DE102011003679A1 - Producing piezoelectric workpieces, comprises producing ceramic raw material from a starting material, producing several piezoelectric layers as green film, laminating a block, releasing and sintering block or parts of block, and separating - Google Patents

Abstract

Producing piezoelectric workpieces (7), comprises producing a ceramic raw material from at least one starting material, producing several piezoelectric layers (2) as a green film from the raw material, laminating a block (1) made of several piezoelectric layers and several electrode layers arranged between the piezoelectric layers, releasing and sintering the block or parts of the block, and (v) separating the piezoelectric workpieces from the block or parts of the block, where calcium is added quantitatively to the starting material and/or during the preparation of the ceramic raw material. Producing piezoelectric workpieces (7), comprises (i) producing a ceramic raw material from at least one starting material, (ii) producing several piezoelectric layers (2) as a green film from the raw material, (iii) laminating a block (1) made of several piezoelectric layers and several electrode layers arranged between the piezoelectric layers, (iv) releasing and sintering the block or parts of the block, and (v) separating the piezoelectric workpieces from the block or parts of the block, where calcium is added quantitatively to the starting material and/or during the preparation of the ceramic raw material to obtain a specific concentration of calcium in the raw material. An independent claim is also included for a system for producing the piezoelectric workpieces by the above method.

Description

The present invention relates to a method for the production of piezoelectric workpieces according to the preamble of claim 1 and a plant for the production of piezoelectric workpieces according to the preamble of claim 13.

State of the art

Piezoelectric actuators are used for various technical applications. For example, serve piezoelectric actuators for controlling injectors in internal combustion engines. The core of the piezoelectric actuators is a piezoelectric workpiece.

From ceramic starting materials or raw materials, a powder or powder mixture is produced by grinding. The powder is then calcined and the calcined powder mixture dopants, for. As binders, plasticizers and solvents, is added, so that a breiinger slip forms as a ceramic raw material. It may be necessary that water is required to mill a starting material. In the water lime is contained as calcium carbonate (CaCO ₃ ) and thus also calcium carbonate in ionic form (Ca ²⁺ ) due to the solution in water, so that calcium in the form of dissolved ions and complexes is present. As a result, calcium enters the powder, which is produced during grinding with water, so that the concentration of calcium in the powder and thus also in the raw material is subject to considerable fluctuations.

From the calcining powder mixture as a ceramic raw material with the dopants z. B. with rollers or casting a green sheet in a layer thickness of z. B. 0.1 mm. The block technique is also used to produce piezoelectric workpieces. In the block technique, the ceramic green sheet is first printed as a piezoelectric layer with an electrode material, so that an electrode layer is formed. These green sheets with the electrode layers are then stacked into a block and pressed, that is laminated. After this process step of lamination there is a monolithic block in which the green sheets are no longer different from each other. The laminated block is separated into sub-blocks and the sub-blocks are debinded and sintered. From the sintered sub-blocks, the piezoelectric workpieces are separated. Notwithstanding this, the piezoelectric workpieces can be separated from the block as blanks and then the piezoelectric workpieces are unbound as blanks and sintered.

The DE 197 57 877 A1 shows a method for parallel production of multiple piezoelectric actuators. From an unfired piezoelectric ceramic material thin films are produced and introduced into these films, a first and second connection opening, wherein each actuator is associated with a first and second connection opening. The films are then coated with a plurality of electrodes, wherein at least one electrode is associated with each actuator in each film. The plurality of films are then stacked on top of each other, wherein the layer is chosen as a result of the film so that the superposed connection openings are alternately surrounded only in every second layer of film by a recess of the electrodes. Subsequently, a burning of the stacked arrangement and a severing of the stacked arrangement into individual actuators takes place.

From the DE 102 17 097 A1 For example, a method for producing a ceramic laminate by laminating a plurality of pieces of ceramic layers is known.

