Abstract:
A sintering apparatus for silver clay wherein a silver clay composition can be readily and easily sintered by exposing a silver clay composition obtained by molding to a flame of a solid alcohol fuel.

Description:
The present application is a national stage of PCT/JP02/07049, filed Jul. 11, 2002 and claims the benefit of Japanese Patent Application No. 2001-216321, filed Jul. 17, 2001 and Japanese Patent Application No. 2002-155605, filed May 29, 2002. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method and an apparatus for easily sintering a silver clay composition. 
   2. Description of the Related Art 
   In general, silver clay is obtained by mixing a powder of pure silver or silver alloy with binder and the like. An accessory is manufactured by heating and sintering a silver clay composition which is obtained by forming the silver clay to a predetermined shape and drying it in an electric furnace or a gas furnace whose heating temperature can be controlled. 
   While the above electric furnace or the gas furnace is relatively suited to sinter a lot of work pieces simultaneously since the furnace is relatively large, it is difficult for an individual worker to prepare this type of furnace. Accordingly, a sintering method in which the silver clay composition is inserted into a sintering box which absorbs microwave and generates heat, and is sintered by setting the sintering box in a household microwave oven has been proposed recently. However, this sintering method is inconvenient since the special sintering box which absorbs microwave and generates heat has to be prepared. Furthermore, since temperature control is difficult and the heating condition of the silver clay composition in the sintering box cannot easily be observed, occasionally the clayish composition melts due to excessive heat beyond a melting point thereof. 
   In addition, a sintering method for the silver clay in which the silver clay composition is sintered by being directly exposed to the flame of a gas burner has been proposed recently (see Japanese Patent Application, First Publication No. 2000-80404). In this method, the flame of the gas burner can be freely controlled and the silver clay composition can be sintered anywhere merely by preparing a portable gas bottle and a gas burner. 
   However, in the method in which the silver clay composition is sintered using the gas burner, the gas burner is generally used without a cover and thus the flame of the gas burner is visible whole the sintering operation. In this case, the flame of the gas burner often ignites explosively even though it can be controlled, and as a result, when a person uses the burner, the desire to manufacture an accessory by heating the silver clay may be dampened due to a fear of the gas burner. While a method in which the silver clay composition is heated and sintered by the flame of the gas burner in a receptacle that is made of a fireproof material has been proposed, however, in the case of performing the sintering in the receptacle, the operability is decreased unless the space in the receptacle is enlarged so that the gas burner can be moved within the receptacle. As a result, the receptacle becomes larger, and therefore, labor for installing the receptacle and a space for storing the receptacle after the sintering operation are necessary. 
   Furthermore, though the gas burner is convenient in that the flame thereof can be freely controlled, it is difficult to adjust the temperature of the flame to the optimum temperature for the sintering of the silver clay composition. Therefore, the temperature of the flame often deviates from the optimum temperature for the sintering of the silver clay composition as a result of controlling of the flame. Consequently, it is difficult to obtain desired accessories. 
   SUMMARY OF THE INVENTION 
   The inventors of the present invention have carried out investigations to develop a method for readily and easily sintering the silver clay, and learned the following.
         (a) The flame of a solid alcoholic fuel is the best for sintering the silver clay composition. Therefore, the silver clay composition can easily be sintered by using the flame of the solid alcoholic fuel as a heat source for sintering the silver clay composition and directly exposing the silver clay composition to the flame of the solid alcoholic fuel.   (b) The solid alcoholic fuel can easily be handled since a lamp having a candlewick for using the liquid alcoholic fuel is unnecessary. Furthermore, since an area of a disc shaped burning part can be enlarged, a flame which sufficiently covers the silver clay composition can be formed by enlarging the area of the burning part which produces the flame.       

   The present invention is achieved based on the above knowledge, and provides:
         (1) a sintering method for the silver clay for heating and sintering the silver clay composition by the flame of the solid alcoholic fuel, and   (2) a sintering method for the silver clay for heating and sintering the silver clay composition by placing the silver clay composition on a screen and exposing the silver clay composition to the flame of the solid alcoholic fuel.       

