JPS6033576B2 - Die casting method for bronze castings - Google Patents

Description

[Detailed description of the invention] The present invention relates to a die casting method for bronze castings.

Generally, copper alloy castings include yellow steel, blue steel, aluminum bronze,
There are materials such as lead bronze, which are cast using sand molding, metal mold casting, or special molding methods.

Among the various alloys mentioned above, brass whose main components are copper-zinc and high-strength brass have a short liquid-solid coexistence region as shown in the equilibrium phase diagram in Figure 1, so when the metal is poured into a mold, A strong solid phase is formed at the contact area of the molten metal with the mold, and it quickly progresses into the interior, so it can be easily manufactured using various manufacturing methods, including die casting and die casting. can.

That is, as shown in Figure 2, when molten metal is poured into the mold, a solid phase S is immediately formed at the mold contact area (Figure A), and this Oka phase S then rapidly transforms into B, C, and D. It develops inside the casting as shown in the figure.

However, bronze and lead bronze castings mainly composed of copper and tin have a long liquid-solid coexistence castle, as shown in the Cu-Sn equilibrium phase diagram in FIG. For example, in Figure 3, Cu90%, Sn
In a copper-tin alloy having a component of
The temperature range for liquid-solid coexistence is as wide as 195°C. Therefore, as shown in Figures A, B, C, and D of Figure 4, even if a small amount of Oka phase S is formed in the contact area of the Rakuyo mold, most of it will spread as a solid-liquid coexistence region, especially in the center of the casting. It is a liquid phase and its strength is extremely weak.

In other words, in Figures C and D showing the solidification process, the area where the molten metal contacts the mold exhibits a so-called "itchy state" in which a liquid phase exists within the solid phase, and the center of the casting is still in a liquid phase, and as time progresses, The progress of solidification is also slow, and when solidification occurs in the center, tensile stress due to contraction acts on the gun-shaped contact area of the molten metal, and cracks occur at the boundary between the liquid phase and the solid phase at the contact area of the molten metal with the mold. Cheap. For this reason, the sand mold method has traditionally been used exclusively when casting copper-tin bronzes and lead bronzes, etc., and in mold casting methods, particularly die casting methods, a core may be attached to the mold. The current situation is that the mold restricts the molded product, causing hot cracks in the molded product and making it impossible to cast. In view of the above, an object of the present invention is to provide a die-casting method for bronze castings, which allows bronze castings containing copper-tin as the main components to be cast into molded products with a clean mirror surface without hot cracking.

Examples of the present invention will be described below.

FIG. 5 shows a casting apparatus according to the present invention, and reference numeral 1 denotes a base, on which a support plate 2 is pivotally mounted by an arm 3, and a hydraulic cylinder fixed to the base 1. 4 so that it can be held diagonally.

When the device is in operation, the hydraulic sill 4 is extended as shown to tilt the support plate 2 approximately 15 degrees, and when the device is not in use, it is shortened to hold the support plate 2 horizontally on the base 1. Machine frames 5, 5 are fixed to both ends of the support plate 2, and a slide 6 is provided between the machine frames 5, 5.
, 6 are provided, and a movable die 7 is slid along these slide rods 6, 6 by a mold clamping cylinder 8 fixed to the machine frame 5, and a movable die 7 is provided at the tip of the piston rod 9 of the mold cotton cylinder 8. The mold 7 is attached, and the ratchet 12 of the presser member 11 for pressing the movable mold 10 is inserted into the drilled recess 9a at the tip of the piston rod, and the movable mold 10 is held in the machine frame 5 by the presser material 11. It is in contact with a fixed mold 12 that is fixed.

The molten metal M injected into the sleeve 14 is inserted into the cavity 13 formed between the movable mold 10 and the fixed mold 12 by a plunger 16 located at the tip of the piston rod of the injection cylinder 15. The molten metal M is injected from the hot water supply port 14a of the sleeve.

Reference numerals 17 and 17 are detection members for detecting the position of the plunger 16 in the sleeve 14, and the support piece 18 located at the rear end of the piston rod comes into contact with this detection member 17 during injection. ing.

