Plastics Construction Materials pounds, 1 pound more than the combined weight of the plastic tank and the air load. Burst strength of the unit is 7000 pounds per square inch. The reservoir is manufactured by winding a continuous roving of fiber glass impregnated with epoxy resins onto a mold made of low melting point alloy. The aluminum alloy air inlet and outlet connections are cast into the mold. After a 2-hour cure a t 240’ F. the mold material is melted out and re-used. The future also points toward a much wider utilization of the highly chemical-resistant fluorinated hydrocarbons. Expanding processing methods must be developed, and much work is presently being done along these lines. Poly(tetrafluoroethylene), for example, has the greatest chemical resistance of all the plastics, even a t higher temperatures. With this material, service temperatures above 550’ F. are possible. The only materials which will attack this plastic are molten alkali metals or fluorine above 300’ F. No solvent will dissolve or even swell it. I n addition the impact strength of poly(tetrafluoroethy1ene) is so good that standard impact testing machines will indicate no failure a t room temperature or above. The greatest drawback in wider application of this material is the extremely high melt viscosity of the molten resin which makes difficult its utilization in many of the fabrication methods presently employed. One-piece fabrication of large vessels and structures in thermoplastics, such as polyethylene, appears quite promising as techniques in molding constantly improve. Experimental moldings of surprising size, such as the hollow polyethylene sphere shown in Figure 13, have been produced for evaluation. The spherical vessel shown is 53 inches in diameter and has a-wall
thickness of 1 inch. The weight of the entire sphere is 340 pounds. I n fabrication, two molded single piece hemispheres are welded together to produce the final sphere. I n molding, walls can be made thick enough to provide for selfsupporting vessels as compared to today’s conventional welded and lined structures. Cost savings in fabrication time should be realized, although mold costs per unit will, of course, be high on small runs. It appears entirely feasible that one-piece moldings in polyethylene as large in weight as 1000 pounds can and will be produced within the next 5 years, paving the way for further applications of plastics as materials of chemical construction for large vessels. I n conclusion, it should again be emphasized that plastics are not substitute materials of construction, nor are they materiah representing a panacea for all chemical construction difficulties. It is just as important that one acquaint himself with the limitations of plastic materials as it is that one study the advantages of these materials. An honest recognition of today’s limitations is the best foundation for research toward tomorrow. LITERATURE CITED
(1) Haim, G., and Neumann, J. A., “Manual for Plastic Welding,” Vol. 11, Industrial Book, Cleveland, Ohio, 1954. (2) Haim, G., and Zade, H. P., “Welding of Plastics,” Crosby Lockwood, London, 1947. (3) Bockhoff, F. J., and Neumann, J. A., SPE Journal, 10, No. 5, 17 (1954). RECEIVED for review September 17, 1954.
ACCEPTED April 26, 1955.
Piping, Valves, and Ducts The use of plastics as materials of construction for the production of piping, valves, and ducts has required a sound technical viewpoint in contrast to the simple production approach associated previously with the manufacture of plastic novelties. Manufacturers of plastic materials of construction can no longer depend on their suppliers for the solution of technical problems in their specific plants. Those producing pipes, valves. and ducts must recognize the advantages and disadvantages of all types of plastics and select, design, and fabricate structures in accordance with the principles adopted by the leaders in the plastics industry. In the meantime, conservative design and proper selection have made it possible to construct successful pipelines in excess of‘ 10 miles in length, valves operating at temperatures above 400° F., and exhaust systems with areas greater than 50,000 square feet handling corrosive fumes which would destroy almost all other known materials of construction. RAYMOND B. SEYMOUR Atlas Mineral Products Co., M e r t z t o w n , Pa.
S
PECIFIC thermosetting and thermoplastic materials have been used successfully for over 15 years as piping, valves, and ducts. Both type products have been used extensively for many years in Europe, but until recently American experience for these applications was limited primarily to filled or laminated thermosetting plastics. As indicated by the data in Table I, the use of plastics in corrosion-resistant applications has not paralleled the growth of plastic materials to date. However, the rate of growth of this segment of the plastics industry is now greater than that of the
July 1955
entire plastics field. The propertiea of available plastic laminates and typical thermoplastic structural materials are compared in Tables I1 and 111. Physical properties and practical values for plastic pipe are compared in Tables IV and V. The comparative chemical resistance of plastic pipe is given in Table VI. Proper attention to this type of information will aid engineers in the selection of appropriate material for any specific service. Additional information t h a t can be of assistance in the selection, design, fabrication, and installation of plastic materials of
INDUSTRIAL AND FNGINEERING CHEMISTRY
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construction is also available (69, 31, 64). However, chemical engineers do not need to become experts to determine whether or not a plastic material conforms with standards. Most suppliers comply with the statement of principles of the plastics industry (49) and hence select and design plastic structures that will be suitable under anticipated service conditions. EPOXY RESINS
Epoxy resins, which were introduced commercially in this country in 1948, are prepared by reacting epichlorohydrin with bisphenol A, the product obtained by the condensation of acetone and phenol. While epoxy resins may be modified in many different ways to form coatings and adhesives, the product of greatest interest as a material of construction is t h a t obtained by the reaction of appropriate polyamines with the epoxy resin (14).
Table I. Annual Production and Use of Plastics in Corrosion-Resistant Applications in U. S.A. Year
Production Million Lb:
Use in Corrosion-Resistant Applications (Estd.), Million Lb.
