CN1394706A - Core material for making core of pouring forming process and method for making core by using said core material - Google Patents

Abstract

A core material for a casting core, the components and content of the core material include: 6-18% of ammonium dihydrogen phosphate with particles smaller than 200 mesh, 30-55% of quartz particles with 30/140 mesh and/or fused silica %, 20-40% of quartz and/or fused silica with particles smaller than 200 mesh, and 5-12% of magnesium oxide with particles smaller than 270 mesh. The method for making a core for investment casting with the above-mentioned core material sequentially includes three process steps of preparing slurry, pouring, and demolding, and the method for making a core for sand casting with the above-mentioned core material is in addition to the above three process steps In addition, the roasting and degassing steps should be added. Because the core material and water and/or silica sol can form a slurry with good fluidity and solidification, it is convenient to use the casting method to make the core, so it is easy to produce a thin, fine, smooth surface and accurate size core, and This kind of core has high normal temperature strength and high temperature strength after strengthening treatment.

Description

Core material for casting core and method for making core with the same

1. Technical field

The invention belongs to the field of casting molding technology, and in particular relates to a core material used for making thin cores and cores requiring fine contours and a manufacturing method of such cores.

2. Background technology

It is understood that there are two existing methods for forming narrow or precise internal cavities of metal castings. One is to set a core in the mold, and the other is to make a core block extending into the cavity (that is, with its own core).

For sand casting, the cores usually used are clay sand cores, organic binder sand cores and water glass sand cores. The cores of the above materials have low strength and rough surfaces, and some even need to be coated with paint before they can be used. It is difficult to make a small-sized and thin core that meets the requirements or a core that requires high precision. With sand casting, it is also difficult to make pellets that extend into the cavity.

Smaller castings with narrow inner cavities or castings requiring precision inner cavities usually adopt investment casting process, because the air bubbles in the paint, floating sand, and coating and sanding are easy to cause channel blockage, so it is difficult to form a self-contained core that meets the requirements Shell, even the latest silica sol shell-making process, due to the limitation of drying speed, it is difficult to make a shell for castings with narrow or deep holes, so prefabricated cores have to be used. Conventional cores for investment casting are quartz glass ceramic cores. Not only the cost of core materials is high, but also expensive special equipment (such as hot pressure injection equipment and high-temperature sintering furnaces, etc.) The technical level is very high, so it is generally only used in the production of advanced precision castings in military enterprises or aerospace enterprises, and it is generally not easy to use in civil precision casting factories. Other types of precision cores mostly use the sand-filled core-making process of ordinary sand cores and then add certain special treatments, so it is difficult to mass-produce thin, precise, smooth surface, and accurate-sized cores.

3. Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a new type of core material and a method for making a core with the core material. Using this core material and the corresponding method can not only produce thin and precise molds with smooth surfaces and accurate dimensions. core, and the process is simple, easy to operate, and the cost is greatly reduced.

Technical scheme of the present invention is as follows:

As the core material, a composition that is easy to form a slurry with water or/and silica sol and has good fluidity and curability is selected, so that the core can be made by casting. The components and content of this core material include:

 Particles less than 200 mesh ammonium dihydrogen phosphate

The particles are 30/140 mesh quartz and/or fused silica 30～55%

 Quartz and/or fused silica with particles smaller than 200 mesh      20-40%

 Magnesia with particles smaller than 270 mesh

The above percentages are all percentages by weight.

In order to reduce the air bubbles generated by the core material during the slurry forming process, a defoamer can be added on the basis of the above components. The weight percentage of the defoamer is 0.002-0.2%. The defoamer can be phosphate ester or organic silicon.

In order to avoid cracks in the core with a relatively complex structure, magnesium dihydrogen phosphate with particles smaller than 200 meshes can also be added, and the weight percentage of magnesium dihydrogen phosphate is less than 8%.

Ammonium dihydrogen phosphate, quartz, fused silica, magnesium oxide, phosphoric acid ester, organosilicon, and magnesium dihydrogen phosphate are all commercially available components of the above-mentioned core material. Granularity, and then according to the important percentage of each component, put the ground components into a mixer and mix them evenly to prepare a core material. The prepared core material is sealed and protected from moisture for later use.

