METHOD FOR CASTING CASTINGS

Description

[0001] The invention relates to a method for casting parts, in which molten metal is poured into a mold that encloses a cavity representing the casting to be produced. The mold, being a lost-wax mold, consists of one or more mold parts or cores formed from a molding material comprising a core sand, a binder, and optionally one or more additives for adjusting specific properties of the molding material. In this process, the mold is enclosed in a housing such that a filling space is formed between at least one inner surface section of the housing and a corresponding outer surface section of the mold. The filling space is then filled with free-flowing material, the material having such a low bulk density that the packing formed there after filling is permeable to a gas flow.The molten metal is poured into the enclosed mold, whereby the mold begins to radiate heat as the molten metal is poured in, a consequence of the heat input caused by the hot molten metal, and as a result of the heat input caused by the molten metal, the binder of the molding material begins to evaporate and burn, so that it loses its effect and the mold breaks into fragments.

[0002] The basic features of the procedure as described above and the practical implementation advantages of this procedure are described in WO 2016 / 016035 A1.

[0003] As explained there, in the field of iron casting, quartz sands mixed with bentonite, lustrous carbon formers, and water are typically used as the molding material for the casting components that form the outer casing of the mold. The casting cores, which create the internal cavities and channels of the casting, are usually formed from commercially available core sands mixed with an organic or inorganic binder, such as a synthetic resin or water glass.

[0004] Regardless of the type of core sand and binder, the basic principle in the production of molds made from molding materials of the aforementioned type is that, after shaping, the binder is hardened by a suitable thermal or chemical treatment, so that the grains of the core sand stick together and the dimensional stability of the respective molded part or core is ensured for a sufficient period of time.

[0005] Especially when casting large-volume iron castings, the internal pressure exerted on the mold after the molten metal has been poured can be very high. To withstand this pressure and reliably prevent the mold from bursting, either thick-walled, large-volume molds or support structures must be used to brace the mold on its outer surface.

[0006] One possible form of such a support structure is an enclosure that is placed over the mold. The enclosure is typically designed like a shell, surrounding the mold on its sides, but with a sufficiently large opening at the top to allow the molten metal to be poured into the mold. The enclosure is dimensioned so that, after placement, a space remains between the inner surfaces of the enclosure and the outer surfaces of the mold, at least in the areas crucial for supporting the mold. This space is filled with a free-flowing material, ensuring that the respective area is supported by the enclosure over a large surface area.To achieve the most uniform filling of the mold cavity, equally uniform contact between the mold and the filling material, and correspondingly uniform support for the fragile casting material, fine-grained, free-flowing materials such as sand or steel grit with a high bulk density are typically used. After filling, the material is further compacted. The aim is to create the most compact possible filling mass, which, like an incompressible monolith, ensures the direct transfer of supporting forces from the housing to the mold.

[0007] The molten metal is poured into the mold at a high temperature, causing the mold components and cores to also heat up considerably. As a result, the mold begins to radiate heat. If the mold temperature exceeds a certain minimum, the binder in the molding material begins to evaporate and burn, releasing further heat. This causes the binder to lose its effectiveness. This decomposition of the binder breaks the bond between the granules of the molding material from which the mold components and cores are made, and the mold, or rather its components and cores made of this material, disintegrate into individual fragments.

[0008] Building on this, WO 2016 / 016035 A1 proposes using a preheated filler material to fill the space between the mold and the housing. The filler material's temperature is high enough that, starting from the filler temperature, process heat generated by the heat radiated from the mold and the heat released during the combustion of the binder raises the material's temperature above a critical temperature at which the binder evaporating from the mold and coming into contact with the filler material ignites and combustion begins. In this way, the filler material acts as a heat storage medium, pre-heated and designed to ensure that the decomposition of the binder in the molding material, from which the mold components and cores are made, progresses largely during its residence time in the housing due to temperature exposure.500 °C has been considered a suitable lower limit for the range of filling temperatures.

[0009] Based on this, the task arose to improve the known process in such a way that the rapid and energy-efficient decomposition of the casting mold is achieved with reduced effort.

[0010] The invention has solved this problem by the method specified in claim 1.

[0011] Advantageous embodiments of the invention are specified in the dependent claims and are explained in detail below, as is the general concept of the invention.

