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INNOVATIVE TECHNOLOGY                                                                                                                                                                                     INNOVATIVE TECHNOLOGY
        HARD ALLOY COATING TECHNOLOGY                                                                                                   At this stage, the following processes take place:

                                                                                                                                        ● recrystallization of tungsten carbide through the liquid phase;
                                                                                                                                        ●  splicing  of  neighboring  grains  due  to  the  predominant  growth  of  one  grain  at  the
                                       The  article  discusses  the  production  of  wear-resistant  composite                   expense of others;
                                       coatings  using  electrocontact  sintering  of  powders.  It  is  shown
                                       that  electric  contact  sintering  provides  for  electric  heating  of  a                                                                                       steel
                                       metal powder, poured between the part and the electrode, due to
                                       the  thermal  energy  released  by  the  electric  current  at  the  active
               A significant increase in the performance of many types                resistance.
        of products is achieved by applying coatings on their surfaces
        based  on  a  compound  of  tungsten  and  titanium.  The  use  of
        such coatings allows not only to increase the wear resistance
        of  products and  tools several times,  but also to design
        fundamentally new types of tools and friction units.
               Unlike  other  types  and  methods  of  applying coatings,
        electrocontact  sintering  allows forming  a  working layer  with a  thickness  of  0.5  ...  2.5  mm
        directly in the process. Thus, the resulting coating is no longer an integral part of the surface
        of the product, which improves its properties, but works as an independent body, taking on the
        entire load.
               Obtaining wear-resistant  composite coatings by electrocontact  sintering of  powders is                              coating                                                     substrate
                                                                      most competitive on tools, on the working
                                                                      surfaces of which it is practically impossible
                                                                      for technical reasons to solder cutting hard-              Fig. 2. Changing the values of microhardness "coating - substrate
                                                                      alloy plates using known technologies.
                                                                             These  products include complex-
                                                                      profile tools, complex-profile working bodies                     ●  development  of  contacts  between
                                                                      of various crushers and the entire series of               grains  with  a  tendency  to  form  dihedral
                                                                      disc cutting tools. However, it is necessary               angles characteristic of a given system;
                                                                      to  fulfill  a  number  of  requirements,  which                  ●  adhesion  (adhesion)  of  grains  that
                                                                      are as follows:                                            had contacts and received, in the process of
                                                                             ● ensure the hardness of the coating                regrouping during compaction, an orientation
                                                                      is at   least 82 ... 85 HRC,                               that satisfies the requirement of a dihedral
                                                                                                                                 angle.
                                                                             ●  ensure  reliable  adhesion  of  the
                                                          unit   control    powder coating to the substrate surface,                    The  formation  of  coatings  is carried

                                                                             ● The size of the applied coating must              out in several stages.  Initially, electrical
                                                                      satisfy  the  conditions  of  maximum  wear                contact local heating of the sample surface
                                                                      resistance for the given operation.                        is performed.  In  the  process  of  feeding
        Fig. 1. Schematic diagram of a coating installation with             In  our  case,  a  technology  has  been            the  powder,  the  tungsten  carbide  binder  is
        electrocontact method                                         developed  for  applying  a  wear-resistant                partially melted into the product. At this stage, an adhesive layer is partially formed, which
                                                                      composite  coating  on  an  installation                   determines further, the strength of adhesion of the coating to the surface of the part or tool.
        mounted based on a lathe, and it is shown in Fig. 1.                                                                     Peel strength at a current of 2 kA is 30 ... 112 MPa in the direction perpendicular to the coating
               Deep regulation of the power required to reach temperatures of the order of 1500-2000                             surface. Further build-up of the layer is carried out according to the "coating - coating" scheme
        °C is provided by thyristor voltage control on the primary winding of the power transformer.                             and already depends on the thermophysical properties of the coating material. Studies show
        Experimental data show that the depth of the transitional diffusion layer reaches 0.1 ... 0.15                           that even with significant currents /2...5 kA / the process of building up the coating is practically
        mm, which indicates good adhesion of the coating to the substrate. The results are shown in                              stops when the thickness reaches 2.0 ... 2.5 mm.
        Fig. 2.                                                                                                                         Powder baking is carried out in the following modes:
               The  developed  technology  refers  to  low-waste  and  resource-saving ones.  It  becomes                               ● voltage 3.0 ... 5.0 V;
        possible, without the  use  of  complex  molds, to make  hard-alloy heat-resistant  coatings on                                 ● pressure 40 ... 60 MPa;
        complex-profile tools and working bodies of crushing plants.                                                                    ● current strength 1.5 ... 2.0 kA depending on the composition of the powder;
               Using this technology, a coating was carried out on the working bodies of crushers for                                   ● layer porosity 8 ... 12 %;
        crushing  rocks  and  agricultural  products.  The  test  results  were  compared  with the  working                            ● hardness HRC 80 ... 85.
        bodies made of hardened steels of the ShKh15, 65G type. Tests show that crusher life is 10 to                                   Recommended powder materials:
        12 times longer than traditional hardened steel materials.                                                                      ● hardfacing alloys, in particular stellites (based on tungsten carbide and cobalt), renites
               Coatings  applied to  circular  cutting tools designed  for  cutting rocks,  such  as  granite,                   (based on an alloy of tungsten and carbon of eutectic composition), sormites (based on iron -
        marble and others, almost completely replace diamond tools, however, the cost of coated tools                            chromium - manganese - nickel - titanium and other metals, metal carbides and nitrides);
        is 3-4 times lower than diamond ones.                                                                                           ●  powder  mixtures,  in  particular  wokars  (mixture  of  tungsten  and  carbon  of  different
               In technologies of electrocontact sintering of tool carbide powders, compositions based on                        ratios), boride mixtures;
        tungsten carbide and cobalt are mainly used. When an electric current is applied in the sintering                               ●  crushed  powders  of  U40Kh28NS2VM  alloys  (based  on  high-alloy  steels  containing
        stage following the powder compaction, the final formation of the alloy structure occurs.

   28   Stanochniy park                                                                                                                                                                                                     Stanochniy park       29
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