JPS6312702B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention is suitable for precision casting, especially precision casting in which a suitable cavity is formed in a casting that is combined with a pre-formed member and placed in a mold, and the pre-formed member is integrally incorporated after casting. The present invention relates to a method for manufacturing a cast rotor with a ventilation duct for an induction motor using a water-soluble or water-disintegrable core. [Technical background of the invention and its problems] In general, cast rotors for induction motors are
As shown in the cross-sectional view of the figure, a core laminated block 5 in which disk-shaped core plates 4 having conductor holes are laminated with a ventilation gap (duct space) 11 in between is fixedly formed on the outer periphery of the rotor shaft 6. The conductor holes of the laminated block 5 are filled with conductors 12 penetrating in the axial direction, and short circuit rings 19 are provided at the upper and lower ends of the laminated block 5 to electrically connect the conductors 12.
is provided. Further, cooling vanes 18 are provided on the short circuit ring 19 as necessary. Cooling ventilation flows in from the side of the rotor shaft 6 as indicated by arrows in the figure and flows out through each ventilation gap 11. FIG. 6 shows an example of a cast rotor according to another embodiment. In this example, a ventilation hole 4a is formed in the iron core plate 4, and cooling air flows as shown by the arrow in the figure. do. Normally, monolithic casting using a core is often preferable in order to form an appropriate space in a complex-shaped casting. As one typical example, the present inventors have already proposed a method for manufacturing a cast rotor with a ventilation duct for an induction motor using a water-soluble core (Japanese Patent Laid-Open No. 70443/1983). That is, after core plates such as silicon steel plates are laminated and tightened, molten metal such as aluminum is injected into slots (conductor holes) formed by punched holes in the core plates to form a conductor. A method of manufacturing a rotor for a squirrel-cage induction motor (cast rotor) by integrally molding a short-circuit ring and cooling vanes is widely known. Generally, die casting method or low pressure casting method is used for casting. Among these cast rotors, for large-capacity induction motors, in order to increase the cooling efficiency of the rotor during motor operation, only a conductor is installed between the blocks of each laminated iron core plate. There is a cast rotor with a ventilation duct (cast rotor with ventilation duct) that has a space where the iron core plate is not present and is connected to the rotor. Conventionally, methods for forming this ventilation duct include casting molten conductive metal and then drilling holes for the ventilation gap, or forming thin steel plates shaped into the shape of the rotor slots (conductor holes) for the number of slots. A method in which a conductor metal is cast after welding to the core slot part to create a ventilation gap, a duct spacer is formed in advance using a low melting point metal and has a slot similar to the width of the ventilation duct and the slot in the core plate, and then the core block is There is a method in which a conductive metal is laminated between the two, and then the rotor is heated to the melting point of the low melting point metal to melt it, and the molten low melting point metal is removed while rotating the rotor as necessary. However, all of these methods not only require a large number of man-hours, but also the method of drilling with a drill risks damaging the rotor bar (conductor) during drilling, and the method of welding has the risk of damaging the rotor bar (conductor) during casting. There is a drawback that the molten metal of the conductor blows out from the gap between the steel plates and clogs the ventilation gap. In addition, when a duct spacer is made of a metal with a low melting point, it melts into the conductor metal when it is cast, and when it is removed, it requires high-temperature work for heating, resulting in a poor working environment. Furthermore, when rotating the rotor to improve removal efficiency, the rotation speed must be slow to prevent deformation of the conductor, and it takes a long time to remove the spacer. As mentioned above, the use of water-soluble cores as spacers instead of low-melting point metal formations for the formation of ventilation ducts eliminates most of the major drawbacks associated with conventional ventilation duct formations described above. . That is,
If such a water-soluble core is used, it becomes possible to dissolve or disintegrate the core by applying water to the cast body after casting the conductive metal, and to easily remove the core without deteriorating the working environment. Ventilation ducts are formed. However, there are also some problems with the method of manufacturing a cast rotor with a ventilation duct using such a water-soluble core. This is mainly because conventional water-soluble core materials do not meet the suitability required for use in precision casting for cast rotors as described above. Generally, the following properties are required for water-soluble cores or their materials. (a) Having appropriate formability; (b)
