Pressing characteristics of tungstenless KNT16 alloy powder

Abstract

A tungstenless KNTI6 alloy powder and VK6, VKI5, and VK20 alloyt powders produced under industrial conditions were chosen for investigation. A comparison was made of the apparent densities of these powders and of the densities and strengths of compacts pressed from them under the same pressure. Apparent density was determined by the method described in [2, pp. 28-29]. The powders were compacted into cylindrical specimens of dimensions d = 12 and h = ii mm. The density of a compact was calculated as the ratio of its weight to its volume after removal from the die. The strength of a compact was assessed, as described in [2, p. 27], by its ability to withstand disintegration during tumbling in a screen barrel. As a strength indicator the ratio between the compact weights after and before tumbling, expressed in percent, was used. To study the effect of the use of a plasticizer, mechanical characteristics were determined for powder charges with and without rubber additions. The mixing of the powders with rubber was performed in accordance with processing instructions for the corresponding groups of alloys (the amount of rubber added to 1 kg of the KNTI6 alloy powder was twice that added to each of the WC-Co alloys). The relative apparent density of the KNTI6 alloy powder was found to be slightly less than that of the WC-Co alloys. This difference should be taken into account in the designing of new pressing tools: The die height and the pressing and ejection strokes should be increased by 10-15%. In spite of the difference in apparent density, the relative densities and hence coefficients of shrinkage of compacts from the KNTI6 and WC-Co alloy powders pressed under the same pressure were practically identical (Table i). Slight differences attributable to technological variations in properties among different batches of powders can easily be allowed for by varying the pressing pressure. Thus, for pressing tungsten and tungstenless alloys it is possible to use die sets calculated for the same extent of shrinkage. The strength of KNTI6 alloy compacts proved to be no different from that of WC-Co alloy compacts pressed under the same pressure. Unexpectedly, the plasticizer was found to have very little effect on the strength of KNTI6 alloy compacts: In the absence of the plasticizer the strength indicator of the tungstenless alloy was still very high, while that of WC--Co alloy compacts was close to zero. Together with determinations of pressing characteristics, an assessment was made of the technology of industrial production of parts in VKTI6 alloy from the point of view of accuracy of manufacture of cutting tips. Essentially, the assessment consisted in comparing the fields of scatter of tip dimensions with the allowance fields laid down by [3]. From each of five batches of KNTI6 alloy 12 parts were selected, and several of their parameters, including weight, were measured. The scatter of any dimension was determined as the difference between the extreme values of this dimension for the series of tips selected, referred to the