Thermal expansion of dental casting alloys and phosphate-bonded investments.
For a dental investment to render accurate castings, it is essential 1) that the setting expansion is low enough not to cause any distortion of the wax pattern, and 2) that the thermal expansion is high enough to compensate fully for the solid thermal contraction of the casting alloy used1-8). However, all phosphate-bonded investments known today when used according to the manufacturers' instructions, are characterized by a relatively high setting expansion, and by a thermal expansion insufficient to compensate adequately for the solid thermal contraction of conventional casting alloys. Recent studies9) have shown that the setting expansion of representative European brands of phosphate-bonded investments may be reduced to an acceptable low value by modifying the mixing liquid. It was the purpose of the present work to study the thermal expansion of thus modified products, and for comparison also the thermal expansion of several dental casting alloys.
Deformation of Crowns Cast in Thermal Expansion Inhibited Investment.
Experimentally thermal expansion inhibited investment was produced to discuss a problem, the compensation of metal casting shrinkage is to be dependent upon setting expansion. Using the various concentration of colloidal silica solution as mixing liquid, idealized full cast crowns were made, the each size were measured and the following results were obtained. On this investment: 1. As the more concentration of silica, the more expansion appeared. 2. The shrinkage in cooling is slight. 3. The expansion in ringless method is greater than that of ring method. On the deformation of crowns: 1. In the external width, both ring and ringless method in 10% and 20% showed shrinkage, the more concentration, expansive tendency appeared. The inhibition of expansion appeared in 40% by ring method. The expansion of cervical showed larger than occlusal. 2. Internal width in 10% appeared shrinkage by both methods, they showed more expansion, increasing of concentration. The internal tendency appeared that occlusal was greater than cervical. The expansion of internal showed greater than external. 3. Despite of methods the more expansion appeared, increasing concentration. The more expansion appeared in the internal height than in external. The mention above following conclusion were obtained. It was cleared that the various deformation of crowns appeared due to the setting expansion of investment alone. Accordingly it was considered that the deformation occur in the stage of setting expansion before thermal stage in the present dental casting procedure. It can be said that the setting expansion is the great factor of the deformation in cast crowns.
Preparation and performance evaluation of swine manure bio-oil modified rubber asphalt binder
Abstract In order to study the effect of the preparation process of swine manure bio-oil modified rubber asphalt binder on the rheological properties of the binder, the matrix asphalt and asphalt rubber were used as the control group, and swine manure bio-oil modified rubber asphalt binders were obtained by three preparation processes. Then the rheological properties of five binders were evaluated by rotational viscosity, DSR, MSCR and BBR tests. The results show that the addition of swine manure bio-oil to asphalt rubber is beneficial to the workability, but cause negative effect on its high temperature performance, fatigue performance and low temperature crack resistance. The preparation method of premixing bio-oil and rubber powder can reduce the degradation of high-temperature performance of asphalt rubber caused by addition of swine manure bio-oil to a certain extent. The fatigue properties of the three bio-binders are close, and the critical temperature is less than 25 °C. The process of premixing bio-oil and rubber powder will increase the creep stiffness and reduce the low-temperature performance. However, the low-temperature performance of the binder obtained by this process is still better than that of the matrix asphalt and can meet the requirements of use. Therefore, it is recommended to use the preparation process of premixing bio-oil and rubber powder to prepare swine manure bio-oil modified asphalt rubber.