Equipment Construction of accurate scale models of plants and units or groups of equipment may save time and result in an arrangement which is safer to operate bar C k h s Oraerc Brown present time there is an increasing trend to buy scale models of small and large engineering projects. This is not a new idea, but a revival of a very old custom-one which has been dormant for a period sufficiently long t o lead one t o believe that the practice had really expired with the stagecoach and Gibson Girls. The writer was wondering just what had revived it, and this led to some constructive thinking about the real usefulness of scale models. It was the custom 50 years ago to require a working model with every application for an appliance or equipment patent. Some of these models really worked, some were probably the basis for rejecting the patent, and some were neutral, as it were. The custom may have been discarded because the number of models grew to a bulk volume that threatened to crowd the bureaucrats out of Washington, and also because better descriptive geometryand progress in technical training produced such useful and faithful one-page drawings, which could be filed with the case wrapper in no space a t all, that models really served no useful purpose. Few realize that models, even though made to scale, are void of visual dimensions, whereas a wellmade drawing contains innumerable size notations. There are many other reasons why dependence on models waned, but it is not so clear why the art is currently making a rapid comeback. There are always groups of enthusiastic men who so enjoy their work and value records and historical facts so keenly that they are willing to create and pay for souvenirs by which t o remember some achievement. We must remember also that managements of large corporations spend a great deal of money on
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various diversions, without much serious thought t o the value received; it can always be charged to advertising. Such policies have inspired railroad executives to spend $38,000.00 on a model of a new locomotive about 4 feet long, with all the moving parts operated by a small electric motor. The gold plate on the base gave the name of the president whose decision put the road in ownership of twenty such engines, but otherwise it was just an interesting toy in a glass case. Our Department of Defense bought a beautiful model of a new destroyer cut through the keel to show all the inside details, and has it mounted in a glass case in the reception lobby of the War Department, where it is of great value in educating the Russians just how to put such a modern naval vessel together. The type of boilers, number of tubes. location of explosives, ammunitionhandling, and many more details are faithfully set forth for all to see. Models like these and for similar purposes will always be made. We do not believe this factor is sufficient t o account for the popularity and revival that model-making is now enjoying. Constructively, the value of models is not general or universal-it is very special. A8 applied to chemical manufacturing and chemical equipment, our readers may find these comments useful. A company manufacturing paper or chemicals from minerals or ores has a large tonnage of waste to dispose of which today must be taken care of by the company. Bark and digestor liquors must be stored in vacant lots by paper manufacturers, a calcium chloride-lime waste by soda plants, and cinders or calcined ash by gas plants and chromates producers. These operations are costly and can be much more intel-
ligently planned to reduce expenses and increase the safety of the operation if a model of the ground and the pile is' made and used to guide the work over a period of years. Chemical companies who conduct mining operations for coal, ores, and metals would be lost without a model of their operations. The model for waste disposal dumps may be considered just the corollary of the mine model. Both are usually made of glass plates held on edge, either in contact or separated t o represent two, four, five, or any suitable number of feet separating two parallel planes of actual ground. The workings and ore removal are plotted to scale and painted on the proper glass plate or intermediate plate, which is then replaced in the bundle. The total bulk or ,all the volume of the plates should represent a little more than the total or available volume of ground. The models of mining operations also plot the probable location of the ore deposit as shown by the cores of diamond drills and are the basis for fixing the mining operations, direct and overhead underground expenses, and the way to recover maximum ores from the deposit. The building of a waste disposal dump must take care of variations in operating rate. If production is to be doubled, there must be some place t o store the waste. Two alkali waste dumps have been so badly planned that a rupture of the retaining wall permitted the entire mass to flow away for several miles, causing loss of life, houses, and millions of dollars damage to other property.
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Equipment and Design Many chemists have the task of designing and building entire projects from one t o twenty buildings of equipment. Today many of these projects buy scale models. This type of scale model has a real competitor in a well made threedimensional or isometric pencil drawing at a small fraction of the cost of the scale model. These drawings are much more “alive” and informative than the best of models and often convey important impressions which are lost on the best of models. The model is difficult to carry around but may show interbuilding spaces and material-handling problems more clearly than the isometric picture. The timing on such a project seems t o be against model-making for full usefulness. In order to make a good model, rather complete engineering data must be furnished and from it some drawings. It is the custom to start the project from these drawings, not the model. A scale model is not well adapted for development work. It is much easier and faster to erase lines from a piece of paper than to modify a model. The usual practice is still t o make all mistakes as far as possible on paper. When a model has been completed showing the buildings, outside equipment, structures, and access roads, it is questionable how much real value it has over the drawings from which it is made, except t o those who cannot read and visualize a good drawing. Projects which must be sold t o bankers and financed with bonds and stocks sold publicly are often helped by models, but this is because there is ample time t o make the model, and its uses might better be classed as publicity or advertising than engineering. Using a working model of a group of equipment for carrying out a unit operation may touch upon the field of pilot plants. Models of such equipment units are often made t o show the accessibility of the equipment for operations, the working space and light quality resulting from a (Continued on page 80 A ) 78 A
certain arrangement, and the requirements for safety in operation. Sometimes it is necessary to put a group of equipment into the remaining space in an existing building. A model of the building and the equipment group is made to show not only how the equipment will look installed in the available space, but more to the point, how the equipment can be moved into the space and placed on location without wrecking the building. A great many lead towers consist of a skeleton steel frame which supports a sheet lead shell. These are often constructed in place, usually resting on the floor in a horizontal position. The lead is received in rolls. It must be unrolled, smoothed out flat, measured and marked, then cut to size and dragged into the frame or shell through one end. The frame is then moved around and a second piece of lead dragged into the inside, joining the first piece. The new lead is always on the bottom until it is fitted, all joints burned, and all supports securely in place. The next step should be merely raising the tower in one operation to a vertical position on its foundation. A 1ow:cost model of the space, the tower, and other surroundings would prove the room adequate for all these operations more clearly but not more cheaply than drawings. In another case a group of several tanks, with all piping, valves, and supports, was studied for final arrangement and height levels, with a model. These tanks were used to receive a spent liquor, a refortified liquor, a conditioning liquor, a new make-up liquor, and finally a tank was used as a mixing and feed tank from which the finished liquor was returned to process. This model was actually used as a pilot plant-a small one but very definitely a pilot plant. As an engineering model, it served no purpose, not more quickly and cheaply shown by dra.wings. Correspondence concerning this column will be forwarded promptly if addressed to the author, yo Editor, INDUSTRIAL AND ENQINEERINQ CHEMISTRY, 1155-16th St., N.W., Washington 6, D.C.
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