Abstract:
A method of manufacturing mineral fibers includes rotating an orificed spinner and supplying molten mineral material to the spinner to centrifuge streams of molten mineral material. A downward annular flow of attenuating gases is directed to attenuate the streams of molten mineral material into mineral fibers. A mixture of combustion air and combustion gas is supplied to an annular burner positioned around the spinner. Heat from the annular burner is directed toward the spinner and the streams of molten mineral material to heat the spinner and assist in attenuating the streams of molten mineral material into mineral fibers. A pressure sensor senses the pressure of the combustion air prior to the introduction of the combustion air to the burner. The pressure of the combustion air is controlled in response to the sensed pressure to maintain the pressure of the combustion air at a specific pressure.

Description:
TECHNICAL FIELD 
     This invention relates to apparatus and a method of fiberizing mineral fibers, such as glass fibers, from molten mineral material using a rotary process. 
     BACKGROUND OF THE INVENTION 
     The production of mineral fibers such as glass fibers by a rotary process is well known. In this process, molten glass is fed at a high temperature into a metallic spinner which revolves at a high rotation rate. The spinner has a peripheral wall containing a multiplicity of orifices. The molten glass flows by centrifugal force through the orifices and forms small diameter molten glass streams. The streams are directed downward toward a collection surface by an annular blower which surrounds the spinner. The flow generated by the blower attenuates the molten glass streams into a finer diameter, and the streams are cooled to form glass fibers. An annular burner is also positioned around the spinner, and combustion gases and heat from the burner are directed downward to provide a fiber attenuating environment suitable for allowing the initial streams of glass to be attenuated to the desired final diameter. The downward annular flow of hot gases facilitates attenuation of the streams of molten mineral material into mineral fibers by the blower, and also maintains the spinner at a temperature suitable for fiberizing. 
     SUMMARY OF THE INVENTION 
     According to this invention there is provided a method of manufacturing mineral fibers including rotating an orificed spinner and supplying molten mineral material to the spinner to centrifuge steams of molten mineral material. A downward annular flow of attenuating gases is directed to attenuate the streams of molten mineral material into mineral fibers. A mixture of combustion air and combustion gas is supplied to an annular burner positioned around the spinner. Heat from the annular burner is directed toward the spinner and the streams of molten mineral material to heat the spinner and assist in attenuating the streams of molten mineral material into mineral fibers. A pressure sensor senses the pressure of the combustion air prior to the introduction of the combustion air to the burner. The pressure of the combustion air is controlled in response to the sensed pressure to maintain the pressure of the combustion air at a specific pressure. 
     According to this invention there is also provided a method of manufacturing mineral fibers including rotating an orificed spinner and supplying molten mineral material to the spinner to centrifuge steams of molten mineral material. A downward annular flow of attenuating gases is directed to attenuate the streams of molten mineral material into mineral fibers. A mixture of combustion air and combustion gas is supplied to an annular burner positioned around the spinner. Heat from the annular burner is directed toward the spinner and the streams of molten mineral material to heat the spinner and assist in attenuating the streams of molten mineral material into mineral fibers. The temperature of the combustion air is sensed with a temperature sensor prior to the introduction of the combustion air to the burner. The temperature of the combustion air is controlled in response to the sensed temperature to maintain the temperature of the combustion air at a specific temperature. 
     According to this invention there is also provided a method of manufacturing mineral fibers including rotating an orificed spinner and supplying molten mineral material to the spinner to centrifuge steams of molten mineral material. A downward annular flow of attenuating gases is directed to attenuate the streams molten mineral material into mineral fibers. Heat and combustion gases are directed toward the spinner and the streams of molten mineral material. Combustion gases and combustion air are supplied to the burner, and the combustion air is dried prior to its introduction to the burner. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view in elevation of apparatus for forming glass fibers. 
