"Rule of Thumb" vs. Engineered Lock Selection
A guide that applies engineering principles is designed to help engineers select properly sized alignment components.
Traditionally, designers have relied on a general “feel” or “rule of thumb” to decide which alignment locks to insert within a mold, considering sizes and mounting preference. That’s adequate, right? Maybe not. Selecting an alignment lock based only on gut feel could result in an undersized selection and, down the line, can result in costly mold damage and downtime as well.
The following guidelines for alignment lock selection can help designers make an objective decision. Figure 1 was developed to enable them to match a mold’s size and weight with appropriate alignment lock sizes. By adhering to these guidelines, proper alignment selection and alignment component maintenance should directly result in the elimination of unscheduled mold stoppages due to worn and damaged shut-offs.
Consider what is being lifted. First and foremost, it is important to look at what the moving mold half is being bolted to before looking at the lock and mold base. The moveable platen sizes and weights shown in the table were arrived at in consultation with press manufacturers and after review of molding machine specs. Clearances between the tie bar and bushings were used to calculate how much sag can be expected on a brand new press.
Typically, a mold designer looks at the tie bar location to verify that the mold will fit in the press and that there’s no interference with cylinders or other components, but he or she is not calculating the amount of locking surface required to lift the mounting mold half and engage the platens.