Effective date : The invention relates to a method for the production of quartz glass molded bodies which, in particular as containers or crucibles for the liquefaction of non-metals or non-ferrous metals and in particular for the production of silicon blocks, from which photovoltaic modules are produced, have an improved surface purity. For the production of silicon blocks mainly sintered quartz glass containers are used. Such containers or moldings and their production methods are for example from DE 51 A1 or the DE 44 C1 known.
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- GST Rate & HSN Code for Glasses, Mirrors, Flasks - Chapter 70
- US5665133A - Process for production of pure transparent quartz - Google Patents
- EP0801026A1 - Process for producing synthetic quartz powder - Google Patents
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- EP0801026A1 - Process for producing synthetic quartz powder - Google Patents
- DE102006060561B4 - Process for producing a quartz glass molded body - Google Patents
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Effective date : The invention relates to a method for the production of quartz glass molded bodies which, in particular as containers or crucibles for the liquefaction of non-metals or non-ferrous metals and in particular for the production of silicon blocks, from which photovoltaic modules are produced, have an improved surface purity. For the production of silicon blocks mainly sintered quartz glass containers are used.
Such containers or moldings and their production methods are for example from DE 51 A1 or the DE 44 C1 known. The containers are manufactured essentially with the following method steps. When removing the green body from the plaster mold, experience has shown that there are always problems, in particular when dealing with large-sized containers. Such problems are for example in the DE 51 A1 treated.
There it is proposed to use a composite of several plates container instead of a finished cast quartz glass container. Another problem arises from the fact that it is often desirable to provide the container wall connected to the melt with a fine-grained microstructure, on the other hand, however, the strength of such a container suffers.
Finally, the green body is sintered after demolding to a stable container. In principle, both the hollow casting process and casting with core can be used in casting.
Both methods are in the production of quartz glass containers of the type mentioned in the prior art. In the case of the hollow casting process, a plaster mold, which precisely reproduces the later outer contour of the crucible, is normally filled with the slip mass. After a period of a few minutes to hours, depending on the composition of the slurry and the size of the mold, a solid layer of several mm thickness has settled on the mold inner surface. The remainder of still liquid slip is removed from the mold and can be used for a next casting.
The remaining layer in the mold is then sintered. The mold does not have to be completely filled with slurry in this process. It is sufficient to fill the mold in part and to ensure by a rotation or pivoting movement that the surface is completely wetted by the slip mass sludge.
So gradually builds up a corresponding layer on the mold wall. A further variant consists of immersing a mold, which forms the inner contour of the container to be produced, in a suitable container with the slip mass until a layer of the desired thickness has settled on the outside of the mold.
Casting with core is in the 6A to 6C shown. The Schlickergussform has a core and an outer shape on, between which a gap-shaped shaping space is formed, in which the slip mass is filled. For ease of demolding, the walls of the mold are tapered at an angle educated. The forming surfaces of the mold may be known to be provided with a release agent to prevent the adherence of the dried slurry mass.
As a release agent, for example, graphite powder or wax is used. The layer thickness must not obstruct the water absorption of the mold or only insignificantly. It must therefore be ensured that the pores of the plaster mold are not closed by the release agent.
Such slip casting molds can be round, square, rectangular or polygonal. They typically have a diameter of up to mm and a height of up to mm. The through the gap-shaped shaping space defined wall thickness of the container is depending on the size of the container to be produced between 6 and mm.
The material of the slip casting mold is typically gypsum or, more rarely, clay. In 6A the casting is shown with a centrally pierced core. Through the central hole the slip mass is poured into the forming space. Simultaneous venting of the space takes place through the gap between the core and the outer shape , The advantage of feeding the mold through a central bore in the core is a uniform distribution of the mass, the high isotropy leads to uniform shrinkage during sintering.
The disadvantage of this mold is that the slip has to cover a long flow path within the casting mold and this requires a correspondingly high casting capacity of the silt. This must be taken into account when designing the slurry. In the mold according to 6B is the slip by at least two or more, if possible symmetrically around the lateral surface of the outer mold distributed openings The venting takes place as before through the gap between the core and the outer shape , In the simplest variant, the sprue takes place at only one corner not shown.
Here also very long flow paths and also an uneven or asymmetrical filling of the form result. In contrast, in the according to 6B Case presented the problem that may arise at the points where the individual material flows flow together so-called flow fronts. At these points, the bottom of the container thus produced may be inhomogeneous and particularly susceptible to cracking and breakage.
