JPH0124600B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a coated arc welding rod containing iron powder, which exhibits good productivity and excellent welding workability. In the welding fields of shipbuilding, steel frames, bridges, etc., coated arc welding rods containing a large amount of iron powder in the coating material are widely used in order to improve work efficiency and bead shape. However, this type of welding rod has a coating material that contains a large amount of iron powder compared to welding rods such as illuminite or lime titania, so the coating speed is slower and the amount of coating per unit time is lower. There's a problem. That is, if a large amount of iron powder is contained in the coating material, the extrusion resistance (coating pressure) of the coating material is high, and the extrusion speed (coating speed) of the coating material relative to the feeding speed of the core wire cannot be sufficiently increased. Under the above-mentioned circumstances, the present inventors have conducted research to improve the coating properties of coating materials containing a large amount of iron powder and to increase the productivity of coated arc welding rods.
First, we investigated the effect of improving paintability on organic substances such as sodium alginate, and hydrated minerals such as mica and talc, which are conventionally known as raw materials for improving paintability. As a result, it was found that when a large amount of sodium alginate or the like is added, although paintability is improved, welding workability is significantly reduced. The upper limit of the compounding amount that does not impede welding workability is for all coating materials.
Although the amount is about 1.5% by weight, coating properties are hardly improved at that amount. Furthermore, even if mica or talc is added in large amounts, the paintability is hardly improved, and the negative effect on welding workability is far greater. Therefore, if we focused on the iron powder that is mixed in large amounts in coating materials and adjusted its bulk specific gravity, particle size, fluidity, and other properties, we thought that it might be possible to improve coating properties without adversely affecting welding workability. I thought about this and proceeded with my research along those lines. The present invention was completed as a result of such research, and its composition is such that 25 to 60
When manufacturing a coated arc welding rod by applying a coating material made by kneading a coating material containing % iron powder with a binding agent to the outer periphery of a mild steel core wire, the fluidity is
The gist lies in the use of iron powder of 19-33 seconds/50g (JIS Z 2502). In order to coat the outer periphery of the core wire with a coating material with uniform density, without defects, and in a short time, it is effective to increase the fluidity of the coating material, and this fluidity is due to the large amount of iron contained in the coating material. It is thought that it is largely influenced by the fluidity of the powder. However, the relationship between the fluidity of iron powder and paintability has not been reported so far. When we measured the fluidity of iron powder used for welding rods such as JIS D 4327, it was approximately 35 to 40 seconds/50g, and the paintability of coating materials containing such iron powder was as described above. It was extremely bad. Therefore, we conducted the following experiment to clarify the relationship between the fluidity of iron powder and paintability. That is, the coating material for welding rods specified in JIS D 4327 was used as the basic composition, and the fluidity and paintability of iron powder were investigated. However, water glass is used as the fixing agent, and the fluidity of iron powder is JIS Z 2502.
Measured by. Furthermore, the paintability was tested using the test equipment shown in Figure 1, using a certain amount (1 kg) in cylinder 1.
A constant pressure (600 kg/cm ² ) was applied by the piston 3, and judgment was made based on the time it took for the coating material 2 to flow out from the orifice (8.0 mm hole diameter) 4. The results are shown in Figure 2. As is clear from Figure 2, as the fluidity of the iron powder increases, the flow time of the coating agent increases.
When the fluidity exceeds 33 seconds/50 g, this tendency becomes more pronounced and the coating properties are extremely reduced. The paintability decreases as the iron powder content increases, but the fluidity is 33
The same trend is shown in that the paintability changes markedly at around 50g/sec. In addition, the points indicated by black circles in Figure 2 indicate the flow time of the illuminite coating agent (which is judged to have good paintability), but if iron powder with a fluidity of 33 seconds/50 g or less is used, the illuminite coating agent Substantially the same flow rate as the system coating is obtained. As is clear from the above results, it is preferable that the fluidity of the iron powder is low, judging only from the paintability. However, it has been found that if the fluidity is too low, the density of the coating material decreases and the welding material becomes loose, resulting in poor welding workability (particularly arc concentration). Therefore, we conducted an experiment to clarify the correlation between the fluidity of iron powder and the density of the coating material, and found that the third
The results shown in the figure were obtained. The results of preliminary experiments show that the lower limit of coating material density that can ensure excellent welding workability is
2g/cm ² , and in order to ensure this density, the fluidity of the iron powder needs to be 19 seconds/50g or more. As is clear from the results shown in Figures 2 and 3 above, in order to simultaneously satisfy coating properties and welding workability, it is essential to use iron powder with a fluidity of 19 to 33 seconds/50g. By the way, regarding the amount of iron powder mixed in the coating material, as is clear from FIGS. 2 and 3, as the amount added increases, the coatability tends to decrease. If it exceeds 60%, coating properties cannot be improved even if the flow rate is adjusted appropriately, and furthermore, the insulation properties of the coating are lost, which impairs safety. On the other hand, if the iron powder content is less than 25%, although good paintability can be obtained, contact welding, which is a characteristic of coated arc welding rods containing high iron powder, becomes difficult.
