US20030185698A1

US20030185698A1 - Manufacturing technique of powder metallurgy

Info

Publication number: US20030185698A1
Application number: US10/392,937
Authority: US
Inventors: Jenn-Shing Wang; Wen-Hao Lin; Chih-Cheng Chen
Original assignee: Individual
Current assignee: Far East University
Priority date: 2002-03-28
Filing date: 2003-03-21
Publication date: 2003-10-02
Also published as: TW534845B

Abstract

The manufacturing technique for powder metallurgy of the invention includes the steps of: mixing ceramic powder with binders, fillings or lubricants for casting a body; forming a microwave-absorbent body using molding, extrusion, forging, injection or doctor blade; placing the body into a microwave oven for heating and debinding; placing the half-finished product after debinding in a sintering oven for sintering the debinded half-finished product; and finally obtaining a finished product after sintering and temperature lowering.

Description

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The invention relates to a manufacturing technique of powder metallurgy, and more particularly, to a manufacturing technique of powder metallurgy for accelerating the production procedure, and reducing equipment and resource cost thereof, as well as being capable of quickly drying and removing binders, fillings or lubricants in order to suit ceramic material fabrications.

(b) Description of the Prior Art

In common manufacturing processes of powder metallurgy, in order to facilitate ceramic powder to form a green body more easily, macromolecules are frequently added as a forming additive. Such type of forming additives includes binders, surfactants, fillings or lubricants. The forming additives are mixed with macromolecules for casting bodies that may be formed by such as molding, forging, extrusion, injection molding or doctor blade methods. Then the green bodies are placed into furnaces for debinding as the next step.

Injection molding from ceramic powder possess properties of general plastic injections, and are materials that can be used with high efficiency. When injection moldings from ceramic powder are adopted for products having complicated shapes in mass production, the products have relatively better microstructures because sizes thereof are evenly contracted. Therefore, the injection molding products approach near net shapes or net shapes, and do not require a great amount of subsequent processing, and thus significantly saving production cost thereof by reducing the processing expenses. However, the binder used come as high as 30 vol%, and defects incurred are prone to arise during removing macromolecules in the debinding process; to be more precise, the debinding process stands as a rather major manufacturing process.

In the present invention, issues like green body forming, sintering, materials of powder, or ingredients of additives shall not be discussed. Instead, the invention is targeted at providing another method for the debinding step in the manufacturing process.

As described above, common debinding processes currently used include solvent debinding and thermal debinding, wherein:

1. Solvent debinding is implemented by the steps of dipping a body into a solvent, and extracting dissolvable binders, fillings, surfactants or lubricants from the body. However, such means of solvent debinding brings about environmental and recycling issues and thus further increases the processing expense thereof.

2. Thermal debinding is implemented by the steps of placing a body into a furnace, and eliminating any binders using a high temperature to remove binders, fillings, surfactants, lubricants or macromolecules in sequence. This method may be used to remove binders directly or after solvent debinding with only human-friendly gases produced that give no environmental, recycling or human-hazardous issues as the solvent debinding, and is therefore the most extensively applied debinding process. Nevertheless, it is necessary to pre-heat the furnaces to a temperature required for thermal debinding, meaning that the time and energy of pre-heating and the energy consumed during maintaining the heat sum up to considerable amounts of money, and thus resulting in an efficiency problem often abstained by the manufacturing process. Also, defects are prone to occur during the time-consuming thermal debinding process, and hence reforms with respect to the above shortcomings can yet be advanced.

Furthermore, the modern times is an environmental-friendly era, especially regarding to uses and recycling of resources. It shall be taken into consideration that chemical solvent, which is non-eco-friendly and is limited to a certain number of times to be used, is adopted for solvent debinding; and furnaces employed for thermal debinding are quite energy consuming. Therefore, it is a vital task as how to provide a manufacturing technique for debinding capable of rapidly accomplishing the debinding process and reducing resource wastage, as well as being environmental-friendly.

