WO1989003298A1 - Process and device for manufacturing mouldings from particulate materials - Google Patents

Abstract

The invention concerns a process for compacting a particulate material consisting of plastics, coal, metals or ceramics by applying pressure to the material in a sealed mould cavity. In the process, a pressure of 10 to 104 N/cm2 is applied simultaneously with sound at a frequency of 10 to 100 kHz.

Description

METHOD AND DEVICE FOR PRODUCING MOLDED BODIES FROM PARTICULATE MATERIAL

The invention is directed to a method for producing shaped bodies by compressing and connecting particulate materials and to a device suitable therefor. The method according to the invention is particularly suitable for the production of porous material parts.

Various methods for pressing, hot pressing, sintering of particulate materials for the production of solids are already known. For example, powdery material is compressed in a die of a press. The material compacted into a compact is a so-called green compact. This is then annealed or sintered in a furnace at high temperature. The material loses brittleness, and the tightness from the previous pressing process is tied to certain limits. In addition, the complexity of the shapes is limited by the forces required during the pressing process. In order to compress pasty masses and convert them into solids, devices with a vibrating vibrating table and with a molding box arranged thereon with a covering weight are known. The components of the pasty masses are first compacted by shaking and shaking and a so-called green compact is formed, which is then subjected to a heat treatment for sintering the material.

A method is known from DE-A-31 38 223 in which sound energy is introduced into a homogeneous mass in order to determine its consistency. From the detailed information and the intended purpose of measuring the consistency, it follows that the total energy introduced is extremely low and cannot cause any changes in the material structure. According to the teaching of this document, this is in principle not intended.

For example, from plastics

Injection molding also produces moldings of complex shapes, but it is not possible to produce porous molded parts with high strength by injection molding.

The object of the invention is to provide an improved method for producing moldings from particulate material and a device suitable for carrying out the method, which avoids the disadvantages of the known pressing and sintering methods.

The object is achieved by the method for producing molded articles by compressing particulate material made of plastic, carbon, metal or ceramic by simultaneously treating the in a form space enclosed material with a pressure between 10 N / cm ² and 10 ⁴ N / cm ² and sound of a frequency of 10 to 100 kHertz, which is characterized in that the amplitude of the sound energy is 5 to 100 microns and on their frequency and on the elastic modulus of the material to be treated according to the formulas

in denen ⋋ die Wellenlange der Schallenergie, Δ L die Amplitude, V die Schallgeschwindigkeit im material, f die Frequenz, ε die Dehnung des Materials bedeuten so abgostimmt sind, daß die eingebrachte Schallenergie in Form von Stoßwellen auf das zu verdichtende Material und durch Reibung in Wärme umgewandelte Energie an den Berührungsflächen der Teilchen einwirken und eine feste Verbindung der Teilchen Miteinander durch Verschmelzen oder Verkleben de r ßerührungsstellen erzeugt wird.

in which ⋋ the wavelength of the sound energy, Δ L the amplitude, V the speed of sound in the material, f the frequency, ε the elongation of the material mean that the sound energy introduced is in the form of shock waves on the material to be compressed and by friction in Heat-converted energy act on the contact surfaces of the particles and a firm connection of the particles to one another is produced by fusing or gluing the contact points.

Different particulate materials are preferably joined together at the contact surfaces. For example, you can use graphite powder with tar or

Mix pitch and form a paste, using tar or pitch as a binder.

By simultaneously applying pressure and shock waves to the material at a selected frequency and amplitude and intensity that is adapted to the material, the position of the particles is oriented towards one another, the gaps between the particles initially reducing and be filled almost completely. The design of the vibrating body transmits shock waves that transmit considerable amounts of energy. Sound energy is converted into impact energy, whereby only the longitudinal waves are used. Amounts of energy from 1 to 3 KW can be transmitted. This leads to the desired compression of the material if at the same time the stamp designed as a vibrating body tracks the material which is compacting and thus shrinks in volume and a pressure load of the material is maintained. The compression state is higher in this mode of operation than in the known pressing processes in which the material is only subjected to a pressing pressure. This is due to the fact that the compressive forces of the vibrating body act locally on the material according to the frequency over the length of the amplitude during the pressing process. The vibrating body constantly detaches from the mass at the frequency corresponding to the amplitude.

