ES2599641T3 - Method for producing a cemented carbide or ceramic metal powder using a resonant acoustic mixer - Google Patents

Abstract

A method of producing an agglomerated cemented carbide or ceramic metal powder without grinding, wherein the powder constituents are subjected to a mixing operation without grinding comprising the steps of: forming a suspension of one or more powders forming hard constituents, metal binder powders and a mixing liquid, wherein said one or more powders are selected from borides, carbides, nitrides or carbonitrides of metals from groups 4, 5 and 6 of the periodic table; mixing and dehydrating said suspension to form an agglomerated powder, where the mixing is carried out in a resonant acoustic mixer, this being a non-contact mixer in which acoustic waves are used that achieve resonance conditions.

Description

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

DESCRIPTION

Method for producing a cemented carbide or ceramic metal powder using a resonant acoustic mixer

The present specification refers to a method for producing a cemented carbide or ceramic metal powder in which the powder constituents are subjected to a mixing operation without grinding by the use of an acoustic mixer.

Background

Cemented carbide and ceramic metal powders that are used to produce sintered bodies for, for example, cutting tools, wear parts, etc. they are generally produced by first forming a suspension by milling the powdered constituents together with metallic binder powders, organic binder (eg, polyethylene glycol) and a milling liquid in a ball mill or an attrition mill for several hours. Next, the suspension is generally subjected to a spray dehydration operation to form the granulated cemented carbide or ceramic metal powders that can be used to press non-sintered parts that are subsequently sintered.

The main objective of the milling operation is to obtain a good distribution of the binder phase and a good wettability between the hard constituent grains and the binder phase powder. A good distribution of the binder phase and good wettability are essential to obtain high quality cemented carbide and ceramic metal materials. If the phase distribution or wettability is not good, pores and cracks will form in the final sintered body that are detrimental to the material. However, obtaining a good distribution of binder phase and wettability is very difficult for these types of materials and requires a high energy input, that is, quite long grinding times, generally 10 to 40 hours, depending on the type of mill used and / or the degree of cut produced.

Ball mills and attrition mills both provide a good, homogeneous mixture of the constituents in powder, the metallic binder powders and the organic binder. These processes provide a large energy input that can overcome the static friction and binding forces necessary to obtain a good distribution of the binding phase and good wettability. However, in these mills the powders will undergo a milling operation. Accordingly, the powders, both the hard constituent powders and the binding metal powders, will partially crush and form a fine fraction. This fine fraction can cause uncontrolled grain growth during subsequent sintering. Consequently, the reduced size raw material can be destroyed by grinding.

It is difficult to produce microstructures with reduced grain size with good control since the milling produces a fine fraction that contributes to an uncontrolled grain growth during sintering.

Various attempts have been made to solve this problem. A method designed to obtain a powder comprising coarse grained WC with a good binder phase distribution is to deposit a salt, for example, cobalt acetate, on the WC particles, then subject the coated WC grains to an elevated temperature reducing thus cobalt to cobalt acetate. By following this method before grinding, a good distribution of cobalt can be obtained in a reduced crushing time. These types of processes are quite complicated and time consuming. An example of this type of process is described in European patent EP752921B1.

Other types of mixing methods without grinding have also been evaluated to avoid the crushing of the powders and thus maintain the properties such as the grain size of the raw materials.

European patent EP 1 900 421 A1 describes a process in which the suspension is homogenized in a mixer comprising a rotor, a dispersing device and means for circulating the suspension. The dispersing device contains moving parts.

Publication WO 02/06545 describes a hard hard filler metal having a porosity classification of substantially A06, B00, C00 or better. The hard-filled hard metal is formed by mechanical mixing (including ultrasound mixing), molding of the mixture to form a non-sintered part and consolidation of the non-sintered part at a temperature, preselected hyperatmospheric pressure and time at temperature and time at hyperatmospheric pressure sufficient to form the hard metal of hyper hard filling.

European patent EP 1231288 describes a method for manufacturing a composite material. The method comprises an ultrasound mixing stage.

An object of the present invention is to obtain a combination of homogeneous powders without grinding.

Another objective of the present invention is to obtain a powder combination in which the grain size distribution of the raw materials can be maintained and still obtain a homogeneous powder combination.

Another objective of the present invention is to obtain a combination of powders by using a process of

5

10

fifteen

twenty

25

30

35

40

Four. Five

fifty

55

mixture that does not contain any moving parts and that is subject to minimal wear.

Detailed description of the present invention

The present invention relates to the method defined in claim 1. It is a method for producing an agglomerated powder of cemented carbide or ceramic metal without grinding in which the powder constituents are subjected to an operation that does not include grinding, which it comprises the steps of first forming a suspension of one or more powders forming hard constituents, wherein said one or more powders forming the hard constituents are selected from borides, carbides, nitrides or carbonitrides of metals of groups 4, 5 and 6 of the periodic table, metallic binder powders and a mixing liquid. Next, the suspension is mixed and dehydrated to form an agglomerated powder. The mixing is carried out in a contactless mixer in which acoustic waves are used that achieve resonance conditions. Such types of mixers are commonly referred to as resonant acoustic mixers.

