JPS61259856A - Core in casting propeller for ship - Google Patents

Abstract

PURPOSE:To decrease fine shrinkage cavities, to improve quality and to economize a feeding rate by constituting a core for casting a propeller of a tapered cylindrical body, chiller inserted to the inside circumferential surface thereof via a lubricating film and backup sand packed to the upper side of the chiller. CONSTITUTION:A gate part 7 is first molded of a sand mold, then a flange 16 of a hanging bar 15 is bolted 17 to the chiller 14. The cylindrical body 21 having the taper equal to the taper in the inserting part of a propeller shaft is formed and the lubricating film 22 is formed on the inside circumferential surface. The chiller 20 is inserted into the tapered cylindrical body 21 by using a hanger 18. The body 21 and the chiller 20 are imposed in the gate part 7 via a spacer 19 and a bolt 17 in such a manner that the axial center thereof coincides with the axial center of the gate part 7. Sand 24 is packed into the spacing in the fitting part between the gate part 7 and the body 21 and the backup sand 23 is packed into the body 21. The core 4 molded in such a manner is inserted into the cavity 3 for casting the propeller.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a core for marine propeller casting.

(Prior art) When casting a marine propeller, the core shown in Fig. 5, which has been molded by the method shown in Fig. 6, is inserted into the cavities of the upper and lower molds shown in Fig. 4 and pushed up. This is done by pouring molten metal.

That is, in FIG. 4, 1 is the upper mold made of sand mold, 2
are lower molds made of sand molds, which are fitted together to form a propeller casting cavity 3.

4 is a core made of gas type, cement type, etc., and a scraping board 6 rotated around a shaft 5 as shown in FIG.
The core 4 is inserted into the cavity 3, and the molten metal is poured from the runner 9. As a result, a propeller 12 consisting of a boss portion 10 and blades 11 is cast.

In this case, if the molten metal causes turbulence, it will cause casting defects, so a push-up method is adopted. If the solidification rate is low, defects will occur in the cavities, and if the cast product part, that is, the riser part solidifies earlier than the propeller, shrinkage cavities will occur.

(Problems to be Solved by the Invention) By the way, if the core 4 is a sand mold, shrinkage defects will occur unless the feeder portion 10 is enlarged or the feeder portion 13 is heated. If the core 4 is a sand mold, the heat capacity is smaller than that of molten metal, so the effect of promoting solidification is small.
Microscopic pores were likely to form in the boss portion 10.

The present invention aims to improve quality by promoting directional solidification of the boss portion and reducing fine cavities, as well as to reduce the amount of feeder used for casting a marine propeller. provide it.

(Means for Solving the Problems) The technical means taken by the present invention to achieve the above-mentioned object are characterized in that a propeller casting cavity 3 is formed by an upper mold 1 and a lower mold 2 that are matched with each other. A runner 4 in which a core 4 having a hot water spout 7 and a boss inner molding shaft 8 connected thereto is connected to the cavity 3, and pours molten metal into the cavity 3 in an upward direction. A core 4 in marine propeller casting having a diameter of 9 is targeted, and a boss inner molded shaft portion 8 of the core 4 includes an upwardly expanding tapered cylinder body 21 made of a metal material having a melting point higher than that of the molten metal, and the tapered cylinder body 21 A chiller 20 is inserted into and removed from the inner peripheral surface of the chiller 20 via a lubricating film 22, and backup sand 23 is filled in a tapered cylinder 21 above the chiller 20.
The point is that it is configured with the following.

(Function) The molten metal poured from the runner 9 is pushed up into the cavity 3, where 1. Turbulent flow of the molten metal is prevented.

The molten metal in the cavity 3 solidifies directionally toward the feeder, and this directional solidification is promoted by the chiller 20 absorbing the amount of heat held by the molten metal.

Further, since the amount of increase in the inner thickness of the boss portion 10 exceeds the amount of increase in the chill metal 20, solidification progresses from the bottom of the converter.

After the molten metal has solidified, the cooling metal 20 is pulled out within the time required for solidification.

That is, if the drawing is not performed, the cooling metal 20 cannot be removed due to shrinkage of the casting (propeller) during cooling, and not only will it become impossible to reuse it, but also cracks may occur in the casting.