Another known embodiment is in 6C shown in which the slip through a central opening in the bottom of the outer mold he follows. Again, venting is through the gap between the core and the outer shape , The advantages and disadvantages are similar to those of the embodiment 6A , wherein the flow paths are slightly shortened in this case.
There are other embodiments in which a basically similar constructed mold over head, that is, with a bottom arranged core and an outer shape over it, is fed. In this case, in addition to the feed openings vents are now provided in the upper floor area of the outer mold, since the gap between the core and outer mold is directed downwards and is closed by the slip mass right at the beginning. The mold has a porous outer shape, preferably of plaster, and an inner shape of a non-porous material, preferably an elastic rubber material.
The removal of water from the slip mass is therefore via the porous outer shape. For subsequent demolding compressed air is introduced into the outer mold. The EP 1 A2 discloses a method of making a casting from a ceramic or vitreous composite, in which the slurry is introduced into a liquid impermeable form for the liquid contained in the slurry and cooled to a cooling temperature below the freezing point of the liquid after casting to form a frozen blue body. The subsequent drying is carried out by heating the frozen blue body to a heating temperature below the boiling point of the liquid.
The EP A1 also relates to a process for the production of quartz glass products by means of slip casting, after which the slurry is filled under vibration in a plaster mold, then subjected to several hours of service life and then air-dried and sintered after removal of the plaster mold.
From the US 6,, A For example, a method for producing a ceramic shaped body is known, in which the slurry is filled into a water-absorbent casting mold and the slurry in the casting mold is subjected to a hydrostatic pressure or the water-absorbent casting mold is subjected to a negative pressure or the slip is exposed to an excess pressure of at most 3 bar.
The EP A1 discloses a process for the production of ceramic moldings in a water-repellent mold, in which a green body is produced in a two-stage process, this then in another porous mold inserted and finished by pouring additional slip to a one-piece, ceramic molding is completed. The resulting from the prior art problems are summarized air pockets, which occur in particular at the confluence of streams of material "flow fronts" , because there the air can not escape and is trapped in the material.
Furthermore, the container thus produced is less resilient at the locations of the flow fronts, which may additionally be due to contamination of the slip mass by mixing release agent residues. Due to the long flow paths increased flowability is necessary. To achieve this fluidity, a minimum level of water must be present in the slurry, which is removed during drying of the mass. This can result in an increased porosity or a low material density of the container produced.
Finally, the risk of cracking due to drying, especially in the area of accumulations of material in the corners or in the bottom area of the container, is increased. The object of the present invention is to provide a process for the production of improved quartz glass molded bodies, which permits reliable charging, controlled drying and simple demoulding and thus enables process-reliable production of the quartz glass containers. The object is achieved by a method having the features of patent claim 1.
The method of the type mentioned above according to the invention comprises the following steps:. Another advantage of the invention is evident in terms of the purity of the molding. While the purity or impurity in the total volume of material of the molded article is currently determined mainly by the purity of the raw material, the casting process additionally greatly influences the impurities in its surface area, that is.
Both together lead in the known manufacturing processes to contamination levels on the surface of sometimes significantly more than about 0. The proportion of impurities attributable to the raw material can be given for standard raw materials of less than 0. This also corresponds to the works inside the moldings. But this also means that especially when using expensive high-purity raw materials, the contamination by the casting process is particularly significant and limits the purity of the molding as a whole.
Now, the method according to the invention makes it possible to considerably reduce the content of impurities of the molded body produced as a result of the casting process compared with the prior art. It can be produced by the method according to the invention moldings having a contamination content in the surface region of less than 0. Depending on the quality of the raw material, the contamination in the surface area is even less than 0.
The cladding is preferably smooth, waterproof layers. Preferably, only partial surfaces of the casting mold are lined, since otherwise the removal of the water from the slip through the generally porous casting mold made of gypsum or clay can not take place sufficiently quickly.
By covering parts of the mold with silicone rubber, the following advantages result: The flow resistance of the slip mass is reduced. As a result, the casting can be done faster and more evenly, the slip mass takes less impurities, z.
As release agent residues, abrasion of the plaster molds, etc. This leads to a better quality of the finished container. Furthermore, the dehydration can be controlled in one direction. The fine fraction of the glass grains used in the slip production preferably accumulates on the side at which the water is removed. This creates a denser surface. In the water that is removed from the slurry, components of the gypsum used dissolve and diffuse into the green body.
This effect is also reliably avoided by a lining. The container surface which is formed in this part has a significantly higher purity, in particular a lower content of alkali and alkaline earth metals.
