CN101224361A - Spumy ceramic filter capable of high slag resistance and thermal stability, and fabricating method thereof - Google Patents

Abstract

The invention relates to a froth ceramic filter used for filtering melted metal liquid. A main mineral phase of the invention is 50 to 70 percent of carborundum, with high heat transmission efficiency, and then the heat can be quickly transmitted in an instant flow to avoid forming a cold liquid face and to further avoid filtering delay so as to result in a prompt actuation. A combined phase is 20 to 45 percent of amorphous silicon oxide in which boron nitride is scattered, with a low heat expansion coefficient, and 0.5 to 2.0 percent of boron nitride is scattered into the combined phase so as to get bigger elasticity and heat plasticity. The filter has a three-dimensional mutual-connecting open-hole froth structure. The amorphous silicon oxide of the combined phase is introduced by compounding 15 to 20 Mum of electric-melting silicon, 0.4-0.6Mum of amorphous silicon powder and 15 to 20nm of nanometer silicon dioxide bond. The invention is good for adsorbing tiny impurities in the deep level of the melted metal liquid. The adopting of the silicon dioxide bond can realize low temperature sintering so as to effectively avoid phosphor pollution. By adopting a second time coating process, the mechanical strength of the filter can be effectively enhanced at the normal temperature.

Description

A kind of ceramic foam filter and preparation method with high resistance to slag high thermal stability

Background technology

The present invention relates to a kind of foam silicon carbide ceramics filter and process for making that is used for filtering molten metal.

It is a kind of ceramic foam filter that improves performance that has.Its prominent features is to have high resistance to slag, high heat endurance and good filtration adsorption activity.

It is combined that the acquisition of these characteristics depends on improved thing, with the enforcement of improved technical method.

In the process of ceramic foam filter filtering molten metal, resistance to slag has determined the inflow-rate of water turbine and the overcurrent time of filter filtering molten metal hydrothermal solution, and the chemical stability of filter.Whether heat endurance has then determined filter can be washed away by molten metal moment.

The present invention is to traditional monocalcium phosphate monohydrate bonding mullite bonded carborundum, and the improvement done on material and manufacture craft of mullite sinter bonded foam silicon carbide ceramics filter.Therefore ceramic foam filter of the present invention has not only kept all advantages of used ceramic foam filter in the past.Such as the highly porous skeleton structure of three-dimensional interconnection, big specific area, tortuous flow path, low pressure loss, priming fast also will make the resistance to slag of filter, heat endurance be improved, and do not reduce the intensity of filter, do not improve the cost of filter.

At present, the carborundum filter generally adopts mullite as in conjunction with phase, use phosphoric acid and phosphate easy fired to make the binding type filter, or high temperature sintering is made the slug type filter.

But use phosphoric acid and phosphate binders that following disadvantage is arranged:

At first, phosphoric acid and phosphate is instability when high-temperature phase-change, produces sometimes and peels off.

Secondly, the refractoriness under load of the reduction filter that phosphoric acid and phosphate can be strong.

Once more, the high temperature phosphorus of volatilization down not only can form bubble in melt metal liquid, also can cause the heat/unstable chemcial property of metal.

This shows more outstanding on the binding type filter.Though the slug type filter improves to some extent, the negative effect that oxidation produced of carborundum is still very important when the pollution of residual phosphorus and high temperature sintering.

Therefore, constantly the someone invents new filter and improves phosphoric acid and phosphate bonded filter.

Technical field

Filter of the present invention is used for melted metal filtering, belongs to casting and metal smelt technical field.

Be generally used for filter that molten metal bath filters known refractory fibre net, straight hole formula amplifier case, ceramic foam filter arranged.

The refractory fibre web filter is because intensity is low, and refractoriness is low, and filter efficiency is low, is eliminated substantially.Straight hole formula ceramic honeycomb filter is with the compression strength height, the stable performance of high temperature calorifics, and low price is still in a large amount of uses.And ceramic foam filter is with than higher filter activity, and higher filter efficiency, effect are in main flow and leading position.

In the present technique field, formed at present filtrate steel fused alumina zirconia, fused alumina zirconia-mullite, pure corundum,, filter zirconium mullite, the mullite bonded carborundum of ferroalloy; The cordierite that filters non-ferrous alloy is in conjunction with mullite, mullite bonded carborundum and magnesia spinel ceramic foam filter; Mostly use phosphoric acid and phosphate bonded or as reinforcing agent.

