[Fellow]History and Current Situation of Wire-feeding of Cored Wire, Wire-feeding Process, Limits of Wire-feeding Technology in Molten Iron Treatment, Difference between Using Wire-feeding Treatment and Pour-over Treatment,
The Common Problems of Wire-feeding Appli...
There are more than 10 kinds of frequently-used technologies for spheroidization of ductile cast iron. Pour-over process is the most widely used process of spheroidization in China at present.
Pour-over has many advantages:
Low magnesium absorptivity;
Unsteady spheroidization effect;
Dense magnesium light dust and
bad working environment.
Spheroidization process is getting improved.
With rising of requirements on overall performances of ductile cast iron and environmental protection, efforts are being made to improve pour-over or replace with other spheroidization processes for casting.
Wire-feeding process is a new technology which has a good prospect.
Feeding of Cored Wire:
Feeding of cored wire is to wrap some additives with cored wire machine by using cold-rolled law-carbon steel strip to make a cored wire and then, feed the cored wire of specified length to the bottom of the processing ladle at a certain speed with a wire feeder to fuse the ladle material at the bottom of the processing ladle to deoxidize desulfurize microalloy and modify the treated solution.
Good Development Trend of Wire-feeding Technology
In 1970s, feeding of cored wire was applied to refined molten steel. In later 1980s, Germany and the United States began to apply it to casting industry.
The industrial developed countries in the world generally pay attention to the application of wire feeding technology in ductile iron production. Although in China, it was late to start applying this technology to ductile iron production, started late, from the development trend, it is more and more, especially under the pressure of environmental protection at present, new green technologies are urgently needed to replace the conventional technologies.
History and Current Situation of Wire-feeding of Cored Wire
Application of wire-feeding in iron started at the end of 1980s, including spheriodization and inoculation of molten iron.
At the beginning, German tested more than 50 different combinations of alloy. As the result, two kinds of special high magnesium alloy materials with different purposes were selected. The first one was used for high- sulfur molten iron which the original sulfur was 0.03～0.10%. In this case desulfurate, spheroidize and pre-inoculate in the same processing ladle by using cored wire provides ability to produce ductile cast iron with grey molten iron directly. The second one was used for low-sulfur molten iron which the original sulfur was less than 0.03%. In this case, the cored wire was mainly used for spheroidization and pre-inoculation.
After more than 10 years of unremitting efforts and improvement, wire-feeding technology and products have got a significant development.
In Germany, wire-feeding method has accounted for 35% to 40%.
In China, the factory using wire-feeding spheroidization technology has developed to several thousand from one before 2000.
In terms of wire-feeding spheroidization technology, cored wire variety and wire-feeding equipment have been as good as that of foreign countries, even in some aspects have been ahead of that of foreign countries.
Production of high-quality ductile cast iron and vermicular graphite cast iron requires strict process control, while cored wire feeding technology has provided reliable process means of high degree of automation.
Also, due to increasingly strict requirement on environmental protection, continuous improvement of wire-feeding technology and magnesium efficiency of new type cored wire as well as continuous price fall of cored wire and wire-feeding equipment, wire-feeding treatment technology of molten iron has a broad development prospect.
The main advantages of application of wire-feeding treatment technology in casting industry are:
Molten Iron containing up to 0.09% of sulfur content can be spheroidized without desulphurization pretreatment. Finally, sulfur content can be controlled in the range of 0.010% to 0.018% according to different mass of molten iron to be treated;
Weight of the molten iron to be treated may be 300kg/ladle to 40 tons/ladle; with strong adaptation, molten iron ladle can be used for automatic pouring wire ladle;
In order to avoid spheroidization degradation, the treatment station system can be set nearby the pouring location as possible;
With dust collection system, the treatment station can realize environment-friendly of the treatment location;
Automatic feeding of magnesium controlled by computer is realizable to control the amount of magnesium to be added precisely;
Control and adjust amount of remainder magnesium precisely with good reproducibility;
Less amount of alloy (cored wire) addition and slag generated, high degree of purity of iron liquid;
Labour force for spheroidization and inoculation treatment can be saved;
With no influence of human factors, the process of spheroidization is steady.
