CA2041668C - Method of preparing cemented carbide or cermet alloy - Google Patents
Method of preparing cemented carbide or cermet alloyInfo
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- CA2041668C CA2041668C CA002041668A CA2041668A CA2041668C CA 2041668 C CA2041668 C CA 2041668C CA 002041668 A CA002041668 A CA 002041668A CA 2041668 A CA2041668 A CA 2041668A CA 2041668 C CA2041668 C CA 2041668C
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- organic binder
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
- B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
- B22F3/1017—Multiple heating or additional steps
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/10—Sintering only
- B22F3/1017—Multiple heating or additional steps
- B22F3/1021—Removal of binder or filler
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
- B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2201/00—Treatment under specific atmosphere
- B22F2201/10—Inert gases
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2201/00—Treatment under specific atmosphere
- B22F2201/20—Use of vacuum
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
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- Manufacturing & Machinery (AREA)
- Mechanical Engineering (AREA)
- Powder Metallurgy (AREA)
Abstract
A method of preparing a cemented carbide or a cermet alloy by mixing and kneading cemented carbide powder or cermet alloy powder with an organic binder, shaping this mixed powder into a prescribed configuration by an injection molding method and thereafter removing the organic binder from this compact and sintering the same, in order to obtain a dense alloy. Removal of the organic binder is performed in a first step in an inert gas atmosphere as a first removal step, and continued under a vacuum of not more than 1 Torr as a second removal step. In the first removal step, the pressure is held in excess of atmospheric pressure, to prevent the formation of imperfections in the compact. After continuous pores are formed in the interior of the compact, the pressure is brought close to a vacuum, thereby facilitating the evaporation of gas from the surface and desorption of gas generated in the interior of the compact.
Description
~~ ~ss~ ~.~
The present invention relates to a method of preparing a cemented carbide or a cermet alloy, and more particularly, it relates to a method of preparing a cemented carbide or a cermet alloy by shaping cemented carbide powder or cermet alloy powder into a prescribed configuration by injection molding, then removing organic binder therefrom and sintering the compact.
Cemented carbide and cermet alloys are materials having high melting points. In order to obtain a cemented carbide sintered compact or a cermet alloy sintered compact, a powder metallurgical method of press-molding or CIP-molding a powder raw material and thereafter sintering the same has generally been employed. In this method, however, the range of manufacturable configurations is significantly restricted. In order to obtain a complicated final configuration, it is necessary to grind the sintered compact with a diamond grindstone after sintering, leading to extremely high cost.
The technique of molding plastic by an injection molding method is widely known. Japanese Patent Publication No. 62-33282 discloses a method of kneading metal powder or ceramics powder with an organic binder and shaping the same into an article having a complicated configuration by injection molding.
When such a powder injection molding technique is applied to a cemented carbide or a cermet alloy, however, the following problems arise. Cemented carbide powder and cermet alloy powder are fine powders having an average particle diameter of about 1 Vim. Further, such alloys have high specific gravity. In addition, tolerance for carbon concentration in the alloy is low. Due to such material properties of the cemented carbide or the cermet alloy, deformations and imperfections are easily caused during debinder processing. Besides, it is impossible to obtain an alloy of good quality, due to the influence exerted by residual carbon which is caused by decomposition of the organic binder. In order to avoid such problems, it is necessary to perform processing for binder removal for an extremely long time. Due to presence of the aforementioned problems, an injection molding technique for a cemented carbide and a cermet alloy has not yet been substantially put into practice.
An object of the present invention is to provide a method of obtaining a cemented carbide or a cermet alloy of high quality by efficiently shaping cemented carbide powder or cermet alloy powder by an injection molding method, and through subsequent debinder processing and sintering processing.
Another object of the present invention is to provide a method which avoids deformation and imperfection of a compact in debinder processing.
Still another object of the present invention is to provide a method which can perform debinder processing in a short period of time.
The present invention relates to a method of preparing a cemented carbide or a cermet alloy, and more particularly, it relates to a method of preparing a cemented carbide or a cermet alloy by shaping cemented carbide powder or cermet alloy powder into a prescribed configuration by injection molding, then removing organic binder therefrom and sintering the compact.
Cemented carbide and cermet alloys are materials having high melting points. In order to obtain a cemented carbide sintered compact or a cermet alloy sintered compact, a powder metallurgical method of press-molding or CIP-molding a powder raw material and thereafter sintering the same has generally been employed. In this method, however, the range of manufacturable configurations is significantly restricted. In order to obtain a complicated final configuration, it is necessary to grind the sintered compact with a diamond grindstone after sintering, leading to extremely high cost.
The technique of molding plastic by an injection molding method is widely known. Japanese Patent Publication No. 62-33282 discloses a method of kneading metal powder or ceramics powder with an organic binder and shaping the same into an article having a complicated configuration by injection molding.
When such a powder injection molding technique is applied to a cemented carbide or a cermet alloy, however, the following problems arise. Cemented carbide powder and cermet alloy powder are fine powders having an average particle diameter of about 1 Vim. Further, such alloys have high specific gravity. In addition, tolerance for carbon concentration in the alloy is low. Due to such material properties of the cemented carbide or the cermet alloy, deformations and imperfections are easily caused during debinder processing. Besides, it is impossible to obtain an alloy of good quality, due to the influence exerted by residual carbon which is caused by decomposition of the organic binder. In order to avoid such problems, it is necessary to perform processing for binder removal for an extremely long time. Due to presence of the aforementioned problems, an injection molding technique for a cemented carbide and a cermet alloy has not yet been substantially put into practice.
An object of the present invention is to provide a method of obtaining a cemented carbide or a cermet alloy of high quality by efficiently shaping cemented carbide powder or cermet alloy powder by an injection molding method, and through subsequent debinder processing and sintering processing.
Another object of the present invention is to provide a method which avoids deformation and imperfection of a compact in debinder processing.
Still another object of the present invention is to provide a method which can perform debinder processing in a short period of time.
~ ~ '~ 66~
A method of preparing a cemented carbide or a cermet alloy according to the present invention comprises mixing/kneading cemented carbide powder or cermet alloy powder with an organic binder, shaping this mixed powder into a prescribed configuration by an injection molding method, and thereafter removing the organic binder from the compact and sintering the same. Removal of the organic binder is first performed in an inert gas atmosphere as a first removal step, and then, directly following the first removal step, is performed in a vacuum of not more than 1 Torr as a second removal step.
According to one aspect of the present invention, the organic binder contains a plurality of types of binders, which are divided into a group removable under a low temperature and a group removable under a high temperature.
Compositions of the respective binders contained in the organic binder are selected to satisfy such a condition that the loss rate of the high-temperature removable group is within 5% when the low-temperature removable group is lost by 30% of the whole in an inert gas atmospheric pressure heating loss test (TG) for only the organic binder.
Preferably the rate of the binder belonging to the low-temperature removable group with respect to the overall organic binder is set to be at least 30% and not more than 90%.
In a preferred embodiment, the organic binder contains a plurality of types of binders including a group removable under a low temperature and a group removable at a high temperature, and assuming that a~ , a2, . . . , a~
represents ratios of respective binders of the low-temperature removal group including i types of binders with respect to the overall organic binder, b~, b2, . . . , b~
represent ratios of respective binders of the high temperature removal group including j types of binders with respect to the overall organic binder (Ear + Ebb = 1), xT~, xT2, ..., xT~ represent loss rates of a single substance of the respective binders belonging to the low-temperature removal group at a certain temperature T in inert gas atmospheric pressure heating loss tests (TG), and yT~, yT2, ..., yT~ represent loss rates of a single substance of the respective binders belonging to the high-temperature removal group at the temperature T in inert gas atmospheric pressure heating loss tests, compositions of the respective binders contained in said organic binder are selected to satisfy the following conditions:
E (b~ x yT~ ) 5 0 . 05 Ebb >_ 0.1 at the temperature T for which E(a~ x xT~) - 0.3.