The method for making a core for investment casting with the above-mentioned core material comprises the following steps in sequence:

1. Preparation of slurry

Prepare slurry with core material and water or/and silica sol as raw material, the weight ratio of core material and water or/and silica sol is core material: water or/and silica sol=100:13～22, under normal temperature and pressure The core material is mixed with water or/and silica sol to form a slurry. The core made of slurry mixed with core material and silica sol has high strength after firing but is not resistant to boiling, while the core made of slurry mixed with core material and water has lower strength than the former after firing but is resistant to boiling , can be selected according to the casting process.

2. Pouring

Pouring is to inject the slurry into the core box at normal temperature and pressure. The core box can be made of silicone rubber, polytetrafluoroethylene plastic, wood, metal and investment materials.

3. Demolding

After the slurry injected into the core box forms a core and is completely cured, it can be demolded. The time for complete curing varies with the temperature, generally 0.5 to 2 hours.

In order to further improve the strength of the core at room temperature and high temperature, the core after demolding can be baked at 400-800°C for 0.5-2 hours, then impregnated with silica sol and dried.

Compared with the method of making a core for investment casting with the above-mentioned core material, a roasting and degassing step should be added, that is, the core after demoulding is roasted at 400-800°C To meet the limit requirements of gas volume during sand casting. This is because the core for sand casting is not like the core for investment casting, which will be degassed by high-temperature roasting together with the shell. If the strength of the core needs to be further improved, the calcined and degassed core should be impregnated with silica sol and dried.

In order to accelerate the floating speed of air bubbles in the slurry, slurry preparation can be carried out under slight vibration; in order to facilitate the filling and forming of slurry in the core box, pouring can be carried out under slight vibration.

The core made by the above method, its components and the content of each component are shown in the table below.

The components of the cast core and the content of each component (percentage by weight)

The present invention has the following beneficial effects:

1. Since the core material and water or/and silica sol can form a slurry with good fluidity and solidification, it is convenient to use the method of pouring to make the core, so it is easy to produce a thin, precise, smooth surface and accurate size core .

2. Since the core is poured and formed by gravity under normal temperature and pressure, there is no special requirement for the material of the core box, and no expensive special forming equipment is required, so the cost can be greatly reduced.

3. The components of the core material are easy to obtain, the manufacturing method of the core has simple technological steps, and the technical requirements for operators are not high, which is convenient for mass production and popularization.

4. The intensified firing temperature of the core is much lower than the firing temperature of 1200°C for the hot-pressed quartz glass-ceramic core, so energy can be saved.

5. The strengthened mold core has high normal temperature strength and high temperature strength. It can be pre-placed in the pressure mold of investment casting to press the investment mold. It will not soften and deform when roasting the mold shell and pouring metal, and will not be preserved for a long time. Decreased strength and pulverization occur.

4. Specific implementation

Example 1:

In this embodiment, a prefabricated precision core for investment casting of a nozzle casting for an industrial boiler is made. The material of nozzle castings for industrial boilers is ZGCr ₂₅ Ni ₂₀ high-nickel-chromium heat-resistant steel. The structural feature is that the nozzle is a 5mm thick slit. The surface is bulged and drilled iron cannot be polished and cleaned, resulting in scrapping, so the quality requirements for the core are very high.

The core material that present embodiment uses is (percentage by weight):

 Particles smaller than 200 mesh ammonium dihydrogen phosphate        9%

 Magnesium dihydrogen phosphate particles less than 200 mesh                        

 The particles are 30/140 mesh fused silica                                   

  Fused silica with particles smaller than 200 mesh                        

  Magnesium oxide particles less than 270 mesh                              

  Organosilicon (Defoamer)                                                                

The process step of making core in the present embodiment is:

1. Preparation of slurry

Five cores are poured each time, and one kilogram of slurry is prepared each time. Prepare the slurry with the above-mentioned core material and silica sol as raw materials, the weight ratio of core material and silica sol is core material: silica sol=100:18, and the core material and silica sol can be formed by mixing at normal temperature and pressure for 2 minutes. Slurries with fluidity requirements.

