JPS5938878B2 - Adhesive for welding coatings with low moisture absorption - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-hygroscopic adhesive for welding coatings, and in particular, it suppresses the hygroscopicity of the coating after drying and solidification, and increases the adhesive strength so that it does not survive exposure to humid environments. The object is to enable good welding work with a coated welding rod without the fear of welding defects occurring.

Weld metal cracking is a serious and dangerous welding defect, and low-temperature cracking is a particular concern when welding high-strength steel.

This cold cracking is caused by hydrogen penetrating into the weld metal, and the sources of this diffusible hydrogen are mainly water vapor penetrating into the arc from the atmosphere during welding, as well as crystal water and hygroscopic water in the coating material. . For this reason, H is particularly prone to weld cracking.
When welding T6O, HT80, and C-Mo steels, in order to minimize the intrusion of hydrogen into the weld metal, we not only cut off the arc from the atmosphere, but also use carefully selected coatings as welding materials. A lithium-containing water glass with low hygroscopicity or water glass with a high molar ratio of SiO2 component to alkali component is used as a fixing agent, and is further dried and solidified at a high temperature of 400°C or higher. low hydrogen welding materials are used.

Although the above-mentioned adhesion agents are effective in terms of hygroscopicity, they have problems in terms of adhesion, and the adhesion between solvent particles and between the coating material and the core wire is weak. Since high temperature drying is carried out at 400° C. or higher to reduce hydrogen, the curing speed during drying is high and drying cracks are likely to occur.

With welding materials such as this, where the adhesion of the coating material is weak, the formation of a protective tube at the rod end during welding is unstable, making it difficult to expect normal welding and causing defects such as blowholes.

In addition, it has disadvantages in terms of maintenance and management, such as lowering the product yield during manufacturing and requiring careful handling since the coating tends to peel off during transportation. In this regard, recently, monomethyltriethanolammonium hydroxide [N(C2H4OH)3(
Attempts have been made to improve adhesion by adding ammonium compounds such as CH3)OH and low melting point frits, but the former contains hydrogen atoms in its components, resulting in an increase in hydrogen in the weld metal. However, the latter has not been put into practical use because it is difficult to obtain frits with a softening point of around 400°C.

Under these circumstances, it has been desired to develop a fixing agent with low hygroscopicity and strong fixing power.

The present invention advantageously satisfies the above-mentioned needs, and provides a welding coating material that improves adhesion strength while maintaining the moisture absorption property of the coating material, thereby improving welding workability without deteriorating the properties of the weld metal. This paper proposes a fixing agent for

By the way, as already mentioned, it is known that a coating material using lithium silicate water glass as a fixing agent exhibits poor hygroscopicity after drying and solidification.

Therefore, the inventors took advantage of this property and investigated the issue of insufficient adhesion strength, and as a result of numerous experiments aimed at solving the above problem by adding other ingredients, the inventors found that lithium silicate aqueous solution It was discovered that the desired objective can be advantageously achieved by mixing a sodium silicate aqueous solution and a potassium silicate aqueous solution with a low molar ratio and a high SlO2 concentration in specific proportions. That is, this invention is an aqueous solution of an alkali metal silicate,
Molar ratio of SiO2 component to alkali component and Sl
O2 concentration is 2-4.5, 10-30 weight? Lithium silicate aqueous solution: 15 to 35% by weight and 1.5 to 2% by weight
．． 5, 20-30% by weight aqueous sodium silicate solution: 2
0-60 weight? and also 1.5-2.5, 20-3
0% by weight potassium silicate aqueous solution: This is a fixing agent for welding coatings for non-moisture-absorbing injections, which is a mixture of 20 to 60% by weight.

This invention will be specifically explained below with reference to the experimental results that led to this invention.

Figure 1 shows the molar ratio of SiO2 to Li2O in the aqueous solution when coating is performed using a lithium silicate aqueous solution as a fixing agent, i7120 and S
The results of a preliminary investigation into the relationship between iO2 concentration and coating shedding rate are shown.

The shedding rate was evaluated by the peeling rate of the coating when 10 coated welding rods were dropped from a height of 1 m. The adhesion strength of the coating depends on the molar ratio and SiO2 concentration,
In any case, when the SiO2 concentration exceeds 4.5 in terms of molar ratio, the dropout rate increases rapidly, and when the SiO2 concentration is less than 10% by weight (hereinafter simply expressed in %), the adhesion strength is extremely low regardless of the molar ratio. .