Advantageously, the temperature T for transition from the first removal step to the second removal step is selected to satisfy the following conditions:
E(a~ x xT~) > 0.3 E{b~ x (1 - yT~) } > 0.05.
a:
According to another aspect of the present invention, the temperature for transition from the first removal step to the second removal step is selected to satisfy the following condition: The condition is such a condition that the amount of removal of the binder belonging to the low-temperature removable group is at least 30% with respect to the overall organic binder, while the residual rate of the binder belonging to the high-temperature removable group is at least 5% with respect to the overall organic binder. A binder for serving as the main component of the low-temperature removable group is preferably prepared from wax having hydrophilic polar groups, with a melting point of not more than 80~C.
After the organic binder is removed from the compact by the aforementioned method, sintering processing may be performed. Alternatively, the compact may be cooled after the organic binder is removed, to be thereafter sintered.
An injection-molded compact is formed by powder and a binder, substantially with no voids. When the compact is subjected to rising temperature in this state, the binder first escapes by expansion of the binder, and then debindering progresses due to evaporation from the surface.
When debindering of 30% occurs by such a process, pores communicating with the surface are formed in the interior of the compact. Gas generated in the interior of the compact escapes through the pores, to further promote debindering.
.;
However, if the gas is generated in the interior of the compact in a debindering state of less than 30%, the compact tends to become cracked or blistered. In order to prevent such cracking or blistering of the compact, it is necessary to suppress generation of the gas in the interior of the compact with a loose programming rate. Therefore, a long time is required for the debinder processing. Wax serving as a plasticizer and high polymer resin serving as a binder are required as the binders. Since wax evaporates at a low temperature with no decomposition, it is possible to perform debindering relatively easily. On the other hand, high polymer resin is apt to cause imperfections in the compact in an initial stage of debindering, since the same generates a large quantity of gas on decomposition.
The inventors have noted the aforementioned points, to achieve the present invention. In more concrete terms, a high polymer resin is selected which will not commence decomposition even if the temperature reaches such a level that the wax is removed by an amount of at least 30%
of the whole, and this high polymer resin is mixed with the wax. In an initial state of debinder processing, debindering of at least 30% is facilitated by evaporation of the wax alone, to form continuous pores in the interior of the compact. After the pores are formed, decomposition of the high polymer resin is caused to start.
Hoechst wax, carnauba wax, montan wax, ozokerite wax, auriculine wax, candelilla wax, beeswax, microcrystalline wax and the like can be cited as major wax materials of the low-temperature removal group. Low density polyethylene, low molecular weight polyethylene, ethylene-vinyl acetate, polypropylene, acrylic resin and the like can be cited as binders of the high-temperature removal group.
In the initial state of debinder processing, the pressure is maintained in excess of atmospheric pressure, thereby preventing the compact from creating imperfections.
After continuous pores are formed in the interior of the compact, the pressure is brought to a decompressed state, or a state close to a vacuum, thereby facilitating evaporation of gas from the surface and desorption of gas generated in the interior of the compact.
The strength of the injection-molded compact should be noted. When the high molecular resin serving as a bonding agent is removed, bonding strength between the powder particles is significantly reduced, such that a cemented carbide etc. having high specific gravity inevitably collapses. In order to prevent this, it is necessary to attain strength by bonding powder materials for forming the alloy. However, since the surfaces of the alloy powder materials are covered with thin oxide films, bonding is insufficiently achieved by diffusion. The inventors have found that, when removal of the binder is performed in a vacuum, the surfaces of the alloy powder materials are _ 7 _ deoxidized by ambient carbon, whereby bonding strength is attained between the alloy powder materials. Thus, according to the present invention, debindering in a vacuum is facilitated thereby bonding the powder particles with each other. When the powder particles are bonded with each other, the compact will not collapse until debindering is terminated. In a preferred embodiment of the present invention, the debinder processing is performed in two stages, namely a first removal step and a second removal step. The first removal step is carried out under atmospheric pressure, and the second removal step is carried out under a vacuum. In transition from the first removal step to the second removal step, the bonding agent must be left in an amount of at least 5%. If the residual amount of the bonding agent is not more than 5%, the compact will collapse before bonding strength is attained between the powder particles.
The atmosphere for the debinder processing will now be described. The first removal step is preferably carried out in an atmosphere of an inert gas such as NZ or argon. If the debinder processing is performed in an oxidizing atmosphere such as air, surface oxidation of Co, Ni and the like inevitably progresses during progress of the debindering. If such surface oxidized layers are present, bonding strength by reduction is inevitably lowered in the second removal step. Further, since oxidation of only a portion exposed to the ambient atmosphere progresses with _ g _ ,, ~t ,.'. , progress of debindering, carbon concentration in the alloy is non-uniform and a liquid phase appearance temperature in sintering is non-uniform, whereby significantly reducing dimensional accuracy. It is possible to attain reduction of the oxide films on the surfaces of the alloy powder materials, by carrying out the second removal step not in a vacuum but in an H2 atmosphere. If debinder processing is performed in an H2 atmosphere, however, a reaction is simultaneously caused such that carbide C, which is a hard phase forming component of the cemented carbide or the cermet alloy, reacts with hydrogen to form CH4. Thus, the carbon content of the alloy is reduced.
The types of wax will now be described. The surface of cemented carbide powder or cermet alloy powder is hydrophilic. On the other hand, wax such as n-paraffin is hydrophobic. Therefore, the wettability between a wax such as n-paraffin and cemented carbide powder or cermet alloy powder is inferior. In order to attain the viscosity which is required for injection molding, therefore, it is necessary to use a larger amount of wax. The inventors have studied various wax materials, and have found that the amount of the binder can be reduced by employing a certain type of natural wax having hydrophilic polar groups. When the compact is taken out from a metal mold in injection molding, the compact is easily broken since wax is friable.
In order to prevent such breakage, it is preferable to use a wax having a melting point of not more than 80~C. So far g k .. .:::.t as the wax has hydrophilic polar groups with a melting point of not more than 80~C, its effect remains unchanged whether it is a synthetic or natural wax. While stearic acid or the like may be employed as a lubricant, the effect of the present invention remains unchanged even if such a minor additive is employed.
The following Examples illustrate the invention.
Example 1 80% of WC powder having a particle diameter of 2 to 4 Vim, 10% of TiC powder having a particle diameter of 1 to 2 Vim, and 10% of Co powder having a particle diameter of 2 to 4 ~m were mixed in a wet ball mill for 3 hours, and dried. 6.0% of beeswax and 1.0% of low molecular weight polyethylene were added to 100% of this mixed powder, and the mixture was kneaded at 120~C for 30 minutes. Then, this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw material particles of 0.5 to 2.0 mm in particle diameter. Then, injection molding was performed with a mold (20 x 20 x 6 mm) having the configuration of a throw-away tip, to prepare a compact.
