banner-300x100

Electric spark alloying and HVOF spraying

PDF Print E-mail

Surface hardening by applying elektroiskorovogo doping wear layers of Stellite, chromium carbide on installations Intal and Intal-1500-3000.

Developed systems for high wear-resistant, heat-resistant and corrosion-resistant metal layers thickness 0,01-0,80 mm with a capacity of up to 40 sm2/min. Study some particular ESA-speed steel.

It is known that for the spark alloying (ESA) are widely used refractory metals, hard metals and less heat-resistant high-alloy steels and alloys with high mechanical properties. In many cases, the reason for this is the difficulty of the process ESA related to "sticky" at the anode using a vibrator. In our opinion, the main reasons for "sticking" are: lack of energy impulse discharge, high strength material applied, much its melting point, the lack of power of the vibrator and is also not an optimal speed of its movement to the workpiece.

To enhance the ESA, both in terms of increasing the range of different metals, alloys and materials, and to improve process performance ESA, the thickness of the applied layer, increasing its density (reduced porosity) while simplifying the process of ESA developed high power setting INTAL-1500 and INTA-3000.

Installation creates a new (modern) electronic components with a total capacity of 1,500 permanent and 3,000 uF, with a smooth change of the voltage and current of the battery of capacitors, ie regulation of energy parameters, such as energy level and frequency of these discharges. Pulse energy ranges from 0.3 to 21.0 J, and the frequency of 30 to 400 Hz, the voltage of the capacitor charging varies from 20 to 115, and a current of 3 to 25 A.

The figure shows the dependence of the energy of a single pulse from the charge voltage capacitors. It is determined from the expression . Pulse energy E depends on the chosen value of the voltage U, as capacitance C in plants in 1500 and 3000 mF constant and adjusting it is not possible.

If you change the strength of the current charging the capacitor, it will change the frequency of the pulse charging and discharging capacitors. Most installations for ESA pulse frequency is associated not only with the established parameters mode (voltage capacitor charging and capacity), but also to the presence (or absence) of a contact electrode (anode) to the product (cathode) which is created by the vibrator. Vibrators often work at power frequency of 50 Hz, so the frequency of the pulse is constant and usually only in the ideal case, up to 100 Hz.

In the described installations INTAL-1500-3000 and INTA frequency can be selected either in the range of 30 to 400 Hz based tasks. In this installation, the pulse repetition frequency is free, as in the master oscillator, ie depends only on the set voltage and charging current of capacitors and does not depend on the presence or absence of contact with the workpiece. This eliminates the use of a vibrator and move the electrode of a hardening product by rotating disk or cylindrical electrode. Since the electrode is in contact with the product, the process of changing the transfer of the metal and its oxidation decreases caused by metal more dense, non-porous and the surface roughness does not deteriorate as the number of layers.

In systems used inverter converter, thus improving efficiency of plants, significantly reducing their size and weight. The plants have a soft start system, after entering into a network of 220 V. The primary current of the network does not exceed 15 amps, so they can be incorporated into a standard electrical outlet.

Since the installation is energy intense device (due to the small size and weight), to ensure normal temperature regimes of power semiconductor devices used mechanical ventilation and introduced overheating protection, blocking work units in an invalid thermal regime.

Зависимость энергии одиночного импульса от напряжения на конденсаторах

The energy of a single pulse of the voltage on the capacitors.

Зависимость тока от напряжения для частот 50 – 400 Гц

The dependence of the current on voltage for frequencies 50 - 400 Hz

The figure shows the dependence of the current on the voltage pulse repetition frequency steps of 50 Hz. The figure shows that the higher frequencies can be obtained only at voltages less than 70 V, ie by more soft modes with the average energy of the pulse. At an energy level close to the maximum, at a voltage of 110 V frequency is about 150 Hz.

If we draw the line for the voltage to 60 V (or any other) parallel to the axis abscess (current), then the lines of intersection with frequencies of 50, 100, 150, 200, 300, 400, we get the amount of current that must be set for any of these frequencies. In the installation INTAL-3000 pulse frequency at the same installing INTAL-1500 current charging capacitor is 2 times lower.

The coating is used as the anode with a diameter of 20-200 mm and a width of 3-5 mm, or a cylindrical rod with a diameter of 2-10 mm and a length of 150 mm. Rotational speed of the disc 2 / s, about 5 bar / s. The coating is applied without vibration.

Table 1

Technical characteristics of equipment for ESA.

p / p

Parameter name, the dimension

Inta-

1500

Inta-

3000

1.

Voltage supply, V

220

220

2.

The maximum primary current, A

15

15

3.

Battery capacity capacitors microfarad

1500

3000

4.

Charging voltage capacitors,

20-115

20-115

5.

Pulse energy, J

0,3-10,5

0,4-21,0

6.

Pulse repetition rate, Hz

30-400

15-200

7.

