Parts for use in rotary gear pump

Abstract: A drive gear (2) and a driven gear (3) for use in a rotary gear pump exhibiting good sliding characteristics against a pump case (4) made of light metals such as alumi­ num alloys. One or both parts are formed from an aluminum alloy material obtained by subjecting an aluminum alloy powder which has been rapidly solidified at a cooling rate of 100°C/sec or more, or aluminum alloy powder having a particle size of 350µm or less, to powder compaction fol­ lowed by hot extrusion and optionally hot forging, or alternatively to powder forging.

Description: The present invention relates to parts for use in a rotary gear pump exhibiting good sliding characteristics against a pump case formed of light metals, such as aluminum alloys, and in particular to parts, such as driven gear and drive gear, for use in a rotary gear pump obtained by extrusion of aluminum alloy powders, which have been rapidly solidified, and/or by powder forging. A drive gear (inner rotor) and a driven gear (outer rotor) in a rotary gear pump have commonly both been formed of the same kind of iron material. Such gear pumps have tended to give rise to difficulties such as increased noise and loss of motive power during operation. It has been pointed out that noises produced when the driven gear is engaged with the drive gear are particularly loud. In addition, the loss of motive power results from an increase in torque required during the operation. These disadvantages have been seen mainly in terms of the toothed shape of the driven gear and drive gear and of errors in this toothed shape. Accordingly, also counter-measures against these problems have also been considered largely in terms of the tooth shape, so that no effective solution has been achieved. JP-A-60-128983 discloses the use of light metals, such as aluminum alloys, and sintered alloys, such as ceramics, having small specific densities as one method of reducing the weight of the driving and driven gears, and thus reducing noise and motive power loss. JP-A-63-213604 discloses a process for producing an Aℓ-Si alloy member having a surface layer with high wear resistance and an inner layer integral therewith, by subjecting a shaped body of a composite Aℓ/Si powder, having a larger Si grain size near the surface than near the centre, to violent plastic working by hot extrusion. In pumps having an iron case, the conventional drive gear and driven gear formed of sintered aluminum alloys are superior in abrasion and sliding characteristics, but if the pump case is formed of a light metal such as an aluminum alloy, to reduce its weight, the pump case tends to stick to the driven gear, resulting in increased abrasion and impaired sliding characteristics. A similar problem is liable to occur between the driven gear and the drive gear. The present invention consists in a part for use in a rotary gear pump, such as a driven gear having good sliding characteristics against a pump case made of light metal or a drive gear having good sliding characteristics against said driven gear, said part being formed from an aluminum alloy powder characterised in that said alloy material is obtained by subjecting aluminum alloy powder, which has been rapidly solidified at a cooling rate of 100°C/sec or more, and has a particle size of 350µm or less, to powder forging or to powder compaction followed by hot extrusion. The invention also provides a pair of aluminum alloy parts for use in a rotary gear pump, such as a driven gear and a drive gear, wherein one said part is as defined above and made by subjecting the rapidly solidified aluminum alloy powder to powder compaction, then to hot extrusion and then to hot forging, and the other part is formed of an aluminum alloy obtained by melting. Preferred embodiments of the invention will now be described with reference to the accompanying drawings wherein: FIG. 1 is a plan view showing an inscribed type trochoidal toothed pump; and FIG. 2 is a plan view showing a driven gear composed of two layers formed of different materials. Referring to the drawings in detail, Fig. 1 is a plan view showing an inscribed type trochoidal toothed pump as one example of a rotary gear pump. In this rotary gear pump, a drive gear (inner rotor) 2 is driven by a drive shaft 1 and a driven gear (outer rotor) 3 is driven with the drive of said drive gear 2. This driven gear 3 is housed in a space formed in a pump case 4. A fluid is sucked through a suction port (not shown) and discharged through an exhaust port by the rotation of the drive gear 2 and the driven gear 3. According to one embodiment of the present invention, materials are prepared by the use of aluminum alloy powders, which have been rapidly solidified, and the driven gear and drive gear are produced from these materials. The aluminum alloy powders, which have been rapidly solidified, are usually produced by the atomizing method. In the air atomizing method, the cooling rate is 100°C/sec or more. Or, if aluminum alloy powders have particle diameters of 350µm or less, they are powders which have been rapidly solidified. It is preferable if the cooling rate is 1000°C/sec or more and the particle diameter is 150µm or less. Aluminum alloys with a large proportion of alloying component added, which have not hitherto been obtained by usual materials (cast materials, wrought materials) obtained by ingot metallurgical process, can be obtained by rapid solidification. In addition, a uniform and fine structure can be obtained. For example, in order to improve the Al-Al sliding characteristics, alloys containing Si in a quantity of 11 to 42% and transition metals, such as Fe and Ni, in a quantity of 1 to 12% can be obtained. Si crystals and intermetallic compounds of these alloys (powder-extruded materials and powder-forged materials) have sizes of 20 µm or less. Accordingly, these alloys exhibit both a high abrasion and wear resistance, high Young's modulus and low thermal expansion coefficient due to a high content of alloy elements and superior mechanical properties, such as high strength and high heat resistance, and a superior machinability due to the absence of segregation and uniform and fine microstructure in spite of a high content of alloy elements. Also the above described alloys with hard particles and self-lubricating particles dispersed therein can be produced depending upon the conditions under which they are used. In order to improve the sliding characteristics against the light metals, such as aluminum against that of the pump case, a quantity of A l atoms on the sliding surface which have high mutual cohesiveness is reduced as far as possible. That is to say, alloys containing a large amount of covalent-bonding Si crystal and intermetallic compound (A l ₃Fe, A l ₃Ni and the like) are obtained. However, the conventional aluminum allous have contained Si in a quantity of at most 12% and if the cast product is simple in shape, they have contained Si in a quantity of at most 17% and Fe in a quantity of at most 1%. It is a method of producing materials by the use of aluminum alloy powders, which have been rapidly solidified, that has overcome these alloys limitations in the quantities of Si and transition metals such as Fe. The aluminum alloy powders, which have been rapidly solidified, are subjected to powder compaction to form a billet which is subjected to the hot extrusion to obtain the material. The materials can also be obtained by molding the powders in a die cavity, removing the binder and then subjecting the powder compacting to the hot powder forging. In every case, the near net shape can be obtained but the dimensional accuracy is not satisfactory, so that subsequent machining is required. In every case of the powder extrusion method and the powder forging method, as shown in Fig. 2, particularly in the driven gear 3, a side 3a brought into contact with the pump case and a side 3b brought into contact with the drive gear can be formed of materials congenial to the respective other parts in a double-layer structure. In addition, the materials are in powder form, so that a powder mixture comprising two or more different kinds of powder, which have been rapidly solidified, a powder mixture with ceramics particles, such as A l ₂O₃ powders, SiO₂ powders, Si₃N₄ powders and SiC powders, added, a powder mixture with self-lubricating particles, such as graphite, BN and MoS₂, added or mixtures comprising all the above described materials can be prepared by powder extrusion and powder forging. It goes without saying that in the event that the required characteristics are not satisfied even by the use of the aluminum alloy powders, which have been rapidly solidified, surface treatments similar to those used for the conventional aluminum alloys, for example an anodizing treatment, a plating treatment or coating with fluorine resins, can be adopted. In this case, the thermal expansion coefficient of the materials obtained by the powder extrusion and the powder forging is reduced to that of iron owing to the high content of Si added. Various characteristics, such as the high Young's modulus, the high strength in spite of a high content of alloy elements and the good machinability, are kept. The present invention will be further described with reference to the specific examples. The respective combinations of the driven gear 3 and the drive gear 2 formed of the materials shown in Table 1 and having an outside diameter of 80 mm and a wall thickness of 10 mm were subjected to the pump test for 20 hours at 4,000 rpm. After the test, the surface state was investigated, showing that a remarkably good surface state is obtained when the driven gear and drive gear according to the present invention are used. As above described, according to the present invention, the sliding characteristics between the pump case and the driven gear and the sliding characteristics between the driven gear and the drive gear can be remarkably improved by forming the driven gear and the drive gear of the materials obtained by subjecting the aluminum alloy powders, which have been rapidly solidified and have particle sizes of 350µm or less, to powder forging or to compaction followed by hot extrusion and optionally further hot forging.

