CN105710333A - Centrifugal casting process for large heat-resistant steel furnace bottom roller body - Google Patents

Abstract

The invention discloses a casting process for a large heat-resistant steel furnace bottom roller. The centrifugal casting process is adopted, and the interval between two supporting wheels at the rear end of a rolling wheel centrifugal machine adopted by centrifugal casting is set to be 1366 mm. The centrifugal casting process has the following advantages that (1) when the length of a casting exceeds the capability scope of the centrifugal machine, equipment can be modified and a short shaft system of the centrifugal machine is replaced by a long shaft system so as to meet the operation requirement of a casting mold under the condition that the motor power, the centrifugal rotating speed, the machine body strength and the wheel interval of the equipment can bear the long shaft system; and (2) vibration of the casting mold is reduced as much as possible, a water cooling measure is not adopted for the casting mold so as to avoid large temperature jump during solidification of the casting, a coating layer is thin and even so as to avoid and impede contraction of the casting, and therefore the cracking defect can be better prevented.

Description

The centrifugal casting technique of the large-scale heat resisting steel furnace bottom body of roll

Technical field

The present invention relates to hearth roll technical field, the casting technique of especially a kind of large-scale heat resisting steel hearth roll.

Background technology

Hearth roll is the parts of most important in continuous roller-hearth heat treatment furnace, most rapid wear, works under the high temperature of 900 DEG C, and these parts make that consumption is big, the life-span is low, generally from external import, expensive.In hearth roll, the part of most critical is the furnace bottom body of roll, and centre spinning method can only be adopted to produce.Length external diameter being compared to the making of very big Large Furnace bottom roller body, the requirement of centrifuge instrument is high, and centrifugal casting parameter coupling is also very exquisite, because its influence factor is many, complex process, the defect such as foundry goods easily cracks, cold shut interlayer and pore, thus centrifugal casting is very difficult.

The material of Large Furnace bottom roller body is ZG40Cr25Ni20Si2, and this steel is Austenitic heat resisting cast steel, and it is good that this high-chromium-nickel steel has good high-temperature oxidation resistance and elevated temperature strength, structure stability and welding performance.Using maximum temperature is 1150 DEG C～1200 DEG C, has good heat resistance when using under≤1000 DEG C of conditions.The chemical composition of ZG40Cr25Ni20Si2, ambient temperature mechanical properties and mechanical behavior under high temperature are in Table 1, table 2 and table 3.

The chemical composition of table 1ZG40Cr25Ni20Si2

The ambient temperature mechanical properties of table 2ZG40Cr25Ni20Si2

The mechanical behavior under high temperature of table 3ZG40Cr25Ni20Si2

Large Furnace bottom roller body, casting length reaches 2950mm, and casting section thickness is 50.5mm, and casting quality is 1250kg, and centre spinning method can only be adopted to produce.Casting dimension parameter is: length/external diameter=2950/388=7.6, and owing to length external diameter is than very big, therefore traditional centrifugal casting difficulty is very big；External diameter/internal diameter=1.35, the centrifugal rotational speed such as can adopt.

According to casting dimension, there is two categories below situation: the length that the first kind is this foundry goods is longer, beyond the accommodation scope of existing equipment, first have to solve the problem that capacity of equipment is not enough；Equations of The Second Kind is that to produce the risk of following three kinds of casting flaws significantly high: 1. this casting length is very long and external diameter is less, foundry goods is in the process of cooling meat, it is subject to the resistance of casting mold and coating relatively big, adds that large-scale roller centrifuge is in operation bigger vibrations, it is easy to crack defect；2. owing to foundry goods external diameter is Ф 388mm, length is 2950mm, thus molding work surface area is very big, in the starting stage of cast, if aluminium alloy rapidly and uniformly in molding work surface paving type and reach certain thickness, then can not very easily produce cold shut interlayer defect；3. the length external diameter of foundry goods is than very big, reaches 7.6, and the gas in casting mold is difficult to discharge, it is easy to produce gas hole defect.Prevent the generation of three of the above defect, it is necessary in technique, take a series of countermeasure.