Excellent mold strength. In particular, when manufacturing a cast rotor with a ventilation duct as described above, in order to use it in combination with a pre-formed member (iron core plate), tightening is performed to improve the integrity of the assembled body. Pressure is required. Further, mold strength is also necessary to withstand the pressure of molten metal in pressure casting methods such as low pressure casting method and die casting method. (c) It must be able to disintegrate quickly. (d) It does not have excessive hygroscopicity and can be stored at least in a normal dryer. (e) Must have appropriate dimensional accuracy. (f) To provide a smooth casting surface. Although many materials have been proposed as water-soluble core materials, they do not necessarily satisfy the above-mentioned required characteristics. For example, a molten molded product of sodium carbonate with a small amount of barium carbonate added (Special Publications 1973-
Molten molded products of water-soluble salts, such as those produced in Japanese Patent Publication No. 15211, have excellent strength and casting surface, but generally have a large coefficient of thermal expansion, poor dimensional accuracy, and take time to disintegrate and remove. There are disadvantages such as high production costs due to the use of molten salt. In addition, a kneaded molded product of alumina sand and water-soluble carbonate (sodium carbonate or potassium carbonate) (Special Publication No. 50-28057) has good disintegration and moldability, but has low mold strength and is gravity cast. Regardless of the method, it cannot be used in low-pressure casting methods that apply pressure on molten metal and die-casting methods that require higher pressures. Furthermore, it cannot withstand the pressure when tightened together with the above-mentioned iron core plate and the like. [Object of the Invention] An object of the present invention is to provide a method for manufacturing a cast rotor with a ventilation duct using a water-soluble core made of a new material that satisfies the various properties required for a water-soluble core as described above. do. [Summary of the Invention] According to the research conducted by the present inventors, when potassium carbonate is used alone as a binder for foundry sand, a core with limited strength (resistance force) can only be obtained. ,
By using this together with a second binder selected from barium carbonate and alkali silicate, a water-soluble core with dramatically improved strength and excellent disintegration and other properties can be obtained. Furthermore, it was discovered that by using this core, a cast rotor with a ventilation duct can be manufactured easily and economically. That is, the method for producing a cast rotor of the present invention involves the production of a cast rotor for an induction motor in which iron core plates having shaft holes and conductor holes are laminated on the outer periphery of a rotor shaft with gaps for ventilation ducts interposed therebetween. Shape of a ventilation duct having shaft holes and conductor holes made of a mixture of aggregate, a first binder consisting of potassium carbonate, and at least one second binder selected from barium carbonate and sodium silicate. A disc-shaped water-soluble core formed in the above is sandwiched between a cylindrical laminated core having shaft holes and conductor holes so that the positions of the shaft holes and conductor holes match, and the resulting laminate is tightened. is placed in a mold and a conductive metal is poured into it, a conductor made of the metal and a short circuit ring are integrally formed in the laminate, and then the cast body taken out from the mold is treated with water to form a core. It is characterized by forming a ventilation duct in the iron core by dissolving and removing it. [Embodiments of the Invention] Hereinafter, the present invention will be described in more detail with reference to drawings showing embodiments. In the following description, "department"
and "%" are based on weight unless otherwise specified. The water-soluble core used in the present invention is, for example, embodied as a core for forming a ventilation duct of a cast rotor, as shown in a perspective view in FIG. This core 1 has a conductor hole (slot) 2 and an inner hole (shaft hole) 3, and is in the shape of a disk having the same thickness as the width of the ventilation duct of the rotor. As mentioned above, this core is made of foundry sand, a mixture of potassium carbonate (first binder), barium carbonate, and sodium silicate (second binder),
After kneading these raw materials with an appropriate amount of water, they are charged into a mold having a predetermined shape, such as a wooden mold or a foamed plastic mold, and are solidified and shaped.
Obtained by drying. As the sand aggregate, those commonly used as sand aggregates for foundry sand, such as alumina side, zircon side, and silica sand, are used. Among these, alumina side is preferable for applications requiring particularly high strength.
Zirconside is preferable for applications where the occurrence of shrinkage cavities is avoided. Generally, the most desirable results are obtained when using an alumina side blended with 10 to 50% zirconide. The average particle size of foundry sand is 35~
Approximately 150 meshes is preferable. Potassium carbonate is 10 to 50 parts per 100 parts of sand aggregate.
