ボリビニルアルコール合成纎維(化しないもの)の各温度に於ける收縮率の時間的變化を測定した。測定方法は前報と同様である。この結果と前報に於て報告した化した纎維についての結果と比較した。特に注意すベき相異點は,化したものははつきりした融點をもつに對し,化しないものは融點がはつきりしないこと,前者は融點を越しても切斷しないのに對し,後者は220°Cで全部切斷すること等である。

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A polyacetal gear of module 2 is engaged with a steel gear coated by gear oil or grease only initial stage, and different loads are applied to the set. Bending strengths and wears of polyacetal gear teeth under lubricated conditions are compared with those obtained under unlubricated conditions. Experiments are also carried out under the conditions of forced lubrication, and similar comparative studies are made on the results. Obtained test results are summarized as follows : (1) Reduction of bending strength of gear teeth caused by temperature increase is suppressed by lubricating gears. Furthermore, it is found that the extent of reduction of bending strength of gear teeth varied according to the lubrication methods applied even under the same load. The smallest is in the case of forced oil lubrication in which large amount of oil is used, followed by the case of grease coating, and the largest is in the case of oil coating. (2) Marked improvement of allowable loads, in which wears of gear teeth are taken into consideration, are recognized under the lubricated conditions compared to those obtained under unlubricated conditions.

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This report concerns the relationship between the extent of intermesh and the degree of toothsurface wear when a polyacetal spur gear is engaged with a steel gear. In the present study, a change in backlash was observed by measuring the electrostatic capacity across the sectorial electrodes mounted on the side of the tested gear. By measuring the distribution of temperature from the circumference to the center of the gear caused by frictional heat on the tooth surface, a study was made on the wear on the tooth surface with respect to the effect of thermal expansion on backlash. Results obtained are as follows : (1) Observing changes in backlash during operation, it was found that when the amount of thermal expansion is greater than the amount of wear, backlash is reduced below that immediately after the starting operation. (2) A greater load on the tooth increased the amount of wear per one revolution resulting in rapid increase in backlash. (3) It was found that the wear rate was largely influenced by the applied load and less influenced by the number of revolutions.

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The film of fibrous cellulose triacetate which was made by the vapour phase acetylation, is brittle due to its molecular symmetry and crystallinity.
In order to improve this defect, its molecular symmetry must be broken, with this object in view, the properly pretreated cellulose was mix-acylated by the vapour of acetic and propionic or butyric anhydride mixtures of various mol ratios using ZnCl₂ catalyser and the reactions were investigated kinetically.
Given reaction extents (mol fraction) of the mixed acylation as x, y, the applied rate equation becomes:
In the acetylation-propionation or acetylation-butyration, the total rate constant k is the sum of the anhydride mol-fractional means of the respective independent rate constants, but acetylation rate tends to become smaller and propionation or butyration rate larger than the mol-fractional mean. This was worked out also from the activation energies.
The films of the soluble mixed triesters, containing more than 20 mol% of propionyl group or more than 10 mol% of butyryl group are not brittle.

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In this paper, effect of the Hertzian contact stress, bending stress and pitch line velocity on the strength of polyacetal gears, cut from extruded polyacetal copolymer rod, engaged with steel or cast iron spur gears were investigated employing gear test machine with closed load cycle under load per teeth width 20-60 kgf/cm, at room temperature and in unlubricated condition. The results obtained are summarized as follow: (1) Allowable load per teeth width from bending stress (P_fa) is calculated by Lewis equation using coefficient of K_t(υ) obtained from temperature-rise during running test instead of 'f_υ'. (2) Allowable load per teeth width from wear limit (P_c) is calculated by Hertzian contact stress applied to wear equation derived from present experiment. (3) Allowable load per teeth width is given by P_fa or P_c, which has smaller value. (4) Wear greatly effects to the use limits of polyacetal gear, than strength in unlubrication running without short life running and lower pitch. line velocity. (5) The use limits is more advantageous of steel gear than cast iron gear, because the former is few wear than the latter.

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