Nowadays the logistic jobs or material handling industry need heavier and more powerful floor conveyor systems and industrial
trucks with high-performance wheels that can tolerate a higher dynamic load under extensive weight increase and long run.
Compared to wheels of solid metal wheels with an elastic solid bonded tyre of synthetic material have the benefit that they wear
little that they affect the opposite face little that they are low noise that they absorb the impacts by an intern attenuation that their
friction tests are good, and that they are low-cost. Due to their better mechanic features compared to rubber products massive
polyeruthane has become accepted as the material for the massive tyre of heavy load wheels in many logistic systems.
Standstill period in logistic systems due to unexpected malfunction of those wheels can cause great economic damage. To
guarantee the most potential availability of those systems different damage processes of heavy load wheels and their use must
be analysed so that the conditions can be improved. In the following the mechanisms are recorded which can lead to a failure of the heavy load wheel.
1. Thermal failure
Especially for rapid running wheels of polyurethane the temperature of the wheel body affects the acceptable mechanic load.
High dynamic loads caused by high deformation and speed lead to a heat build-up in the middle of the tyre as a result of
material damping of the visco-elastic elastomer face. Since plastics are bad heat conductors the heat cannot dissipate quickly
enough due to the thermic insulation of the polyurethane. As a result a heat accumulation appears in the roll-tread. The material
melts inside of the wheel and liquid leaks out of the flanks.
 |
 |
2. Mechanical Wear
Currently finished examinations have shown new conclusions about the abrasive behaviour under real use conditions.
Especially the abrasion under action of intermediate material in the contact area between the tread and the contact surface, on
which the wheel rolls off, is analysed in the project about abrasion behaviour of powered synthetic coated wheels for the friction
gear actuation piece goods handling which is sponsored by the “Bundesvereinigung Logistik” (BVL). It is now possible to have
access to findings on the impact of boundary conditions for the choice of material and the dimensioning of drive wheels. As to
the intermediate material an abrasive effect appeared at the material which affects especially the crack dispersion. On the other
hand it showed a chemical effect to the polymer material of the heavy load wheel in particularly at liquid materials. For the
analysis of these impacts a testing system is developed. This helps to experiment the abrasive behaviour of heavy load wheels
with polymer tread under the influence of intermediate materials with a highly realistic copy of the loading collective. The
abrasive behaviour was acquired by the loss in weight of the samples within the testing period of 24 hours under rated load.
Additionally the surface damage of the wheel is viewed and assessed both macroscopically and microscopically. For feeding the
intermediate material into the contact area compressed air is used both for liquid and solid materials. The contact area is
perpendicularly arranged in order to obtain a certain self cleaning mechanism. The supply of the intermediate material is
adjusted in such a way that in each case one kg solid and one litre of liquid is fed into the contact zone per hour. A permanent
presence of intermediate material between test wheel and counter wheel is ensured during the tests.
3. Tread delamination
The damage mechanisms like thermal overload, or abrasion which lead to the breakdown of the wheels, have been analysed in
many research projects. However the failure of the joint area has not been tested yet. Due to the various expansion behaviour of
elastomer and body in the joint area between both components there is a stiffness difference. This unsteadiness in the
elongation run leads to higher tensions which especially occur on the edges and on the smaller thicknesses of the massive
polyurthane tyre. Consequently the partial groove is a weak point which often causes the material bond to fail. Apart from the
external load the thickness and the hardness of the tread are basic influencing variables on the tension in the partial groove.
The harder and thinner they are, the higher the tensions are. A cohesion fracture in the range of elastomer is called an R-defect
(rubber). If the bond of elastomer and adhesive cement gets separated, it is an RC-defect (rubber-cement). It is a CP-defect, if
the adhesive cement and the primer break. An M-defect means that the adhesive cement solves from the metal
 |
 |
