Fracture propagation in the flexural test under confining pressure is discussed theoretically from the viewpoint of linear fracture mechanics and compared with the experimental results on Akiyoshi marbles.
Taking the effect of pre-existing cracks into account, the differences in the test results between fine grained and coarse grained marbles with respect to the bending moment-outer fiber strain diagram and the stability of fracture propagatior are explained by the stress intensity factor as a function of fracture crack length provided that the external forces are kepi constant after fracture initiation (Fig. 8 (a) and (b)).
Fracture toughness and the effective length of pre-existing crack for fine and coarse grained marbles are evaluated fronthe relationship between the confining pressure and the outer fiber bending stress at fracture initiation. This is summarizec in Table 1 which shows that the effective length of pre-existing crack is approximately 8 times grain size for fine grainec marble and approximately 3 times for coarse grained marble, and that fracture toughness increases with the confining pressure, especially when the confining pressure is greater than 120 kg/cm².
Also, it is shown that the number of fracture cracks initiated between the two loading points is determined by the relaxation zone created by the initiation of fracture crack and, therefore, the number of fracture cracks depends directly or the average length of arrested fracture crack (Figs. 9 and 10).

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Authors had discussed the experimental results of the dredging paths of buckets on the Continuous Line Bucket (C. L. B.) mining system under the limited experimental conditions, that the rope circulation speed was faster than or the same as the ship speed, in the previous report in this journal (Vol.92, No.1055, 1976). The present report is concerned with the experimental results and the empirical equations which were obtained from further experiments and considerations under the experimental conditions that the rope circulation speed was slower than the ship speed together with the previous experimental conditions. The theoretical analysis of dredging paths are also discussed in this report.
The empirical equations are expressed on the basis of the ratio of ship speed to rope circulation speed and the ratio of height to base of a right-angled triangle which is simulated from the shape of both waiting and dredging lines. The theoretical analysis of dredging paths was performed on the basis of the initial dragged-out angle of a bucket and by using the equilibrium equations for the forces of the each linear element into which the main rope line was divided at bucket attaching points to the main rope line and whose length was the same as the bucket spacing.
Furthermore, some tests were conducted in the indoor test tank in order to obtain actual dredging paths under various experimental conditions. As a result, experimental values agreed with both calculated values obtained by the empirical equations and the theoretical equations as shown in Figure 17, in which solid lines indicated actual dredging paths of buckets and symbols o and x indicated co-ordinates of buckets obtained by the respective equations.

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In Yubari-Shin Colliery, main roadways are driven in the thick Horokabetsu shale below the workable coal seams at the depth of about 1000m from the surface. The roadways converge seriously, particulary due to floor heave, because rock strength is weak against rock pressure, and many maintenance works are carried out for the roadways.
For the purpose of relief of roadway maintenance works, a rock bolting test by Rock Bolt Setter was carried out in addition to the steel arch support (weight 34.7 kg/m) in the present operation. Rock Bolt Setter used in this test is equipped with 1 power unit, 1 boom, 1 universal roofbolting turret, 1 hydraulic rotary drill and 1 hydraulic rotary bolting motor mounted on a chassis of 642 H loader.
The test results were as follows: 1. The capacity of bolting by Rock Bolt Setter was 45 bolts/shift (average) in a 15° inclined roadway, 50 bolts/shift (average) and 65 bolts/shift (maximum) in a level roadway.
2. By system rock bolting, convergence of roadways was improved to about half compared with the steel arch support only.

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The separation of galena from sphalerite is one of the most important steps in the flotation of complex sulphide ores. Depressants widely used in the separation of galena from sphalerite are cyanides or sulphites. Although cyanides are known as an effective depressant, the use of cyanides remains pollution control problem to the disposal of waste water. It is desired to exploit a novel flotation method for the separation of galena from sphalerite without cyanides. This study was done as a part of fundamental studies on the flotation process of complex sulphide ores.
In this paper, the applicability of a sulphatization-flotation process for the separation of artificial Pb/Zn ores was discussed. This method consists of a sulphatization of a Pb/Zn bulk concentrate, followed by the depression of galena during sphalerite flotation.
As the first step, the optimum conditions for sulphatization of galena and sphalerite were studied independently from the flotation aspects. On the basis of the optimum conditions of sulphatization-flotation obtained, a series of the differential flotation tests were done using an artificial Pb/Zn mixture. It is evident that the separation of Pb/Zn ores is effectively achievable by a sulphatization-flotation method.

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A new method of obtaining metals from their oxides by use of the D. C. arc plasma jet was examined. Decomposed gaseous substance was injected into a molten bath of the constituent metal of each oxide through the plasma flame. More than 90 pct. of NiO could be decomposed and recovered as metallic nickel by this method with Ar plasma. Aluminum could not be obtained, however, because of the stable oxide films formed on the surface of the bath. TiO₂ was reduced merely to its suboxides due to the great affinity of titanium to oxygen. The results indicate that the possibility of the reduction is affected by the affinity of each metal to oxygen at the surface temperature of the metal bath.

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Operational results of blast furnaces have increasingly improved in conjunction with improvement of iron ore agglomerates such as sinter and pellets, and blast furnace operation technique.
And in order to maintain the quality of sinter and pellets, many properties, such as chemical compositions, size distribution, crushing strength, reducibility, high temp. reduction, softening and melting down temp., etc, are examined. However, it is not clear that which properties are regarded as significant for the blast furnace operation. Therefore, it is necessary to make clear the significant properties of the iron ore agglomerates.
For the purpose of the stable operation of the furnace and improvement of fuel rate, the authors proposed one method to regulate the heat balance in the blast furnace by three factors, i.e. oxygen volume in blast, ore to coke ratio, and JIS reduction rate of burden. It was proved from the examinations of operational results of many blast furnaces that the well stabilization of heat balance in the furnace was obtained in the range from 150° to 210° of the angle θ, which is made by plotting the data of the three factors on the diagram. It is possible to control the angle θ by adjusting both the mean JIS reduction rate of burden materials and ore to coke ratio as burden conditions.
Judging from these analyses, it is evident that the angle θ can be employed as an index which reflects the heat balance in a furnace and that the most important quality of burden for a blast furnace is the JIS reduction rate. However, high reducibility does not always mean a better results but it should be determined in relation with the heat balance.

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