Hysteresis is defined as a lag or differential in the expected output force of a spring caused by friction. This is most evident when the output force measured during extension and compression. This measures the efficiency of a spring e.g., the lower the friction the higher the efficiency. Four points defined as P1, P2, P3 and P4 are recorded but with dynamic testing the resulting graph can be viewed in real time.IGS provides P1 to P4 graphs for specific springs as a means to predict the suitability of a particular spring design in an application.
Gas springs are high friction devices. If tested on a common weight scale, this leads some users to conclude the spring is set at an incorrect force. Users will notice a spike in the force required to first compress a gas spring compared to the rated P1 force of the spring. Sometimes referred to as “sticktion” or “breakaway friction”, this characteristic of most gas springs is the result of the “setting in” of the main seal on the rod, especially when the spring has not been cycled for a few hours. The chrome micro-cracked surface “sets in” against the seal, squeezing out lubricant. This normally results in a momentary “spike” in the force required to compress the spring. High pressure in the cylinder compresses the seal against the nitrided or chrome plated rod. “Sticktion” is minimized by using special fluids, low friction seals and varying rod finishes.
