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A miniature vacuum hot press has been developed especially for forming research quantities of radioactive materials in a glove box or manipulator cell. The hot press can be readily disassembled and...

The advantages of using vacua in the hot pressing of refractory materials are demonstrated. A simple apparatus is described which enables powders to be pressed at temperatures up to 2500°C at gas pressures of 95% theoretical density can be prepared with an impurity oxygen content of the order of 0.01 wt.-%.

Some refinements have been introduced into the hot press canning of internally and externally cooled fuel elements. This report outlines the specifications for the process including these refinements. Specifications cover components, dies, and punches, furnace condition, nickel plating, component cleaning, component assembly, sizing, hot pressing and inspection.

The hot press process has been altered so as to eliminate the slight wrinkling near the ID base. This was done by incorporating a three minute time delay in the pressing cycle. The pressing time was decreased to five minutes to restrict formation of the brittle intermetallic compound, Ni{sub 2}Al{sub 3}.

Hot press canning of internally and externally cooled fuel elements has been developed to a point where the process is feasible. Complete specifications have been written for the process covering component, dies and punches, furnace construction, nickel plating, component cleaning, component assembly, sizing, hot pressing and inspection. Drawings covering each major item are included.

During hot pressing, we measured continuously the transition of temperature at various positions in the particle board as shown in Fig. 1, made of hammier-mill type particles (splinters) from waste lauan veneer and soya bean flour as shown in Table 1, with the alumel-cromel thermocouples (diameter 0.3 mm). The hot press cycles were varied and then the physical and the mechanical properties of the board were tested. The results of this study are as follows; 1) The temperature of the outer layer of board raise rapidly at first then slowly approach to the hot platen temperature, but the temperature of the inner layer raise gradually and reach to the maximum value, the lower to the minimum value, and raise again up to the hot platen temperature gradually. Therefore the difference of the temperature between the outer layer and the inner layer of board decrease after passing the minimum value of inner layer temperature of the board. (Fig. 3) 2) The longer the hot press cycle, the higher the value of modulus of elasticity, modulus of rupture and Brinell hardness, but the lower the impact bending absorbed energy of the particles, and the feeding quantity of heat. There is not significant relation between the specific bending strength and the hot press cycle. (Fig's. 4 and 5) 3) The water absorptivity of board is remarkably high at 27 min. hot press cycle, but its value is low at longer than 32 min. cycle and it varys a little as shown in Fig. 6. (This is owing the fact that the quantity of heat feeded is not enough at 27 min. hot press cycle to cure the adhesives in the board.) There is not singificant relationship between the hygroscopicity of board and hot press cycle as shown in Fig. 7. 4) In conclusion; the longer the hot press cycle, the more curing the adhesives, therefore the strength properties except the impact bending absorbed energy, and the water absorptivity are improved, but the more fragile the wood particle, therefore the impact bending absorbed energy decrease contrary.

After describing briefly the production of plywood by hot-gluing from undried and dried veneers, the paper narrates the progress made in the last 15 years by European plywood manufacturers. This advance, says the author, is the result of the publication of articles in the technical and trade journals, cooperative research by press and glue manufacturers, shortage of raw material, and development of new bonding processes that required greater accuracy. Resin films are credited with improvements that have been made in equipment and accuracy of working. Column-type presses have been replaced by the so-called compensated or side-plate machines which can be guaranteed not to exceed a maximum deflection under full load of 0.0015 in. Heating of presses by steam has been replaced with hot water under high pressure, and an electric heating plate that was developed in 1925 is described. New applications of plywood to the production of tennis-racket frames, barrels, structural shapes, and straight blocks or curved material having from 45 to over 70 plies are commented upon briefly. Restrictions upon importation of certain hardwoods into some countries has led to development of multilaminated substitutes, which would not have been possible, in the author’s opinion, without the progress that has been made in hot-gluing. Development of cold-setting resin glues in the last four years is also commented upon, the point being stressed that different manufacturing methods and equipment must be used before the process will offer serious competition.

With the development of thermo-setting synthetic resin adhesives, bonding operations employing hot-platen or roller have been widely practiced in various wood and paper processing, such as plywood, particle board, over-laid panel or resin treated paper production, in order to increase their production rate and improve their bonding quality. In an adhesive-curing procedure at higher temperature, minimum pressing duration under a specified temperature which assure a sufficient resin curing will be found in order to obtain a desirable bond strength. Maximum allowable pressing duration will be also found, because of thermal degradation of adherend and cured adhesive layer as summarized Figs. 8 and 9. From empirical data of synthetic thermo-setting resin, such as amino- or phenolic resin adhesive, it was found that a plot of logarithm of reciprocal of suitable minimum pressing duration against reciprocal of absolute pressing temperature gave in good straight line relation, from which bonding activation energy was calculated. It is interesting to note that the relation of suitable minimum pressing duration with the pressing temperature was able to express with an exponential or hyperbolic formula as equations (9, 11), which would be available for estimating an optimal pressing temperature making production rate greater without loss of bonding strength. However, it is difficult to obtain a general simple formula including board thickness.

A small vacuum hot-press is described which is easily operated and maintained within a Harwell MK II glove box. The press incorporates a sliding vacuum seal.