An apparatus for manufacturing aluminum alloy strip for a lithographic printing plate supports includes a filter, a launder connected to the filter, a liquid level controller connected to the launder, and a melt feed nozzle connected to the liquid level controller. The liquid level controller includes a step to trap settled particles within an aluminum melt which forms the alloy strip. The launder has a length L (m) which satisfies the condition 4≧L≧V×270×1.2×D, where V is the flow velocity in meters per second of the aluminum melt in the launder and D is the depth in meters of the aluminum melt in the launder.