Therefore, when used as a fixing agent, the molar ratio is 1.5 to 4.
5. Si02 concentration: Must be 10% or more. On the other hand, the solidification temperature and cloudy temperature of the lithium silicate aqueous solution also depend on the SiO2/Li2O molar ratio and the SlO2 concentration, as shown in Figure 2, and both temperatures decrease as the SiO2 concentration increases, and the molar Since it tends to show a peak at a ratio of 3.5 to 4, for stable industrial use, it is desirable that the molar ratio is 2 to 4.5 and the SiO2 concentration is 30% or less.

Therefore, considering the above two characteristics, the lithium silicate aqueous solution has a molar ratio of 2 to 4.5 and a Si02 concentration of 1.
It is necessary to set it to 0-30%. Even when the above conditions are satisfied, water glass containing only lithium silicate has a considerably low viscosity of 1 to 10 centiboads at 20° C., and its adhesion strength is hardly sufficient.

In this regard, it may be possible to mix other water glasses with high viscosity and strong adhesion to lithium silicate as long as it does not impair its hygroscopic properties. For example, 20% SlO2, Li2
O: 2.5%, molar ratio: 4 Sodium silicate (SiO
2:22%, Na2O: 11%, molar ratio: 2.1) and potassium silicate (SlO2: 26%, K2O: 13.5%
, molar ratio: 3.0), the mixing ratio of lithium silicate must be at least about 50%, as shown in Figure 3, in order not to impair the moisture absorption properties of the coating material. be.

However, when the mixing ratio of lithium silicate is high, it is still difficult to expect a reduction in the shedding rate, making it difficult to use it practically. However, the inventors took this point one step further, and in order to lower the mixing ratio of lithium silicate and strengthen the adhesion without impairing the hygroscopic properties, the molar ratio of each of sodium silicate and lithium silicate was increased. Comprehensive experiments were carried out regarding the concentration of S1O2 and SlO2 as well as their mixing ratio.

In Figure 4, 30% of the fixing agent is a lithium silicate aqueous solution that satisfies the predetermined conditions, and the remaining 70% is SiO2.
The results of an investigation on the hygroscopic properties and shedding rate of coating materials when coatings were applied using fixing agents with various mixing ratios of sodium silicate and potassium silicate aqueous solutions with varying concentrations are shown.

As is clear from the figure, the three-component mixed solution improves both moisture absorption properties and adhesion strength regardless of the SiO2 concentration compared to the two-component mixed solution, but the SlO2 concentration of sodium silicate and potassium silicate is 30% each. If it exceeds 20%, the moisture absorption properties tend to decrease, and if it is less than 20%, the adhesion strength tends to decrease. Therefore, the SlO2 concentration of both sodium silicate and potassium silicate is preferably in the range of 20 to 30%.

In addition, the mixing ratio of both is 2% of the total fixing agent.
It was found that excellent effects were obtained in the case of 0 to 60%. Although the reason for this has not yet been clearly elucidated, mixing the three types of water glass lowers the softening temperature of the adhesive, making it easier to sinter the constituent particles of the coating, increasing the surface area of the coating. This is thought to be due to the decrease.

In fact, when the surface area of these coatings was measured by the BET method using inert He and N2 gas that forms a single molecule adsorption layer, it was found that those with low hygroscopicity had a surface area of 20 to 30%.
It was confirmed that the degree of Next, FIG. 5 shows the results of investigating the influence of the molar ratio of sodium silicate and potassium silicate on the moisture absorption properties and shedding rate of the coating material. Figure 5 shows the mixing ratios of lithium silicate, sodium silicate, and potassium silicate at 30% and 30%, respectively.
% and 40%, and the mole ratio of sodium silicate and potassium silicate was varied in various ways. If the molar ratio of both is less than 1.5, the moisture absorption properties will be poor, while if it exceeds 2.5, the shedding rate will be high, so the molar ratio must be in the range of 1.5 to 2.5. be.

Next, FIG. 6 shows the results of an investigation regarding the mixing amount of lithium silicate when the mixing ratio of sodium silicate and potassium silicate of 1:1 was set at an appropriate molar ratio and SiO2 concentration.

If the mixing ratio of lithium silicate is less than 15%, the moisture absorption properties will deteriorate, and if it exceeds 35%, the shedding rate will increase.
In the range of 5%, all showed good characteristics.

Examples of the present invention will be described below.

