JP2015536381A - Porous component manufacturing method and component - Google Patents

Abstract

The present invention provides a porous component (1) to be used as a flow restricting member, whose basic foundation includes a metal injection molding process enhanced to obtain a component having an evenly distributed open porosity. It relates to a method for manufacturing. Such a flow restricting member is dimensioned to regulate the flow rate of the gas flowing to the static pressure gas bearing of the mechanical system, such as a hermetic compressor composed of a piston that moves relative to the cylinder. At least one porous component (1) having at least one constricted portion with a constant porosity. The invention likewise relates to a flow restricting member in which the porous component (1) is accompanied by a dense material layer in the use and production of the porous component (1) obtained by powder injection molding or powder injection molding of multi-material parts. I.e. without any open pores on the outer surface parallel to the flow direction in which the flow through the porous component (1) should occur and inserted into the bearing system without interfering with the porous structure of the core It also relates to the use and production of porous components, which are flow limiting members that are made possible (dual porosity). The invention also relates to a seal that exists between the porous component (1) and its housing.

Description

  The present invention relates to an enhanced powder injection molding process for obtaining a porous component intended to limit and control the distribution of gaseous fluid flow within a hydrostatic gas bearing of a mechanical system such as a hermetic compressor Concerning MIM.

Currently, it is very common to use piston and cylinder sets driven by electric motors for applications in gas compressors of refrigeration equipment such as residential, commercial and industrial refrigerators, freezers and air conditioners.
A technical challenge found in this type of gas compressor is to avoid any direct contact between the piston and the cylinder.
Therefore, due to the relative movement between the piston and the cylinder, the piston is carried by using the fluid installed between the movable surfaces of the piston-cylinder set to avoid contact between moving parts and premature wear thereof. Needed.

In general, in order for hydrostatic gas bearings to function efficiently, a flow restrictor that can throttle the flow of compressed fluid originating from the high pressure region in the compressor is used, and the gap between the piston and cylinder is The gas pressure inside is relatively low and needs to be appropriate for a particular field of use.
In other words, such a restriction would allow the pressure in the bearing area to be reduced or controlled through control of the flow rate of compressed gas originating from the high pressure area in the compressor and load loss, as disclosed by the document. It is aimed.
Several embodiments have already been developed to enable the implementation of a restrictor for providing a reduced pressure in the bearing area.
For example, Patent Document 1 describes a restrictor that uses a porous strip with a compression ring in a restrictor that includes a porous medium.
The disadvantage of this type of construction is that high dimensional accuracy is required in the production of the compression ring, and thus the higher the dimensional accuracy, the higher the cost for manufacturing the mechanical component. As a result, the production process becomes more expensive.
Another U.S. Pat. No. 5,637,028 is formed by a microchannel disposed on the outer wall of the cylinder, forming an isolated closed channel derived from a plurality of restrictors with a sleeve into which the cylinder is inserted. It describes the restrictor to be used.
As in the case of the aforementioned patent, the disadvantage of this type of configuration is the accuracy requirements during sleeve production which further increases production costs.
Another disadvantage of this technique is due to the fact that this type of configuration formed with microchannels is prone to clogging due to particles or dirt found in the compressor.
Therefore, a filter is needed to ensure that the fluid reaches the restrictor without any type of dirt, as dirt is believed to interfere with the proper functioning of the device.
Patent Document 3 describes a restrictor composed of minute holes arranged on a cylinder wall generated using a laser.
Again, the generation of micropores requires high accuracy, which may hinder the production of compressors at market competitive prices.
In addition, the micropores can be clogged by particles or dirt found in the compressor.
Thus, to date, to provide a gas flow restriction used in a bearing between a piston and a cylinder of a gas compressor that has excellent reliability, performance and availability and at the same time is low in cost. An efficient and satisfactory solution is unknown.
Thus, the present invention is technically enabled by using purified porous material to control fluid flow, which can be produced through a processing path adapted from powder injection molding and sintering techniques for parts. Describes a solution to fill this gap.

Technically, in the engineering system, the expression “porous material” allows the engineering function of the material by the presence of pores in the volume that have different volume percentages, sizes and distributions depending on the specific field of application. Used when
If some materials have residual pores as a result of the production process, but the pores are not necessary to perform their engineering function, these pores are considered acceptable if they do not adversely affect the field of application, If they have a negative impact on the performance of the material in the intended application or field of use, it is considered undesirable.
With regard to the type of pores, the material must be a material with closed pores that can be used as a structural support, or primarily fluid transport, for example, inflow control, filtration, catalyst support, thermal insulation and sound insulation, lubricating oil deposition, etc. Can be classified into materials having open pores that can be used.
The process used to produce the porous material defines the properties of the material such as (closed or open) porosity, volume percentage of pores within the volume, size and shape, pore distribution uniformity and interconnectivity To do.

Structures with open pores can be replicated, controlled material deposition (INCOFOAM), rapid prototyping techniques, powder metallurgy techniques, eg sacrificial phases combined with (metal or ceramic) matrix powders that are removed during the sintering step ( It can be formed by a processing path such as sintering of a powder mixture including a space holder.
Materials with closed pores are a combination of a metal matrix and a hollow element (“syntactic foam”), consolidation of a mixture of blowing agent and alloy powder, sintering of the powder simply poured into the container, direct into the cast metal Can be produced by simple gas injection or addition of a pore-forming agent into the cast metal.