The movable mold 10 and the fixed mold 12 are made of an iron-based base material, and the surfaces on which their cavities 13 are formed are made of heat-resistant tungsten, molybdenum, or an alloy containing 50% or more of these materials, which have excellent heat conductivity. Although a metal layer is provided, it is also possible to use a mold based on tungsten or molybdenum instead of both of these molds.

Note that a pressure reduction hole 19 is formed in the movable mold 10 to reduce the pressure in the cavity 13, and this pressure reduction hole 19 is connected to the pipe 2.
0 to a vacuum pump (not shown).

Next, we will discuss casting conditions when casting using the above-mentioned apparatus, namely mold temperature, injection speed, injection pressure, mold holding time, and mirror temperature.

1 Mold Temperature If the mold temperature is low, if molten metal flows into the mold, it will immediately solidify and shrink on the contact surface of the mold, forming an air gap between it and the casting, which will inhibit heat transfer, or The solidified layer remelts due to overflowing molten metal inside, causing cracks and hot cracking.

On the other hand, if the mold temperature is high, it does not adversely affect hot cracking, but it not only shortens the life of the mold but also reduces productivity. Taking these points into consideration, it has been found that the mold temperature suitable for manufacturing bronze castings is 300-420 pm. 2 Injection speed This experiment was first conducted at intervals of 0.08 h/sec,
．． At 0 arc/sec and 0.1 h/sec, not only did the flow of the molten metal become irregular, but also the flow of the molten metal became irregular, resulting in a temperature difference in the setting sun, and the injection pressure was not applied sufficiently, causing hot cracking.

Especially at 0.1 h/sec to 0.15 h/sec.
When I experimented at 0.1m/sec, it was 0.13h/sec.
Many of the above-mentioned defects appeared up to 0.14 m/s.
With EC, the defect occurrence rate was low, and at 0.18 h/sec, the above-mentioned defects hardly occurred. therefore,
The injection speed suitable for bronze casting is 0.18 h/sec to 1.
The enemy is h/sec. If the speed is higher than this, the molten metal will flow turbulently, causing mirror cavities and cracks. 3. Injection pressure The pressure injected into the cavity 13 depends on the overflow of the molten metal, but if the molten metal temperature is at an appropriate temperature (described later), the higher the injection pressure, the closer the injection pressure is to the mold, the more effective the heat transfer. Since there is no temperature difference and no accompanying changes in structure occur, hot cracking does not occur.

However, if the injection pressure is too high, it will not only shorten the life of the mold, but also cause distortion and stress in the product, which is undesirable.Moreover, if the injection pressure is too low, the hot water will not be supplied to every corner of the mold, making it difficult to form an accurate shape. Not only is it impossible to form, but air bubbles remain in the product, making it easier for cavities to occur.
Zero pressure is appropriate. 4. Mold Holding Time The heat contained in Ayayu held in the mold cavity 13 is transferred through the mold.

It is clear that if the heat content is large, the holding time of the molded article will be long, and if the heat content is large, the holding time of the molded article will be short. However, if the holding time for the same molded product is too short, solidification will be insufficient, and if the molded product is held for too long, it will be restrained by the mold and will not be able to shrink freely, causing cracks in the molded product. Therefore, the range in which hot cracking does not occur in the molded product depends on the weight of the molded product.
It will look like Table 1. Within this range, hot cracking will not occur. Table 1 Mold retention time for molded products 5 Casting temperature If the temperature is low, a solid-liquid coexistence state will occur, making it difficult for the injection pressure to work sufficiently, resulting in poor molten metal circulation and associated shrinkage and cracking. Cheap.

Furthermore, if the temperature is too high, the macrostructure tends to form columnar crystals, which causes hot cracking. Table 2 shows the degree to which defects appear when the rusting temperature is changed.

Table 2 Relationship between temperature and defects of bronze castings (equivalent to BC-6) Therefore, the temperature of bronze castings is 100% higher than the liquidus temperature.
~170 ko0 (for BC-6, 115 ko<mirror temperature<125 ko) is appropriate.

Next, the effect will be explained.

