Molded articles comprising at least one layer of polyurethane are produced in a batch process by mixing polyurethane-forming components to form a reactive mixture that is flowed through a channel having at least one opening through which a gas is introduced and sprayed on a substrate surface. The device suitable for carrying out this batch process includes a cylindrical mixing chamber, a flow channel through which the reactive mixture flows and is sprayed onto the surface of a substrate where it cures thereon. The flow channel is cleaned by a stream of gas.