. The Bell System technical journal . Fig. 6—Modified Brinell machine for flow-test of insulator laminations. employed for metals testing, has been modified to use a flat-endedplunger resting on a pile of insulating material. The test materialis first cut into pieces jA square and then subjected to atmosphericconditions which would cause it to take up an amount of moisturecomparable to that expected under manufacturing conditions. Thepieces are then stacked and a pressure of 2,000 pounds per square inchapplied. The testing apparatus is installed in a heat insulated box DEVELOPMENTS IN COMMUNIC
. The Bell System technical journal . Fig. 6—Modified Brinell machine for flow-test of insulator laminations. employed for metals testing, has been modified to use a flat-endedplunger resting on a pile of insulating material. The test materialis first cut into pieces jA square and then subjected to atmosphericconditions which would cause it to take up an amount of moisturecomparable to that expected under manufacturing conditions. Thepieces are then stacked and a pressure of 2,000 pounds per square inchapplied. The testing apparatus is installed in a heat insulated box DEVELOPMENTS IN COMMUNICATION MATERIALS 243. Fig. 7—Flow-test apparatus of Fig. 6 enclosed for temperature control. 7 65 5 ^^ ^AP^ ^^ ^■——-^ Z 1-OlU i:^ 3 / ^ / f PRESSURE 2000 LB PER SQUARE INCH TEMPERATURE 120° F UJ o 2 / / P HENOL . FIBRE 1 U ^ 0 f 24 48 72 TIME IN HOURS 96 120 Fig. 8—Flow-test results for hard rubber and phenol fiber. 244 BELL SYSTEM TECHNICAL JOURNAL shown in Fig. 7, so that the temperature throughout the 24 hour testmay be maintained at 120° F. corresponding to the maximum Hkely tobe experienced in service. The amount of shrinkage or flow is meas-ured on the dial previously shown. Fig. 8 shows the relative per-formance of hard rubber and phenol fiber under the conditions of thistest. Molded PlasticsIn recent years there has been great activity on the part of manu-facturers of molded plastics to develop improved molding compounds,and we have endeavored to keep informed of new developments byexamining new compounds as they became available. An interestingproblem presented itself in the applicatio
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
