You should use CloudExport to export an expression in a specific format to the cloud.
e.g.
In[7]:= model = RevolutionPlot3D[
Piecewise[{
{y = 6, 0 < x <= 3},
{y = -0.5*x + 7.5, 3 < x <= 4},
{y = 5.5, 4 < x <= 5},
{y = 0.5*x + 3, 5 < x <= 6},
{y = 6, 6 < x <= 7},
{y = 0.5*x^2 - 9 x + 89/2, 7 < x <= 9},
{y = 4, 9 < x <= 10}
}],
{x, 0, 10},
Mesh -> None,
RevolutionAxis -> {1, 0, 0}];
In[26]:= obj = CloudExport[model, "STL", "stlObj.stl"]
Out[26]= CloudObject["https://www.wolframcloud.com/obj/damanjits/\
stlObj.stl"]
In[32]:= CloudImport[obj, "STL" ]
