Detail of GB/T 20914.5-2023

Introduction of GB/T 20914.5-2023

GB/T 20914.5-2023 Tools for pressing - Gas springs - Part 5: Safety instructions for gas springs 1 Scope This document describes the safety requirements for gas springs in accordance with ISO 11901‑1, ISO 11901‑3 and ISO 11901‑4 intended for use in press tool and their correct installation instructions. The instructions and operating conditions described in Annex A help to maximise lifetime and ensure the safe operation of nitrogen gas springs. 2 Normative references There are no normative references in this document. 3 Terms and definitions No terms and definitions are listed in this document 4 Safety protection for nitrogen gas springs 4.1 General Incorrect use of nitrogen gas springs can pose a risk to people and the machine/die. Some potential causes of damage and the mode of operation of the protection equipment used to avoid them are described in 4.2 to 4.4. 4.2 Uncontrolled return stroke safety protection It is possible that the piston rod of the nitrogen gas spring does not immediately follow the return stroke of the press: this can be caused by a jammed tool part or cam (see Figure 1). As a result, when the jammed part is released, the piston rod of the nitrogen gas spring exceeds the permitted speed during the return stroke and the piston rod slams unchecked onto the final stop (return stroke of the rod pushing out the jammed part without stamping counterforce). This can seriously damage the nitrogen gas spring or cause it to fail. To avoid this, nitrogen gas springs shall be designed to vent the gas to the atmosphere - thereby depressurizing the spring - in the event that the maximum permitted piston rod speed is exceeded. This reduces the risk of injuries caused by the ejection of gas spring parts. 4.3 Overtravel safety protection If the piston rod is pushed into the nitrogen gas spring to a depth exceeding the nominal stroke length, overtravel will occur. Overtravel may damage the spring (see Figure 2) and cause sudden separation of components (such as the spring seat). Therefore, the nitrogen gas spring should be equipped with overtravel safety protection, which can discharge gas into the atmosphere in a controllable manner in case of overtravel. 4.4 Overpressure safety protection If the internal pressure of the nitrogen gas spring exceeds the allowable limit due to fluid infiltration or incorrect inflation, the spring may disengage. Therefore, the nitrogen gas spring should be equipped with overpressure protection. When the overpressure protection system is activated, the gas is released into the atmosphere. Annex A (informative) Instructions for use A.1 General Nitrogen gas springs use should comply with the following instructions to ensure their safe operation. Moreover, compliance with the operating instructions of the nitrogen gas springs manufacturer is also required. A.2 Symbols The symbols in Table A.1 are used throughout this annex. A.3 Operating conditions Nitrogen gas springs for installation in stamping dies should be designed for ——at least two million full strokes at maximum charging pressure, and ——maximum operating temperature. Furthermore, they should be designed for all permitted mounting options listed in A.10. Ideally, nitrogen gas springs should be mounted within the die (see A.10). CAUTION - For mounting and demounting operations the gas spring rod should be fully extended and free of any outside load. Dies fitted with nitrogen gas springs should carry an appropriate warning and caution sign. Figure A.1 shows an example.

Contents of GB/T 20914.5-2023