METHOD AND DEVICE FOR PRODUCING FOAMED GLASS UNDER
The invention relates to the production of foamed glass based on the extrusion principle, and, more specifically, it relates to a method as disclosed in the preamble of independent claim 1 , and a device as disclosed in independent claim 3.
Production methods for foamed glass using extrusion techniques are previously known. See, for example, US Patents 2 322 581 and 2 255 238.
The production of foamed glass by extrusion has major advantages, which separate tests have shown, and is described in the Applicant's NO Patent Application Nos. 97 4760 and 2002 21350. The inventor has also established through tests that major problems relate to varying product quality and high costs.
To the best of the inventor's knowledge, none of these problems have been solved in an adequate or satisfactory manner, and it is assumed that this has been a contributing factor to the failure of known extrusion processes for producing foamed glass to achieve satisfactory success.
The object of the invention is to remedy the defects of the known techniques, and this is achieved by means a method and a device of the type mentioned above, which are characterised by the features disclosed in the characterising clause of the respective independent claims.
Advantageous embodiments of the invention are disclosed in the dependent claims.
In an extrusion process of the type in question, expansion or foaming agent is added to molten glass under pressure in a heat range that is optimal for the process.
The invention provides the option of a device for feed-in of expansion or foaming agent into an extrusion chamber with molten glass under pressure in the extrusion process.
Glass is fed into the melting chamber by a feed screw or similar device and is melted in the melting furnace to an optimal temperature for the process.
According to the invention, a device is also provided that is of importance for supplying thermal energy in the centre of the melting furnace.
The invention makes it possible to provide an arrangement of a feed screw or similar device which is located in a chamber in the extension of the melting chamber and constitutes a container in which molten glass is mixed with expansion or foaming agent and passed into the extrusion chamber, which has an optimal form for the final mixing step in the mixing process.
The invention relates to a device where feed-in of expansion or foaming agent is handled by a feed screw or similar device which will displace the back pressure from the molten glass and permit mixing under pressure through to the extrusion chamber outlet.
According to the invention, there are nozzles provided in the outlet of the extrusion chamber, which are essential to the control of the production process. In an especially advantageous manner, process-controlled valves are used to adjust the nozzle orifice and thus the quality of the foamed glass product and the magnitude of the volume flow which expands through the nozzle. Tests have shown that by increasing or decreasing the pressure in the extrusion chamber, the size of the air voids in the end product, the foamed glass, will also vary correspondingly, giving corresponding variation in the density of the product. The pressure in the mixing chamber, in one of several variants, can be provided by calculation of height of the glass column containing liquid glass.
The invention will now be described with reference to the drawing, which shows the whole extrusion unit without external connections.
Reference numeral 1 indicates a device for introducing glass into the melting chamber;
2 indicates a feed screw for feeding glass to the melting chamber;
3 indicates a melting chamber for glass;
4 indicates an internal heat source with a profile or shape which provides efficient heat transfer and optional stirring of molten glass;
5 indicates a feed screw / mixer for molten glass and expansion or foaming agent;
6 indicates a feed housing / tube for the feed screw; 7 indicates a mixing chamber / extrusion chamber;
8 indicates a beater / mixer in the extrusion chamber;
9 indicates outlet pipes from the extrusion chamber;
10 indicates adjustable nozzles / nozzle orifices, which are handled by automatic control;
1 1 indicates a sensor for recording zone temperature in the molten mass and / or the extruder; 12 indicates a pressure sensor for the extrusion chamber;
13 indicates a feed screw for expansion or foaming agent;
13.1 indicates a feed screw that is angled up towards an adjacent feed screw;
14 indicates a device for introducing expansion or foaming agent into the feed screw;
15 indicates sensors for recording zone temperatures in the molten mass and / or the melting chamber;
16 indicates an outlet pipe / safety valve for any gases that may be produced in the chamber; 17 indicates heating elements which supply heat to the melting chamber / mixing chamber / extrusion chamber;
18 indicates external insulation of the extruder unit; 19 indicates a pressure sensor for the melting chamber;
The drawing shows a device 1 for introducing glass into the feed screw 2 which then passes the glass into the melting chamber 3. Here, the glass is supplied with heat energy from the heat sources / heating elements 17 and the internal heat source 4 that melts the glass which is passed by the feed screw 5 into the feed housing / tube 6 that is surrounded by heating elements 17.
In the area within the feed housing / tube 6, the feed screw 13 has its outlet and here expansion or foaming agent is introduced through the feed screws or the like 13 and 13.1 , which must have a favourable geometric location that allows them to provide a pre-determined pressure in relation te the pressure in the extrusion chamber 7 with access to expansion or foaming agent through the introduction device 14.
When the feed screw 5 is rotated, it draws with it molten glass which passes the outlet from the feed screw 13, where molten glass and expansion or foaming agent flow together and start a mixing process under pre-determined pressure through to the extrusion chamber 7, where the mixture is given a final stirring by the mixer 8 as it moves towards the outlets 9 through an adjustable outlet nozzle 10, where the expansion takes place and the mixture in the extrusion chamber 7 becomes foam that is cooled from a liquid state into a solid form as the product, foamed glass, is formed.
Sensors 1 1 and 12 record the temperature and the pressure in the extrusion chamber 7, which are of major importance for process control.
The melting chamber 3 has sensors 15, which sense and record the zone
temperature, and sensor 19, which senses and records the zone pressure. All information about the process is of crucial importance for process control and the end product.
The purpose of the outlet pipe 16 is to release gases which may be produced during the melting process in the melting chamber 3 and also to be able to evacuate undesired pressure.
The extrusion chamber 7 outlet pipe 9, feed housing / tube 6 and heating chamber 3 with internal heating profile / stirrer 4 are produced of heat resistant material and are surrounded by heating elements 17 which, together with the internal heating profile 4, are controlled by the sensors / thermostats 15 and 1 1 to a pre-determined temperature in the melting chamber 3 and in the extrusion chamber 7 with separate pressure sensor 12 To prevent energy loss from the melting chamber 3, the feed housing 6, the outlet pipe 9, feed screw 13 and the extrusion chamber 7, where the temperature lies within the melting temperature for glass, there is provided suitable external insulation 18 in the form of a "frame" for the production unit. A detailed description of an embodiment of the invention has been given above, and many modifications will be possible. For example, the production unit according to the invention could easily be provided as a production battery consisting of a row of cells arranged in parallel. The invention is thus not limited to the illustrated embodiment, but includes all modifications and equivalents which fall within the scope defined by the following patent claims.