For this purpose, the chiller 20 is inserted into the inner circumferential surface of the tapered cylinder 21 with a lubricating film 22 interposed therebetween, and the taper cylinder 21 is cast around the chiller 20 and the molten metal. The lubricating film 22 makes it easy to pull out the chiller 20.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

In FIG. 3, an upper mold 1 consisting of sand molds that are matched with each other.
The propeller casting cavity 3 is formed by the lower die 2 and the lower die 2, the middle school 4 has a hot water weir part 7 made of a sand mold and a boss inner molding shaft part 8, and a runner 9 pours the metal into the cavity 3 by pushing up. It is similar to the prior art in that it has a propeller 12 consisting of a boss part 10 and a wing part 11, and also has a riser part 13. In particular, the present invention improves the core 4 as follows. That's what I'm doing.

In FIG. 1, reference numeral 14 denotes a metal core of the water bath, to which a lower end flange 16 of a hanging rod 15 for transporting the core is attached with bolts 17.

Reference numeral 18 denotes a cold metal hanging tool, which has a pipe structure with a larger diameter than the hanging rod 15, and has a spacer 19 at the lower end. It is placed on the weir core metal 14.

Reference numeral 20 denotes a chiller, and in this embodiment, it is ring-shaped with a tapered outer peripheral surface, and is fitted onto a hanger 18 and supported by a spacer 19.
The inner circumferential surface of 0 has a slight clearance from the outer circumferential surface of the hanging tool 18, or the inner circumferential surface shown by the chain line 20A in FIG. It can also be filled with sand.

A tapered cylinder 21 is made of a metal material having a higher melting point than the melting point of the molten metal and protects the chiller 20. If the molten metal is A1803 type, a mild steel plate is suitable.

This tapered cylindrical body 21 can be made from a canned product, but it may also be made from sheet metal presses, etc. If the strength is high, there is a possibility that cracks may occur during casting shrinkage. Since it is a material, the thinner it is, the better, and considering the rigidity during handling, a thickness of 3 to 9 ml11 is appropriate.

The degree of taper of the cylindrical body 21, which has an upwardly expanding tapered shape, is the same as the inner taper of the propeller boss portion 10ρ.

The tapered cylindrical body 21 has a lubricating film 22 on its inner circumferential surface, and the chiller 20 is inserted through the lubricating film 22 so that it can be freely pulled out in the axial direction. The tapered cylindrical body 21 in is filled with backup sand 23.

The lubricating film 22 prevents the tapered cylindrical body 21 and the chiller 20 from being burned together, and also reduces the frictional force when the chiller 20 is pulled out. It is appropriate to use cardboard in a cylindrical shape, which can reduce the heat conduction resistance between the cooling metal 20 and the cooling metal 20.

Furthermore, the backup sand 23 is for backing up the upper side of the tapered cylindrical body 21. That is, since the convert bottom side of the tapered cylindrical body 21 is backed up by the chiller 20, the upper side is backed up. In this case, in order to perform directional solidification, the chiller 2
Sand with a low heat capacity and low thermal conductivity is preferable in the upper part of 0.

In addition, when using the chiller 20 having the inner circumferential surface 20A shown by the chain line in FIG. 1, the backup sand 23 is also filled in the radially inward direction of the inner circumferential surface 2OA.

Further, the chiller 20 is inserted into the converting part at least 40% from the bottom to just below the feeder, and has a tapered outer circumferential surface to facilitate pulling out after solidification. It has good adhesion with the lubricating film 22 and increases the heat absorption rate.

To this extent, the chiller 20 may be made of ring-shaped blocks stacked in stages as shown in the figure, or may be made into a single block without stacking, or may be made of a combination of large and small rings arranged concentrically in the circumferential direction. There may be.

Next, a method for molding the core 4 will be explained.

First, the boiling water part 7 is molded in the conventional manner using a sand mold such as a gas mold or a cement mold.

In other words, if the temperature of the molten metal to be poured in the hot water weir section 7 decreases significantly, the surface of the molten metal will start to solidify, and the product will likely have defects such as molten metal borders or oxide entrainment defects. In addition, when considering workability, molding is performed using foundry sand as before.

Next, attach the flange 16 of the hanging rod 15 to the core bar 14 with the bolt 1.
Install in step 7.

A cylindrical body 21 having a taper equal to the insertion portion of the propeller propulsion shaft is created, a lubricating film 22 is applied to the inner peripheral surface of the cylindrical body 21, and the chiller 20 is attached to the tapered cylindrical body 21 using a hanger 18.
The taper cylindrical body 21 and chiller 20 are placed so as to align with the axis of the hot water tap 7 via the spacer 19, pole 17, etc.

