1 Introduction

Welding is one among the effective methods for joining metallic modules. It is estimated that roughly 3 million working population across the world is involved in welding and its allied jobs [1]. The most commonly employed method of all the welding processes is shielded metal arc welding (SMAW). Many types of SMAW electrodes are being manufactured, and depending on the main constituent of their flux, they are grouped into three categories: rutile, basic, and cellulosic coating materials. Rutile-based electrode is the most commonly employed and considered to be the most welder-friendly flux because of its excellent control properties on the arc stability and hence its better weldment [2]. Among the rutile-based welding electrodes, the primary arc-stabilizing material is natural rutile (TiO2), which constitutes about 40–48% by weight of the electrode flux. However, due to its higher cost and growing concern on its long-term availability, in the recent past, there is an impetus to find a potential substitute for it, hence the development of synthetic rutile [3]. Synthetic rutile which contains 96% TiO2 content is normally obtained normally through a chemical treatment method from a naturally occurring ore, so-called ilmenite (FeTiO3) [4, 5]. The mines and reserves of ilmenite in the world are found abundant and surpassed natural rutile.

Chen et al. [6] reported that synthetic rutile could be a possible replacement material for natural rutile in the welding electrode flux owing to its excellent mechanical and thermal properties. While natural rutile has a granular structure composed of single crystals, synthetic rutile concentrates are in the form of ultra-fine crystals ensuing potential advantages in terms of its chemical reactivity in the welding arc. Yet, prior to recommending synthetic rutile as a substitute for natural rutile in the welding flux, its effect on tailoring the hazardous emissions from welding such as emission of toxic metallic fumes, ultraviolet (UV) radiation, ozone concentration, and hexavalent chromium in fumes need to be addressed.

There are quite a lot of studies reported on the characterization and mitigation of fumes from a SMAW process. However, a breakthrough in this study happened when it was realized that arc-stabilizing materials in the welding electrode flux such as Al2O3 and TiO2 gave a better performance in their nanostructured form. This was first proved by Sivapirakasam et al. [7] where the authors introduced the nano-sized Al2O3 on core welding wires prior to flux coating and reduced the fume concentration without any adverse effect on the weld quality. The authors confirmed that nano-alumina participated in ionization reactions and improved the stability of the arc atmosphere, thereby having reduced fume levels.

Another report by Mohan et al. [8] indicated the favorable influence of introducing nanostructured TiO2 on the electrode wire on reducing the welding fume concentration. Later, Sivapirakasam et al. [9] deposited nano-aluminum oxide and titanium dioxide coating on stainless steel welding wires and studied its effect on the concentration of hexavalent chromium (Cr(VI)), a potential carcinogen for humans, in welding fumes. Intriguingly, the authors noted a trade-off between the generation rates of fume and hexavalent chromium concentration.

Vishnu et al. [10] developed a method for concurrently reducing fume and hexavalent chromium by utilizing multi-layered nanostructured Al2O3 and TiO2 for fume mitigation and as tertiary material ZnO for Cr(VI) reduction. In a subsequent investigation, the scientists found a drop-in fumes and Cr(VI) concentrations when micro-sized CaCO3 was replaced with its nano-sized counterpart in the welding flux. However, the research on control of fumes and its hazardous constituents from a SMAW process is still premature and needs further development.

Other than fumes, welders are also exposed to hazardous UV radiation and ozone whose formations in the weld atmosphere are essentially interrelated. Ozone is generated through the reaction of UVC radiation and oxygen in the welding atmosphere [10,11,12,13]. Ozone, being an irritant gas, has detrimental effects on the skin, mucous membrane, and throat of the welder. When ozone reaches the lungs, it reduces the rate of pulmonary ventilation and lower the generation of CO2. Besides, ozone is actually not a very stable compound, and it converts chromium from its lower oxidation state to Cr(VI) in welding fume due to this strong oxidation property. Thus, it is apparent that, in order to curtail the Cr(VI) concentration, it is required to control the generation of ozone and UVC radiation from welding. However, no such studies for a SMAW process reported till date.

The objective of this paper is to characterize the impact of replacing natural rutile with synthetic rutile in the welding electrode flux on the hazardous fume emissions in an occupational environment. In order to check the efficacy of the addition of synthetic rutile and to address the uncertainty in fully replacing natural rutile with synthetic rutile, its concentration was varied in definite proportions in the welding electrode flux. As a concurrent method for the combined reduction of fume formation rate and hexavalent chromium concentration, Zn, a reactive metal, was also incorporated into the electrode flux. Ozone and UVC concentrations in the arc atmosphere, chemical compositions of fume, and elemental deposition are also reported. The proposed knowhow of substituting natural rutile with synthetic in the electrode welding flux is expected to be an effective technique for the welding electrode manufacturing in the future.