The compact was disposed in a furnace, and the interior of the furnace was held at 1 atmosphere pressure with an argon atmosphere. The temperature in the furnace was raised to 425~C at a programming rate of 8~C/hour under the condition of an argon flow rate of 3 E/minute, to perform debinder ,: ~.~.._-::
processing. Then the temperature in the furnace was raised to 700~C at a programming rate of 50~C/hour with the interior of the furnace being maintained at a pressure of not more than 0.5 Torr with a vacuum pump, and the furnace was held at that temperature for one hour, and thereafter cooled. Thus, the debinder processing was terminated.
Then, the interior of the furnace was brought to a vacuum state of 0.05 Torr and the temperature was raised to 1400~C
at 200~C/hour, and the furnace was held at that temperature for one hour, and thereafter cooled. The as-formed sintered body had absolutely no imperfections, and was excellent from the viewpoint of alloy characteristics. A heating loss test for the binders used in this Example was carried out, whereby the beeswax was lost to the extent of 95% before reaching 425~C under conditions of NZ and 1 atmosphere. On the other hand, the loss of the low molecular weight polyethylene was 13% at 425~C.
Example 2 90% of WC powder having a particle diameter of 0.5 to 2 ~m and 10% of Co powder having a particle diameter of 2 to 4 ~m were mixed in a wet ball mill for 20 hours, and dried. 5.5% of carnauba wax and 1.0% of low molecular weight polypropylene were added to 100% of this mixed powder, and kneaded at 140~C for 30 minutes. Then, this raw material mixture was cooled/solidified and thereafter .
pulverized, to prepare raw material particles of about 0.5 to 2.0 mm in particle diameter. Then, injection molding was performed in a mold (20 x 20 x 6 mm) having the configuration of a throw-away tip. This compact was arranged in a furnace. The interior of the furnace was maintained under an argon atmosphere at a pressure of 1 atmosphere, and the temperature was raised to 430~C at a programming rate of 10~C/hour under the condition of a flow rate of 3 E/minute, to perform initial debinder processing.
Then, the temperature was raised to 700~C at a programming rate of 50~C/hour while maintaining the interior of the furnace at a pressure of not more than 0.2 Torr with a vacuum pump, and the furnace was held at that temperature for one hour. Thus, the debinder processing was completed.
Thereafter the temperature in the furnace was raised to 1350~C at a rate of 200~C/hour under a vacuum of 0.05 Torr, and the furnace was cooled after the same was held at that temperature for one hour. The as-formed sintered body exhibited absolutely no imperfections, and was excellent from the viewpoint of alloy characteristics. A heating loss test was performed on the binders employed in this Example, whereby the carnauba wax was lost by 92% before reaching 430~C under conditions of N2 and 1 atmosphere. On the other hand, loss of the low molecular weight polypropylene was 8%
at 430~C.
Example 3 88% of WC powder having a particle diameter of 0.1 to 1 Vim, 6% of Co powder having a particle diameter of 2 to 4 ~Cm and 6% of Ni powder having a particle diameter of 2 to 4 ~m were mixed in a wet ball mill for 25 hours, and dried.
0.5% of beeswax, 4.5% of n-paraffin, 0.2% of stearic acid, 0.5% of ethylene-vinyl acetate and 1.0% of low molecular weight polyethylene were added to 100% of this mixed powder, and kneaded at 120~C for 30 minutes. Then this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw material particles of about 0.5 to 2.0 mm in particle diameter. Then, injection molding was performed with a mold (20 x 20 x 6 mm) having the configuration of a throw-away tip. This compact was arranged in a furnace.
The interior of the furnace was supplied with an N2 atmosphere at a pressure of 1 atmosphere and the temperature was raised to 380~C at a programming rate of 13~C/hour under the condition of a flow rate of 2 E/minute, to perform initial debinder processing. Then, the temperature was raised to 700~C at a programming rate of 50~C/hour while maintaining the interior of the furnace at a pressure of not more than 0.5 Torr with a vacuum pump, and the furnace was cooled after being held at that temperature for one hour.
Thus, the debinder processing was completed. Then, the interior of the furnace was brought to a vacuum of 0.05 Torr, and its temperature was raised to 1350~C at a rate of 200~C/hour, and cooled after being held at that temperature for one hour. The as-formed sintered body had absolutely no imperfections, and was excellent from the viewpoint of alloy characteristics. A heating loss test was performed on the binders employed in this Example, whereby the beeswax was lost by 60% and the n-paraffin was lost by 100% before reaching 380~C under conditions of N2 and 1 atmosphere. On the other hand, loss of the low molecular weight polyethylene was 7.0% and loss of the ethylene-vinyl acetate was 10% at 380~C.
Example 4 88% of WC powder having a particle diameter of 1 to 2 ~Cm and 12% of Co powder were mixed in a wet ball mill for 15 hours, and dried. 5.5% of montan wax and 0.8% of low density polyethylene were added to 100% of this mixed powder, and kneaded at 120~C for 3 hours. Then, this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw material particles of about 0.5 to 2.0 mm in particle diameter. Then injection molding was performed with a mold (20 x 20 x 6 mm) having the configuration of a throw-away tip. This compact was arranged in a furnace. The interior of the furnace was supplied with an argon atmosphere at a pressure of 1 atmosphere, and the temperature was raised to 350~C at a programming rate of 10~C/hour under the condition of a flow I ': ~.~?
rate of 3 E/minute, to perform initial debinder processing.
Then, the temperature was raised to 650~C at a programming rate of 50~C/hour while maintaining the interior of the furnace at a pressure of not more than 0.5 Torr with a vacuum pump, and the furnace was cooled after being held at that temperature for one hour, to complete the debinder processing. Then, the interior of the furnace was brought to a vacuum of 0.05 Torr, the temperature was raised to 1400~C at a rate of 200~C/hour, and the furnace was cooled after being held for one hour. The as-formed sintered body had absolutely no imperfections, and was excellent from the viewpoint of alloy characteristics. A heating loss test was performed on the binders employed in this Example, whereby loss of the montan wax was 93% before reaching 350~C under conditions of NZ and 1 atmosphere, while loss of the low density polyethylene was 0% on measurement at 350~C.
Example 5 Cermet powder (50% of TiCN, 10% of TaC, 12% of MoZC, 13% of WC, 5% of Ni and 10% of Co) having a particle diameter of 0.5 to 1 ~m was mixed in a wet ball mill for 10 hours, and dried. 7.8% of montan wax, 2.7% of n-paraffin, 2.7% of low density polyethylene and 0.3% of stearic acid were added to 100% of this mixed powder, and kneaded at 120~C for 3 hours. Then, this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw _ 15 _ material particles of about 0.5 to 2.0 mm in particle diameter. Then, injection molding was effected into a mold having a ball end mill configuration of 10 mm in diameter, to obtain a compact. This compact was arranged in a furnace. The interior of the furnace was supplied with an argon atmosphere at a pressure of 1 atmosphere, and the temperature was raised to 350~C at a programming rate of 10~C/hour under the condition of a flow rate of 3 E/minute, to perform initial debinder processing. Then, the temperature was raised to 650~C at a programming rate of 50~C/hour while maintaining the interior of the furnace at a pressure of not more than 0.5 Torr with a vacuum pump, and the furnace was cooled after being held at that temperature for one hour, to complete the debinder processing. Then, the interior of the furnace was brought to a vacuum of 0.05 Torr and the temperature was raised to 1400~C at a rate of 200~C/hour, and the furnace was cooled after being held for one hour, and thereafter HIP processing was performed at 1350~C. The as-formed sintered body had absolutely no imperfections, and was excellent from the viewpoint of alloy characteristics. A heating loss test was performed on the binders employed in this Example, whereby loss of the montan wax was 93% under conditions of NZ and 1 atmosphere before reaching 350~C and loss of the n-paraffin was 100%, while loss of the low density polypropylene was 0% on measurement at 350~C.
ry-.-Example 6 A plurality of raw material particle compacts were prepared under the same conditions as those in Example 1.