[0012] The invention therefore provides a method for casting castings, in which, in accordance with the prior art described above, a molten metal is poured into a mold which encloses a cavity representing the casting to be produced, wherein the mold is a lost mold consisting of one or more mold parts or cores formed from a molding material consisting of a core sand, a binder and optionally one or more additives for adjusting certain properties of the molding material, comprising the following steps: Providing the mold; enclosing the mold in a housing, forming a filling space between at least one inner surface section of the housing and an associated outer surface section of the mold; filling the filling space with free-flowing material, wherein the material filled into the filling space has such a low bulk density that the packing of material formed there after filling the filling space is permeable to a gas flow; and pouring the molten metal into the mold, wherein the mold begins to radiate heat as a result of the heat input caused by the hot molten metal, and wherein, as a result of the heat input caused by the molten metal, the binder of the molding material begins to evaporate and burn, so that it loses its effectiveness and the mold breaks into fragments.

[0013] According to the invention, the material being filled into the filling chamber has a temperature that does not negatively affect the properties of the molding material before casting. For this purpose, the material's temperature when filled into the filling chamber is limited to less than 100 °C. A key aspect of the invention is that the material is not deliberately heated to a specific target temperature. Instead, the material is advantageously filled into the filling chamber at its current temperature, i.e., the temperature it has reached as a result of, for example, the ambient temperature at the location where it was stored, or process heat generated, for instance, in a recycling process or similar.Accordingly, the filling material temperature provided for according to the invention is preferably at least equal to the room temperature prevailing in the vicinity of the storage location of the filling material or the respective filling device, or at the temperature at which the filling material reaches the filling device, into whose filling chamber it is filled, without targeted, active heat input. The filling material temperatures at which the filling material is filled into the filling chamber are typically in the range of 10 °C to 45 °C, in particular 18 to 45 °C, with typical room temperatures, depending on the season, being in the range of 10 to 25 °C, in particular 18 to 25 °C.

[0014] Surprisingly, it has been found that, contrary to the prior art described at the outset, preheating the filling material is not necessary. Rather, it turns out that the gases escaping from the mold after the molten metal has been poured, consisting of evaporating binder components, begin to burn simply due to the heat transferred from the casting material. According to practical tests, this combustion occurs when there is sufficient gas flow through the filling material package placed in the filling chamber, without the need for any additional heat input.

[0015] By using a filling material according to the invention that is so cold that it does not negatively affect the properties of the molding material when in contact with the mold and when filled into the filling chamber of the casting device used according to the invention, the inventive method can be implemented with significantly simplified plant technology compared to the prior art. To ensure that the filling material has a temperature below 100 °C, and in particular a maximum of 45 °C, when filled into the filling chamber, the filling material can be actively or passively cooled if necessary.

[0016] The invention thus allows for the temporal decoupling of the filling process with the fill material from the filling of the mold with the respective molten metal. Since it is no longer necessary for the fill material in the filling chamber to have a specific high temperature, such as the minimum 500 °C considered practical in the prior art, but rather a temperature at which there is no adverse effect on the mold material, the filling chamber can be filled long before the molten metal is poured. This temporal decoupling of the filling process from the casting process makes the process control significantly more robust and stable. As a result, optimized operational reliability is achieved while simultaneously simplifying the practical implementation of the process.

[0017] In the process according to the invention, the cooling of the casting occurs more quickly than in the prior art described above, since the filler material, which is inserted cold (i.e., at a temperature of less than 100 °C, in particular at most 45 °C, preferably at room temperature), acts as a heat sink, drawing heat from the mold until the temperature equalizes. The resulting faster solidification of the casting leads to increased dimensional stability of the workpiece. Furthermore, since the energy input required for heating the filler material in the prior art is avoided, the process according to the invention also proves to be more energy-efficient.

[0018] It has also been shown that with a suitably spacious design of the filling frame surrounding the filling chamber, the gases produced in the mold after the molten metal has been poured escape from the mold already in flames and then continue to burn off. In this way, the molding material parts and cores of the mold disintegrate into fragments to such an extent that these fragments fall off the casting, and the casting, after removal of the housing, is largely free of adhering mold parts or cores, at least in the area of ​​its outer surfaces.

[0019] At this point, the cores have also broken down into at least coarse fragments, which form channels or cavities inside the casting, so that the core sand and the molding material fragments of these cores either trickle out of the casting automatically within the housing or can be removed from the casting in a manner known per se, for example by mechanical methods such as vibration, or by rinsing with a suitable fluid.

