CUTTING IMPROVEMENTS BY ADDING DILATANTS FLUID
Effect of addition of viscoelastic additive on the stability and precision enhancement of the abrasive waterjet is studied. Cornstarch is chosen to be added to the mixture of water and abrasive for it is readily available in large quantities at low cost. Yet it shows major nonlinear properties valuable for waterjet machining. It is shown that the normal stresses developed in the nonlinear viscoelastic cornstarch remain substantially unchanged throughout effective jet length resulting in an almost completely prismatic jet, most desirable for precision and straight machining. Furthermore, the jet becomes more stable upon increasing the cornstarch percentage. The additive also causes the jet to produce less friction with the surrounding air avoiding possible jet disintegration. Clearly, due to the increase of elastic as well as viscous effects, there is restriction to the pump delivery upon adding the dilatant cornstarch. Different percentages of the additive are therefore examined. It is found that, a 22% additive results in the best performance based on the precision, available pump power and stability of the jet. The experiment was carried out on three products; marble, aluminum and glass. In all cases, kerf angle was reduced significantly. Simulation of the problem is in good agreement with the experimental observations.
Effect of amylose content on the rheological property of rice starch
The effects of starch variety and amylose on the rheological property of rice starch during heating were investigated with mechanical spectrometry. The results indicated that the storage modulus (G)' of Kaoshiung Sen 7 (KSS7, indica) starch with sufficient concentration increased dramatically at gelatinization temperature (T G ,). T G' was close to TΦ = 1, the temperature for the starch granule to become close-packed. Nevertheless, T G' was slightly lower than TΦ = 1 in the low starch concentration system, and slightly higher in the high concentration system. The addition of amylose inhibited the swelling of the starch granule, and consequently, T G , raised slightly. With the addition of amylose, the G' of the starch gel decreased during heating, but may have reinforced the close-packed swollen granule matrix during the period of aging process at 5°C. The waxy rice starch (Taichung waxy 70, TCW70) with trace amylose content, showed much higher swelling power than that of indica rice starch (KSS7). Paste was formed even at high concentration. The rigidity of starch granular structure might be in proportion to its amylose content and in inverse proportion to the degree of granular swelling. Hence, the higher G' for KSS7 rice starch than that for TCW70 can be explained by its high inherent amylose content, which could enhance the rigidity of the starch granular structure. Also, the high G' value for the system with the high starch concentration could be attributed to the low swelling and the strong interaction among the granules. From these results, it was concluded that the major influencing factors on the rheological property of the starch during heating were the granular structure and component, followed by the amount of leached-out amylose in the process.
Palm oil shell aggregate for lightweight concrete
Publisher Summary Increased agricultural production and the development of agro-based industries in many countries of the world have brought about the production of large quantities of agricultural wastes, most of which are not adequately managed and utilized. Low-cost building materials can be produced using inexpensive indigenous raw materials. Agricultural wastes that are renewable and are found in abundance in many countries present an interesting alternative to the traditional and sometimes imported building materials, particularly for low-cost construction. The use of agricultural wastes as aggregates in lightweight concrete can provides an alternative to conventional methods for the production of lightweight concrete. Lightweight concrete results in a reduction in the overall deadweight of a structure and provides a significant saving in the overall cost of construction. The use of less expensive alternative lightweight aggregates in the production of the concrete can provide further reductions in expense. The material properties and structural performance of lightweight concrete with palm oil shells as aggregates are similar to lightweight concrete produced using the more common lightweight aggregates such as clinker, foamed slag, and expanded clay. The palm oil shells are hard and are received as crushed pieces because of the process used to release the oil. Manual sieving is necessary to remove the large amount of fine particles. The shells are then air-dried before use. Because the palm oil shells are lighter than the cement matrix, the shells tend to segregate in wet concrete mixes. On the other hand, dry mixes using palm oil shells are relatively more difficult to work with when compared to ordinary concrete. Trial mixes are necessary to achieve a good mix design.