For crack defect, mainly start with from three aspects and 1. alleviate the vibrations that casting mold is subject to as far as possible, including: the angle theta (center angle) in casting mold axle center and supporting axle axial connecting line is rationally set；Commissioning device, reduces the gap between casting mold raceway and bogie wheel；During design casting mold, it should be noted that casting mold raceway outside dimension with at the ratio of raceway inside dimension, make that casting mold is on-stream has good stationarity.2. avoid foundry goods to have big temperature jump in process of setting as far as possible, avoid adopting casting mold water-cooled measure as far as possible.3. dope layer is uniform and thin, must not have the projection hindering foundry goods to shrink.

For cold shut interlayer defect, mainly start with from three aspects and 1. improve initial poring rate, to meet the paving type thickness δ in initial 3s_{Paving type}；2. pouring temperature is properly increased, to strengthen the mold-filling capacity of aluminium alloy；3. molding work temperature is properly increased, to strengthen the paving type ability of aluminium alloy.

For gas hole defect, mainly start with from following two aspects and 1. adopt special coating, microcosmic exhaust passage can be formed on casting mold inner circle coating top layer, help the gas in casting mold to discharge；2. the baking type temperature of casting mold is improved, to dry the moisture in casting mold.

Summary of the invention

The present invention is directed to the deficiencies in the prior art, it is proposed to the casting technique of a kind of large-scale heat resisting steel hearth roll, rationally, conforming product rate is high in operation.

In order to realize foregoing invention purpose, the present invention provides techniques below scheme: the casting technique of a kind of large-scale heat resisting steel hearth roll, adopts centrifugal casting technique, and the rear end two of the roller centrifuge adopted in described centrifugal casting supports wheel spacing and is set to 1366mm.

Further, the material of described hearth roll is carbon cast steel ZG230-450.

Further, casting mold axle center is 110 ° with the angle of two described bogie wheel axial connecting lines.

Further, casting mold rotating speed is 532.4～692.2r/min.

Further, casting-up temperature is 1580 DEG C～1620 DEG C.

Further, molding work temperature is 180 DEG C～220 DEG C.

Further, gate pin is by Φ_InThe refractory brick tube of=80mm makes, and outer tube is made by the heat resisting pipe that material is ZG40Cr25Ni20Si2, and the external diameter of heat resisting pipe, internal diameter are of a size of Ф 145mm/ Ф 125mm.

Further, when laying of casting mold inner circle coating, mold temperature is 80 DEG C～100 DEG C, and rotating speed is 100r/min.

Further, having laid the casting mold of coating and entered stove and toast, baking type temperature is 350 DEG C～380 DEG C, and temperature retention time is 5h～6h.

Compared with prior art, the invention have the advantages that

(1) when casting length is beyond centrifuge capacity scope, at the power of motor of equipment, centrifugal rotational speed, when device body intensity and wheel spacing can both be born, can reforming equipment, change the short axle system of centrifuge into long axis system, to meet the operation needs of this casting mold.

(2) alleviate the vibrations that casting mold is subject to as far as possible；Casting mold is not adopted water-cooled measure, to avoid foundry goods to have big temperature jump in process of setting；Dope layer is uniform and thin, it is to avoid hinders the contraction of foundry goods, can contribute to preventing the generation of crack defect.

(3) improve initial poring rate, meet the requirement of paving type thickness in initial 3 seconds；Properly increase pouring temperature, strengthen the mold-filling capacity of aluminium alloy；Properly increase molding work temperature, strengthen the paving type ability of aluminium alloy, cold shut interlayer defect can be effectively prevented and produce.

(4) adopt special coating, microcosmic exhaust passage can be formed on casting mold inner circle coating top layer, help the gas in casting mold to discharge；Improve the baking type temperature of casting mold, to dry the moisture in casting mold, gas hole defect can be effectively prevented and produce.

Detailed description of the invention

Describing the present invention below in conjunction with detailed description of the invention, the description of this part is only exemplary and explanatory, and protection scope of the present invention should not have any restriction effect.

Conventional large-size horizontal roller centrifuge, power of motor is 30kW, and motor maximum (top) speed is 740r/min, and centrifuge bogie wheel diameter is d=450mm.The maximum casting dimension that this equipment can hold is: external diameter Ф 300mm～Ф 800mm, length 800mm～2300mm, and during work, loading capacity W should be less than 5t, and motor stabling current can not more than 63A.As can be seen here, equipment, as 2950mm, beyond the limit range of this equipment, will be transformed, and each technical parameter needs through strict calculating and accounting by this large-scale heat resisting steel hearth roll.