         FIG. 2  is a schematic diagram of the air and gas flow leading to the fiberizer shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The description and drawings disclose apparatus and a method for manufacturing loosefil fibrous insulation of glass fibers. It is to be understood that the invention can be carried out using any molten mineral material, such as molten rock, slag and basalt, to make mineral fibers. Also, the process can be used to manufacture mineral fibers that are used to make other fibrous products, including insulation products, such as insulation batts and blankets, and including structural fibrous products such as duct board and pipe insulation. 
     As shown in  FIG. 1 , the fiberizing apparatus, indicated generally at  10 , includes a spinner  12 , an annular burner  14  and an annular blower  16 . The spinner is rotated on an axle or quill  18 . A stream  20  of molten glass is delivered from a glass melting furnace, not shown, and the molten stream  20  drops into the interior of the rotating spinner  12 . The centrifugal forces of the rotating spinner force the molten glass to emanate from the spinner through orifices  22  in the spinner peripheral wall  24 . The molten glass is centrifuged in the form of fine glass streams  26  that are turned downwardly and attenuated into glass fibers  28  by the action of the blower  16 . The blower  16  has sufficient force that it induces a flow of air from the surrounding environment. The blower gases and the induced air attenuate the glass fibers  28  into their final fine diameter, typically within the range of from about 3 to about 8 microns, although fibers of other diameters can be used. The burner  14  is typically gas fired and supplies heat to the spinner and to the fiber forming environment into which the molten glass streams  22  are flowing. It is to be understood that the attenuating gases can be provided by the annular blower  16 , or can be supplied by the burner  14  itself, or by any other mechanism. 
     Subsequent to the fiber forming process, various additives can optionally be added to the glass fibers  24 . These additives can include oils, lubricants and binders. Water can also be sprayed in the vicinity of the fibers  28  to control the environment. The glass fibers  28  travel downwardly after attenuation, and are collected as insulation products by an appropriate fiber collection apparatus, many of which are known to those skilled in the art. After collection, the glass fibers are packaged in bags or other appropriate packaging for transportation to the customer. The glass fibers  28  can be used in the form of loosefil insulation products suitable for use as blowing wool insulation, or can be formed into batts or blankets useful for insulating insulation cavities in buildings or for structural insulation products, such as ductboard or pipe insulation products. 
     As shown in  FIG. 2 , the burner  14  of the fiberizer  10  is supplied with an air and gas mixture by means of an air/gas mix conduit, such as air/gas line  32 . The air/gas line  32  is supplied with air by an air supply conduit, such as air supply line  34 . The air/gas line  32  is also supplied with combustible gas by a gas conduit, such as gas supply line  36 . The gas supply line  36  is supplied with combustion gas from any suitable source, such as a pressurized gas supply  38 . The combustion gas from the gas supply line  36  is mixed at the mixing junction  40  with the air from the air supply line  34  to form the mixed air and gases flowing through the air/gas mix line  32 . 
     As shown in  FIG. 2 , the air supply line  34  is supplied with air from an air intake  44 , which can be connected to outside air or air from any other suitable source. A fan  46  is positioned in the air supply line  34  to drive the air through the system all the way to the fiberizer  10 . The fan  46  can be positioned at any suitable location along the air supply line  34  or the air/gas line  32 . Any other suitable means for driving the air through the system, such as an air compressor, can be used. A heat exchanger  48  is positioned to control the temperature of the air flowing through the air supply line  34 . In common operational situations the air from the intake must be chilled, so typically the heat exchanger  48  is a chiller configured to cool the intake air. The heat exchanger can be any mechanism for changing the temperature of the intake air in a controllable way, such as, for example, cold water chiller, a hot water or steam heater, an evaporative cooling apparatus, and an electric heater. Although the heat exchanger  48  is shown as being positioned downstream from the fan  46 , it could be placed upstream of the fan. A relief valve  50  can optionally be positioned in the air supply line  34  to allow some air to escape from the system in situations where the air pressure in the supply line  34  exceeds a specified level. The relief valve can be any mechanism for reducing the pressure in the air supply line when the pressure is greater than desired. The relief valve  50  can be controlled by any suitable mechanism, such as a controller  52 , or can be configured to operate automatically to allow air to escape from the air supply line  34  when the pressure exceeds a specified value. 
