High-pressure steam curing

Autoclave sterilization is one of the most difficult common sterilization environments for a medical adhesive, and it is commonly used in hospitals and health care facilities for reusable devices. Autoclaves sterilize with high-pressure steam. Temperatures inside the sterilization chamber typically can reach 130°C with pressures above ambient. Certain adhesive systems, such as polyurethanes, may show hydrolytic degradation in such environments especially after multiple cycles. Epoxies perform the best under multiple autoclave exposures. However, on certain substrates, light-cured acrylics and cyanoacrylates will also perform fairly well. 

At the high temperatures encountered in deep wells, pozzolanic admixtures are essential to prevent strength retrogression, as in high-pressure steam curing (Section 11.7). Silica flour (finely ground quartz) and silica sand are the most commonly used. There are few data on the effects of prolonged... 

Two types of pulp sand mortar were used as the core plate of sandwich specimens. Mortar of Type M was made by mixing high-early-strength Portland cement, silica fume and pulp sand. Mortar of Type P was made directly with pulp sand. Mix proportions of each type of mortar are shown in Table 1 and Table 2. Pressurized forming was used to produce mortar plates of each type, whose pressure was lOMPa. Then specimens were put in a moist room of 20 C for about one day. After steam curing at 50 C for 24 hours, they were autoclave-cured on condition of 180 C for 3 hours. Finally they were dried out in an electric oven of 110 C for 24 hours. The geometry of the specimen was 50x10x200 (mm). 

In autoclave curing best results can be obtained with high pressure and curing temperatures, i.e., at 3 to 4 kg/cm2 pressure and 134 °C to 144 °C temperature. The usual procedure followed is to subject the rubber lined vessel to air pressure of about 2 kg/cm2 at the beginning of the cure cycle which ensures good contact between metal and rubber and then introduce steam and raise pressure and temperature to complete the cure. Typical cure cycles for ebonite and soft rubber are represented in the curves as shown in Figures 6.2a and 6.2b. 

Phenolic resins cure by a condensation reaction, evolving H2O and care must be taken to release this water (actually as steam) during the cure cycle, or use high pressures to compress the voids, as otherwise, blistering will occur. 

The above cements applied at 10-15% of the fabric weight are excellent primers for the adhesion of elastomers to fabric. The cements can be applied by any of the conventional methods, and the primed fabric can be used after solvent removal or stored in a dry place until needed. The composite product may be cured by the methods conventionally used for curing rubber (press, hot-air oven, high-pressure steam vulcanization (autoclaving), air-pressure vulcanizers). High pressures are unnecessary and the good contact between the two surfaces is sufficient to produce a strong bond. 

Hydrothermal cements are produced from finely ground lime and silicates mixed together and cured in high-pressure steam (autoclaving). The obtained material is used mostly to produce bricks. As silicates, the fly ash may be used, but its addition increases the hydration time (Venuat 1984). 

Peroxide and maleimide systems are satisfactory for high pressure steam cure, but have not been studied in other moisture cures Acid acceptors only. Accelerators and curatives are not needed... 

ACI Committee 515, High pressure steam curing, modern practice and properties of autoclaved products, J. Amen Concr. Inst 62,1965, 869-908. 

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