RU2439005C2 - Granular mixture for making foamed glass and method of preparing said mixture - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to foamed glass. The granular mixture for making foamed glass contains the following components in wt %: liquid glass 5-15; water - 5-15; foaming agent which contains glycerine 1-2; kaolin or kaolinite 1-3; ground glass (sown) - the rest, wherein the carbonate foaming agent used is CaCO₃ or MgCO₃ or BaCO₃ or SrCO₃ in amount of up to 1 wt % in a mixture with glycerine. When preparing the mixture, proportions of components are experimentally determined at maximum and minimum allowable density of the ground glass taking into account density of liquid glass, as well as average density of the mixture after mixing and adding minimum amount of water needed to obtain moist granules. Further, the size of the granules and quality of the mixture is controlled, while increasing the amount of water fed within given limits and controlling density of the mixture during its preparation.

EFFECT: efficient recycling of different glass wastes and possibility of producing foamed glass from unconventional glass of varying composition while maintaining high quality of the obtained product.

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Description

These inventions relate to the production of light bulk glass-based building materials, and more specifically to methods for the production of foam glass or foam silicate, for example, with the commercial designation PENOSTEK, which are also heat insulating and refractory materials and can be used, for example, for thermal and fire insulation of machines, buildings and structures, as a filler in the production of concrete structures and in other areas of technology.

State of the art

The positive properties of foam glass, its scope, production technology are known. It is known that this foam-glass heat-insulating porous material is mainly obtained by sintering a mixture of fine glass powder with a blowing agent and is usually used in the form of small granules, for example, as a filler. There are various methods for producing granulated foam glass, including crushing and grinding utilized glass or glass products to form finely ground dispersed glass powder, on the basis of which, when a foaming agent is added, a mixture is obtained for the production of foam glass (see, for example, Demidovich B.K. Production and the use of foam glass. - Minsk: Science and technology, 1972, p.100-122; Schill F. Foam glass. - M .: Publishing house of building literature, 1965, p.14-18; RF patent No. 2307097, С03С 11/00, 09/27/2007).

Due to the almost mandatory inclusion in the descriptions of the methods for producing foam glass, at least a brief description of the composition of the charge and methods for its preparation, the selection of information about analogues for each of the declared objects is difficult and further, for clarity, description of links to known analogues of the proposed technical solutions are combined based from the problem being solved.

Various formulations, mixtures, compositions, ingredients for producing a charge are known as the basis for obtaining the final product, foam glass. Two examples can be cited as examples of the most effective compositions and methods for producing a charge: the first is a special glass melting of the required chemical composition, and the second is the use of a composition based on glass powder from cullet (glass waste) of a heterogeneous or uniform chemical composition and the selection of a blowing agent followed by foaming into the process of heating the entire mass of glass. Glass powder is obtained by grinding either from specially welded glass masses (see, for example, patents of the Russian Federation No. 2023982, С03С 11/00, 04/30/1995, US No. 4192664, class С03В 19/08, 1980; US No. 3403990, class. 65-22, 1968), or from the battle of window, container and other glasses (for example, RF №2149146, С03С 11/00, 05/20/2000; RF №2051869, С03С 11/00, 10.01.96; US №4198224 Cl. C03B 19/08, 1980). In some cases, granulate of specially welded glass is used to produce foam glass (RF No. 2361829, С03С 11/00, 11/27/2008; DE No. 2010263, class С03С 11/00, 1979).

The use of certain other methods and compositions for the production of foam glass can be caused by a number of independent features and local conditions, for example, the presence of a specific raw material base, environmental problems, the composition and nature of the utilized garbage and waste, the cost of energy resources, the need and economic feasibility of using foam glass, a specific purpose and specified characteristics. The consequence of this diversity is the creation of a large number of compositions and technologies that take into account the specific features of such production.

Based on this, among close analogues of the proposed composition of the granular charge for the manufacture of foam glass, one can distinguish a mixture, for example, containing ground glass and a carbonate blowing agent, which confirms the feasibility of using carbonates (RF patent No. 2266874, С03С 11/00, 10.11.2003). However, the possibilities of recycling garbage and glass waste in the analogue are not considered enough.

