ing foundry should be kept in "fighting trim" and one of the most, if not the most important contributions to such a condition, is a satisfactory floor.

Five Basic Features

The five basic mechanical features of a successful foundry may be analyzed as follows: (a) Good, firm, level and clean floors; (b) well prepared molding, facing and core sands; (c) the best of pattern and flask equipment; (d) efficient mechanical molding devices and equipment; and (e) correctly proportioned casting metals. Each plays its part, has its function to perform and contributes to the sum-total result.

There exists in the minds of many foundrymen a misconception regarding the practical use of concrete for foundry molding floors, although it is generally agreed among the users of this material that it surpasses other forms of pavement. No pavement is perfect, yet all have merit, concrete seeming to possess the fewest deficiencies.

The four most common objections to the use of concrete may be summed up as follows: First, spattering or "popping" of molten iron spilled from the ladles may occur where concrete floors are used. This is caused from an almost instantaneous generation of steam when the molten metal comes in contact with the concrete, which is more or less moist at all times. An explosion follows and particles of red-hot metal are apt to fly 5 or 6 feet in all directions, resulting in painful burns. Occasionally such an accident has been responsible for loss of eyesight. This complaint may be entirely overcome by properly finishing the surface of the concrete, as described later.

The second objection lies in the crumbling and breaking down of concrete floors due to general weakness in design, faulty aggregate composition, insufficient curing when green and disintegration from violent expansion and contraction caused from the piling of very hot castings on the concrete floor after a shake-out. All these complaints may be automatically corrected in newly laid floors if the specifications and directions given in this paper are followed.

The third objection, of which less is heard, is the likelihood of tripping and falling over small iron balls of iron or shot,

formed from ladle spillage. This objection may be overcome by properly roughening the wearing surface of the floor.

The fourth objection to concrete for molding floors is found in the somewhat exaggerated claim that molders voice discomfort while working on it. Any solid pavement permits a pounding shock, as we walk over it. This is transmitted all through the lower extremities of the body, and results in minor physical injury, producing slight leg and hip fatigue and dull pains or soreness in the instep and leg muscles. Usually it is from molders who are unaccustomed to working on concrete floors that the complaints come, and then only for a short period until their muscles harden. We are all of us accustomed to pavements, and granting as we must, that the result is not entirely satisfactory in this one physical sense, yet we find their combined benefits eclipse this one disadvantage, and so it is or should be in the foundry. None of us would consider dirt walks or streets, nor would a foundryman who has experienced the results from a good concrete floor return to clay or sand floors. It would perhaps be of benefit and but little trouble and expense, to make a die and cut out full soles from a cheap grade of rubber, attaching them as often as required to the molders' shoes.

Advantages of Concrete Floors

A concrete floor has the advantage of presenting a clean and dry surface thereby preventing pneumonia and chronic rheumatism, especially during the winter season, when sand and clay floors are apt to be continually damp, cold and frequently full of frost during the forenoon. There are not a few such floors, built over boggy land, which have induced a high mortality rate.

The results to be gained from paved foundry floors are genuinely worth while. For instance a foundry in Toledo found after careful time studies that it would be possible to reduce the casting losses and improve the quality of the output by the installation of a pavement on which the molds would rest firmly and evenly. A brick floor was installed and the result was approximately a 5 per cent gain, divided between reduced losses and increased production. Level molds are an advantage

not to be lightly overlooked in these days of intricately cored, difficult, thin-walled, delicately sectioned castings. Also such a pavement provides a mechanical guarantee and eliminates the human element which must otherwise be depended upon to level each mold set down on the usual irregular sand or clay floor.

Brick pavement is not recommended, as its structure deteriorates much faster than concrete. Furthermore, it breaks down on the edges, forming holes, and is disagreeable to shovel on. A Belgian sawed block, set on concrete, makes a splendid floor but is very expensive.

In a general way it may be said that the use of concrete for floors, pits, foundation walls, etc., is not thoroughly understood by the average contractor. The unsatisfactory results so frequently experienced from concrete floors, leaky pits, cracked masonry, etc., arises from the ignorance of those having the preparation, laying and curing in hand, or in attempting to hasten the completion and use of the structure.

Prepared pavings, such as brick, wood block, etc., are scientifically manufactured to set standards and identical results, under average conditions, may be anticipated and guaranteed from Maine to California. With concrete, the conditions are different. The Portland cement itself is standard, but it forms only a small percentage of the total aggregate which is composed of rock, gravel, sand and water. Each plays an important part in the finished result. Being bulky, the coarse aggregates must be secured locally, each varying, as is to be expected, in quality, structure, etc., according to origin. The preparation of the mixture, a highly important and little understood factor, is too often supervised in a careless manner or by a person who possesses experimental ideas of his own, and in consequence the result is apt to be unsatisfactory.