Over the years, several alternative processing methods for the production of porous materials have been proposed.
However, for specific intended applications, ie fluid flow control for hydrostatic gas bearings in hermetic compressors, the cost of the porous component must be low.
Thus, it may be possible to produce these components as a large number of equivalent parts through a high productivity process with a high level of automation and easy control.
For this purpose, powder metallurgy technology is a processing technology with high potential.
Due to the high open porosity and high load loss simultaneously required in the proposed porous components, it is necessary to produce a refined porous structure, thus an alternative powder metallurgy called powder injection molding There is a need to use fine powders with a narrow grain size distribution to allow a narrow distribution of pore sizes such as those used in the art.
This technique is performed at a temperature low enough to avoid significant densification due to incomplete sintering, i.e., sintering of the unfired parts, due to the use of very fine powders and a narrow size distribution. It enables the acquisition of a general refined microstructure that includes all the microstructure elements, including the pore structure in the case of
Thus, to obtain a porous component with a high percentage of fine (several micrometers) open pores that are distributed uniformly within the volume of the porous component and allow precise control of load loss and flow therethrough Where the porous component is a flow restricting member.
Unlike the field of application described herein, i.e. the production of porous bodies, powder injection molding techniques are used in the engineering sector for the very fine powders used (typically about 1 depending on the powder production process). It is emphasized that it is known as a technology that makes it possible to obtain high density components (low residual porosity) due to the high sintering capacity exhibited by powders having an average size of ˜40 micrometers) This is very important.
Typically, powder injection molding performed at normal conditions leads to components with volume percent residual closed pores (not in communication with each other) of less than 5%.
However, as shown in the present invention, through the use of correctly selected powder raw materials and appropriate processing parameters, the engineering function intended in the present invention, i.e., the static pressure of the cylinder-piston set in a hermetic compressor. Obtaining a sintered porous material having a porosity and pore size suitable for the production of porous components having application as a porous restrictor allowing precise control of gas fluid flow for gas bearings It is possible.

Metal injection molding (MIM) has become a very attractive process because it combines the versatility and productivity of plastic injection molding with the unique properties of metal materials.
The powder injection molding process (hereinafter referred to as PIM) is a prominent technology for producing materials from powdered raw materials such as ceramic powders, composites and more recently metal powders.
More specifically, one of the advantages of powder injection molding (in view of conventional techniques such as matrix uniaxial pressing, extrusion and gluing) is high in its shape The ability to produce parts with geometric capacity.
These parts, when produced by other processes, require a lot of additional work to add such complexity to their shape.

Currently, potential markets incorporating products manufactured based on this molding process inherently include parts that require large-scale production with low mass and dimensions and high densification rates.
In other words, the main market supplied with materials and parts obtained by the powder injection molding process is mainly the medical industry as well as the automotive, orthodontic, defense and weapons, electro-electronic equipment market.

From a process point of view, PIM is basically divided into metal injection molding (MIM) process and ceramic injection molding (CIM) technology.
In short, the basic principles of the powder injection molding process lie in two industrially established technologies: polymer injection and conventional powder metallurgy.
In summary, the (ceramic and / or metal) powder is mixed with an organic system formed of a polymer with other organic materials (eg paraffin and polypropylene).
Thus, these organic products are vehicles for transporting loads of metals, ceramic particles (powder) or a mixture of both to fill any mold cavity with the shape of the part (component) to be obtained. Used as.

  Currently, in engineering practice, the material that is intended to be obtained when a metal injection molding process (MIM) is used is that of conventional powder metallurgy, that is, a powder having an average particle size 10 times larger (approximately 100 μm). Significant improvements in mechanical properties of components such as hardness, strength and ductility (due to the high sinterability of the fine powder used) when compared to sintered materials produced through matrix uniaxial machining High density (i.e. having a low residual porosity content) that allows (through a reduction in residual porosity).

More specifically, currently utilized PIM processes attempt to completely remove material pores through the formation of contacts between powder particles and the increase of these contacts during sintering at high temperatures.
On the other hand, sintering of the components after injection molding at high temperatures results in strong volume shrinkage that can lead to dimensional variations and distortions in the resulting final part.
In order to obtain components with high densification (low residual porosity percentage) in addition to the use of powders with high sinterability, generally the “green” density of the injected elements is high. There must be.
That is, the load of solid particles present in the injection feedstock should be as high as possible.
Thus, in powder injection molding, the field of application of components produced under powder injection molding requires these properties, so that pores can be reached to achieve the final high density material quality with high geometric accuracy. Attempts have been made to minimize the presence of.
Current major applications include bone grafts, orthodontic appliances, surgical tool components, firearms, and automotive parts.

  Unlike what is currently practiced in powder injection molding, the method encompassed by the present invention is, for example, reducing raw material losses as much as possible, facilitating precise control of the desired chemical composition, A useful and enhanced form of pore-forming properties based on PIM technology by providing advantages such as eliminating processing operations, superior surface finish, easily automated production processes, products obtained in high purity, etc. It is intended to be used in.

