Abstract : The electroslag surfacing process of seamless flux cored ribbons was realized by experiments. The best parameter of electroslag surfacing welding of seamless flux cored ribbons was determined by orthogonal method.
Keywords: seamless flux cored strip electroslag surfacing orthogonal method
Foreword
The flux cored submerged arc welding technology has been applied to the continuous casting machine guide rollers, extrusion press rollers and the surface of large-caliber power station valves. The most important feature of this technology is that it can be used to adjust the type, content and ratio of the alloy in the core to make the hard and hard-to-abrasive coating material that is difficult to be rolled out into a continuous strip-shaped welding consumable to achieve automatic surfacing [ 1]. However, the temperature of the flux-cored submerged arc welding process is high, and the precious metal is severely burned. The use of flux cored welding with electroslag welding technology, can increase the deposition efficiency and alloy utilization, reduce the dilution rate, more advanced than the submerged arc welding, scientific and technical rationality.
1 characteristics of flux cored tape
The seamless flux-cored welding strip is made of various alloys required for wrapping inside the metal skin. Compared with the solid welding strip, the seamless flux-cored welding strip has the following characteristics: the core of the seamless flux cored tape is composed of metal powder It is a mechanical bond between granular, powder particles and powder particles, and between powder particles and external metal skin; it can realize the alloy composition difficult to roll into a solid core ribbon; usually, the thickness of seamless flux cored tape is ≥ 1.0 mm. The flux-cored ribbon with the same cross-sectional area of ​​core tape thickness ≤ 0.5 mm has a smaller heating area than that of the solid ribbon in the electroslag surfacing process. The cross-sectional dimension of the flux-cored tape is that the thickness of the core is greater than the thickness of both sides. The thickness of the middle metal skin is less than the thickness of the metal skin on both sides.
Flux is essential in the welding of stripped electroslag. The electroslag welding flux must have good conductivity while ensuring good slag removal performance [2].
According to the introduction of the literature, combined with the characteristics of the flux cored tape, a ceramic flux with a ceramic flux H06 for electroslag surfacing was developed. The alkalinity of the flux (B1) is determined using the flux alkalinity calculation formula recommended by the International Welding Society:
B1≈3.07
For high alkali flux.
2 Orthogonal method to determine the best parameter of electroslag surfacing for flux cored strip
The test conditions are as follows:
Surfacing power supply: Lincoln DC - 1000-level characteristic power supply, reverse polarity connection.
Test plate material: Q235 steel, the size of 240 mm × 80 mm × 16 mm.
Voltage acquisition: XY function recorder, working range X 50 mv Y 10 V.
Ribbon: B3, DF cored ribbon (20 mm × 1.0 mm).
Flux: H06 type ceramic flux.
In the determination of process parameters, the method of approximation was mainly used to conduct experiments. For the determination of the best process parameters, orthogonal experiments were used. The impact on the stability of the electroslag surfacing process in addition to flux cored tape and flux, the main surfacing voltage, surfacing current, surfacing speed and flux thickness and other factors. Therefore, the surfacing parameters are selected according to the orthogonal method, as shown in Table 1.
Table 1 surfacing parameters selected for orthogonal experiments
Table1 Surfacing parametet of orthogonal means experimentation
This is an orthogonal experiment with 3 factors, 3 levels, +1 factors and 2 levels. 
Orthogonal table. The electroslag surfacing parameters of flux cored strips should be considered in three aspects: 1) no short circuit, 2) no significant arcing, and 3) low dilution rate. And these three aspects are used as evaluation indicators for the stability of electroslag surfacing. When a short circuit phenomenon and an obvious arc occur, this shows that this specification is not a stable electroslag process. Both of these phenomena can be recorded by the XY function recorder. Waveform to detect. If a short circuit occurs or a significant arc is generated, it is rated as “0â€, otherwise it is rated as “1â€. If the dilution rate is higher than 20%, it is rated as “0â€, otherwise it is rated as “1â€. Measured in cross section.
Among them: A - deposited metal area
B - molten matrix metal area
Table 2 Orthogonal Test Table for Electroslag Surfacing Standard of Seamless Flux-cored Welding Zone
Table2 The electroslag surfacing criterion essentially means experimentation tabulation about seamless cored strip
In order to evaluate the stability of the flux-cored electroslag welding of the flux-cored welding zone as a whole, the scores of the three indexes were summed to obtain a comprehensive total score. Table 3 shows the overall specifications of the electroslag surfacing for the flux cored welding zone.
Table 3 Synthetic scoring of each parameter of electroslag welding with flux cored tape
Table3 Synthetical instance about the surfacing criterion parameter
Index scores. The K1, K2, and K3 in Table 3 indicate the correspondences in the parameter columns in Table 2. The comprehensive scores of the 1, 2, and 3 positions in the orthogonal table are added, and K1, K2, and K3 are added to K1.
Divide K2 and K3 by 6, that is, they represent the composite score average scores corresponding to the three specification levels of different specification parameters.
The results were analyzed using visual analysis. Figure 1 shows that the best parameters for the electroslag surfacing of the core tape of this experiment are: surfacing voltage 29 V, surfacing current 600 A, and surfacing welding speed 150 mm/min.
3 Conclusion
1. The optimum parameters of the electroslag surfacing welding of the Chinese traditional Chinese medicine core welding zone in this experiment are as follows: surfacing voltage 29 V, surfacing current 600 A, surfacing welding speed 150 mm/min;
2. Compared with submerged arc welding, the characteristics of seamless flux cored welding with electroslag surfacing are:
(1) Low dilution rate The dilution rate of submerged arc welding is generally above 30%. The use of seamless flux cored welding with electroslag surfacing can stably control the dilution rate below 20%.
Figure 1 Analysis of the relationship between each specification parameter and comprehensive score
Fig.1 The connecion analysis about criterion parameter and synthetical instance
(2) Voltage Waveform When the smooth submerged arc welding is performed, both the short circuit and the arc phenomenon are generated at a very high density. During the electroslag surfacing, the voltage waveform is very smooth.
(3) arc arc rarely seamless flux cored tape submerged arc welding flux layer is mainly based on the arc, and flux cored electrode with electroslag surfacing, the slag pool is exposed, rarely seen through the welding of protective lenses Arc generated by the arc, see Figure 2.
Fig. 2 Photograph of flux-cored electroslag surfacing process
Fig.2 A photograph about the seamless cored strip electroslag surfacing process
(4) Alloy transition coefficient When the flux-cored tape is covered by submerged arc welding, the alloy transition coefficient of Cr is 70%. When the seamless flux cored strip is used for electroslag surfacing, the transitional coefficient of Cr alloy can reach more than 90%.
(5) High deposition efficiency The deposition rate can reach 30 Kg/h.
4 Application
The process has been successfully applied to the manufacture and repair of large-caliber power station valves, concrete pump scrapers and other products with good results.
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