[0020] This has shown that the crushing systems available in the prior art, in combination with the invention, enable economical processing of casting mold fragments.

[0021] The core sand fragments can be crushed, for example, in a conventional grinding mill. The regenerated sand obtained after processing can be mixed with new sand in a manner known per se.

[0022] Unlike the prior art, the inventive method is based on the idea of ​​using the filling material not only to stabilize the mold, but also to accelerate the heat dissipation in order to produce high-precision castings in a technologically and economically efficient manner.

[0023] The filling material, which is filled into the filling space formed between the casting and the housing according to the invention, is free-flowing, so that it completely fills the filling space even if undercuts, cavities and the like are present in the area of ​​the outer surfaces of the casting mold.

[0024] The filling material used according to the invention has a bulk density, as known from the prior art, that is so low that even after the filling chamber is filled and the filling material has been compacted, it is still permeable to gas. Thus, in contrast to the aforementioned prior art, the invention expressly does not create a highly compacted packing in the filling chamber, which, while ensuring optimal support of the mold, is largely impermeable to gas. Rather, the filling material used according to the invention is selected to be permeable to gas flow, which occurs, for example, as a result of thermal convection. This occurs when the mold is heated by the molten metal poured into it and the evaporating binder components of the molding material of the mold parts and cores begin to evaporate and burn, releasing heat.

[0025] When we refer to a binder that evaporates and burns, we are always referring to those binder components that become vaporous and flammable when heated. This does not preclude the possibility that other binder components, in solid or other forms, such as cracking products, may remain in the mold and ideally also decompose there when exposed to heat.

[0026] The ability to allow a gas flow through the filling material in the filling chamber, as provided for in the invention, and the correspondingly adapted large-volume design of the filling frame surrounding the filling chamber, not only create the possibility for the binder evaporating from the mold to burn in the area of ​​the filling material itself and thereby heat the filling material, but also allow the supply of oxygen, which supports the combustion of the binder.

[0027] The process according to the invention is particularly suitable for molds whose molded parts and cores consist of molding material bound by an organic binder. For this purpose, commercially available solvent-based binders or binders whose effect is triggered by a chemical reaction are suitable, for example. Such binder systems are currently used in the so-called "cold-box process".

[0028] The filling material temperature, which the filling material has when being filled into the filling chamber, is, as mentioned, selected according to the invention such that even if the filling material is filled into the filling chamber before casting, no negative effects occur on the molding material and in particular on the binder by which the grains of the molding material are held together from which the parts and cores of the casting mold are formed.

[0029] From a cost perspective, it proves particularly advantageous that the effects achieved by the invention occur even when the temperature of the contents during filling of the filling chamber is equal to the ambient temperature, i.e., equal to the temperature prevailing at the location where the contents are stored before being filled into the filling chamber. In this embodiment of the invention, therefore, no temperature control of the contents is carried out, so that, unlike in the prior art, no costs are incurred for temperature control and any potentially necessary thermally insulated storage of the contents.

[0030] As already mentioned, typical filling material temperatures provided for according to the invention are in the range of up to 45 °C.

[0031] As the binder escapes, burns, and decomposes, the molded parts and cores of the casting mold, formed from the molding material, disintegrate into loose fragments. These fragments can either be disposed of and processed after the housing is removed, or, advantageously, removed from the housing during the dwell time between pouring the molten metal and removing the housing. For this purpose, the casting mold can be placed on a sieve tray, and the fragments of the mold trickling through the tray can be collected. Conveniently, the openings of the sieve tray are designed so that the mold fragments and the filler material trickle through together, are collected, processed, and then separated. This has the advantage that no loose filler material remains in the housing when the housing is removed.

[0032] The mold housing can consist of a sufficiently rigid sheet metal material surrounding the mold at a distance adequate to form the filling chamber, and no special requirements are placed on its thermal insulation. A perforated support plate, acting as a sieve plate, can be provided, upon which the mold rests. An exhaust vent can be provided to allow for the controlled release of exhaust gases generated in the filling chamber.