Furthermore, the effect of improving welding efficiency is also insufficient, which is not preferable. The other components of the coating material used in the present invention are not particularly limited, and conventionally known slag forming agents, arc stabilizers, deoxidizing agents, etc. may be appropriately selected and used.
Furthermore, it is also effective to add a small amount of an organic substance such as sodium alginate or a hydrous mineral such as mica or talc as a fluidity improver to further improve the coating properties. Further, the type of fixing agent is not particularly limited, but the most common one is water glass. Further, the coating agent may be applied to the outer periphery of the mild steel core wire by a conventional method, and the coverage ratio may be appropriately set depending on the purpose of use. Next, experimental examples will be shown, but they do not limit the present invention. Experimental example 1 Coating material raw material powder having the composition shown in Table 1 was kneaded with water glass, and this was mixed into a mild steel core wire (5.0 mmφ x 700
mm) to manufacture a coated arc welding rod. Paintability (painting speed) of each coating material during manufacturing
Table 1 summarizes the welding workability when fillet welding was performed using the obtained welding rods.

[Table] ○: Good, △: Slightly poor, ×: Poor From these experimental results, the following can be considered. (1) Experiments Nos. 1 to 6 are examples that satisfy the requirements of the present invention, and both paintability and welding workability are good. The coating speed varies slightly depending on the fluidity and amount of iron powder mixed, but it is in the range of 200 to 250 m/min, and the coating performance is comparable to that of titania-based coatings. show. (2) Experiment No. 7 is a comparative example in which the fluidity of iron powder is too low, and the paintability is good, but the welding workability (especially arc concentration) is poor. (3) Experiment No. 8 is a comparative example in which the fluidity of iron powder is too high, and the paintability is poor and the object of the present invention cannot be achieved. (4) Experiment No. 9 is a comparative example in which the amount of iron powder blended is too large, and it cannot be put to practical use because the paintability cannot be improved and the insulation properties of the coating deteriorate. (5) Experiment No. 10 is a comparative example in which the amount of iron powder blended is too small, and the paintability is good, but the welding workability (especially contact weldability) is poor. Experimental Example 2 Coating material raw materials having the composition shown in Table 2 are kneaded with water glass, and this is mixed into a mild steel core wire (5.0 mmφ x 700 mm
) to produce a coated arc welding rod. In this experiment, we investigated the influence of the fluidity of iron powder on paintability and welding workability, and also investigated the influence of the fluidity of silica sand, which is the main slag-forming component in the coating material. This study was conducted to investigate the effects on paintability and welding workability of steel sheets (which have poor angularity but are not angular but have high fluidity). Table 2 summarizes the coating properties of each coating material during the manufacture of coated arc welding rods and the welding workability when fillet welding is performed using each of the obtained welding rods.

[Table] Based on Table 2, the following considerations can be made. (1) Experiments Nos. 11 to 16 are examples in which silica sand with different fluidity was used under conditions in which the content of iron powder and fluidity both satisfied the requirements specified in the present invention. Paintability and welding workability are both good regardless of whether the fluidity is good or bad. (2) Experiment Nos. 17 and 18 are experimental data when using iron powder whose fluidity exceeds the specified range of the present invention, and using silica sand with different fluidity. Regardless of the method, the paintability is poor and the object of the present invention cannot be achieved. (3) Experiment Nos. 19 and 20 are experimental data when silica sand with different fluidity was used for cases where the fluidity of iron powder was too high and the amount of iron powder blended was insufficient, but the paintability was still poor. and poor welding workability. (4) Experiment Nos. 21 and 22 are experimental data when silica sand with different fluidity was used for cases where the iron powder content was insufficient, and although the paintability was good, the welding workability was poor. (5) As is clear from these experimental results, the fluidity and blending ratio of iron powder have a more significant effect on paintability and welding workability than the fluidity of silica sand.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the main parts of the coating agent paintability (flow time) measuring device, Figure 2 is a graph showing the relationship between iron powder flow rate and coating agent flow time, and Figure 3 is iron powder. 3 is a graph showing the relationship between the fluidity of the coating material and the density of the coating material. 1...Cylinder, 2...Coating material, 3...Piston, 4
...orifice chair.