Sand 24 is filled into the gap between the hot water spout 7 and the tapered cylindrical body 21, and backup sand 23 is also filled into the cylindrical body 21.

The core 4 molded in this manner is inserted into the cavity 3 as shown in FIG.

Next, the core according to the conventional example shown in FIG. 5 and the one in which the cooling metal 208 is applied to this core as shown in FIGS. 7 and 8 are the same as those using the core according to the embodiment of the present invention. The comparative test results are shown below.

The test was conducted using a 15t propeller and the feeder section was not heated.

The results are shown in Figures 9 to 12, in which the horizontal axis represents solidification time, the vertical axis represents temperature, and
Symbol A is the solidification curve of the feeder section, and symbol B is the solidification curve of the product section.

FIG. 9 shows an example of the present invention in which the chiller 20 is provided up to just below the feeder part, and FIG. 10 shows an example of the present invention in which the chiller 20 is provided up to 40% of the axial length of the shaft part 8. Figure 11 shows an example using the core shown in Figures 7 and 8, in which a conventional core is coated with a cold metal 20B, and Figure 12 is an example using a conventional core without a cold metal. This is an example.

As a result of this experiment, it was found that in the conventional method, evacuation cavities were created under the feeder;
Fine cracks were also formed inside the boss, and even when the cooling metal 208 was applied as shown in FIGS. 7 and 8, almost no effect was observed.

When using the core according to the present invention, not only no cavities occur, but also the amount of feeder (27,500 kg) of the conventional example is reduced to 2T.
It was found that even if the iO2 kg was used, no hives were generated.

In addition, looking at the time elapsed from casting to uncasting, conventionally it was possible to complete solidification in 12 hours from casting and take out the product in 48 hours, but when using the core according to the present invention, Solidification was completed in 6 hours, and 30
The product can be taken out in a timely manner, and even if the cast cylinder 21 is subsequently removed by machining, the solidification time can be significantly shortened and the rotation rate of the casting pit can be improved.

(Effects of the Invention) According to the present invention, the boss inner surface molding shaft portion 8 of the core 4 in marine propeller casting includes an upwardly expanding tapered cylinder body 21 made of a metal material having a melting point higher than that of the molten metal, and the tapered cylinder body 21
A chiller 20 is inserted and removably inserted into the inner peripheral surface of the chiller 20 via a lubricating film 22, and a tapered cylindrical body 2 is disposed above the chiller 20.
Since the back amplifier sand 23 is filled in the boss part 10, directional solidification of the boss part 10 is promoted, fine cavities are reduced, and quality is improved. Alternatively, the amount of feed water can also be reduced.

Furthermore, since the chiller 20 can be inserted into and removed from the tapered cylinder 21, it can be used repeatedly.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention and a conventional example, and FIG. 1 is an elevational cross-sectional view of a core according to the present invention, FIG. 2 is a perspective view of the core, and FIG.
The figure is a cross-sectional view of the main parts of the casting device, Figure 4 is a cross-sectional view of the conventional example, Figure 5 is a perspective view of a conventional core, Figure 6 is a perspective view of an example of molding a conventional core, and Figure 7 is a perspective view of a conventional core. FIG. 8 is a cross-sectional view of the same half, FIGS. 9 and 10 are solidification curve diagrams according to the present invention, and FIGS. 11 and 12 are solidification diagrams according to the conventional example. It is a curve diagram. 1...Top mold, 2-Bottom mold, 3-Cavity, 4-
- Core, 20 - Cold metal, 21 - Tapered cylinder, 2
2---Lubricating film, 23--Backup sand.

Claims (1)

[Scope of Claims] 1. A propeller casting cavity 3 is constituted by an upper mold 1 and a lower mold 2 that are matched with each other, and has a molten metal part 7 and a boss inner molding shaft part 8 connected thereto. The object is a core 4 in marine propeller casting in which a core 4 is connected to the cavity 3 and has a runner 9 for pouring molten metal into the cavity 3 in the upward direction, and the boss inner surface molding shaft part of the core 4 Reference numeral 8 denotes an upwardly expanding tapered cylinder 21 made of a metal material with a melting point higher than that of the molten metal, and a chiller 20 inserted into and removed from the inner peripheral surface of the tapered cylinder 21 via a lubricating film 22. Backup sand 23 filled in the tapered cylindrical body 21 above the chiller 20
A core for casting marine propellers, characterized by comprising: