Document jNeNjZaMEkJepDQo0eBrb7xO

lOodi Interesting Technical Data Compiled From Field Survey MINERAL WOOL RETIJJW TO By J. H. THOENEN* Supervising Engineer, Non-metallic Mining Section, Mining Division, Bureau of Mines LORA3Y nteresting technical data on mineral 6. Consumer's specification require I wool has been compiled as a result ments. of a field survey recently completed by Raw materials for the manufacture the Bureau of Mines. Certain general of mineral wool present an extended conclusions and data were published in list today, and include the natural the report of the American Institute of "wool rock" of Indiana, classed as a cal Mining Engineers' meeting appearing in careous shale or argillaceous limestone; Rock Products, November, 1937, page common shale, clay; combinations of 48. but the complete report of the survey calcareous and silicious materials, in is now available. cluding waste glass, waste china, and The report classifies mineral wools even soil; and iron, copper, and lead into three groups; rock wool, slag wool, blast furnace slags. The Illinois Geo and glass wool, and describes the vari logical Survey also suggests the possi ous marketable forms and uses. Due to bility of manufacturing wool from the confidential character of the infor charges containing sand and gravel, mation, names of producers are not common clay, or other unconsolidated given; but the plants are designated by materials. Unconsolidated fine materials, number. Under each plant are listed the however, cannot be used in water-jack following data: raw material, but not eted or brick-lined cupolas because of the proportions, although the methods the difficulty of forcing a draft through of proportioning and the manner in them. This confines the selection of which it is fed are given in some cases; raw materials for cupola melting to recovery of loose wool as compared with products in sizes large enough to permit raw material fed into the cupola; fuel free passage of furnace gases. In addi ratio; plant capacity; cupola dimen tion, it is necessary that the material sions and specifications; slag stream retain its shape to the melting zone. length; steam jet; type and steam pres The greatest variation, however, lies sure; wool rooms: type of granulator; in the chemical composition of the raw and methods of removing shot. material. Some operators attempt to Although the manufacture of mineral wool is a comparatively simple process and requires a relatively small amount of capital, (estimated at $50,000 to $60,000 for a plant producing 1000-lb. per hour) demands for specification products will necessitate more technical knowledge and closer control of opera tions. However, as mineral wool is a bulky material (usually not more than 12 tons can be packed in a freight car), it is expensive to ship long distances and for that reason, and the wide dis tribution of raw materials, the manu facture of mineral wool will continue to be a so-called decentralized industry. Items in the manufacturing process that require careful technical study and control by an established producer and that hold potential trouble for the pros pective producer are, as follows: 1. Chemical and physical composition of raw materials. 2. Type of melting furnace. 3. Melting and blowing temperature. 4. Blowing technique. 5. Shot prevention or removal. achieve and maintain a chemical bal ance between acids and bases in the cupola charge. Others contend that this is not necessary and that better wool results when there is a definitely greater percentage of acids over bases, or vice versa. While neither contention is sup ported in the report, it is pointed out. that similar chemical compositions in the cupola charge may be obtained by combining two. three, four, or more of a large number of natural or waste ma terials and that the chemical composi tion of the charge is reflected in the chemical composition of the wool. Practically all mineral wool is made in water-jacketed cupolas, the original brick-lined cupola having almost dis appeared. While cupolas require raw material to be in lump form to permit the passage of furnace gases, one manu facturer has been successful in briquet ting fine unconsolidated materials so that they may be melted in a cupola. Another operator is using a conical cupola instead of the cylindrical type. The reverberatory type of furnace has been used in the manufacture of min Abstracted from Bureau of Mines Infor eral wool, and glass wool is being made mation Circular 6984. in a similar type of furnace. Finely divided unconsolidated materials can be handled in this type of furnace as it is not necessary to pass furnace gases through them. With cupolas there is considerable waste in the form of shot, but with the reverberatory type furnace the shot can be remelted to make more wool. It is difficult to determine the tem peratures maintained in the melting zone and the blowing temperature or temperature of the issuing slag stream. Thermocouples have been placed in the furnace wall or near the melting zone from which actual melting temperatures are calculated. The blowing temperature is gauged by the color. Both melting and blowing temperatures are important in mineral wool manufacture as the phys ical characteristics of the wool (shot content, fiber diameter, fiber length, etc.), with the same raw materials, will vary with different temperatures. A change in chemical composition or physical characteristics of the furnace charge may require a radical difference in melting temperature, whereas better wool may result without change in the original blowing temperature. The length of drop of the slag stream from tap hole to steam jet has a very appreciable effect on the characteristics of the wool. Melting and blowing tem peratures as well as chemical composi tion affect the viscosity of the slag which is an Important factor in the shearing action of the steam or air jet and its ability to produce fine or coarse fiber and a minimum or maximum of shot. The diameter of the descending slag stream also is an important factor in evaluating the ability of the steam jet to shear or break it into globules. One experimenter found that the farther he could drop the slag to the steam jet without cooling or destroying the con tinuity of the stream, the better wool he could make. For blowing, the conventional V-type nozzle is commonly used, but the length and width of the slots and the angle between them is still a matter of pref erence. Recent improvements of the nozzle include: a curved face nozzle, a recessed nozzle to avoid objectionable air currents, and a newly patented nozzle with an annular steam orifice through the center of which the slag is passed. (Corctiniffii on page 40) MTC 017125 37 Chain Mtr installation ahead of Jaif gyrotoy crash#? 