The present invention have studied two cases using conventional equipment before this, as the analysis foundation of roller centrifuge instrument ability and transformation.

Case 1, large-scale high manganic aluminum bronze heavy wall nut for large-scale metallurgical equipment, nut is of a size of (Φ 772mm × 208mm) Φ 673mm/ Φ 350mm × 766mm, casting quality is 1666kg, this casting mold material selection ZG20CrMo, casting mold maximum outside diameter is Φ 1000mm, and casting mold greatest length is 1100mm, mold quality is 3190kg, therefore full payload W=W_{Foundry goods}+W_{Casting mold}=1666kg+3190kg=4896kg.Casting mold rotating speed n=490r/min, now β=1.008, during casting mold zero load, centrifuge stabling current is 42A, and in casting process, centrifuge stabling current is 43A.This case is that the wheel spacing about super-magnum centrifuge is not enough, causes casting mold wall thickness relatively thin, and centrifugal rotational speed is also slightly not enough and the centrifugal casting classics case successfully poured into a mould^[3]。

Case 2, Large size Aluminium bronze bushing for dredger, liner size is (Φ 822mm × 94mm) Φ 721mm/ Φ 616mm × 1615mm, casting quality is 1530kg, these casting mold material selection ZG230～450, casting mold maximum outside diameter is Φ 960mm, and casting mold length is 1898mm, mold quality is 2603kg, therefore full payload W=W_{Foundry goods}+W_{Casting mold}=1530kg+2603kg=4133kg < 4500kg.Casting mold rotating speed n=521r/min, now β=1.42, during casting mold zero load, centrifuge stabling current is 42A, and in casting process, centrifuge stabling current is 38A～42A, be maximum permissible value 63A about 63.5%.This case is that the wheel spacing about super-magnum centrifuge is not enough, and casting mold wall thickness is also slightly eccentric and the centrifugal casting classics case successfully poured into a mould^[4]。

It can thus be appreciated that: if 1. can control within 5000kg by full payload W, then the power of motor of equipment can bear, and device body intensity can be born；2. this example casting mold external diameter is not as big, and the wheel spacing of super-magnum centrifuge is enough；3. calculating from behind is it can be seen that centrifugal rotational speed also can meet；4. owing to casting length is 2950mm, then casting mold length is 3235mm, and the outer end of centrifuge head and the tail bogie wheel is of a size of 1450mm, casting mold two ends are of a size of 892.5mm (> 1450/2mm=725mm) beyond head and the tail bogie wheel, obviously, if not transforming, horizontal roller centrifuge cannot hold this casting mold and run thereon.

This equipment is carried out following transformation, has again made the axle system of a set of lengthening, changed long axis system into by the short axle system of centrifuge rear end two bogie wheel, by moving 360mm behind the position of tail end bogie wheel, moved to the outside of bearing block, so can meet the operation needs of this casting mold.

Casting mold material selection carbon cast steel ZG230-450.Three raceway supporting operatings, two ends symmetric design, reduce axial float as far as possible and reduce radially vibrations, can relatively even running when cast.Casting mold gross mass (containing the end, cover plate) is 2950+74=3024kg, and casting quality is 1250kg, and during operation, gross deadweight is W_{Foundry goods}+W_{Casting mold}=1250kg+3024kg=4274kg, during by work, loading capacity W controls less than 5t.

The designing points of casting mold is: 1. casting mold adopts symmetric design, casting mold raceway outside dimension be 700/1830/700=1/2.61/1 at the ratio of raceway inside dimension, casting mold stationarity operationally is better；2. casting mold end-play between centrifuge bogie wheel is 15mm；3. casting mold inner chamber does not put tapering, and casting mold stack shell does not drill through pore；4. casting mold casting section thickness is than for δ_Type/δ_Part=(84.5～69.5)/50.5=1.67～1.38, meet δ on handbook_Type/δ_PartThe requirement of=1.2～2.0；5. foundry goods reduced scale is 2.2%, therefore casting mold inner chamber is of a size of Φ 401mm × 3015mm；6. casting mold raceway (with supporting the mo(U)ld face that wheel contacts) diameter D=580mm.