With respect of the aforesaid shortcomings, domestic and international patent publications or related information are taken into reference. Referring to Patent Publication No. 333482, “Manufacturing Process for Carbon Chromium/Aluminum Oxide Ceramic Devices Having Complicated Shapes Using Injection Molding Technique”, it is observed that several defects are derived from the debinding process thereof:

1. The furnaces are troublesome and time-consuming in raising and lowering the temperatures thereof. The production cost can be reduced and the manufacturing efficiency can be elevated if the time of heating from room temperature to a temperature required for debinding and lowering temperature after debinding completed can be shortened.

2. Energy cannot be concentrated entirely on the body. During heating of a common furnace, a major part of the energy is absorbed through the furnace body and dissipated into the atmosphere, and thus leaving as little as 30 percent of the original energy for debinding the body. It is indeed uneconomical to waste such great amounts of energy for merely achieving the purpose of debinding.

3. Common furnaces take up large spaces for that they are massive in volume and heavy in weight, and difficulties may arise for moving such furnaces, thus lacking mobility.

4. Furnaces have high equipment cost. Expense burdens and maintenance fees thereof may be worsened by problems and shortening of lifespan of heating bodies and heat-resistant materials caused by any contamination of binder decompositions in the furnaces.

5. Chemical solvents are limited to certain expiration periods. In solvent debinding, chemical extraction properties of chemical solvents are inevitably lowered after using for a period of time or when increasing the number of bodies. Besides, expired chemical solvents may become another environmental dilemma.

In addition, referring to Patent Publication No. 167524 disclosing a method for thermal processing unstable ceramics using microwave, wherein microwave technique is applied during the sintering process of ceramics. In the prior invention, a microwave sensor is formed from an appropriate powder bed that is characterized regarding to heating, protection, deoxidization and thermal conductance as required. However, the characteristics are provided for the requirements of the “sintering” process of ceramics; that is, this prior invention confers nothing upon the “debinding” process of ceramic bodies before the sintering process. Therefore, the shortcomings of the aforesaid debinding means (solvent debinding and thermal debinding) are not resolved by the Patent Publication No. 167524.

Conclusive from the above, as described by shortcomings and issues of the conventional debinding means, the handling of the solvent used are troublesome, uneconomical and non-eco-friendly, and furnaces adopted for thermal debinding are time-consuming for heating and temperature lowering. Therefore, it is a vital task of the invention as how to provide a manufacturing technique for powder metallurgy capable of overcoming the prior disadvantages such as having high production and equipment cost, lack of mobility and being unable to concentrate energy.

SUMMARY OF THE INVENTION

The primary object of the invention is to provide manufacturing technique capable of accelerating production procedure, reducing production cost, and rapidly drying and removing binders, fillings or lubricants. The technique is suitable for debinding of cast bodies after powder materials are mixed with binders, fillings or lubricants, and is able to avoid energy waste in heating and temperature lowering as well as keeping away from being bulky in size.

Another object of the invention is to provide manufacturing equipment and method for elevating manufacturing efficiency by shortening the time of heating and temperature lowering.

Another object of the invention is to provide manufacturing equipment and method with energy concentration for saving energy.

The other object of the invention is to provide manufacturing equipment and method with low equipment cost and mobility for reducing production cost and facilitating the moving thereof.

