KR101788216B1 - Precision casting method - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precision casting process, and more particularly, to a precision casting process for improving the quality and productivity of a mold by improving a conventional casting and drying process.
The present invention has the following effects.
In other words, by using the chemical forced drying method, the drying time can be remarkably shortened, and when the molten metal is injected, the bonding force between the refractory particles forming the mold is weakened during the heating and cooling of the mold, can do.
In addition, it is possible to ensure stable product quality by minimizing the variation caused by environmental changes of the natural drying method.

Description

Precision casting method {omitted}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precision casting process, and more particularly, to a precision casting process for improving the quality and productivity of a mold by improving a conventional casting and drying process.

Precision casting is a casting method in which ceramics are put on a circular mold which easily dissolves in heat like paraffin to make a mold. After the original shape is melted, the mold is injected and molded. It is used to make small and precise products by making a thin ceramic mold and breaking it after molding. One of the most precise methods of casting is that there are fewer pating lines and the gate is also very small, which makes the finishing after molding almost unnecessary compared to other plastic processes.

However, the conventional precision casting method has a problem in that it takes the longest time in the casting process due to the necessity of model injection and assembly, mold coating and drying process.

In particular, when making a ceramic mold, the refractory around the wax model is repeated 6 to 9 times depending on the product size to perform a coating operation to form a constant thickness that can withstand the pressure of the molten metal. In this process, And coating the refractory particles and drying the mold for 18 to 24 hours as shown in FIG. 2, which is the most time-consuming bottleneck process.

Specifically, the process of immersing the mold in a refractory slurry and then sanding the sand into a sand tank to dry it naturally is repeated a number of times. After 18 hours or more after the first coating, 18 hours or more after the second coating Dry for 20 hours each for the third to sixth back-ups, and air-dry for 24 hours at the last seven dips. This results in a total mold drying time of 140 hours (6 to 7 days).

On the other hand, natural drying should be carried out under constant temperature (20 ~ 24 ℃) and humidity (50 ~ 65%) condition.

Japanese Patent Application Laid-Open No. 10-2014-0087281 (Jul.

The problems to be solved in the present invention are as follows.

In other words, we propose a precision casting method that can improve the productivity by dramatically shortening the drying time by using the chemical forced drying method and ensure the stable product quality by minimizing the variation due to the environmental change of the natural drying method .

In order to solve the above problems,

Manufacturing a mold according to a design drawing (SlOO); a step (s200) of assembling a wax model prepared by injecting wax into a metal mold of step s100 to manufacture a wax tree; a step (s300) of forming a mold by applying a refractory on the surface of the wax tree in step s200 and drying the refractory; a step (S400) of dissolving and removing the wax tree by treating the mold of step S300 with high temperature and high pressure; heating the wax-free mold of step S400 to preheat and injecting the molten metal (S500); (S600) desorbing the shape of the mold into which the molten metal is injected in step S500; a step (S700) of cutting each metal object by removing metal from the metal in step S600; (s800) of polishing the surface of the object to be manufactured in step s700, and in step s300, the step (s310) of immersing the wax tree of step s200 in a slurry and then drying (S330) of immersing the wax tree of step S320 in a slurry, followed by natural drying by covering the sand with the sand, and step S310 is a step (S330) of immersing the sand in the acid slurry, chemically drying the sand with a weakly basic gas After immersing the wax tree in the slurry and covering the sand with the sand, the process of natural drying for 3 to 7 hours is repeated 1 or 2 times. In step s320, the wax tree is immersed in the acidic slurry and then the sand is coated and exposed to the basic gas for 15 minutes And then natural drying for 15 minutes is repeated four times. In step s330, the wax tree is immersed in an acidic slurry, followed by natural drying for 20 to 30 hours. In step S310, (NH3) with a weak basic gas concentration of 0.05 MPa in step s320 and an acidic slurry in the steps of s320 and s330. Is a mixture of Chamot powder and ethyl silicate stock solution in a weight ratio of 7: 3, and the sand is a Chamotte sand,
The chemical drying process in step S320 is performed in the chemical drying facility 100. The chemical drying facility 100 includes a conveyor 110 having a latch 111 capable of hanging a plurality of wax trees at predetermined intervals, A weak basic gas chamber 120 filled with ammonia (NH3) gas, and an opening 130 separated from the weak basic gas chamber so as to be in contact with the outside air, so that the wax tree, And the chemical drying proceeds in the course of coming out to the open part through the opening,
In step S310, the wax tree is immersed in the slurry to cover the sand, and then the sand is coated. In step S310, the surface of the wax tree is coated with the slurry for 4 to 5 hours (s311) (S312) during the naturally drying process.