After heating molten bronze having various proportions of copper and tin to 100 to 170°C above its liquidus temperature and injecting it from the hot water supply port 14a of the sleeve 14, the injection speed of the injection cylinder 15 was set to 0.1 and Rh. /sec~1. 300-420 h/sec and its injection pressure with 200-50 arm eaves
The molten metal is injected under pressure into the depressurized cavity 13 of the mold which has been preheated to ℃, and is held as it is for a period of time corresponding to the weight of the molded product.
A dowel pin (not shown) to separate it from the fixed mold 12
Release the mold using a member such as

In this type of casting method, the molten metal poured into the cavity 13 comes into contact with the tungsten or molybdenum layer, which has excellent thermal conductivity, under high pressure, so the mold and the molten metal come into close contact, and the heat of fusion is rapidly removed. Moreover, since the inside of the cavity 13 is kept in a vacuum (reduced pressure), there is no inhibition of heat transfer by air, and therefore the surface and center of the molded product are uniformly and rapidly cooled.

Figure 6 shows the JIS standard BC~6 alloy at a temperature of 1200.
℃, mold temperature 350℃, injection speed 0. This is a microscopic photograph showing a part of the structure of the cross section of a valve molded at 10 mm/sec, an injection pressure of 30 aerophobic pressure, and a mold holding time of 6 seconds. These are micrographs at the same magnification of the structure of bronze castings sand-cast at high temperatures.
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Therefore, the molded product has excellent strength (10 to 30% higher than that of a sand mold), and there is no fear of cracking. On the other hand, in the sand mold, which has a lower thermal conductivity than the mold, both the Q phase (white part in the photo) and the eutectic group (black part in the photo) in the structure of the molded product grow significantly. . In this example, bronze 5 C was described, but similar to BC, other bronze castings (lead bronze, phosphor bronze, sildine bronze) having a wide liquid-solid phase range can also be cast under the same die-casting conditions.

As explained above, the present invention reduces the pressure in the cavity formed in the mold made of a heat-resistant metal with good thermal conductivity, heats the mold to 300 to 42,000 degrees Celsius, and adjusts the temperature of the coin to the liquid of the coin coin. The temperature is 100 to 170 qo plus the phase temperature, the injection pressure is 200 to 50 aerobic pressure, and the injection speed is 0.15.
~1. Since the mold holding time was set to 5 to 17 seconds depending on the weight of the molded product and the bronze casting was die-cast, the molded product was rapidly cooled and high pressure was applied. As a result, the rust surface is beautiful, the crystal grains are fine, and molded products with excellent strength and no hot cracking can be cast.

[Brief explanation of drawings]

Figure 1 is a copper-zinc equilibrium state diagram, Figure 2 is a solidification progress diagram of a copper-zinc alloy after twilling, and Figure 3 is a copper-tin equilibrium diagram.
Fig. 4 is a diagram showing the progress of solidification of the copper-tin alloy after depositing, Fig. 5 is an explanatory diagram of the main parts of the die-casting machine according to the present invention, and Fig. 6 is a bronze casting (equivalent to BC-6) formed by this method. ) and a micrograph showing the structure of a sand-cast bronze casting (corresponding to BC-6) enlarged to 10 tones.
This is an enlarged micrograph. 1...Base, 2...Support plate, 4...
...Hydraulic cylinder, 7...Moving die, 10.
...Moving mold, 12...Fixed mold. Multi-Z drawing Leopard 2 drawing Multi-gu drawing 3 Multi-school younger brother Ku drawing Younger brother Ku drawing

Claims (1)

[Claims] 1. Reduce the pressure in the cavity formed in the mold made of a heat-resistant metal with good thermal conductivity, 1. Heat the mold to 300 to 420°C, 2. Adjust the casting temperature to the liquid of the cast metal. phase temperature 100~170℃
3. The injection pressure is 200 to 500 atm. 4. The injection speed is 0.15 to 1.0 m/sec. 5. The mold holding time is 5 to 17 m/sec depending on the weight of the molded product.
A die-casting method for bronze castings, characterized in that the bronze castings are cast under each of these set conditions. 2. The die casting method for bronze castings according to claim 1, wherein a heat-resistant metal layer made of tungsten, molybdenum, tungsten alloy, or molybdenum alloy is formed on the cavity forming surface of the mold. .