JPH03189057A - Mold for precise centrifugal casting - Google Patents

Abstract

PURPOSE:To facilitate separation of a product and a runner by arranging product cavity through a gate at outside of the runner having center axis matching to rotating axis of a mold and neck part having small cross sectional area on the way of the above gate. CONSTITUTION:Below a sprue (not shown in the figure), the runner 2 connected with this, is arranged. At the outside of this runner 2, the product cavity 4 connected with this through the gate 3 is arranged as horizontal and radial state at one or more steps, and the mold for precise centrifugal casting making the center axis of runner 2 the rotating axis, is constituted. In the above mold, on the way of the above gate 3, the neck part 6 reducing the cross sectional area, is arranged. Reducing ratio of this cross sectional area is desirable at about 5 - 30%. Then, if necessary, ceramic bar 7 for reinforcing, feeder head 9, etc., are set. The product cast into the product cavity 4 with this mold can be easily separated from the runner 2 with the above neck part 6, and casting yield can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a precision centrifugal casting mold used in a lost wax casting method.

<Prior art> The centrifugal casting method, in which a fully curved molten metal is injected into a rotating mold and the centrifugal force acting on the molten metal fills the mold cavity or presses it against the inner wall of the mold, is mainly used for casting tubes, rolls, etc. This is a casting method that is used for manufacturing everything from large castings to small castings such as ornaments.

Among these, lost wax molds are sometimes used as molds, and the purpose of this is to ensure reproducibility of minute shapes, prevent casting defects such as pinholes, or improve casting yield.

By the way, in precision casting using a lost wax mold, it is common to simultaneously cast many products in one mold, and it is necessary to separate these many products from the runner at the weir. A cutting tool is used for cutting, but
This poses a problem of low casting yields due to restrictions on product placement, or large cutting man-hours.

To solve this problem, JP-A-53-77836 focused on the fact that centrifugal force pushes the molten metal in the mold in the radial direction, and there is no molten metal around the rotating shaft. We are proposing a casting method that eliminates cutting.

In other words, a centrifugal casting mold is used that is equipped with a molten metal flailing receiver near the top of the runner to allow excess molten metal to escape during pouring, and after pouring a certain amount of molten metal, the mold is rotated and centrifugal force causes the molten metal to flow through the runner. By raising the molten metal along the molten metal and supplying the molten metal to each product cavity and each layer, and releasing the excess molten metal into the molten metal flaring receiver, no unnecessary molten metal remains in the runner after casting.

However, in the above method, even if excess molten metal escapes into the molten metal flaring receiver, unless the runner has an ideal parabolic shape, molten metal will remain in the runner, and it will be necessary to separate the product from the runner. there were.

That is, the shape of the molten metal in the runner when the rotation is continued until the completion of solidification is as shown in FIG.

The ideal runner shape in this case is a parabola shown by the shape of the molten metal A, and its equation is expressed as y−gox''+ah−(1).

In reality, it is impossible to make the runner shape a parabola expressed by equation (1), and usually the tangent at y-a in equation (1), that is, h y = -x 10a 2h (2) The shape represented by B is taken as the best one.

In this case, if the radius r of the runner in the molten metal flange receiver is 6
cm, rotation speed n during centrifugal casting is 300 rpm + m,
Height a from the bottom of the runner is 15c+m and height a is 5c+a
The thickness of the remaining hot water in the runner at the pan in the area is calculated using equations (1) and (2).
) is calculated as the difference between 0.1 am and 1 am, respectively.
．． It becomes 0cm. That is, the runner and the product are connected via a weir, and some kind of separation means is required.

In this case, if the cast metal is a brittle metal such as cast iron or a relatively weak metal such as aluminum,
Since the remaining molten metal in the runner is thin, the product can be easily separated by impact or twisting, but cutting is required for strong and ductile metals such as cast steel.

<Problem to be solved by the invention> As mentioned above, even in centrifugal casting, it is practically impossible to separate the product and the runner without a cutting process by simply optimizing the shape of the runner and installing a molten metal flaring receiver. It is possible.

However, in the lost wax precision casting method, the key to improving the casting yield is how much product can be added to one mold, and this inevitably makes it difficult to separate the product from the runner. , which increases the number of cutting steps.

Therefore, an object of the present invention is to propose a precision centrifugal casting mold that can easily separate the product and the runner and improve the casting yield.

Means for Solving the Problems> The present invention provides a vertical runner connected to the lower part of the sprue, and a horizontal section of one or more tiers connected to the runner on the outside of the runner, which covers the entire mold. In a precision centrifugal casting mold in which a weir and a product cavity are provided in a nearly radial shape, and the center axis of the runner coincides with the rotation axis, a neck part is provided in the middle of the weir to reduce its cross-sectional area. This is a precision centrifugal casting mold characterized by the following:

<Operation> The lost wax method is characterized by the fact that the shape of the cast product can be more complex than that obtained by conventional casting methods, but at the same time, the internal quality must be excellent. In particular, great attention has been paid to the location, number, and size of weirs to avoid the presence of gas holes or gas holes.

By applying centrifugal casting to the lost wax casting method, the present inventors aim to improve the internal quality due to centrifugal force, and reduce the role of the weir on quality, that is, the ability to replenish molten metal during solidification and contraction of the product part. , we succeeded in creating a degree of freedom in the shape of the weir. As a result, in the present invention, a neck portion is provided in the middle of the weir to reduce its cross-sectional area.
It has become easier to separate the runner and the product.