14-ft. long. One of these screens Is a new 3Vi- x 12-ft. horizontal double-deck screen, and the other a 3Vi- x 12-ft. double-deck screen, made from two 3Vix 6-ft. screens joined together. The top decks of these two screens have either 6/16-, Vi- or Vi-in. openings, and the bottom decks have three cloth screens, 28-mesh, 10-mesh and Vi-in,, for three dust sizings. The screen openings on the preceding screens, of course, may be varied to meet conditions. For example, a typical screen arrangement will pro duce, lVi- to 2 Vi-in., 1- to lVi-in., 1- to %. to Vi. Vi- to Vi. Vi- to 5/16, Vi- to Vi. 5/16- to Vi, Vi- to Vi, minus 10 mesh taglime). minus 28 mesh (agllme in sacks) and minus Vi-in. plus 10 mesh r one sizes to meet any specification. The addition of four bins of 1000 tons combined capacity has Increased the total live storage capacity of the plant to 2100 tons in 18 bins. Bins are ar ranged in two rows, with each screen being placed over a bin. Below the bins, the loading-out belt conveyor has been extended under the four additional bins and new chutes installed so that any combination or blending can be done by drawing stone from any of the 18 bins on a single belt conveyor. The 36-in. loading-out belt conveyor on 360-ft. cen ters, carries stone to the railroad load ing tipple and truck loading bins. Stone sizes In the several bins are fed to the loading-out belt conveyor through an accurately calibrated gate feeder so that exact grading specifications may be maintained on the loadlng-out belt con veyor. A final vibrating screen in the loading-out tower removes any casual dust from materials loaded in cars or sent to retail bins. This interesting combination of close screen sizing and blending from all bins offers a challenge to any specification. Ihoj Trap Rock Co. Woonsocket, R. I., has resumed operations after a shut-down of two years. A new cor poration, the East Woonsocket Trap Rock Co.. Inc., has been formed which holds a lease on the land, buildings, crushing equipment, rock, shovels, and other equipment of the Iron Trap Rock Co. Frederick Pelletier is president. Granite stoni producers in New Eng land have opened a campaign against tariff regulations which they claim per mits granite from Finland to compete with domestic stone. Load It dlrldod botwoon two 4 x l it. vibrating *cr##u with lVtln. and 1-In. openings. At tbit point, tbt baliatt it tabon out and pattod to bint. when larger Hone from Ibt #caipin<j #cre#n It allorntd to patt to til# semaiag plant, and th# 1- to 1 \*in. itone ij screen#d oat Mineral Wool {Continued /r.<m f.tur 77) Various angles of blowing steam jet or compressed air against the slag stream are used, but the conventional angle is always somewhat acute in that the slag drops vertically and the steam jet or air is usually directed upward to as much as 30 deg. above the horizontal. Shot-free wool is very much desired, but none of the plants are able to en tirely eliminate the shot. Glass wool made with a reverberatory furnace is the closest approach to it, but in the manu facture of rock or slag wool in a cupola furnace, shot is a waste product with which all producers have to contend. It is believed that the production of shot is caused by the globule cooling in its passage through the air before it has been entirely converted into fiber. Two remedies are suggested; one to manipu late the blowing operation so smaller globules will be made, and the other to raise the speed of the particle by in creased steam pressure. Raw wool con tains from 15 to 50 percent shot, rang ing from microscopic size to Vi-in. or more in diameter. It is difficult to remove the shot without breaking the fibers, but experiments are now being made which it is believed will result in the production of relatively shot-free wool. The manufacture of granulated wool eliminates the shot by passing the raw wool through hammer mills, feed threshers, or other types of granulators and then screening, but the fibers are broken up. Customer Specifications There is a definite trend toward the manufacture of a product which will meet certain specifications. The follow ing have been mentioned as probable factors to be covered by specification: chemical composition, shot content, fiber size, ductility or softness, water proofing, and thermal conductivity. It is reported that mineral wool in which the percentage content of lime is too high, slowly disintegrates under atmospheric conditions. If the sulphur in the wool is in the form of sulphite or sulphate no corrosive action is notice able, but if sufficient air is present to assure oxidizing conditions in the cupola, sulphur may appear as a sulphide which is unstable In the presence of moisture. Acid formed from the combination of sulphides and moisture is corrosive and haimful. Excessive shot content is not desirable because the shot has no in sulating value. Wool of small diameter fiber has greater insulating value, and the longer fiber is desirable because it gives a better supporting bond. Ductil ity or softness is of value as it makes the wool easier to shape. 40 HOCK PRODUCTS MTC 017126 frcJIj, CPa-6 dfA^i , I <\ ^cf- 51 s- ^0 MTC 017127