Fixed Dimensions — Are parallel to the mold parting line or the parting lines of major mold sections and are those dimensions that are not affected by flash thickness variation.
- Example – A Sample wheel, with half of the wheel formed in each half of the mold and the flash line located around the O.D.
- The fixed dimensions are the OD and the hub diameter
Closure Dimensions — Are vertical to the mold parting line or to the parting lines of the major mold sections and are those dimensions that are affected by flash thickness variation.
Closure dimensions will be affected by a number of factors additional to those listed above including, weight and shape of raw material stock, flow characteristics of that stock, and types of flash grooves or other relief devices in the mold. These variables will all affect the final degree of mold closure.
Although affected by variations in flash thickness, closure dimensions are not always related to basic flash thickness. In manufacturing processes that include machine or die trimming a molded rubber product, the mold itself will be designed with a thicker artificial flash than rubber parts that are designed for hand deflashing or tumbling. Thus, although the same rubber part from two different sources may meet drawing dimensions, they may also exhibit a difference in basic flash thickness at the parting line depending on the molding process and deflashing method employed.
Most molded rubber parts will have a logical place for the mold designer to locate the parting line that allows for the soundest control of dimensions.