Among the close analogues of the method for producing a charge for foam glass, one can distinguish a method comprising mixing a glass-forming component and powdery additives containing, among other things, carbon containing a gas-forming agent, in which an aqueous alkaline solution of sodium silicate and / or potassium (liquid glass) is used as a glass-forming component , the content of which is 50-70 wt.%, finely ground cullet is used as a powder additive (RF patent No. 2255058, С03С 11.00, 06/27/2005). But even in it the possibilities of recycling dissimilar glass wastes are not considered.

It is known that the features of using glass trash and random glass waste for the production of building materials can cause a large spread in the composition and characteristics of such raw materials. It is obvious that glass of different composition and grades can differ in physico-chemical and technical characteristics by several times, and the analysis of garbage with the release of glass waste with approximately the same characteristics can be economically impractical. At the same time, well-known technologies for the production of foam glass have been developed and are mainly designed specifically for the use of raw materials with stable characteristics, and are not intended for the use of random and waste glass waste in the form of raw materials. Ecological programs adopted around the world require a new approach and the development of new technologies for waste recycling and energy saving.

These inventions and the technical result of their use are primarily aimed at solving environmental problems in the disposal of a variety of glass wastes, including those of different composition and shape, ensuring profitability of recycling and the possibility of producing foam glass from non-standard glass of variable composition while improving the quality of the final product ( building materials containing foam glass). They are also aimed at expanding the technological range focused on the processing of glass waste.

Based on the problem being solved, the technical result achieved and the totality of the essential features of the inventions, as a common closest analogue - the prototype of the proposed composition of the mixture and the method for its preparation, we can consider the granular mixture to produce foam glass and its production method according to the known method (technology) for producing granular foam silicate ( RF patent No. 2291126, С03С 11/00, 07/10/2007).

The granulated charge for foam glass indicated therein contains finely ground ground glass, a carbonate converter, liquid glass and water.

The specified known method for producing silicate foam gravel includes drying and crushing of cullet and blowing agent (foaming agent, blowing agent), in the form of a mixture of carbonate and carbon materials, for example, in mills, feeding the ground mixture into the storage hopper, dosing and pore formation before mixing, mixing the mixture in drum mixers granulation of the charge using an aqueous solution of liquid (soluble) glass and a granulator, for example, a drum type, preliminary drying-firing of the obtained granules you, the amount of carbonate blowing agent mixture with carbon may be from 5 to 95 wt.%. After receiving the granular charge, it is sent to a furnace with a temperature of 300 to 900 ° C, where the charge is converted into foam silicate gravel.

The description of the known method (RF patent No. 2291126) is very informative. Nevertheless, in it and in the reference materials, features related to waste processing and the unstable characteristics of raw materials and the final product are poorly considered. So, in particular, it practically does not indicate a range of changes in the density of raw materials, which is one of the most important characteristics of cullet and can vary several times depending on its density. Apparently, for this reason, the indicated amount of the blowing agent can vary from 5 to 95 wt.%, That is, in a very wide range, and other optimal numerical indicators of all the ingredients of the charge are practically not indicated. This makes it difficult to use this method, as well as other known methods, in the processing of glass waste with a large random spread of their characteristics and concerns the determination of the full specific composition of the charge for a random batch of cullet and its production technology in granular form.

Disclosure of inventions

As indicated above, the data of the invention and their technical result are primarily aimed at solving environmental problems when disposing of various glass wastes and garbage, at producing charge and building foam glass from this secondary raw material while minimizing costs and simultaneously improving the quality of the final product with a fairly wide range and the variation in the characteristics of the feedstock (garbage).

In terms of the composition (ingredients) of the granular charge, this is achieved in that it includes finely ground ground glass (cleaned with cullet, for example, obtained after garbage disposal), liquid glass, a foaming agent (blowing agent), including carbonate, and water (for example, in a liquid solution glass), which is known from the prototype, and also includes glycerin and kaolin or kaolinite in the following ratio of ingredients used, wt.%:

Liquid glass - 5-15;

Foaming agent, including glycerin - 1-2;

Water - 5-15;

Kaolin or kaolinite - 1-3;

Ground glass (seeded) - the rest.

Moreover, CaCO ₃ or MgCO ₃ , or BaCO ₃ , or SrCO _{3 is} used as a carbonate blowing agent in it.

When increasing the average density of the ground glass used, it is recommended to reduce the fraction of glycerol and use a carbonate converter with a higher specific density.