Disclosure of the invention

Advantages of the invention

A method of producing piezoelectric workpieces according to the present invention, comprising the steps of: preparing a ceramic raw material from at least one raw material, forming a plurality of piezoelectric layers as a green sheet from the raw material, laminating a block of the plurality of piezoelectric layers, and a plurality of interposed between the piezoelectric layers Electrode layers, debonding and sintering of the block or parts of the block, separating piezoelectric workpieces from the block or parts of the block, wherein to the at least one starting material and / or during the production of the ceramic raw material calcium is added selectively quantitative, d. H. preferably in a detected and / or predetermined amount to obtain a certain concentration of calcium in the raw material. As part of the block next to the sub-blocks and the piezoelectric workpieces, even as blanks before binding and / or sintering, understood.

The calcium is thus added selectively in a certain or predetermined amount, so that a certain or predetermined concentration of calcium can be achieved in the raw material and thereby ultimately in the piezoelectric workpieces. The concentration of calcium in the raw material or in the green sheet has a significant influence on the electrochemical properties and on the Durability of the piezoelectric workpiece. By deliberately adding calcium, a certain concentration of calcium in the raw material or in the piezoelectric workpiece can be achieved and thereby the electromechanical properties and the durability of the piezoelectric workpieces can be substantially improved, because a certain predetermined concentration of calcium can be constantly achieved ,

In particular, prior to the addition of the calcium, the concentration of calcium in the at least one starting material is determined and, depending on the concentration of calcium in the at least one starting material, the calcium is purposefully added. At least one starting material may contain calcium, also calcium in a compound. In order to obtain a given concentration of calcium in the raw material, it is necessary to determine this concentration of calcium in the at least one ceramic starting material and then to add the calcium depending on the determined or detected concentration of calcium or given concentration of calcium in the raw material.

In a further embodiment, in a production step for producing the ceramic raw material from the at least one starting material, calcium is added to the raw material to be produced on the basis of the preparation step, this addition of calcium is quantitatively detected and the calcium is selectively added depending on the detected quantitative addition of the calcium.

In a supplementary embodiment, the production step is a grinding process in which water is added and / or needed. From a ceramic starting material is prepared by grinding powder. In the grinding process, the addition of water may be required or it may be necessary for procedural reasons water for grinding, so that thereby enters the ceramic starting material during grinding, the water. In the water calcium in the form of lime (CaCO ₃ ) in ionic form (Ca ²⁺ ) is contained due to the solution in the water, so that calcium is in the form of dissolved ions and complexes, and thereby enters into the powder produced during grinding calcium. The addition of water as well as the concentration of calcium in the water is subject to great fluctuations, so that the concentration of calcium in the powder, which is produced with this grinding process, is also subject to strong fluctuations. As a result, with this production step, the raw material is enriched with calcium and the addition is exposed to strong fluctuations. By quantitatively detecting the addition of calcium in this grinding operation and the targeted addition of calcium to achieve a certain concentration of calcium in the raw material, a substantially constant concentration of calcium in the ceramic raw material or in the piezoelectric workpieces can be achieved. The more calcium is added uncontrolled and untargeted in the grinding process, the less calcium is deliberately added in the process of the invention and vice versa. Thereby, a substantially constant concentration of calcium in the ceramic starting material or in the piezoelectric workpiece can be achieved and thus also constant electromechanical properties and a constant durability of the piezoelectric workpieces produced can be achieved.

Preferably, the calcium is added as a chemical compound targeted.

In one variant, at least one starting material is ground to a powder for the production of the ceramic raw material, and preferably the powder is calcined. The powder is, for example, a PZT powder, d. H. a lead zirconium titanate powder.

Suitably during the manufacture of the ceramic raw material at least one dopant, for. As binders and / or plasticizers and / or solvents, added, in particular, the at least one dopant is added to the powder. The dopant is preferably added to the powder or calcined powder after milling.

In a further embodiment, the calcium is specifically added to the at least one starting material, in particular before the grinding, and / or the calcium is added selectively to the powder, in particular together with the at least one dopant. For example, the calcium may be added quantitatively to the ceramic raw material prior to milling, or it may be selectively added quantitatively as a dopant after grinding to the powder to obtain a predetermined concentration of calcium in the raw material.

In particular, such an amount of calcium is deliberately added so that the concentration of calcium in the raw material is between 10 and 600 ppm, preferably between 50 and 300 ppm, in particular between 150 and 200 ppm.

In another embodiment, the concentration is a mass fraction in mg per kg.