   The solid alcoholic fuel is usually formed into a disc shape or a conical shape that has upper and lower planes with a relatively large area. Therefore, the relatively large and gentle flame is produced by igniting this relatively enlarged upper plane, and the silver clay composition can be sintered while the composition is surrounded by this relatively large and gentle flame. 
   However, since the flame of the solid alcoholic fuel has the defect that the flame may caused to flicker greatly due to a light breeze, it is preferable that the solid alcoholic fuel is burned in a sintering space which is surrounded by a heat insulating material in order to prevent the flicker of the flame of the solid alcohol fuel by the light breeze. 
   Hence, the present invention also provides:
         (3) a sintering method for the silver clay according to the above (1) or (2), and the sintering is performed by exposing the silver clay composition to the flame of the solid alcoholic fuel while they are surrounded by a wall member which is made of the heat insulating material.       

   When placing the solid alcoholic fuel in the sintering space which is surrounded by the wall member and igniting it, the temperature in the sintering space reaches 700° C. or higher in a relatively short time, however, the temperature does not exceed 830° C. As a result, the temperature of the sintering space is maintained between 700 and 800° C. while the solid alcoholic fuel is burning. Since this temperature between 700 and 800° C. is an optimum temperature range for the sintering of the silver clay composition, it is unnecessary to implement a special handling for temperature control when the silver clay composition is sintered using the solid alcoholic fuel. 
   Furthermore, the present inventors were able to implement readily and simply a sintering method for a silver clay disclosed in the above (1) and (2), and additionally carried out investigations to develop an apparatus that has as narrow the sintering space as possible and is thus easily stored. As a result, the following was found.
         (c) When an apparatus having an air hole in at least a side wall thereof and the solid alcohol fuel necessary for one sintering are prepared, and spreading the flame produced by the burning of the solid alcohol fuel placed in the apparatus over a wide range and completing the burning simultaneously with that of the sintering of the silver clay composition; it is possible to sinter the silver clay in a narrow sintering space. Thus, it is unnecessary to maintain a space to move the gas burner such as the case of sintering which is performed by the gas burner.   (d) In the apparatus having this narrow sintering space, it is preferable that the sintering apparatus is composed of a plurality of parts in order that a lid is in place and thus it is difficult to view from the outside during the sintering of the silver clay composition, and the lid is opened and the sintered body is removed after the sintering has completed. Furthermore, it is preferable that the sintering apparatus is assembled from the parts when the sintering apparatus is used, and after the completion of the sintering of the silver clay composition, the sintering apparatus is disassembled and stored.   (e) More preferably, in order to remove the sintered body by opening the lid immediately after the completion of the sintering, a handle part that is not heated by the sintering is provided on the lid.       

   Based on this knowledge, the present invention provides:
         (4) a silver clay sintering apparatus comprises a burning cylinder with a bottom that has air holes in at least a side wall thereof, a burning lid part that covers an upper part of this burning cylinder with a bottom and has a lower end opening part that engages an upper end opening part of the burning cylinder with a bottom; wherein a screen can be engaged on the upper end opening of the burning cylinder with a bottom, and a roof having an exhaust hole in the ceiling thereof is provided on the burning lid part that has the lower edge opening part,   (5) a silver clay sintering apparatus that provides a burning cylinder with a bottom providing air holes in at least the side wall and a burning lid part that covers the upper part of this burning cylinder with a bottom and has a lower end opening part that engages an upper end opening part of the burning cylinder with a bottom, wherein a screen can be engaged on the upper end opening of the burning cylinder with a bottom, and furthermore, a roof having an exhaust hole in the ceiling thereof and a cylinder handle are provided on the burning lid part that has the lower edge opening part, and the roof is integrally provided in the inner side of the cylinder handle; and   (6) a silver clay sintering apparatus wherein the burning cylinder and the burning lid part described in the above (4) and (5) can each be segmented into a plurality of parts.       

