the same row each support structure comprises a fixed support adapted to be suitably mounted in a furnace or the like as generally illustrated in fig1 and having a rail 3 which protrudes obliquely upwards and to the left then curves to proceed more horizontally to the left slidingly supported on the rail 3 is a grate contact member in this instance a carriage 1 the grate 2 is draped over the supports so as to hang in a trough like catenary in the interval between each two neighboring support structures at 6 the grate 2 is pinned to each grate contact member 1 along the downstream marginal edge of the respective grate contact member 1 at a location near its upstream marginal edge each grate contact member is pivoted to the outer end of a reciprocating rod structure 4 which is movably mounted to the respective fixed support 5 in the instance depicted the fixed support 5 comprises a cylinder of a fluid pressure operated piston cylinder arrangement and the rod structure 4 comprises the piston rod of a piston not shown slidably mounted in the aforementioned cylinder control lines not shown are fitted to the cylinders so that each may be operated manually or automatically coordinately or entirely individually extend and retract the piston rods 4 in fig1 all the piston rods 4 are in a fully thrust condition this slides the carriages 1 up and leftward on the rails 3 until each carriage 1 is resting on the generally horizontal upper end portion of the respective rail note the shape of the cascade of the grate 1 in fig2 all the piston rods 4 are in a fully retracted condition this slides the carriages 1 down and rightward on the rails 3 until each carriage.