Acoustic mixers are known in the art, see, for example, WO 2008/088321 and US Patent 7,188,993. These mixers use high intensity and low frequency acoustic energy to mix. They have exhibited good results when mixing fragile organic compounds and have also been used to mix other types of materials. Acoustic mixers are contactless mixers, that is, they do not contain any mechanical means to mix as stirrers, baffle plates or propellants. Instead, the mixing is carried out by creating mirrored zones throughout the entire mixing vessel by mechanical resonance applied to the materials that will be mixed through the propagation of an acoustic pressure wave in the mixing vessel.

In the method according to the present invention, the grain size of the powders that form the hard constituents depends on the application of the alloy and preferably is from 0.2 to 30 pm. If not indicated otherwise, all amounts provided herein in% p are% p of the total dry weight of the dry powder constituents.

The binder metal powders may be in a single binder metal powder or in a combination of powders of two or more metals, or in a powder of an alloy of two or more metals. Binding metals are selected from Cr, Mo, Fe, Co or Ni, preferably from Co, Cr or Ni. The grain size of the metallic bonding powders added is suitably between 0.5 and 3 pm, preferably between 0.5 and 1.5 pm.

When the method according to the present invention relates to producing a cemented carbide powder, it means here that the cemented carbide is a powder from WC-Co, which also contains, in addition to WC and Co, additions such as inhibitors. of grain growth, cubic carbides, etc. Commonly used in the technique for the production of cemented carbides.

In one embodiment of the present invention, a cemented carbide powder is produced with hard constituents that adequately comprise WC with a grain size between 0.5 and 2 pm, preferably between 0.5 and 0.9 pm. The content of binder metal is suitably between 3 and 17% p, preferably 5 to 15% p of the total dry weight of the dry powder constituents. Cemented carbides produced with these powders are commonly used in cutting tools such as grafts, augers, strawberries, etc.

In one embodiment of the present invention, a cemented carbide powder is produced with hard constituents that suitably comprise WC having a grain size between 1 and 8 pm, preferably between 1.5 and 4 pm. The content of binder metal is suitably between 3 and 30% p, preferably 5 to 20% p of the total dry weight of the dry powder constituents. Cemented carbides produced with these powders are used

commonly in tools for forming tools and wear parts, for example, keys for drilling augers, minena or asphalt milling, hot rolling rollers, minena application parts, wire drawing, etc.

In one embodiment of the present invention, a cemented carbide powder is produced with hard constituents that suitably comprise WC having a grain size between 4 and 25 pm, preferably between 4.5 and 20 pm. The content of binding metal is suitably between 3 and 30% p, preferably 6 to 30% p of the total dry weight of the dry powder constituents. Cemented carbides produced with these powders are used

Commonly in keys for drilling augers, minena or asphalt milling, hot rolling rollers.

In another embodiment of the present invention, the method refers to producing a ceramic metal powder. In the

present, ceramic metal powder means a powder in which the hard constituents comprise large amounts of TiCN or TiC. Ceramic metals comprise hard constituents of carbonitride or carbide embedded in a metal binder phase. In addition to titanium, elements of the Via group are also added, such as Mo, W and sometimes Cr, to facilitate wetting between the binder and the hard constituents and to strengthen the binder by means of hardening the solution. You can also add elements of group IVa or Va, that is, Zr, Hf, V, Nb and Ta, to the alloys currently available in the market. All these additional elements are generally added as carbides, nitrides or carbonitrides. The grain size of the powders that form the hard constituents is generally <2 pm.

In addition, an organic binder is optionally added to the suspension in order to facilitate granulation during

5

10

fifteen

twenty

25

30

35

40

Four. Five

dehydration operation by subsequent spraying and also to function as a pressing agent for any subsequent pressing and sintering operations. The organic binder can be any binder commonly used in the art. The organic binder can be, for example, paraffin, polyethylene glycol (PEG), long chain fatty acids, etc. The amount of organic binder is suitably between 15 and 25% vol based on the total dry powder volume, the amount of organic binder is not included in the total dry powder volume.

To form a suspension, a mixing liquid is needed. Any liquid commonly used as a milling liquid can be used in the conventional manufacture of cemented carbide. The grinding liquid is preferably water, alcohol or an organic solvent, more preferably water or a mixture of water and alcohol and more preferably even a mixture of water and ethanol. The properties of the suspension depend on the amount of crushing liquid added. Since dehydration of the suspension requires energy, the amount of liquid should be minimized in order to keep costs down. However, sufficient liquid must be added to achieve a suspension that can be pumped and prevent clogging of the system.