In terms of the method of producing a mixture for the production of foam glass, the above is achieved by the fact that the method includes obtaining ground glass with possible preliminary cleaning of impurities and dirt, for example, when washing cullet in water and drying, further grinding, dosing and mixing ground glass and a foaming agent containing carbonate component, when a glass-forming component is added to them in the form of an aqueous solution of liquid glass, followed by granulation and partial drying of the obtained granules, which is known from the description prototype. In addition, in this method of producing a charge, solid crushed components of a charge are pre-sieved with a particle size of not more than 5 microns, the average density of ground glass is determined, an aqueous solution of water glass and an aqueous solution of glycerin are added in separate containers with a carbonate component, for example calcite or magnesite, together forming a foaming agent, in predetermined proportions in which the total volume of water does not exceed 5% of the total mass of the charge, then in the process of their simultaneous independent stirring produces a dosed gradual supply of solutions of liquid glass and a foaming agent into the mixer, for example, a planetary screw type, with ground glass moistened before this, where the mixture is mixed until the specified uniformity of the crude mixture is achieved, with the possible addition of water or liquid glass solution to it, then the charge is sent to a granulator, mainly of a plate type, to which water is also added, and after the formation of granules, they are sent to the furnace for preliminary firing, and the general ratio the components in the mass of the mixture before firing is: for liquid glass and water, 5-15 wt.%, for foaming agent 1-2 wt.%, and for ground glass - the rest.

The proposed method may also suggest that in the production of the charge, at the stage after receiving the granules in the granulator, but before preliminary firing, the granules are sorted by size and 1-3% by weight of kaolin or kaolinite powder are added to the mixture, which cover the surface of the granules, for example, at their pollination. In the production of the charge, it is also desirable to experimentally determine the proportions of the components at the maximum and minimum permissible density of ground glass, taking into account the density of liquid glass, as well as the average density of the mixture of the mixture after mixing and adding to it the minimum value of water necessary to obtain raw granules, which is taken for a given , and then regulate the size of the granules and the quality of the mixture, increasing the flow of water within the specified limits and controlling the density of the mixture in the process of obtaining it, while it is possible With a decrease in the density of the mixture, increase the proportion of glycerol in the foaming agent, and with an increase in the density of the mixture, reduce the fraction of glycerol by regulating the quality of the mixture.

In support of the achievement of the technical result, it should be noted that the importance of solving environmental problems and the practical beneficial use of secondary raw materials and garbage, which until recently were not considered, is currently confirmed throughout the world. In this regard, even costly technologies that do not provide direct cost savings, but contribute to waste disposal and environmental conservation, should be considered as progressive. It would be easier to produce building materials such as granular foamglass from good standard raw materials using proven technologies, but in these inventions the main task is to develop recycling technology and, as experiments show, it is successfully solved, which confirms their industrial applicability. The full set of their main essential features indicated in the independent claims is not found in the information patent information search and examination of the identified analogues. This allows you to highlight the dependent claims and confirm the criterion of novelty in the claimed group of inventions. From the point of view of the prior art, it should be noted the choice of an analogue prototype, which, on the one hand, is quite close in essence and implementation to the claimed technical solutions, and on the other hand, contains a large information selection, which, when considered, shows that the tasks for disposal and the use of different types of waste during the rapid regulation of technological processes for the production of foam glass in the face of a significant random change in the characteristics of raw materials and the conditions of foaming to an adequate degree We solved. For example, the issues of the need for ongoing measurement of such characteristics as the density of the glass being processed, which can change 2-3 times during one cycle, are considered rather poorly, and there are practically no ways to manage such processes in the selection of documents for the indicated IPC rubric. This allows us to conclude that with the relative general popularity of the methods for producing granulated foam glass and compositions of ingredients, specific methods for the current operational management of technological operations and compositions of the mixture, for example, with a rapid change in the nature of recycled household waste, have not been studied. In this regard, these inventions are, as it were, a new direction in the development of known technologies, which quite unobviously distinguishes the proposed technical solutions from the known ones and confirms their compliance with the criterion of the prior art.

