Application of Metal Dynamic Seal in Fuze Air Resistance Mechanism Song Liping (Department of Mechanical and Electronic Engineering, North China Institute of Technology, Taiyuan 030051, China) has a metal dynamic sealing structure. Conclusion Metal dynamic seals are feasible for fuze-resistance mechanisms - when the gas flows through the porous throttling elements in the porous throttling element, the viscosity of the gas impedes its flow, resulting in the ends of the porous throttling element. The pressure difference, which is the resistance of the movement of the air resistance mechanism. The speed of movement of the air-resistance mechanism can be adjusted by selecting porous throttling elements with different gas permeability coefficients, which is the working principle of the air-resistance mechanism.
The time control characteristic of the air resistance mechanism can be used in the design of the safety system of the fuze, and the final de-explosion of the fuze flameproof component is controlled, and the deferred release insurance function of the fuze is realized. This use is reflected in the US military's small-caliber fuze series M757, M758, M760 and the forced fuze M717. The time control function of the air resistance mechanism must be completely sealed with the mechanical working chamber. According to the practice of the use of air-resistance mechanism by foreign fuze products, the sealing of the working chamber of the mechanism is made of rubber material. As we all know, fuze is a very special device, which is a disposable product, and its effective storage period before use is up to 15 years. Unfortunately, at present, it is not possible to provide rubber materials with mechanical properties and anti-aging properties that can meet the requirements of fuses for more than 15 years. The gas chamber dynamic sealing becomes a bottleneck technique that hinders the use of the air resistance mechanism in the fuse.
The key to the air resistance mechanism.
1 Metal dynamic sealing principle Metal dynamic sealing has a precedent for application on cylinders and pumps. The metal sealing element is made of gray iron, low alloy cast iron, spring steel, beryllium bronze, etc., generally adopts a hollow "C-ring, split ring and other structural forms. When sealing the rotating shaft, the inward elastic opening ring is used.
There is a significant difference between the sealing of the fuse and the sealing of the general cylinder pump by the metal dynamic seal. First, the purpose of use is different. The metal dynamic seal is used in general cylinder pumps to expand the range of cylinders or pumps. The cylinder pump with metal dynamic seal can work at ambient temperature up to 200C, while the air resistance mechanism uses metal dynamic seal. In order to solve the long-storage problem of the fuze; the second is the use of different requirements, the use of metal dynamic seals in general cylinders, pumps, the friction requirements are not strict, and allow a certain leakage, and the air-resistance mechanism on the friction generated by the seal There are strict requirements with leaks. The metal dynamic sealing meter of the working chamber of the sealing air resistance mechanism is sealed with a double-opening ring as shown. 1 two open metal rings with a rectangular cross-section, using the fit between the ring and the cylinder wall, the upper ring and the groove surface of the piston, and the opening and the misalignment of the upper and lower rings to seal the cylinder Working air chamber. If the watch oil is applied between the split rings and between the double-opening ring and the cylinder wall, lubrication (reducing sliding friction) and auxiliary sealing can be used.
2 The design of the split ring can be designed as an outward elastic split ring without considering the influence of the rotation. For this kind of ring, since the split ring is radially compressed after assembly, the ring will exert a certain pressure on the cylinder wall surface, and the surface pressure p is the elastic modulus material E/GPa spring steel 210 of several commonly used materials of Table 1. The elastic modulus of several commonly used materials for bronze 105 aluminum alloy 70 is shown in Table 1.
For a set of structural dimensions suitable for use in a gas-resistance mechanism, the pressure formed by the split ring against the cylinder wall surface is shown in Table 2 when different materials and different gaps are selected.
Table 2 Several design data of the split ring Material gap G/mm bore diameter D/mm thickness t/mm width b pressure p/Pa pressure F/N spring steel é“ bronze aluminum alloy spring steel é“ bronze aluminum alloy 3 seal formed friction Influence on the kinematic performance of the mechanism Under the premise of the reliable sealing of the working chamber of the gas-resisting mechanism, the effect of the sealing on the performance of the mechanism is expressed by the friction force. The friction of the mechanism is the movement of the air-resisting mechanism. The thickness can be described by the following formula. , m; B is the gas permeability coefficient of the throttling element, m2; Z is the gas viscosity coefficient, PaSk is an empirical coefficient less than 1; - is the mechanism of half of the maximum displacement of the mechanism, m. 9. Equation / 3,) The motion consists of a linear motion and a damped oscillatory motion. As shown, d is bounded by 1 . When t > t1f .0, the damped oscillatory motion tends to zero.
The organization can enter the stable movement phase in a short period of time.
Friction also affects the size of the first peak xi of the mechanism motion, with xi decreasing as /.
According to the above analysis, the increase of the mechanism motion friction force is conducive to the reduction of the mechanism motion oscillation amplitude and the shortening of the mechanism oscillation motion time, but the mechanism friction force cannot be increased indefinitely, otherwise it will affect the reliable operation of the mechanism. The dynamic frictional force of the metal directly affects the magnitude of the decaying oscillation motion duration ti. It can be seen from equation (3) that as the frictional force /0 is large, t decreases, and the upper limit of the frictional force of the mechanism formed by the seal is 4 conclusions. Actually, the frictional force of the movement of the air-resistance mechanism formed by the metal dynamic seal is not It may be a certain value, and many factors affect the size of this value.
R into equation (1) shows that due to the machining tolerance of the split ring, the radial clearance G, the assembly diameter D of the ring, the thickness t of the ring all vary within a certain range, and the ambient temperature is also not fixed, thus, the opening is The positive pressure formed by the ring assembly is a variable distributed within a certain range. According to the formula (5) and the formula (1), the design of the split ring should satisfy the sensitivity to reduce the influence of the size parameter of the split ring on the friction force, and the open ring should be made of an aluminum alloy having a small elastic modulus E.
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