However, in a_ high-output diesel engine, conventional VMQ seal caused coolant leakages in engine tests. Thus the improved VMQ coolant seal has been developed. high brittle point (-20 8C). The HNBR also has not enough low temperature property (TR 10% : -25 8C) for a cold district. Since the EPDM is not resistant to mineral oils, the EPDM coolant seal may cause a swelling problem by leaked oil from adjacent oil seals. Thus VMQs have the best durability over a wide range of temperature (TR 10% : -48 8C) and have been adopted to the coolant seals. Bot oil sea equal he cy o those of the p inder-head and h compression ratio of the coolant seals and the s were in the same range, from 20 to 35 %, as hose of previous engin he seal temperature of es. The seal compression and his high-output engine are also revious engines. However, the displacement, caused by engine combustion, between he steel plate head-gasket is airly large comparing with that of the previous engines. Thus, we have investigated the mechanical factors of he seal crack small quantity of silica filler, show high tensile strength and high elongation. The low silica VMQs Fig. 3 - Effect of contact surface on rubber compression stress(H. Kaneko) 3) Fig. 4 - Relationship between silica filler content and VMQ properties In a trial generator engine for an emergency use, the previous VMQ-P cracked after only in 18 operating hours (Fig. 9). This engine had been used for two years without a coolant change. White precipitation was deposited on the seal surface and the coolant smelt strongly of mold. From a thermogravimetric analysis (TGA), it was found that the VMQ-P polymer was decomposed to lower molecular weight materials (Table 1). In the cracked seal, the polymer fraction of lower decomposition temperature (880 - 440 8C) increases and the polymer fraction of 440 - 530 8C decreases. The white precipitation contained salts of strong Fig. 7 - S-N Diagram of VMQ coolant seals t, : Seal thickness. t, : Gasket thickness Table 3 indicates the organic acids immersion test results. Since the improved VMQ-O is adopted a water resistant silicone polymer, the elongation change is smaller than that of the previous VMQ-P. Furthermore, the endurance seal tests on the immersed both VMQ seals in a 10% acetic acid were conducted using the head-gasket seal tester. The results are shown in Fig. 11 - 12. The fatigue life of the previous VMQ-P was drastically dropped to 1/50 by 10 % acetic acid. The failure of the Fig. 10. lon chromatography analysis of white precipitation not generate the bubble. By a pressure-sensitive paper (Fuji Paper), the changes of seal pressure distribution changes were measured at several compression ratios. The previous VMQ-P caused the unequal contact above 28% compression ratio (Fig. 17), but the contact of the improved VMQ-O is quite uniform up to 50% (Table 4). These in homogeneous contact of the previous VMQ-P can cause the coolant leakage. Both the improved VMQ-O and the VMQ/EPDM-R, contained only fine silica, show the uniform contact. The previous VMQ-P and commercial VMQ-A, contained coarse diatomite (Fig. 18), show unequal contact. These facts indicate that the unequal contact originates from the diatomite. SUMMARY Table 4 — Upper limit of compression ratio for uniform contact Fig. 16 - Visual observation of VMQs seal contact APPENDIX II VMQs compatibility with various coolants REFERENCES APPENDIX I Environmental stress cracking test results a eee FF LE ol! oT of Me ore re ene Ae oe og fo Yon 7 2 | ee Test conditions : 50% compression, 1508C X 7Ohrs Dipping in distillate water with 2% SCA
