One of the most common jobs of moulding that is done in louin is that of large engine cylinders. In this work partial patterns are usually provided. These patterns ordinarily consist of the core boxes for the ports and adjacent parts. The core and the cope are built in a manner similar to that deaoribed for the simple cylinder with internal flanges. Fig. 76 illustrates, n vertical section of the mould of a steam cylinder. In this case the flanges are upon the outside of the Cylinder. Here they serve to hold the studs for bolting on the cylinder heads. In the building up of the cope, a plate a is built into the brickwork to carr what now becomes an overhang of the cope instead of an overhang of the core as in the previous example. This plate is of the form shown ill Fig. 77. A part is out away at a Fig, 77, to permit of the placing of the pattern which is to form the print for the core which forms the steam passages and ports. This plate should be; seated on the lower layer of bricks as already described for the simple cylinder. In general the use of pattern in connection with loam moulding is troublesome. The pattern must be well oiled in order to prevent the loam from sticking to it.. After the pattern is withdrawn the mould must be well washed. If all of the oil is not washed from the loam the finishing coat will not stick to it and the mould will be apt to scab. For these reasons some moulders prefer to build the loam for the core prints from drawings. Where a pattern is used, as in Fig. 76, it should reach from the point b to the point c. The overhung flanges of the steam chest at d d are made in loose pieces that are left in the mould when the main pattern is withdrawn and are themselves removed afterward. The pattern should be made so as to present a surface for the outer surface of the steam passages from e to e and from b to f. It also car-ries a core print extending back into the brickwork to the points g and A. This pattern should be accurately set when work is commenced on the cope. Measure up from the lower end of the cylinder to the center. Fix the center of the pattern at that point. Hold the pattern in position by props and stays so arranged as not to interfere with the progress of the brickwork. Oil the face of the pattern, which is to come in contact with the loam, with coal oil and build the brick work around it. Let the bricks be about an inch from the pattern and fill the intervening space with a stiff loam. At the center, opposite the location of the ports, pipes should be built into the brickwork. These pipes serve the twofold purpose of permitting the admission of bolts to hold the cores in position and of providing a means of escape for the generated gases. After the brickwork has been carried up to the parting line A B the pattern is withdrawn. Carefully wash away all of the oil that may adhere to the surface of the loam. Then apply a coat of skinning loam as directed for the simple cylinder. After this the mould is to be blackened and dried as before. The cap-plate i does not differ essentially from the one that has already been described. Above the cap-plate are placed the pouring basins and runners as before. The mould is strengthened by ramming sand about the outside as in the case of the simple cylinder.
Loam moulding is extensively used for large castings where only a few, possibly but one of a kind are to be made, and where complete patterns would be expensive. It is also a convenient method of making large complicated castings where, if they were to be moulded in green or dry sand, three, four or five-part flasks would be required. Other instances of a common use of loam moulding are to be found in screw propellers, kettles, condensers and the like.