The duration of treatment, the frequency and amplitude of the sound energy are matched to the modulus of elasticity of the material to be treated in such a way that the compacted material combines at the contact surfaces of the particles and a shaped body corresponding to the shape of the mold space is formed. The connection is based on the fact that the individual particles rub against one another under the influence of the shock waves emanating from the vibrating body and the material heats up. The sound energy is particularly effective in the so-called ultrasonic range. In contrast to conventional ultrasonic welding, it is not only the amplitude of the resonance unit that is important, but also the forces generated during the action. For example, if you assume a frequency of 20 kHz and one An amplitude of 35 my is obtained using the formula

λ = Wellenlänge der Schallenergie V = Schallgeschwindigkeit im Material f = Frequenz

λ = wavelength of sound energy V = speed of sound in the material f = frequency

for steel a wavelength of 0.225 m (assuming V = 4,500 m (sec). The underlying amplitude of 35 my is the change in length of the vibration system in 1/4 ⋋. The associated tension is calculated as follows:

∂ = tension of the material

E = modulus of elasticity of the material ε = elongation of the material ΔL = amplitude of the sound energy

In this case, this results in a tension of approximately 13 kN / cm ² .

The main difference from conventional pressing is that the energy required for treatment only has to be applied to the material at a point in time when the upper punch has already been inserted into the die, ie there is no risk of any damage up to this point can injure the operator on the die in any form. The method according to the invention also enables the production of composite materials if, for example, different particulate materials are mixed with one another and treated as a mixture in a molding die by means of pressure and sound. If the different materials are arranged alternately in layers in the die, multilayer composite materials can be produced that consist of two or more layers. In such a case, the frequency of the sound energy must be matched to the elasticity modules of both or more materials. In order to be able to achieve a firm connection, the elasticity modules of the different materials should be similar and should not differ too much.

In the context of the production of composite materials, the method according to the invention is also suitable for providing predetermined shaped articles with layers of the same or different material, the layers applied preferably having a porous structure and being firmly connected to the carrier material. Basically, the connection of compressed porous or non-porous materials with porous or dense materials is the same or different

Origin possible. Composites can be produced from different plastics as composite materials, for example from thermosets, ie spatially closely cross-linked polymers and thermoplastics. Polymer substrates with a dense macroscopic structure can be provided with both porous and dense layers. If necessary, porous support structures can also be closed with macroscopically dense plastic layers. Suitable plastics are phenolic resins, cresol resins, novolaks, resols, urea resins, melamine resins, alkyd resins, ie polyester resins formed from polybasic acids and polyhydric alcohols, but also unsaturated polyester resins, epoxy resins, crosslinked polyurethanes, thermoplastics such as polyolefins, polyvinyl chloride, polystyrene, styrene and polystyrene, styrene and Polyacrylates and polymethacrylates, polycarbonates, cellulose acetobutyrate, cellulose acetopropionate can be processed according to the invention.

Examples of composite materials are also metal or ceramic composites with the aforementioned plastics. For example, sintered metals of iron, copper, silicon, aluminum, titanium, bromine can be coated and bonded with plastics or carbon materials with silver, gold, and platinum group metals. In principle, it is also possible with the method according to the invention to provide and connect metallic substrates with ceramic layers.

An example of composite material with only different macroscopic structures is a copper plate that has been coated with metallic copper granulate and a porous surface layer has been formed.

Such a composite material has the mechanical strength of the base / or carrier material. The porous surface layer can be used for the later

Soak use with liquids so that the cavities of the surface layer are filled with them and the properties of the surface are modified compared to the carrier material. Shaped bodies with surfaces modified in this way are, for example, as Self-lubricating slide filters can be used if lubricants are stored in the porous structure. The person skilled in the art has no difficulty in transferring the basic principle of the treatment to materials other than those mentioned by way of example and thus increasing the applicability of the method according to the invention.

