Modelling the effect of coating on the stresses and microstructure evolution in chill casting of wind turbine main shafts

Abstract

The purpose of the present work is to quantify the effect of the inside coating on chills for casting of large wind turbine main shafts with respect to the evolution of internal stresses. These are known to affect the lifetime of the chills, and this is a major cost for the foundries today. Simulations of the casting process are performed with four different heat transfer coefficients (HTCs) between the casting and the chill, and the resulting transient stress fields are reported in the chill. The microstructural evolution in the casting in terms of the nodule count is also modelled in the simulations. The outcome is validated by comparisons with samples taken out from a critical region of main shafts cast in sand and in chills. The results reveal minor reductions in the maximum principal stresses on the inner and outer surfaces of the chill of 3.1% and 18.5%, respectively, from changing the HTC from 2000 to 500 W m À2 K À1 . These results indicate that the lifetime of the chill will not be significantly improved by adding a thicker layer of coating. The microstructure evolution is not very much affected by the HTC value with a maximum reduction in nodule count of 6.5%. Therefore, it is concluded that the material quality obtained from casting the main shafts in chills (and hence the performance of the part) is still much better than for sand casting, even though a very thick layer of coating is applied.

Impact of micro-scale residual stress on in-situ tensile testing of ductile cast iron: Digital volume correlation vs. model with fully resolved microstructure vs. periodic unit cell

“…In particular, the mechanical behavior of the graphite particles was investigated via nano-indentation in (Andriollo et al, 2018a) and the constitutive response of the matrix at various temperatures was determined by manufacturing and testing an alloy possessing equivalent metallurgical features in (Andriollo et al, 2018b). Simulation of the manufacturing process of the full-size DCI component, considering DCI as a homogeneous material, was addressed in (Sonne et al, 2017).…”

Uncovering the local inelastic interactions during manufacture of ductile cast iron: How the substructure of the graphite particles can induce residual stress concentrations in the matrix

“…Effects like visco-elasto-plastic material behavior, varying heat transfer coefficient at the casting-mold interface and latent heat release associated with phase transformations can all be accounted for. A thorough discussion of MAGMA5, its features and the specific setup used to simulate the casting of the main shaft of figure 6 (a) is outside the scope of the present paper, but can be found in (Sonne et al, 2017). Here, only the results strictly relevant to the current analysis are reported.…”

Residual Stresses around Individual Graphite Nodules in Ductile Iron: Impact on the Tensile Mechanical Properties

“…3 (a). The specific parameters used to setup the simulation can be found in [9], whereas the simulation outcome, in terms of cooling curve predicted at the abovementioned location, is reported in Fig. 3 (b).…”