This invention relates to apparatus for forming a portion of a sand core, and more particularly to such an apparatus which utilizes an inflatable and expandable bladder in association with a mold body to form and press sand into the desired shape.
U.S. Pat. No. 3,606,921 to Grawey discloses the use of a sand core on which the invention of that patent, i.e., a tube-tire, is formed. In that patent, the sand core, after the formation of such tube-tire, is disintegrated and removed from within the tube-tire.
The problem of the formation of the sand core itself is a serious one, since, because of the extremely great size of such tube-tire to be formed, the core, by necessity, must be extremely large in overall dimension. Such a large core will, of course, be relatively heavy and unwieldy, so that any saving in weight thereof will aid in the ability to handle such core conveniently. Naturally, even though the weight may be reduced, there can be no sacrifice in overall strength in the core for the purpose for which it is designed. For these reasons, a hollow core would be quite advantageous in this use, and the apparatus should be designed to so form such a core.
Furthermore, the apparatus itself should be relatively simple and convenient for such use.
In addition, in the production of the type of tube-tire disclosed in the above-mentioned patent, the formation of the outer core surface is quite critical, since it is on this outer surface the tube-tire will be formed. Meanwhile, the formation of the inner surface of the hollow core, and the shaping thereof, is not critical. Furthermore, as the core material cross-section is reduced in producing a hollow core it becomes increasingly important that the core be of uniform overall strength. Therefore, the apparatus should be capable of exerting uniform compressive force upon the total surface area of the core material regardless of whether such material is evenly distributed within the mold.