ORNAMENTAL IRONWORK.

INTRODUCTION.

1. Iron is used in building construction to serve two purposes, one structural and the other ornamental; but becomes an element of architectural consideration only when both purposes are combined. Unfortunately, the facility with which iron may be cast or wrought into any desired form, renders the execution of the whole facade of a building as simple as though it were constructed of wood, and imbues the ironwork designer with a tendency to ignore the characteristics of the material with which he is working, and to execute columns, capitals, and friezes in cast iron, with fidelity to original examples which were carved in stone, and whose designs are ill suited to iron.

However, the incombustible character of this material, and the fact that its use materially shortens the time and decreases the expense of erecting a building, render it certain that iron as a building material is as important at the dawn of the twentieth century, as was stone before the Christian era; and instead of condemning it as an "unarchitectural material," as some are inclined to do, it is our duty to study its character and possibilities in design, and to develop a system. or scheme of design which will be consistent with the conditions imposed by the material and its structural use.

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To do this it will be necessary for the student to understand the method of manufacture, and difficulties attendant upon the execution of any design in ironwork, so that in preparing a design he may keep it free from impossible demands. For instance, if the design is for a piece of cast-iron work, the designer must provide a means of molding the form properly, and of getting the fluid metal into the mold without injuring any of the finer details. If the design is for a piece of wrought-iron work, such as a grille or a railing, provision must be made for enough space to permit riveting, hand welding, etc.

Thus it will be seen that a careful consideration of the methods used in general shop practice, will be the best way for the ironwork designer to advance in the comprehension of his work. This section will, therefore, treat of the details of shop and field work in connection with the manufacture of iron for architectural purposes; and, therefore, the illustrations of working drawings used herein to elucidate the text are reproductions of drawings which have actually been used in the preparation of ironwork for some of the most important buildings.

The first part of the paper will consider cast-iron work, while the manufacture of wrought iron and the combination of cast and wrought iron will follow consecutively.

CAST-IRON WORK.

METHOD OF MANUFACTURE.

DEFINITIONS OF TERMS.

2. Cast iron is the term given to that quality of iron which exists when the melted metal is poured into a suitable receptacle, or mold, and allowed to cool and solidify. Cast iron is hard, brittle, and somewhat crystalline in its composition-that is, it shows on its fractured surfaces an appearance resembling an aggregation of small crystals,

instead of a fibrous fracture like wrought iron. It is used, architecturally, for columns and newel posts, and, under certain conditions, for lintels or beams; but, owing to its lack of elasticity, it is not well adapted to conditions of transverse strain. It is also formed into slabs for the purpose of stair treads, pavements, etc., and some forms of ornament are cast and attached to purely structural details.

3. Molds are the receptacles into which the molten metal is poured to give it some definite form consistent with the purpose the cast iron is to serve in the building. The molds are made by impressing in sand a cavity or a number of cavities which correspond, in shape and relation of parts, with the contour of the object to be cast. The process of so impressing the sand is called molding, and is effected by means of a wood or plaster model of the object, called a pattern, which is so embedded in the sand that it will leave its impress when withdrawn.

4. Patterns are generally made of wood, though sometimes of plaster, and occasionally partly of each. Where there are to be a great many castings of one kind, the pattern is sometimes made of bronze or iron, in order to stand the wear, but even in such cases the bronze or iron pattern would be cast in a mold originally impressed with a wood or plaster model. Whether a pattern shall be of wood or plaster depends entirely on the character of the work. Plain straight work, such as molded panels, stair strings, columns, etc., is generally made of wood; but ornamented moldings, decorated panels, complicated capitals, etc. are first modeled in clay or wax, from which a cast is taken in plaster.

All patterns must have an allowance made for shrinkage -that is, the contraction and consequent decrease in size which every casting undergoes in the process of cooling. In ordinary work this amounts to about inch per foot in every direction, so that the patternmaker in working from full-size drawings must use a shrinkage rule to lay out his work. The shrinkage rule is usually a little over 2 feet in length and

the divisions on it corresponding to 1 foot are in reality 1 foot and inch, and the subdivisions are proportionately excessive. Consequently, the pattern for a cast-iron bar 1 foot long, 3 inches wide, and 1 inches thick, would measure 1 ft. 0 in. long, 3 inches wide, and 13 inches thick.

In order that they may be freely withdrawn from the mold, patterns are worked with a draft, or taper. For example, if the object to be cast is a solid bar 1 ft. 3 in. long and 3 inches square in section, as at (a), Fig. 1, it

tendency is overcome, and the sides of the mold are left clean and sharp; therefore, in all cases where it is possible, all surfaces that occupy a vertical position in the mold should have an allowance for draft. The exact amount of this allowance cannot be given, as in some cases it is desirable that there should be as little as possible, while in others it may be quite considerable without in any way impairing either the purpose or the appearance of the part.

5. Casting is the operation of pouring the molten iron through the inlets or gates, as they are called-into the sand mold from which the pattern has been withdrawn. All the above described details culminate in the casting. The making of the pattern, with its allowances for shrinkage and draft, the preparation of the mold with its inlets and gates, and all the details attendant thereon, are for the sole purpose of securing a perfect casting, and all conditions and contingencies must be considered before the metal is poured.

6. Suppose, for example, a newel post, such as is shown in Fig. 2 (d), is to be cast with ornamental panels on each of the