Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
2000-12-28
2002-09-17
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C419S064000, C419S065000, C419S066000
Reexamination Certificate
active
06451082
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention is directed to iron-based powder compositions for use in powder metallurgy.
2. Description of Related Art
In general, an iron-based powder composition for powder metallurgy is produced by mixing an iron powder with an alloying powder such as copper powder, graphite powder or iron phosphide powder, and where needed, with a cutting improver powder, and a lubricant such as zinc stearate, aluminum stearate or lead stearate. Such a lubricant has heretofore been chosen by taking into account miscibility with metallic powder and freedom from elimination during sintering.
Recently, a growing demand has been made for the development of sintered materials with great strength. To cope with this trend, warm molding techniques have been proposed, which can form a molding having high density and great strength by molding a metallic powder with heating, as disclosed in Japanese Unexamined Patent Application Publication No. 2-156002 and Japanese Examined Patent Application Publication No. 7-103404 and U.S. Pat. Nos. 5,256,185 and 5,368,630. With regard to lubricants to be used in these molding techniques, importance is further placed on lubricity during heating in addition to the requirements of miscibility with metallic powder and freedom from elimination during sintering.
Namely, when being partly or wholly dissolved during warm molding, a lubricant needs to be uniformly dispersed in between the particles of a metallic powder. This brings about reduced friction resistance between the metallic particles and between the resultant compact and the corresponding die, consequently leading to improved compactibility.
However, the above-mentioned metallic powder composition has a first drawback that it causes undesirable segregation in its starting mixture containing an alloying powder and the like, and a second drawback that it suffers poor flowability during warming.
To alleviate the first drawback, i.e., to prevent the metallic powder composition from being segregated, a technique is known which employs a binding agent, as disclosed in Japanese Unexamined Patent Application Publication Nos. 56-136901 and 58-28321. However, when the binder is added in large amounts in preventing the metallic powder composition sufficiently from segregation, another problem arises that the powder composition becomes less flowable.
The present inventors have previously proposed to use as a binder a metallic soap or a composite melt composed of wax and oil, as disclosed in Japanese Unexamined Patent Application Publication Nos. 1-165701 and 2-47201. These techniques are capable of reducing segregation and dusting in a metallic powder composition to a markedly great extent, thus imparting improved flowability to the powder composition. But, the techniques are considered unsatisfactory in that the flowability of the powder composition becomes worse with time due to the means provided above for preventing the problem of segregation.
For that reason, the present inventors have further proposed that a high-melting composite melt composed of an oil and a metallic soap be used as a binding agent, as disclosed in Japanese Unexamined Patent Application Publication No. 2-57602. This technique has the advantage that such a composite melt does not vary significantly flowability with time, allowing the stock powder composition to be less susceptible to flowability variation even after a lapse of time. In such an instance, however, there is posed another problem that the powder composition becomes varied with respect to apparent density because an iron-based powder is mixed with a saturated fatty acid that has a high melting point and is solid at room temperature and with a metallic soap.
In an effort to solve this problem, the present inventors have proposed a technique in which an iron-based powder is coated on its surface with a fatty acid, followed by bonding additives to the coated surface of that powder with the aid of a composite melt composed of a fatty acid and a metallic soap, and by successive application of a metallic soap to the coated bonded surface of the iron-based powder. This technique is described in Japanese Unexamined Patent Application Publication No. 3-162502.
Segregation, dusting and other problems have been appreciably alleviated by virtue of the techniques disclosed in Japanese Unexamined Patent Application Publication Nos. 2-57602 and 3-162502, both of which are described above. However, these techniques provide no satisfactory solution to flowability. This is particularly true of flowability during heating in so-called warm compaction in which a powder composition after being heated up to about 150° C. is filled in a die heated at a similar temperature and then is compacted.
Also, in the techniques of Japanese Unexamined Patent Application Publication No. 2-156002, Japanese Examined Patent Application Publication No. 7-103404 and U.S. Pat. Nos. 5,256,185 and 5,368,630 which, as cited above, are designed to improve compactibility in warm compaction, a metallic powder composition suffers from poor flowability during warming because a low-melting lubricant component forms wet crosslinking in between the metallic particles. Insufficient flowability makes compacting less productive, and moreover, causes irregular density in the compacts, which in some cases gives a sintered product having varied properties.
With regard to insufficient flowability of a metallic powder composition during warming that is described above as the second drawback, the present inventors have proposed processes for producing an iron-based powder composition, which are disclosed in Japanese Unexamined Patent Application Publications Nos. 9-104901 and 10-3 17001. Each such process permits an alloying powder to be free of segregation during warming and also permits a metallic powder composition to be more highly flowable during warming.
In the above processes, the alloying powder can be prevented from being segregated during warming, and the metallic powder composition can be improved in respect of flowability during warming, which effects are attained by the steps of coating at least one of an iron-based powder and an alloying powder with a surface-treating agent; mixing the iron-based powder and alloying powder with lubricants such as a fatty acid, a fatty acid amide and a metallic soap; after mixing, heating the resultant mixture at a temperature higher than the melting point of at least one of the lubricants, thereby melting at least one lubricant; cooling the mixture with stirring, thereby bonding an alloying powder to the surface of the iron-based powder; and, after further cooling, incorporating the cooled mixture with lubricants such as a fatty acid, a fatty acid amide and a metallic soap.
According to the techniques of Japanese Unexamined Patent Application Publication Nos. 9-104901 and 10-317001 both cited above, the flowability of the iron-based powder mixture in warm compaction is remarkably improved. From studies made by the present inventors, it has been presumed that such a desirable effect could be obtained by coating the surfaces of an iron-based powder and an alloying powder with a surface-treating agent composed of an organic component, thus decreasing the potential difference between the associated lubricants of low electric conductivity and the surface of the iron-based powder or alloying powder of high electric conductivity. This reduces the possibility of the iron-based powder or alloying powder sticking to the lubricants by contact electrification and enhances the possibility of the iron-based powder and alloying powder becoming wettable with the molten lubricants in a warm region. Unfavorably, however, such an iron-based powder composition is less flowable at relatively high temperatures. To ensure high flowability during warm compaction, the temperatures of the iron-based powder and the corresponding die should be strictly controlled. According to studies made by the present inventors, the insufficient flowability at relatively high temperatures
Ogura Kuniaki
Ozaki Yukiko
Uenosono Satoshi
Kawasaki Steel Corporation
Mai Ngoclan
Oliff & Berridg,e PLC
LandOfFree
Iron-based powder mixture for powder metallurgy, process for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Iron-based powder mixture for powder metallurgy, process for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Iron-based powder mixture for powder metallurgy, process for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2894287