With respect to these compacts, the programming rate in the first removal step of debinder processing and the transition temperature to the second removal step were changed, to examine the conditions after debindering. Table 2 shows the results. Table 1 shows the results of heating loss tests of beeswax and low molecular weight polyethylene (PE). As is obvious from the results of Tables 1 and 2, excellent conditions are attained after debindering according to the inventive method, and debindering times can be shortened.
Table 1 Heating Loss Rate (N2 1 atmosphere, Temperature Rising at 10~C/minute) Beeswax 0.03 0.12 0.32 0.50 0.l4 0.95 0.99 1.00 (xT) Low Molecular 1 Weight PE p,01 0.03 0.05 0.07 0.09 0.13 0.30 0.85 0 (yT) Table 2 Test Results of Transition Temperature in Second Removal Step Test Transiti~ 1st RemovalBeeswax PE ResidualCondition 2 No. TemperatureStep Loss Rate After 0 in 2nd ProgrammingRate Debindering Renaval Rate b x (1-yT) Step a x xT
1 300 8C/hour 0.10 0.14 bursting state 2 300 4C/hour 0.10 0.14 significantly cracked and blistered 3 350 8C/hour 0.27 0.14 5 cracks 4 350 4C/hour 0.27 0.14 gd 2 5* 375 8C/hour 0.43 0.13 gd 6* 400 8C/hour 0.64 0.13 gd 7* 425 8C/hour 0.81 0.12 gd 8* 450 8C/hour 0.85 0.10 gd 9 475 8C/hour 0.86 0.02 collapsed *: Inventive Method a = 0.86 b = 0.14 .~
Example 7 8 types of samples were prepared by using an alloy powder which was similar to that of Example 1 and changing the rate of beeswax to low molecular weight polyethylene (PE) as to binder compositions (tests Nos. 10 to 17), to perform debindering tests. Table 3 shows the results. The transition temperature from the first removal step to the second removal step was set at 450 ~ C. As is obvious from Table 3, the inventive compositions give excellent results.
Table 3 Test Conditions and Results Test Binder 1st RemovalBeeswax PE b x yT Condition 1 No. CompositionStep Loss Residual after Beeswax/LowProgrammingRate Rate (a x xT=0.3)Debindering Molecular Rate Weight a x x,5ob x (1-y4so) PE
partially 10 6.5/0.5 10C/hour0.92 0.05 0.005 formed 11* 6.0/1.0 10C/hour0.85 0.10 0.008 gd 12* 5.0/2.0 10C/hour0.71 0.20 0.018 gd 2 13* 4.0/3.0 10C/hour0.57 0.30 0.032 gd 14* 3.0/4.0 10C/hour0.42 0.40 0.045 gd 15* 3.0/4.0 4C/hour 0.42 0.40 0.045 gd not reachingsignificantly 16 2.0/5.0 10C/hour0.28 0.50 a x xT=0.3cracked 2 not reaching 17 2.0/5.0 4C/hour 0.28 0.50 a x xT=0.32 cracks *: Inventive Method 30 Binder Composition: Rate with respect to 100% of Alloy Powder Example 8 Alloy powder similar to that of Example 3 was used and debindering tests were performed by changing the types and compositions of binders. Table 4 shows the results.
Debindering conditions were identical to those of Example 3.
Good injection and debindering were possible in tests Nos.
18 to 20. In test No. 21 employing n-paraffin, however, it was impossible to effect a good injection, unless the amount of n-paraffin was increased. In test No. 22, on the other hand, distortion was caused in debinder processing. In test No. 23 of mixing beeswax and n-paraffin at a 1/1 ratio, no deformation was recognized in debindering although it was necessary to add a slight amount of the binder.
Tsble 4 Wax Type and Result TestWax Type Binder CompositionInjection Debinder Condition No. Wax/Low Molecular Weight PE
2 1g* Carnauba Wax 5.0/1.5 possible good Beeswax 5.0/1.5 possible good 20* Nontan Wax 5.0/1.5 possible good 21 n-Paraffin 5.0/1.5 impossible ---22 n-Paraffin 7.0/1.5 possible distorted 2 23* B~swax+n-Paraffin3+3/1.5 possible good *: Inventive Method Binder Composition: Rate with respect to 100% of Alloy 30 Powder Example 9 In a preparation method similar to test No. 5 of Table 2, the pressure and type of atmosphere for the first removal step and the second removal step were varied as shown in tests Nos. 24 to 30 in Table 5. As is obvious from the results of Table 5, the inventive atmospheres are effective. It was impossible to advance the samples of tests Nos. 26 and 29 to sintering, since the bodies collapsed in debindering. Other samples were capable of progressing to sintering steps.
Table 5 Test1st 2nd Removal Result Removal Step: d Step: 350 Si up to 700C t to 1 No. n 5 ere ( Gas Flow RatePressure AtmosphereFlow PressureBody) Rate Atmospheric 5* Ar 3 t/minutePressure Vacuum 0.5 Torrgod Atmospheric Pressure 24* Ar 0.1 t/minute Vacuum 0.5 Torr9od 2 Atmospheric 25* N 3 t/minutePressure Vacuum 0.5 Torrgood Atmospheric AtmosphericCollapsed (in Pressure N Pressuredebindering) 26 N 3 t/minute Z 3 t/minute 27* N 3 t/minute600 Torr Vacuum 0.5 Torr9d 2 Atmospheric distorted, 28 Air 3 t/minutePressure Vacs 0.5 Torrcracked Atmospheric 29 Ar 3 tlminutePressure pr 5 Torr collapsed Atmospheric Atmosphericlow carbon Pressure N 3 t Pressurea~e~
i 3 30 Nz 3 t/minute z nute aused 0 /m Ph *: Inventive Method ;.
,, The present invention is effectively applied to a method of preparing a cemented carbide or a cermet alloy by shaping cemented carbide powder or cermet alloy powder into a prescribed configuration by an injection molding method and thereafter sintering the compact upon removal of an organic binder.
A method of preparing a cemented carbide or a cermet alloy according to the present invention comprises mixing/kneading cemented carbide powder or cermet alloy powder with an organic binder, shaping this mixed powder into a prescribed configuration by an injection molding method, and thereafter removing the organic binder from the compact and sintering the same. Removal of the organic binder is first performed in an inert gas atmosphere as a first removal step, and then, directly following the first removal step, is performed in a vacuum of not more than 1 Torr as a second removal step.
According to one aspect of the present invention, the organic binder contains a plurality of types of binders, which are divided into a group removable under a low temperature and a group removable under a high temperature.
Compositions of the respective binders contained in the organic binder are selected to satisfy such a condition that the loss rate of the high-temperature removable group is within 5% when the low-temperature removable group is lost by 30% of the whole in an inert gas atmospheric pressure heating loss test (TG) for only the organic binder.
Preferably the rate of the binder belonging to the low-temperature removable group with respect to the overall organic binder is set to be at least 30% and not more than 90%.