Plant efficiency

0.90

0.92

8.

Dimensions in mm

length

550

650

Width

300

400

Height

500

550

9.

Weight, kg

28

37

10.

Coating system

without vibration, rotational

11.

Coaster

Spanner

These plants has been investigated applying stellite, chromium and tungsten carbide. The samples of low-alloy steel 20HN2 70h20h10 size at different voltages for 1 min produced ESA. Anode - drive this alloy and a cathode - a sample of steel 20HN2 weighed before and after the ESA on an analytical balance with an accuracy of 1 mg. For better clarity, we describe a further study on application stellite. Erosion of the anode and cathode gain shown in the figure in absolute terms, without regard to sign (minus to plus for the anode and cathode). The absolute difference between the erosion and weight gain - permanent loss of coating material.

In particular, the figure shows the effect of current (frequency) of the erosion of the anode (curve 1) and the gain of the cathode (curve 2) at a constant voltage of 80 V. The voltage 80 V was chosen because it is the average for this installation, and also allows you to explore most of the current range (frequencies) that can run the installation.

As can be seen the erosion of the anode current increases from 6.1 A (frequency 50 Hz) to 24.4 A (frequency 200 Hz) changes almost linearly from 180 to 580 mg. Increase gain cathode currents from 6.1 to 18.3 A (respectively, frequencies of 50 Hz and 150 Hz) also increases linearly. The section from 18.3 to 24.4 and the gain decreased, probably due to the overheating of the sample due to its lack of weight, with increasing current erosion and gain curves diverge, suggesting that the loss of the anode increases.

Влияние тока (частоты) на эрозию анода и привес катода

The influence of current (frequency) of the erosion of the anode and cathode gain.

Влияние тока (частоты) на эрозию анода и привес катода

The influence of stress on the erosion of the anode and cathode gain.

The figure shows the effect of voltage (energy level) to the erosion of the anode and cathode gain. The figure shows that the curves of erosion and weight gain in the area of ​​60-100 are almost equidistant and are slightly increasing. In the area from 100 to 115, a sharp increase in the erosion of the anode with a moderate increase in weight gain of the cathode. Most likely due to increased erosion of the cathode heating it to 500-550 0C because of high current and small size of the cathode and the lack of cooling. Tendency to increase with an increase in growth of the cathode voltage (pulse energy) in our opinion is favorable, because improves the performance of the process and application of a thicker coat.

As follows from energy impulse to improve the performance of the process can be increased as the ESA by increasing the charge voltage capacitors, and by increasing the capacity of the capacitor bank. Further voltage increase is undesirable for safety and so we had to increase the energy of a single pulse increased 2-fold to 3,000 uF capacitor capacitance.

The figure shows the effect of the energy of a single pulse to the erosion of the anode and cathode to gain stellite.

Влияние энергии единичного импульса на эрозию анода и привес катода

As seen from the figure increased energy single pulse with 10 J (setting INTAL-1500) up to 20 J (setting INTAL-3000) has increased the erosion of the anode from 460 to 1300 mg, that is, 2.82 times, and the gain of the cathode increased from 270 to 610 mg, ie of 2.26 times. Erodibility coefficient of efficiency of the material down with from 0.58 to 0.47, ie, erodibility material loss increased by 1.23 times, which we think is acceptable.

It is known that the parameters of the regime ESA, and in general, pulse energy (power) is influenced not only by the thickness of the applied layer, but also on the depth of the heat affected zone (HAZ). [2] In order to determine the effect of the charging capacitors at a constant voltage charging (U = 100 V) to a depth of HAZ we performed the following experiment. The samples of size 70h20h5 mm annealed steel U11 produced ESA-speed steel. Capacitor charging current of 10, 15, 20 and 25 A at 100 V, while ESA 1 min. After the ESA of the samples were taken to measure transverse sections microhardness microscope PMT-3 with a load 200 microhardness measurements were performed with a pitch of 50 microns. The measurement results are shown in Fig.

Влияние тока (мощности) на глубину упрочненного слоя (U=100B)

As can be seen from the increase in the charging capacitors 10 and 20 and microhardness at 50 microns increased from 16,000 to 19,500 MPa, and an increase in current up to 25 A leads to a decrease in microhardness to 17000MPa, due probably to the fact that there significant heating of the sample, causing a reduction in the cooling rate applied layer and HAZ. Increase in the current 10 to 25 A leads to an increase in the hardened layer with the HAZ from 200 to 450 microns. Increase hardened HAZ in this case is an additional advantage with increasing power at ESA.

Appearance of one of the transverse sections with pricked over in the deposited layer, HAZ and base metal is shown in Fig. The boundary between the hardened HAZ and the base metal is easily distinguished as the hardness (size prints), and on different surfaces etched transverse sections.

Поперечный шлиф образца с нанесенными наколами