[0033] In the inventive method, the material filled into the filling chamber can also be compacted in a manner known per se to create a preload between the mold and the housing. This preload ensures a secure, positionally accurate hold of the mold, even when the mold is designed as a core package composed of a multitude of mold parts and cores. As mentioned, however, the low bulk density of the material also ensures the permeability of the gas flow, even with such a compacted filling.

[0034] Channels specifically incorporated into the mold can also be used to accelerate the cooling of certain zones on or in the casting, or to avoid such accelerated cooling in order to achieve specific properties of the casting in the respective zone.

[0035] Granules or other granular bulk materials have proven suitable as filling materials. Bulk materials with bulk densities of max. 4 kg / dm³, and in particular less than 1 kg / dm³ or even less than 0.5 kg / dm³, are especially suitable for the purposes of the invention.

[0036] When using a granular, free-flowing, and pourable filler material, practical tests have shown that it is advantageous for the granules to be spherical. Preferably, the diameter of the spheres is in the range of 1.5–100 mm, particularly 1.5–40 mm.

[0037] In principle, all thermally stable bulk materials that meet the aforementioned conditions and are sufficiently temperature-resistant are suitable as filling materials. Non-metallic bulk materials, such as granules made of ceramic materials, are particularly suitable. These can be irregularly shaped, spherical, or contain cavities to ensure good gas permeability of the filling material while maintaining low heat storage capacity. The filling material can also consist of ring-shaped or polygonal elements that only make point contact with each other, leaving sufficient space between them to guarantee good airflow.

[0038] The filling material can consist of ceramic or refractory materials, for example.

[0039] The casting exposed after demolding according to the invention can undergo heat treatment in a manner known per se after the disintegration of the mold, in which it is cooled in a controlled manner according to a specific cooling curve in a manner known per se in order to produce a specific state of the casting.

[0040] Of course, in the inventive method, several casting molds can be housed together in one enclosure at the same time, and these casting molds can be filled with molten metal in parallel or in close succession over time.

[0041] In principle, the process according to the invention is suitable for any type of metallic casting material whose processing generates sufficiently high process heat. The process according to the invention is particularly suitable for producing castings from cast iron because, due to the high temperature of the molten iron, the temperatures intended for the combustion of the binder according to the invention are reached with particular reliability. In particular, GJL, GJS, and GJV cast iron materials, as well as cast steel, can be processed in the manner of the invention.

[0042] The method according to the invention is particularly suitable for the casting of cylinder crankcases and cylinder heads for internal combustion engines. Especially when the components in question are intended for commercial vehicles, they and the mold required for their production have a comparatively large volume, in which case the advantages of the inventive method are particularly evident.

[0043] The invention will now be explained in more detail with reference to a drawing illustrating an exemplary embodiment. The figures in the drawing schematically depict: Fig. 1 - 10 different phases of the implementation of the method according to the invention with components shown in a section along their longitudinal axis.

[0044] As in the prior art known from WO 2016 / 016035 A1, casting mold parts and cores are provided in the inventive method.

[0045] The casting cores and molded parts are produced conventionally using the cold-box process from a conventional molding material, which may be a mixture of commercially available core sand, a commercially available organic binder, and optionally added additives that, for example, improve the wetting of the core sand grains by the binder. After molding, the resulting casting cores and molded parts are gassed with a reactive gas to harden the organic binder through a chemical reaction, thereby giving the casting cores and molded parts the necessary rigidity.

[0046] A mold 1 is assembled from the conventionally provided mold parts and cores in a known manner to form a mold 1 known as a "core package". The mold 1 may also include components made of steel or other indestructible materials. These include, for example, cooling trays and the like, which are arranged in the mold 1 to achieve directional solidification of the casting G by accelerating the solidification of the molten metal coming into contact with the cooling tray.

[0047] The mold 1 is intended for the casting production of a casting G, which in the present example is a cylinder crankcase for a commercial vehicle internal combustion engine.

[0048] Likewise, new filling material, for example granular, especially spherical, ceramic granules with a grain size of 1.5 - 25 mm determined conventionally by sieving, is provided, which has room temperature (typically 18 - 25 °C), whereby filling material temperatures of up to 45 °C are practical here.

[0049] Furthermore, these raw materials can be reused in the cycle, as explained below.

[0050] The in the Figures 1 - 8 The apparatus T shown in various phases of the inventive process has a sieve plate 2 on which the casting mold 1 prepared for pouring an iron casting melt is placed.