In a preferred embodiment, the organic binder contains a plurality of types of binders including a group removable under a low temperature and a group removable at a high temperature, and assuming that a~ , a2, . . . , a~
represents ratios of respective binders of the low-temperature removal group including i types of binders with respect to the overall organic binder, b~, b2, . . . , b~
represent ratios of respective binders of the high temperature removal group including j types of binders with respect to the overall organic binder (Ear + Ebb = 1), xT~, xT2, ..., xT~ represent loss rates of a single substance of the respective binders belonging to the low-temperature removal group at a certain temperature T in inert gas atmospheric pressure heating loss tests (TG), and yT~, yT2, ..., yT~ represent loss rates of a single substance of the respective binders belonging to the high-temperature removal group at the temperature T in inert gas atmospheric pressure heating loss tests, compositions of the respective binders contained in said organic binder are selected to satisfy the following conditions:
E (b~ x yT~ ) 5 0 . 05 Ebb >_ 0.1 at the temperature T for which E(a~ x xT~) - 0.3.
Advantageously, the temperature T for transition from the first removal step to the second removal step is selected to satisfy the following conditions:
E(a~ x xT~) > 0.3 E{b~ x (1 - yT~) } > 0.05.
a:
According to another aspect of the present invention, the temperature for transition from the first removal step to the second removal step is selected to satisfy the following condition: The condition is such a condition that the amount of removal of the binder belonging to the low-temperature removable group is at least 30% with respect to the overall organic binder, while the residual rate of the binder belonging to the high-temperature removable group is at least 5% with respect to the overall organic binder. A binder for serving as the main component of the low-temperature removable group is preferably prepared from wax having hydrophilic polar groups, with a melting point of not more than 80~C.
After the organic binder is removed from the compact by the aforementioned method, sintering processing may be performed. Alternatively, the compact may be cooled after the organic binder is removed, to be thereafter sintered.
An injection-molded compact is formed by powder and a binder, substantially with no voids. When the compact is subjected to rising temperature in this state, the binder first escapes by expansion of the binder, and then debindering progresses due to evaporation from the surface.
When debindering of 30% occurs by such a process, pores communicating with the surface are formed in the interior of the compact. Gas generated in the interior of the compact escapes through the pores, to further promote debindering.
.;
However, if the gas is generated in the interior of the compact in a debindering state of less than 30%, the compact tends to become cracked or blistered. In order to prevent such cracking or blistering of the compact, it is necessary to suppress generation of the gas in the interior of the compact with a loose programming rate. Therefore, a long time is required for the debinder processing. Wax serving as a plasticizer and high polymer resin serving as a binder are required as the binders. Since wax evaporates at a low temperature with no decomposition, it is possible to perform debindering relatively easily. On the other hand, high polymer resin is apt to cause imperfections in the compact in an initial stage of debindering, since the same generates a large quantity of gas on decomposition.
The inventors have noted the aforementioned points, to achieve the present invention. In more concrete terms, a high polymer resin is selected which will not commence decomposition even if the temperature reaches such a level that the wax is removed by an amount of at least 30%
of the whole, and this high polymer resin is mixed with the wax. In an initial state of debinder processing, debindering of at least 30% is facilitated by evaporation of the wax alone, to form continuous pores in the interior of the compact. After the pores are formed, decomposition of the high polymer resin is caused to start.
Hoechst wax, carnauba wax, montan wax, ozokerite wax, auriculine wax, candelilla wax, beeswax, microcrystalline wax and the like can be cited as major wax materials of the low-temperature removal group. Low density polyethylene, low molecular weight polyethylene, ethylene-vinyl acetate, polypropylene, acrylic resin and the like can be cited as binders of the high-temperature removal group.
In the initial state of debinder processing, the pressure is maintained in excess of atmospheric pressure, thereby preventing the compact from creating imperfections.
After continuous pores are formed in the interior of the compact, the pressure is brought to a decompressed state, or a state close to a vacuum, thereby facilitating evaporation of gas from the surface and desorption of gas generated in the interior of the compact.
The strength of the injection-molded compact should be noted. When the high molecular resin serving as a bonding agent is removed, bonding strength between the powder particles is significantly reduced, such that a cemented carbide etc. having high specific gravity inevitably collapses. In order to prevent this, it is necessary to attain strength by bonding powder materials for forming the alloy. However, since the surfaces of the alloy powder materials are covered with thin oxide films, bonding is insufficiently achieved by diffusion. The inventors have found that, when removal of the binder is performed in a vacuum, the surfaces of the alloy powder materials are _ 7 _ deoxidized by ambient carbon, whereby bonding strength is attained between the alloy powder materials. Thus, according to the present invention, debindering in a vacuum is facilitated thereby bonding the powder particles with each other. When the powder particles are bonded with each other, the compact will not collapse until debindering is terminated. In a preferred embodiment of the present invention, the debinder processing is performed in two stages, namely a first removal step and a second removal step. The first removal step is carried out under atmospheric pressure, and the second removal step is carried out under a vacuum. In transition from the first removal step to the second removal step, the bonding agent must be left in an amount of at least 5%. If the residual amount of the bonding agent is not more than 5%, the compact will collapse before bonding strength is attained between the powder particles.
The atmosphere for the debinder processing will now be described. The first removal step is preferably carried out in an atmosphere of an inert gas such as NZ or argon. If the debinder processing is performed in an oxidizing atmosphere such as air, surface oxidation of Co, Ni and the like inevitably progresses during progress of the debindering. If such surface oxidized layers are present, bonding strength by reduction is inevitably lowered in the second removal step. Further, since oxidation of only a portion exposed to the ambient atmosphere progresses with _ g _ ,, ~t ,.'. , progress of debindering, carbon concentration in the alloy is non-uniform and a liquid phase appearance temperature in sintering is non-uniform, whereby significantly reducing dimensional accuracy. It is possible to attain reduction of the oxide films on the surfaces of the alloy powder materials, by carrying out the second removal step not in a vacuum but in an H2 atmosphere. If debinder processing is performed in an H2 atmosphere, however, a reaction is simultaneously caused such that carbide C, which is a hard phase forming component of the cemented carbide or the cermet alloy, reacts with hydrogen to form CH4. Thus, the carbon content of the alloy is reduced.
The types of wax will now be described. The surface of cemented carbide powder or cermet alloy powder is hydrophilic. On the other hand, wax such as n-paraffin is hydrophobic. Therefore, the wettability between a wax such as n-paraffin and cemented carbide powder or cermet alloy powder is inferior. In order to attain the viscosity which is required for injection molding, therefore, it is necessary to use a larger amount of wax. The inventors have studied various wax materials, and have found that the amount of the binder can be reduced by employing a certain type of natural wax having hydrophilic polar groups. When the compact is taken out from a metal mold in injection molding, the compact is easily broken since wax is friable.
In order to prevent such breakage, it is preferable to use a wax having a melting point of not more than 80~C. So far g k .. .:::.t as the wax has hydrophilic polar groups with a melting point of not more than 80~C, its effect remains unchanged whether it is a synthetic or natural wax. While stearic acid or the like may be employed as a lubricant, the effect of the present invention remains unchanged even if such a minor additive is employed.
The following Examples illustrate the invention.
Example 1 80% of WC powder having a particle diameter of 2 to 4 Vim, 10% of TiC powder having a particle diameter of 1 to 2 Vim, and 10% of Co powder having a particle diameter of 2 to 4 ~m were mixed in a wet ball mill for 3 hours, and dried. 6.0% of beeswax and 1.0% of low molecular weight polyethylene were added to 100% of this mixed powder, and the mixture was kneaded at 120~C for 30 minutes. Then, this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw material particles of 0.5 to 2.0 mm in particle diameter. Then, injection molding was performed with a mold (20 x 20 x 6 mm) having the configuration of a throw-away tip, to prepare a compact.
