JP4400149B2 - Method and apparatus for cleaning inner surface of mold for VAR - Google Patents

Description

The present invention relates to a polishing method for cleaning an inner surface of a crucible called “mold” used for VAR (vacuum arc remelting), which is a metal refining means, after each charge. The invention also relates to a polishing apparatus used to carry out the method.

Metals that require high heat resistance and corrosion resistance, such as high-alloy special steels, nickel-base alloys, and cobalt-base alloys, are generally required to have extremely high cleanliness. If machine parts are manufactured in a state where foreign matter is mixed in, machine parts with low reliability can be produced, and for applications that require extremely high reliability such as aircraft engine shafts, it becomes a fatal defect. High cleanliness must be achieved at the material production stage prior to Therefore, a high degree of degassing is required in the refining process, and VAR is performed as a means for this.

As is well known, VAR operations are carried out in batch operations using a cylindrical mold made of copper and having a flange on the top. After the ingot generated as a result of refining is pulled out, spatter generated by the arc adheres to the inner surface of the mold. For the next operation, it is necessary to remove the ingot.

Conventionally, the inner surface of the VAR mold has been cleaned manually using a wire brush. However, the wire brush cleaning is not perfect as a means for cleaning, and rarely the wire of the wire brush itself adheres to the mold, so that improvement is required. Therefore, especially for products with a strong demand for mold inner surface cleaning, after removing the wire brush, the removal of foreign matter was done completely with a manual grinder. Since the work is expensive and cost increases, and the work takes 8 hours, for example, it is a disadvantageous work, so rationalization has been demanded.

In order to sharpen the inner surface of a long tubular member, such as a mold of a centrifugal casting machine, the applicant attaches a brush to the tip of a flexible rod, rotates the rod, and sharpens the inner surface of the tubular member with the brush. The device was invented and already proposed (Patent Document 1). However, to the extent that it can be reached with this type of apparatus, it is insufficient as a means for polishing the inner surface of the mold for dissolving the metal that requires high cleanliness.

In addition to the above, the applicant has inserted a machine with a number of chains attached to the shaft into the mold, and rotated the shaft by centrifugal force. We developed a tool that hits the inner surface and cleans it (Patent Document 2). This is difficult to use as a means of polishing a soft copper mold.

For cleaning to remove scale adhering to the inner surface of the mold that casts the molten metal into the ingot, a cleaning method is proposed in which a polishing nozzle is inserted into the mold and moved up and down while jetting the particles for cleaning with compressed gas. (Patent Document 3). It is said that the “casting grit” with corners, which is used for cleaning the surface of the casting, is suitable as the polishing particles.

The inventors considered the adoption of a technique for polishing the inner surface of the mold using an impeller-type shot blast. As a result of the experiment, the cast grit with corners can remove foreign matter adhering to the inner surface of the mold, but it is inconvenient to damage the inner surface of the mold, and by using the “round” type grit without corners, I learned that the inner surface of the mold has been cleaned and the background color of copper, which is the material of the mold, is restored. It has also been found that it is preferable to use a grit that is difficult to transfer the surface oxide to the inner surface of the mold, such as that made of stainless steel.

When the experiment was further advanced, even when round type grit was used, powdered materials (such as exfoliated mold deposits, scraped mold material, and shredded pieces of grit) remained on the inner surface of the mold. I was still unsatisfied. Therefore, it was confirmed that the inner surface of the mold can be highly cleaned by adding a wiping operation using a mop.
JP-A-7-8931 JP-A-7-32130 JP 2-179342

An object of the present invention is to make use of the above-described experience of the inventors, and requires a manual operation in a polishing method for cleaning the inner surface of a VAR mold, which is necessary as a premise of obtaining an ingot having a very high cleanness by VAR. It is an object of the present invention to provide a polishing method that can be carried out automatically without any problem and that the inner surface of the mold after cleaning is highly cleaned. It is also within the scope of the present invention to provide a sharpening device that is useful for performing the method.

The polishing method of the present invention is a method of cleaning the inner surface after using a copper mold for VAR, inserting an impeller-type shot blasting device into the mold, rotating the impeller while moving it up and down, After projecting round type grit from the impeller onto the inner surface of the mold and removing the deposits on the inner surface of the mold by the impact, wiping the inner surface of the mold with a mop makes it possible to remove the remaining powdery foreign matter. This is a method for polishing the inner surface of a mold for VAR.

As the grit, a round type by punching a stainless steel cut wire is preferable. The wiping is conveniently performed by rotating the mold while pressing the mop on the inner surface of the mold.