In these filters, the foam silicon carbide ceramics filter is with high thermal conductivity, low thermal coefficient of expansion, and good chemical stability has reasonable adaptability to various melt metal liquid, and cost is also low, thereby extremely payes attention to.At present the carborundum filter is generally with mullite bonded, with phosphoric acid and phosphate as bond.

Use the advantage of phosphoric acid and phosphate binders to be that the about 800-1100 of low temperature ℃ is finished bonding or sintering.But under this temperature, mullite can't be ripe.Must high temperature sintering can cause the oxidation of carborundum again, the thermal coefficient of expansion of filter is increased, reduce the heat endurance of filter.That is to say that mullite needs the high-temperature oxydation of high temperature sintering and carborundum to form contradiction, and be difficult to be in harmonious proportion.

Foam silicon carbide ceramics filter of the present invention, the amorphous silicon oxide combination of covalent compound boron nitride of having adopted disperse.The new thing phase that does not have necessary high-temperature process just can form just can realize sintering at 1050-1180 ℃, and intensity is fine.Not only avoid the high-temperature oxydation of carborundum, and had good adsorption activity.

In the patent of notification number CN 88 1 01382 A, having described a kind of is in conjunction with phase with silica, is the carborundum filter of bond with silica gel.Very similar with filter of the present invention, but the combination of filter of the present invention is amorphous silicon oxide mutually, and in order further to improve the resistance to slag of filter, also disperse boron nitride.Filter of the present invention cannot not need to introduce alundum (Al yet.And in the description of the patent of CN 88 1 01382 A, be allowed to, and enumerated by emphasis as claim.Be exactly that foam silicon carbide ceramics filter of the present invention has used a kind of nano-silicon bond in addition, better than the employed silica gel bond of patent performance at CN 88 1 01382 A.

The present invention also improves the manufacture craft of ceramic foam filter, will describe in detail below.

Summary of the invention

The invention belongs to of the improvement of former filter device therefor, can be used for the non-ferrous metal liquid of filtering molten, also can be used for filtering ferroalloy at material and process aspect.Be characterized in having higher resistance to slag and heat endurance, wash away, improve inflow-rate of water turbine, have remarkable advantages for it stands the molten metal bath hot-fluid.

The characteristics of foam silicon carbide ceramics filter of the present invention:

1. the principal goods of filter is a carborundum mutually, thereby has high thermal conductivity factor.Heat is very fast in overcurrent moment transmission, can not form cold liquid level and sluggish the filtration, priming fast.

Simultaneously, the thermal coefficient of expansion of carborundum is 4.4-4.7 * 10 ^-6/ ℃, all lower than the thermal coefficient of expansion of corundum, mullite, so be not easy under hot-fluid impacts, crack or burst and cause damage.

2. combination is the amorphous silicon oxide of 20-45% mutually, not only thermal coefficient of expansion is little, and high-temperature liquid-phase viscosity is very big, has bigger elasticity and thermoplasticity, melt metal liquid is difficult to its infiltration, thereby having higher resistance to slag and thermostable type, this is favourable to the inflow-rate of water turbine that improves molten metal bath.

In conjunction with disperse in mutually boron nitride.Boron nitride is the covalent bond compound, and its chemical property and thermochemical property are very stable.Especially under the little situation of anoxic and oxygen concentration, its chemical property and thermochemical property are more stable.The very big again help of raising to the filter resistance to slag.Boron nitride has strong facilitation to the generation of carborundum simultaneously, and can suppress carborundum decomposing oxidation at high temperature.

4. in conjunction with the electric smelting silicon of phase amorphous silicon oxide by 15-20 μ m, the compound introducing of nano silicon bond of 0.4-0.6 μ m amorphous silica flour and 15-20nm.In collaborative carbon coated silicon carbide particle, form rough coarse surface, help small being mingled with in the filter deep layer absorption molten metal bath.

5. adopt nano silicon to make bond, can realize low-temperature sintering.And when improving filter refractoriness under load and high-temperature stability, effectively avoided the phosphorus pollution.

6. amorphous silica will be lower than carborundum in conjunction with the thermal coefficient of expansion of phase, because the two-phase coefficient of thermal expansion mismatch can produce micro-crack at crystal boundary.These micro-cracks can delay the transgranular fracture that may occur when filter bears thermal shock, thereby the raising of the heat endurance of filter is had the bonus point effect.

