CN114700465A - A kind of roasting method of investment casting mould shell of last stage guide vane of double shell pump - Google Patents

Abstract

A roasting method for the investment casting mold shell of the last stage guide vane of a double shell pump, which adopts the first roasting at a low temperature of 600-650 °C and a secondary roasting at a high temperature of 950-980 °C, and the secondary roasting adopts the method of sand box roasting. To ensure that the inside of the mold shell is completely burned through, and the outside of the mold shell will not suffer from strength deterioration, mold shell cracking, and casting leaks, casting pores, inclusions and other defects caused by long-term high-temperature roasting. The invention adopts the secondary roasting to enable the silica sol-water glass composite mold shell to have low gas generation and good air permeability, also to reduce the temperature difference between the molten metal and the shell, and to improve the mold filling ability of the molten metal.

Description

A roasting method for investment casting mould shell of last stage guide vane of double shell pump

technical field

The invention belongs to the field of investment casting precision casting, and in particular relates to a roasting method for investment casting precision casting shells of the last stage guide vane of a double-shell pump.

Background technique

Investment casting refers to the use of fusible materials (such as paraffin wax, etc.) to make fusible models (referred to as investment models) and weld them into modules, and then coat several layers of refractory materials on the surface of the modules, after drying and hardening, The mold is heated with steam or hot water to melt out the mold material to form a mold shell, and the mold shell is placed in a roasting furnace for high-temperature roasting. After the mold shell is roasted, molten metal is poured into it to obtain a casting.

The final stage guide vane of the double-shell pump is also made by investment casting process. Double shell pumps are generally used for units above 135MW, and have the advantages of large capacity, high lift and high efficiency. The final guide vane is the final output channel of the pump. It not only withstands high temperature and high pressure, but also plays a vital role in improving the stability of the pump outlet flow field, improving efficiency and reducing pump vibration. Because of this, in the structural design of the last stage guide vane, in addition to the flow channel profile of the other guide vanes of the feed pump, its wall thickness is generally designed to be thicker and heavier in weight. The maximum outer diameter of the final guide vane is generally above Φ400mm, and the weight of the blank is generally above 100Kg. At present, the maximum diameter of the final guide vane we produce is Φ642mm and the maximum weight is 294Kg.

Shell roasting is one of the key links in investment casting. The quality of the mold shell roasting directly affects the quality of the casting. If the mold shell is not burned through, it will not only cause the high temperature strength of the mold shell to deteriorate, the mold shell will crack, but also cause the mold shell to break out during casting, and the casting will produce pores and inclusions. defects, etc. Continuous high-temperature roasting will also lead to mold shell cracking and decrease in strength. Moreover, after the mold shell is dewaxed, a certain amount of wax, salt, saponification, moisture and organic matter in the refractory material will inevitably remain in the mold shell. The existence of these residues directly affects the quality of castings and must be eliminated by high-temperature roasting.

SUMMARY OF THE INVENTION

In view of the large volume, heavy weight and large wall thickness of the final guide vane of the double-shell pump in the prior art, it is difficult to burn the mold shell through the conventional roasting process, which is easy to cause the high temperature strength of the mold shell to deteriorate, the mold shell to crack, and cause There are defects such as breakout in mold shell casting, pores and inclusions in castings, etc. The invention provides a roasting method for the investment casting mold shell of the last stage guide vane of a double shell pump.

The purpose of this invention is to realize in the following way:

A roasting method for a double-shell pump final-stage guide vane investment casting precision casting shell, comprising the following process steps:

(1) Check whether the mold shell to be fired is defective;

(2) Furnace with mold shell;

(3) One roasting:

Turn on the power of the roasting furnace, perform a roasting, the roasting furnace is heated to 300~400 °C, open the furnace door by 1/4~1/3 to discharge water vapor, close the furnace door after the steam discharge is completed, and continue to heat up to 600~650 °C, Keep warm for 1.5 to 2 hours, and then cool down with the furnace;

(4) The mold shell is released;

(5) Form shell packing: first lay filling sand at the bottom of the sand box, the thickness of the sand layer is 60~80mm, then put the once-baked mould shell into the sand box, and fill the sand around the mould shell;

(6) Furnace the sand box loaded into the mold shell;

(7) Secondary roasting:

Turn on the power of the roasting furnace, carry out secondary roasting, heat up to 950~980 °C, keep the temperature for 1.5~2 hours, and then cool down to not less than 600 °C with the furnace and wait for pouring to complete the roasting process.

The to-be-baked mold shell described in step (1) is a mold shell that is naturally dried for 18 to 24 hours after dewaxing.

The time for discharging steam in step (3) is 30 to 45 minutes.

Step (4) The furnace temperature is lowered to below 150 ℃ and the mold shell is released, and the dust and sundries in the mold shell are cleaned.

Step (5) The filling sand at the bottom of the sand box and around the mold shell is 6-10 mesh.

Compared with the prior art, the present invention adopts the secondary roasting to enable the silica sol-water glass composite mold shell to have low gas generation and good air permeability, also to reduce the temperature difference between the molten metal and the shell, and to improve the filling of the molten metal. ability.

The invention is suitable for the mould shell roasting process of relatively large investment casting precision castings, and has certain popularization value.

Description of drawings

Fig. 1 is a sectional view of the structure of the final guide vane part of the double-shell pump of the present invention.

Figure 2 is a top view of the structure of the final stage guide vane part of the double-shell pump of the present invention.