The VAR mold inner surface polishing apparatus of the present invention for carrying out the above method is an apparatus for polishing the inner surface of a VAR copper mold after use, as shown in FIG. The mold carriage (3) for moving the mold (4) on the common part is a common part, and is composed of a combination of a shot blasting mechanism (I) and a wiping mechanism (II).

The shot blasting mechanism (I) includes an impeller inserted into a mold (4) and suspended in a rotatable manner, as shown in FIG. (11) In the lower part of the rotating and raising and lowering supply pipe (12) for rotating the impeller and raising and lowering the grit (5), the guide unit (13) for guiding the raising and lowering of the rotating and raising and lowering supply pipe, and the mold carriage (3), Lower screw conveyor (14) for recovering the projected grit, piping and dust collector (not shown) for sucking and removing dust, bucket conveyor (15) for transporting the recovered grit, Upper screw conveyor (16) and shot for removing powder and large foreign bodies from the grit and circulating the grit to a rotating lifting supply pipe Separator (17), and, a driving source for driving the driving source and the conveyor to rotate and lift the rotary elevating supply pipe (these are not shown).

The wiping mechanism (II) includes a mop (21), a main pillar (22), and a mop along the mop inserted into the mold and pressed against the inner surface of the mold, as shown in FIG. Mop elevating shaft (23) for moving up and down, swivel arm (24), pressure equalizing means for interposing between mop and mop elevating shaft to keep pressing pressure of mop against mold inner surface at a predetermined value, mold It comprises driving means for rotating the mold provided on the carriage (3) around its axis, and a driving source (also not shown) for raising and lowering the mop lifting shaft.

As a result of replacing the conventional [wire brushing + grinder work] with [shot blasting + wiping], the method for polishing the inner surface of the VAR mold of the present invention becomes easy to automate, reduces the addition of workers, and The time required for cleaning was significantly shortened. The effect of the scouring is assured and the inner surface of the mold becomes smooth with the foreign matter completely removed. Therefore, the ingot obtained by the next VAR operation is clean without any contamination. There is little wear on the inner surface of the mold, and the mold can withstand many uses.

The polishing apparatus for the inner surface of the VAR mold according to the present invention comprises [shot blasting mechanism + wiping mechanism], which is easy to operate automatically and is useful for cost reduction. Recovery of the projected grit-It is possible to obtain a high-quality ingot by avoiding contamination to the VAR work by performing dust absorption during circulation reuse and wiping with a mop.

The operation of the illustrated apparatus will be described. First, the mold (4) from which the ingot produced by the VAR apparatus is extracted is placed on the mold carriage (3) and carried to the shot blasting mechanism (I). There, an impeller-type shot blasting device descends into the mold from above, and a rotating lift supply pipe (12) rotates the impeller while raising and lowering the impeller, and the grit supplied through this pipe is supplied to the impeller (11 ) To the inner surface of the mold. As shown in FIG. 3, the grit is projected in the combined projection direction (S) of the circumferential speed vector (P) in the tangential direction and the centrifugal vector (C) in the radial direction by the high speed rotation of the impeller, and is applied to the inner surface of the mold. collide. Due to the collision, the deposit on the inner surface of the mold is crushed or peeled off, and polishing is performed. The projection is performed at least once, if necessary for more reliable scouring, several times.

At this time, the projection density ρ (kg / m ² ) per unit area of the inner surface of the mold is the shot blasting device's lifting speed V (m / min.), Projection amount (kg / min.), Mold inner diameter D (m) Assuming that the mold length is L (m), it is expressed by the following formula.
ρ = L / V · M / (1 / πDL) = M / πDV
In other words, when the target is a mold having a constant inner diameter in a shot blasting apparatus with a fixed capacity, the projection density is determined by the ascending / descending speed V. The optimum conditions for shot blasting, including the projection density, may be determined appropriately by those skilled in the art depending on the dimensions of the mold to be polished.

As described above, the grit is a round type. Those with corners are unsuitable for the polishing intended in the present invention because they damage the inner surface of the mold and possibly remain stuck there. The material is usually preferably stainless steel. If the surface rusts, the rust is transferred to the inner surface of the mold by projection, which is inconvenient. According to the experience of the inventors, a grit having a rounded corner with a SUS304 wire cut to an appropriate length and blanked in advance toward a hard object as described above was suitable.

The projected grit falls downward, passes through a hole provided through the mold carriage (3), and is collected and carried out by the lower screw conveyor (14). The carried grit is carried upward by the bucket conveyor (15), transferred to the upper screw conveyor (16), and moved to the shot separator (17). In the shot separator, for example, deposits that have been peeled off from the inner surface of the mold are separated and put out of the system by a sieve that does not allow foreign matters larger than grit to pass through. Dust is removed by suction as much as possible below, but what remains is removed by an air classifier. The grit thus cleaned is circulated to the rotary elevating / lowering supply pipe (12) and reused.