The compact was disposed in a furnace, and the interior of the furnace was held at 1 atmosphere pressure with an argon atmosphere. The temperature in the furnace was raised to 425~C at a programming rate of 8~C/hour under the condition of an argon flow rate of 3 E/minute, to perform debinder ,: ~.~.._-::
processing. Then the temperature in the furnace was raised to 700~C at a programming rate of 50~C/hour with the interior of the furnace being maintained at a pressure of not more than 0.5 Torr with a vacuum pump, and the furnace was held at that temperature for one hour, and thereafter cooled. Thus, the debinder processing was terminated.
Then, the interior of the furnace was brought to a vacuum state of 0.05 Torr and the temperature was raised to 1400~C
at 200~C/hour, and the furnace was held at that temperature for one hour, and thereafter cooled. The as-formed sintered body had absolutely no imperfections, and was excellent from the viewpoint of alloy characteristics. A heating loss test for the binders used in this Example was carried out, whereby the beeswax was lost to the extent of 95% before reaching 425~C under conditions of NZ and 1 atmosphere. On the other hand, the loss of the low molecular weight polyethylene was 13% at 425~C.
Example 2 90% of WC powder having a particle diameter of 0.5 to 2 ~m and 10% of Co powder having a particle diameter of 2 to 4 ~m were mixed in a wet ball mill for 20 hours, and dried. 5.5% of carnauba wax and 1.0% of low molecular weight polypropylene were added to 100% of this mixed powder, and kneaded at 140~C for 30 minutes. Then, this raw material mixture was cooled/solidified and thereafter .
pulverized, to prepare raw material particles of about 0.5 to 2.0 mm in particle diameter. Then, injection molding was performed in a mold (20 x 20 x 6 mm) having the configuration of a throw-away tip. This compact was arranged in a furnace. The interior of the furnace was maintained under an argon atmosphere at a pressure of 1 atmosphere, and the temperature was raised to 430~C at a programming rate of 10~C/hour under the condition of a flow rate of 3 E/minute, to perform initial debinder processing.
Then, the temperature was raised to 700~C at a programming rate of 50~C/hour while maintaining the interior of the furnace at a pressure of not more than 0.2 Torr with a vacuum pump, and the furnace was held at that temperature for one hour. Thus, the debinder processing was completed.
Thereafter the temperature in the furnace was raised to 1350~C at a rate of 200~C/hour under a vacuum of 0.05 Torr, and the furnace was cooled after the same was held at that temperature for one hour. The as-formed sintered body exhibited absolutely no imperfections, and was excellent from the viewpoint of alloy characteristics. A heating loss test was performed on the binders employed in this Example, whereby the carnauba wax was lost by 92% before reaching 430~C under conditions of N2 and 1 atmosphere. On the other hand, loss of the low molecular weight polypropylene was 8%
at 430~C.
Example 3 88% of WC powder having a particle diameter of 0.1 to 1 Vim, 6% of Co powder having a particle diameter of 2 to 4 ~Cm and 6% of Ni powder having a particle diameter of 2 to 4 ~m were mixed in a wet ball mill for 25 hours, and dried.
0.5% of beeswax, 4.5% of n-paraffin, 0.2% of stearic acid, 0.5% of ethylene-vinyl acetate and 1.0% of low molecular weight polyethylene were added to 100% of this mixed powder, and kneaded at 120~C for 30 minutes. Then this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw material particles of about 0.5 to 2.0 mm in particle diameter. Then, injection molding was performed with a mold (20 x 20 x 6 mm) having the configuration of a throw-away tip. This compact was arranged in a furnace.
The interior of the furnace was supplied with an N2 atmosphere at a pressure of 1 atmosphere and the temperature was raised to 380~C at a programming rate of 13~C/hour under the condition of a flow rate of 2 E/minute, to perform initial debinder processing. Then, the temperature was raised to 700~C at a programming rate of 50~C/hour while maintaining the interior of the furnace at a pressure of not more than 0.5 Torr with a vacuum pump, and the furnace was cooled after being held at that temperature for one hour.
Thus, the debinder processing was completed. Then, the interior of the furnace was brought to a vacuum of 0.05 Torr, and its temperature was raised to 1350~C at a rate of 200~C/hour, and cooled after being held at that temperature for one hour. The as-formed sintered body had absolutely no imperfections, and was excellent from the viewpoint of alloy characteristics. A heating loss test was performed on the binders employed in this Example, whereby the beeswax was lost by 60% and the n-paraffin was lost by 100% before reaching 380~C under conditions of N2 and 1 atmosphere. On the other hand, loss of the low molecular weight polyethylene was 7.0% and loss of the ethylene-vinyl acetate was 10% at 380~C.
Example 4 88% of WC powder having a particle diameter of 1 to 2 ~Cm and 12% of Co powder were mixed in a wet ball mill for 15 hours, and dried. 5.5% of montan wax and 0.8% of low density polyethylene were added to 100% of this mixed powder, and kneaded at 120~C for 3 hours. Then, this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw material particles of about 0.5 to 2.0 mm in particle diameter. Then injection molding was performed with a mold (20 x 20 x 6 mm) having the configuration of a throw-away tip. This compact was arranged in a furnace. The interior of the furnace was supplied with an argon atmosphere at a pressure of 1 atmosphere, and the temperature was raised to 350~C at a programming rate of 10~C/hour under the condition of a flow I ': ~.~?
rate of 3 E/minute, to perform initial debinder processing.
Then, the temperature was raised to 650~C at a programming rate of 50~C/hour while maintaining the interior of the furnace at a pressure of not more than 0.5 Torr with a vacuum pump, and the furnace was cooled after being held at that temperature for one hour, to complete the debinder processing. Then, the interior of the furnace was brought to a vacuum of 0.05 Torr, the temperature was raised to 1400~C at a rate of 200~C/hour, and the furnace was cooled after being held for one hour. The as-formed sintered body had absolutely no imperfections, and was excellent from the viewpoint of alloy characteristics. A heating loss test was performed on the binders employed in this Example, whereby loss of the montan wax was 93% before reaching 350~C under conditions of NZ and 1 atmosphere, while loss of the low density polyethylene was 0% on measurement at 350~C.
Example 5 Cermet powder (50% of TiCN, 10% of TaC, 12% of MoZC, 13% of WC, 5% of Ni and 10% of Co) having a particle diameter of 0.5 to 1 ~m was mixed in a wet ball mill for 10 hours, and dried. 7.8% of montan wax, 2.7% of n-paraffin, 2.7% of low density polyethylene and 0.3% of stearic acid were added to 100% of this mixed powder, and kneaded at 120~C for 3 hours. Then, this raw material mixture was cooled/solidified and thereafter pulverized, to prepare raw _ 15 _ material particles of about 0.5 to 2.0 mm in particle diameter. Then, injection molding was effected into a mold having a ball end mill configuration of 10 mm in diameter, to obtain a compact. This compact was arranged in a furnace. The interior of the furnace was supplied with an argon atmosphere at a pressure of 1 atmosphere, and the temperature was raised to 350~C at a programming rate of 10~C/hour under the condition of a flow rate of 3 E/minute, to perform initial debinder processing. Then, the temperature was raised to 650~C at a programming rate of 50~C/hour while maintaining the interior of the furnace at a pressure of not more than 0.5 Torr with a vacuum pump, and the furnace was cooled after being held at that temperature for one hour, to complete the debinder processing. Then, the interior of the furnace was brought to a vacuum of 0.05 Torr and the temperature was raised to 1400~C at a rate of 200~C/hour, and the furnace was cooled after being held for one hour, and thereafter HIP processing was performed at 1350~C. The as-formed sintered body had absolutely no imperfections, and was excellent from the viewpoint of alloy characteristics. A heating loss test was performed on the binders employed in this Example, whereby loss of the montan wax was 93% under conditions of NZ and 1 atmosphere before reaching 350~C and loss of the n-paraffin was 100%, while loss of the low density polypropylene was 0% on measurement at 350~C.
ry-.-Example 6 A plurality of raw material particle compacts were prepared under the same conditions as those in Example 1.