It is crucial for this embodiment of the method according to the invention that the energy introduced by sound, in particular ultrasound and converted into heat by friction at the contact surfaces of the particles acts on the material and that the particles are firmly bonded to one another by fusing or gluing the contact points .

By means of the method according to the invention, porous material parts can be produced particularly inexpensively, which, if necessary, can also be subjected to a thermal aftertreatment if this is necessary because of the special properties of the material and leads to a further improvement in the strength or other properties of the moldings. For example, so-called green bodies can be produced by pure compression and then subjected to the usual sintering or post-treatment steps. However, it is particularly preferred to bring about the connection directly through the action of pressure and sound energy, so that post-treatments can be dispensed with.

Examples of material parts that can be produced according to one embodiment of the method according to the invention are, in particular, porous plastic, sintered metal, ceramic or carbon molded parts such as bearings, seals and others. The invention The method is generally also suitable for the production of complicated molded parts, such as bearings with complicated shapes that could not be produced with the previous pressing technologies.

When adjusting the frequency and amplitude of the sound, frequencies in the range of 10 kHz, preferably above 15 kHz, are used. Frequencies between 20 and 40 kHz or 20 to 60 kHz are particularly preferred. The amplitudes are between 5 and 100 μm, preferably in the range from 10 to 40 μm. The pressure to be exerted at the same time is between 10 and 10 ⁴ N / cm ² , preferably from 50 to 1500 N / cm ² . Pressures of 200 to 1000 N / cm ² are particularly suitable.

The invention also includes a device for carrying out the method according to the invention. This device for treating particulate material with a molding space for the material to be treated has a die and an upper punch and a lower punch, both of which are designed to be movable in a cavity of the die. A Scha 11 generator and a sound converter are also available. The characteristic of the device according to the invention is that either the lower stamp or the upper stamp or both stamps are designed as oscillating bodies. They are exposed to sound with a frequency of 10 to 100 kHz from the Scha 11 converter. The upper and lower punches are designed to be movable towards and away from one another in the die in order to exert simultaneously on the material with sound and a pressure of 10 to 10,000 N / cm ² . The holder of the die and the movable upper and lower punches are more conventional with those Comparable presses, ie dies and adapters have a similar structure to the known presses. The upper stamp or the lower stamp or, if applicable, both stamps are adapted to the vibration system. Both upper and lower temperature sensors and a stepper motor or other length measuring system can be moved precisely to certain positions. The tracking of the stamp from a certain position takes place automatically, ie the stamp is slightly pre-tensioned by means of a suitable device, such as a compressed air cylinder. This path is thus given as a fixed path. Press path corrections are possible using stepper motors. The exact setting via stepper motors is carried out by means of a crank screw drive or similar systems. Sound must not be transmitted to these parts of the apparatus.

In principle, it is possible to combine several treatment stations and to apply the acoustic energy to the vibrating bodies from a frequency generator via corresponding converters.

The frequency of the sound lenergie can basically vary in the specified range and also if necessary during a pressing process z. B. can be changed in an optimized manner, if necessary to improve the coordination to the elastic modulus or modulus of the materials during the phase of connecting the particles to one another.

The invention will now be explained in more detail with reference to the figures.

FIG. 1 schematically shows a device for compacting and sintering the powdery, pasty materials or granules with a die (1) trained mold space, which can be closed by an upper stamp (3) and a lower stamp (2). The upper and lower punches (2, 3) are arranged so that they can be moved individually or both into and out of the free interior of the die. The stamp (2) is a conventional stamp as is usually used in presses. The stamp (3) is designed as a vibrating body in order to be able to apply a vibration to the material (4) arranged in the mold space of the die (1). The outer edges of the punches (2, 3) lie close to the inner wall of the die. The position of the punches (2, 3) relative to the die is set by means of hydraulic, pneumatic, electrical or mechanical movement devices (8), for example with cylinders which act on the lower and upper punches. The piston rod (9) of the lower movement device (8) acts on the conventionally designed lower punch (2) as in known presses. The upper punch (3) designed as a vibrating body is connected to an amplifier (5) which is held by a carrier (7). The movement device (8) engages by means of a fixed connection or coupling of the cylinder (8) to the carrier (7). Above the amplifier (5) and connected to it, a vibration generator (5) is arranged, which serves as a source for the excitation of the upper punch (3) designed as a vibrating body.