A Specification for Molding Floors

The data given in the following are based upon practical experience rather than theory, and it is hoped this paper will be of benefit and may bring forth voluntary reports from foundrymen and foundry engineers who may see fit to adopt its suggestions.

The first thing to consider is a specification for concrete molding floors. This specification is as follows:

(A concrete mixture is composed of three prime elements: Portland cement, fine aggregate and coarse aggregate. The proportions are always referred to in the order given above, as 1:2:3 mix, which is composed of one (1) sack of Portland cement, two (2) cubic feet of fine aggregate and three (3) cubic feet of coarse aggregate. A cubic yard of concrete in place shall contain not less than six and eight-tenths (6.8) cubic feet of Portland cement.)

Subbase.-Concrete floors laid over ground having soft spots or on boggy ground should in the first instance have the soft spots dug out and filled, and in the latter instance the entire ground covered or filled with from 3 inches to 5 inches of gravel, crushed slag or steam coal cinder free from particles of unburned coal, soaked thoroughly, tamped and rolled into an unyielding mass. It is important this subbase be well soaked immediately prior to placing concrete thereon.

Thickness. With proper subbase a 3-inch concrete floor will suffice for light and medium heavy work. For heavier work and over boggy and sloppy land a 4-inch floor is recommended. For heavy-work center bay floors the thickness should be increased to 5 inches. A foundry melting floor should always be one course, that is, laid solid to the thickness desired in one operation without a second finish coat.

Fine Aggregate.-Fine aggregate shall consist of natural clean sand or screenings from hard, tough rock or gravel which, when dry, will pass a No. 4 wire mesh screen.

Coarse Aggregate. This shall consist of clean, hard, tough crushed rock or pebbles graded to size and shall contain no soft, flat or elongated particles. The size shall range from three-quarters (4") inch maximum for a 4-inch or 5-inch floor down to one-half (1⁄2") inch maximum for a 3-inch floor. Limestone and shale should be avoided if possible as the structure of either is none too good. New England trap rock surpasses all other stone for coarse aggregate and where the freight rate is not prohibitive its use is recommended.

Coarse Iron Aggregate.-This aggregate should be composed of cast-iron borings, preferably from cylinder, piston or similar iron. These borings contribute a bonding strength to the concrete and form avenues for the absorption and escape of excessive heat from hot metal spillage and the piling of hot castings on the floor, thereby preventing undue expansion and contraction of the concrete and consequent deterioration. This iron aggregate may be extended all through the entire molding floor with very beneficial results if desired, in which even only 10 per cent (10%) by volume of the total concrete mix need be borings, except for the gangway where the

borings should be increased to 2:1:3 of borings, or a 1:1:1 mixture plus 1 of borings. In the event only the gangway aggregate is to be treated with borings, it should be amply deep to provide for laying hot castings thereon.

Machine Mixing.-The ingredients of the concrete floor shall be mixed to an even consistency in a mechanical batch mixer of improved design and mixing shall continue for at least one minute, preferably somewhat longer, after all the materials are in the drum. Raw materials shall not be permitted to enter the drum until all the material of the preceding batch has been discharged. It is impossible to secure an even, thorough, homogeneous mix by hand methods, which should never be attempted.

Retempering. Retempering of unused concrete which has partly hardened; that is, remixing with or without additional materials or water, shall not be permitted under any circumstances. Such material shall be discarded.

Water. Use the smallest quantity of water which will produce a workable mix. It is highly important that the proportion of water in the concrete mix be too little rather than too much. A normal plastic workable 1:2:3 mix should present what is termed a quaky state, to secure which the average minimum water per sack of cement used should run five and one-half (5%) gallons to not more than six (6) gallons. The function of water in concrete is two-fold: (1) To supply the water necessary for hydration of the cement, (2) and for the purpose of producing a plastic mix. The influence of the water-ratio on the strength of concrete may be readily understood when by way of illustration it may be said that one pint more water than necessary to produce a plastic concrete in a 1:2:3 mix, for example, reduces the strength to the same extent as though 2 to 3 pounds of Portland cement were omitted from a one-bag batch. The reason that a rich cement mixture gives higher strength than a lean one is not that more cement is used, but because the concrete can be and usually is mixed with a lower water ratio in the case of the richer mixture. In general it will not be feasible to use concrete of a consistency which will give the maximum strength, since it is somewhat too stiff for satisfactory working. Hence some sacrifice of strength is necessary in order to secure a workable mix. It is urged that the water content here specified be not exceeded for foundry floors.

Placing. Before placing concrete thereon the subbase should be thoroughly soaked. After mixing the concrete shall be handled rapidly and in successive batches, within thirty (30) minutes after water has been added to the dry materials, and shall be deposited in a continuous operation completing (when laid in slab form) individual sections to the required length and depth without stoppage for any cause. Any excess of concrete over that needed to complete a