The basic dimensions of the casting blank that is machined before casting dimensions, including the necessary machining allowance. Dimensional tolerances for the allowable amount of variation in dimension, the tolerance limit equal to the maximum size and minimum size limit of the absolute value of the algebraic difference; also equal to the algebraic deviation and lower deviation of the absolute value of the difference.
Tolerance zone should be symmetrical with respect to the basic size, which is half on the basic size, half under the basic dimensions. For special reasons, the foundry and the purchaser agreed tolerance band can be asymmetrically distributed. In this case, the tolerance should be separately listed on the rear basic dimensions.
According to the provisions of GB / T 6414-1999, the casting dimensional tolerance code of CT tolerance level is divided into 16, for general tolerance dimensions on drawings using tolerance code unified labeling, such as: "general tolerances GB / T 6414-CT12" ; not suitable for general tolerances of size, should provide individual tolerances required in the design behind the basic dimensions of individual tolerances.
Different scale of production and production methods produce castings casting molds can achieve dimensional tolerance level is different. For high-volume repetitive manner, it is possible by careful adjustment and control core position reaches more refined than table below tolerance levels; when using the sand casting method for casting small batch and single production, through the use of metal appearance and research and development equipment and casting process to achieve a small tolerance approach is often impractical and uneconomical, the table gives a wider suitable for this mode of production tolerances.
Many affected by the size of the casting parting surface and core, and thus the need to increase the size tolerances. In view of the designers did not need to understand the arrangement of mold and core used, therefore, these tolerances increase the amount has been included in the table. http://www.cnwxyszj.com |
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