The implementation of the invention

The main objective of these inventions is to provide the possibility of obtaining from random trash and glass waste sufficiently high-quality transportable granular charge for the further production of high-quality foam glass while minimizing the cost of such production. The main difficulty in solving it is that in order to obtain high-quality foam glass, it is necessary to brew a glass of constant predetermined composition according to standard proven technology. But the usual cheap procedure for the disposal of garbage can not provide a constant specified composition during the production of the charge and then with the release of glass. The fineness of the components also affects the quality of the product, which also requires process control. These inventions propose to control the process of obtaining the mixture by constantly monitoring the mass and density of the resulting mixture, taking into account the density of the ingredients included in it, based on which they are selected.

According to the invention, the proposed granular charge for producing foam glass contains finely ground ground glass, liquid glass, water and a foaming agent in the form of a mixture of a carbonate ingredient and glycerin, as well as kaolin or kaolinite in the following ratio of applied ingredients, wt.%: Liquid glass 5-15%; water 5-15%; a foaming agent, including glycerin, 1-2%; kaolin or kaolinite 1-3%; seeded ground glass - the rest, from 65 to 88%. In this case, CaCO ₃ or MgCO ₃ , or BaCO ₃ , or SrCO ₃ in a volume of up to 1 wt.% In a mixture with glycerin is used as a carbonate ingredient. Such a selection of components and the indicated percentage ratio were not chosen randomly. A significant mass inclusion of water and water-soluble liquid glass in the mixture is partly due to the fact that their density and mass can significantly affect the average density and mass of the entire mixture and somewhat compensate for changes in the density of cullet. So, according to the Great Soviet Encyclopedia (BSE, t.24-1, 1976), the glass density depending on the composition can vary from 2200 to 8000 kg / m ³ (in practice, less). In addition, the density of ground glass and other components of the same grade varies depending on the fineness of grinding. The density of liquid glass and water is approximately 1.5 times different, but significantly lower than the density of the glass, and with the indicated fractions they can significantly reduce the density and regulate other physical characteristics of the charge as a whole, penetrate between the pores of the ground glass. When mixing the ingredients, this significantly affects the degree of homogeneity of the resulting mixture, the distribution of the foaming agent, which allows liquid glass and water with a current change in their fractions within the specified limits, for example, when controlling the density of the mixture, to additionally perform the function of a process controller. Glycerin, like liquid glass, dissolves well in water and, as experiments have shown, also promotes the formation of a homogeneous mixture and, as a foaming agent, helps carbonate ingredients to penetrate the mixture more evenly. Moreover, according to preliminary data, with an increase in cullet density, it is possible to use carbonate blowing agents with a higher density, for example, instead of CaCO ₃ (chalk), BaCO ₃ (witerite), whose density is about 1.5 times higher, can be used. The choice (and fractional ratio) of kaolin or kaolinite (1-3%) was made on the basis of experiments and provides an improvement in the surface quality of the granules of the charge and foam glass. Such a composition and the indicated proportion of ingredients were not found during the search, which allows us to talk about its novelty.

It is advisable to consider the proposed method for producing a granulated charge in the form of a list and description of a specific sequence of all technological operations characterizing it, which is indicated below.

A1. The implementation of this method actually begins with the primary collection and processing of waste, which, although not included in the proposed claims, they actually initiate and direct all subsequent actions to obtain and ensure the quality of the mixture, derived from the quality of raw materials. When collecting garbage, the primary selection and storage of various types of glass waste visually suitable for recycling is carried out. Then, waste waste such as dirty cans and bottles is transferred to washing chambers such as tanks with a reinforced bottom and a device such as a suspended hammer for crushing glass. After crushing, the cullet is washed with technical water under pressure, and the water level in the chamber may exceed the cullet level (washing in immersion mode). After soaking, the water is drained, if possible, from the upper level and the bottom of the tank and filtered for reuse with a possible repeated repetition of the operation.

A2. Further, grinding and washing of cullet is continued until cleaner and finer fractions are obtained in other devices such as ball mills and special chambers with washing devices, where finer grinding of cullet is produced to obtain ground powder. In this case, special attention is paid to cleaning cullet from any dirt and impurities that are unacceptable for the production of foam glass. To do this, cullet is passed, for example, through magnetic or other separators to remove, for example, metal and other impurities and contaminated glass fragments of cullet, not subject to processing. The resulting cullet is filtered on large sieves, then sent for drying and, possibly, for re-separation.

