Plastics Technology

SEP 2018

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If the value of this ratio is greater than 100, you can expect the pin will fail due to buckling. Working back- wards, I used a Slenderness Ratio value of 100 and solved for L, the maximum unsupported length of ejector pins of various diameters. Table 1 details the results for 1/32-in. through ¼-in. ejector pins. Euler developed another, much more involved formula, and I will spare you from going into too many details about it other than to say the formula allows you to calculate the amount of force a slender column, like an ejector pin, can withstand before it buckles. The formula is very useful in understanding how the unsupported length of a pin is directly related to the amount of force it can apply to eject a part before buckling. For example, Table 2 shows that a 5/64-in. ejector pin, with an unsupported length of 3 in. can push a plastic part with 99 lb of force before it buckles. A pin with that same diameter and an unsup- ported length of 1.5 in. can push a part with 394 lb of force before it buckles. While that may be four times the amount of force, you need to be careful here. This quadruple relationship only occurs when you cut the unsupported length in half. If you reduce that same pin's unsupported length by just 1/2 in., from 3 in. to 2.5 in., the force only increases by 43 lb, which is a factor of just 1.4 times. Regardless, are Minimum Force to Buckle, lb Pin Diam., in. 1/32 1/16 5/64 3/32 7/64 1/8 Unsupported Length, in. 0.50 222 1123 3548 8663 17,964 56,774 1.00 55 281 887 2166 4491 14,194 1.50 25 125 394 963 1996 6308 2.00 14 70 222 541 1123 3548 2.50 9 45 142 347 719 2271 3.00 6 31 99 241 499 1577 3 . 50 5 23 72 177 367 1159 TABLE 2 Buckling Force of Ejector Pins Spacer blocks on the back of a mold solve a minimum stack-height problem. @plastechmag 47 Plastics Technology T O O L I N G www.absolutehaitian.com In North America, our servo-hydraulic and all-electric injection molding machines continue to offer molders affordable technology. We've doubled down with new products and facilities including: • Expansion of our Worcester, MA headquarters • Construction of a new 116,000-sq-ft operations center near Charleston, SC • The new Jenius Series (506 to 3,709 U.S. tons) with electric injection unit and servo-hydraulic two-platen clamp • Upgrades to our best-selling Mars servo-hydraulic molding machines: the MA II S (67 to 3,709 U.S. tons) To our customers, thank you for your partnership. To molders looking for a machinery supplier committed to your success, call us at 508-459-5372 or 216-452-1000. COMMITTED TO OUR CUSTOMERS' SUCCESS FLEXIBILITY WITH TECHNOLOGY TO THE POINT The new hybrid Jenius Series is ideal for large precision-molded parts The Mars II S reflects Haitian's commitment to continuous improvement

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