Example 1 A mild steel core (diameter 4.0 mm) equivalent to JIS G8528 was coated with an alkali silicate aqueous solution having the composition shown in Table 2 as a fixing agent (approximately 15 CC per 1009 solvent). After coating, the coating was pre-dried at 1000C for 2 hours and then baked for 1 hour with 400C to prepare a coated arc welding rod sample with a coating diameter of 6.30mm.

For each of these welding rods, the yield, coating shedding rate, and moisture absorption characteristics were investigated when 30 kg was manufactured, and the results are shown in Table 3.

When the molar ratio of potassium silicate and sodium silicate is larger than the specified range (/F6l~3) and smaller (/F6.l3~15), the product yield is extremely low and the coating material falls off. The rate is high, 62l! In the r seats 1 to 3, even if the mol ratio is appropriate, if the SlO2 concentration exceeds the appropriate range (應4
, 7), and when it was not satisfied (No. 12), the product yield was still low and the rate of shedding of the coating material was also high.

On the other hand, in waterfalls 5, 6 and 8 to 11, which satisfy the conditions of the present invention, the product yield is as high as 90% or more, the shedding rate of the coating material can be suppressed to about 2%, and the amount of moisture absorbed is also low. It exhibited excellent hygroscopicity of 0.3 to 0.5%. Example 2 Lithium silicate, potassium silicate, and sodium silicate with the appropriate molar ratio and concentration shown in Table 4 were mixed in the proportions also shown in Table 4 to prepare a sticking agent. A coated arc welding rod was produced by the same process as in Example 1 using the coating materials shown in Table 1.

Table 4 also shows the results regarding the shedding rate and moisture absorption characteristics of the coating material for these welding rods (A6.16-24).

In waterfalls 16 in which the amount of lithium silicate mixed is less than the appropriate range, the amount of moisture absorbed is large, while in waterfalls 22 to 24 in which the amount of lithium silicate is too large, the adhesion of the coating material is weak and the coating material is likely to fall off.

Furthermore, even if the mixing ratio of lithium silicate is appropriate, if the mixing ratio of potassium silicate and sodium silicate is not appropriate (Rolls 19 and 20), the amount of moisture absorbed increases. On the other hand, the mixing ratio of three types satisfies the specified range of this invention. 4617, 18 and 21 had extremely low coating shedding rates and hygroscopic moisture content. Note that potassium has an effective effect on welding arc breakage, so making the mixing ratio of potassium silicate a little higher than that of sodium silicate is even more effective for smooth welding. be.

Although the present invention has been described above mainly in the case where it is applied to a coated arc welding rod, the present invention is not limited thereto, and can also be applied to fluxes for submerged arc welding, backing fluxes, consumable nozzles for electroslag welding, and the like. Thus, according to the present invention, it is possible to satisfy both the anti-hygroscopic property and the adhesion strength of the welding coating material, which have hitherto been contradictory properties that could not be satisfied at the same time. Welding with good workability can be advantageously achieved without any problems.

[Brief explanation of the drawing]

Figure 1 shows the SiO2/Li lithium silicate aqueous solution fixing agent.
A graph showing the relationship between the 2O molar ratio and coating agent shedding rate. Figure 2 is a graph showing the relationship between the SiO2/1120 molar ratio and the solidification temperature and cloudiness temperature of the lithium silicate aqueous solution. Figure 3 is a graph showing the relationship between the SiO2/1120 molar ratio and the solidification temperature and cloudiness temperature of the lithium silicate aqueous solution. A graph showing the relationship between the mixing ratio of lithium silicate in the material, coating material shedding rate, and moisture absorption characteristics,
Figure 4 is a graph showing the relationship between the SlO2 concentration and mixing ratio of sodium silicate and potassium silicate, and the hygroscopic properties and shedding rate of the coating material.
A graph showing the relationship between the 2/K2O molar ratio and the SiO2/Na2O molar ratio and the hygroscopic properties and shedding rate of the coating material. It is a graph showing the influence on the dropout rate.

Claims (1)

[Claims] 1 It is an aqueous solution of alkali metal silicate, and SiO_2
Lithium silicate aqueous solution with molar ratio of component to alkaline component and SiO_2 concentration of 2 to 4.5, 10 to 30% by weight: 15 to 35% by weight, and 1.5 to 2.5, 2
0-30% by weight aqueous sodium silicate solution: 20-60
% by weight and the same 1.5-2.5, 20-30% by weight
Potassium silicate aqueous solution: A non-hygroscopic fixing agent for welding coatings in a mixture of 20 to 60% by weight.