Therefore, each spring needs to have 100 ÷ 4 = 25 lb of preload force. Let’s also assume the mold is of average size and that you would like to use a total of four springs. Now let’s assume you estimated that 100 lb of force is needed to keep the ejector plates firmly against the stop buttons. Looking at the manufacturer’s chart (see table), a 6-in.-long spring with a 1½-in. return pins and that’s where you would like to mount the springs, you would need springs for a 1½-in. Now round that value up to a standard length of 6 in. Therefore, the free length of your spring should be about 2 ÷ 0.35 = 5.7 in. Perhaps you want to use the blue, medium-duty springs, which have a recommended operating range of 25% to 35% compression. Assume the annual run quantities of the mold are fairly low-about 100,000 cycles per year and you decide to use the 35% recommended long-life compression value. For the sake of example, let’s say a mold has an ejector stroke of 2 in.
When selecting which die spring you need, start with determining the operating length, which is the amount the spring needs to compress.
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