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Among the possible explanations of the disagreement in the model, shear forces in the contact between rock and liner is the one that is addressed in this paper.
2. Method
2.1. Wear model
The wear model presented by Archard suggests that wear is proportional to sliding distance and applied pressure. In the previous work carried out by the author it was found that wear occurs even if there is no macroscopic sliding motion between rock material and liner. This is the case in a cone crusher
where there is no macroscopic sliding motion between liner and rock. The mantle is free to roll against the bed of rock material. On at least one point, the point of moment equilibrium for the mantle, there is pure rolling between the mantle and of material. At other points the relative sliding motion is very small, since the concave is designed nearly as an ideal cone with the generatrix of the mantle intersecting the pivot point of the main shaft (see Fig. 5).
The wear model presented by Archard suggests that wear rate is proportional to sliding velocity. If a worn crusher liner is inspected, no ploughing grooves can be observed. The wear mechanism is squeezing wear without macroscopic relative motion between the bed of rock particles and the steel surface.On a small scale there is of course some relative motion since particles are rearranged as they are crushed, but the direction of this motion is random. A wear model like Archard’s that is dependent of sliding velocity would in the case of cone crushers,yield no wear. Therefore, Lindqvist and Evertsson adapted the wear model used for cone crushers.
In the model for wear prediction, described by Lindqvist and Evertsson it is proposed that the amount of wear in a single crushing action is proportional to the maximum average pressure p that occurs during the crushing event . In this constitutive equation W is the wear resistance coefficient, a material parameter unique for each combination of rock material and steel. Wear w is here expressed in mm, pressure in N/mm2 and hence the unit for the wear resistance will have the unit N/mm3.
The “average pressure” expressed in Eq.(1), consists of a large number of contact loads of different magnitude acting on the steel surface. The wear that occurs is a function of the mechanical properties of the steel, the number and magnitude of the contact loads, and the shape and mechanical properties of the rock particles. The wear resistance coefficient W is determined by the mechanical properties of the steel and rock, and is verified in experiments or in full-scale measurements.
The wear resistance parameter W in Eq.1 was found to be 94 kN/mm3 in a previous study.The material was highly abrasive quartzite in combination with austenitic manganese steel. It was shown in that study that the wear model in combination with the crusher model yielded an underprediction of wear in the upper part of the crushing chamber. The objective here is to present a model that will address this discrepancy.
If a particle squeezed between oblique surfaces, as in Fig. 6, the shear force increases as the nip angle increases. Among several mentioned and partly investigated reasons, a shear force in a contact is here assumed to change the stress state around the contact and increase the wear rate. As mentioned, it is not possible to observe any ploughing grooves on a worn liner surface. This indicates that there is no macroscopic sliding motion between the rock particles and the steel surface and that friction is not fully developed.
If a particle is squeezed between oblique surfaces, the shearforce in the contact can be computed. Consider the particle squeezed between two oblique surfaces in Fig. 7. Since the particle does not slip, the friction is not fully developed.