Claims: A part for use in a rotary gear pump, such as a driven gear (3) having good sliding characteristics against a pump case (4) made of light metal or a drive gear (2) having good sliding characteristics against said driven gear, said part (2, 3, 4) being formed from an aluminum powder alloy characterised in that said alloy material is obtained by subjecting aluminum alloy powder, which has been rapidly solidified at a cooling rate of 100°C/sec or more, and has a particle size of 350µm or less, to powder forging or powder compaction followed by hot extrusion. A part according to claim 1 wherein said aluminum alloy powder has a silicon content of 11 to 42%. A part according to claim 1 or claim 2, wherein said aluminum alloy powder contains ceramics particles as hard particles and/or graphite particles as self-lubricating particles. A part according to any preceding claim wherein said aluminum alloy has a transition metal content of 1 to 12%. A part according to any preceding claim, which has an anodized surface. A part according to any one of claims 1 to 4, which has a plated surface. A part according to any one of claims 1 to 4, which has a surface coated with fluorinated resin. A part according to any preceding claim made by subjecting the rapidly solidified aluminium alloy powder to the powder compaction treatment followed by hot extrusion, and thereafter to hot forging. A part according to claim 8 in combination with another rotary gear pump part formed of an aluminium alloy obtained by melting.

Inventors: AKECHI KIYOAKI C O ITAMI WORKS, AKECHI, KIYOAKI C/O ITAMI WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1989
Main classification: F04C2
IPC codes: F04C2