<Example> Next, the present invention will be explained in detail based on examples.

FIGS. 1 and 2 are cross-sectional views showing the layer shapes of the present invention, respectively. A weir 3 and a product cavity 4 are provided on the outside of a runner 2 provided vertically at the bottom of the sprue. In FIG. 1, a 7-shaped groove 6 is formed. Further, in FIG. 2, the filter 8 is used to reduce the cross-sectional area of the weir.

The cross-sectional area reduction rate at this time is preferably 5 to 30%.

If it is less than 5%, alignment will occur in the inflow of the molten metal, and if it exceeds 30%, the effect of simplifying cutting will be lost.

The above-mentioned 7-shaped groove and filter are formed by previously incorporating a ceramic plate or filter having this shape into the row model of the dish portion, or by making a 7-shaped cut in the row model.

However, simply providing a reduced cross-sectional area portion weakens the strength of this portion, and this portion may be damaged during mold making or subsequent handling.

Therefore, when assembling the raw model, it is desirable to perform reinforcement across the reduced cross-sectional area.

This reinforcement is achieved by embedding a ceramic rod 7 in the raw model as shown in FIGS. 1 and 2, which is sufficient in terms of strength.

In addition, in the case of centrifugal casting, centrifugal force is applied to the molten metal that has passed through the reduced cross-sectional area, so even if the reduced cross-sectional area solidifies first, the molten metal in the pan between this and the product part remains liquid. If so, the internal quality of the product will not deteriorate because it will act as a feeder for the product. However, if it is desired to further improve the internal quality, a riser 9 may be provided between the reduced cross-sectional area and the product as shown in FIG.

The integrated raw model (called a tree) created in this way is molded according to the lost wax method.
After de-waxing, it is fired and centrifugally cast.

There is no limit to the number of revolutions during centrifugal casting, and it may be rotating while pouring the molten metal or after casting.
Rotation must be continued until the molten metal in the mold is completely solidified.

After solidification and cooling, the mold is removed, and if the cast metal is a brittle material such as cast iron, the reduced cross-sectional area is broken off with a hammer, or if it is a soft metal such as aluminum, it is bent and cut. In addition, in the case of hard and strong metals such as steel, it is better to gas-cut this part. This way, products can be separated even if there is no room for a cutting tool. Of course, if possible, a high speed rotary grindstone cutting machine may be used.

Further, FIG. 3 shows another embodiment. These are all sprues made of raw material! , hot water path 2. This is a tree 5 made by joining the weir 3 and the product 4. Number of products: 6 pieces per tier, 3 tiers, total 1
There are 8 pieces. The diameter of runner 2 at the joint with sprue 1 is 12C.
ID, has an inverted truncated cone shape with a bottom of 5.4 cm and a height of 20 cm. Weir 3 has a cross-sectional area of 6es', with a cross-sectional area of Q,
It has a reduced cross-sectional area 6 of 9 cm" and is reinforced with a ceramic rod 7 of 5 mm diameter.

The coating process using a special refractory slurry refractory stucco was repeated according to the lost wax method, followed by dewaxing, firing, and cooling to room temperature to obtain a precision casting mold. 5.0 kg of a titanium alloy containing 6% /lf and 4% v was melted into this in vacuum and centrifugally cast at a rotational speed of 300 rpa+. After cooling, the mold was removed, and the weir was cut by acetylene-oxygen gas cutting at the reduced cross-sectional area to separate the product from the runner.

The thickness of the part to be fused was thin, and it could be fused in a short time and easily without affecting the product with heat or adhering the fused spunter.

Conventionally, a high-speed rotary grindstone cutter was used to cut the dish, and the only product that could be cut with a cutting wheel was 4 pieces per stage and 12 pieces per mold.This improved casting yield and reduced cutting man-hours. Not only was it possible to reduce the number of molds produced, but it was also possible to reduce the number of molds manufactured and the number of castings by two-thirds.

<Effects of the Invention> According to the present invention, it is easy and simple to separate the runner and the product, so the number of cutting steps is greatly reduced, and there is no need to consider the cutting method when separating the two, so only one mold can be used. This made it possible to increase the number of products that could be attached to the mold, and significantly reduce the number of mold manufacturing steps.

Furthermore, the occurrence of internal defects in the product, which was a concern due to the reduction in the cross-sectional area of the weir, was not observed at all due to the pressurizing effect of centrifugal casting.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views showing the layered shape of the present invention, Figure 3 is a cross-sectional view of a tree-shaped embodiment, and Figure 4 is an explanation showing how the mold is filled with molten metal during centrifugal casting. It is a diagram. L... Sprue, 2... Runway, 3... Weir, 4... Product, 5... Tree 6... Cross-sectional area reduction part, 7... Ceramic rod, 8... Filter 9...Rice water.

Claims (1)

[Claims] At the bottom of the sprue, a runner is vertically connected to the sprue, and on the outside of the runner, a weir and a product cavity are provided so that the horizontal cross-section of one or more stages is almost radial as a whole of the mold. A precision centrifugal casting mold in which the central axis of the runner coincides with the rotation axis, characterized in that a neck portion is provided in the middle of the weir to reduce its cross-sectional area.