US Pat. No. 6,901,845 US Pat. No. 6,293,184 International Publication No. 2008/055809

  The present invention is applied to static pressure gas bearings, for example, between pistons and cylinders of gas compressors, which allows for the throttling of gas flow in an accurate and reproducible manner even at low levels of flow. The object is to supply a porous component to be used as a flow restricting member produced by injection molding.

The present invention is also utilized in hydrostatic gas bearings that allow accurate and reproducible gas flow throttling through powder injection molding processes, even at low level flow rates such as 5-50 cm ³ / min. To achieve through low cost production of porous components.

  The objectives of the present invention are also achieved by a method of manufacturing a porous component through powder injection molding that includes detailed control of primary porosity via a combination of temperature and powder material.

  The object of the present invention is further accompanied by totally open pores that allow the component to be fixed on the bearing, for example via interference, without changing the porous structure inside the porous component responsible for gas flow control. This is achieved by a method for producing a porous component with no dense outer layer through powder injection molding.

  The present invention also relates to a porous component that can be fixed on the interface between the porous component and the mechanical system in which the porous component is inserted inside to be used in different fields of application without sealing defects. There is also a provision of a manufacturing method.

The object of the present invention is to provide a method for producing a porous component to be used as a flow restricting member in a hydrostatic gas bearing applied to a hermetic compressor,
The component is
Step i): homogenizing at least one preparation comprising an organic binder composed of a) a part of a metal powder and b) a mixture of thermoplastic polymer and wax;
Step ii): granulating at least one preparation obtained in step i);
Step iii): heating at least one granulated preparation obtained in step ii) to at least the initial melting temperature of the binder;
Step iv): filling the mold cavity with at least one mixture obtained in step iii);
Step v): compressing at least one mixture obtained in step iii) at a constant speed and pressure until it is completely filled in the mold cavity;
Step vi): removing the organic binder in at least one step using at least one of a thermal process and a chemical process;
Step vii): pre-sintering the material obtained in step vi) to a temperature that promotes at least mechanical strength sufficient to handle the material;
Step viii): Control the shaped material obtained in step vii) at a temperature that promotes an interconnected matrix of substantially greater than 5% open pores in at least one central portion of the porous component (1). Sintering in a shaped form, which can be performed simultaneously with the preceding steps;
Is achieved by providing a method obtainable through powder injection molding techniques.

The object of the present invention is further a method for producing a porous component to be used as a flow restricting member in a hydrostatic gas bearing applied to a hermetic compressor,
A porous component with a double porosity,
Step i): homogenizing two different preparations comprising an organic binder comprising a) a first part of a metal powder and b) a mixture of thermoplastic polymer and wax;
Step ii): granulating at least two different preparations obtained in step i) in separate stages;
Step iii): heating the preparation obtained in step ii) to the initial melting temperature of the binder;
Step iv): filling the mold cavity with at least one mixture obtained in step iii);
Step v): injecting at least one mixture obtained in step iii) at a constant speed and pressure into the cavity of the mold until completely filled;
Step vi): The second material obtained in step iii) is either used by using a mold under injection and with an insert, or both materials obtained with an injection machine with two spools and step iii) Injecting by using simultaneous injection of
Step vii): removing the organic binder in at least one step by using at least one of a thermal process and a chemical process;
Step viii): pre-sintering the material obtained in step vii) at a temperature that promotes sufficient mechanical strength to handle the material for subsequent steps;
Step ix): Promotes densification of the shaped material obtained in step viii) through sintering to a residual porosity of less than 5% on the outer part of the porous component and at the same time the porous component Sintering in a controlled manner at a temperature that maintains a volume percentage of open pores substantially higher than 5% in the inner portion of the substrate, which may be performed simultaneously with the preceding steps;
This is accomplished by providing a method obtainable through powder injection molding techniques for multi-material parts.

  The invention will now be described in more detail on the basis of an embodiment represented in the drawings of the accompanying drawings.

2 shows an example of a porous component obtained through powder injection molding. 1 is a perspective view of a first preferred embodiment of the present invention. FIG. 6 is a perspective view of a second preferred embodiment of the present invention.

  The method for producing a porous material in the present invention is a porous structure having the characteristics required for a particular desired field of application, i.e., porous for the uniform distribution of the gas fluid required by the hydrostatic gas bearing. It is a powder injection molding (PIM), which is a variant of the powder metallurgy technology improved in the present invention to make it possible to obtain components (flow restricting members).

One of these applications is found in compressor hydrostatic gas bearings, which are achieved through a gas layer that can keep the linear motion of the piston balanced within the cylinder. The
For this reason, the amount of gas involved in the loading of the piston is required to be constant, and in order to control the fluid flow rate, not only the flow rate can be adjusted but also in the system to be loaded. It is necessary to use a porous component 1 with a homogeneous porous structure that also allows a uniform distribution of the flow.
The development of a porous component 1 called a porous restrictor and the pair of particulate materials to be used are likewise covered by the method of the invention.

The porous component 1 is composed, for example, of ceramic, metal or any other porous material in order to precisely control the gas flow rate into the hydrostatic gas bearing between the piston and cylinder pair of the compressor. It's okay.
The material must exhibit excellent chemical resistance, in particular corrosion resistance, and avoid degradation that leads to changes in the properties of the porous components as a result of corrosion and thus changes in pore morphology.

Several materials that can be used include stainless steel.
The porous component 1 can be manufactured using powder injection molding, which provides better porosity control, reproducibility of gas flow at relatively low flow rates and low production costs. Because.
Accordingly, the flow rate is preferably (but not necessarily) within the range of 5-50 cm < ³ > / min.

  Thus, the advantages of the present invention are the typical advantages of processing through powder metallurgy techniques, such as reducing raw material losses as much as possible; easy and precise control of the chemical composition of materials; excellent surface finish, easy Production processes automated; products obtained in high purity; achieving controlled homogeneous porosity;

These properties can be obtained in sintered components formed by powder injection due to several features of the method of the present invention when compared to other processing technologies currently on the market. .
Such a method (PIM) makes it possible to uniformly control the porosity level, the pore size and the homogeneous distribution of the pores throughout the volume of the component without adding high production costs.
One of these properties lies in the use of fine powders having a particle size in the range of 1 to 40 micrometers, the particle size dispersion is preferably rather narrow, and thus the resulting porous groove diameter is small and porous It will be well distributed over the entire cross section of the component 1.

Another property of this powder injection molding process was applied, because of the low viscosity of the injection mass (cast organic material and powder mixture), such mass has a behavior similar to that of fluid The point is to carry the stress completely in all directions and on all sides.
This ensures that the stress is evenly distributed throughout the volume of the component being injected, avoids the formation of density gradients on such a volume, and ensures isotropic shrinkage during the sintering stage. become.

  The third characteristic of this powder injection molding process is the control of pore size and geometry through detailed control of the size and size distribution of these powders used as raw materials and through adjustment of parameters in the sintering process. There is a possibility to do.

  In order to ensure the maintenance of a porous structure with a high percentage of open pores, the present invention is 850 ° C., which is lower than the concentration commonly used in sintering high density mechanical components (1200-1400 ° C.). Use low sintering temperatures in the range of ~ 1200 ° C.

  For the sake of clarity, a high-density mechanical component has a certain percentage of residual closed pores (less than 5% by volume) but does not have open pores and is therefore subject to fluid penetration. It is a mechanical component that cannot be used.

If some control is required with the flow rate variable over the entire length of the hydrostatic gas bearing, it is inserted over the entire length of the bearing where such variation can be obtained at the desired flow rate. It is possible to manufacture and apply restrictors with different flow rates.
These porous elements with different flow characteristics can be obtained by varying the properties of the metal powder used in their production or by varying the sintering temperature at which the injected components are sintered. Can be obtained.
It should be noted here that the components need only be slightly different in order to produce distinctly different porosity levels on each porous component 1.

  In view of this flexibility in designing the porous structure required by hydrostatic gas bearings, the provision of a porous element 1 produced by powder injection molding is a very attractive technology in terms of economy.

In this regard, the method of the present invention includes the following steps detailed below:
Step i): homogenizing at least one preparation comprising a) a first part of a metal powder and b) a binder comprising a mixture of thermoplastic polymer and wax to at least one homogenization point;
Step ii): granulating the preparation obtained in step i);
Step iii): heating the granulated preparation obtained in step ii) to at least the initial melting temperature of the binder;
Step iv): filling the mold cavity with at least one mixture obtained in step iii);
Step v): compressing at least one mixture obtained in step iii) at a constant speed and pressure until it is completely filled in the cavity of the mold;
Step vi): removing wax from the material obtained in step v) using chemical extraction;
Step vii): removing the thermoplastic polymer from the material obtained in step vi) using chemical extraction;
Step viii): pre-sintering the material obtained in step vii) to a temperature that promotes at least mechanical strength sufficient to handle the material;
Step ix): Sinter the shaped material obtained in step viii) in a controlled manner at a temperature that results in a sintered body with a significant percentage of open pores (in the range of 6% to 50%) Step.

  The manufacturing method in the present invention selects the composition of a preparation (feedstock) that includes a first portion of metal powder and a mixture of a thermoplastic polymer and a wax that functions as a vehicle for transporting the particles during injection. It starts with that.

  Preferably, the production methods herein use metal powders such as iron powder, nickel powder, copper powder or stainless steel powder 316L and 17-4PH.

In order to obtain excellent results in the metal injection molding process, the selected powder has certain properties such as high particle loading, excellent injection ability and the ability to help retain the shape of the component to be molded, etc. Note that it is necessary to have
Preferably (but not necessarily), the metal powder used in this process has a narrow crystal size distribution in which virtually all particles have similar diameters.
Thus, an interconnected matrix of open pores in the volume of porous material obtained by the end of the process can also exhibit very small diameter variations.

  The mixture of thermoplastic polymer and wax that contains the preparation and functions as a binder is responsible for ensuring flowability to the preparation to be molded and helping to obtain the homogeneity of this first mixture. .

The binder used in this type of process is generally composed of a mixture of polymers with low molecular weight and larger chains.
Low molecular weight polymers such as paraffin, beeswax and carnauba wax facilitate the spillage of metal powder preparations and binders during their molding.
Similarly, larger chain polymers have the purpose of adequately supporting the shaped material, especially in the early stages of the process.
Examples of these polymers are polypropylene, polystyrene and ethyl vinyl acetate.

  Thus, preferably (but not necessarily), the binder used in this process is a mixture of thermoplastic polymer and wax.

More specifically, the thermoplastic polymer used in the preparation of the organic binder and powder mixture in the present process can impart mechanical strength to the preparation (feedstock) molded by injection. Yes (step v).
For this purpose, the thermoplastic polymer of the preparation does not affect its structure during the first step of removing the wax (chemical extraction, step vi).

  It should be noted that preferably the relationship between the metal powder of the preparation and the mixture of thermoplastic polymer and wax is in a ratio in the range of 20% to 80%, preferably 40% to 60%.

Once the components for the preparation (feedstock) have been defined, these preparations continue into step i) of the method in which the preparation is to be homogenized to at least one homogenization point.
Such a homogenization point must achieve a sufficiently homogeneous preparation without voids.
Ultimately, the homogeneity within the components of the preparation increases the interaction of the metal powder with the mixture of thermoplastic polymer and wax.

  This first step i) is performed using a mixer that allows a high shear rate evenly distributed throughout the chamber, such as a Z or cam type planetary mixer.

The homogeneously mixed preparation obtained in step i) continues into step ii), where the preparation is granulated (or pelletized) and the replenishment of the injector is improved.
This step is performed by a pelletizer.

Once granulated, the preparation made in step ii) continues into step iii) where the preparation is heated to at least the initial melting temperature of the thermoplastic polymer and wax mixture. .
This step is performed to favor the rheology and spill properties of the preparation that will be inserted into the mold later (steps iv and v).

The properly heated preparation then goes into step iv) where the mold cavity is filled with the heated preparation.
It should be noted here that the mold chosen for the process must be able to withstand higher pressures and longer cooling times than the molds commonly used in polymer injection molding. .

  The mold cavity of step iv) filled with the preparation then goes into step v), where at least one mixture obtained in step iii) is completely filled into the mold cavity. Until compressed at a constant speed and pressure.

For this step v), the molding is carried out using equipment units similar to those used for conventional polymer injection molding which are so-called injectors.
In this regard, during the molding step, the spool compresses the material load so that the material is consolidated and fills the entire mold cavity.
By the end of this step v) the preparation has been consolidated as a porous component 1 having the shape of the mold from which it was injected, where the form is preserved by a mixture of thermoplastic polymer and wax. Yes.

Subsequent step vi) involves removal of the wax from the shaped prepared material obtained in step v) using chemical extraction.
The chemical extraction is to immerse the material formed in step v) in a part of the fluid, the ultimate purpose of which is to dissolve the wax of the preparation.
By the end of this stage, a shaped material with an open pore structure is obtained, which still contains metal powder agglomerated by the thermoplastic polymer in its composition.
This final structure helps the heat extraction step vii).
Preferably, but not necessarily, the removal of the organic binder in step vi) is carried out in a portion of the liquid for at least 1 hour at a temperature in the range of 20 ° C to 60 ° C. Can take longer or shorter depending on the liquid and temperature selected.

Thereafter, the shaped material obtained in step vi) continues into step vii), where thermal extraction is used to remove the isothermal polymer remaining in the material.
This procedure consists of heating the shaped material at suitable conditions and the accompanying pyrolysis of the thermoplastic polymer.
In other words, the shaped material is heated to cause activation, which leads to a gradual breakage of the polymer chain of the thermoplastic polymer, and the porous component 1 instead of the gradually extracted polymer. It is possible to form an initial sintered contact that can guarantee the preservation of the shape of the material.

  Preferably, but not necessarily, the thermal extraction of the thermoplastic polymer is performed by heating the shaped material in a plasma assisted furnace or a conventional resistance furnace.

  By the end of step vii), it is possible to obtain a certain amount of metal powder particles from the initial preparation that are weakly bonded in the shaped component geometry by the sintered contacts that are still in the initial stage.

Next, this laminated metal powder obtained in step vii) continues and enters step viii) consisting of pre-sintering of the material obtained in step vii).
In essence, this step prompts the start of a process to remove the hollow spaces contained between many metal powder particles.

  Preferably, step viii) is performed by heating the shaped material obtained in step vii) to a temperature that promotes at least mechanical strength sufficient to handle the material.

Thus, step viii) is at least sufficient to provide, for example, the desired porous structure for the proposed engineering field, i.e. a flow restricting member or to allow mechanical strength for handling. It is carried out in a plasma assisted furnace or in a conventional resistance furnace at a temperature in the range of 400 ° C. to 1200 ° C. for hours.
The time required to finally obtain the desired properties is in the range of minutes to hours depending on, for example, whether presintering is to be performed and also the combination of steps viii and ix. It's okay.

  Finally, at the end of step viii), the shaped material was obtained in step viii) in order to provide a controlled homogeneous porosity material that is the object obtained by the method covered by the present invention. Enter step ix) which involves sintering the shaped material in a controlled manner.

  Typically, the final porosity of the component obtained through powder injection molding is brought about as a result of this last sintering step ix) taking into account heat-activated mass transport, and the contacts within the particles Resulting in a reduction in free specific surface area due to an increase in the volume, their coalescence, volume reduction, and changes in pore geometry, to its full densification.

In this method, step ix) can be divided into three stages:
Step 1: Sintered contact formation. The contacts between the particles form a “bridge”. That is, the substance is in a continuous state within the contact area. At this stage there is no massive movement (or contraction) of the particles;
Stage 2: As the “cervical radius / particle radius” ratio increases, the particles progressively lose their strength. At this stage, the sintered material has two “continuous” phases. That is, the phase of the material (solid phase) and the “hollow” phase (an interconnected matrix of open pores). The crystal grain size increases and results in a new microstructure. Most of the contraction occurs at this stage.
Stage 3: Pore sequestration, rounding and coalescence occur (greater than 90% theoretical density). If the pores contain insoluble gases in the main component metal, complete densification is not possible. Complete densification can occur if the pores are hollow or contain a soluble gas in the matrix.

In this way, the shaped material from step viii) is subjected to a sufficiently low sintering temperature, so that in step 2 the sintering does not progress so much and does not reach step 3 and there are open pores in the final material. Keep the interconnect matrix.
That is, the sintering in the method of the present invention, unlike the current state of the sintering process for powder molding, has led to a conventional third stage where pore interconnectivity is reduced, coalesced and lost. Absent.

  In a preferred embodiment, the end of the method of the invention means a sintering process carried out in a vacuum furnace or plasma assisted vacuum furnace, for example, where the porous structure of the component and the desired properties are obtained.

  As an example, in the state of the art, stainless steel has been sought for the complete removal of particle voids, i.e., virtually zero void porosity, which is one characteristic inherent in the final material after passing through a conventional sintering process. The sintering step of powder 316L or 17-4PH is usually performed at a temperature in the range of 1250 ° C to 1380 ° C, and for iron and nickel powders, it is performed at a temperature in the range of 1200 ° C to 1300 ° C.

For the method for producing the porous component 1 of the present invention, when stainless steel powder is used, sintering is performed at a lower temperature in the range of 900 ° C to 1200 ° C.
Similarly, for iron or nickel powders, the sintering process is performed at a temperature in the range of 700 ° C to 1100 ° C.
Therefore, void removal is minimized and a controlled void porosity (6% to 50% uniformly distributed gaps) remains.

Similarly, it should be noted that the volume shrinkage increases as the amount of binder phase increases.
Therefore, the largest dimensional variation of this method is statistically in the injection step (step iv).
If the injection step (step iv) includes an unfired density gradient in the injected element, deformation occurs during sintering that may be intentional or unintentional in view of the desired porosity. .

  In a preferred embodiment, step ix) is performed in a furnace at a temperature in the range of 700 ° C. to 1200 ° C., depending on the material selected for the production of the porous component.

  For this reason, the method according to the invention makes it possible to obtain results that differ from the results of the sintering processes known in the state of the art, and for the components obtained, the advantages previously anticipated (for example, Energy efficient, homogeneous and controlled that is easy to implement in the industry in this field and easily usable in the market as well as achieving geometric complexity and full use of the injected material) It also adds a process for producing a material with porosity.

Furthermore, as can be seen in FIG. 2, this method of manufacturing the porous component 1 is versatile in obtaining complex geometries in the finished state due to its rheological properties. It has become.
It is therefore possible to obtain a prominent geometric shape such as a thread in a certain part of the part of the final porous component 1.
It is equally possible to obtain some protruding protrusions.

  One very significant advantage of this method is that geometric variations are achieved without the need for additional machining steps as illustrated by FIG.

In view of the above, the method for manufacturing a porous component 1 according to the present invention may also include components having regions or layers with very different porosity.
That is, the porous component may be configured to have a relatively high porosity in the inner region and a relatively small porosity or even a zero porosity in the outer region (FIG. 3). Want to be confirmed).

Such a configuration can be achieved as follows:
That is, step i) may involve independent homogenization of two or more preparations, which are granulated separately (step ii) and then gold depending on the expected final material. Used to fill the mold cavity (step iii).
Thus, depending on the selected component, for example, two preparation materials, ie a preparation that becomes dense at the sintering temperature on the outside of the mold, and remains porous at such a sintering temperature. It is possible to inject another preparation inside the mold.
According to this method, at the end of step ix), it is possible to obtain a final material that does not contain pores at the edges and is porous in the core.

Alternatively, the same material in powder form with different crystal grain sizes can be used for the preparation.
Thus, for example, some finer grain size powders with higher sinterability are used on the outside of the mold, and some larger grain size powders are used on the inside of the mold.
Finer powders, i.e., powders with smaller crystal grain sizes, achieve higher density at the same sintering temperature, while powders with larger crystal grain sizes achieve lower densification and thus higher porosity.

The production of these components with different porosities on the surface layer is likewise a type called powder injection molding, in particular a multi-material part powder injection molding, or a type also called two-component powder injection molding, or final. This is possible through powder injection molding of the type known only as co-injection.
In this process, a first material constituting the most porous inner side and then a second material constituting a dense outer coating are injected.

