CN101690976B - Method for eliminating carbon defects by adopting high-performance coating, negative-pressure firing, vacant shell pouring and quick airflow cooling in lost foam casting - Google Patents

Abstract

The invention discloses a method for eliminating carbon defects by adopting a high-performance coating, negative-pressure firing, vacant shell pouring and quick airflow cooling in lost foam casting. The process comprises the following steps: placing a mould into a sand box; filling dry sand into the sand box; sealing the upper surface of a sand layer with a plastic thin film; starting a vacuum pump, igniting and gasifying the foam mould from a pouring gate under a negative pressure condition so as to form an intact vacant shell cavity, wherein over 95 percent of carbon is discharged out of the molding sand box; pouring molten iron and steel; lifting or cutting the sealing thin film on the top surface of the sand box when the molten iron and steel is in a temperature area where a liquid phase and a solid phase coexist, and then sucking cold airflow into the sand box so as to quickly cool a cast piece; and after stopping the pouring, continuing extracting air for 3 to 6 minutes, and then stopping the vacuum pump. The method can realize the elimination of the carbon defects of the cast piece, grain refinement, and easy falling-off of the coating by discharging and reducing carbon andpouring the vacant shell in the lost foam casting, makes the cast piece have bright and clean surface to comprehensively improve the quality of the cast piece, saves energy and reduce consumption, ishigh in efficiency and benefit and is applied to industrialized mass production.

Description

Lost foam casting adopts the cold elimination carbon defects of high-performance coating negative-pressure firing ghost cast gas velocity method

Technical field

The present invention relates to lost foam casting, the cold elimination foundry goods of particularly a kind of employing high-performance coating negative-pressure firing ghost cast gas velocity carbon defects method.

Background technology

Lost foam casting (international be called for short LFC) is a casting technology of represent 21 century, and existing in the world 50 years history was China entering industrial applications also soon 20 years; About 2000 of lost foam casting factory has been built up in the whole nation at present; And just with swift and violent gathering way in development, but technical prematurity still, even the original invention ground U.S. of international lost foam casting; The serious carbon defects problem of disappearance die casting also still is in the research tackling key problem phase, and their objective of the struggle is to strive for being tending towards ripe in 2013.The main performance of carbon defects be produce serious carburetting, carbon slag pore, carbon ash elephant skin in the 10mm of foundry goods top layer, crystal grain is thick, mechanical performance descends, welding performance worsens and crackle etc.Carbon defects (the particularly carbon defects of steel-casting and nodular iron casting) has become the obstacle that the lost foam casting heavy industrialization is used and development is maximum in decades both at home and abroad.Britain is in order to solve the carburetting problem of lost foam cast steel spare, and the method (Ceramic Shell method) of imitative dewax model casting has been invented in research---and adopt the highdensity foam plastics mould of EPS, be coated with 3-4 layer (thickness 3 ~ 5mm) high-temperature resistant coating; Every layer of stucco; EPS is disappeared, and the shell roasting more than 1-2 hour, is slowly cooled off again; Then the cold mould shell is placed and fill dry sand in the sandbox, cast under no condition of negative pressure.This method not only operation is loaded down with trivial details, and cost is high, and efficient is low; Operating reliability is poor---and shell is prone to bump break and splits, and molten steel is prone to lift case or spalling shell during cast, and only is applicable to the production that carburetting is had the small casting steel of specific (special) requirements; Can't in industrialized production, use, more be difficult to promote in China.Therefore, how fundamentally eliminating carbon defects, improve the credit rating of disappearance die casting, and adapt to lost foam casting industrial and large-scale application and development, is the common great technical barrier of tackling key problem with all strength of paying close attention to also of current domestic and international lost foam casting circle.

Summary of the invention

The objective of the invention is for overcoming the deficiency of prior art; And a kind of casting that adopts the cold elimination foundry goods of high-performance coating negative-pressure firing ghost cast gas velocity carbon defects disclosed; This method is not only efficient, simple, reliable; And pollution-free, low-cost, adapt to large-scale industrial production and use.