   In this case, it is preferable that the cross-section of the burning cylinder with a bottom and the sintering lid part is circular, and the burning cylinder with a bottom is a circular cylinder with a bottom, however, the cross-sectional shape of the burning cylinder with a bottom is not limited thereby, and elliptical shapes and polygonal shapes are also possible. 
   According to the silver clay sintering method and apparatus for the same of the present invention, because the worker can assemble the sintering apparatus individually, it is possible to fabricate precious metal decorations by readily and simply sintering a small number of silver clay compositions, and it is convenient because the silver clay sintering apparatus can be easily stored after the sintering is complete. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a cross-sectional diagram showing an example of the silver clay sintering apparatus. 
       FIG. 2  is the temperature curve of the interior of the sintering apparatus obtained by burning a solid alcohol fuel. 
       FIG. 3  is a cross-sectional diagram showing an example of the silver clay sintering apparatus of the present invention. 
       FIG. 4  is an upper perspective drawing of the silver clay sintering apparatus shown in  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Next, the apparatus of the present invention that implements the sintering method for silver clay will be concretely explained with reference to the figures. 
     FIG. 1  is a cross-sectional diagram showing an example of the silver clay sintering apparatus of the present invention. This silver clay sintering apparatus comprises a burning cylinder with a bottom  15  that provides air holes  7  in at least the side wall and a burning lid part  20  that covers the upper end of burning cylinder with a bottom  15  and engages the upper end opening part of burning cylinder having a bottom  15 . The burning cylinder having a bottom  15  can be segmented into a ring-shaped upper enclosure  3  made of an insulating fire-resistant material, a ring-shaped platform enclosure  5  made of an insulating fire-resistant material, and a platform  12 , and the burning lid part  20  can be segmented into a ring-shaped lower enclosure  4  made of an insulating fire-resistant material and a cone-shaped roof  6  having an exhaust hole  14 . In addition, this apparatus is made of an insulating material, and in particular, preferably the burning cylinder having a bottom  15  and the burning lid  20  are both also made of an insulating material. As an insulating material, an insulating alloy such as stainless steel can be used, however, because insulating characteristics are required, preferably mullite, alumina, magnesia, zirconia, silica, earthenware or the like are used, and mullite is most preferably from the point of view of cost. 
   In addition, in  FIG. 1 , reference numeral  1  denotes a silver clay composition and  2  and  2 ′ denote screens. Any of the following can be used as these screens  2  and  2 ′: screens made of a heat-resistant alloy such as stainless steel, a coating screen on which a fire-resistant material has been coated on a metal screen, or a screen with superior heat-resistant characteristics such as a ceramic screen. A recess  9  for engaging the screen  2  is provided in the upper end of the upper enclosure  3  of the burning cylinder having a bottom  15 , and a recess  9 ′ is provided for engaging the screen  2 ′ in the upper end of the platform enclosure  5 . These recesses  9  and  9 ′ are for stabilizing the screens  2  and  2 ′ when the screens  2  and  2 ′ are mounted on the upper edge of the upper enclosure  3  and the platform enclosure  5 , however, the sintering is possible even if the recesses  9  and  9 ′ are not provided. 
   In addition, in the side wall of the upper enclosure  3  and the platform enclosure  5 , at least one pair of air holes  7  are provided so as to face each other. A ring-shaped projection  8  is provided on the platform  12  to fasten the platform enclosure  5 , and the platform enclosure  5  is detachably fastened to the platform  12  by engaging the ring-shaped projection  8 . In addition,  10  denotes a pan for receiving the minute amount of ash generated during burning of the solid alcohol fuel  11 . 
   To sinter the silver clay using this silver clay sintering apparatus, the silver clay sintering apparatus is assembled as follows: first, the tray  10  is placed at the center part of the platform  12 , the platform enclosure  5  is fastened by being set on the ring-shaped projection  8  of the platform  12 , the screen  2 ′ is placed into the recess  9 ′ of the upper end of the platform enclosure  5 , the solid alcohol fuel  11  is placed on the screen  2 ′, the upper enclosure  3  is mounted on the platform enclosure  5 , the screen  2  is placed into the recess  9  on the upper end of the upper enclosure  3 , the lower enclosure  4  is placed on the upper edge of the upper enclosure  3 , and then the roof  6  is mounted on the lower enclosure  4 . 