The multi-material component is then at the temperature expected for the firing of the core material to remain porous so that it can have the specific properties described above that are necessary for the porous component 1. Sintered.
At this temperature, the sinterability of the material or powder of the outer cover is great, so such a cover tends to be denser with no open pores, ie, the pore content is substantially less than 10%. is there.

In order to have different porosity levels within the two regions mentioned, it is necessary to use different materials and / or powders within each region of the porous component 1 (see FIG. 3).
Therefore, this requires that the selected material pairs have sintering compatibility so as not to cause cracks on the joint interface.
Similarly, for the same sintering temperature, the material (placed inside the porous component of FIG. 3) has a lower sintering level than the material placed on the outer cover, in other words, the inner material's It should also be assumed that the porosity is in the range of 6% to 50%, while the outer material has no more open porosity (less than 6%).

  It is therefore possible to apply any powder and / or material that has the properties necessary for the porous component 1 to function optimally after the sintering process.

Many possibilities include combining the same materials, such as stainless steel, if the powders used have significantly different average particle sizes.
The larger particle size powder placed inside the porous component 1 is used to inject the outer cover of the porous component 1 because the amount of metal contacts per unit volume present between the particles is small. It is less sinterable compared to fine powders, thus resulting in higher porosity levels of preferably 6% to 50%, as mentioned above.

  Another solution for the selection of the material of the porous component 1 represented in FIG. 3 is that any material that allows the desired porosity level inside the component and the selected ideal This is achieved by the use of another material that forms a liquid phase at a suitable sintering temperature and promotes sintering through the liquid phase, producing a high level of densification on the outside.

An example of many of the available ones is the stainless steel inside the porous component 1 representing the functional part of the combination and another steel with a liquid phase forming element such as boron, phosphorus or copper, for example. There is use.
Because this outer part has higher density and smaller pores, they have higher capillary forces, thus holding the liquid and consequently towards the inside of higher porosity and pore size with lower capillary forces. Prevent the liquid from moving.
In this way, it is possible to maintain the characteristics of fine structure and precise flow control.

  In addition, the use of elements that form a liquid phase during sintering and form a soft material (that is plastically deformed) after solidification, such as copper, also facilitates the solution of interference fixation, which is a soft material. This is because leakage and efficiency loss are avoided without easily deforming and sealing the porous restrictor without changing the porous structure of the inner part of the porous component 1 involved in the control of the gas flow rate.

  If there is an escape path on the interface between the porous restrictor and the hydrostatic gas bearing to which it is fixed, leakage may occur, making flow control difficult and impeding the proper functioning of the hydrostatic gas bearing. There is a case.

Another method of associating the porous component 1 with a hydrostatic gas bearing is gluing.
However, the use of glue (liquid adhesive) is appropriate in the presence of open pores because it penetrates into the interconnected matrix of open pores via capillary forces and partially clogs the pores. Not.
This change in the porous structure of the porous component 1 can interfere with its performance in the intended field of use.
The solution proposed and developed in the present invention has a greater sinterability and typically more than the granular material different from the porous core, i.e. the granular material constituting the porous core of the injected component. It consists of obtaining a dense layer on the side of the porous component 1 through co-injection or double injection / encapsulation of the layer with an injection feedstock constituted by a particulate material having a low sintering temperature.
Thus, a greater densification occurs on the sides of the porous component during sintering.
At this time, since the high density portion does not participate in the flow rate control and plays a role of ensuring the fixing of the restrictor on the mechanical system without interfering with the porous structure, a plurality of fixing methods ( The porous component 1 can be efficiently fixed by interference, gluing, tapping and the like.

  Finally, another solution for selecting the material of the porous component of FIG. 3 is simply to combine a different sinterable material such as stainless steel in the inner region and a nickel powder in the outer region. It is to combine.

The porous material production method described above may be used in the production of multiple types of porous components 1 for applications in different applications.
In this connection, the present invention is preferably used in the production of a porous flow restricting member for a hydrostatic gas bearing.

Normally, in order for a hydrostatic gas bearing to function effectively, a flow restricting member capable of restricting the flow rate of compressed gas derived from a high pressure region in the compressor is used, and the gap between the piston and the cylinder is set. It is necessary to ensure that the gas pressure present is lower and appropriate for the field of application.
In other words, such a restriction seeks to reduce or control the pressure on the bearing area by restricting the flow of compressed gas originating from the high pressure area of the compressor.

The flow restricting member is linked to a housing in the bearing having at least one restrictor portion sized to throttle the flow of gas flowing through the compressor from the inner cavity to the bearing gap. It is comprised by the porous component 1 made.
Thus, the gas travels through the porous component 1 towards the bearing gap and forms a gas mattress.

  The main advantage of producing a porous flow restricting member for hydrostatic gas bearings through the method herein is that a flow restricting member having a controlled porosity that is homogeneously distributed over the volume of the material is obtained. It is in that it is.

  Having described examples of preferred embodiments, the scope of the present invention encompasses other possible variations and fields of use, and is limited only by the content of the appended claims, the content of which is considered equivalent It is understood that objects are also included.

