Taking into account retrieved by many researchers (Trofimov G.A., Kiselyov V.A., Sazonov E.K. and others) positive results of experiments on application of electrohydropulse treatment for internal stresses relief in casts, the specialists of the Center carried out (jointly with PTIMA of NAS of Ukraine) the explorations aimed to specify the influence produced by electrohydropulse treatment on stabilization of geometrical sizes of casts (see the paper by Gorenko V.G., Prihod’ko V.V. The Binary Process of a Core Knockout and Stabilization of Geometrical Accuracy of Casts by the Electrohydraulic Effect. Metal and Moulding of Ukraine (1994), Issue No.3). The research results contributed into development of the binary technological process of a core knockout and stabilization of geometrical sizes of casts, and also the initial requirements to electrohydropulse equipment development are defined. In particular, it was established that:

• The influence of cast material microstructure on the process of internal stress relief by EH treatment is described by the same laws as for other kinds of pulse treatment;
• The maximum possible value of residual stresses (s ₀) in a pig-iron cast does not depend on its complexity and is defined by the value of ultimate strength of a cast material (s _B). This relation can be described by the following empirical dependence:
  s ₀/s _B =K s _B+0,064
  
  where К = 0.00168 MPa-1, however, with higher cast complexity the field of residual stresses grows more complex;
• The level of residual stresses relief by the EH method corresponds to the level reached at heat treatment and sizeably exceeds the level attained at vibration treatment (see the table below);
• Determining contribution into changed stress-deformed condition of a cast at EH treatment is made by a pressure pulse of the discharge channel;
• For a normal course of a binary process the following dependence should be observed:
  s_EHI +s₀> (0,8 - 0,85) s _T,
  
  where s _EHI - the pressure arising in a cast at electrohydropulse treatment; s ₀ - residual stresses in a cast treatable zone; s _T - material yield strength.
• -1, thus the dynamic factor of yield strength does not exceed 2;
• Due to presence of a considerable number of factors influencing the process of cast material crystallisation, the value of internal stresses in a certain point of identical casts can change in a very wide range that does not allow for predicting a field of residual stresses in a certain cast on basis of statistical data;
• Admitted initial value of reserved energy in a pulse is determined by a dependence:
  [W]=[ W₀](1- s ₀/ s _B)
  
  where s ₀ - the maximum value of residual stresses in a cast; s _B - ultimate strength of a cast material; W₀ - the admitted value of energy in a pulse at EH treatment of an unstressed cast;
• Power consumption of a binary electrohydropulse technological process of a core knockout and stabilization of geometrical sizes of casts is 10 times less than at traditional processes and does not exceed 16 kW/t.

Currently, the Science and Technology Centre "VEGA" at IPPT of NAS of Ukraine commenced the development of a range of electrohydropulse equipment for a core knockout and stabilization of geometrical sizes of casts.

Application of a binary electrohydropulse technological process and the equipment will serve to unite two finishing operations - core knockout and stabilization of geometrical sizes of casts into one, having thus refused from power-intensive operation - heat treatment and providing:

• Productivity increase by a factor of 2...3;
• Power consumption decrease by a factor of 8...10;
• Reduced occupied areas by a factor of 2...2.5.

The level of residual stresses relief by different methods

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