The possibility to simulate and predict cone crusher performance is of great interest for the development of crushers as well as for the design and optimization of crushing plants. To calculate the output from a cone crusher, models for size reduction and flow ave needed The interaction between these two models is quite complex as the overall size reduction in a cone crusher is a result of a repeated consecutive comminution process. The flow model is important since it describes how the rock material moves through the crusher chamber. Thereby the flow model provides input to the size reduction model. In turn, the sire reduction model predicts the size distribution after compressing the rock material. Previously presented flow models have only in a simplified way described the material flow. In the present paper the way an aggregate of particles moves down a crusher is described based on the equations of motion. A constitutive relation between size distribution and the uncompressed bulk density of the material is presented. Along with compatibility conditions from the crusher geometry, mass continuity is preserved. This is a very important aspect of flow modelling. Three different mechanisms are assumed to describe the material flow: sliding, free fall and squeezing. For a single particle only one of these three can be active at a time. Sliding occurs when a rock particle is in contact with the mantle and slides downwards. If the mantle accelerates away rapidly enough, the corresponding particle will fall freely. When a particle comes into contact with both mantle and concave or when the density of a material volume exceeds a critical value, squeezing will occur. During squeezing, particles will be compressed and thereby crushed. The flow model provides detailed information about how different machine parameters affect the flow of the rock material through the crusher chamber. From the model it can be explained why crushers with smaller inclination of the mantle require a larger stroke compared to the ones with steep inclination.