Casting mold axle center and the angle theta supporting axle axial connecting line, for the furnace bottom body of roll heat resisting steel foundry goods very easily cracked, particularly important.If θ is too small, the vibrations that casting mold is subject to are relatively big, and under extreme case, the casting mold of high-speed rotation can jump from bogie wheel；If θ is excessive, then the frictional force supported between wheel and casting mold raceway can be too little, and Active support wheel cannot drive casting mold to rotate by frictionally.Handbook^[5]On generally introduce θ=90 °～120 °, we generally take θ=110 °～115 °, it is contemplated that furnace bottom body of roll casting mold is longer, for reduce resistance to avoid power loss, take into account casting mold shock conditions simultaneously, this example takes θ=110 °.

Then the wheel spacing of two supporting axles is L-d=844-450=394 (mm), and taking wheel spacing is 400mm.

Before casting mold uses, will being placed on centrifuge and debug, the clearance requirement < 0.3mm between centrifuge bogie wheel and casting mold raceway, to alleviate circular runout, available chi of inserting checks；Additionally, casting mold itself requires to be in level, in case axial float, available water level checks.

Casting mold rotating speed

Casting mold rotating speed is to ensure that one of important parameter of centrifugal casting quality.If casting mold rotating speed is too high, when cast, then very big vibrations can be caused, it is easy to cause that foundry goods cracks；If casting mold rotating speed is too low, oxide inclusion is difficult to from aluminium alloy emersion, and aluminium alloy also can be caused time serious to drench.

Required centrifugal rotational speed is:

$n=\frac{55200}{\sqrt{\mathrm{\&gamma;}\&CenterDot;R_0}}\mathrm{\&beta;}\mathrm{...}\left(2\right)$

In formula: n is casting mold rotating speed, r/min；γ is the density of cast alloy, N/m³；R₀For the inside radius of foundry goods, m；β is regulation coefficient, and the centrifugal casting to steel-casting takes β=1.0～1.3.

For the furnace bottom body of roll of heat resisting steel ZG40Cr25Ni20Si2, ρ=7.49 × 10⁴N/m³, R₀=0.1435m, therefore the centrifugal rotational speed needed for casting mold is

$n=\frac{55200}{\sqrt{\mathrm{\&gamma;}\&CenterDot;R_0}}\mathrm{\&beta;}=\frac{55200}{\sqrt{7.49\&times;{10}^4\&times;0.1435}}\&times;(1.0~1.3)=532.4\&times;(1.0~1.3)=(532.4~692.2)r/min$

Super-magnum centrifuge has five grades of rotating speeds, n_{Driving shaft}=1.4n_Motor, drivewheel diameter d=450mm, casting mold raceway place diameter D=580mm, each shelves rotating speed n of motor_MotorRespectively 430,460,500,670,720r/min, therefore the maximum (top) speed that casting mold can reach is

n_{Type max}=d n_{Driving shaft}/ D=450 × 1.4n_Motor/ 580=782r/min

Therefore centrifugal rotational speed can be met, but this equipment can not stepless time adjustment, if take the 4th gear rotating speed, n_Type=728r/min, now β=1.37；If taking the 3rd gear rotating speed, n_Type=543r/min, now β=1.02.For ensureing that molten metal does not produce pouring and falls, when starting to pour into a mould, casting mold rotating speed fourth speed rotating speed, when molten metal condensation enters into solid phase area, casting mold rotating speed is reduced to third gear, to reduce the risk that foundry goods cracks.

Pouring temperature

For ZG40Cr25Ni20Si2 alloy, it is contemplated that the surface area of this Large Furnace bottom roller body is relatively big, and length is very long, and for preventing cold shut defect, taking pouring temperature is 1580 DEG C～1620 DEG C.

