621.762A study has been made on the effects of separating materials on the expulsion pressure and porosity for iron powder pressings. A rapid method is proposed for selecting substances with low coefficients of friction. There are substances that reduce the external contact friction of the compact with the die surfaces at pressing forces of 800 MPa and more. The most promising are some standard lubricants: flour, polyvinyl alcohol, wax, and pork fat.

We have studied the reaction of M45 and SK20 glass enamels with PZhR3 iron and an iron − phosphorus alloy containing 0.8 mass% phosphorus using the "sessile" drop method in the temperature range 1000-1300°C. We have established that when the M45 glass enamel reacts with the iron, then oxides of alkali metals Mg and Na oxidize it to Fe 2 O 3 . The iron in the contact zone of the iron − SK20 glass enamel system is oxidized by zinc oxide, while the iron oxide formed dissolves in the glass enamel.Adhesion of the SK20 glass enamel to the iron surface is significantly better than in the Fe − M45 system. The best adhesion properties are observed in the iron-phosphorus alloy − SK20 glass enamel system, due to the more vigorous reaction between the components.

621.762A study has been made on the effects of separating materials on the expulsion pressure and porosity for iron powder pressings. A rapid method is proposed for selecting substances with low coefficients of friction. There are substances that reduce the external contact friction of the compact with the die surfaces at pressing forces of 800 MPa and more. The most promising are some standard lubricants: flour, polyvinyl alcohol, wax, and pork fat.Keywords: external contact friction, extrusion pressure.Powder metallurgy resembles any other direction in material science in having shortcomings whose elimination considerably governs development. One can assume with high probability that the world tendency (preparing 85-90% of components from iron powder by pressing in closed dies and subsequent sintering) will continue for a fairly long time [1]. This determines the need for improvement in the scheme used.A major long-standing deficiency is the high external contact friction, which results in uneven density and inadequate general density of pressings, which is not eliminated by sintering [2]. Elevated wear on the press tools due to external contact friction is not only an adverse economic factor, since it is no less important that it restricts the upper pressing limit, i.e., on the one hand it does not allow one to realize the strength capacity in the pressing tool and on the other it restricts the scope for researching and using of consolidation fenomenon. The latter conclusion is illustrated by the data of [3] on pressing vanadium powder in a separable mold. The rate of reduction in the density increase in the pressure range from 500 to 900 MPa alters at higher pressures (900-1000 MPa), which is quite sharp and involves subsequent slow increase in the density. That density step may be due only to change in the predominant compaction mechanism, which is not realized at ordinary forming pressures.Our purpose is to perform a model evaluation of the scope for substantial reduction in the external contact friction at pressing forces of 800 MPa and above in application to the compaction of any material.In the first model experiments, we used a nonextractable soft layer for the vertical layered location of powders, which was made as follows. In a cylindrical holder, we placed two layers of paper of thickness 0.2 mm, and after locating the outer edge with rubber glue, we obtained a tube with internal diameter 16 mm. A rigid cardboard bottom of diameter 18.8 mm was attached to one of the ends. This paper vessel was filled with 15 g of iron powder (PZhRV-200), after which the vessel was placed coaxially on the lower plunger, being completely inserted in the closed steel die with a working diameter of 19 mm. The gap between the vessel and the wall of the die was filled with powder involving tapping. Then the lower plunger was withdrawn from the die to half its height and the upper plunger was inserted. When pressing the resulting powder assembly at 800 MPa, the iron powder acted as a wedging core which pressed the test pow...