Fig. 3 is the primary firing curve diagram of the last stage guide vane mould shell of the present invention.

Fig. 4 is the secondary roasting curve diagram of the last stage guide vane mould shell of the present invention.

Detailed ways

A roasting method for a double-shell pump final-stage guide vane investment casting precision casting shell, comprising the following process steps:

(1) Check whether the mold shell to be calcined is defective, and the mold shell baked in the furnace is preferably a mold shell that is naturally dried for 18 to 24 hours after dewaxing;

(2) Furnace with mold shell;

(3) Primary roasting: Check whether the furnace condition of the roasting furnace is normal, turn on the power of the roasting furnace, and perform a roasting. The steam time varies depending on the condition of the mold shell. Generally, it is 30-45 minutes. After the steam is discharged, the furnace door is closed, and the temperature is raised to 600-650 °C for continuous roasting, and the temperature is kept for 1.5-2 hours. 3;

(4) The mold shell is released from the furnace, and the mold shell is released after the furnace temperature drops below 150 °C, and then the dust and debris in the mold shell are cleaned;

(5) Form shell packing: first lay filling sand at the bottom of the sand box, preferably 6-10 mesh filling sand, the thickness of the sand layer is 60~80mm, and then put the once calcined mould shell into the sand box, and put the sand around the mould shell. Packing sand, preferably 6-10 mesh filling sand;

(6) Furnace the sand box loaded into the mold shell;

(7) Secondary roasting:

Turn on the power of the roasting furnace, carry out secondary roasting, heat up to 950~980 °C, keep the temperature for 1.5~2 hours, and then cool down to not less than 600 °C with the furnace and wait for pouring to complete the roasting process. The secondary calcination curve is shown in Figure 4.

As shown in Figure 1 and Figure 2, the final guide vane of the double-shell pump is large in volume, heavy in weight, and thick in wall. It is difficult for the conventional baking process to burn through the mold shell with thick wall thickness, which is easy to cause the high temperature strength of the mold shell to change. Poor, mold shell cracking, pouring steel leakage, and it will cause defects such as pores and inclusions in the casting, resulting in the scrapping of the casting. The present invention adopts the method of secondary roasting to roast the mould shell. First, 600-650°C low-temperature roasting is used to burn through the surface of the mould shell to obtain the corresponding strength. At this time, the inside of the mould shell is not completely burnt through. For the second roasting, during the second roasting, the mould shell after the first roasting is placed in the sand box, and the filling sand is placed at the bottom and around the mould shell, and the mould shell is roasted together with the sand box. During the secondary roasting process, the filling sand plays a role of protection (thermal buffering) on the mold shell, so that the strength of the mold shell will not be damaged. The strength will deteriorate and the mold shell will crack.

First low temperature and then high temperature secondary roasting, and the secondary roasting adopts the method of sand box roasting, which can ensure that the inside of the mold shell is completely burned through, and the outside of the mold shell will not suffer from poor strength and cracking of the mold shell due to long-term high-temperature roasting. And defects such as casting breakouts, casting pores, inclusions, etc. caused by the quality of the mold shell. The invention adopts the secondary roasting to enable the silica sol-water glass composite mold shell to have low gas generation and good air permeability, also to reduce the temperature difference between the molten metal and the shell, and to improve the mold filling ability of the molten metal.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, some changes and improvements can be made without departing from the overall concept of the present invention, and these should also be regarded as the present invention. scope of protection.

Claims (5)

1. a roasting method of double shell pump final stage guide vane investment casting mould shell, is characterized in that, comprises the following processing steps: (1) Check whether the mold shell to be fired is defective; (2) Furnace with mold shell; (3) One roasting: Turn on the power of the roasting furnace, perform a roasting, the roasting furnace is heated to 300~400 °C, open the furnace door by 1/4~1/3 to discharge water vapor, close the furnace door after the steam discharge is completed, and continue to heat up to 600~650 °C, Keep warm for 1.5 to 2 hours, and then cool down with the furnace; (4) The mold shell is released; (5) Form shell packing: first lay filling sand at the bottom of the sand box, the thickness of the sand layer is 60~80mm, then put the once-baked mould shell into the sand box, and fill the sand around the mould shell; (6) Furnace the sand box loaded into the mold shell; (7) Secondary roasting: Turn on the power of the roasting furnace, carry out secondary roasting, heat up to 950~980 °C, keep the temperature for 1.5~2 hours, and then cool down to not less than 600 °C with the furnace and wait for pouring to complete the roasting process. 2. The roasting method of the final guide vane investment casting mould shell of a double shell pump according to claim 1, wherein the mould shell to be roasted described in step (1) is naturally dried for 18-24 hours after dewaxing formwork. 3 . The roasting method for the investment casting mold shell of the last-stage guide vane of a double-shell pump according to claim 1 , wherein the time for discharging steam in step (3) is 30 to 45 minutes. 4 . 4. A roasting method for the investment casting mold shell of the last stage guide vane of a double shell pump according to claim 1, characterized in that, in step (4), the furnace temperature is lowered to below 150 ℃ and the mold shell is released, and the dust and dust in the mold shell are cleaned up. sundries. 5. The roasting method for the investment casting mold shell of the last stage guide vane of a double shell pump according to claim 1, characterized in that, in step (5), the filling sand loaded around the bottom of the sand box and the mold shell is 6-10 mesh .

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