The use of wavelet analysis to assess the degree of wear of working elements of food extruders

The extrusion treatment of food products is one of the most popular production processes of processing starch in the processing industry [12]. The principal process parameters of this process are the die pressure and temperature profile inside the extruder barrel. Those operational parameters have further significant influence on the extruder drive line load [10]. From the technological point of view the outlet die pressure in screw extruders is a function dependent on extrusion process parameters such as: raw material type and their moisture, screw configuration and wear of extruder working elements (screws, barrel) [3, 8]. The outlet die pressure also impacts the quality parameters of obtained products, thus maintaining the stable pressure value level during whole process time is a key factor in industrial production processes. During proper operation of extruder working elements and with constant process parameters, the pressure value change should impact the extruder drive line load change. Pressures generated inside of an extruder barrel are however result variables, which depend on the extrusion process parameters and work quality of extruder elements, among others the wear level of those elements. In single screw extruders transport properties depend on friction forces difference between friction generated by transported material and inner barrel surface from one side and friction generated by transported material and screw surface other side. Transported material will be able to move along the barrel, only when tangent friction force of the material on inner barrel surface will be greater than the tangent friction force of the material on a screw surface [14]. This is of key importance, both for extrusion process stability and the quality of final products. In case of single screw extruders to ensure the good transport conditions, the grooves milled are done on the inner surface of barrel or in longitudinal trapezoidal shape channels longitudinal wedges are mounted. Both mentioned solutions may be used to improve friction between moved material and barrel surface. In the observed extruder, constructors used the second solution to improve friction he mounted longitudinal wedges made from a hard cast steel on the inner barrel surface [Fig.1]. During working the working wedges are gradually being worn down, and along with the reduction of their height, extruder transport properties get worse. As a consequence, this leads to the worsening of the quality of the extrudated product. Adam EkiElski Tomasz ŻElAziński karol DurczAk