To better understand the manufacturing process and functions of the present invention, descriptions shall be given with the accompanying drawings below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic drawing illustrating the manufacturing process according to the invention. [0024]
FIG. 2 shows a comparison diagram illustrating the time required for heating to sintering temperatures of the invention and a prior art. [0025]
FIG. 3 shows a comparison table illustrating the compressive resistance of relative densities after sintering by the present invention and a prior art. [0026]
FIG. 4 shows manufacturing flow diagrams for comparing time required for debinding in the present invention and a prior art.[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the manufacturing method implementing the manufacturing technique for powder metallurgy according to the invention comprises the steps of: [0028]
a. forming a [0029] body 1; the body 1 is formed by mixing ceramic powder with binders, fillings or lubricants, and then by performing cast methods such as molding, extrusion, injection or scraping;
b. heating and debinding; the [0030] body 1 is embedded into a non microwave-absorbent medium 2 placed in a crucible 3 so as to promote capillarity thereof using the medium 2, and is then placed into a microwave oven 4 for heating and debinding according to time and temperature required for heating and debinding;
c. sintering; a half-[0031] finished product 4 is put in a sintering oven 6 for sintering the degreased, half-finished product 4;
d. finishing product; temperature is lowered according to general procedures, and a [0032] finished product 7 is obtained from the originally half-finished product 5 placed in the sintering oven 6.
According to the invention, the technique provided lies mainly in the heating and debinding stage, and the characteristics thereof are: [0033]
before entering the debinding process, the microwave-[0034] absorbent body 1 is placed in the microwave oven 4 and debinded by using adjusted microwave frequency required, and direct observations through a window may be carried out during the debinding process; in addition, the degreased half-finished product 5 using microwave or a degreased body obtained by other methods is directly heated to the sintering temperature using microwave, and is then placed into the sintering oven 6 after having reached the sintering temperature or sintered directly by microwave, and thus saving time and resources for gradual heating; referring to FIGS. 2 showing a comparison diagram illustrating the time required for heating to sintering temperatures of the invention and a prior art, and FIG. 3, tests at sintering temperatures 1400°0 C. and 145020 C. are performed for a duration of two hours, and when comparing the relative densities of the present invention to the prior art, it is clearly observed that the product from the invention has excellent sintering densities; also, referring to FIG. 4 showing time differences for debinding in the manufacturing process, the time for debinding according to the invention is merely half of that of the prior art, and thus effectively reducing the production time thereof.
It is perceived from the above that, the appeal according to the invention is aimed at heating by microwave for accomplishing the debinding process. The technique provided by the invention is capable of overcoming disadvantages existing in the prior art: 1. inconvenient heating and temperature lowering of furnaces, and lengthened production time; 2. distracted heating energy, and uneconomical; 3. furnaces bulky in size with poor mobility; 4. inefficiency and environmental issues of chemical solvent. According to the invention, the method and equipment provided are able to accelerate production process, reduce production cost, rapidly remove binders, fillings or lubricants, as well as being environmental friendly for that the medium can be used for absorbing microwave for a multiple of times. Therefore, the invention is totally suitable for debinding process of cast bodies from mixing ceramic powder with binders, fillings or lubricants. [0035]
In addition, the microwave-absorbent cast bodies mentioned above, the ceramic powder contained therein may be carbon, carbide, nitride, titanate, oxide, sulfide or a compound: wherein the carbide may be SiC, TiC or WC; the nitride may be TiN, AIN or Si[0036] ₃N₄; the titanate may be barium titanate, calcium titanate, strontium titanate or lead titanate; the oxide may be NiO, CoO, CaMnO₃, LaMnO₃, SnO₂, TiO₂, MgWO₄, MgO, NiO, SrTiO₃or SrZrO₃; the sulfide may be FeS or MnS; the compound may be Fe₂O₃—MeO, wherein the Fe₂O₃may be mixed with NiO, CoO, MoO, MgO, ZnO, CuO, Li₂O, CaO, FeO, B₂O, PbO, SrO, La₂O₃, Cr₂O₃, SnO₂or WO₃, and NiO, CoO, MoO, MgO, ZnO, CuO, Li₂O, CaO, FeO, B₂O, PbO, SrO, La₂O₃, Cr₂O₃, SnO₂or WO₃may be used independently or mixed with others; in addition, the aforesaid nitride may be added with compounds such as Li₂O, La₂O₃, CaO, SrO, TiO₂, Sb₂O₅, Ta₂O₅or Cr₂O₃.
It is of course to be understood that the embodiment described herein is merely illustrative of the principles of the invention and that a wide variety of modifications thereto may be effected by persons skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims. [0037]

Claims

What is claimed is:

1. A manufacturing technique for powder metallurgy comprising the steps of: mixing ceramic powder with binders, fillings or lubricants for casting a body; forming a microwave-absorbent body using molding, extrusion, forging, injection or doctor blade; placing the body into a microwave oven for heating and debinding; placing the half-finished product after debinding in a sintering oven for sintering the debinded half-finished product; obtaining a finished product after sintering and temperature lowering; and the characteristics thereof are:

before the body enters the debinding process, the body is placed in a microwave-absorbent medium, and the body along with the medium are placed in the microwave and debinded with adjusted temperature and time required.