With respect to these compacts, the programming rate in the first removal step of debinder processing and the transition temperature to the second removal step were changed, to examine the conditions after debindering. Table 2 shows the results. Table 1 shows the results of heating loss tests of beeswax and low molecular weight polyethylene (PE). As is obvious from the results of Tables 1 and 2, excellent conditions are attained after debindering according to the inventive method, and debindering times can be shortened.
Table 1 Heating Loss Rate (N2 1 atmosphere, Temperature Rising at 10~C/minute) Beeswax 0.03 0.12 0.32 0.50 0.l4 0.95 0.99 1.00 (xT) Low Molecular 1 Weight PE p,01 0.03 0.05 0.07 0.09 0.13 0.30 0.85 0 (yT) Table 2 Test Results of Transition Temperature in Second Removal Step Test Transiti~ 1st RemovalBeeswax PE ResidualCondition 2 No. TemperatureStep Loss Rate After 0 in 2nd ProgrammingRate Debindering Renaval Rate b x (1-yT) Step a x xT
1 300 8C/hour 0.10 0.14 bursting state 2 300 4C/hour 0.10 0.14 significantly cracked and blistered 3 350 8C/hour 0.27 0.14 5 cracks 4 350 4C/hour 0.27 0.14 gd 2 5* 375 8C/hour 0.43 0.13 gd 6* 400 8C/hour 0.64 0.13 gd 7* 425 8C/hour 0.81 0.12 gd 8* 450 8C/hour 0.85 0.10 gd 9 475 8C/hour 0.86 0.02 collapsed *: Inventive Method a = 0.86 b = 0.14 .~
Example 7 8 types of samples were prepared by using an alloy powder which was similar to that of Example 1 and changing the rate of beeswax to low molecular weight polyethylene (PE) as to binder compositions (tests Nos. 10 to 17), to perform debindering tests. Table 3 shows the results. The transition temperature from the first removal step to the second removal step was set at 450 ~ C. As is obvious from Table 3, the inventive compositions give excellent results.
Table 3 Test Conditions and Results Test Binder 1st RemovalBeeswax PE b x yT Condition 1 No. CompositionStep Loss Residual after Beeswax/LowProgrammingRate Rate (a x xT=0.3)Debindering Molecular Rate Weight a x x,5ob x (1-y4so) PE
partially 10 6.5/0.5 10C/hour0.92 0.05 0.005 formed 11* 6.0/1.0 10C/hour0.85 0.10 0.008 gd 12* 5.0/2.0 10C/hour0.71 0.20 0.018 gd 2 13* 4.0/3.0 10C/hour0.57 0.30 0.032 gd 14* 3.0/4.0 10C/hour0.42 0.40 0.045 gd 15* 3.0/4.0 4C/hour 0.42 0.40 0.045 gd not reachingsignificantly 16 2.0/5.0 10C/hour0.28 0.50 a x xT=0.3cracked 2 not reaching 17 2.0/5.0 4C/hour 0.28 0.50 a x xT=0.32 cracks *: Inventive Method 30 Binder Composition: Rate with respect to 100% of Alloy Powder Example 8 Alloy powder similar to that of Example 3 was used and debindering tests were performed by changing the types and compositions of binders. Table 4 shows the results.
Debindering conditions were identical to those of Example 3.
Good injection and debindering were possible in tests Nos.
18 to 20. In test No. 21 employing n-paraffin, however, it was impossible to effect a good injection, unless the amount of n-paraffin was increased. In test No. 22, on the other hand, distortion was caused in debinder processing. In test No. 23 of mixing beeswax and n-paraffin at a 1/1 ratio, no deformation was recognized in debindering although it was necessary to add a slight amount of the binder.
Tsble 4 Wax Type and Result TestWax Type Binder CompositionInjection Debinder Condition No. Wax/Low Molecular Weight PE
2 1g* Carnauba Wax 5.0/1.5 possible good Beeswax 5.0/1.5 possible good 20* Nontan Wax 5.0/1.5 possible good 21 n-Paraffin 5.0/1.5 impossible ---22 n-Paraffin 7.0/1.5 possible distorted 2 23* B~swax+n-Paraffin3+3/1.5 possible good *: Inventive Method Binder Composition: Rate with respect to 100% of Alloy 30 Powder Example 9 In a preparation method similar to test No. 5 of Table 2, the pressure and type of atmosphere for the first removal step and the second removal step were varied as shown in tests Nos. 24 to 30 in Table 5. As is obvious from the results of Table 5, the inventive atmospheres are effective. It was impossible to advance the samples of tests Nos. 26 and 29 to sintering, since the bodies collapsed in debindering. Other samples were capable of progressing to sintering steps.
Table 5 Test1st 2nd Removal Result Removal Step: d Step: 350 Si up to 700C t to 1 No. n 5 ere ( Gas Flow RatePressure AtmosphereFlow PressureBody) Rate Atmospheric 5* Ar 3 t/minutePressure Vacuum 0.5 Torrgod Atmospheric Pressure 24* Ar 0.1 t/minute Vacuum 0.5 Torr9od 2 Atmospheric 25* N 3 t/minutePressure Vacuum 0.5 Torrgood Atmospheric AtmosphericCollapsed (in Pressure N Pressuredebindering) 26 N 3 t/minute Z 3 t/minute 27* N 3 t/minute600 Torr Vacuum 0.5 Torr9d 2 Atmospheric distorted, 28 Air 3 t/minutePressure Vacs 0.5 Torrcracked Atmospheric 29 Ar 3 tlminutePressure pr 5 Torr collapsed Atmospheric Atmosphericlow carbon Pressure N 3 t Pressurea~e~
i 3 30 Nz 3 t/minute z nute aused 0 /m Ph *: Inventive Method ;.
,, The present invention is effectively applied to a method of preparing a cemented carbide or a cermet alloy by shaping cemented carbide powder or cermet alloy powder into a prescribed configuration by an injection molding method and thereafter sintering the compact upon removal of an organic binder.
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of preparing a cemented carbide or a cermet alloy by mixing and kneading cemented carbide powder or cermet alloy powder with an organic binder, shaping this mixed powder into a prescribed configuration by an injection molding method and thereafter removing the organic binder from this compact and sintering the same in order to obtain a dense alloy, wherein removal of the organic binder is performed in an inert gas atmosphere as a first removal step, and then continued under a vacuum of not more than 1 Torr as a second removal step.
2. A method according to claim 1, wherein said second removal step is carried out at a higher temperature than said first removal step.
3. A method according to claim 1, wherein the organic binder contains a plurality of types of binders including a group removable under a low temperature and a group removable at a high temperature, and assuming that a1, a2, ..., a i represents ratios of respective binders of said low-temperature removal group including i types of binders with respect to the overall organic binder, b1, b2, ..., b j represent ratios of respective binders of said high temperature removal group including j types of binders with respect to the overall organic binder (.SIGMA.a i + .SIGMA.b j = 1) , xT1, xT2, ..., xT j represent loss rates of a single substance of said respective binders belonging to said low-temperature removal group at a certain temperature T in inert gas atmospheric pressure heating loss tests (TG), and yT1, yT2, ..., yT j represent loss rates of a single substance of said respective binders belonging to said high-temperature removal group at said temperature T in inert gas atmospheric pressure heating loss tests, compositions of said respective binders contained in said organic binder are selected to satisfy the following conditions:
.SIGMA.(b j x yT j) ~ 0.05 .SIGMA.b j ~ 0.1 at said temperature T for which .SIGMA.(a j x xT i) = 0.3.