[0051] The mold 1 delineates a mold cavity 3 from the surrounding area U, into which the molten iron is poured to form the casting G. The molten iron flows into the mold cavity 3 via a gating system, which is not shown here for clarity.

[0052] The sieve plate 2 is supported at its edge on a circumferential rim 4 of a collection container 5. A sealing element 6 is incorporated into the circumferential bearing surface of the rim 4.

[0053] After the mold 1 is positioned on the sieve plate 2, an enclosure 7, also belonging to the device T, is placed on the circumferential rim 4 of the collection container 5. The enclosure 7 is shaped like a hood and encloses the mold 1 on its outer circumferential surfaces 8. The circumference of the space enclosed by the enclosure 7 is larger than the circumference of the mold 1, so that after the enclosure 7 is placed on the sieve base 2, a filling chamber 10 is formed between the outer circumferential surface of the mold 1 and the inner surface 9 of the enclosure 7. With its rim corresponding to the collection container 5, the enclosure 7 sits on the sealing element 6, thus ensuring a tight seal of the filling chamber 10 against the surrounding environment U.

[0054] The enclosure consists of a sheet metal material for which no special requirements are placed on thermally insulating properties. The sheet metal material is designed in a manner known per se to ensure the necessary dimensional stability of the enclosure 7. At its top, the enclosure 7 encloses a large opening 11 through which the mold 1 can be filled with molten iron and the filling chamber 10 with material F ( Fig. 2 ).

[0055] To fill the filling chamber 10 with the unheated filling material F, i.e., provided at a filling material temperature that is at least equal to room temperature and at most 45 °C, a storage container V is positioned above the opening 11, from which the unheated filling material F is then allowed to trickle into the filling chamber 10 via a distribution system 12 ( Fig. 3 ).

[0056] Once the filling process is complete, the package of material filled into the filling chamber 10 can be compacted if necessary. A lid 13 is then placed on the opening 11, which also has an opening 14 through which the molten iron can be poured into the mold 1. Fig. 4 ).

[0057] The molten iron is then poured into mold 1 ( Fig. 5 ).

[0058] Oxygen-containing ambient air can enter the filling chamber 10 through a gas inlet 15 molded into the lower edge of the housing 7. Likewise, ambient air entering the collection container 5 via an access point 16 is drawn into the filling chamber 10 through the sieve bottom 2. Fig. 6 ).

[0059] The deliberate destruction of the mold 1, which begins with the casting of the molten iron, and the associated demolding of the casting G, takes place in two phases.

[0060] In the first phase, the solvent contained in the binder evaporates. The solvent vapor exiting mold 1 ignites due to the heat radiated from the casting G as it exits the mold. The combustion of the binder components and other potential contaminants exiting mold 1 continues without further energy input until no more binder vaporizes from the mold. Any remaining vapors then exiting mold 1 are oxidized or otherwise rendered harmless by the high temperature prevailing in the filling chamber 10.

[0061] Likewise, the oxygen-containing gas streams S1,S2, formed from ambient air and entering the filling chamber 10 of the housing 7 via the gas inlet 15 and the sieve bottom 2, contribute to the complete combustion of the gases emerging from the casting mold 1.

[0062] Since the bulk density of the filling material F is so low that good gas permeability of the filling material package in the filling chamber 10 is ensured even after compaction, thorough mixing of the gases exiting the mold 1 with the gas streams S1,S2 providing oxygen for its combustion is guaranteed. At the same time, the filling material package in the filling chamber 10 supports the mold 1 at its circumferential surfaces 8 and thus prevents the molten iron from breaking through the mold 1.

[0063] The mold parts and cores of the casting mold 1 disintegrate into fragments B or individual grains of sand, which fall through the sieve plate 2 into the collection container 5 and are collected there. Depending on the progress of the disintegration of the casting mold 1, the sieve plate 2 can be opened so that fill material F also enters the collection container 5 ( Fig. 7 ).

[0064] The progress of the disintegration of mold 1 and the solidification process of the molten iron poured into mold 1 are coordinated so that the casting G has solidified sufficiently when the disintegration of mold 1 begins. The low temperature of the filler material F contributes to the rapid cooling of mold 1 and, consequently, the casting G. This results in particularly good dimensional accuracy of the casting G.