2 Experimental procedure

2.1 Welding

Welding was carried out on a SS316L circular plate of 360 mm diameter and 12 mm thickness. The electrode employed was E316 L of the dimension 350 mm × 4 mm [14]. Table 1 shows the chemical composition of the base metal and the core welding wire. The flux chemistry of E316 L, as given by the electrode manufacturer (Logos Weld Products), is given in Table 2. The experimental electrodes E1, E2, E3, and E4 were prepared by substituting the natural rutile in the conventional electrode flux with TiO2-enriched synthetic rutile in definite proportion by weight of 25%, 50%, 75%, and 100% in that order. Fixed concentration (1% by weight) of Zn was added to each electrode flux with the aim of reducing Cr(VI) concentration in welding fume. All the electrodes were produced using an electrode manufacturing setup (make: Logos, model: EP 50) through a sequence of operations, namely dry mixing, wet mixing, slug pressing, extrusion, and baking under identical conditions. For measuring the density of conventional and experimental electrode flux formulations, the 10 mL volume of powder specimens measured using a standard cylindrical flask was gravimetrically weighed using a precision weighing balance (precision: 0.01 g, make: Metis, model: 007). The chemical compositions of the synthetic and natural rutiles were tested using X-ray fluorescence spectroscopy (precision: 0.1%, make: Panalytical, model: PW4400/40) [15,16,17].

Table 1 Base metal and core wire chemical composition
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Table 2 Flux chemical composition
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2.2 Fume formation rate, arc stability, and droplet transfer

The fume formation rate (FFR) was determined by sampling welding fumes in an AWS F1.2 standard fume test chamber [18, 19]; the test chamber’s schematic diagram is depicted in Fig. 1. The base plate was cleaned with a wire brush prior to welding to remove any contaminants. A constant current power source of an inverter type ARC/TIG welding machine (make: Rilox, model: TIG 200) was employed for welding. The electrode used in the study was having the dimension of 350 mm length × 4 mm diameter, with a permissible current range of 110–150 A and a voltage of 5–50 V. In order to effectively profile the fume emission from the electrode, a higher set current of 140 A was used. Welding was carried out for 60 s, and the extractor fan was let operational for 90 s more in order to achieve higher fume collection efficiency.

Fig. 1
figure 1

Schematic of the AWS F1.2 standard fume test chamber

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An experienced welder deposited bead on plate welds on the revolving base plate while maintaining a draw angle of 15°–30°. Consistent welding speed and feed rate of 15 cm/min and 18 cm/min, respectively, were maintained throughout the process. During 60 s of welding, fumes were collected on a glass microfiber filter paper (253 mm × 204 mm and 1.6-µm pores) at a flow rate of 900 L/min.

The FFR was determined gravimetrically using a dynamic high-precision weighing balance (accuracy 0.1 mg, precision ≤ 0.1 mg/ ≤ 0.05 mg, make: Shimadzu, model: AUW220D). The mass concentration of fumes was estimated from the weight difference of the filter paper prior to and after sampling as per the following equation (Eq. (1)):

$$\mathrm{Fume\;formation\;rate }\,(\mathrm{FFR})=\frac{{F}_{\mathrm{w}}-{I}_{\mathrm{w}}}{t}\mathrm{ g}/\mathrm{min}$$
(1)

where Iw is the initial weight of filter paper, Fw is the final weight of filter paper, and t is the time taken for welding. The fume collection and measurement were carried out in triplicate for each type of electrode, and an average value of FFR was recorded in the study.

The filter paper was then digested and extracted in accordance with the NIOSH 7300 standard, and the individual metallic constituents in fumes such as Ti, Ni, Si, Fe, Mo, Cr, and Mn were determined using the inductively coupled plasma atomic emission spectroscopy (ICP-AES) (precision: 3.3–7.7%, make: PerkinElmer, model: Optima 5300DV).