It is preferable to use it within a range of 100%. If the potassium carbonate content is less than 10 parts, the strength of the core will be insufficient, and if it exceeds 50 parts, the strength will even decrease, which is economically disadvantageous. Particularly preferably, a range of 10 to 30 parts is used. The second binder selected from barium carbonate and alkali silicate provides a core with dramatically improved strength when combined with potassium carbonate. ~30
Parts of alkali silicate, preferably sodium silicate, are preferably used in the range of 1 to 15 parts, especially 1 to 6 parts. If less than 1 part of any of these is added, the effect of addition is poor; if added in excess, the fluidity of the core molding composition becomes excessive, making molding difficult, and as the amount of alkali silicate added increases, the disintegration after casting increases. It also gets worse. Increasing the amount of barium carbonate added to increase the counter pressure is not preferable because it increases the cost required for molding. These barium carbonate and alkali silicate can be used together, and when used together, each can be used within the above range of amounts. If used in combination, a core with further improved strength can be obtained. Water dissolves the water-soluble components in the above raw material components,
Used to give the overall molding composition a consistency suitable for molding, generally an amount that renders the composition more like a wet sand than a slurry, e.g.
The amount used is 5 to 20 parts (including the amount of water contained in the alkali silicate, since it is stored in a water glass state) based on 100 parts of sand aggregate. Considering that the mold pressure is increased by drying after molding, it is appropriate to use a smaller amount as long as it does not interfere with molding. To explain a more preferable embodiment for forming a core from the above raw material components, first, soluble potassium carbonate (if an alkali silicate is used, this and an alkali silicate) are mixed in a predetermined amount, preferably at a temperature close to boiling water. The solution is added to sand aggregate (if barium carbonate is used, a mixture of barium carbonate and barium carbonate) that has been separately preheated to about 100 to 150°C and kneaded. The molding strength of the resulting core is better when the solution and sand aggregate are kneaded before cooling. Next, put the kneaded material into a predetermined mold,
After compacting and shaping, it is dried at 80 to 110°C for 2 to 5 hours, and then cut out to obtain a core. In order to store the molded core, it is best to store it in a dryer or a moisture-impermeable bag with a desiccant such as silica gel to prevent strength loss due to moisture absorption. A method of manufacturing a cast rotor using the core 1 obtained as described above will be explained with reference to FIGS. 2 to 4. First, a large number of disk-shaped iron core plates 4 made of silicon steel plates or the like are prepared by further punching slots with predetermined outer and inner diameters. Next, using a rod-shaped jig 6 having the same outer diameter as the inner diameter of the iron core plate 4 as a guide, the iron core plates 4 are stacked on the outside thereof while aligning the slots. After a predetermined number of cores are laminated, a core 1 prepared in advance is placed thereon in such a way that the conductor hole (slot) 2 communicates with the slot of the iron core plate 4. Furthermore, by repeating the work of laminating the core plates 4 and placing the core 1 on top of this, a predetermined number of core plates (5 in the illustrated example)
A core block 5 having a predetermined stacking thickness is obtained by sandwiching the cores 5 and 6. Next, this iron core block 5 is sufficiently compressed and tightened using a pressing machine such as a press, and is firmly fixed using a fixing jig 6a. Next, as shown in FIG. 2, this iron core block 5 is placed in a normal mold 7, and molten metal such as aluminum is poured into the mold by die casting or low pressure casting to form the conductor holes 5. , the cooling vane molding space 8 and the short circuit molding space 9 in the mold 7 are filled. FIG. 3 shows the cast molded product taken out from the mold 7. This molded body includes a conductor 12, a cooling blade 1
8 and a short circuit ring 19 are formed, but the core 1 is still interposed. Therefore, if this molded body is immersed in water or hot water, or if water is poured over the core 1 portion, the water-soluble binder in the core 1 will dissolve and the core 1 will disintegrate. After removal, as shown in FIG. 4, which is a partial side view seen from the - line direction in FIG. 3, a cast rotor is obtained in which a ventilation gap (duct) 11 is formed. The disintegration of the core 1 with water can be easily carried out even after the cast body has cooled down, but if it is done while it is still hot,
After removing the core, the cast rotor can be easily dried due to residual heat. [Effects of the Invention] As described above, the present invention provides a water-soluble core that has excellent required characteristics such as moldability, strength, and disintegrability, and is particularly suitable for forming a mold by combining with already formed parts. By using the present invention, an easy and economical method for manufacturing a cast rotor with a ventilation duct is provided. Below, examples of characterizing the water-soluble core used in the present invention will be shown. Example Core characteristic evaluation test pieces (diameter
A cylindrical shape (50 mm x height 50 mm) was fabricated. That is, the sample was prepared by adding a solution of potassium carbonate (and sodium silicate) dissolved in a predetermined amount of boiling water to sand aggregate (and powder mixture with barium carbonate) preheated to approximately 150°C and kneading for 3 minutes. Then, while still hot, put it into a cylinder for producing test pieces, ram it three times, and harden it.
