A surface-treatment wheel comprising:
an inner element rotatable about an axis; and
an outer ring fixed rotationally on the inner element, centered on the axis, and formed unitarily with
an annular array of radially outwardly projecting teeth defining outwardly open notches, and
respective angularly extending ridges in the notches.
2. The surface-treatment wheel defined in claim 1 wherein the teeth are substantially identical and have a predetermined radial height and a predetermined axial thickness, the ridges all being substantially identical and having a predetermined radial height shorter than that of the teeth and a predetermined axial thickness shorter than that of the teeth.
3. The surface-treatment wheel defined in claim 2 wherein the ridges are axially centered in the respective notches.
4. The surface-treatment wheel defined in claim 2 wherein the ridge height is equal to about two-thirds of the tooth height.
5. The surface-treatment wheel defined in claim 4 wherein the tooth height is equal to between 7 mm and 9 mm.
6. The surface-treatment wheel defined in claim 2 wherein the tooth thickness is equal to between one-fifth and two-fifths of the tooth thickness.
7. The surface-treatment wheel defined in claim 2 wherein the teeth have angularly directed flat flanks defining the notches and the ridges are unitarily joined to the respective teeth at the faces thereof.