Torque-time behaviour

There are two aspects in the question of uniformity. The first one is a black swan , so-to-speak. If the specification is for the shape of the bird, a black one will not be noticed. This is illustrated in Figure 13.2, by two torque-time curves obtained in the usual Mooney index measurements [2]. These two rubbers give exactly the same torque at 4 minutes of the rotation, e.g., ML (1+4), and yet their behaviours are very different. If the specification is the value of ML (1+4) only, the black swan goes unnoticed. 

In addition to the torque-rise behaviour the steepness of the curve may be expressed with the torque/time ratio, which is the stress/strain ratio, i.e., modulus. Between the two gum-rubbers in question, there is a significant difference in modulus. The gum rubber giving a steeper curve is stiffer than the other one. The peak may be interpreted as the failure point [4]. The stiffer rubber has a smaller strain to break and the softer rubber is more deformable. The former tends to fall in Region I of mill processability and the latter in Region II. The former may contain macrogel in a significant amount, if it is an emulsion-polymerised diene rubber. See Chapters 4 and 6 for additional information. 

Van Buskirk et al. claimed that the flow behaviour of SBR-black compounds was a function of mixing work input. Flow behaviour was independent of mixer size, speed and mixing time as long as the temperature-time profiles were identical. From this they introduced the unit work concept. In a later paper Turetzky et al. suggested that rather than using the second peak of the torque-time curve as in the BIT test described above, it would be more appropriate to take a later point on the torque-time curve, the so-called t point. The position of this t point is illustrated in Fig. 1. 

As discussed before ( 5.2), a molten polymer shows also elastic behaviour, particularly on a short time-scale the fluid is visco-elastic. This can, in a simple experiment, be demonstrated in two ways. When we let a bar rotate around its axis in a viscoelastic fluid, then, after removal of the driving torque, it will rotate back over a certain angle. Moreover the fluid will, during rotation, creep upward along the bar, which indicates the existence of normal stresses next to shear stresses. 

The initial cost of a mixer including its impeller, gear box and motor is closely related to the torque, T, requirement rather than its power. Deduce the relationship between torque and size of the impeller for the same mixing time as a function of geometrical scale, for turbulent conditions in the vessel. Does your answer depend upon whether the fluid is Newtonian or inelastic shear-thinning in behaviour What will be the ratio of torques for a scale-up factor of 2 ... 

Several methods have been su ested for measuring the non-Newtonian rheological behaviour of surfadant and polymer films. For example, Haydon et al. [61] constructed a special apparatus to measure the two-dimensional creep and stress relaxation of adsorbed protein film at the 0/W interface. In creep experiments, a constant torque (in mN m ) was apphed and the resulting deformation (in radians) was recorded as a fimction of time. In the stress relaxation experiments, a certain deformation y was produced in the film by applying an initial stress, and the deformation was kept constant by gradually decreasing the stress. 

Repeated shear cycles on the test sample will enable one to determine whether the sample exhibits time-dependent flow behaviour such as thixotropy. If the up and down curves for the first and successive cycles coincide, the sample is undergoing steady-state shear. However, if hysteresis loops between the up and down curves are observed for each successive cycle, the sample is exhibiting time-dependent flow behaviour. In such cases, it is advisable to repeat the experiment with the speed (or torque) held constant until the torque (or speed) attains a steady value before changing the speed (or torque) to the next value. This will yield an equilibrium flow curve in which the up and down curves coincide. 

The functional safety concept that has been chosen to achieve the safety goal, named Distributed detection and mitigation of torque errors, is based on degradation whereby all faults that can lead to excessive acceleration are detected within an acceptable time interval. On detection of a fault, the vehicle acceleration is limited to a value below that specified in the safety goal. The concept is based on the assertion that only malfunctioning behaviour of the Item that can violate the safety goal (which is specified in terms of vehicle- QVQ behaviour acceleration) is the delivery of... 

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