In addition, other components known in the art can be added to the suspension, for example, dispersing agents, pH regulators, etc.

Dehydration of the suspension is preferably carried out in accordance with known techniques, in particular, spray dehydration. The suspension containing the powdered materials mixed with the organic liquid and possibly the organic binder is sprayed through a suitable nozzle in the dehydration tower in which the small drops are instantly dried by a stream of hot gas, by example, a stream of nitrogen, to form agglomerated granules. The formation of granules is necessary, in particular, for the automatic feeding in the compaction tools that are used in the later stage. For experiments on a smaller scale, other methods of dehydration, such as dehydration on oven pans, can also be used.

Next, the non-sintered parts are formed with the dehydrated powders / granules. Any type of operation can be used to give a known shape in the art, for example, injection molding, extrusion, uniaxial pressing, multiaxial pressing, etc. If injection molding or extrusion is used, additional organic binders are also added to the powder mixture.

The non-sintered parts formed with the powders / granules produced according to the present invention, are subsequently sintered according to any conventional sintering method, for example, vacuosinterizacion, HIP sintering, plasma sintering, etc. The sintering technique used for each specific suspension composition is preferably the technique that would have been used for said suspension composition if it had been produced in accordance with conventional methods, that is, in ball mill or attrition mill.

Example 1

Different suspensions of cemented carbide were prepared by combining powders of hard constituents such as Wc and Cr3C2, Co and PEG with a liquid with an ethanol / water ratio of 90/10 by weight. The WC grain size and Co grain size provided is the Fisher grain size (FSSS). The composition of the dry constituents of the suspensions and the properties of the raw material are shown in Table 1. The amount of Co, WC and Cr3C2 provided in% p is based on the total dry powder constituents in the suspension. The amount of PEG is based on the total dry powder constituents of the suspension, where the amount of PEG is not included in the dry powder constituents of the suspension.

Table 1

 Suspension

 Co (% p) Co (pm) Cr3C2 (% p) WC (pm)% p of PEG

 Composition 1

 10.0 0.5 0.5 0.8 2

 2nd composition

 6.0 0.5 - 2.5 2

 Composition 2b

 6.0 0.5 - 5 2

 3rd composition

 6.3 0.9 - 5 2

* Approximately 2% p of cobalt originates from the WC powder that has been coated with Co by the sol-gel technique as described in European patent EP752921B1.

Example 2

The suspension with Composition 1 of Example 1 was then subjected to a mixing operation using a Resodyn Acoustic Mixer (LabRAM) mixer according to the invention or a conventional paint stirrer (Natalie de

Lux), then the suspensions were dried on rods in an oven at 90 ° C. Mixing conditions are shown in Table 2.

Table 2

 Powder

 Composition Mixer Mixing time (s) Energy (G)

 Invention 1

 Composition 1 RAM 300 95

 Comparison 1

 Composition 1 Natalie 300 N / A

5 Next, the powders were first subjected to a uniaxial pressing operation to form a non-sintered part which subsequently underwent a HIP sintering operation at a sintering temperature of 1,410 ° C.

The properties of the sintered material produced with the powders are shown in Table 3. As a further comparison a suspension is included as Reference 1 with Composition 1 produced according to conventional techniques. Reference sample 1 was first produced by producing a suspension by means of a ball mill for 56 hours and then subjecting it to a spray dehydration operation. Then the powder was pressed and sintered in the same way as for the other samples. Ball milling did not affect the average grain size for the fine grain WC. When two values are provided, they represent measurements made on two different pieces of the same sintering batch.

15 Table 3

 Powder

 Density (g / cm3) Com Hc (kA / m) Porosity HV3

 Invention 1

 14.47 / 14.46 8.06 / 8.03 18.76 / 18.77 A00, B00, C00 1,676 / 1,706

 Comparison 1

 14.11 / 14.32 8.30 / 7.69 18.97 / 18.50 A00, B00, C00 Co concentrations 1,643 / 1,701

 Reference 1

 14.48 8.5 20.4 A00, B00, C00 1,650

As can be seen in Table 3, the cemented carbide produced according to the invention obtains approximately the same properties as the samples of Comparison 1 and Reference 1.

Example 3

The suspension with Composition 2a of Example 1 was subjected to a mixing operation using a Resodyn Acoustic Mixer (LabRAM) mixer or a conventional paint stirrer (Natalie de Lux); then the suspensions were dried on baking sheets at 90 ° C. Mixing conditions are shown in Table 4.

Table 4

 Powder

 Composition Mixer Mixing time (s) Energy (G)

 Invention 2

 Composition 2nd RAM 300 95

 Comparison 2

 Composition 2nd Natalie 300 N / A

Next, the powders were pressed and sintered in the same manner as for the samples in Example 2.