The arc stability during welding was determined using an online measurement of the probability density of arc voltage. Arc voltage and current data were collected and analyzed using a digital storage oscilloscope (DSO) instrument (precision: 0.05/time per div, make: Agilent Technologies, model: DSO7054B). A differential probe was used to detect the voltage, while the current was monitored using a current probe of clamp type (precision: 500 µA, make: Chauvin Arnoux, model: PAC12) (1 mV/A and 10 mV/A). Another technique for measuring arc stability was to use an infrared camera to capture the spatters produced during welding (make: Flir; model: SC7500-MB). The lens employed had a focal length of 25 mm, and the camera was kept near to the weld zone at a distance of approximately 1 m.

The dynamic behavior of the molten droplet transfer from the electrode was visualized using a high-speed camera (make: Photron, Fastcam model: 775 K-M1). The video was shot at 7000 frames per s and resolution of 700 × 400 pixels. Cavitar Cavilux HF illumination system was used for enabling clear visualization of welding processes as if they were essentially cold by eliminating welding brightness.

2.3 Cr(VI) formation rate, UVC, and ozone concentrations

Concentration of Cr(VI) in welding fumes was measured following the NIOSH 7600 standard. Accordingly, the filter paper was digested in a solution of 2% NaOH-3% Na2CO3 and subjected to analysis in a UV–visible spectrophotometer (precision: ± 2 nm, make: Shimadzu, model: UV-2600) at a wavelength of 540 nm. The analysis gave the weight percentage of Cr(VI) in welding fumes which is then expressed as hexavalent chromium formation rate.

UVC emission from the welding source was identified using a UV light meter (precision: 0.01 mw/cm2, make: Lutron Electronic, model: YK-37UVSD) capable of capturing UV radiation in the range of 200–280 nm. The detector head of the UV meter was attached to a mechanical system as shown in Fig. 2 and positioned at an angle of 15° from the center of the arc facing it [20]. The effective irradiance of UVC was measured at a distance of 1 m from the center of arc. An average of three replicates was taken, and the percentage error was found to be ± 10%.

Fig. 2
figure 2

Schematic of UVC and ozone measuring apparatus

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The concentration of ozone produced during welding was determined using a UV absorption ozone analyzer (precision: 0.001 ppm, make: Faraday Ozone, model: OA-964). Figure 2 gives the schematic illustration of the experimental method. Using the analyzer, the concentration of ozone could be measured within 0–5000 parts per billion (ppb) in a 0.5-s response time. The analyzer’s inlet probe was angled 60° away from the arc’s center and 1 m distant from it to ensure optimal collection efficiency. The probe was linked to the analyzer through a polytetrafluoroethylene (PTFE) tube with a 37 mm diameter and a 0.5-m PTFE filter to prevent welding fume from entering the ozone analyzer. Prior to the start of the studies, the sample probe, connecting tube, and filter were conditioned for 10 min with ozone generated by an ozone generator [21, 22]. The ozone concentration was averaged during a 60-s period following the initial welding.

In general, UVC and ozone measurements can be influenced by the ambient conditions of the test environment. However, during the measurements, utmost care was taken in order to eliminate such disturbances. All the measurements were carried out under controlled test room conditions. The room dimensions were 3.04 m × 3.04 m × 2.74 m with a small ventilation of size 0.60 m × 0.30 m, and there were no source of UVC and ozone. While measuring the UVC and ozone concentrations, the door was kept closed in order to avoid external influences.

2.4 Weld chemistry and delta quantity

For elemental measurements of alloying elements in the weld such as Cr, Mn, Fe, Ni, Mo, Si, and Ti, a tube-based portable hand-held X-ray fluorescence (XRF) device (precision: 0.1%, make: S1 Titan, model: 800) was used [23]. Prior to measurements, good brushing to clean off the weld spatter, scaling, and rust was carried out by using a wire brush. It is essential to take a minimum of 3 tests across the welded area to get more accuracy of the result.

The loss of elements during the welding process via transfer from the weld metal to the slag contributes to fumes by its evaporation [24, 25]. This elemental transfer can be calculated using the element’s delta quantity (Eq. (2)) which is shown below:

$$\Delta\;\mathrm{Quantity}=\mathrm{Analytical\;composition}-\mathrm{Nominal\;composition}$$
(2)

The nominal composition can be calculated from the following relation:

$$\frac{\mathrm{Dilution}\times \mathrm{Baseplate\;composition}+\left(100-\mathrm{Dilution}\right)\times \mathrm{Wire\;composition}}{100}$$

The analytical composition, on the other hand, refers to the weight fraction of each element in the weld.