Conditions to realize Intelligent casting are available.
Ⅲ. Wire-feeding Process
Production process producing ductile iron cast by using wire-feeding process is as below:
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Fusion of Original Molten Iron
Fuse molten iron in medium frequency furnace; Tapping temperature of molten iron is 1450~1500℃ (to be adjusted properly according to pouring temperature).
See also the form for the range of the components of the original molten iron (%)
|
Components |
C |
Si |
Mn |
P |
S |
|
Range (%)
|
3.50-3.7 |
1.7-1.9 |
0.3-0.6 |
<0.070 |
0.030 |
The Interrupted Front Treatment
Dam-less spheroidized iron ladle is used, which the height-diameter ratio is 1.5: 1.
In order to keep some space for churning molten iron, the amount of molten iron is reduced.
Inoculant and alloy materials are added in.
Wire-feeding Treatment:
Add high magnesium alloy cored wire and inoculation wire into the spheroidization ladle with wire feeder for spheroidization and innoculation by using computer automatic control.
Adding speed and length of spheroidization wire and inoculation wire depend on weight, content of sulfur and temperature of molten iron. The high-magnesium alloy cored wire adopted is 30Mg wire of Ф13mm (0.35mm of thickness of skin), the adding amount of spheroidizing agent is approximately 0.75%；
The inoculation wire is Φ13mm inoculation wire. The adding amount of inoculatnt is approximately 0.4%.
Treatment time of spheroidization + inoculation: about 4 minutes.
Molten iron temperature fall: 30-50 C°.
Technical Parameters of Cored Wire
|
Name of Cored Wire
|
Alloy Component，%
|
g/m
|
|
Mg
|
RE
|
Ca
|
Si
|
Total Weight
|
Weight of Powder
|
Magnesium
|
Silicon
|
|
30Mg Spheroidized Wire
|
29~31
|
2~3
|
2~4
|
40~44
|
350
|
210
|
62
|
80
|
|
Inoculation Wire
|
Moderate Amount
|
Moderate Amount
|
Moderate Amount
|
54~56
|
430
|
290
|
|
|
Technical Parameters of Spheroidization and Inoculation Processing
|
Spheroidization Temperature ℃
|
Amount of Spheroidized Core Wire Added(1000kg)
|
Feeding Speed of Spheroidized Core Wire
|
Amount of Inoculation Core Wire Added（1000kg）
|
Feeding Speed of Inoculation Core Wire
|
Content of Remainder Sulphur (%)
|
Amount of Remainder Magnesium (%)
|
|
1450~1500
|
20~30 m
|
20~25m/s
|
20~25 m
|
20~25m/s
|
≤0.016%
|
0.03~0.045
|
Molten Iron Pouring:
Temperature of Pouring: 1350-1400 C°.
The time from wire-feeding process to finishing pouring should be controlled in 8 minutes.
Ⅳ. Limited Link of Wire-feeding Technology in Molten Wire Treatment
By the end of 1970s, wire-feeding technology had been widely applied in steel industry, which solved the problem that reactive or oxidizable material is added into molten steel.
Application in cast iron started at the end of 1980s for mainly spherioidization and inoculation of molten iron.
After unremitting efforts of casting workers of various countries, wire-feeding technology has got mature in spheroidization and inoculation treatment of molten iron and has been accepted by casting workers gradually for its stability of quality and advantages in production control.
Cost Input
Application of wire-feeding technology may lead to slight rising of direct treatment cost and input for relevant equipment, which requires effective balance between improvement of product quality and cost input. It is one of limits of application of wire-feeding technology in molten iron treatment at present.
Therefore, the main problem at present and a long time in future is how to reduce the treatment expense of wire-feeding process (i.e. how to reduce consumption cost of cored wire), as a result, the main subjects are studies and application on high-magnesium alloy cored wire and relevant wire-feeding technology.
nUniversal use of alloy cored wire which magnesium content reaches up to 30% means that the cost treatment problem has been solved well.