The properties of the sintered material produced with the powders are shown in Table 5. As a comparison, a suspension is included as Reference 2 with Composition 2b. Reference sample 2 was produced with Composition 2b according to conventional techniques, that is, it was ground with balls for 20 hours and then underwent a spray dehydration operation.

30 Next, the powder is pressed and sintered in the same way as for the other samples. The grain size of WC before the ball grinding stage is 5 pm. Then the WC grain size is drastically reduced through the grinding operation. After the sintering stage the WC grain size is approximately 2.7 pm. All values provided herein for grain size

of WC measured in the sintered material were estimated from the value of Hc. Table 5

 Powder

 Density (g / cm3) Com Hc (kA / m) porosity HV3

 Invention 2

 15.00 / 14.98 5.30 / 5.36 9.90 / 9.81 A00, B00, C00 1,408 / 1,536

 Comparison 2

 14.79 / 14.77 5.36 / 5.34 9.76 / 9.77 A00, B00, C00 concentrations of Co 1,419 / 1,502

 Reference 2

 14.95 5.7 11.7 N / A 1,430

As can be seen in Table 5, the cemented carbide produced according to the invention obtains approximately 5 the same properties as the samples of Comparison 2 and Reference 2. Also, for Invention 2, the distribution of WC grain size Reduced WC raw material is maintained in the sintered structure. This can be seen in Fig. 1 showing an SEM (Scanning Electron Microscope) image of the Invention 1. Figure 2 shows an LOM (Optical Microscope) image of the Reference 2 sample that has been clearly affected by grinding, this can be observed by the presence of several 10 larger grains caused by the growth of grain from the fine fraction of the WC grains.

Example 4

The suspension with composition 3a of Example 1 was subjected to a mixing operation using a Resodyn Acoustic Mixer (LabRAM) mixer; the suspension is then dehydrated on a baking sheet at 90 ° C. Mixing conditions are shown in Table 6.

15 Table 6

 Powder

 Composition Mixer Mixing time (s) Energy (G)

 Invention 3

 Composition 3rd RAM 300 95

Next, the powders were pressed and sintered in the same manner as for the samples in Example 2 and 3.

The properties of the sintered material produced with the powders are shown in Table 7. For comparison, a suspension is included as Reference 3 with Composition 3b. Reference sample 3 was first produced by wet mixing the powders and then subjecting them to a spray dehydration operation. Then the powder was pressed and sintered in the same way as for the other samples.

Table 7

 Powder

 Density (g / cm3) Com Hc (kA / m) porosity HV30

 Invention 3

 14.97 5.72 5.65 A02, B00, C00 1.240

 Reference 3

 14.95 5.7 6.8 <A02 1.280

As can be seen in Table 7, the cemented carbide produced according to the invention obtains approximately the same properties as the samples of Comparison 3 and Reference 3. In addition, it can be seen that approximately the same properties can be obtained for Invention 3 with the uncoated WC compared to Reference 3, that if the WC had been coated with Co with the use of a complex and expensive sol-gel process.

In conclusion, the Examples show that the method according to the present invention can lead to products that have the same properties as products that have been produced with conventional methods. Consequently, considerably shorter grinding times can be achieved that lead to a reduction in energy consumption. In addition, the use of the commonly used complex sol-gel process can be avoided.

Claims (7)

1. A method for producing an agglomerated powder of cemented carbide or ceramic metal without grinding, where the powdered constituents are subjected to a mixing operation without grinding comprising the steps of: forming a suspension of one or more powders forming hard constituents, binder metal powders and a mixing liquid 5, wherein said one or more powders are selected from borides, carbides, nitrides or carbonitrides of metals of groups 4, 5 and 6 of the periodic table; mixing and dehydrating said suspension to form an agglomerated powder, where the mixing is carried out in a resonant acoustic mixer, this being a contactless mixer in which acoustic waves are used that achieve resonance conditions. The method according to claim 1 wherein the suspension contains an organic binder. 3. The method according to any of the preceding claims wherein the dehydration is carried out by spray dehydration. 4. The method according to any of the preceding claims wherein the metal binding powders is one or more selected from Cr, Mo, Fe, Co or Ni. The method according to any one of the preceding claims in which a carbide powder is produced cemented 6. The method according to claim 5 wherein the hard constituents comprise WC with a grain size between 0.5 and 2 pm, and a binding metal content between 3 and 17% p. 7. The method according to claim 5 wherein the hard constituents comprise WC having a size of 20 grain between 1 and 8 pm, and a binding metal content between 3 and 30% p. 8. The method according to claim 5 wherein the hard constituents comprise WC having a size of grain between 4 and 25 pm, and a binder metal content between 3 and 30% p. 9. The method according to any one of claims 1 to 4 wherein a ceramic metal powder is produced.