Effect of Temperature and Humidity of Glueroom on Open Assembly Time

Factors affecting the maximum permissible open assembly time in gluing large structural members that can be controlled are the time taken to: 1) spread the glue, 2) lay up the assembly, and 3) apply pressure to the assembly by mechanical means. Factors which change from day to day (if uncontrolled) include glue room temperature and relative humidity. This study was made to determine the effect of these two factors on open assembly time. Selected Douglas-fir laminating stock which had been kiln-dried and planed, straight-grained and defect free, was glued up into standard shear blocks using casein and resorcinol. To make comparison, the temperature levels of 70? and 90?F, and relative humidities of 35 and 75 percent were used. The results showed that for temperatures below 90?F, resorcinol is less sensitive to atmospheric conditions than casein because it sets due to the combination of solvent, loss and polymerization. At the same temperature, high relative humidities permit longer assembly times than low relative humidities–75 percent compared to 35 percent. Lowering the temperature and increasing the relative humidity simultaneously results in a substantial increase in maximum allowable open assembly time. An indication of how much the maximum permissible open assembly time could be increased by controlling glue room temperature and relative humidity can be gained by drawing a limit of acceptability of 900 psi shear failing load. For casein, the effective time is increased from 15 minutes at the high drying condition to 45 minutes at the low drying condition.

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