     The air supply line  34  also includes a pressure sensor  54  for measuring or sensing the air pressure within the air supply line  34 . The pressure sensor  54  can be any mechanism for sensing the air pressure in the line  34 . An example is a Rosemount Hart Tri-loop analog pressure signal converter. The pressure sensor  54  is connected to a controller  52 , and signals from the pressure sensor  54  provide the controller  52  with information regarding the air pressure in the air supply line  34 . 
     The air supply line  34  further includes a temperature sensor  60  for measuring or sensing the air temperature within the air supply line  34 . The temperature sensor  60  can be any mechanism for sensing the temperature of the air in the line  34 . Examples include thermometers and thermostats. One suitable temperature sensor is a Rosemont Smart Head Mount temperature XMTR and sensor assembly, single element, spring loaded. The temperature sensor  60  is also connected to the controller  52 , and signals from the temperature sensor  60  provide the controller  52  with information regarding the air temperature in the air supply line  34 . 
     The air supply line  34  is also provided with a moisture sensor  64  for measuring or sensing the moisture level of the air within the air supply line  34 . The moisture sensor  64  can be any mechanism for sensing the moisture level of the air in the line  34 . An example of a moisture sensor is a humidistat. A Vaisala model DMP248-B1A0A2AA2EL5P dew point transmitter can also be used. The moisture sensor  64  is connected to the controller  52 , and signals from the moisture sensor  64  provide the controller  52  with information regarding the moisture level of the air in the air supply line  34 . 
     When the fiberizer  10  is in operation, the air/gas line  32  supplies a mixture of air and gas to the burner  14 . The pressure sensor  54  operates to sense the pressure of the combustion air prior to the introduction of the combustion air to the burner. The controller  52  receives a signal from the pressure sensor  54 . The controller can be configured to control the relief valve  50  in response to the sensed pressure by the pressure sensor  54 . By controlling the relief valve  50 , the pressure of the combustion air in the air supply line  34  is controlled in response to the sensed pressure to maintain the pressure of the combustion air reaching the burner  14  at a specific pressure. 
     The relief valve  50  is not the only way to change the air pressure in the line  34  in response to the sensed pressure, as other mechanisms can also be used. One other method for controlling the air pressure in response to the sensed pressure is to modify the fan  46  to change the air pressure in the air supply line  34 . An additional method is to control the flow of air in the air supply line  34  with a valve  56 . 
     Controlling the pressure of the combustion air is a useful tool in controlling the overall fiberizing process for making glass fibers. The pressure of the combustion air can be modulated to affect the flame and combustion process occurring in the burner  14 . The flame and combustion process can affect product properties for the glass fibers, including such properties as the strength of the fibers, the length of the fibers, the stiffness of the fibers, and the K-value of insulation products made with the fibers. The air pressure modulation can be used to counteract or overcome external process variations that occur over both short and long time spans. External process-affecting variations include the temperature, atmospheric pressure and the moisture level of the intake air. Other process variations that can possibly be countered by adjustment of the pressure of the combustion air include the nature or quality of the combustion gas, and the chemical nature, viscosity or other characteristics of the molten glass. 
     Although the pressure sensor  54  is shown as being positioned upstream of the mixing junction  40 , in an alternative embodiment the pressure of the mixture of combustion air and combustion gas can be sensed at a position downstream from the mixing junction  40 . Pressure sensor  74  is connected to the air/gas line  32  to sense the pressure of the mixture of combustion air and combustion gas at a location subsequent to the mixing of the air and gas at the mixing junction  40 . The pressure sensor  74  is connected to the controller  52 , and the fiberizing process can be controlled in response to the pressure sensed by pressure sensor  74 . 