Molding work temperature

The operating temperature of casting mold and casting dimension, castings material are relevant.For good fluidity, shrink greatly, in the heat resisting steel of Layer by layer solidification characteristic, it is desirable to the operating temperature of casting mold is higher.Especially for the casting mold that length is very long, if molding work temperature is too low, high temperature alloy liquid can quickly be solidified by the effect of casting mold Quench, thus accelerates the setting rate of follow-up aluminium alloy, it is easy to makes foundry goods produce pipe and cold shut defect.Particularly at the paving type thickness δ poured into a mould in initial 3s_{Paving type}When not rich, can make up by properly increasing pouring temperature.

For ZG40Cr25Ni20Si2 alloy, molding work temperature is advisable at 160 DEG C～260 DEG C, and taking molding work temperature is 180 DEG C～220 DEG C.

The estimation of casting mold maximum temperature

Castings material is heat resisting steel ZG40Cr25Ni20Si2, is of a size of Ф 388mm/ Ф 287mm × 2950mm, casting quality M_Part=1250kg.The pouring temperature t of ZG40Cr25Ni20Si2₁=1600 DEG C, liquidus temperature t₂=1440 DEG C, solidus temperature t₃=1400 DEG C, foundry goods calcining temperature t₄=700 DEG C.The solid-state specific heat capacity c of ZG40Cr25Ni20Si2_Gu=0.502kJ/kg DEG C, liquid specific heat appearance can push away and be calculated as c_Liquid=(1.25～1.65) c_Gu=(1.25～1.65) × 0.502kJ/kg DEG C=0.628kJ/kg DEG C～0.828kJ/kg DEG C, take C_Liquid=0.703kJ/kg DEG C, latent heat of fusion L=251.2kJ/kg.Casting mold material is ZG230-450, and mould dimension can regard Ф 570mm/ Ф 401mm × 3235mm, mold quality M as_Type=3024kg.Molding work temperature T_{Operating temperature}=200 DEG C.

The temperature first presetting casting mold jacket casing is 550 DEG C, and the ZG230-450 specific heat capacity when 550 DEG C is c_{Jacket casing}=0.706kJ/ (kg DEG C).The minimum mass of required casting mold is

β is coefficient correction, takes β=1.0 when being covered with more than 3mm tamper on molding work surface；All the other situations take β=1.05.The then lift-off value △ of mold temperature T=550 DEG C-200 DEG C=350 DEG C

I.e. carbon casting element steel cylinder set minimum mass M_{Jacket casing min}During=3039kg, just can meet the requirement that casting mold is 550 DEG C, and the jacket casing quality of the ZG230-450 of reality is 2950kg, difference is 3039kg-2950kg=89kg, it is slightly lower than the jacket casing prescription (< 3%) that jacket casing temperature is 550 DEG C, therefore the maximum temperature of casting mold is not higher than 570 DEG C.

Therefore, casting mold maximum temperature is suitable, it is not necessary to adopt water-cooled measure, and this is critically important for preventing from foundry goods from cracking haveing the drawback that.

The design of running gate system

Have been discussed above that the surface area of furnace bottom body of roll centrifugal casting mould inner chamber is relatively big and casting mold is very long, if poring rate is too slow, then easily produce foundry goods became uneven, particularly in initial flow big not time, aluminium alloy can not be paved with mo(U)ld face soon and produce pipe even cold shut.If poring rate is too fast, then aluminium alloy splashes serious, produces a large amount of oxide inclusion, pore.For heat resisting steel ZG40Cr25Ni20Si2, first big plume, high-head, rear little plume, low-head, the without interrupting the flow method of steadily cast should be adopted.Namely being rapidly filled with mo(U)ld face when the initial stage of cast with big plume, high-head aluminium alloy, afterwards along with the decline of alloy liquid level, plume speed slows down gradually, is poured into last without interrupting the flow.

It is important to note that the internal diameter of furnace bottom body of roll foundry goods is Φ 287mm, at the bottom of casting mold, the diameter of bore of cover plate be Φ 220mm, gate pin must be able to meet claimed below: in 1., pipe can bear high-temperature molten steel and passes through；2. outer tube can bear casting mold inner chamber high-temperature molten steel heat radiation baking and indeformable.Therefore interior pipe adopts Φ_InThe refractory brick tube of=80mm makes, and the heat resisting pipe that outer tube adopts material to be ZG40Cr25Ni20Si2 makes, it is possible to bearing≤the high-temperature baking of 1000 DEG C, the external diameter of heat resisting pipe, internal diameter are of a size of Ф 145mm/ Ф 125mm.

