The influence of the moisture content of raw materials on the structuring of the extrudates

The article presents the results of studies on the model systems of extrudates conducted with a view to determining the function of moisture during the process of forming the structure of starch pastes. There was studied the influence of the moisture content of raw materials on a starch gelatinization point. Studies showed that 15% moisture content in raw materials is sufficient for its constituent phase – starch gelatinization, as well as for the transition of the whole mass to a fluid-viscous state. Further increase in the moisture content is accompanied by a decrease in a gelatinization point. In order to study the influence of moisture on the formation of a porous structure of extrudates, we studied the relationship between the different-type starch pastes and the degree of its transparency and its embrittlement temperature. It has been found that during the process of thermal and mechanical impacts, there occurs the process of the formation of a structure of starch pastes, in particular, samples with the different moisture contents can have an amorphous or crystalline structure. There has been established the relationship between the moisture content of raw materials on the modulus of elasticity of starch pastes based on them. The modulus of elasticity of samples was determined one hour (cooling time to room temperature) and one week after obtaining the starch paste. The above studies showed that minimal physico-chemical and mechanical transformations occur in starch pastes, which are in an amorphous state, that is, in the conditions of a low moisture content. We have established that the moisture content of raw materials, on the one hand, ensures the transition of a high-dispersive phase to a fluid state, or implementing the ex process of extrusion, and on the other hand, influences on the formation of a porous structure in the extrudates.

Use of Nonlinear Acoustic Measurements for Estimation of Fracture Performance of Aged Asphalt Mixtures

This study evaluated the oxidative aging of asphalt mixtures by both nondestructive and fracture performance tests and investigated the possibility of estimating the low-temperature fracture properties of aged mixtures by using a nonlinear ultrasonic approach. Asphalt mixture samples, oven aged for 12, 24, 28, 32, and 36 h at 135°C, were compacted, made into test specimens, and evaluated by using a noncollinear wave-mixing approach. In addition, the embrittlement temperature and fracture energy of the replicate samples were assessed by using the acoustic emission test and the disk-shaped compact tension test. Comparison of results from the three testing methods clearly showed similar trends. This finding suggests that the fracture properties of mixtures can be estimated by using the noncollinear ultrasonic wave-mixing approach, which is a nondestructive method which does not require core extraction in the field.

Mechanism of Hot Cracking Welds of Nickel Alloy Inconel 625

Generally, nickel superalloy Inconel 625 is good weldability. However, it should be kept in mind his tendency to hot cracking during welding. Gamma matrix is strengthening by the alloying elements chromium, titanium, niobium. These elements favour the formation of carbides and intermetallic compounds that may cause embrittlement and hot cracking in a welded joint. Based on research the system Gleeble 3800 and transvarestraint test appointed criterion for susceptibility to hot cracking and high embrittlement temperature range (HTBR). Analysis of results allowed for evaluation of hot cracking structural mechanism of welded joints Inconel 625.

Effect of Texture on Secondary Work Embrittlement of IF Steels

The relationship between texture and secondary work embrittlement of interstitial-free steels was studied by X-ray analysis technique and scanning electron microscopy analysis technique. The results indicated that the stronger the γ fiber texture was, the higher the plastic strain ratio (r-value) was, and Secondary work embrittlement temperature rose as r-value increased or γ fiber texture intensified. The mode of secondary work embrittlement fracture was a blend of cleavage fracture and intergranular fracture, and the fraction of cleavage fractures decreased gradually as secondary work embrittlement temperature rose.

Critical Embrittlement Temperature for Tube Steels Used at Atomic Power Stations

During the exploitation of the atomic power stations the tubing metal is exposed to the influence of temperatures in the range of 290-320С. It can lead to thermal ageing and to the decrease of the embrittlement resistance. The critical embrittlement temperature is the main value which is needed to calculate the embrittlement resistance of materials. The metal properties degradation is taking into account by introduction of the shift of critical embrittlement temperature. The presented data ensure the prognosis of tube steels properties and shift of the critical embrittlement temperature for 60 years resource.

Improvement of Chip Breaking in Machining Low Carbon Steel by Cryogenically Precooling the Workpiece

Ductile materials such as AISI1008 low carbon steel characteristically exhibit poor chip breaking in conventional machining practices. This paper presents an environmentally clean cryogenic machining process which improves the breakability of AISI1008 chips by lowering the chip temperature to its embrittlement temperature. In this study, the brittle-ductile transition temperature of AISI1008 was experimentally determined to be between −60°C and −120°C. The discussion is focused on whether the chip can reach the embrittlement temperature before it hits an obstacle. A finite element simulation predicted the chip temperatures under various cutting conditions. Liquid nitrogen (LN2) was used to prechill the workpiece cryogenically. The results from the cutting tests indicate a significant improvement in chip breakability for different feeds and speeds by using this cooling technique. However, the effectiveness of cryogenetically prechilling the workpiece was found to be heavily dependent on cutting speed.

Magnetic Properties of Composite Amorphous Powder Cores

Composite amorphous powder core made by field-annealing with new insulations could improve the high frequency AC magnetic and mechanical properties. All of the amorphous ribbons with composition Fe78B16Si5C and Fe40Ni38Mo4B17Si were annealed at temperature higher than their embrittlement temperature but lower than the crystallization temperature. After the ribbons become brittle, they were mechanically crushed and milled to produce powders with size about 50 ∼ 250μm. To make a core, the amorphous powders combined with insulation binder were put into an evacuted toroidal followed by hot mechanical compaction. The weight percentages of binder were about 3 wt%, 5 wt% and 10 wt%. Field-annealings were carried out for different conditions in an Ar (or N2) atmosphere chamber at elevated temperature with applied field about 10 Oe. The initial magnetization curve and saturation magnetization were measured by vibrating sample magnetometer (O≤H≤10 KOe). DC and AC magnetic properties such as permeability, coercive force, core loss, etc. were tested by B-H loop tracer. It shows the AC properties can be improved by increasing the particle size of the amorphous powder and by increasing the interparticle contacts at high frequency.