2. Pouring

The detachable core box made of polytetrafluoroethylene plastic is placed on a small vibration table, and the slurry is injected into the core box under the state of slight vibration. The whole pouring process is carried out under normal temperature and pressure.

3. Demolding

After the mold core formed by the slurry injected into the core box is completely cured, it can be demoulded, and the time for complete curing is 1 hour.

4. Enhanced treatment

After demoulding, the core was melted at 500°C for 1 hour, impregnated with silica sol, and then dried at 200°C to obtain the desired core.

The core is used as a prefabricated precision core and put into the mold to press the wax mold. After the shell is coated and hung according to the conventional water glass shell making process, the core and the shell are integrated, and the investment casting process can be used to produce the quality that meets the requirements. nozzle castings.

Example 2:

This embodiment makes the tooth part core of the tooth mandrel shaft on the hydraulic automatic return iron door. The material of the tooth mandrel is ZG35, and the structural feature is that the part where the tooth shape is located is difficult to machine, and it is formed by casting, which requires a certain precision.

The core material used in the present embodiment is (percentage by weight):

  Ammonium dihydrogen phosphate particles less than 200 mesh                            

The particles are 30/140 mesh quartz 49.9975%

  Quartz with particles smaller than 200 mesh                   25%

  Magnesium oxide particles less than 270 mesh                              

  Organosilicon (defoamer)                                                      

The process step of making core in the present embodiment is:

1. Preparation of slurry

10 cores are poured each time, and 0.4 kg of slurry is prepared each time. Prepare slurry with above-mentioned core material and water as raw material, the weight ratio of core material and water is core material: water=100: 15, core material and water are mixed under normal temperature and pressure for 2 minutes and can form the fluidity requirement. slurry.

2. Pouring

The core box is a disposable core box of fusible mold, which is placed on a small vibrating table for micro-vibration casting, and the whole casting process is carried out under normal temperature and pressure.

3. Demolding

The core can be completely solidified 1 hour after pouring, and the core can be removed by hot water demoulding.

4. Enhanced treatment

After demoulding, the core was melted at 700°C for 1 hour, impregnated with silica sol, and then dried at 200°C to obtain the desired core.

Put this core as a prefabricated core into the mold to press the wax mold, and then coat and hang the shell according to the conventional water glass shell making process. Tooth mandrel.

Example 3:

In this embodiment, an artificial joint inner cavity core is made. The material of the artificial joint is ZG1Cr ₁₈ Ni ₉ , and its structural feature is that there is a reverse slope in the inner cavity that is difficult to pull out, which makes it difficult to pull the core out of the wax mold. Manufacturing the investment mold with the usual process will make the structure of the mold very complicated.

The core material used in the present embodiment is (percentage by weight):

  Ammonium dihydrogen phosphate particles less than 200 mesh           15%

 The particles are 50/100 mesh fused silica

The particles are 50/100 mesh quartz 17%

  Quartz with particles smaller than 200 mesh                                  

  Fused silica particles less than 200 mesh                                

  Magnesium oxide particles smaller than 270 mesh                                      

  Phosphate (Defoamer)                                                

The process step of making core in the present embodiment is:

1. Preparation of slurry

5 cores are poured each time, and 0.2 kg of slurry is prepared each time. Prepare the slurry with the above-mentioned core material, water and silica sol as raw materials, add 10 parts by weight of water and 7 parts by weight of silica sol for every 100 parts by weight of the core material and mix for 2 minutes to form a slurry that meets the fluidity requirements. Carried out under normal temperature and pressure regulation.

2. Pouring

The core box is a disposable core box of fusible mold, which is placed on a small vibrating table for micro-vibration casting, and the whole casting process is carried out under normal temperature and pressure.

3. Demolding

The core can be completely solidified 1 hour after pouring, and the core can be taken out by steam demoulding.

4. Enhanced treatment

After demoulding, bake the core at 800°C for 0.5 hour, impregnate it with silica sol, and then dry it at 200°C to obtain the desired core.

The core is used as a prefabricated core and put into the mold to press the wax mold. After the shell is coated and hung according to the conventional water glass shell making process, the core and the shell are integrated, and the investment casting process can produce a quality that meets the requirements. Artificial joint castings.

