| 摘要 |
To improve the accuracy of making a casting pattern from a casting model or mold (2, 2') in a molding material (M) retained in a foundry form, a single pressure pulse (P) is applied to the molding material which, however, has two phases of pressure gradient, namely a first or initial phase (1) of low pressure gradient extending up to about 1 to 3 bar during between about 10-100 m/sec, for example about 50 m/sec, to initiate fluidization of the molding material. The then fluidized and still fluidized molding material is compacted by raising the pressure from the initial low pressure pulse abruptly at a second and much higher pressure gradient to the customary compaction pressure of between 3 to 6 bar. The two-phase pressure pulse can be applied, selectively, only in a region above the model or throughout the entire mold. The pressure pulse can be generated by applying the pulse but controlling a gas admission valve (11) for an initial slow valve-opening movement, for example by throttling hydraulic counterpressure (35, 36), and then permitting rapid opening movement of the valve (11) by inhibiting the throttling; or (FIG. 4) by applying the full pressure pulse from the valve and interposing a throttle (41) in the path of the air flow from a compressed air chamber (5) to the mold box (3, 4), for example by a relatively shiftable apertured plate operable above a similarly apertured counter plate for selective alignment and misalignment of the respective apertures.
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