Page 45 - MetalForming March 2011
P. 45

     overheating will not necessarily cause immediate damage, after prolonged operation it will damage the seals and lead to premature spring failure.
During the design stage, process conditions that may reduce spring life can be offset by reducing percent-travel and pressure, and by adding surge- tank volume to a linked sys- tem. Manufacturers also offer special cylinder types designed for lower pressure-rise factors and higher production rates.
Further, designers should aim to distribute loads evenly among the springs so that none of the springs must work to full capacity. This allows the springs to run cooler and max- imizes their life expectancy.
Consider Gas-Spring Accessories
Additionally, think about
adding nitrogen-gas spring accessories to the die design to
assist with spring operation. Consider piping gas springs together to provide the ability to monitor, control and adjust force from outside the die. Many gas-spring manufacturers offer a wide selection of hoses, fittings, control pan- els and other equipment to simplify piping operations. Including a nitro- gen-gas surge tank to a piped system adds volume to maintain a lower pres- sure rise.
Metalformers also can install elec- tronic pressure monitors to a setup, to examine system pressure from outside the die. Transmitting pressure read- ings, they can either signal the press controller or directly shut down the press prior to production problems.
Avoid Misalignment and Contamination
Always use the top of the piston rod as the strike surface, never the bottom of the spring. By designing dies with the proper guide conditions (adding guide retainer sets, roller bearings and wear plates), and using a hardened strike
surface, the metalformer helps to ensure long spring life. Improper or inade- quate guidance within the die can lead to side loading, which occurs as a result of axial or contact misalignment. This can cause damage to the bearing, seal and piston rod, significantly decreasing spring performance. A standard rec- ommendation is to maintain less than 1 deg. of side load on the piston rod.
Contamination within a die may cause premature spring failure. Die designers should specify drainage holes within the spring pockets to prevent fluid from pooling around the springs. During production, protect gas springs from direct exposure to caustic draw- die compounds and contaminants. Where this is unavoidable, the metal- former should contact the spring man- ufacturer to discuss possible protec- tive measures for the gas springs.
There are two popular alternatives used in the field to minimize the inges- tion of fluid. One option is to add a protective cover to the gas-spring rod to prevent exposure; the second is to
Tooling Technology
   Some springs have been designed to be recharged, but not rebuilt. Check with the manufacturer prior to repair to verify repairability and to obtain the appro- priate instructions and repair kit. In some cases, standard bench tools can be used to repair gas springs. However, using the recommended load cells, removal and installation tools, and filling equipment is highly suggested.

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