Claims (18)

In a method for producing a porous component (1) to be used as a flow restricting member in a hydrostatic gas bearing applied to a hermetic compressor,
Such components are
Step i): homogenizing at least one preparation comprising an organic binder composed of a) a part of a metal powder and b) a mixture of thermoplastic polymer and wax;
Step ii): granulating at least one preparation obtained in step i);
Step iii): heating at least one granulated preparation obtained in step ii) to at least the initial melting temperature of the binder;
Step iv): filling the mold cavity with at least one mixture obtained in step iii);
Step v): compressing at least one mixture obtained in step iii) until it is completely filled in the cavity of the mold;
Step vi): removing the organic binder in at least one step using at least one of a thermal process and a chemical process;
Step vii): pre-sintering the material obtained in step vi) to a temperature that promotes at least mechanical strength sufficient to handle the material;
Step viii): The shaped material obtained in step vii) is controlled at a temperature that promotes an interconnected matrix of open pores substantially greater than 5% in at least one central portion of the porous component (1). A step of sintering in a form that can be performed simultaneously with the preceding step;
Obtained through powder injection molding technology, including
A method characterized by that.   The porous component (1) according to claim 1, characterized in that the preparation of step i) comprises at least part of a metal powder such as iron, nickel, stainless steel AISI 316L, 304 or 17-4PH. Manufacturing method.   Process for producing a porous component (1) according to claim 1, characterized in that the preparation of step i) comprises metal powders having different crystal grain sizes.   The process for producing a porous component (1) according to claim 1, characterized in that the preparation of step i) comprises metal powder and organic binder in a proportion of 20% to 80% by volume. .   The porous construction according to claim 1, characterized in that the removal of the organic binder from step vi) is carried out in some liquids for at least 1 hour at a temperature in the range of 20 ° C to 60 ° C. Manufacturing method of element (1).   The process for producing a porous component (1) according to claim 1, characterized in that the removal of the organic binder from step vi) is carried out in a plasma assisted furnace or a conventional resistance furnace.   2. The method for producing a porous component (1) according to claim 1, characterized in that the pre-sintering step vii) is carried out at a temperature in the range from 400C to 1200C.   The method for producing a porous component (1) according to claim 1, characterized in that step vii) is carried out in a conventional furnace, in a vacuum furnace or in a plasma assisted vacuum furnace.   The process for producing a porous component (1) according to claim 1, characterized in that step viii) is carried out in a furnace at a temperature in the range of at least 700 ° C to 1300 ° C. In a method for producing a porous component (1) to be used as a flow restricting member in a hydrostatic gas bearing applied to a hermetic compressor,
A double porosity porous component (1)
Step i): homogenizing two different preparations comprising an organic binder comprising a) a first part of a metal powder and b) a mixture of thermoplastic polymer and wax;
Step ii): granulating at least two different preparations obtained in step i) in separate stages;
Step iii): heating the granulated preparation obtained in step ii) to the initial melting temperature of the binder;
Step iv): filling the mold cavity with at least one mixture obtained in step iii);
Step v): injecting at least one mixture obtained in step iii) into the mold cavity until completely filled;
Step vi): The second material obtained in step iii) is either used by using a mold under injection and with an insert, or both materials obtained with an injection machine with two spools and step iii) Injecting by using simultaneous injection of
Step vii): removing the organic binder in at least one step by using at least one of a thermal process and a chemical process;
Step viii): pre-sintering the material obtained in step vii) at a temperature that promotes sufficient mechanical strength to handle the material for subsequent steps;
Step ix): Promotes densification of the shaped material obtained in step viii) through sintering to a residual porosity of less than 5% on the outer part of the porous component (1) and at the same time porous Sintering in a controlled manner at a temperature that maintains a volume percentage of open pores substantially higher than 5% in the inner part of the quality component (1), which can be carried out simultaneously with the preceding steps Steps,
Obtained through powder injection molding of multi-material parts, including
A method characterized by that.   Powders with different crystal grain sizes are used, finer powders are used in the denser part outside the porous component (1), and powders with larger crystal size are used in the porous component ( The method for producing a porous component (1) according to claim 10, characterized in that it is used in the core of (1).   11. Powder according to claim 10, characterized in that a powder with a similar grain size is used and in the outer part of the porous component (1) liquid phase forming elements are used as well during the sintering step. A method for producing a porous component (1).   The method for producing a porous component (1) according to claim 11, wherein the liquid phase forming element is composed of at least one of materials of boron, phosphorus and copper. On the outer part of the porous component (1), a material is used that can achieve a high level of densification during step ix),
On the inner part of the porous component (1), a material is used that can achieve a low level of densification during step ix).
A method for producing a porous component (1) according to claim 10, characterized in that   The method for producing a porous component (1) according to claim 14, characterized in that the metal material used is selected from iron and stainless steel; nickel and stainless steel; copper and stainless steel.   The porous component (1) can be inserted into a hydrostatic gas bearing through interference, gluing, sealing utilization, mating geometry, or for hermetic insertion into a hydrostatic gas bearing system 11. A method for producing a porous component (1) according to claim 1 and 10, characterized in that it is screwable.   Porous component (1), characterized in that it is obtained by the method according to one of claims 1 or 10.   A porous component (1), characterized in that it is a porous limiting member for use in a hydrostatic gas bearing.

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