   After the apparatus is assembled, when the solid alcohol fuel  11  is ignited and burned, air that is supplied from the air holes  7  provided in the side wall of the platform enclosure  5  rises due to a chimney action, is rectified by passing through the screen  2 ′, the silver clay composition  1  is evenly heated by making the direction of the flame  13  of the solid alcohol fuel  11  constant, and sintering occurs. The apparatus shown in  FIG. 1  comprises the burning cylinder having a bottom  15  and the burning lid part  20 , and the burning cylinder having a bottom  15  can be segmented into the ring-shaped upper enclosure  3 , the ring shaped platform enclosure  5 , and the platform  12 , and the burning lid part  20  can be segmented into the ring-shaped lower enclosure  4  and a roof  6 . Thus, a comparatively large sintering apparatus can be manufactured by adjusting the space between the silver clay composition  1  and the solid alcohol fuel  11  during assembly, and therefore, a large silver clay composition can be sintered. In addition, after sintering has completed, the silver clay sintering apparatus can be easily disassembled and can be stored in a narrow location. 
     FIG. 3  is a cross-sectional diagram showing another silver clay sintering apparatus for implementing the sintering method for silver clay of this invention. This sintering apparatus also comprises a burning cylinder having a bottom  15  and a burning lid part  20  that covers the upper end of the burning cylinder having a bottom  15  and has a lower end opening that engages with the upper end opening part of the burning cylinder having a bottom  15 . 
   Air holes  7  that introduce air are provided in the side wall of the burning cylinder having a bottom  15 . The air holes  7  are indispensable, and an ignition hole  17  may be provided depending on necessity. The air holes  7  are preferably provided so as to be on the side of the location where the fuel is disposed. In addition, both the burning cylinder having a bottom  15  and the burning lid part  20  are preferably made of a heat-resistant material or a heat-resistant insulating material. Preferably materials identical to those of the apparatus shown in  FIG. 1  can be used as the heat-resistant material or heat-resistant insulating material. 
   The burning cylinder having a bottom  15  and the burning lid part  20  shown in  FIG. 3  are respectively integrally formed. A ledge  16  is provided on the upper end opening part of the burning cylinder having a bottom  15 , and this ledge  16  supports the screen  2 . The material of the screen  2  is identical to that used in the apparatus shown in  FIG. 1 . In addition, a solid alcohol fuel  11  that fills the pan  10  is mounted on the platform  12  of the burning cylinder having a bottom  15 . 
   The burning lid part  20  comprises a tubular handle part  18  and a roof  6  integrally provided on the inside of the tubular handle part  18  and an exhaust hole  14  is provided in the ceiling. An edge  19  that extends towards the inside to improve the strength of the tubular handle part  18  is provided on the upper end of the tubular handle part  18 . In this structure, because the tubular handle part  18  is separated from the exhaust hole  14  provided in the ceiling of the roof  6 , the tubular handle part  18  does not become hot at the heat necessary to sinter a silver clay composition. Furthermore, it is preferable that the roof  6  is slanted. The air heated by the solid alcohol fuel is discharged to the outside from the exhaust hole  14 , however, when the roof  6  is formed at an angle, the flow of the air speeds up here, and fresh air can be easily supplied from the ignition hole  17 . 
   Next, the silver clay sintering method using the silver clay sintering apparatus shown in  FIG. 3  will be explained. First, the pan  10  filled with the solid alcohol fuel  11  that is the heat source is placed at the platform  12  of the burning cylinder having a bottom  15 . The post-processing and handling of the solid alcohol fuel  11  are easy because almost no remaining waste such as ash is generated. Furthermore, because it is possible to calculate the size of the block of the solid alcohol fuel  11  previously such that it burns and then burns out when the sintering has completed, it is not necessary to perform a stopping operation of the burning as is the case with a gas tank, an alcohol lamp, a gas burner, or the like. 