7. filter of the present invention adopts secondary hanging technology.The thermal coefficient of expansion of the used mud of secondary hanging is lower than the used mud of primary pulp hanging.So after sintering was finished, the surface of filter will form compression.Can effectively improve ceramic foam filter mechanical strength at normal temperatures.

8. the content of the amorphous silicon oxide in the used mud of secondary hanging is higher, makes the oxidation resistance of filter also higher.

In sum, the present invention aims to provide more superior filter for molten metal of a kind of performance and process for making.By specific embodiment, aforesaid advantage can reach,

Description of drawings (nothing)

The specific embodiment

The quality of the operating characteristics of the mechanical performance of filter, thermodynamic property and mud has direct relation.Good dipping mud possesses thixotroping shape, stability and tack, and can not flow bob by moment guarantor type, is subjected to the thinning flowability that is of shearing force.

At first mud will have associativity and suitable viscosity.Viscosity is low excessively, and it is little to show as mud balance, good fluidity, but can cause foam absorbent slurry deficiency, make the undercapacity of filter.Though the excessive suction slurry amount that can improve foam of viscosity increases intensity, causes plug-hole and surface to fall slag easily.

It is less important to have a thixotroping shape, so that adhere to easily during at dipping mud at foam, and presents flowability under the situation of extruding or roll-in, and unnecessary mud is discharged from.

Mud will have stability once more, even leave standstill for a long time, still keeps evenly, does not stratifiedly precipitate.

1. slurrying

1.1 raw material condition

Material name	SiC	SiO2	Sif	Cf	Fe2O3	AL2O3	Granularity
								Carborundum	98.12	0.98	0.05	0.25	0.60		" 61 microns
Electric smelting silica		99.80					The 15-20 micron
								Amorphous silica powder		90.13					The 400-600 nanometer
Boron nitride							2 microns
								The nano-silicon bond		32.33					The 15-20 nanometer

1.2 the preparation of single-steeping mud

1.2.1 dipping mud prescription

Carborundum 50.0-70.0%

Fused silica 10.0-15.0%

Amorphous silica powder 5.0-10.0%

Boron nitride 0.5-2.0%

Bentonite 1.0-5.0%

Nano-silicon bond 5.0-20.0%

Dispersant 0.01-0.1%

Water 10.0-15.0%

1.2.2 dipping slurrying

At first by accurately metering of prescription, order by amorphous silica powder, fused silica, boron nitride, bentonite, nano junction mixture, dispersant, water adds in the ball mill (can certainly be colloid mill, vibromill, sand mill or stirring mill) fine grinding one hour.Half carborundum of packing into then, fine grinding one hour.Drive mill and sieve, sneak into second half carborundum, stirred two hours.Can obtain flooding required mud.

1.3 the preparation of secondary hanging mud

1.3.1 hanging mud prescription

Carborundum 45.0-65.0%

Fused silica 10.0-15.0%

Amorphous silica powder 10.0-25.0%

Boron nitride 0.5-2.0%

Bentonite 1.0-5.0%

Nano-silicon bond 5.0-20.0%

Dispersant 0.01-0.1%

Water 10.0-20.0%

1.3.2 dipping slurrying

At first by accurately metering of prescription, order by amorphous silica powder, fused silica, boron nitride, bentonite, nano junction mixture, dispersant, water adds in the ball mill (can certainly be colloid mill, vibromill, sand mill or stirring mill) fine grinding one hour.Half carborundum of packing into then, fine grinding one hour.Drive mill and sieve, sneak into second half carborundum, stirred two hours.Can obtain the required mud of secondary hanging.

2. body preparation

2.1 the processing of framework material

2.1.1 the requirement of framework material

The mechanical strength of filter, aperture and surface nature depend on foam precursor to a great extent.Require foam to have three-dimensional open mesh structure, high resilience, strongly hydrophilic and lower softening temperature.Should have certain hot shortness, good toughness.

2.1.2 the processing of framework material

At first satisfactory polyurethane foam plastics is immersed in the industrial alcohol and soaked 2 hours.

Next polyurethane foam plastics soaked 1 hour in the sodium hydroxide solution of 10-20%.

Clean polyurethane foam plastics with deionized water once more.

2.2 skeleton dipping

Baking temperature and method are very big to the influence of base substrate.Baking temperature is too high, and rate of drying is too fast, can cause the base substrate collapse-deformation.But also can cause the slurry reaction excessive velocities, and make the too fast base substrate localized cracks that causes of setting rate, reduce the mechanical strength and the high-temperature mechanics intensity of filter.