A kind of lost foam casting adopts the cold elimination foundry goods of high-performance coating negative-pressure firing ghost cast gas velocity carbon defects method; Comprise the preparation of foundry goods Foam Pattern, on apperance, be coated with, place sandbox to fill dry sand with coating and dry coating; Cover film sealing sandbox, different with prior art is:

(1) adopts the coating brushing apperance of high-performance (high strength, high ventilative, anti-burning and high temperature crack resistance are strong); Coating layer thickness＞1.5mm; Room temperature tensile strength>=1.2Mpa, coating is dried down at 50-55 ℃, the tensile strength>=1Mpa of apperance burning back coating; Surface strength＞400g/mm, normal temperature gas permeability＞1.0cm ²/ pa.min.

(2) negative-pressure firing starts vacuum pumping pump before the cast, be evacuated to vacuum degree and be-40～-80Kpa promptly lights Foam Pattern afterwards, and making Foam Pattern was that combustion gasification stays intact ghost in tens seconds;

(3) ghost cast, treat that Foam Pattern is burnt till ghost after, be-25 at vacuum degree～-state of 50Kpa under, pour into a mould iron and steel water immediately;

(4) gas velocity is cold, after cast finishes, when the foundry goods top layer is in liquid-solid phase coexisting state, raises or cut the plastic sheeting that the sealing of sandbox top covers, and in the powerful suction sandbox of cold air, foundry goods is cooled off fast.Can close vacuum pumping pump after several minutes and stop exhausting.

The time of gas velocity cold (promptly pouring into a mould the final vacuum pump that finishes works on) decides according to the size of foundry goods:

(1) conventional structure 200kg/ spare is heavy middle-size and small-size foundry goods 3-4 minute;

(2) conventional structure 200-500kg/ spare is heavy middle-size and small-size foundry goods 4-5 minute;

(3) conventional structure 500-1000kg/ spare is heavy middle-size and small-size foundry goods 5-6 minute;

(4) conventional structure 1000kg/ spare heavy than heavy castings more than 6 minutes.

Said Foam Pattern elder generation combustion gas changes into after the ghost cast and with the cold elimination carbon defects of gas velocity; Promote that simultaneously coating is to confirm to break original negative pressure state in the temperature province of iron and steel water liquid phase-solid phase coexistence of different Cheng Du with reference to the Fe-FeC phasor with operating process that foundry goods is peeled off automatically, the input cold air flows.

The coating of described employing high-performance (being that high strength, high ventilative, anti-burning, high temperature crack resistance are strong); Be that Foam Pattern is then burnt the prerequisite of annotating after first combustion gas changes into ghost under the dried sand negative-pressure condition; The coated coating that the present invention uses; By following batching and materials weight part ratio, mix together:

Ingredients by weight part

Refractory aggregate 100

Lost foam paint specialist additive 10

Water 130-150

Wherein: refractory aggregate is a 180-270 purpose powder, and the lost foam paint specialist additive is No. 5 lost foam paint specialist additives in Guilin that the Central-South casting smelting in Guilin Materials Research Laboratories is produced.

Advantage of the present invention is:

1, row's carbon that Foam Pattern vacuumizes combustion gasification under the condition in negative pressure before the cast subtracts the carbon rate and reaches more than 95%; Burning the notes process with domestic and international lost foam casting tradition for a long time compares; Shell is tending towards carbon-free before the cast; Or the carbon amount is atomic, and iron and steel water no longer included carbon slag collection and attaches with being coated with interlayer after cast finished, thereby can fundamentally realize eliminating all carbon defects of disappearance die casting;

2, the high temperature foundry goods adopts cold air stream fast after the cooling, the casting crystalline grain refinement, and dense structure, mechanical performance is improved, and coating is easy to foundry goods and separates and peel off, and is prone to the shelling cleaning, and surface quality of continuous castings obviously improves.

3, this method can be adapted to small-sized, medium-sized, large-scale, the dried sand negative-pressure of super-huge all kinds of foundry goods of all unlike materials or the lost foam casting production under the non-dried sand negative-pressure condition, high efficiency, simplification, low cost (comparing no additional cost with existing EPS lost-foam casting method) reliably.