   After the solid alcohol fuel  11  is placed at the platform  12  of the burning cylinder having a bottom  15 , the screen  2  is placed on the ledge  16  of the upper end opening of the burning cylinder having a bottom  15 , and after placing the silver clay composition  1  on the screen  2 , the burning lid part  20  having the tubular handle part  18  covers by aligning with the upper end of the burning cylinder having a bottom  15 .  FIG. 4  shows that upper perspective drawing of the state in which the burning lid part  20  covers the burning cylinder having a bottom  15 . 
   Then, the solid alcohol fuel  11  is ignited from the ignition hole  17 , and after the solid alcohol fuel  11  burns out an the sintering of the silver clay composition  1  has completed, the burning lid part  20  is removed, and the silver clay sintered body is taken out. After the sintering has completed, the silver clay composition can be removed by removing the burning lid part  20  after the silver clay sintering apparatus has cooled, however, in this burning lid part  20 , the tubular handle  18  does not become hot even during the burning of the solid alcohol fuel  11 , and thus the burning lid part  20  can be removed and the silver clay composition can be taken out immediately after the sintering is complete. Other operational effects are identical to the silver clay sintering apparatus shown in  FIG. 1 . 
   EXAMPLE 1 
   Below, an example will be illustrated and the effect of the present invention explained. The following were previously prepared:
         a mullite platform enclosure having an outer diameter of 110 mm, an internal diameter of 90 mm, a height of 30 mm, and having an air hole with a diameter of 10 mm in the side wall;   a mullite lower enclosure having an external diameter of 110 mm, an inner diameter of 90 mm, a height of 60 mm;   a mullite upper enclosure having an external diameter of 110 mm, an inner diameter 90 mm, and a height of 60 mm;   two 12 mesh stainless steel screens;   pan;   20 g of solid alcohol fuel; and   a mullite platform.       

   In addition, a commercially available pure silver clay is molded and dried, and a pure silver clay composition having a diameter of 20 mm, a height of 2 mm is fabricated. 
   As shown in  FIG. 1 , the pure silver clay composition and the 20 g of solid alcohol fuel  11  are respectively placed on the screens  2  and  2 ′ and the sintering apparatus is assembled, and igniting the solid alcohol fuel  11 . As a result, the generated flame  13  surrounds the pure silver clay composition and sintering occurs. After 10 minutes, the solid alcohol fuel has burned out, the pure silver clay composition is removed, and the pure silver clay composition is sufficiently sintered. 
   In addition, when the temperature is measured in the vicinity of the pure silver clay composition in the sintering apparatus over the 10 minutes from the beginning to the completion of the sintering, the temperature curve shown in  FIG. 2  is obtained. As is clear from  FIG. 2 , in this sintering method, the temperature in the sintering apparatus rises to 700° C. in 1 minute and 30 seconds, and it is confirmed that the sintering temperature is reached comparatively quickly. In addition, a temperature between 700 and 800° C. is maintained for 7 minutes, and it is confirmed that sufficient sintering is possible for the pure silver clay composition. 
   EXAMPLE 2 
   A burning cylinder having a bottom  15  and a burning lid part  20  that form the assembled silver clay sintering apparatus as shown in  FIG. 3  are each fabricated from mullite. Then the pure silver clay composition  1  fabricated in example 1 is placed on the 12 mesh stainless steel screen  16  that has been placed on the upper end of the burning cylinder having a bottom  15  as shown in  FIG. 3 , and a block of solid alcohol fuel  11  having a diameter of 40 mm and a height of 20 mm is ignited. As a result, the generated flame  13  surrounds the pure silver composition, and sintering occurs. Next, when the solid alcohol fuel  11  has burned out, the tubular handle  18  is grasped, the burning lid part  20  is removed, the pure silver clay composition is taken out, and the pure silver clay composition is sufficiently sintered.