It is an important problem that how to minimize the cost for wire-feeding treatment under the premise of ensuring ideal treatment effect.
Various cored wire technology is being innovated at present to meet the quality requirement as lowering the cost.
Convenience of Reliable Operation of Wire-feeding Equipment
Reliability and operation convenience of equipment of wire-feeding treatment station is one of important links that influences application of wire-feeding spheriodization.
nReliability of wire-feeding equipment influences use of wire-feeding technology directly. If wire-feeding equipment often goes wrong, production might be delayed with large influence.
On the other hand, with unstable feeding equipment, the stability of the adding amount of cored wire is difficult to guarantee, which will directly affects the spheroidization effect.
Whether operation of some links of wire-feeding treatment station is convenient or not also influences experience.
Ⅳ. Limits of Wire-feeding Technology in Molten Wire Treatment
Stability and Consistency of Quality of Cored Wire
Stability and consistency of quality of cored wire is one of more important links that influences application of wire-feeding spheroidization technology.
Quality of cored wire is crucial too. If cored wire is empty or broken, spheroidization process will be influenced.
Fluctuation of Mg content in cored wire with poor consistency will cause instability of quality of spheroidization to influence using effect of wire-feeding technology.
Pour-over process is the most widely used spheroidization in China.
But this method has many disadvantages: low magnesium absorptivity, instability of spheroidization effect; dense magnesium light dust, bad working environment, etc.
Advantages of wire-feeding treatment of cored wire are: good effect of desulfuration and deoxygenation, less temperature reduction, relaxed requirements on original molten iron; small fluctuation range of amount of remainder magnesium; less slag amount and high alkalinity of slag; reduced dust and magnesium light in the process of treatment; precise amount of adding alloy and automatic work are available.
Therefore, wire-feeding process is a new technology that has good development prospect.
The two methods have the following differences in quality and treatment cost:
Ⅴ. Difference between Using Wire-feeding Treatment and Pour-over Treatment
Differences in Quality
At present, most of ductile iron production in China adopts pour-over process. The spheroidization has got considerable improvement in many aspects after several generations’ efforts,
but there are still many disadvantages (some of them are even insurmountable):
1) Unsteady effect of spheroidization;
2) Large consumption of spheroidization agent and low yielding rate of Magnesium.
Comparing with pour-over spheroidization, the advantages in quality are:
Small amount of spheroidal graphite iron casting w (S remainder) produced by using wire-feeding process;
Small fluctuation of amount of w (Mg remainder);
Good effect of casting spheroidization, large quantity and small size of graphite nodule, high spherical degree of high spheroidization rate;
Good mechanical and steady performances of casting
Differences in Treatment Cost
Value of Mg/Si in core agent is about 3 times that of pour-over alloy, as a result, for getting the same amount of remainder magnesium, the amount of supplementing silicon is merely about one third of that got by means of pour-over process.
For calculating wire-feeding cost separately, i.e., with no cost of supplementing silicon, when most of cored wire parameters and wire-feeding parameters are matched with parameters of treating molten iron, the cost of wire-feeding spheroidization of high-magnesium alloy cored wire is lower than cost of spheroidization by using pour-over process.
Comparing under the condition that the amount of supplementing silicon is same as that of pour-over process, the direct cost by using wire-feeding treatment is 15 to 30 yuan per ton higher than that of pour-over process.
When inoculation cored wire is used for inoculation, rising of cost brought by steel strip must be borne.
Wire-feeding inoculation is to wrap inoculant into cored wire and feed in molten iron with wire feeder and after steel strip is disable, the inoculation reaction is implemented with molten iron. Obviously, wire-feeding inoculation is a post-inoculation process of molten iron with no restrict on location of molten iron. Wire-feeding inoculation is done where is close to the pouring area as possible.
Comparing cost of wire-feeding inoculation with that of pour-over process inoculation under the premise of the completely same amount of adding inoculant:
1) Steel strip of inoculation cored wire has a negative influence on cost of inoculation;
2) Yield in molten iron of inoculation element in inoculation cored wire is high and has a positive influence on cost of inoculation;
3) Protected by steel strip of cored wire, inoculant has little oxidization, which facilitates to get a good solubility;
4) Amount of adding Inoculant is accurate, which reduces waste and has a positive influence on cost.
