Page 33 - ST Sept
P. 33

INNOVATIVE TECHNOLOGY                                                                INNOVATIVE TECHNOLOGY

 as  a  result  of  which  the  electrode  consumable  material  is transferred  and  deposited  onto   Table 1. Characteristics of the installation for plasma-spark coating.
 the  surface  of  the  product.  This technology  is called electrospark  alloying  (electrospark  or
 plasmaspark coating) [2]. In this case, a plus is supplied to the electrode (Fig. 1) from the   Power consumption, kW  0,5
 source of the pulse generator, and to the product - minus from the source.  Mains supply voltage, V  220
    The method of coating is based on the use of a spark discharge with a short duration of its   Pulse energy, J  0,11 – 10
 existence 10-6≤t and≤10-3 s and the passage of powerful pulse currents during the discharge
 of a capacitor with a current density of up to 106 A / mm2. The plasma temperature in the   Pulse frequency, Hz  5 – 1600
 interelectrode gap can reach 7000 - 11000 ° C. As a result of the thermal and gas-dynamic   Electrode vibration frequency, Hz  600
 effect of the spark discharge, the erosion of the electrode (anode) material and the transfer   Number of modes  70
 of erosion products in the liquid, solid and vapor phases to the product (cathode) occur. In
 this case, a composite material is formed on the surface of the product due to the course of   Overall dimensions of the generator, mm  160х320х360
 metallurgical  processes,  which includes the  materials  of  the  electrode  and  the  product,  the   Generator weight, kg  14
 products of their interaction with each other and with elements of the interelectrode medium.    Maximum coating thickness of T15K6 alloy on 45 steel, microns 500

        Height of irregularities in the profile of the coating Ra, μm                               2,0

        Height of irregularities in the profile of the coating Ra, μm                               15

    and connecting cables. Table 1 shows the technical characteristics of this unit
            Glow discharge
            Glow discharge is an independent electric discharge in gas with cold electrodes at currents
    of  10-5  - 1.0  A  and  low pressure  (5  • 10-2-103  Pa),  which has  a  characteristic  structure
    in the form of alternating luminous areas of different colors and different glow intensity. Its
    distinguishing feature is the existence of a layer near the cathode with a large positive space
    charge, a strong field at the surface, and a significant drop in potential of 100 - 400 V and
 a  b  c  more. The glow discharge got its name due to the presence of the so-called glow on one of the
    electrodes (cathode).

 Fig. 2. Installation for plasma-spark coating (a), application wear-resistant coating made of VK8 alloy (b), applying an   Cooled vacuum chamber
 electrically conductive silver plating (c.
                           Argon
    An important factor in the qualitative formation of the coating is the effect of cathode   Ammonia  Control blockr
 cleaning, which ensures the destruction and removal of surface films from the treated surface of   Propane
 the product (cathode) due to the high density of the released energy in the microcathode spots   Air
 of the spark discharge.


    The main areas of application of this technology are:                     Plasma source
    ● restoration and hardening of machine parts, tools, stamps;
    ● application of functional (wear-resistant, electrically conductive, decorative) coatings;
    ● reduction of the transition resistance of electrical contacts (tin plating, pretinning, nickel   Pump
 plating, silver plating). Hard alloys (T15K6, T17K12, VK6, VK8, VK20, etc.), materials based on   (discharge up   Glow discharge  Anode
 metal carbides and borides (TiC, WC, Mo2B5, CrB2, TaB2, etc.), graphite and etc. are used as   to 0.2 mbar)
 electrodes to strengthen the tool and technological equipment.   Cathode

    The main advantages of this technology are:  Fig. 3. Scheme of plasma nitriding.
    ● the possibility of local formation of coatings in strictly specified places with a radius of
 fractions of a millimeter or more, without protecting the rest of the surface;     One of the applications of the glow discharge is the technology of plasma chemical-thermal
    ● application of coatings on large and massive parts with local zones for pretinning, tin   treatment of metals, which are designed to increase the hardness, wear resistance, fatigue
 plating, nickel plating, silver plating, etc.;  strength, scuff resistance, heat resistance and corrosion resistance due to saturation of the
    ● high adhesion of the coating to the substrate;  surface of the processed products with nitrogen, carbon, boron, cadmium and several elements
    ● lack of heating and deformation of the product during processing;  at the same time. During processing, the products are immersed in a glow discharge plasma
    ●  the  possibility  of  using  various  conductive  materials  as  electrodes,  both  from  pure   that burns between the cathode (products) and the anode (walls of the vacuum chamber) and
 metals and their alloys, powder materials, etc.  contains the necessary saturating element. The positively charged ions of the saturating element
    ● comparative simplicity of the technology, which does not require special preliminary   under  the  action  of  the  electric  field  are  accelerated  towards  the  product,  bombarded  and
 surface treatment;  penetrated into their surface layer. In this case, the energy of ions is thousands of times higher
    ● ease of maintenance and reliability of equipment, which is small-sized and transportable;  than the energy of atoms during gas chemical-thermal treatment. The heating temperature of
    ● low energy consumption of manual and mechanized processes (0.5 - 2.0 kW);  products during processing is 300 - 600 ° C.
    ● high coefficient of material transfer (60 – 80 %).     The most demanded process in the world is the process of plasma nitriding (nitriding in a
    Fig. 2 shows the installation and process of coating. The equipment for plasma-spark   glow discharge, ion-plasma nitriding, Fig. 3, 4). Ammonia, argon, propane, natural gas, etc. are
 coating consists of a block of equipment combined with a pulse generator, an electric vibrator   used as working gases. Regulation and control of the technological process is fully automated


 32  Stanochniy park                                                                            Stanochniy park      33
   28   29   30   31   32   33   34   35   36   37   38