The mold that has been blasted by shot blasting is moved to the adjacent wiping mechanism (II) while placed on the mold carriage (3), and the mop (21) is pressed against the inner surface while rotating around its axis. Wipe off any remaining powder. For mold rotation, it is advantageous to use a mold rotation driving apparatus as shown in FIG. Specifically, an upper and lower double ring bearing is provided on the mold carriage, the lower plate (31) of the bearing is fixed to the mold carriage, and the flange portion of the mold is placed on the upper plate (32) of the bearing. The upper plate is rotated in a rim drive manner by a gear (34) coupled to a motor (35) and a gear (33) provided around the upper plate.

Needless to say, the mop (21) is preferably pressed against the inner surface of the mold (4) with a constant pressure. As shown in FIG. 5, the pressure equalizing means used for this purpose is such that the position of the mop elevating shaft (23) inside the mold can be changed by the swivel arm (24), for example, a torsion using a rubber spring. It is recommended to configure with the bar (25) interposed.

The conceptual side view which shows the whole structure about the polishing apparatus of the inner surface of the mold for VAR of this invention. The shot blasting mechanism (I) is seen from the front, and the wiping mechanism (II) is seen from the side (direction different by 90 degrees). The longitudinal cross-sectional view which shows the principal part of a shot blasting mechanism in the polishing apparatus of this invention. The top view which showed the impeller part among the principal parts of the shot blast mechanism shown in FIG. The side view which shows the structure of the mold rotation drive apparatus for implementing wiping. The top view which showed the part of the pressure equalization means among the wiping mechanisms shown in FIG.

Explanation of symbols

I Shot Blasting Mechanism 11 Impeller 12 Rotating Elevating Supply Pipe 13 Guide Unit 14 Lower Screw Conveyor 15 Bucket Conveyor 16 Upper Screw Conveyor 17 Shot Separator
II Wiping mechanism 21 Mop 22 Main column 23 Mop lifting shaft 24 Rotating arm 25 Torsion bar 3 Mold carriage 31 Bearing lower plate 32 Bearing upper plate 33, 34 Gear 35 Motor 4 Mold 5 Grit

Claims (5)

This is a method of sharpening the inner surface of a VAR copper mold after using it. Insert an impeller-type shot blasting device into the mold and rotate the impeller while moving it up and down to mold a round type grit from the impeller. A method for polishing the inner surface of a mold for VAR, which comprises projecting onto the inner surface, removing the deposit on the inner surface of the mold by the impact, and then wiping the inner surface of the mold with a mop to remove the remaining powdery foreign matter. . 2. The polishing method according to claim 1, wherein the grit is a round type made by punching a stainless steel cut wire. 2. The polishing method according to claim 1, wherein the wiping is performed by rotating the mold while pressing a mop on the inner surface of the mold. A device for polishing the inner surface of a copper mold for VAR after using the mold carriage (3) for moving the mold on it as a common carriage for the polishing equipment , has a combination of a blast mechanism (I) and wiping mechanism (II),
A shot blasting mechanism (I) is inserted into the mold and is rotatably suspended from an impeller (11), a rotary lifting / lowering supply pipe (12) for rotating and rotating the impeller and supplying grit, A guide unit (13) for guiding the raising and lowering, a lower screw conveyor (14) for collecting the projected grit at the lower part of the mold carriage (3), a dust collecting device for sucking and removing dust, and the collected grit Bucket conveyor (15) for transporting to the upper part, upper screw conveyor (16) and shot separator (17) for removing the powder and large foreign matter from the grit transported upward and circulating the grit to the rotary lifting supply pipe , And a drive source for rotating and raising and lowering the rotary elevating supply pipe and a drive for driving each conveyor Is constructed from a source,
The wiping mechanism (II) is inserted into the mold and pressed against the inner surface of the mold, the mop (21), the main column (22), the mop lifting shaft (23) for raising and lowering the mop along the main pillar (22), the swivel arm (24 ), Which is interposed between the mop and the mop lifting shaft, and is a combination of a rubber spring and a means for changing the position of the mop lifting shaft inside the mold, and keeps the pressing pressure on the inner surface of the mop at a predetermined value. A polishing apparatus for an inner surface of a VAR mold, comprising pressure means, drive means for rotating a mold provided on the mold carriage (3) around its axis, and a drive source for raising and lowering a mop lift shaft . The shot separator (17) constituting the shot blasting mechanism (I) separates the foreign material having a certain size exceeding the size of the grit and carries it out of the system. The scouring device according to claim 4 , comprising an airflow classifier.

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