The calculating of initial poring rate and paving type thickness

Rule of thumb, for large cast steel lining, if in initial 3 seconds of cast, aluminium alloy can carry out paving type and paving type thickness δ equably when molding work temperature is suitable_{Paving type}During >=4mm, it is possible to more efficiently prevent the generation of pipe, cold shut defect.But the diameter that the diameter of bottom pour ladle tapping hole is Φ 50mm, Gu Tun bag tapping hole is also taken as Φ 50mm.

Praising (Osann) hydraulic formula according to Austria, we can calculate the aluminium alloy casting quality G in the initial 3s of cast_T=3s。

$F=\frac{\mathrm{\&pi;}}{4}{d}^2=\frac{G}{\mathrm{\&rho;}t\mathrm{\&mu;}\sqrt{2gH}}$

In formula: F is the minimum sectional area storing up bag tapping hole, cm²；G is aluminium alloy casting quality, kg；H is aluminium alloy fall head, cm；ρ is aluminium alloy density, kg/cm³；T is the duration of pouring, s；μ is flow consumption coefficient, for cast steel centrifugal casting, takes μ=0.5；G is acceleration of gravity, cm/s².Store up minimum diameter d, the cm of bag tapping hole.

In this example, ρ=7.75 × 10^-3kg/cm³, μ=0.5, t=3s, H=130cm (stores up bag pressure head+bottom pour ladle pressure head), g=980cm/s², cast initial 3s in aluminium alloy casting quality G_T=3sFor

$G_{t=3s}=\frac{\mathrm{\&pi;}}{4}{d}^2\mathrm{\&rho;}t\mathrm{\&mu;}\sqrt{2gH}=\frac{\mathrm{\&pi;}}{4}\&times;5^2\&times;7.75\&times;{10}^{-3}\&times;3\&times;0.5\&times;\sqrt{2\&times;980\&times;120}=115.2\left(kg\right)$

Namely initial poring rate is 38.4kg/s, can obtain the paving type thickness δ in initial 3s_{Paving type}

{401²-(401-2 δ_{Paving type})²}×π÷4×3015×10^-6× 7.75=115.2kg

δ can be calculated_{Paving type}=3.95mm, is slightly smaller than δ_{Paving type}The condition of >=4mm, can make up by properly increasing pouring temperature and molding work temperature.

Gate pin gos deep into 100mm after casting mold cover plate, can calculate the actual falling point of the aluminium alloy 1380mm place after cover plate, be about the position of distance casting mold front end 46%.

Coating and laying method

We adopt special coating, and the coating applied thickness of casting mold inner circle is 2mm, and the coating applied thickness having groove-bottom cover plate is 5mm.It is noted that the viscosity of coating is prepared slightly lower, in order to uniformly shakedown type.

The laying method of casting mold inner circle coating is: adopt seamless steel pipe to make coatings tank, coatings tank two end-stopping plate is welded rotation axle.After casting mold is laid on centrifuge, by the bottom plate of coatings tank traverse casting mold, it is placed on the bracing frame of casting mold two outer end.Putting into the quantitative coating prepared in coatings tank, coating carries out paving type in coatings tank rollover process.Mold temperature when hanging coating is 80 DEG C～100 DEG C, and now casting mold rotating speed controls at about 100r/min.Casting mold rotates in the direction of the clock, and coatings tank then overturns counterclockwise, and coating rotates in casting mold just can tentatively dry for about 15 minutes.The coating of bottom plate lays and individually carries out.

It should be noted that special coating can form microcosmic exhaust passage in casting mold inner circle, although the length external diameter ratio of furnace bottom body of roll foundry goods is up to 7.6, we successfully solve the furnace bottom body of roll and produce a difficult problem for gas hole defect.

The determination of baking type and calcining temperature

The casting mold hanging up properly coating to be entered stove again toast, to dry the moisture in casting mold.Baking type temperature is 350 DEG C～380 DEG C, and temperature retention time is 5h～6h.It is noted that casting mold come out of the stove after to cast interval time should be as far as possible of short duration.

