oven roof 1 the transverse member 4 is supported by lifting mechanisms 5 and 6 which are mounted on and supported by lorry car 20 in a manner such that they are horizontally displaceable with respect to lorry car 20 expansion and contraction of lifting mechanisms 5 and 6 will allow for lowering and raising of transverse member 4 an electromagnet 7 forms a cover holder and is rotatably mounted on transverse member 4 rotary motion is imparted to electromagnet 7 in a conventional manner for example by means of a chain drive 8 shown within a housing in fig5 which is connected through worm gearing to a motor 9 which is mounted on transverse member 4 current may be supplied to electromagnet 7 by means of conventional slip ring elements incorporated into the electromagnet such slip ring elements in and of themselves form no portion of the present invention and would be readily understood by those skilled in the art and thus are not shown or further described herein the lorry car or hopper truck 20 also has associated therewith conventional coal filling connections 16 which may be moved into positions to fill coal through filling holes 2 into the oven chamber connections 16 can be lifted and lowered in a conventional manner to align with and extend into filling holes 2 such connections 16 are conventional.