PLASTICS — ^KLINE 237 



At the close of 1935 there were approximately 75 injection mold- 

 ing machines in use in America, mostly of i/o to 11/2 ounces per cycle 

 capacity and suitable only for the molding of small articles, such as 

 buttons, pocket combs, and costume jewelry. The demands of molders 

 for machines of increased capacity and sturdier construction to be 

 used for turning out parts for industrial applications led domestic 

 press manufacturers to construct injection molding machines with 

 radical changes in the design of the heating cylinders, spreading de- 

 vices, injection plungers, and clamping devices. By combining sev- 

 eral cylinders, each feeding into a different inlet in the same mold, 

 parts of considerable size weighing up to 36 ounces can be produced. 

 It is estimated by the Institute of Plastics Research that at the close 

 of 1940 there were in the United States 1,000 injection molding 

 presses, 11,000 compression presses, 650 preform presses, and a rapid- 

 ly growing number of plastic extruding machines. 



SUMMARY OF 1940 ADVANCES 



No really new plastics appeared on the market during 1940, but 

 outstanding progress in developing increased volume and new mar- 

 kets can be credited especially to the vinyl ester resins and cellulose 

 acetate butyrate. Vinylidene cliloride resin is commanding attention 

 in its applications as high-strength fibers and seat coverings. Nylon 

 resin is entering the industrial field as bristles for brushes used in 

 the textile-printing trade. There was further activity in the manu- 

 facture of melamine resins, which, in combination with the chemically 

 similar urea resins, are finding ready acceptance by the automotive 

 industry as a hard, durable, rapid-baking finish for car exteriors. 



Improvements in injection and compression molding presses have 

 been concerned primarily with various operating features, partic- 

 ularly heating and automatic controls. The technique of continuously 

 extruding thermoplastic materials also advanced considerably dur- 

 ing 1940, and extruded plastics are replacing reed and rattan in 

 woven furniture. A process for forming molds by spraying metal 

 against a model has been perfected to the point where production 

 molds have been made and are being tested in service. 



The aircraft industry was spotlighted during the past year, and 

 further important strides were made in the use of plastic plywood 

 for molding airplane wings and fuselages. An outstanding develop- 

 ment in this field was the laminated plastic tab for insertion in 

 aileron, elevators, and rudders to aid in balancing and controlling 

 the aircraft during flight. The reinforced plastic contributes a saving 

 in weight and greater rigidity in this part. Other military applica- 

 tions of plastics include transparent plastic windshields for airplanes, 

 luminescent resins for various devices, cellulose acetate chutes for 