Being poured rear casting mold to continue to run on centrifuge, observing foundry goods inner surface is that kermesinus (about 600 DEG C) can be shut down.Generally, for middle-size and small-size foundry goods, can stop after solidification completely from casting mold, take out foundry goods, or from centrifuge, casting mold be taken off together with foundry goods simultaneously, then carry out the demoulding.Consider that this casting dimension is relatively big and wall thickness is relatively thin, for preventing casting mold and foundry goods to be deformed, after shutdown, casting mold is hung together with foundry goods lower centrifuge simultaneously, lie in ground, when foundry goods is cooled to below 200 DEG C, carry out the demoulding again.

Practical condition

When the actual production of Large Furnace bottom roller body, Rated motor value is 63A, and after start, voltage is 330V, and electric current progressivelyes reach stationary value 38A～40A, be maximum permissible value 63A about 62%, centrifuge work time load suitable.

In the trial production of the 1st furnace bottom body of roll, to technological parameter also among the process groped, after the foundry goods demoulding, it has been found that the furnace bottom body of roll middle part, have the oblique crackle that four or five places are deeper, it is impossible to saved by repair welding, can only scrap.

In the follow-up furnace bottom body of roll produces, molding work temperature is 190 DEG C, when starting to pour into a mould, and casting mold rotating speed the 4th grade of rotating speed, n_Type=728r/min, now β=1.37, the duration of pouring is 55s, and casting quality is 1295kg.After pouring about 8 minutes, when molten metal condensation enters into solid phase area, casting mold rotating speed is reduced to the 3rd grade of n_Type=543r/min, now β=1.02.When foundry goods inner circle is kermesinus, centrifuge stops, and casting mold has run altogether 45 minutes on centrifuge.Then shut down, casting mold is hung together with foundry goods lower centrifuge simultaneously, lies in ground, when foundry goods is cooled to below room temperature, carry out the demoulding again.

Follow-up foundry goods flawless, cold shut interlayer and gas hole defect, after roughing, quality is good, meets the requirement of user.

The above is only the preferred embodiment of the present invention; it should be pointed out that, for those skilled in the art, under the premise without departing from the principles of the invention; can also making some improvements and modifications, these improvements and modifications also should be regarded as protection scope of the present invention.

Claims (9)

1. a casting technique for large-scale heat resisting steel hearth roll, adopts centrifugal casting technique, it is characterised in that: the rear end two of the roller centrifuge adopted in described centrifugal casting supports wheel spacing and is set to 1366mm.

2. the casting technique of large-scale heat resisting steel hearth roll as claimed in claim 1, it is characterised in that: the material of described hearth roll is carbon cast steel ZG230-450.

3. the casting technique of large-scale heat resisting steel hearth roll as claimed in claim 1, it is characterised in that: the angle of casting mold axle center and two described bogie wheel axial connecting lines is 110 °.

4. the casting technique of large-scale heat resisting steel hearth roll as claimed in claim 1, it is characterised in that: casting mold rotating speed is 532.4～692.2r min.

5. the casting technique of large-scale heat resisting steel hearth roll as claimed in claim 1, it is characterised in that: casting-up temperature is 1580 DEG C～1620 DEG C.

6. the casting technique of large-scale heat resisting steel hearth roll as claimed in claim 1, it is characterised in that: molding work temperature is 180 DEG C～220 DEG C.

7. the casting technique of large-scale heat resisting steel hearth roll as claimed in claim 1, it is characterised in that: gate pin is by Φ_InThe refractory brick tube of=80mm makes, and outer tube is made by the heat resisting pipe that material is ZG40Cr25Ni20Si2, and the external diameter of heat resisting pipe, internal diameter are of a size of Ф 145mm Ф 125mm.

8. the casting technique of large-scale heat resisting steel hearth roll as claimed in claim 1, it is characterised in that: when laying of casting mold inner circle coating, mold temperature is 80 DEG C～100 DEG C, and rotating speed is 100r min.

9. the casting technique of large-scale heat resisting steel hearth roll as claimed in claim 8, it is characterised in that: having laid the casting mold of coating and entered stove and toast, baking type temperature is 350 DEG C～380 DEG C, and temperature retention time is 5h～6h.