env.workspace = "My raster folder"
rasterList = arcpy.ListRasters("*.img")
print rasterList
#works
OutDir= "My output raster folder" + raster [0:7] + ".img"
#Here is my loop that won't work
for raster in rasterList:
    OutRaster = Con(IsNull(raster), 0, raster)
outCon.save(OutDir)
#this prodices only one raster out of the 50 rasters in the List.

Con(IsNull(raster1), 0, raster1)
Con(IsNull(raster2), 0, raster2)
Con(IsNull(raster50), 0, raster50)