     Another variable besides air pressure that can be monitored and used to control the operation of the fiberizer  10  is the temperature of the combustion air. The temperature sensor  60  operates to sense the temperature of the combustion air prior to the introduction of the combustion air to the burner  14 . The controller  52  receives a signal from the temperature sensor  60 . The controller can be configured to control the temperature of the air flowing through the air line  34  in response to the temperature sensed by the temperature sensor  60 . This control of the temperature by the controller  52  in response to the temperature sensor  60  can be by control of the operation of the heat exchanger  48 . For example, when the signals from the temperature sensor  60  indicate that the temperature of the combustion air is higher than a desired or set point temperature, the controller  52  can operate the heat exchanger  48  to cool the air by an amount appropriate to return the temperature of the air in the air line  34  to the desired level. As used in this specification, a reference to a set point or specific value of pressure or temperature or moisture level, can mean a specific desired value or a range of acceptable values for the parameter. Other means besides the heat exchanger  48  can be used to modify the temperature of the combustion air in response to the sensed temperature of the combustion air. 
     Although the temperature sensor  60  is shown as being positioned upstream of the mixing junction  40 , in an alternative embodiment the temperature of the mixture of combustion air and combustion gas can be sensed at a position downstream from the mixing junction  40 . Temperature sensor  80  is connected to the air/gas line  32  to sense the temperature of the mixture of combustion air and combustion gas at a location subsequent to the mixing of the air and gas at the mixing junction  40 . The temperature sensor  80  is connected to the controller  52 , and the fiberizing process can be controlled in response to the temperature sensed by temperature sensor  80 . 
     The heat exchanger  48  is shown as being positioned upstream of the mixing junction  40 . In an alternate embodiment, a heat exchanger  86  is positioned downstream from the mixing junction  40 , for controlling the temperature of the mixed air and combustion gas in response to the command of the controller. 
     During operation of the fiberizer, signals from the moisture sensor  64  can be used to control the fiberizing process. When the moisture level of the air in the air supply line  34  is too high, the air can be dried by cooling the air in the heat exchanger  48 , or with any other means, such as a regenerative desiccant dryer. A pre-engineered packaged refrigerant type air dryer can also be used. A moisture sensor  84  can be positioned downstream from the mixing junction  40  to sense the moisture level of the combined air and combustion gas. 
     Another process step that can be used to control the fiberizing process is the use of a calculated flame temperature. The flame temperature can be calculated using polynomial curves fit to data from a commercial computer code, as would be known by those skilled in the art. Once calculated, the flame temperature can be used in conjunction with the moisture content of the air, as measured by the moisture sensor  64 , to modify the air/gas ratio to maintain the flame temperature at a constant. In some fiberizing operations the air/gas ratio is controlled to maintain a high level of quality of the glass fibers. The air/gas ratio can be controlled in any manner, such as by using a valve  90  in the combustion gas line  36 . Typical air/gas ratios are between 9.6 and 10.6 to 1, although other ratios can be used. This allows a residual oxygen level within the range of from about 0.25 percent to about 2.0 percent. According to this process, the air/gas ratio is controlled to maintain the calculated flame temperature substantially constant in response to the measured moisture content of the combustion air. The modification of the air/gas ratio can be controlled by the controller  52  using an algorithm. 
     The process disclosed above includes sensing of the pressure, temperature and moisture content of the combustion air using sensors  54 ,  60 ,  64 ,  74 ,  80  and  84 . When using the process of the invention, it should be recognized that closer the sensors are to the burner  14 , the more accurate will be the sensed parameters. 
     The principle and mode of operation of this invention have been described in its preferred embodiments. However, it should be noted that this invention may be practiced otherwise than as specifically illustrated and described without departing from its scope.