A3. In order to obtain ground glass with a particle size of not more than 5 μm, the finely chopped glass is re-finely crushed, for example, in special crushers, ball or hammer mills, in fine grinding mills with the possible re-sorting, washing and drying of glass powder using special cleaning and sorting machines, with fractionation, with the possible separation of fractions of 3, 4, 5 microns, for example, by sieving on sieves and accumulating in storage hoppers with weight batchers, where the average density is also determined s ground glass.

A4. In drives with dispensers, water is prepared with the possibility of its metered supply to the mixers in an amount of up to 20% by weight of glass powder for 1 load (with a certain margin).

It should be noted here that in the description and the claims, the ratios of the ingredients are indicated with respect to the total weight of all components in one loading batch, taking into account possible tolerances and deviations of its mass, but it is proposed to make weight or volume samples of the ingredients, for example, relative to a fixed mass of ground glass in 1 batch. The total mass of 1 batch of the charge, which is designated and called full load, is approximately 20-30% more than the mass of glass in it, which is amended accordingly and these data are entered into the accompanying document.

A5. Simultaneously with the loading of storage bins and other operations in separate containers, glycerol is dosed (blowing agent) in volumes (weighed), for example, 0.1; 0.2; 04% by weight of glass powder in 1 load.

A6. Simultaneously with the loading of storage bins and other operations in separate containers, a carbonate foaming agent is dosed, which is used as CaCO ₃ (calcite or chalk) or MgCO ₃ , or BaCO ₃ , or SrCO ₃ . Typically, a particular selected carbonate, such as calcinite, is used within a single charge. But for different loads, even on one shift, depending on the characteristics of the ground glass and the requirements for the charge, different carbonate blowing agents and in different volumes can be used, which requires preparation and the presence in the warehouse of different hanging with different ingredients, for example, volumes (weigheds) ) 0.1; 0.2; 04% by weight of glass powder in 1 load.

A7. After performing operations A5 and A6, the foaming agent is combined in separate containers by dosing (weighed) mixing glycerol and the selected carbonate, usually in a ratio of 1: 1 in a standard volume of 1% by weight of glass powder for 1 charge. During the process, this volume can be increased up to 2 times both while maintaining the proportion of ingredients, and due to one of them, based on the specific parameters of the charge.

A8. Simultaneously with the loading of storage bins and other operations in separate containers, dosing of liquid glass (binder) in the amount of several batches is carried out, for example, 1, 2, 5 and 10% of the mass of powder in 1 load (we propose to produce the mixture cyclically, in separate batches, although it is possible to carry out a continuous cycle, for example, due to drives and pooling parties).

A9. Simultaneously with the loading of storage bins and other operations in separate containers, kaolin or kaolinite powder is prepared for pollination or roll-off of the charge in a total volume of 1% by weight of glass powder, usually in the form of 3 doses per 1 load (for visual control of flow).

A10. After performing operations A4 and A8, an aqueous solution of liquid glass is prepared by mixing them in a predetermined ratio, in which the mass of water is less than the mass of liquid glass and amounts to no more than 5% of the total calculated mass of the charge (per 1 charge). This is due to the fact that part of the water is spent on pre-wetting the glass powder, and part is added during granulation.

A11. Then go directly to the production of granules of the mixture. To do this, thoroughly wash the mixer, for example, of the planetary-screw type and pour the calculated mass (weight) of ground glass with a known dry density into it with a small addition of dosed water from the dispenser, which removes dust and helps mixing. Then pour the water mixture of liquid glass and the foaming agent into separate small mixers, include them and the main mixer, and during the mixing process add the liquid glass solution and the foaming agent to the mixer to the ground glass, where they are thoroughly mixed. In the mixing process, after about 10-15 minutes, a sample is taken in the form of obtained clods of the charge, which are formed, for example, due to the operation of the screw screw of the mixer, the screw pitch of which is selected taking into account the required diameter of the granules. The density and volume of clods is determined by weighing and immersion in water. The density and visual state of the mixture determine the quality of mixing, judge its homogeneity, the need for additional additives of water and liquid glass in a given range both in the mixer and in the granulator, as well as the need for additional mixing. The total operating time of the mixer can be about 20-40 minutes per 1 load. Temperature mode - positive temperatures.