The present invention has the following effects.

In other words, by using the chemical forced drying method, the drying time can be remarkably shortened, and when the molten metal is injected, the bonding force between the refractory particles forming the mold is weakened during the heating and cooling of the mold, can do.

In addition, it is possible to ensure stable product quality by minimizing the variation caused by environmental changes of the natural drying method.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow chart showing the manufacturing process of the present invention step by step.
FIG. 2 is a photograph of an example of a process of naturally drying a mold.
Fig. 3 is an exemplary photograph of a runner with a wax pattern attached thereto. Fig.
4 is an exemplary photograph of a mold having a refractory applied on the surface of a wax tree in step s300;
5 is a photograph (a) of a chemical drying plant and a schematic view (b) thereof.
Figure 6 is a graph of gel time versus slurry binder and pH.
Fig. 7 is a request for quality inspection of the strength of each case. Fig.
8 is a quality inspection request form for the air permeability of each embodiment.
Fig. 9 is a comparative photograph of a type in which a crack occurred in the appearance of a mold and a case in which no crack occurred.
10 is a diagrammatic representation of the manufacturing process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the scope of the present invention should be understood from the description of the claims. Further, the description of known technology which obscures the gist of the present invention is omitted.

The precision casting method of the present invention includes the steps of making a mold (s100), producing a wax tree (s200), forming a mold (s300), removing wax (s400), introducing a molten metal (s500) Step s600, object separation step s700, and surface processing step s800.

s100: Step of producing a mold according to a design drawing

The mold 11 is manufactured according to the design drawing of the object 10 to be manufactured. It is preferable to use an aluminum alloy, and the shape and dimensions of the mold are produced in consideration of the expansion and contraction of the mold and the metal which are generated during the manufacturing process.

s200 is a step of assembling a wax model prepared by injecting wax into a mold in step s100 and assembling the mold into a runner to produce a wax tree

A wax model prepared by injecting wax into a mold of step s100 is assembled into a runner to produce a wax tree. Paraffin wax having a solid state at room temperature is suitable as the wax. This is dissolved in a refining tank to make it into a liquid state, and then injected into an aluminum alloy mold made in s100 to make a wax model (21). A plurality of wax models thus formed are attached to the runner 30 by using a strong adhesive wax (Stick Wax) or the like to produce the wax tree 31 as shown in Fig. The runner is connected to a plurality of frames, and then forms a tundra in step S400.

s300: Step of forming a mold by applying refractory on the surface of the wax tree in s200 and drying the refractory

The refractory is applied to the surface of the wax tree at step s200 and the drying is repeated several times to prepare a mold. More specifically, the mold 40 is manufactured as shown in FIG. 4 by repeating the operation of dipping the wax tree of step s200 in a slurry, coating the surface of the wax tree with the sand, and drying it for a predetermined time.

s400: the mold of step S300 is treated at a high temperature and a high pressure to dissolve and remove the wax tree

The wax tree is melted by removing the wax tree at a high temperature and high pressure in step S300. The wax tree is melted by injecting a mold into an autoclave having an internal pressure of 6 to 10 kg / cm 2 and a temperature of 100 to 170 ° C. Preferably, melting at an internal pressure of 7 to 8 kg / cm 2 and at a temperature of 120 to 150 ° C can prevent melting of the wax before the wax is expanded to cause cracking in the mold. As a result, a bathtub 41 as shown in FIG. 10 is formed inside the mold 40.

s500: heating the wax-free mold of step S400 to preheat and then injecting the molten metal

The wax-free mold of step S400 is heated and preheated, and molten metal is injected into the bath. In the process of preheating the mold, firing for 2 hours or more in the firing furnace removes the residual wax inside the mold and increases the strength of the mold. Then, the material of the material suitable for the design specification is melted and injected into the preheated mold.

s600: Step of removing the contour of the mold into which the molten metal is injected in Step S500

the outer shape of the mold into which the molten metal is injected in step S500 is desorbed by the desorber so that only the injected metal 50 is left.

s700: cutting the metal in step s600, removing the bath temperature, and separating each object to be manufactured

the metal of step s600 is cut with a band saw or the like to grind and remove the molten part to leave only the object 10 to be manufactured.

s800: polishing the surface of the object to be manufactured in step s700

Sandblasting or shot blasting is used to polish the surface of the workpiece in step s700.

