Method for optimising the roughness of a rolling mill roll by means of high-speed thermal spraying

A method for optimising the roughness of a rolling mill roll by means of high-speed thermal spraying, more specifically thermal spraying of a powder by means of a spraying column to form an isotropic roughness (Ra) on the surface of said mill roll, wherein the mill roll rotates at a rotational speed (Vr) about the longitudinal axis thereof and the spraying column moves translationally at a translational speed (Vt), parallel to the axis of the mill roll to deposit the material according to a helical figure, wherein the following operational phases are established:

• a) establishing a granulometry (G) of powder to be sprayed,
• b) establishing an objective roughness (Ra) and an objective thickness (t) of the coating,
• c) finding the corresponding feed flow (Fr) of powder in an empirical table which shows the objective roughness (Ra) on the basis of the feed flow (Fr) and the granulometry (G) according to the formula:
• Ra
• =
• η
• ·
• (
• A
• ⁡
• (
• G
• )
• ·
• Fr
• +
• (
• G
• )
• )
• where η is the efficiency of the process that depends on the type of equipment to be used and A (G) and B (G) are functions of the granulometry of the powder (G),
• d) defining the rotational speed (Vr) and the translational speed (Vt) from an equation that relates the objective coating thickness (t) as a function of the defined feed flow (Fr), the translational speed (Vt) and the rotational speed (Vr), according to the formula:
• t
• =
• η
• ·
• Fr
• ·
• N
• Vr
• ·
• Vt
• ·
• ρ
• where N are the revolutions per minute of the mill roll and p is the density of the spraying powder, while the ratio between the width of the spray cone (d) and the pitch per turn (p) of the screw is greater than one.