Heavy Load Rollers in Logi : stic Systems

Whuk with polyurethane band'ages a.re in c.vmnvn us.e t2loststig vslems uith friction gear actuation. Many researeh projects haae studied the nzechanical construction of these heaay load wheek. The-studii hoot been"theoretial as well as experinicntal. Research interests at the deparhnent of ruchine elements include the wear in the presenu of intermedinte material on the contact area between the bandage surface and.the. contact sr'trface on which lhe uheel rolk off. Thts'probtem, which is obsented uhen examining th,is trihochemical system, has not been studied before. Within this project both one-phase intennidiate nraterinls such as sand,, water, cuttin'g-cooling-emukion, menl splinters and two-phase intermedinte mateials such as sand/uater and combinations of the latter were tahen into-consi.deiltion. In ad.dition, the exposure of the bandage hardness, the cro.ss kyhing agent of tlrc polyurethane, tie meclnnical stress, and the slip are obsented,. The anaQsii of the experirnental resuhs indicates. that friction gear actualors can be constnrcted abrasion-optl*ittd, rahihg into account special interfering fficts in the fonn of interntediate materiak in the contucf area.


Introduction
Rollers and wheels made of thermoplastics or elastomeric plastics are common in various technical areas.They have dis- placed rollers made of grey cast iron, steel, and light metal, especially in the field of light and middle load convevors.The advantages of polymeric materials for use as rollers are shown below: o low deadweight, o quiet running at higher material attenuation, o economically efficient manufacturing, r electrical and thermal insulation.r high breaking strain, o beneficial load transmission features, r self lubrication features, or no need for lubrication, o protection of the lane, o durability against corrosive effects, o physiological safeness.
In particular the good load transmission features, rhe quiet running and the attenuarion features, especially of polyurethane, have led to the use of this material for pon'ered wheels.In this paper, tests are shown concerning wear per- formance and its optimisation for use in transmission during friction actuations for the handling of piece goods.A method is described which experimentally obsen'es the basics for abrasion-optimised construction of powered polyurethane coated wheels, taking into special consideration the influence of intermediate materials.

Basics of heavy load rollers
In principle, a powered wheel consists of a polyurethane bandage on a hub made of material with a higher srrengrh than the bandage.This bandage is casr around the hub by a low pressure system.A hub made of metal is used for wheels which are needed for higher loads.Thermoplastics like polyamide are more widely used for basic applications than materials like steel, cast iron and aluminium.
Since fiiction and the resulting wea4 which is dependent on the presence and the type of abrasive intermediate mate- rial, has to be handled when using polymers in mechanical loaded systems, it is desirable to analyse the wear perfor- mance under the influence of these intermediate materials.
There is a basic difference between the use of plastics as a sliding friction partner of a tribological system and the use of plastics as a roller material in transmission during friction actuations.On the one hand, the sliding friction coefficient should be minimised in order to minimise losses in power resuiting from the wear, and on the orher hand the abrasion coefficient should be high in order ro realise a high posi- tive connection.Indeed, both cases exert minimisation of abrasion.
3 State of the art In the so-called visco-elastic roller contact problem, a usu- ally cylindrical body with visco-elasric behaviour rolls offon a normally even surface rvith high stiffness.This problem has been extensively examined for the tensions and strains occur- ring in the bandage, both in theory and in practice.Indeed, the abrasion is extensively unconsidered in this research.
When considering abrasion, it is common practise to draw conclusions from the rvear due to the sliding action, as de- fined in several standards.The results ofthese considerations are projected to the individual case.The disadvantages of this method are the natural inaccuracy as lvell as the complete ne- glect of the influence of slip, which resuhs from the rangential load transmission, and the eflect of an inferring intermediate material.
An example of an individual case is the air-filled wheel of a motorcal which shows substantial differences from the use of polymeric bandages in handling systems.Due to these differences, the projection ofthe test results on to this case is impossible or deficient.

Experimental setup and execution
In experiments the abrasion performance of heal"y load wheels was studied especially under influence of intermediate materials.The Fig. I shows the process parameters which were chosen.
In addition to the visible changes of the wheel bandage without magnification, the damage was microscopically ana- The transfused torques, the normal force, and the unwind velocity are adjusted to a maximum value dependent on the intermediate material for each wheel.Due to space and costs, heavy load wheels are always used at their mechanical load limit.
Using heary load wheels, abrasion occurs basically inde- pendently of the individual case and also independently of the boundary condit.ions"Thismeansthar a heary load lvheel is subject to fatigue.trig. 2 shows the abrasion in its absolute weight and dependencies on the intermediare material and bandage hardness.The intermediate material affects the slip performance and also the abrasion of a powered fricrion wheel.In addition to the chemical and physical interaction between the intermediate material and the surfaces of the examined roller and counter wheel, a basic influence of the intermediate material is the separation of the n.vo surfaces of the wheels fiom each other.So the power transmission between the surfaces changes.Especially the allocation of the transfused force to the fiiction force components (adhesion, cohesion, hysteresis, and viscosity) fbllows a different parrern.The abrasion under the influence of water is obviously higher than in the other tests.This is especially interesring because of the fact that no effect is expected with water as the intermediate mate- rial.An explanation for the high wear based upon chemical processes lies in the effects of hydrolysis.Under hydrolysis, saponification of the ester groups occurs.If the ester bond bridges are broken up, new alcohol and carboxyl groups are fbrmed.Due to the creation of these groups, the hydroly- Measured variables for determining of the load decrease in diameter and weight.In order to carry out the tests, the following boundary conditions were necessary: o Only heavy Ioad wheels with polymeric bandages and metal hubs are examined.oThe hardness grade ofthe bandages is between 70 andg2 lysed.The abrasion was determined by measuring theThe different abrasion performance over the bandage width is shown in Fig.3.In addition, the impact of rhe stress distribution on the abrasion performance is pointed out.
shown by the results of the experiments in which water and sand were used as a two-phase intermediate material.When examining the abrasion in greater detail, we can see that the tangential stress in the bandage surface is crucial to the expected level of wear, because the crack propagarion is greatly affected by the stress distribution in the surface.In the chemical corrosion of the bandage, on the other hand, the slip plays a decisive role.Since the slip is significantly affected by the process of the normal stress, it is expected that the maximum abrasion, due to chemical corrosion, occurs ar the edges.The reason for this is the occurrence of a Iower normal force under an equal elastic deformation, so that the surface at that particular location starts to slip earlier.under the consideration of maximum power trans- mission.Since the wear of the wheel bandages showed the highest values under the impact of wateq further research in this direction and the examination of potential coherences is recommended.Referencestll Bohm, F., Ihothe, K.: Hochfrequmter Rollhontaht der Fahrzeug'd.d,er.Ergebnisse aus dem gleichnamigen Sonderforschungsbereich an der TU Berlin; Deutsche Forschungsgemeinschaft, Wiley-VCH, 1998.t2lBufler, H.: Beanspruchung und SchLupf beirn Rollen el.astischer Walzzn.Forschung auf dem Gebiet des Inge- nieurwesens 27, No.4, 1961, p. 12l-126.i3lDIN 50320: Veruhleip; Btgrffr; Systemano,lyse uon Ver- is 6 Conclusion For the first time the wear of a wheel body under close- -to-reality loading cases has been examined.It is now possible to design friction gear drives taking into account to cer- materials uhlcifaorgringen; Glizderung dcs Verschleifgebietes.Deutsche Norm, Berlin: Beuth Verlag, Koln 12.1979.l4l DIN 50321: Veruhleif-Messgrdfen Deutsche Norm, Berlin: Beuth Verlag, Koln 12.1979.i E o