2.2.1 the polyurethane foam plastics of will clean, drying immerses single-steeping mud, air is discharged in extruding repeatedly.

2.2.2 after treating full suction mud, unnecessary mud is discharged in extruding.

2.2.3 leave standstill air dry after 6 hours,, thoroughly discharge the free moisture in the base substrate 35-55 ℃ of force drying 8 hours.

2.3 secondary hanging

The base substrate that drying is good gives centrifugal coating or spraying with the mud of secondary hanging, does not make sagging or holiday.

3. dry and sintering

Drying can be air dry or force drying, and is all suitable slowly dry, cannot microwave drying.

Sintering schedule is wanted rationally.Sintering temperature is low excessively, and the mechanical strength of the filter of making is too low, falls slag easily or is washed away by katathermal solution.Sintering temperature is too high, then makes the easy oxidation of carborundum, separates out the heat endurance that cristobalite reduces filter, and the surface-active of the filter of porcelainization reduction simultaneously makes filter reduce the adsorption capacity that is mingled with.

3.1 the foam of secondary hanging was left standstill two hours, in 95-105 ℃ of oven dry 2 hours.

3.2 the foam base substrate loading of kiln after will drying is carried out sintering in 1050-1180 ℃, can obtain the filter that needs.

3.3 calcining system

Calcining system is with five sections insulations, and slowly heating up is principal character.

3.3.1 the evaporation phase

Free water in the base substrate has been discharged when drying.But the crystallization water of polyurethane foam plastics and base substrate needs slowly to discharge, because the crystallization water of foamed plastics and material is that pug course very thin on the plastic silk screen hole wall is outer volatilizees by tightly sticking to, and changes along with materials behavior.Too fast if heat up, the pug layer can destroy or ftracture.

In 20-300 ℃ of this stage, heating rate is 1-2 ℃/min.

3.3.2 reduction period

This stage organic bond and polyurethane foam can burn volatilization, if oxidation is strong, heats up and too fastly still can cause blank cracking.So this stage should be burnt weakly reducing atmosphere, slowly heat up.

This stage is 300-500 ℃, and heating rate is 1-3 ℃/min.

3.3.3 the sintering phase

This stage is accompanied by the particle migration, and filter begins densified.Programming rate can be fast slightly.

This stage is 500-1050 ℃, and heating rate is 2-4 ℃/min.

3.3.4 sintering schedule tabulation

Temperature section ℃	Heating rate ℃/h	Heating-up time h	Temperature retention time h	Remarks
					20-120	60.0	1.67
120	0.0		0.5
					120-300	60.0	3.0		Reducing atmosphere
300	0.0		1.0
					300-500	100.0	2.0		Weakly reducing atmosphere

500	0.0		2.0
					500-1050	150.0	3.67		Oxidizing atmosphere
1050	0.0		2.0
					1050-850	100.0	2.0
850	0.0		1.0
					Add up to		12.34	6.5

Firing period: 18.84 hours

Application example 1

1. single-steeping prescription:

Carborundum 57.00kg

Fused silica 10.00kg

Amorphous silica powder 4.00kg

Bentonite 3.00kg

Boron nitride 1.00kg

Nano silicon bond 10.00kg (moisture content 70%)

Microbial polysaccharide 0.02kg

Water 14.98kg

This prescription provides following solid contents:

Carborundum 57.00kg 73.08%

Fused silica 10.00kg 12.82%

Amorphous silica powder 4.00kg 5.13%

Bentonite 3.00kg 3.85%

Boron nitride 1.00kg 1.28%

Nano silicon bond 3.00kg 3.85%

Add up to 78.00kg 100.00%

The solid content of single-steeping mud: water=78: 22

2. the secondary hanging is filled a prescription

Carborundum 50.00kg

Fused silica 11.00kg

Amorphous silica powder 6.00kg

Bentonite 3.00kg

Boron nitride 2.00kg

Nano silicon bond 10.00kg (moisture content 70%)

Microbial polysaccharide 0.02kg

Water 17.98kg

This prescription provides following solid content

Carborundum 50.00kg 66.67%

Fused silica 11.00kg 14.67%

Amorphous silica powder 6.00kg 8.00%

Bentonite 3.00kg 4.00%

Boron nitride 2.00kg 2.66%

Nano silicon bond 3.00kg 4.00%

Add up to 75.00kg 100.00

Secondary hanging mud provides 75% solid contents.

