  Insight-HXMT is the first Chinese X-ray astronomical mission. With a 1-250
keV bandpass, an energy resolution of 150 eV at 6 keV, and without being
subject to pile-up distortions, it is suitable to study bright X-ray sources
like Galactic black holes. In the present paper, we study Insight-HXMT
observations of the X-ray binaries MAXI J1535-571 and 4U 1630-472 during their
outbursts in 2017 and 2020, respectively. From the analysis of the reflection
features, we are able to infer the black hole spin parameter in the two
sources. For MAXI J1535-571, we find a spin parameter very close to 1, $a_* =
0.9916 \pm 0.0012$ (90% C.L., statistical error), which is consistent with the
previous NuSTAR measurement. For 4U 1630-472, we find a moderately high value
of the black hole spin parameter, $a_* =0.817 \pm 0.014$ (90% C.L., statistical
error), which is lower than the almost extremal value found with NuSTAR data.