2. The manufacturing technique for powder metallurgy in accordance with claim 1, wherein the half-finished body after debinding or a debinded body acquired from other methods is directly placed in the microwave oven for heating to the sintering temperature, and is put in a sintering oven having reached the sintering temperature for sinetering therein using microwave.

3. The manufacturing technique for powder metallurgy in accordance with claim 1, wherein ceramic microwave-absorbent medium containing the microwave-absorbent body is powder mainly made of carbon, carbide, nitride, nitanate, oxide, sulfide or a compound.

4. The manufacturing technique for powder metallurgy in accordance with claim 3, wherein the carbide is SiC, TiC or WC.

5. The manufacturing technique for powder metallurgy in accordance with claim 3, wherein the nitride is TiN, AlN or Si₃N₄.

6. The manufacturing technique for powder metallurgy in accordance with claim 3, wherein the titanate is barium titanate, calcium titanate, strontium titanate or lead titanate.

7. The manufacturing technique for powder metallurgy in accordance with claim 3, wherein the oxide is NiO, CoO, CaMnO₃, LaMnO₃, SnO₂, TiO₂, MgWO₄, MgO, NiO, SrTiO₃or SrZrO₃, ZrO₂or CaO.

8. The manufacturing technique for powder metallurgy in accordance with claim 3, wherein the oxide is added with compounds such as Li₂O, La₂O₃, CaO, SrO, TiO₂, Sb₂O₅, Ta₂O₅or Cr₂O₃or ZnO.

9. The manufacturing technique for powder metallurgy in accordance with claim 3, wherein the sulfide is FeS or MnS.

10. The manufacturing technique for powder metallurgy in accordance with claim 3, wherein the compound is Fe₂O₃—MeO.

11. The manufacturing technique for powder metallurgy in accordance with claim 3, wherein the compound is Fe₂O₃—MeO, and the Fe₂O₃may be mixed with NiO, CoO, MoO, MgO, ZnO, CuO, Li₂O, CaO, FeO, B₂O, PbO, SrO, La₂O₃, Cr2O₃, SnO₂or WO₃.

12. The manufacturing technique for powder metallurgy in accordance with claim 3, wherein the NiO, CoO, MoO, MgO, ZnO, CuO, Li₂O, CaO, FeO, B₂O, PbO, SrO, La₂O₃, Cr₂O₃, SnO₂or WO₃may be used independently or mixed with others.

13. The manufacturing technique for powder metallurgy in accordance with claim 3, wherein ceramic microwave-absorbent medium containing the microwave-absorbent body may be compounds with any compound ratios from carbon, carbide, nitride, titanate, oxide, sulfide or a compound.

14. The manufacturing technique for powder metallurgy in accordance with claim 1, wherein the non microwave-absorbent medium is a compound having any compound ratio from Al₂O₃, SiO₂or ZrO.

15. The manufacturing technique for powder metallurgy in accordance with claim 1, wherein the macromolecules are binders, fillings or lubricant containing any from acrylic, ethyl cellulose, hydroxypropyl cellulose, polypropylene, polyacetal polymer, ethylene vinyl acetate, atactic polypropylene, styrene-butadienecoplymer, methylcellulose, polyethylene, oxidized polyethylene, cellulose acetate, nylon, polystyrenes, polybutylene, polysulfone, polyethylene, paraffin, wax, mineral oil, vegetable oil, fatty acid, fatty alcohols, fatty ester hydrocarbon wax, epoxy, polyphenylene, phenol, stearic acid, ester wax, oleic acid, diethyl phthalate, and formaldehyde.