The present invention is particularly characterized in the mold making step (s300), which includes a surface coating and natural drying step (s310), a back coating and a chemical drying step (s320), a seal coating and a natural drying step (s330) . ≪ / RTI >

s310: immersing the wax tree of step s200 in the slurry, covering the sand and naturally drying

The operation of immersing the wax tree of step s200 in the slurry and covering the sand and naturally drying is repeated once or twice (preferably twice). When the surface of the wax tree is immersed in the slurry to cover the sand surface, the surface of the wax tree is dried for 3 to 6 hours (preferably 4 to 5 hours) after the surface coating (s311). The second cycle is naturally dried for 4 to 7 hours (preferably 5 to 6 hours) after surface coating (s312).

The slurry may be a mixture of zircon powder (Zircon Flour) and colloidal silica, and an additional defoaming agent may be added thereto. Preferably, 18 to 30% by weight of snowtex-30, 68 to 81% by weight of zircon powder and 0.5 to 2% by weight of defoamer are mixed as colloidal silica.

The sand may be a zircon sand or alumina (Al ₂ O ₃ ) sand.

s320: a step of immersing the wax tree of step S310 in an acidic slurry, covering the sand and chemically drying with a weakly basic gas

The operation of immersing the wax tree of step s310 in the acidic slurry, covering the sand and chemical drying with weakly basic gas is repeated 3 to 5 times (preferably 4 times). When a wax tree is immersed in an acidic slurry and then coated with a sand, it is chemically dried for 25 to 45 minutes after the back coating. Specifically, the coating is exposed to a weakly basic gas for 13 to 20 minutes after the coating of the backing, followed by natural drying for the time.

At this time, the chemical drying equipment 100 shown in Fig. 5 may be used. The chemical drying facility comprises a conveyor 110, a weakly basic gas chamber 120, and an opening 130. A catch 111 is formed on the conveyor for hanging a plurality of wax trees at regular intervals. The weak basic gas chamber is filled with weakly basic gas and the open portion is separated from the weak basic gas chamber and is in contact with the outside air. During the conveyor running, the chemical drying proceeds while the wax tree caught on the conveyor passes through the weakly basic gas chamber to the open part. The drying time can be adjusted by adjusting the feed rate of the conveyor. When staying in the weakly basic gas chamber for 13 to 20 minutes, the concentration of ammonia to be filled in the weakly basic gas chamber is preferably 0.02 to 0.06 MPa.

The acidic slurry is prepared by mixing a chamotte flour with an acidic binder. Preferably, the chamot powder and Ethyle silicate are mixed at a weight ratio of 6: 4 to 8: 2 and mixed for 20 to 30 hours. .

Sand is available with Chamotte Sand.

When the binder is etchilicate, the time from the sol state to the gel state at pH 2 is the longest and stable (see FIG. 6). Therefore, in the slurry state, when working at pH 2, the fluidity of the slurry is good and the application property is good and it can be used for a long time.

After the slurry is applied to the surface of the wax tree, it is required to quickly move from the sol state to the gel state and to be seated. In the present invention, it is not left to natural drying but is rapidly adjusted to a pH of 5 to 6 by using a weakly basic gas such as ammonia Thereby solidifying the sol state of the slurry into a gel state.

s330: dipping the wax tree of step s320 in the slurry, covering the sand and naturally drying

The wax tree of step s320 is immersed in the slurry, covered with the sand, and dried naturally for 20 to 30 hours. The slurry and sand in this step may be configured in the same manner as in step s320, but are not limited thereto.

According to the present invention, it is possible to manufacture a precision casting product that has been produced over 6 to 7 days (140 hours) in only 3 days (36 hours), thereby shortening the working days for 4 days (104 hours).

This is possible by drying the process which was naturally dried for 20 hours after the backup coating, in only 30 minutes by using the chemical forced drying method.

On the other hand, when the desiccation operation is performed by the vibration dash in step s600, the mold manufactured through the chemical drying step in step s320 has a merit that the desiccation work is much easier because it is more easily broken than the conventional mold. This is because the sand mold produced by naturally drying the entire life cycle of the conventional process is not broken even though the sand particles are connected to each other and the intergranular bonding force is maintained in step s600 even after the sludge is heated in step s500. However, in the molds produced by chemical drying, the sand particles are artificially fired and the bonding force between the particles is lowered in the process of heating and cooling in step s500.

An embodiment based on the present invention described above is shown in Table 1.

