Abstract:
An abrasive tool having an elongated handle member, an ultrasonic vibration source operationally connected to the elongated handle member, and a toughened foamed glass ceramic portion operationally connected to the vibration source. The toughened foamed glass ceramic portion includes a first glassy phase and a second glassy phase, wherein the second glassy phase puts the first glassy phase into compression.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The invention relates generally to the field of ceramic abrasives and, specifically, to a method and apparatus for using toughened foamed glass ceramic materials in abrasive tool surface applications. 
       BACKGROUND OF THE INVENTION 
       [0002]    Foamed glass is an established lightweight ceramic material. Typically, foamed glass is made in one of two ways. The first way involves preparing a stable foam from water and foaming agent, preparing a wet mixture or slurry of solid components (where cement is the main substance), quick mixing the foam and the slurry, filling molds with prepared the mixted foam/slurry, and firing the same. The second way to make foamed glass involves making use of the property of some materials to evolve a gas when heated. A foamed glass material may be prepared by mixing crushed glass particles and a foaming agent (such as CaCO 3  or CaSO 4 ), placing the mixture in a mold, heating the mold (such as by passing the mold through a furnace) to a foaming temperature, and cooling the mold to produce foamed glass bodies. 
         [0003]    While useful as insulation and abrasive materials, foamed glass bodies are still relatively fragile. This is especially true when the foamed glass materials are used as abrasive materials. Foamed glass abrasives offer the advantage of being easily ablative and thus relatively mild abrasives. However, there is a gap between the easily ablated foamed glass materials and traditional hard and tough ceramic abrasives. Thus, there remains a need for a tougher foamed glass material. The present invention addresses this need. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention relates to a process for the manufacturing toughened foamed glass materials, and vibratory abrasive tools made from the same. One object of the present invention is to provide an improved foamed glass material. Related objects and advantages of the present invention will be apparent from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a perspective view of a block of foamed glass. 
           [0006]      FIG. 2  is a schematic view of a method for producing toughened foamed glass according to the present invention. 
           [0007]      FIG. 3A  is a perspective view of a first embodiment acoustic abrasive device according to the present invention. 
           [0008]      FIG. 3B  is a perspective view of a second embodiment acoustic abrasive device according to the present invention. 
           [0009]      FIG. 3C  is a perspective view of a third embodiment acoustic abrasive device according to the present invention. 
           [0010]      FIG. 3D  is a perspective view of a fourth embodiment acoustic abrasive device according to the present invention. 
           [0011]      FIG. 3E  is a perspective view of a fifth embodiment acoustic abrasive device according to the present invention. 
           [0012]      FIG. 3F  is a perspective view of a sixth embodiment acoustic abrasive device according to the present invention. 
           [0013]      FIG. 3G  is a perspective view of a seventh embodiment acoustic abrasive device according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    For the purposes of promoting an understanding of the principles of the invention and presenting its currently understood best mode of operation, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, with such alterations and further modifications in the illustrated device and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
         [0015]    White foamed glass (see  FIG. 1 ), in its most simple form, is manufactured by heating a mixture of clear glass powder and a foaming agent (such as limestone) to a temperature sufficient to release the loosely bound gas from the foaming agent (such as the conversion of limestone to lime and carbon dioxide). The foam is produced as the gas is released from the foaming agent and diffuses through the viscous (γ≅10 4-5  Pa*s) melting glass particles/molten mass to form individual cells and/or pores. The resultant glass foam body  10  is then cooled and shaped into as desired. Drywall is an example of a product made thusly from foamed glass. Sometimes, additional chemicals are added to the glass and foaming agent batch to enhance particularly desirable physical properties (such as abrasiveness, resistance to wear, density, color, etc.). 
         [0016]    As illustrated in  FIG. 2 , a foamed glass or cellular ceramic material may be toughened or made more wear-resistant by developing compressive stresses in the foamed glass during fabrication. These stresses are induced by the addition of a predetermined smaller concentration of a second glass frit material  22  to the first or base glass frit material  20  in the batching stage  15 , whereupon the batch is intimately mixed  25 . The first or base glass frit material  20  is typically a soda-lime silica (Na 2 O—CaO—SiO 2 ) glass. Typically, the first glass frit material  20  is composed of a powdered glass cullet, more typically of powdered window, plate and/or bottle glass, although other glass cullet sources may be used. The second or toughening glass frit material  22  typically has a lower coefficient of thermal expansion (CTE) than the base material, and typically substantially retains its chemical identity during the foaming process. 
         [0017]    The average particle size (diameter) of the frits  20 ,  22  is typically between about 8-10 microns, although frits of other particle sizes may also be used. In some applications, the PSD (particle size distribution) of the frits  20 ,  22  may be bimodal, with peaks at about 8 and at about 10 microns; in other applications, the PSD may be trimodal with peaks at about 8, about 10, and about 100 microns. By controlling the PSD, the cell size distribution and/or porosity of the resultant foamed glass may be better controlled. 
         [0018]    The foaming agent  26  is typically limestone or calcium carbonate (CaCO 3 ), magnesite (MgCO 3 ) and/or carbonic acid (SrCO 3 ). The choice of foaming agent  26  may also influence the foaming, porosity and/or cell structure of the resulting foamed glass body  20 . The different foaming agents  26  release their carbon dioxide at different temperatures and may thus be used to foam glass compositions with different softening points of used in combination to vary the rate at which carbon dioxide gas is evolved. For example, the substitution of calcium carbonate with magnesite results in foamed glass bodies  10  having relatively large pores and/or increased foam height. 
         [0019]    Predetermined amounts of the first and second frits  20 ,  22  are mixed to form a batch  32 . A predetermined amount of foaming agent  26  is also mixed into the batch  32 . After mixing, the batch  32  is portioned  33  into one or more molds  34 , and then fired  38  to a temperature sufficient to soften or melt the frits  20 ,  22  and release the bound gas from the foaming agent  26 . The firing temperature and/or the rate at which the batch portion  33  is fired  38  may be varied to control the foaming of the glass (i.e., by varying the temperature and firing profile), the viscosity of the glass and the rate at which gas evolves from the foaming agent  26  may be controlled, thus controlling the foaming of the glass; by ramping faster to higher temperatures, the viscosity of the glass may be decreased while the foaming agent rapidly evolves gas, thus resulting in more vigorous foaming. Conversely, by heating more slowly or to a lower temperature, foaming may be kept more subdued and thus minimized.) 
         [0020]    The resultant glass foam  40  may then be cooled, whereupon the dispersed lower CTE phase contracts less than the higher CTE base phase matrix, putting the base phase matrix in compression and thus rendering the base phase more wear resistant. The toughened foamed glass body  10  may be molded to shape, or pieces  42  may be cut to shape from a block  10  of foamed glass material. The wear resistant glass foam pieces  42  may be incorporated into an abrasive device  50 , such as by connecting the toughened foamed glass abrasive material  42  to an acoustic or vibratory source  52  (see  FIGS. 3A-3G ). 
         [0021]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the invention are desired to be protected.