In a supplementary variant of the block sub-blocks are separated as parts of the block and the sub-blocks are debinded and sintered and / or the piezoelectric workpieces as parts of the block are separated from the block or sub-block before or after debonding and / or sintering. Separation of the piezoelectric workpieces may be performed before or after debonding and / or sintering.

In a further variant, the calcium is added in such a targeted manner that the concentration of calcium in the piezoelectric workpieces produced is essentially constant. Substantially constant means that the concentration of calcium in the piezoelectric workpiece and / or in the ceramic raw material differs by less than 30%, 20%, 10% or 5%. As a result, constant concentrations of calcium can advantageously be achieved on the piezoelectric workpieces. In this case, preferably such concentrations are achieved for which the use of the piezoelectric workpiece has the most optimal electromechanical properties and / or durability. This makes it possible to optimally utilize the positive effects of calcium in the piezoelectric workpieces for the application of the piezoelectric workpiece.

Method according to the invention for producing a valve, in particular a fuel injection valve, comprising the steps: producing a piezoelectric workpiece having a plurality of piezoelectric layers and a plurality of electrode layers arranged between the piezoelectric layers, preferably providing a valve housing, preferably providing a nozzle needle, preferably Connecting the piezoelectric workpiece, the valve housing and the nozzle needle to the valve, wherein the piezoelectric workpiece is produced by a method described in this patent application.

Inventive plant for the production of piezoelectric workpieces, wherein from the plant a method described in this patent application process is executable.

In a supplementary embodiment, the electrode layer is made of an electrically conductive material, for. As metal, with a physical or chemical coating method, for. As vapor deposition, sputtering or screen printing, applied to the green sheet.

In an additional embodiment, the piezoelectric workpieces are separated from the at least one sintered sub-block by a dicing process.

In a supplementary variant, the separated at least one piezoelectric workpiece is ground.

Brief description of the drawings

In the following, an embodiment of the invention will be described in more detail with reference to the accompanying drawings. It shows:

1 a perspective view of a laminated block,

2 a perspective view of a separated from the block sub-block,

3 a perspective view of a separated from the sub-block piezoelectric workpiece,

4 a simplified view of a fuel injector,

5 a highly simplified view of a plant for the production of piezoelectric workpieces and

6 a flow diagram of a method for producing a green sheet.

Piezoelectric actuators 7 They are used for a wide variety of technical applications, for example for moving nozzle needles in fuel injectors 13 of internal combustion engines, used (not shown). The piezoelectric actuators comprise a piezoelectric workpiece 7 ,

A valve 12 as a fuel injection valve 13 ( 4 ) is used as an injector for fuel injection systems of internal combustion engines to inject fuel into a combustion chamber (not shown). The fuel injector 13 includes next to the piezoelectric workpiece 7 one of the workpiece 7 moving nozzle needle, a valve housing preferably a spring element for moving back the nozzle needle and a valve seat body with an opening from the nozzle needle and to be closed injection port and preferably a fuel passage, wherein the valve seat body is preferably formed on the valve housing (not shown).

For the production of the piezoelectric workpiece 7 ceramic raw material is needed. In 6 is a flow chart for the production of ceramic raw material or a green sheet 24 shown. A first source material 14 is doing a grinding process in a mill 17 fed and ground to a powder. In analog Way is also the second source material 15 and the third starting material 16 ground to the powder. Notwithstanding this, at least one starting material may already be present as a powder, so that for this at least one starting material no grinding process 17 is required (not shown). The powder is then calcined (not shown) and subsequently dopants are added to the calcined powder 18 fed. As dopants 18 become a binder 19 , a plasticizer 20 and a solvent 21 added. In addition, according to the invention, calcium is also targeted 22 as dopant 18 quantitatively added to a specific concentration of calcium 22 in the ceramic raw material. There will be such an amount of calcium 22 added that the concentration of calcium 22 in the ceramic raw material is about 150 ppm.