The cladding can take the form of blanks of waterproof mats. In another advantageous embodiment, the casting mold can be lined with a one-piece mold prefabricated from the waterproof substance. For this purpose, in particular prefabricated injection molds made of plastic, particularly preferably made of silicone rubber. According to an alternative embodiment, the mold is at least partially coated with the waterproof substance. This can be done by leaching, pouring or foaming. For example, beeswax may be used as the waterproof coating, which must be applied so thickly that the layer is watertight, meaning that the pores in the casting mold are closed.
Furthermore, as a waterproof coating, paints can also be applied to the casting mold. Both synthetic resin-based and acrylic-based paints can be used for this purpose. In a two-part mold comprising an outer mold and a core, it is advantageous to clad only the partial surfaces of the mold in the outer mold or the partial surfaces of the mold in the region of the core in order to maintain a sufficiently large surface for the necessary dehydration in view of a higher surface quality of the quartz glass container due to the directional dehydration, it is preferable to disguise the partial surfaces which form those container surfaces which will not come into contact with the molten material.
An alternative embodiment of the method is to produce the latter of a combustible material in a mold having an outer shape and a core, which is burned in the subsequent sintering process. The combustible material may be a plastic such as polystyrene or preferably PU foam.
Furthermore, natural materials such as corn pads can also be used. In this way, can be dispensed with manual removal of the core, whereby the manufacturing process is simplified and thus cheaper.
All embodiments of this aspect of the method or the mold or the devices allow the production of crucibles, in particular on their inside have surface structures that are suitable for the adhesion of a coating, for. As a powder coating or an emulsion are suitable. For this purpose, panels with complementary structures can be used.
The use of hazardous or toxic waste to make a glass material a useful product is provided for herein, however, vitrification of hazardous waste for purposes of containment is excluded, see References to Other Classes below. Included within the scope of the class definition are:. Search notes relating to a processes and apparatus and b products will be identified appropriately. Although silicon and silicon dioxide are arbitrarily considered to be glass materials for Class 65, a process of growing these polycrystalline materials is proper for Class 23, even though a rod is used as a bait, unless the shape formed is not a result of crystallization or deposition on the rod.
US5665133A - Process for production of pure transparent quartz - Google Patents
It has been the largest market for Apple iPhones since Since the escalation of tariffs, though, China has stopped buying soybeans and lobsters , and Apple warned it would miss its expected Christmas holiday sales figures because of trade tensions. Skip to navigation Skip to content. From our Obsession Because China. Item HTS code Non-coniferous wood chips or wood pellets Sawdust, wood waste and debris, unbonded Other charcoal, whether or not agglomerated Softwood logs treated with preservatives Pinus koraiensis and Pinus sylvestris var. Item HTS code Rolled newsprint Sheets and other newsprint Other hand made paper and cardboard Photographic base paper Other uncoated paper and paper for writing, printing or similar purposes, weighing less than 40 grams per square metre.
EP0801026A1 - Process for producing synthetic quartz powder - Google Patents
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EP0801026A1 - Process for producing synthetic quartz powder - Google Patents
ECI measures the knowledge intensity of an economy by considering the knowledge intensity of the products it exports. PCI measures the knowledge intensity of a product by considering the knowledge intensity of its exporters. This circular argument is mathematically tractable and can be used to construct relative measures of the knowledge intensity of economies and products see methodology section for more details. ECI has been validated as a relevant economic measure by showing its ability to predict future economic growth see Hidalgo and Hausmann , and explain international variations in income inequality see Hartmann et al. Countries Products. Gear cutting, grinding and finishing machines. Chloroprene chlorobutadiene rubber CR except late. Textile yarn winding or reeling machines. Theodolites and tacheometers.
DE102006060561B4 - Process for producing a quartz glass molded body - Google Patents
For e. Natural or cultured pearls, precious or semi-precious stones, preciousmetals, metals clad with precious metal and articles thereof; immitation jewellery; coin.. Soap, organic surface-active agents, washing preparations, lubricating preparations, artificial waxes, prepared waxes, polishing or scouring preparations, candles and similar articles, modelling pastes, "dental waxes"" and dental preparations with a basis". Explosives; pyrotechnic products; matches; pyrophoric alloys; certain combustible preparations.. Project imports, Laboratory chemicals, passenger's baggage, personal importation by air or post; ship stores.. Inorganic chemicals; organic or inorganic compounds of precious metals, of rare-earth metals, of radioactive elements or of isotopes. New search: For e. Other laboratory and industrial articles of precio..
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