A12. Next, the mixture from the mixer is sent to a granulator, for example, plate type, where the granules get the finished look in the process of running. It can be made in the form of an inclined plate with rotation about its axis. During the granulation process, water is supplied to the granulator, which is necessary for wetting and leveling the outer surface of the granules. At the same time or a little later, metered parts of kaolin or kaolinite are fed to the granulator in parts, which, as it were, collapses the mixture during the granulation process. The total granulation time in 1 cycle is about 15-20 minutes. Previously, the operation of the mixer and granulator is worked out experimentally.

A13. Further, the preforms obtained in a plate granulator are dried at a temperature of from 150 to 400 ° C for 10 to 60 minutes, for example, in tunnel-type drying ovens with subsequent cooling. The indicated can lead to overheating of the working rooms and requires good ventilation to maintain temperatures in the range from +10 to + 40 ° С.

A14. After operations 12, 13 or 14, the obtained granules can be sorted by size and quality, for example, visually. Drying the granules completes their production process. Further, the granules can be immediately sent to obtain foam glass in a heating furnace for foaming or for temporary storage in a warehouse.

A15. A feature of the proposed technology is the likely instability of the characteristics of the raw materials obtained from waste disposal. The main variable parameters are the density of the ground glass and, accordingly, the charge. The process control is carried out by measuring the current density of the mixture, in which the density of the ground glass, and the change in composition is determining. According to experiments, when reducing the density of the mixture and ground sand, it is recommended to reduce the proportion of glycerin, water glass and water within the specified acceptable limits, and if the density of ground sand is increased, increase.

The above set of operations determines the receipt of the specified product (granular charge and foam glass) of good enough quality, which confirms the receipt of the technical result. To implement and test these technologies, a pilot installation and a set of equipment have been created that have proven themselves well. Production does not require large areas, but will require inclusion in a single complex for the collection and processing of other types of household waste, ensuring stability in its delivery and processing. This set and sequence of technological operations can be reproduced on standard or modified equipment of different companies, but it requires certain experimental work in relation to different types of raw materials and specific equipment.

Claims (4)

1. A granular charge for producing foam glass containing finely ground ground glass, liquid glass, a foaming agent, including carbonate, and water, characterized in that it includes glycerin as a foaming agent, and kaolin or kaolinite in the following ratio of applied ingredients, wt.%:
liquid glass 5-15 water 5-15 foaming agent, including glycerin 1-2 kaolin or kaolinite 1-3 ground glass (seeded) rest,
moreover, CaCO ₃ , or MgCO ₃ , or BaCO ₃ , or SrCO ₃ up to 1 wt.% in a mixture with glycerin is used as a carbonate foaming agent. 2. The method of producing the mixture according to claim 1 for the production of foam glass, including washing cullet in water and drying, further grinding, dosing and mixing ground glass and a foaming agent containing a carbonate component, with the addition of a glass-forming component in the form of an aqueous solution of liquid glass, s subsequent granulation and partial drying of the obtained granules, characterized in that the pre-solid crushed components of the mixture are sieved, determine the average density of the ground glass, in a separate container is ready an aqueous solution of liquid glass, to which a water solution of glycerol and a carbonate component are added together, forming a foaming agent in a predetermined proportion, then, in the process of their simultaneous independent mixing, a metered gradual flow of liquid glass and a foaming agent into the mixer is carried out, with ground glass, until the specified density and uniformity are achieved a mixture of the mixture, which is then sent to a granulator, mainly of a plate type, to which water is also added, and after the formation of granules they are burnt in the furnace for preliminary firing, and during the production of the charge, the proportions of the components are experimentally determined at the maximum and minimum permissible density of ground glass, taking into account the density of liquid glass, as well as the average density of the mixture of the mixture after mixing and adding the minimum value of water necessary to obtain raw granules , which is taken for a given, and then regulate the size of the granules and the quality of the charge, increasing the flow of water within the specified limits and controlling the density of the charge in the process of its floor cheniya. 3. The method according to claim 2, characterized in that in the production of the mixture after receiving the granules before preliminary firing, the granules are sorted by size and 1-3% by weight of kaolin or kaolinite powder are added to the mixture, which covers the surface of the granules. 4. The method according to claim 2, characterized in that, in the production of a charge, the proportion of glycerol in the foaming agent is increased while the density of the ground glass decreases, and the proportion of glycerol is decreased when the average density is increased.