistant plastic, to which a pore-forming substance is added during its manufacture, so that the desired porous structure is obtained.

Claims (15)

l. Process for the serial processing of an inorganic and / or organic material, which contains a liquid content of between 3 and 90% by weight, to form a molding by means of core casting and / or hollow casting, the material being introduced into a cavity located between at least two porous shaped bodies and in the Contact with the adjacent moldings is dehumidified, characterized in that the introduction of the material into the cavity mentioned takes place in a first phase in order to avoid turbulence with an initial pressure between ₀ , ₁ and 3 bar and the pressure after the mold cavity has been filled with material is increased several times and held until the material solidifies, the filtrate penetrating under the influence of the prevailing pressure into the moldings, displacing the air in their pores and capillaries and thus making the moldings available for the detachment process in the peripheral layer adjacent to the molding stands. 2. The method according to claim 1, for the processing of said material in hollow casting or combined hollow and core casting, characterized in that after the formation of the molding on the cavity walls, the liquid-containing residual material is blown out of the remaining cavity and then in this cavity a gas pressure is built up, on the one hand to hold the still flowable material on the inner cavity walls and to prevent it from running on, and on the other hand to accelerate the solidification of the molding. 3. The method according to claim 2, characterized in that the build-up of a gas pressure within said cavity is repeated one or more times. 4. The method according to claim 2 or 3, characterized in that the liquid located in the said edge layer of the shaped body is held in the said cavity-side edge layer by a coordinated interaction of said gas pressure with a gas or liquid pressure acting on both shaped bodies from the outside. 5. The method according to any one of claims 2 to 4, for the serial production of crockery or sanitary ware, wherein a mass slip is introduced into the cavity and is dewatered in contact with the adjacent molded bodies made of porous plastic, characterized in that in the said Cavity slurry introduced in order to reduce the filtration time and to achieve an increased strength of the body during a period of action depending on the thickness of the body to be achieved under a pressure of 10 to 50 bar and a part of the filtrate is displaced into the boundary layers of the shaped bodies adjacent to the body and there, optionally in cooperation with a gas or liquid pressure applied from the outside to the porous molded body. 6. The method according to claim 5, characterized in that the back or cavity slip remaining after the body formation is reused without additional preparation. 7. The method according to claim 5, characterized labeled in _- is characterized in that compressed air is used to build the mentioned gas pressure, which is introduced through the Einguss- or hollow casting opening of the mold body into said cavity. 8. The method according to claim 5, characterized in that the two molded bodies tightly holding together during and after the introduction of the slip external pressure is released in different phases, with a slow and in the speed range 0-10 mm / sec. Any adjustable relaxation and opening speed changes to a rapid speed as soon as, depending on the taper and depth of the molded part, the space required for the problem-free opening has been reached. 9. Device for performing the method according to one of claims 1 to 8, with at least two enclosing a cavity, made of porous plastic moldings (la / lb), which are provided with holes (2) for supplying or discharging gas or liquid are characterized in that a finely controllable pressing device (7, 8) acts on two opposite outer surfaces of the molded body (la / lb), and in that the bores (2) mentioned are practically parallel blind bores, the outermost openings of which form a grid-like network of distributor grooves (3a / 3b), which in turn have a surface on the surface facing them Connected plate (4a / 4b) are arranged. 10. Device according to claim 9, with two shaped bodies, characterized in that the parting surfaces of the shaped bodies (la / lb) are arranged vertically and the parallel blind holes (2) of the shaped bodies are arranged practically horizontally. 11. Device according to one of claims 9 or 10, characterized in that at least one of the two molded bodies (la / lb) is provided with reinforcements (A) which extend between the bores (2) mentioned in the relevant molded body. 12. The device according to claim 11, characterized in that the reinforcements (A) are made of the plastic of the shaped body (la, lb), which, however, the pore-producing material component is missing to improve its strength properties, and between the bores (2) in prepared grooves or holes is poured. 13. Device according to one of claims 11 or 12, characterized in that the reinforcements (A) completely penetrate the spaces between the individual bores (2) and thus form a network of intersecting stiffening walls. 14. Device according to one of claims 12 or 13, characterized in that the reinforcements (A) made of pore-free plastic extend practically over the respective length of the bores (2) adjacent to them. 15. Device according to one of claims 12 to 14, characterized in that inserted in the reinforcements (A) made of non-porous plastic to improve the strength properties metal profiles (D), for example one or more metal grids adapted to the mutual spacing of the bores (2) are.

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