Example 4:

This embodiment makes the through-hole core of the block. The material of the block is HT200 gray cast iron, which is basically a block structure. There is a through hole with a cross-sectional size of 6mm×30mm and a depth of 50mm. The through hole of this piece is difficult to make a shell by conventional investment casting.

The core material used in the present embodiment is (percentage by weight):

  Ammonium dihydrogen phosphate particles less than 200 mesh                                

The particles are 50/100 mesh quartz 49.85%

  Quartz with particles smaller than 200 mesh                     28%

  Magnesium oxide particles less than 270 mesh                                

  Phosphate (Defoamer)                                                

The process step of making core in the present embodiment is:

1. Preparation of slurry

10 cores are poured each time, and 0.4 kg of slurry is prepared each time. Prepare the slurry with the above-mentioned core material and water as raw materials, add 13 parts by weight of water to every 100 parts by weight of the core material and mix for 2 minutes to form a slurry that meets the fluidity requirements. Carried out at normal temperature and pressure.

2. Pouring

The core box is a disposable core box of fusible mold, which is placed on a small vibrating table for micro-vibration casting, and the whole casting process is carried out under normal temperature and pressure.

3. Demolding

The core can be completely solidified 1 hour after pouring, and the core can be removed by hot water demoulding.

Directly put this core as a prefabricated core into the mold to press the wax mold, and then follow the conventional investment casting method to make the shell, dewax, roast and pour the casting to produce a set that meets the requirements.

Claims (8)

1, the core material used of a kind of core of castable is characterized in that the component of this core material and content comprise:

Particle is less than 200 purpose ammonium dihydrogen phosphate (ADP)s 6～18%

Particle is 30/140 purpose quartz and/or vitreous silica 30～55%

Particle is less than 200 purpose quartz and/or vitreous silica 20～40%

Particle is less than 270 purpose magnesia 5～12%

Above-mentioned percentage is percetage by weight.

2, the core material used of the core of castable according to claim 1 is characterized in that this core material also contains defoamer, and the percetage by weight of defoamer is 0.002～0.2%.

3, the core material used of the core of castable according to claim 1 and 2 is characterized in that this core material also contains particle less than 200 purpose magnesium dihydrogen phosphates, the percetage by weight of magnesium dihydrogen phosphate＜8%.

4, a kind of method of making core with the described core material of claim 1～3 is characterized in that this method comprises following processing step successively:

(1) preparation slurry

Or/and Ludox is a raw material, core material and water are or/and the weight ratio of Ludox is a core material to the preparation slurry with core material and water: water is or/and Ludox=100: 13～22, and water promptly forms slurry or/and core material mixed in the Ludox accent at normal temperatures and pressures,

(2) cast

Cast is that slurry is injected core box, carries out at normal temperatures and pressures,

(3) demoulding

After forming core and solidify fully, the slurry that injects core box gets final product the demoulding.

5, the method for making core according to claim 4 is characterized in that the core after the demoulding 400～800 ℃ of insulation roastings 0.5～2 hour, then with Ludox dipping and oven dry.

6, a kind of method of making core with the described core material of claim 1～3 is characterized in that this method comprises following processing step successively:

(1) preparation slurry

Or/and Ludox is a raw material, core material and water are or/and the weight ratio of Ludox is a core material to the preparation slurry with core material and water: water is or/and Ludox=100: 13～22, and water promptly forms slurry or/and core material mixed in the Ludox accent at normal temperatures and pressures,

(2) cast

Cast is that slurry is injected core box, carries out at normal temperatures and pressures,

(3) demoulding

Get final product the demoulding at the core that slurry forms that injects core box and after solidifying fully,

(4) firing and removing air

Firing and removing air be with the core after the demoulding 400～800 ℃ of roastings to meeting the sand mold gas forming amount requirement for restriction in when cast.

7, the method for making core according to claim 6 is characterized in that the core behind the firing and removing air is flooded and oven dry with Ludox.

8, according to claim 4 or 5 or the method for 6 or 7 described making cores, it is characterized in that preparing slurry, be cast under little the shaking and carry out.