At this time, the concentration of calcium in the starting material becomes 14 . 15 . 16 and also uncontrolled and untargeted addition of calcium 22 during a grinding process 17 , When grinding the first starting material 14 Water is needed and in the water lime is dissolved as calcium carbonate (CaCO ₃ ) and thereby also calcium ions (Ca ²⁺ ) are contained in the water, so that calcium is present in the form of dissolved ions in the water. As a result, contains from the first starting material 14 ground powder additionally calcium 22 out of the water for the grinding process 17 , These already in the starting materials 14 . 15 and 16 contained concentrations of calcium 22 After the grinding process are detected and determined and then calcium 22 as dopant 18 after calcining in such an amount targeted and controlled added, so that the concentration of calcium 22 in the ceramic raw material is substantially constant at 150 ppm. As a result, it is advantageously ensured that the piezoelectric workpieces made of the ceramic raw material have substantially the same properties, because the concentration of calcium 22 an influence on the electromechanical properties and the durability of the piezoelectric workpiece 7 Has. In the ceramic raw material after the addition of the dopants 18 the green sheet 24 in the process 23 for the production of the green sheet 24 produced.

In the production of the piezoelectric workpiece 7 are first from the ceramic raw material, for example, with rollers or casting, ceramic green sheets 24 in the process 23 made and on these ceramic green sheets 24 For example, an electrically conductive material, preferably a thin metal layer, is applied by chemical or physical surface coating methods, for example vapor deposition, sputtering or screen printing. These electrically conductive metal layers thereby provide electrode layers 3 dar. The piezoelectric layers 2 , which with the electrode layer 3 are coated, then become a block 1 stacked and pressed, that is laminated. Then there is a monolithic block 1 before, in which the piezoelectric layers 2 no longer distinguish. The piezoelectric layers 2 from the unfired ceramic material are further provided with a binder.

After the production of the monolithic block 1 become in a further process step from the monolithic block 1 a variety of sub-blocks 4 separated as parts of the block, that is from the block 1 by separating a plurality of sub-blocks 4 as a bar 5 or plates 6 prepared or separated. Such a bar-shaped sub-block 4 is in 2 represented and from the in 1 represented block 1 can have a larger number of subblocks 4 be prepared by separating.

In a further method step, the sub-blocks 4 debinded and sintered in a debinding and sintering furnace. During sintering, a sintering shrinkage in the range of 17 to 18 percent by volume occurs because the ceramic material is compressed. The debinding serves to the binder, for example plastic, from the sub-blocks 4 to remove. After debonding and sintering of the sub-blocks 4 become from each subblock 4 as shown in 2 five piezoelectric workpieces 7 ( 3 ) separated by a dicing process. The dicing process is a high-speed cut-off grinding. The corresponding separation or working lines on the sub-block 4 are in 2 shown in dashed lines.

Deviating from this, from the block 1 the piezoelectric workpieces 7 as blanks or parts of the block 1 are separated and only then the piezoelectric workpieces 7 debinded and sintered as blanks.

The piezoelectric layers 2 which consists of the ceramic raw material with the enriched calcium 22 thus have a substantially constant concentration of calcium of 150 ppm 22 on. The calcium 22 has significant influence on the electromechanical properties of the piezoelectric workpiece 7 , The addition of calcium 22 to the ceramic raw material leads to an improved compression behavior during sintering of the piezoelectric workpiece by formation of a temporary liquid phase. As a result, a particularly homogeneous grain structure arises in the ceramic of the piezoelectric workpiece 7 , Due to the homogeneous structure, the polishability and the mechanical Stability of the piezoelectric workpiece 7 improves, at the same time the production spread is narrowed.

Also the large signal characteristics are from the calcium 22 affected. The calcium ions (Ca ²⁺ ) are preferably incorporated in the perovskite structure as soft doping on the A-site (as an isovalant substitute for Pb ²⁺ ). The formation of a covalent bond to the oxygen leads to a reduction in the proportion of stable ferroelectric phase and reduced domains. The reduction of the domain structure leads to improved mobility, which in particular the stroke of the piezoelectric workpiece 7 increases.

Also, the improved long-term stability is a consequence of the addition of calcium 22 , The doping of calcium 22 in a certain concentration leads to a particularly advantageous reduction in the number and mobility of oxygen vacancies. This improves the long-term stability of the material against electrical fatigue.