[0065] After the mold 1 has essentially completely disintegrated, the collection container 5 with the molding material-filling mixture contained in it is separated from the sieve base 2 and the housing 7 is also removed from the sieve base 2 ( Fig. 8 ). The largely sand-free casting G is now freely accessible and can be cooled in a controlled manner in a tunnel-like room 17 provided for this purpose ( Fig. 9 ).

[0066] Due to the process, the casting G has a high temperature upon removal, at which point the austenite transformation is not yet complete and rapid cooling would lead to residual stresses and thus to cracks. For this reason, the casting G is slowly cooled in a cooling tunnel 17 according to the annealing curves of the stress-relief annealing process. The supplied cooling air is dimensioned to achieve the product-specific cooling profile.

[0067] The mixture of fill material F, core sand and fragments B, collected in the collection container 5 and still hot, is processed in the manner described in WO 2016 / 016035 A1.

[0068] The core sand obtained through processing is used to produce new casting mold parts and cores.

[0069] The material F obtained through processing is cooled to room temperature in air without additional energy input and stored in the storage container V for refilling of the filling chamber 10.

[0070] The invention thus provides a method for casting castings (G) in which a molten metal is poured into a mold 1, wherein the mold 1 is a lost mold consisting of one or more mold parts or cores formed from a molding material comprising a core sand, a binder and optionally one or more additives for adjusting certain properties.

[0071] The properties of the molding material are present. In the course of the inventive process, the respective mold 1 is provided, the mold 1 is enclosed in a housing 7 forming a filling chamber 10 between at least one inner surface section 9 of the housing 7 and an associated outer surface section 8 of the mold 1, the filling chamber 10 is filled with a free-flowing material F which has such a low bulk density that the packing of material formed there from the material F after filling the filling chamber 10 can be permeated by a gas flow S1,S2, and the molten metal is poured into the mold 1. wherein the mold 1 begins to radiate heat as a result of the heat input caused by the hot molten metal, and wherein, as a result of the heat input caused by the molten metal, the binder of the molding material begins to evaporate and burn, so that it loses its effect and the mold 1 breaks down into fragments B.

[0072] According to the invention, by ensuring that the filling material F has a filling material temperature of less than 100 °C when being filled into the filling chamber 10, the rapid and energy-efficient decomposition of the casting mold 1 can be achieved with reduced effort. REFERENCE MARK

[0073] 1 Mold 2 Sieve plate 3 Mold cavity 4 Circumferential rim 5 Collection container 6 Sealing element 7 Enclosure (housing) 8 Circumferential surfaces of the mold 1 9 Inner surface of the enclosure 7 10 Filling chamber 11 Opening of the enclosure 12 Distribution system 13 Lid 14 Opening of the lid 13 15 Gas inlet 16 Access 17 Cooling tunnel B Fragments FF Filling material GG Casting S1, S2 Oxygen-containing gas flows T Equipment U Environment V Storage container

Claims

1. Method for casting castings (G), in which a molten metal is poured into a casting mold (1) which encloses a cavity (3) forming the casting to be produced, the casting mold (1) consisting as a lost mold of one or more casting mold parts or -cores which are formed from a molding material consisting of a core sand, a binder and optionally one or more additives for adjusting certain properties of the molding material, comprising the following working steps: - providing the casting mold (1); - encasing the casting mold (1) in a housing (7), forming a filling space (10) between at least one inner surface section (9) of the housing (7) and an associated outer surface section (8) of the casting mold (1); - filling of the filling space (10) with a free-flowing filling material (F), wherein the filling material (F) filled into the filling space (10) has such a low bulk density that a gas flow (S1, S2) can flow through the filling material package formed there from the filling material (F) after the filling space (10) has been filled; and - pouring the molten metal into the casting mold (1), - wherein the casting mold (1) begins to radiate heat as the molten metal is poured in, as a result of the heat input caused by the hot molten metal, and - wherein as a result of the heat input caused by the molten metal, the binder of the molding material begins to evaporate and burn, so that it loses its effect and the casting mold (1) breaks up into fragments (B), characterized in that the filling material (F) has a filling material temperature of less than 100 °C when it is filled into the filling space (10).

2. Method according to claim 1, characterized in that the filling material temperature is at most 45 °C when the filling material (F) is filled into the filling space (10).

3. Process according to claim 1, characterized in that the temperature of the filling material (F) is at least equal to the room temperature.