Figure 2 shows schematically another embodiment of the device for compacting and sintering, in which the lower punch (2) is designed as a vibrating body and the upper punch (3) is a conventional press punch, both of which are movable into and out of the interior of the die (1) are arranged. The upper stamp (3) is connected via the piston rod (9) to the movement device (8), which can be a cylinder, for example. The lower movement device (8) is connected or coupled to the carrier (7) in order to be able to move it relative to the die (1). The lower punch designed as a vibrating body is connected to an amplifier (5) which is held by the carrier (7). The amplifier (5) is connected to a vibration generator (6).

The embodiment shown schematically in FIG. 3 differs from that of FIGS. 1 and 2 in that both the upper punch (3) and the lower punch (2) are designed as oscillating bodies which are arranged to be movable relative to the die (1). The movement devices (8) are connected to carriers (7), which each hold the amplifier (5). The vibration generators (6) are connected to the vibrating bodies (2, 3) via the amplifiers (5) and can excite them.

FIG. 4 shows schematically and enlarges the structure of the material created by the method according to the invention. The edge zones of the material parts 1 (16) are more or less intimately connected without the particle structure with voids between the particles being completely eliminated.

However, as is shown schematically in FIG. 5, the method according to the invention is also suitable for connecting different materials (18, 19) to one another in their edge zones and for producing alloy-like structures in the connection region (17). Instead of such structures and connection areas in layer form, a composite structure is also through direct mixing of different materials and their connection possible.

FIGS. 6 and 7 show exemplary embodiments of shaped bodies which can be produced using the method according to the invention. FIG. 6 shows a molded body (flange bearing) (20) with a smooth outer surface (10) and a circumferential flange (11) and broken edges (12), as well as a smooth inner surface (13). Such bushings can be easily produced with appropriately designed matrices and stamps which engage in them. However, more complex forms, as shown, for example, in FIG. 7, can also be produced using the method according to the invention. This molded body (21) has undercuts (14) and openings (15) through the wall jacket between the edges below the peripheral edges (22). Shaped bodies of this type can be produced better with the method according to the invention using appropriate tools than by known methods of pressing or sintering.

Claims

Patent claims - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1. A process for the production of moldings by compressing part-shaped material made of plastic, carbon, metal or ceramic by simultaneously treating the material enclosed in a mold cavity with a pressure between 10 N / cm ² and 10 ⁴ N / cm ² and sound Frequency from 10 to 100 kHertz, characterized in that the amplitude of the Scha 11 energy is 5 to 100 µm and on its frequency and on the elastic modulus of the material to be treated according to the formulas t Λ ± L¬ X and _ k in which ⋏ the wavelength of the sound energy, Δ L the amplitude, V the speed of sound in the material, f the frequency, ε the elongation of the material mean that the sound energy introduced is in the form of shock waves on the material to be compressed and by friction energy converted into heat act on the contact surfaces of the particles and a firm connection of the particles to one another is produced by fusing or gluing the contact points. 2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that one connects different Tei 1 plate-shaped materials at their contact surfaces with each other. 3. Use of the method according to claim 2 for the production of molded parts from composite materials. 4. Device for the treatment of particulate material, with a mold space for the material to be treated, the lower punch designed to move towards and away from one another from a die (1) (2) and upper punch (3) is formed to exert a pressure of 10 N / cm ² to 10 ⁴ N / cm ² on the material, with a vibration generator (6) for sound waves of the frequency from 10 to 100 kHertz and an amplifier (5), characterized in that either the lower stamp (2) or the upper stamp (3) or both are designed as vibrating bodies which can be subjected to sound from the amplifier (5), and the vibrating bodies generated in the vibrating body or bodies Ultrasound energy can act as shock waves on the material to be treated in such a way that the compacted material combines at the contact surfaces of the particles.