With open celled foam flexibel polyurethane Ethyl formate, flood aforesaid single-steeping mud.Make this kind foamed plastics by the mud thorough impregnation, and make it the full mud of inhaling, air is discharged in extruding repeatedly then, extrudes unnecessary mud at last.Whole foam mesh skeleton is still covered by mud, but this covering is along the interconnection of skeleton membrane orienting, the intermembranous formation three-dimensional interconnection of skeleton open-cell foam structure.Foam framework drying with the dipping of gained.Then, coated with aforesaid secondary hanging mud.

With the foam framework drying that makes, discharge free moisture content.Heat up and, be incubated two hours and finish sintering in 1050-1150 Celsius ℃.So that the discharge organic matter, and give foam framework with the needed performance of filtering metal liquid.As essential mechanical strength, good resistance to slag, high heat endurance, high filtration adsorption activity.

The ceramic foam filter of gained has open-celled structure, is made of ceramic netting twine three-dimensional interconnection.

Application example 2

To put into the running channel of a cover cast iron system with the foam silicon carbide ceramics filter that said method is made, carry out the filtration of iron and ferroalloy.And check its filter efficiency and effect.

1. riding position

1. can be placed on the nest seat of outer running channel or sprue;

2. can be placed on cross gate lap-joint and replace hydrolock collection slag cross gate, also can vertically be placed on the cross gate;

3. vertical-parting, filter can be placed on a side of sprue.

2. cast

3. filter effect

Through the iron of filtration and the effect of ferroalloy is significant

1. the percent defective that causes of the slag inclusion of foundry goods, sand holes, pore has descended 70%

2. simplified casting system, product yield improves 10%

3. cost has descended 6%

4. reduced unusual particle, improved cutting ability, tool wear reduces by 50%

5. the rate elongation that has improved mechanical property, particularly material improves comparatively obvious

Claims (10)

1. ceramic foam filter that is used for filtering molten metal liquid, its ore deposit phase main body is the carborundum of 50-75%, in conjunction be mutually 20-45% disperse the amorphous silicon oxide of boron nitride, this kind filter has the three-dimensional interconnection open-cell foam structure, be to immerse in the special ceramic cement slurry by a kind of polyurethane high molecule skeleton, through the secondary hanging, removal moisture drying, a step sintering is made.

2. according to claim 1, contained carborundum solids content is 50-75% in the filter.

3. according to claim 1, contained silica solid content is 20-45% in the filter, and disperse the boron nitride of 0.5-2.0%.

4. according to claim 1, described raw material is prepared in proportion, give powerful the dispersion, (can be ball milling, sand milling, vibromill, colloid mill) makes it to mix, sieve then, make the ceramic cement slurry, a kind of polyurethane high polymer foam framework is immersed in the mud, make it the full mud of inhaling, squeeze out unnecessary mud then, with this high polymer skeleton drying, the secondary hanging is once more after the drying, in 1050-1180 Celsius ℃ sintering, can obtain needed filter.

5. according to claim 4, amorphous silicon oxide contained in the filter is introduced jointly by electric smelting silicon (or fused silica powder) the 5-10% noncrystalline silica flour of 10-15% and the nano silicon bond of 5-20%.

6. according to claim 4, making carborundum used in this filter is 250 orders or littler.

7. according to claim 4, the granularity of making electric smelting silica flour used in this filter is 20 microns, and the granularity of amorphous silica powder is the 0.40-0.60 micron, and the solids particle diameter is the 15-20 nanometer in the nano-silicon bond.

8. according to claim 4, making this filter needs a kind of ceramic cement slurry, and the moisture content of single-steeping mud is 20-25%, and the mud moisture content of secondary hanging is 25-30%, and adds the dispersant of 0.01-0.1%, the sintering aid of 0.5-1.0%.

9. according to claim 1, a kind of polyurethane high molecule compound with interconnected pores good springiness be arranged, this high polymer has PPI10, PPI20, the hole density of PPI30.

10. filter of the present invention adopts secondary hanging technology, the thermal coefficient of expansion of the used mud of secondary hanging is lower than the used mud of primary pulp hanging, so after sintering is finished, the surface of filter will form compression, can effectively improve the mechanical strength under the filter normal temperature like this, the content of the amorphous silicon oxide in the used mud of secondary hanging is higher, makes the oxidation resistance of filter higher.