3 Results and discussion

3.1 FFR and Cr(VI) formation rate

The FFR (g/min) and hexavalent chromium formation rate (Cr(VI)FR) (mg/m3) measured for the conventional and experimental electrodes are represented in Fig. 3. Here, C represents the conventional electrode comprising 100% natural rutile in its flux. With the addition of synthetic rutile to the flux, significant changes in FFR and Cr(VI)FR were detected. The electrode with 50% synthetic rutile in its flux exhibited a significant drop in FFR, up to 31.4% (E2). However, the subsequent addition of synthetic rutile raised the FFR in comparison to the test electrode (E2). Hexavalent chromium formation rate had exhibited a different trend in its variation. Initially, there was a significant reduction in Cr(VI)FR when 25% synthetic rutile was added to the electrode flux (E1). Further addition of synthetic rutile by 50% resulted in a modest rise in Cr(VI)FR, again followed by a decrease when 75% and 100% synthetic rutile was added to the flux. A careful examination of the preceding data indicates that, in order to achieve an acceptable reduction in both FFR and Cr(VI)FR, it would be advantageous to substitute 50% natural rutile in the flux with synthetic rutile (corresponding to the electrode E2). The following sections address the possible cause for FFR and Cr(VI)FR variation due to the presence of synthetic rutile in the flux.

Fig. 3
figure 3

Effect of flux composition on FFR and Cr(VI) formation rate. The error bars show the standard deviation of independent triplicate samples

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3.1.1 Variation in fume formation rate

FFR is dependent of the arc stability. A stable arc is known to produce low fumes and vice versa. In order to get an estimate of the arc stability, the arc voltage probability density was plotted as a function of arc voltage as shown in Fig. 4. To ascertain the difference between the various rutile concentrations, certain portions of probability density plot (designated as a, b, and c in Fig. 4) were enlarged and highlighted.

Fig. 4
figure 4

Probability density distribution of arc voltage during welding

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As can be observed, the probability density distribution of the arc voltage comprises two peaks with comparable shapes [26]. The smaller left-peak sector indicates increased arc stability. The integrated probability ΣUS was computed by integrating the region of the left peak between the minimum and maximum voltages. Reduced ΣUS (%) values indicate a reduced chance of short-circuit and explosion drop transfer, implying increased arc stability. The integrated probability density values of the conventional and experimental electrodes are shown in Table 3.

Table 3 Integrated probability density
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The combination E2 had the lowest ΣUS value of 6.23%, indicating the highest arc stability among the tested electrodes, and justifies its low fume generation behavior, while E4 had a ΣUS value of 7.69% close to that of the conventional electrode, indicating similar arc stability characteristics due to which their FFRs were also comparable.

Apart from arc stability, the droplet characteristics also decided the quantity of fumes generated. Figure 5 shows the variation in the size of the pendent liquid droplet as captured by a high-speed camera. It is obvious that the electrode E2 (with 50% synthetic rutile in its flux) had a smaller droplet diameter of 2.9 mm when compared with the conventional electrode (droplet diameter 4.2 mm) and other experimental electrodes. The considerable reduction in droplet diameter (by as much as 30%) could have ensued lower evaporation and hence a lower FFR. A close examination of Fig. 5d, e further reveals that the droplets from electrodes E3 and E4 were continuous and exhibited wandering effect resulting in splashing of the weld pool. This, in turn, might have resulted in higher fume levels.

Fig. 5
figure 5

High-speed camera images showing droplet transfer from the a conventional electrode, b E1, c E2, d E3, and e E4

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The spatters formed from the electrodes were captured using infrared thermography as shown in Fig. 6 which clearly reveals a variation with the concentration of synthetic rutile in the flux. The images were rendered at 300 frames per s, and the spatters observed in the images were highlighted with blue circles for better understanding. With an increase in the synthetic rutile flux concentration from 0 to 25% and to 50%, it was observed that the arc stability increased and attained a maximum stability at 50% of synthetic rutile flux addition. This is primarily associated with the differences in the droplet transfer characteristics (Fig. 5). For conventional electrodes, the pendent droplets were larger in size due to which, spatters will be generated upon detachment of droplets to the weld pool. With the addition of synthetic rutile up to 25%, the droplet size was found to reduce due to the reduced surface tension and pinching effect provided by the TiO2 in the synthetic rutile. Hence, the spatter reduces for E1 compared to the conventional electrode C. The pinching effect was more pronounced with the 50% addition of synthetic rutile in the flux because of which the droplet size was further reduced for E2 and the droplet transfer was finer and more stable than that of E1. Hence, the spatter density also reduced for E2. Subsequent addition of synthetic rutile up to 75% and 100% in the flux progressively increased the pinching effect and resulted in continuous transfer of droplets from the electrode to the weld pool. This resulted in higher splashing and wandering effects of the weld pool leading to increased generation of spatters.