After demolding, it was dried at 95°C for 3 hours and left to cool in a desiccator to obtain a test piece. As sand aggregate, alumina sand (JIS No. 5), zircon sand (JIS No. 6),
Silica sand (JIS No. 5) was used. The compressive strength is the value obtained by compressing the test piece in the height direction using an Amsler type tester at a compression rate of 4 kg/cm ² /sand, and dividing the breaking load by the cross-sectional area. The moldability is evaluated by the moldability when the sand mixed into the core box is pounded and hardened.If the sand becomes slurry-like and cannot be hardened, or if it is in a dry state and is difficult to shape when pounded and hardened, the moldability is evaluated. Those that are rated as having poor formability and are well packed and molded during compaction have good formability. In addition, collapsibility is measured by pouring molten metal into a molded core and then treating it with water, such as by sprinkling water on the core material, so that the molded sand becomes individual powders that do not lose their cohesive strength. This refers to the degree to which a powder has fluidity and crumbles. The measurement results are summarized in Table 1.

【table】

[Table] Table 1 shows that by adding at least one of barium carbonate and sodium silicate as a binder in addition to potassium carbonate, the resistance pressure increases dramatically, and the appropriate composition ratio If you choose,
It can be seen that a core can be obtained that has excellent pressure resistance, formability, and disintegration properties, and can also be pressure cast. Incidentally, it is desirable to have a counter pressure of 10 Kg/cm ² or more even in the gravity casting method, a counter pressure of 20 Kg/cm ² or more in the low-pressure casting method, and 100 Kg/cm ² or more in the die casting method.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a ventilation duct spacer as an example of the water-soluble core of the present invention, Fig. 2 is a cross-sectional view of the duct spacer laminated between iron core plates and the laminate placed in a mold, Fig. 3 The figure is a cross-sectional view of the cast molded body (cast rotor with spacer held).
Figure 4 is a partial right side view of the product cast rotor.
5 and 6 are cross-sectional views showing the general structure of a cast rotor for an induction motor. 1... Core, 2... Conductor hole, 3... Shaft hole, 4... Iron core plate, 5... Laminated block, 6...
Jig, 7... Mold, 8... Cooling blade forming space, 9
... Short-circuit ring forming space, 11 ... Ventilation duct, 12
...Conductor, 18...Cooling vane, 19...Short ring.

Claims (1)

[Claims] 1. When manufacturing a cast rotor for an induction motor in which iron core plates having shaft holes and conductor holes are laminated on the outer periphery of a rotor shaft with gaps for ventilation ducts interposed, a first rotor made of sand aggregate and potassium carbonate is used. A disc-shaped water-soluble core formed into the shape of a ventilation duct having a shaft hole and a conductor hole by a mixture of a binder and at least one second binder selected from barium carbonate and sodium silicate. is clamped between cylindrical laminated cores provided with shaft holes and conductor holes so that the positions of the shaft holes and conductor holes match, and the resulting laminate is placed in a mold to make it conductive. A conductor and a short circuit ring made of the metal are integrally formed in the laminate, and then the cast body taken out from the mold is treated with water to dissolve and remove the core, thereby creating a ventilation duct in the iron core. A method for manufacturing a cast rotor, characterized by forming a cast rotor.