4, this method adopts domestic the most common, the most cheap EPS GPPS high-carbon foamed plastics (Expandable Polystyrene is called for short EPS) to make apperance and can produce EPMMA and the more stable better foundry goods of the so-called low-carbon (LC) foamed plastics of STMMA quality than the import of high several times price.

Description of drawings

Fig. 1 is for eliminating the apperance vanning sketch map of disappearance die casting carbon defects.

Among the figure: 1 cast gate and running channel 2 rising heads 3 plastic sheeting 4 dry sands, 5 foundry goods (foam) 6 coating shells 7 residual carbon slag blankets 8 exhaust mesh 9 sandbox shells 10 vacuumize connecting port

The specific embodiment

Below in conjunction with the accompanying drawing and the specific embodiment, the present invention is done further description, but be not qualification content of the present invention.

Ghost is poured into a mould and the cold elimination foundry goods of gas velocity carbon defects method after adopting the high-performance coating negative-pressure firing, comprises the steps:

(1) preparation Foam Pattern 5;

The coating shell 6 of the high-performance that (2) brushing prepares on apperance (high strength, high ventilative, anti-burning, high temperature crack resistance are strong), thickness＞1.5mm;

(3) above-mentioned foam real type is placed sandbox, reserve cast gate 1 and rising head 2, fill dry sand 4,3 sealings of dry sand face upper cover plastic sheeting;

(4) start vavuum pump (exhausting), when vacuum degree be-40～-during 80Kpa, light Foam Pattern 5 from cast gate 1 and rising head 2, combustion gasification also excludes carbon outside the sandbox from suction opeing 10 to greatest extent;

(5) after the apperance combustion gas changes into ghost, from cast gate 1 cast iron and steel water;

(6) when the iron and steel water of cast(ing) surface is in liquid-solid state shape coexistence, raise or cut the plastic sheeting 3 of sealing;

(7) stop to continue exhausting number minute again after the casting.

By above operation can obtain not have carbon defects, coating is prone to that shelling is peeled off, grain refinement, quality are superior, the disappearance die casting of any surface finish.

Claims (2)

1. lost foam casting adopts the cold elimination carbon defects of high-performance coating negative-pressure firing ghost cast gas velocity method, comprises the steps:

(1) adopts high strength, high ventilative, anti-burning, coating brushing apperance that the high temperature crack resistance is strong; Coating layer thickness＞1.5mm; Room temperature tensile strength>=1.2Mpa, coating is dried down at 50-55 ℃, the tensile strength>=1Mpa of apperance burning back coating; Surface strength＞400g/mm, normal temperature gas permeability＞1.0cm ²/ pa.min, described high-performance coating coating mixes together by following raw material and materials weight part ratio:

Parts by weight of raw materials

180-250 order refractory aggregate 100

No. 5 lost foam paint specialist additives 10 in Guilin

Water 130-150;

(2) negative-pressure firing: start vacuum pumping pump before the cast, be evacuated to vacuum degree and be-40～-80Kpa promptly lights Foam Pattern afterwards, makes the Foam Pattern combustion gas change into intact shell mould;

(3) ghost cast: after treating that Foam Pattern is burnt till ghost, be-25 at vacuum degree～-state of 50Kpa under, pour into a mould iron and steel water;

(4) gas velocity is cold: after cast finishes, when the foundry goods top layer is in liquid-solid phase coexisting state, raise or cut the plastic sheeting that the sealing of sandbox top covers; In the powerful suction sandbox of cold air; Foundry goods is cooled off fast, stop pouring after, continued exhausting 3-6 minute.

2. method according to claim 1 is characterized in that: after casting stopped, the time that vavuum pump works on was controlled as follows:

(1) conventional structure 200kg/ spare is heavy middle-size and small-size foundry goods 3-4 minute;

(2) conventional structure 200-500kg/ spare is heavy middle-size and small-size foundry goods 4-5 minute;

(3) conventional structure 500-1000kg/ spare is heavy middle-size and small-size foundry goods 5-6 minute.

Images