.SIGMA.(b j x yT j) ~ 0.05 .SIGMA.b j ~ 0.1 at said temperature T for which .SIGMA.(a j x xT i) = 0.3.
4. A method according to claim 3, wherein said temperature T for transition from said first removal step to said second removal step is selected to satisfy the following conditions:
.SIGMA.(a i x xT i) > 0.3 .SIGMA.{b j x (1 - yT j)} > 0.05.
.SIGMA.(a i x xT i) > 0.3 .SIGMA.{b j x (1 - yT j)} > 0.05.
5. A method according to claim 3 or 4, wherein said low-temperature removal group includes a wax having hydrophilic polar groups with a melting point of not more than 80°C.
6. A method for producing a cemented carbide or a cermet alloy, comprising the following steps:
(a) mixing and kneading a cemented carbide powder or cermet alloy powder with an organic binder to provide a powder binder mixture sufficiently viscous for injection molding;
(b) injection molding said powder binder mixture to form a compact having a prescribed configuration (c) removing said organic binder from said compact in a first and in a second binder removal step, said first binder removal step comprising heating said compact to a first removal temperature in an atmosphere of N2 or argon at a pressure of at least 600 Torr for removing at least a portion of said organic binder, said second binder removal step comprising exposing said compact to a vacuum of not more than one Torr at a second removal temperature for substantially removing any remainder of said organic binder, said first binder removal step continuing into said second binder removal step: and (d) sintering said compact.
(a) mixing and kneading a cemented carbide powder or cermet alloy powder with an organic binder to provide a powder binder mixture sufficiently viscous for injection molding;
(b) injection molding said powder binder mixture to form a compact having a prescribed configuration (c) removing said organic binder from said compact in a first and in a second binder removal step, said first binder removal step comprising heating said compact to a first removal temperature in an atmosphere of N2 or argon at a pressure of at least 600 Torr for removing at least a portion of said organic binder, said second binder removal step comprising exposing said compact to a vacuum of not more than one Torr at a second removal temperature for substantially removing any remainder of said organic binder, said first binder removal step continuing into said second binder removal step: and (d) sintering said compact.
7. A method according to claim 6, wherein said second mentioned temperature is higher than said first mentioned temperature.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23884989 | 1989-09-14 | ||
| JP1-238849 | 1989-09-14 | ||
| PCT/JP1990/001171 WO1991004119A1 (en) | 1989-09-14 | 1990-09-12 | Method of producing cemented carbide or cermet alloy |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2041668A1 CA2041668A1 (en) | 1991-03-15 |
| CA2041668C true CA2041668C (en) | 1999-08-03 |
Family
ID=17036179
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002041668A Expired - Fee Related CA2041668C (en) | 1989-09-14 | 1990-09-12 | Method of preparing cemented carbide or cermet alloy |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0443048B1 (en) |
| KR (1) | KR940009337B1 (en) |
| CA (1) | CA2041668C (en) |
| DE (1) | DE69015150T2 (en) |
| TW (1) | TW225493B (en) |
| WO (1) | WO1991004119A1 (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5403373A (en) * | 1991-05-31 | 1995-04-04 | Sumitomo Electric Industries, Ltd. | Hard sintered component and method of manufacturing such a component |
| DE19709651A1 (en) * | 1996-03-16 | 1997-10-30 | Widia Gmbh | Composite material used in production of e.g. cutting plates |
| SE9603936D0 (en) * | 1996-10-25 | 1996-10-25 | Sandvik Ab | Method of making cemented carbide by metal injection molding |
| DE19855422A1 (en) | 1998-12-01 | 2000-06-08 | Basf Ag | Hard material sintered part with a nickel- and cobalt-free, nitrogen-containing steel as a binder of the hard material phase |
| SE526194C2 (en) * | 2003-08-27 | 2005-07-26 | Seco Tools Ab | Method of manufacturing a sintered body |
| SE529202C2 (en) * | 2005-05-17 | 2007-05-29 | Sandvik Intellectual Property | Methods of manufacturing an agglomerated powder mixture of a slurry and agglomerated powder |
| SE533922C2 (en) * | 2008-12-18 | 2011-03-01 | Seco Tools Ab | Ways to manufacture cemented carbide products |
| CN104357696B (en) * | 2014-12-01 | 2016-04-27 | 技锋精密刀具（马鞍山）有限公司 | A kind of sintering process of carbide paraffin production technique goods |
| CN109822089B (en) * | 2019-01-18 | 2022-05-13 | 株洲金佰利硬质合金有限公司 | Forming agent for hard alloy production |
| CN116023143B (en) * | 2021-10-25 | 2024-02-06 | 中国科学院上海硅酸盐研究所 | Preparation method of silicon carbide ceramic |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS51126308A (en) * | 1975-04-28 | 1976-11-04 | Shinroku Saito | Process for producing a super alloy plate |
| US4233256A (en) * | 1978-12-18 | 1980-11-11 | The Carborundum Company | Process for injection molding sinterable carbide ceramic materials |
| US4305756A (en) * | 1980-01-14 | 1981-12-15 | Witec Cayman Patents, Ltd. | Method and means for removing binder from a green body |
| DE3611271A1 (en) * | 1986-04-04 | 1987-10-15 | Licentia Gmbh | Process for producing metal shaped parts |
| JPS63183103A (en) * | 1987-01-26 | 1988-07-28 | Chugai Ro Kogyo Kaisha Ltd | Sintering method for injection molding |
| JPH07116487B2 (en) * | 1988-06-30 | 1995-12-13 | 三菱製鋼株式会社 | Method for degreasing metal powder injection molded body |
| JPH0270004A (en) * | 1988-09-02 | 1990-03-08 | Mitsubishi Metal Corp | Method for degreasing injection molded body |
-
1990
- 1990-09-12 CA CA002041668A patent/CA2041668C/en not_active Expired - Fee Related
- 1990-09-12 KR KR1019910700490A patent/KR940009337B1/en not_active IP Right Cessation
- 1990-09-12 DE DE69015150T patent/DE69015150T2/en not_active Expired - Lifetime
- 1990-09-12 WO PCT/JP1990/001171 patent/WO1991004119A1/en active IP Right Grant
- 1990-09-12 EP EP90913553A patent/EP0443048B1/en not_active Expired - Lifetime
- 1990-09-13 TW TW079107703A patent/TW225493B/zh active
Also Published As
| Publication number | Publication date |
|---|---|
| JPH03177506A (en) | 1991-08-01 |
| DE69015150T2 (en) | 1995-05-04 |
| EP0443048B1 (en) | 1994-12-14 |
| EP0443048A1 (en) | 1991-08-28 |
| KR920700819A (en) | 1992-08-10 |
| EP0443048A4 (en) | 1991-10-30 |
| DE69015150D1 (en) | 1995-01-26 |
| TW225493B (en) | 1994-06-21 |
| CA2041668A1 (en) | 1991-03-15 |
| WO1991004119A1 (en) | 1991-04-04 |
| KR940009337B1 (en) | 1994-10-07 |
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