Fig. 6
figure 6

Infrared camera images of spatter formation

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The variations in arc stability, droplet sizes, and spatter formations were greatly influenced by the physical and chemical characteristics of the rutile flux compositions. There were notable variations in the physical and chemical properties of synthetic rutile compared to natural rutile, which suits its application in welding process. As far as physical properties are concerned, synthetic rutile particles are fine grained and porous in structure compared to natural rutile. The SEM images shown in Fig. 7 clearly indicate that synthetic rutile contains fine-grained TiO2 particles of size 150–212 µm compared to natural rutile having 180–850-µm-sized TiO2 particles and being relatively porous than natural rutile.

Fig. 7
figure 7

a) SEM image of natural rutile. b) SEM image of synthetic rutile

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Yet, another difference in the physical property is the density of synthetic and natural rutiles. The electrode density was found decreasing with an increase in the concentration of synthetic rutile in the flux as shown in Table 4.

Table 4 Density of electrode coating
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This trend is attributed to the lower density of synthetic rutile (2.3 g/cm3) compared to natural rutile (4.23 g/cm3). The variation in density of the electrode could be corroborated with its droplet transfer and fume generation behavior. A decrease in density would mean more quantity of synthetic rutile in a given volume of flux. As synthetic rutile contains a rich content of fine-grained TiO2 particles, its increase in concentration in the flux facilitates better reduction in surface tension of the pendent liquid droplet and hence promotes stable droplet transfer resulting in reduced fume levels [27].

Considering the chemical properties, there are significant differences in the chemical composition of natural and synthetic rutiles. The chemical composition of synthetic rutile and natural rutile as analyzed using XRF spectroscopy is given in Table 5.

Table 5 Chemical composition of natural and synthetic rutiles
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As evident from the results, natural rutile contains 86.27% TiO2 followed by elements such as Fe2O3, SiO2, Al2O3, CaO, MgO, and MnO. On the contrary, synthetic rutile assays 96.2% TiO2 along with traces of other elements.

Hence, for a given quantity of flux, the involvement of TiO2 on the droplet transfer behavior and hence on the reduction of fumes will be more prominent for synthetic rutile when compared to natural rutile.

3.1.2 Variation in hexavalent chromium formation rate

The effect of Zn on the Cr(VI) content in the welding fumes was analyzed. Cr(VI)FR varies with the UVC and ozone concentration in the weld atmosphere. When an amount of UVC in the arc atmosphere increases, more reactive species of oxygen produced would react with normal oxygen molecule to form ozone as given in Eqs. (3) and (4) [28]. Furthermore, ozone, being unstable and a strong oxidizer, readily oxidizes the Cr(0) and Cr(III) to Cr(VI).

$${\mathrm{O}}_{2}+\mathrm{U}\mathrm{V}(<210\mathrm{nm})\to 2\mathrm{O}$$
(3)
$$\mathrm{O}+{\mathrm{O}}_{2}\to {\mathrm{O}}_{3}$$
(4)

Figure 8 shows the plot of UVC radiation intensity, ozone, and Zn concentration for different flux compositions. The effect of flux modification on the intensity of UVC and ozone is apparent from this figure. Interestingly, two distinct trends could be observed in the figure. From conventional electrode to E1 (with 25% synthetic rutile in its flux), there was a trade-off between the UVC radiation and ozone. However, for E2 and other experimental electrodes (E3 and E4), the same linear relation between UVC and ozone (as mentioned in Eqs. (3) and (4)) could be observed. These variations might be attributed to the following reasons.

Fig. 8
figure 8

Intensity of ozone and UV C formation for different flux composition. The error bars show the standard deviation of independent triplicate samples

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Apart from synthetic rutile, the experimental electrodes contain Zn, a reactive metal, in its flux formulation which readily oxidizes to ZnO fumes by reacting with the available oxygen free radical in the arc atmosphere as shown in Eq. (5).

$$\mathrm{Zn}+\mathrm{O}\to \mathrm{ZnO}$$
(5)

This would deprive oxygen free radical for further reaction with O2 (Eq. 4) and hence reduce the formation of ozone in E1. Apparently, the Cr(VI)FR also reduced for E1. However, there was an increase in UVC radiation for E1. This might be attributed to the fact that the intensity of UVC radiation depends on the level of fumes in the arc atmosphere. A higher fume level would ensue a barrier effect for UVC radiation, minimizing its intensity in the arc atmosphere and vice versa [29]. The reason that E1 showed higher UVC than conventional electrode is due to its lower fume levels and hence reduced barrier effect.