Example NH ₃ concentration (MPa) Weak basin gas exposure time (min) Total drying time (min) One 0.02 21 45 2 0.03 19 40 3 0.04 17 34 4 0.05 15 30 5 0.06 13 25

However, the slurry in step s310 was prepared by mixing 25 wt% of Snowtex 30, 74 wt% of zircon powder and 1 wt% of defoamer as colloidal silica, and a zircon sand was used as the sand.

The acid slurry in step s320 was mixed with the chamot powder and the ethyl silicate stock solution in a weight ratio of 7: 3 and mixed for 24 hours. The sand was used as the chamotte sand. The slurry and sand in step s330 are also the same.

Quality tests were performed on each of the above examples. Inspection items were checked for mold quality, strength and air permeability, and mold quality was checked for appearance of cracks as shown in Fig. 9 on the exterior of mold. Air permeability was measured for exhaust air pressure.

The results are shown in Figs. 7 and 8 and Table 2, showing no cracking of the outer appearance of the mold at the ammonia concentration of 0.05 MPa, the weak base gas exposure time of 15 minutes, and the total dry time of 30 minutes, Strength of 2.20 kgf / mm 2, and air permeability of 170 cc / min.

Example Thread cracks Strength (kgf / ㎟) Air permeability (cc / min) One 3 places found - NG 1.95 Not measurable - NG 2 3 places found - NG 1.78 Not measurable - NG 3 1 spot - NG 1.80 200 4 None - OK 2.20 170 5 2 places found - NG 1.83 220

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be clear to those who have knowledge.

10: object to be manufactured
11: Mold
21: Wax model
30: Runner
31: Wax tree
40: Mold
41: Tangdo
50: Metal
100: Chemical drying equipment
110: Conveyor
120: weak basic gas chamber
130:

Claims (3)

Manufacturing a mold according to a design drawing (SlOO);
a step (s200) of assembling a wax model prepared by injecting wax into a metal mold of step s100 to manufacture a wax tree;
a step (s300) of forming a mold by applying a refractory on the surface of the wax tree in step s200 and drying the refractory;
a step (S400) of dissolving and removing the wax tree by treating the mold of step S300 with high temperature and high pressure;
heating the wax-free mold of step S400 to preheat and injecting the molten metal (S500);
(S600) desorbing the shape of the mold into which the molten metal is injected in step S500;
a step (S700) of cutting each metal object by removing metal from the metal in step S600;
(S800) polishing the surface of the object to be manufactured in step S700,

In operation S300,
(s310) of immersing the wax tree of step s200 in the slurry, covering the sand and naturally drying it,
(s320) of immersing the wax tree of step S310 in an acidic slurry, coating the sand and chemically drying it with a weakly basic gas,
(S330) of immersing the wax tree of step S320 in a slurry, covering the sand and naturally drying the wax tree,

In operation S310,
Dipping the wax tree in the slurry, covering the sand and naturally drying for 3 to 7 hours is repeated once or twice,
In operation S320,
After immersing the wax tree in the acidic slurry, the sand was coated, exposed to weakly basic gas for 15 minutes, and naturally dried for 15 minutes.
In operation S330,
After immersing the wax tree in the acidic slurry, the sand was covered and air-dried for 20 to 30 hours,

In step S310
The slurry consisted of 25% by weight of colloidal silica, 74% by weight of zircon powder and 1% by weight of defoamer,
Sand is a zircon sand,

In step s320
The weakly basic gas is ammonia (NH3) at a concentration of 0.05 MPa,

In steps s320 and s330
The acidic slurry was prepared by mixing the chamot powder and the ethyl silicate stock solution in a weight ratio of 7: 3,
The sand is characterized by being a Chamotte Sand
Precision casting method.
The method according to claim 1,
The chemical drying process in step S320 is performed in the chemical drying facility 100,
The chemical drying equipment (100)
A conveyor 110 having a latch 111 capable of hanging a plurality of wax trees at regular intervals,
A weakly basic gas chamber 120 filled with ammonia (NH3) gas at 0.05 MPa,
And an opening (130) separated from the weakly basic gas chamber and in contact with the outside air,
Characterized in that the chemical drying progresses in a process in which the wax tree caught in the conveyor while the conveyor runs while passing through the weakly basic gas chamber to the open portion
Precision casting method.
3. The method according to claim 1 or 2,
When the process of dipping the wax tree in the slurry and covering the sand is referred to as surface coating,
In operation s310,
Followed by natural drying for 4 to 5 hours after the first surface coating (s311),
(S312) of naturally drying for 5 to 6 hours after two times of surface coating
Precision casting method.

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