PURPOSE: To quicken corrosive reaction during aging and reform poor tightness after aging by spraying melted lead or an lead alloy on the surface of a rolled sheet or on the surface of a lattice.

CONSTITUTION: A lattice 2 manufactured by expansion-processing passes through a preheating chamber 7 to be transferred to a surface treatment chamber 8. The preheating chamber 7 is provided so that good wetting may be obtained between the surface of the lattice 2 and fine liquid-drops of lead or a lead alloy atomized by an atomizer. The heating temperature of the lattice 2 for the preheating is 200∼300°C through a heating apparatus 10. In the surface treatment chamber 8, the fine liquid-drops 9 of the melted lead or lead alloy are atomized on the surface of the lattice 2. And here also, cooling speed of the liquid-drops 9 of lead or lead alloy discharged from a nozzle of the atomizer is delayed while maintaining the whole surface treatment chamber 8 at temperature 200∼300°C by means of the heating apparatus 10' for getting good wetting between the liquid- drops and the preheated lattice 2.