For E2, with further addition of 50% synthetic rutile in the flux, there was a significant decrease in the generation of fumes compared to E1. The greater the reduction of fumes, the lesser the barrier effect which enables the reaction between UVC radiation and O2 to form ozone in the arc atmosphere (Eqs. (3) and (4)). The higher concentration of ozone in the arc atmosphere might have caused a modest rise in Cr(VI)FR for E2 compared to E1. However, the Cr(VI)FR was still 20% less than the conventional electrode.

For electrodes E3 and E4, with 75% and 100% synthetic rutile in its flux, respectively, the UVC radiation and ozone were found to decrease which might possibly be attributed to the increase in generation of fumes. It is due to this reason that the Cr(VI)FR decreased for E3 and E4.

The variation in the concentration of Zn in fumes is also evident from Fig. 8. As can be noted from the figure, the concentration of Zn in the fumes decreases from E1 to E2 and then increases for E3 and E4. Overall, the results indicate that Zn is effectively involved in ozone reduction only up to 25% addition of synthetic rutile to the flux. With an increase in the content of synthetic rutile, the effect of UVC in forming ozone was found to surpass the effect of Zn.

The constituent analysis shown in Fig. 9 also reveals that the electrode E2 had the lowest metallic constituent concentration except zinc, while for E4, it was the highest. This variation could be corroborated with the surface tension effect of the synthetic rutile. The enhanced pinching effect caused by an increase in surface tension have reduced the pendent liquid droplet size in E2 and hence its evaporation to fumes. Apart from this, the stable nature of the arc in E2 have favored alloying elements getting dragged to the weld pool (as evident from Table 6) and hence prevented it from oxidizing as fumes. However, for E3 and E4, there were increased wandering and splashing of the weld pool (Fig. 5) leading to higher oxidation and emission of the constituent elements in the arc atmosphere.

Fig. 9
figure 9

Variation of different metallic constituent concentrations in different flux compositions. The error bars show the standard deviation of independent triplicate samples

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Table 6 Chemical composition of weldments
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The above variation in metallic constituent concentration in fumes can be complemented by the results of the delta quantity analysis shown in Fig. 10. Delta quantity gives the amount of alloying elements recovered in the weld pool and is a direct indication of the quantity of metals generated as fumes. It could be observed that the delta quantity was more positive for the electrode E2, indicating better transfer of alloying elements from the flux to the weld and hence a concomitant decrease in its availability for oxidation into fumes [30, 31]. The lower values of delta quantity of E3 and E4 (implying reduced deposition in the weldment) signify transfer of alloying elements to the slag followed by its evaporation into fumes.

Fig. 10
figure 10

Delta quantity analysis of the different combinations. The error bars show the standard deviation of independent triplicate samples

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4 Conclusions

Welding fume is an unwanted but unavoidable byproduct of arc welding process. This paper investigated the influence of introducing synthetic rutile and Zn to the electrode flux on its emission characteristics. The following conclusions could be made from the study:

  • Fume generation rate varies with the quantity of synthetic rutile in the electrode flux. E2 containing 50% synthetic rutile in the flux showed up to 31.4% reduction in FFR than the conventional electrode.

  • Moreover, the addition of Zn to the electrode flux had a significant effect on the intensity of UVC and ozone in the region of the arc, which affects the concentration of Cr(VI) production in the weld environment. E4 had the lowest UVC intensity, ozone concentration, and subsequent Cr(VI) concentration in the arc region compared to other experimental electrode compositions. In comparison, the E2 electrode generated a higher Cr(VI)FR value, but it was still 20% less than the conventional electrode.

  • The enhanced pinching effect caused by an increase in the surface tension have reduced the pendent liquid droplet size in E2 and hence its evaporation to fumes. Thus, E2 was reported to have lower concentration of metallic elements such as Ti, Ni, Si, Fe, Mo, Cr, and Mn in fumes and was also found to have higher weld metal deposition than the conventional and other experimental electrodes.