The calcium 22 is z. B. in a solid calcium compound, for. As CaO, added in the preparation of the ceramic raw material, for. B. before the grinding process 17 to a source material 14 . 15 . 16 or the calcined powder with the dopants 18 becomes calcium 22 added as an organometallic compound.

Overall, with the inventive method for the production of piezoelectric workpieces 7 and a plant according to the invention 25 significant benefits. The calcium 22 is quantitatively added specifically to the effect that a certain predetermined concentration of calcium 22 can be achieved. This allows the properties of calcium 22 to improve the electrochemical properties of the piezoelectric workpieces are used selectively, because the piezoelectric workpieces 7 on the one hand, a substantially constant concentration of calcium 22 and such an amount of calcium 22 is specifically added that for the corresponding application of the piezoelectric actuators 7 These have the best or best electromechanical properties.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19757877 A1 [0005]
• DE 10217097 A1 [0006]

Claims (13)

Method for producing piezoelectric workpieces ( 7 ) comprising the steps of: - producing a ceramic raw material from at least one starting material ( 14 . 15 . 16 ), - producing a plurality of piezoelectric layers ( 2 ) as a green sheet ( 24 ) from the raw material, - lamination of a block ( 1 ) of the plurality of piezoelectric layers ( 2 ) and a plurality of between the piezoelectric layers ( 2 ) arranged electrode layers ( 3 ), - debonding and sintering the block ( 1 ) or parts ( 4 ) of the block ( 1 ), - separating piezoelectric workpieces ( 7 ) from the block ( 1 ) or parts ( 4 ) of the block ( 1 ), characterized in that to the at least one starting material and / or during the production of the ceramic raw material calcium ( 22 ) is added quantitatively in a targeted manner to a certain concentration of calcium ( 22 ) in the raw material. A method according to claim 1, characterized in that prior to the addition of calcium, the concentration of calcium ( 22 ) in which at least one starting material is determined and depending on the concentration of calcium ( 22 ) in the at least one starting material the calcium ( 22 ) is added selectively. A method according to claim 1 or 2, characterized in that in a production step for producing the ceramic raw material from the at least one starting material to the raw material to be produced due to the manufacturing step calcium ( 22 ), this addition of calcium ( 22 ) is quantified and, depending on the quantitative addition of calcium ( 22 ) the calcium ( 22 ) is added selectively. A method according to claim 3, characterized in that the production step is a grinding process in which water is added and / or needed. Method according to one or more of the preceding claims, characterized in that the calcium ( 22 ) is added as a chemical compound targeted. Method according to one or more of the preceding claims, characterized in that for the production of the ceramic raw material at least one starting material is ground to a powder and preferably the powder is calcined. Method according to one or more of the preceding claims, characterized in that during the production of the ceramic raw material at least one dopant ( 18 ), z. B. Binder ( 19 ) and / or plasticizers ( 20 ) and / or solvent ( 21 ), in particular the at least one dopant ( 18 ) is added to the powder. Method according to one or more of the preceding claims, characterized in that the calcium ( 22 ) is added to the at least one starting material, in particular before grinding, specifically and / or the calcium ( 22 ) is added selectively to the powder, in particular together with the at least one dopant ( 18 ). Method according to one or more of the preceding claims, characterized in that such an amount of calcium ( 22 ) is added so that the concentration of calcium in the raw material is between 10 and 600 ppm, preferably between 50 and 300 ppm, in particular between 150 and 200 ppm. A method according to claim 9, characterized in that the concentration is a mass fraction in mg per kg. Method according to one or more of the preceding claims, characterized in that from the block ( 1 ) Subblocks ( 4 ) and the subblocks ( 4 ) are debinded and sintered. and / or the piezoelectric workpieces ( 7 ) before or after debonding and / or sintering of the block ( 1 ) or partial block ( 4 ) are separated. Method according to one or more of the preceding claims, characterized in that the calcium ( 22 ) is added in such a targeted manner that the concentration of calcium ( 22 ) in the manufactured piezoelectric workpieces ( 7 ) is substantially constant. Investment ( 25 ) for the production of piezoelectric workpieces ( 7 ), characterized in that of the plant ( 25 ) a method according to one or more of claims 1 to 12 is executable.

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