By comparing the differences between wire-feeding inoculation and pouring inoculation in cost, generally speaking:
Cost of wire-feeding inoculation is 20 to 40 yuan higher than that of pouring inoculation per ton of molten iron.
There are two methods to reduce negative influences of steel strip on cost of inoculation:
The fist one is to find a way in efficient inoculation that reduces proportion of adding steel strip by reducing the total amount of adding inoculant;
The second is to reduce the proportion of adding steel strip relatively by enlarging the proportion of core iron of the inoculation wire.
When comparing cost under the said conditions of treatment cost, wire-feeding treatment with Mg-bearing cored wire can get advantages in the following cases:
1) The casting factory has foundry return problem or final amount of silicon is high after disposal;
2) As the spheroidization quality obtained by feeding line treatment is improved, better casting quality can be obtained.
3) As wire-feeding treatment has improved casting yield, cost of silicon supplementation caused by wire-feeding process can be made up;
4) The factory that solves the environmental protection problem by means of wire-feeding technology.
Large Fluctuation of Actual Length of Wire-feeding
The most common problem in wire-feeding spheroidization is that the length of actual wire-feeding fluctuates larger in the case of the same amount of remainder magnesium.
Quality Problem of Cored Wire
Fluctuation of weight of core agent of cored wire, fluctuation of content of magnesium of core agent and fluctuation of magnesium oxide of core agent influence the treatment result.
Equipment Problem
The set speed and length of wire-feeding were not achieved;
Break and Empty of Cored Wire
High quality Mg-bearing cored wire is very important the whole wire-feeding process.
For the necessary conditions to secure success of wire-feeding, the first is that no break occurs in the process of wire-feeding, which depends on the quality of the selected steel strip and whether the ratio between core agent of cored wire and the steel strip is appropriate. Extension rate, low strength and content of impurities of the steel strip are all reasons resulting in increasing the probability of break of the cored wire. Overlarge ratio between core agent of cored wire and steel strip results in poor ability of the cored wire resisting bending deformation so that the wire is easy to break.
Amount of adding cored wire is Instable
① Stability of Weight of Core Agent of Cored Wire:
Ø Stability of Core Agent and Magnesium Inclusion of Cored Wire at Unit Length;
Ø Stability and Uniformity of Particle Filling Degree of Cored Wire.
② Stability of Quality of Core Agent:
Ø Smelting quality of silicon-based high magnesium alloy will influence stability of reaction process and absorption process in molten iron;
ØAlloying degree of magnesium and distribution of magnesium phase;
Ø Segregation degree of magnesium in silicon-based alloy;
Ø Segregation of magnesium leads to uniformity of distribution of magnesium in cored wire.
Instability of Wire-feeding Process
For the conditions to guarantee the effect of wire-feeding, stability of wire-feeding process is an important standard to evaluate quality of cored wire.
Structural design of coil of cored wire, influence of wire arrangement quality:
Considering resistance of wire-feeding, the inner diameter design of coil of cored wire will influence on uniformity of resistance distribution of the whole wire-cored in the process of wire-feeding. Over small inner diameter of coil or wrong layer wiring will increase resistance of wire-feeding to influence on realizing wire-feeding speed, and the intensity of reaction between and magnesium and molten iron and stability of absorption.
Structure of wire-feeding station influences on smooth degree in the process of wire-feeding process of wired-cored.
Ⅶ. Conclusions
As an environment-friendly spheroidization process that can realize intelligence, wire-feeding spheroidization has been applied more and more widely. Technical content of wire-feeding process should be continually improved to get more vitality.
Comprehensive cost of spheroidization process is not much more than that of pour-over process. Also, cored wire is constantly innovated to meet the quality requirement and to reduce the cost. Reliability of equipment of wire-feeding processing station and stability of quality of cored-wire are important links to influence on application of wire-feeding spheroidization. Therefore, this is an important direction of improvement in future.
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