The rolling of metal powders in a mill with a single driving roll

Summary It is shown that the distribution of specific pressures along the arc of the rolling angle on the driving roll when the other roll is idle is the same as during the rolling with two driving rolls. The distribution of specific pressures on the idle roll differs slightly in the magnitude and character of variation of the neutral angle and in the slower increase of the rolling angle with increasing maximum specific pressure. The values of the maximum specific pressure and the total pressure of the metal on the rolls are the same in the two types of rolling.A confirmation was obtained for the claim made in [1], according to which the thickness and density of strips rolled from powders in a mill with one and two driving rolls are the same.A connection was established between the rolling angle ratio and the bending of strip in the direction of the idle or of the driving roll.     

Effect of surface oxide films on the properties of pulse electric-current sintered metal powders

Metallic powders with various thermodynamic stability oxide films (Ag, Cu, and Al powders) were sintered using a pulse electric-current sintering (PECS) process. Behavior of oxide films at powder surfaces and their effect on the sintering properties were investigated. The results showed that the sintering properties of metallic powders in the PECS process were subject to the thermodynamic stability of oxide films at particles surfaces. The oxide films at Ag powder surfaces are decomposed during sintering with the contact region between the particles being metal/metal bond. The oxide films at Cu powder surfaces are mainly broken via loading pressure at a low sintering temperature. At a high sintering temperature, they are mainly dissolved in the parent metal, and the contact regions turn into the direct metal/metal bonding. Excellent sintering properties can be received. The oxide films at Al powder surfaces are very stable, and cannot be decomposed and dissolved, but broken by plastic deformation of particles under loading pressure at experimental temperatures. The interface between particles is partially bonded via the direct metal/metal bonding making it difficult to achieve good sintered properties.     

Purification of copper powders produced by cementation from the cementing metal

Conclusions A copper powder produced by cementing copper with iron from a sulfate solution can be purified from iron by treatment with a sulfuric acid solution. Reverse dissolution of copper in this process can be reduced by employing a protective atmosphere generated by the addition of sodium carbonate to the H₂SO₄, solution. A necessary condition for the effective purification of finely divided copper from the cementing metal is deposition of copper in loose form.Translated from Poroshkovaya Metallurgiya, No. 1(289), pp. 5–7, January, 1987.     

Cleaning the basis metal of surface films in the spray-deposition of powders

Conclusions In gasothermic spray-deposition the surface of the basis material experiences self-cleaning as a result of the disintegration of surface films by frictional forces set up by the spreading layer of particles and their subsequent removal to the periphery of the contact zone. The intensity of self-cleaning of the surface of a basis material grows with increasing velocity of the particles being deposited. The self-cleaning phenomenon occurring on the basis material in the zone of collision with particles being deposited facilitates the formation of physical contact with the powder particles subsequently interacting with this zone on the surface of the basis material.Translated from Poroshkovaya Metallurgiya, No. 11(251), pp. 41–47, November, 1983.     

Characteristics of filters from loosely poured metal powders

Conclusions The stopping power of granular filters from metal powders in the purification of water and nitric acid solutions from mechanical contaminants is comparable to that of sintered P/M filters. A protective layer from a coarser spherical powder fraction located under a fine purification layer improves the latter's hydraulic characteristics and increases its debris holding capacity. The coefficient of effectiveness of regeneration of such a filter by 90-sec flow reversal is equal to 0.98 and is virtually unaffected by the number of regeneration cycles.Translated from Poroshkovaya Metallurgiya, No. 2(278), pp. 37–41, February, 1986.     

Distribution of metal torsion in a rotary piercing mill

A three-dimensional state of strain is created in a rotary piercing process. The material undergoes plastic deformation in the circumferential direction and material layers are twisted over the deformation zone. A new analytical methodology of torsion parameters calculation in the outer layers of material is presented. The distributions of torsion parameters were determined over the plastic zone as well as for the final hollow. The torsion parameters are dependent on actual geometric and kinematic conditions in the plastic zone. The theoretical analysis is based on simulation of the feed angle changes. It makes it possible to determine essential technological parameters and torsion factors. In the piercing zone the vector of torsion is oppositely directed to the turning of the hollow while in the wall reduction zone the torsion changes its sign. The influence of the feed angle on total values of torsion parameters in the piercing zone is insignificant while absolute values of these parameters generally decrease with the increase of feed angle in the final hollow. The torsion direction of the final hollow layers is consistent with the hollow turning.     

Controlling the properties of nanodimensional metal oxide powders via introduction of dispersing additions

The influence of additions of difficult-to-reduce Al₂O₃ and MgO oxides on the dispersity and morphology of nickel-based and copper-based nanodimensional compositions during their obtainment by chemical methods is considered. The conditions of directed synthesis of metal oxide nanopowders allowing for the nature and amount of the oxide phase, obtainment of precursors, and properties of their metallization are formulated. The revealed regularities create the prerequisites for the directed design of nanopowdered metal oxide materials with the specified dispersity and composition by methods of chemical dispersion.     

Forward slip in the rolling of strip from metal powders

Conclusions Analysis of metal-powder rolling coefficients has made it possible to approach the examination of velocity conditions from a new angle and obtain an analytical expression for determining the velocity of entry of powder consolidated to its tap density into the rolling-mill rolls. Forward slip in powder rolling is characterized both by the densification coefficient and the ratio h_s/D. It is shown that, in the rolling of porous strip of constant thickness, varying the density under the rolling of porous strip whose thickness and density are strongly affected by changes in rolling velocity, the latter may exert an indirect influence on forward slip. In the rolling of porous strip whose thickness and density are strongly affected by changes in rolling velocity, the latter may exert an indirect influence on forward slip.Translated from Poroshkovaya Metallurgiya, No. 4 (64), pp. 10–14, April, 1968.