Cast Resins In Research Work

Cast resins are playing an important part in widely diversified fields of research in laboratories throughout the country. Their chemical inertness, their isotropic (grairrless) nature, their imperviousness, their ability to be poured into molds and their transparency makes them especially adaptable to a great number of purposes which their makers never dreamed of. A brief sketch of a few new uses here will doubtless suggest many others to research workers with similar problems.

One of the most interesting uses of the materials is in the photoelastic analysis of stresses with plastic models and polarized light at Columbia University, New York City. It seems that certain materials, when placed under stresses, distribute these stress variations in such a way that as the pressure diminishes, a point is reached where the optical constant of the material is such that it will not pass polarized light, and a black streak shows up. As the pressure continues to decrease, farther and farther away from the point of strain, one wave-length of light after another is suppressed, leaving light streaks in between. This property of cast resins permits any type of strain to be analyzed, and the system has become of great value in determining contours of castings or structural elements of machinery, buildings, etc., in such a way as to achieve the greatest strength with the least material. Many strange results have been found, in some cases less material of a certain outline showing up -as stronger than more material in a different shape, and so on. These streaks of light and dark show exactly where the strain occurs and how that particular shape of material would distribute and dissipate it. Intricate shapes and designs to be tested can be quickly made up with cast resins, they have a high optical sensitivity and constant elastic factors, all of which combine to make them ideal for this work. In some special cases, it has been possible to pour and vulcanize the material in the laboratory for the study of intricate shapes by this method. Plate 4K is a good illustration of the "fringe pattern" showing the relative optical sensitivity of two brands of cast resin on the market under equal load conditions, the object in the center being a steel ball, against which a sheet of both materials is being pressed with equal load.

Another typical example of the use of cast resins in research and educational work is a laboratory instrument which was eventually turned into an advertising device, since it demonstrated so clearly the superiority of the brand of hydraulic packing being tested. The problem was to make two transparent cylinders 11 inches in diameter, through the walls of which the workings of various types of packings and installations could be watched in action. Glass would have required months, and been very expensive, but it was found that the cylinders could be cast in synthetic resin and delivered within two weeks. Upon delivery, they were machined with ordinary equipment by a mechanic inexperienced in this work, threads cut at the top and bottom, polished, and have been operating ever since with complete success.

Another odd use is as a bearing-material in certain types of rayon and chemical plants. A glass-carving plant, for example, had to have bearings that would stand up in the presence of hydrofluoric acid, which will eat practically anything but wax. Wooden bearings had previously been used, lasting only a few hoursócast resins were tried and their life extended to months.

The surface has been barely scratched in finding applications such as these, for the material is still new outside of its own laboratories. Its many unusual properties open up vast fields for experimentation that have heretofore been closed by the natural limitations, of one kind or another, of other types of materials.

Of particular interest to experimenters and model-makers of all kinds is another application of cast resinsóthe use of the material to make models, and also as a mold for castings made of materials which pour at atmospheric pressures and temperatures, such as plaster of paris. A striking example of the use of plastics in architectural models is shown in Plate 4L, which is a model of a new movie theatre, made entirely of plastics, in color, and illuminated from within. Such a model of course is not necessary for construction purposes, but where other factors, such as financing for instance are concerned, it should serve its purpose remarkably well. Mechanical models of new apparatus can also be made up quickly in the laboratory, in a fraction of the time and with a fraction of the equipment needed to make the same model in metal, due to the many convenient shapes the material comes in, its easy workability, and the fact that it can be easily bent, cemented and otherwise manhandled quickly into the desired shapes. Of course its effectiveness is much greater than a metal model, due to the high finish and bright colors possible.

Another purpose for which cast resin is frequently used by experimenters and others is the making of small molds for plaster-of-paris and similar materials. A complicated mold can be carved quickly and easily, and the finished cast given a glasslike surface by polishing the mold carefully. Since the mold is non-absorbent and inert, it can be used over and over again without harm, it does not "rob" the plaster of its moisture too quickly and thus weaken the cast, and the plaster will not stick to it.

Very distinctive and attractive display signs are now being made from cast resins, some of these being shown in Plate 4m. Some of these are sliced off special shapes, one shape for each letter, in the style of the loose letters at the bottom of the photo, the wing at the bottom being the base on which the letter stands in a slot, in another specially-shaped bar made for this purpose. Other types of letters shown in the other signs are jig-sawed from sheet stock, polished, and attached to sheets of contrasting color plastics, or other materials and mounted in various ways.

The Future

The future of cast resins?ólimitless. Even now they are being used experimentally for architectural and advertising purposes, which is the prelude to tremendous tonnages, so that their sensational growth from nothing to a half-million tons a year during the past seven years may seem like a trifle ten years from now, because past growth has been based on its use in comparatively small articles, whereas the tendency now is toward greater poundage. Lighting fixtures offer another important field. A large volume of small table-and decorative lamps are now made of plastics, or with plastics trimmings, but the use of large plastics sheets for indirect-lighting panels, and its use in ceiling and large and small chandeliers is growing rapidly. The warm glowing colors of cast resins seem to deal so kindly with light and to be so appropriate around a source of light that is only natural that this trend should follow. The use of plastics in furniture is another field showing rapid expansion, and its future depends only on the good taste of the designers using it. Its complete resistance to acids, alcohol, water and stains makes it an ideal surface for trays and tables, and its colors fit in with any decorative scheme. It is already being widely used for drawer-handles or various types of ornamental color-spots, and in the construction of all types of table accessories. Cast resin coated woods have recently been developed, combining the beauty, strength and low cost of wood with the brilliant finish and trouble-proof surface of cast resins. It is invading the field of fine arts, being incorporated in the better grades of jewelry and art objects, and lately is being used by sculptors to produce some striking work, different from any material heretofore used for these purposes.

The limitless size of the field being opened up for the use of cast resins beggars description. Its beauty, its color, its low cost, its easy workability and its many new and unique characteristics encourage pioneering in its use in every field. It is a material for pioneers, this "gem of modern industry".