Table 1
Parameters of MPS of electrically insulating and resistive coatings
| Parameters | Coating | |
|---|---|---|
| Al2O3 | TiO2 | |
| Electric current, I (A) | 45 | 40 |
| Voltage, U (V) | 30 | 28 |
| Spraying distance, H (mm) | 150 | 150 |
| Plasma-forming gas (Ar) flow rate, Gpl (slpm) | 1.3 | 1.3 |
| Shielding gas (Ar) flow rate, Gsh (slpm) | 4.0 | 4.0 |
| Powder feed rate, Ppow (g·min−1) | 1.2 | 2.0 |
[i] MPS, microplasma spraying; slpm, standard liters per minute
Table 2
Chemical composition of carbon steel St3 according to Ukrainian State Standard DSTU 2651:2005, 2015
| Elements | Wt.% of elements |
|---|---|
| C | 0.14–0.22 |
| Si | 0.15–0.30 |
| Mn | 0.40–0.65 |
| Ni | <0.3 |
| Cu | <0.3 |
| Cr | <0.3 |
| As | <0.08 |
| N | <0.008 |
| S | <0.05 |
| P | <0.04 |
| Fe | Balance amount |
[i] DSTU, State Standards of Ukraine (Derzhavni Standarty Ukrainy)
Fig. 1
Scheme of EHE tests: U – regulated power supply; K – switch for interrupting the supply of electric current; A – ammeter; V – voltmeter; R – a sample with an electric heating coating; T – thermal imager. EHE, electric heating element
Table 3
Intervals of variation of the parameters of MPS of electric heating tracks (TiO2)
| Levels of variation | Factors | |||
|---|---|---|---|---|
| Electric current, I (A) | Plasma-forming gas flow rate, Gpl (slpm) | Spraying distance, H (mm) | Powder feed rate, Ppow (g·min−1) | |
| Upper level + | 45 | 2.0 | 160 | 1.8 |
| Lower level − | 35 | 1.0 | 80 | 0.6 |
| Base level 0 | 40 | 1.5 | 120 | 1.2 |
| Variation intervals | 5 | 0.5 | 40.0 | 0.6 |
[i] MPS, microplasma spraying; slpm, standard liters per minute
Table 4
The CTE values depending on the parameters of the MPS of TiO2 powder
| Run | I (A) | Gpl (slpm) | H (mm) | Ppow (g·min−1) | CTE, % | |
|---|---|---|---|---|---|---|
| Experimental | Calculated | |||||
| 1 | 45 | 2.0 | 160 | 1.8 | 75 | 74 |
| 2 | 45 | 2.0 | 80 | 0.6 | 89 | 96 |
| 3 | 45 | 1.0 | 160 | 0.6 | 44 | 44 |
| 4 | 45 | 1.0 | 80 | 1.8 | 78 | 84 |
| 5 | 35 | 2.0 | 160 | 0.6 | 47 | 50 |
| 6 | 35 | 2.0 | 80 | 1.8 | 88 | 91 |
| 7 | 35 | 1.0 | 160 | 1.8 | 28 | 38 |
| 8 | 35 | 1.0 | 80 | 0.6 | 65 | 61 |
| 9 | 40 | 1.5 | 120 | 0.8 | 68 | 64 |
[i] CTE, coating transfer efficiency; MPS, microplasma spraying; slpm, standard liters per minute
Table 5
Parameters of the metallization figure depending on the parameters of the MPS of TiO2 powder
| Run | I (A) | Gpl (slpm) | H (mm) | Ppow (g·min−1) | Metallization figure height, h (mm) | Large axis, L (mm) | Small axis, l (mm) |
|---|---|---|---|---|---|---|---|
| 1 | 45 | 2.0 | 200 | 1.8 | 2.21 | 9.2 | 7.5 |
| 2 | 45 | 2.0 | 100 | 0.6 | 1.04 | 6.3 | 4.7 |
| 3 | 45 | 1.0 | 200 | 0.6 | 0.53 | 8.2 | 7.4 |
| 4 | 45 | 1.0 | 100 | 1.8 | 2.31 | 7.2 | 5.6 |
| 5 | 35 | 2.0 | 200 | 0.6 | 0.35 | 8.8 | 6.2 |
| 6 | 35 | 2.0 | 100 | 1.8 | 2.27 | 8.6 | 6.6 |
| 7 | 35 | 1.0 | 200 | 1.8 | 0.81 | 7.2 | 7.0 |
| 8 | 35 | 1.0 | 100 | 0.6 | 1.34 | 7.6 | 5.4 |
[i] MPS, microplasma spraying; slpm, standard liters per minute
Fig. 2
Scheme for measuring the metallization figure, where H is the spraying distance, β is the opening angle of the plasma jet, h is the height of the sprayed material, L is the vertical (large) axis, and l is the horizontal (small) axis of the spray spot
Fig. 3
Diagram explaining the loss of material due to the geometric factor
Fig. 4
EHE appearance: (A) EHE Series No 1: two-layer coating of Al2O3 and TiO2; (B) EHE Series No. 2: three-layer coating of Al2O3 and TiO2. EHE, electric heating element
Fig. 5
Microstructure of the three-layer coating of EHE Series No. 2: 1 – steel substrate; 2 – Al2O3 layers; 3 – TiO2 layer. EHE, electric heating element
Fig. 6
Temperature distribution along the electric heating track depending on the heating time; at the beginning of the process (A); every next 35 s (B, C); after 100 s (D)
Fig. 7
Cross section of metallization figures along the spray spot axes (Run 6, Table 5): (A) section along the large axis y = 2.27 × e−0.36x2; (B) section along the small axis y = 2.27 × e−0.78x2; 
graph of the Gaussian distribution (calculated); 
the actual profile of the metallization figure
Fig. 8
Losses of the sprayed material associated with the geometric factor depending on the width of the electric heating track: (A) for the large axis L of the spray spot; (B) for the small axis l of the spray spot