Instruments and methods for studying behaviour

Instruments and methods for measuring the adhesion based on destruction seam adhesive by application of external force (Fig. 2.16). By way of application efforts distinguish the methods of the assumption of uniform and non-uniform) and shift.

Most often adhesiometer for food products is implemented diagram on Fig. 2.16 and. It may be different ways of application of force and registration tear efforts. For example in the instrument of Nikolaev «instantly» comes off the top disk using a lever mechanism; in the device Coleman gradually comes off the lower disk during the filling of suspended him containers with water. Splitting contacting bodies may be three options: adhesive - on a boundary of the product - a wall, the cohesive - layer product - and mixed.

External friction food depends on stickiness and a number of other factors. Friction can be static - before the start offset and dynamic - when moving the product over the surface.

For theoretical substantiation of the external friction proposed molecular-kinetic, mechanical, physical and other theories are similar theories trying to explain the adhesion. However, the available theoretical developments have not yet found an embodiment for analysis of the external friction food.

Coefficients of friction of food materials depending on the rheological properties, the condition of the friction surfaces and the sliding velocity is determined by various methods. The classical type of instrument for measuring the strength of the external friction is a pair of bodies in contact surfaces, the area of which can be from fractions of square millimeters to tens of square millimeters. However, one of the bodies is shifted relative to another. Power shift (friction) is measured strain, torque or any other sensors. For small speeds of friction is implemented straight surface displacement. I.V. Kragelskii distributed known methods of determination of the coefficient of friction on four groups, laying in the basis of geometrical and kinematic principles (figure 2.17).

Fig. 2.16. Schematic diagrams of instruments for measuring the adhesion strength:

Date: 2015-12-24; view: 814