PRODUCTIVITY OF LABOR

Productivity of Labor in the Sheet Department of the Iron and Steel Industry

HIS article presents the results of a study made during 1930 of productivity in the sheet department of the iron and steel industry. The data were obtained through personal visits to the offices of the steel companies and cover the principal operations in standard sheet mills for the years 1925 to 1929. Figures for earlier years were not available.

The lack of uniform practice and the arbitrary treatment of accounting items made the classification of the data difficult. It was necessary to be content with data from the companies that could furnish satisfactory statistics. In many plants the records from which labor hours. may be derived were not available for the earlier years, while in other plants the available data could not be compiled to show a proper distribution of all labor hours. The data for 1929 cover about 10 per cent of the entire production in the United States for that year, and for the years 1925 to 1928 the number of plants studied is considered to be a fair sample of the industry.

The information available would not permit the combination of labor hours and output for all departments combined, as the operations of cold rolling, sheet annealing, and sheet pickling vary in number and sequence, depending on the kind or grade of sheet produced.

The departments covered in this report are those of bar shearing, hot rolling, cold rolling, sheet annealing, and sheet pickling. The unit of output is the net ton and the unit of labor time, the man-hour. A man-hour is an hour's work by one employee.

The labor hours charged against the output of each department include those of all plant labor engaged on the particular process, except the hours spent in repair and maintenance. The hours of plant labor here used include the time of superintendents, foremen, timekeepers, checkers, weighers, cranemen, motor operators, engineers, electricians, machinists, and other direct labor engaged on the particular process, but do not include the time of accountants, clerks, salesmen, and other employees connected with the general office.

Among the factors affecting average productivity are the substitution of machinery for labor, improvement in management, introduction of special piecework and bonus systems, installation of continuous pair and sheet furnaces in the hot mills, more efficient cooling of rolls, better-constructed motors, better-designed machinery, improved lighting systems, improved conveyor systems, serialization of machinery, and improved working conditions. It is impossible to measure separately the effect of these and other factors that influence productivity. While these factors have influenced productivity during the period studied, they have been operative in the industry for several years.

Summary

THE study shows a steady gain in average output per man-hour of labor time during the period covered, except in the annealing operations. The bar-shearing department shows the largest gain in output per man-hour, the increase from 1925 to 1929, inclusive, being 16 per cent. The cold-rolling and sheet-pickling operations show an increase of 12 per cent each, while the hot rolling shows a gain of about 10 per cent. In the annealing department the gain in output per man-hour was more than offset by the increased labor time required to meet the increasing demand for full-finished sheets of deep drawing quality.

In general the real gain in the industry in labor productivity due to improvement in technology and management was obscured by the increase in labor time required to produce full-finished sheets. The output of loose-rolled sheets of auto-body grade alone increased about 100 per cent from 1927 to 1929, the period for which census data are available. There was also a large increase in the production of high-grade sheets for use in the manufacture of electric refrigerators and metal furniture.

Table 1 contains summary data of average labor productivity for all plants, by departments.

TABLE 1.-SUMMARY OF AVERAGE LABOR PRODUCTIVITY IN STANDARD SHEET MILLS, BY YEARS, 1925 TO 1929

THE sheet industry is a part of the rolling-mill branch of the iron and steel industry. The sequence of processes from ore to finished product in the form of sheets is as follows: From the blast furnace to the mixer, to the steel works, to the blooming mills, to the sheet mills.

One net ton (2,000 pounds) of ore will produce about 1,100 pounds of pig iron. When melted and teemed into ingot molds this amount of pig iron will yield about 1,000 pounds of ingots. In the further reduction of this quantity of ingots to sheet bars the output of the latter will weigh slightly more than 900 pounds. This amount of sheet bars will produce about 650 pounds of finished sheets.

The process of making sheets in standard sheet mills may be divided into several distinct operations, depending on the grade of sheet desired. For the purpose of this study the following operations have been studied: (1) Shearing the sheet bars; (2) hot rolling, including roughing, finishing, opening, and shearing; (3) cold rolling; (4) annealing; and (5) sheet pickling.

Hot rolling is the most important of these operations, and requires more labor time than all of the other operations combined. While the sheets are physically complete at the end of the hot-rolling operation, they are still unfit for the many uses to which they are to be put. To obtain the desired grade and quality of sheet, some of the operations referred to may be varied in number and sequence. If a highgrade sheet is desired, the sheet bars are pickled before being rolled in order to remove the scale and prevent its being rolled into the sheet. This gives a smoother surface for painting and enameling.

In standard sheet mills, sheets are made from sheet bars. As the long sheet bars leave the sheet-bar mill, they are usually about 30 feet long, 6 to 12 inches wide, and less than 2 inches thick. The barshearing operation consists in cutting these long, thin bars into the desired lengths for the sheet mills. They are fed into the bar shears three, four, or five at one time. As the steel is never rolled with the grain, the small sheet bars are therefore fed into the sheet mill crosswise. The thickness of the sheet when finished is determined by the width and the gage of the sheet bar.

A single mill consists of two stands of 2-high rolls. After being heated in the pair furnace the bars are broken down on one stand (known as the roughing mill) and finished on the other (known as the finishing mill). It is the practice to "rough down" several bars before putting the "rough downs" through the finishing rolls. After being heated in the pair furnace for about one hour or until the bars are red, they are removed by the pair heater, who drags them in pairs to the roughing rolls and delivers them to the rougher. The rougher passes the hot bars separately between the rolls to the catcher, who returns the flattened piece. After four or five passes the sheets are ready for the finishing mill. After each pass the space between the rolls of the roughing mill is reduced by turning down the screws at the side of the rolls. The screws are operated by the doubler, who is assisted in some plants by the pair heater. In some plants mechanical conveyors carry the sheet bars to the roughing mills.

The "rough-down" sheets, as they are now called, are sometimes pickled before being put through the finishing rolls. This is done to remove the scale that has formed during the previous hot rolling.

Before the sheets are delivered to the finishing mills the "roughdown" pieces are placed together in pairs, with the longest on the bottom. This is known as matching, and the work is done by the matcher. The partially rolled sheets are passed through the rolls to hold them together; they are then delivered to the finishing floor and the pair heater's helper places them in the sheet furnace. When reheated to the desired temperature they are removed from the sheet furnace by the sheet heater and delivered to the roller. The sheets are passed two or three times between the rolls to obtain the length and thickness desired.

All common grades of standard hot-mill black sheets are produced under "tight-rolled" practice, i. e., the pack of from two to eight sheets is rolled and the sheets are separated after rolling. To secure a smooth, flat surface suitable for sheets of high grade, it is necessary to roll the sheets separately. These are known as loose-rolled sheets. This practice permits the surface of the sheet to be kept clean.

For commercial uses sheets are classified according to the number and kind of treatments.

The commercial grades of tight-rolled sheets from standard mills are known as follows:

1. One pass, cold-rolled, box annealed. The treatments are given in the order named. Sheets of this grade are rolled in packs of from two to eight sheets, depending on the gage. When cool, they are opened, given a flattening cold-roll pass, and box annealed.

2. Hot-rolled, pickled, and box annealed. The sheets in this grade are given the same treatments as in the preceding grade, and in addition they are pickled and dried or oiled and limed.

3. Single pickled, full cold-rolled, reannealed. In this grade the treatments are the same as in grade 1, with the extra treatments of pickling, cold rolling (two or three passes), and annealing. This grade is widely used.

4. Full pickled, full cold-rolled, reannealed. Same as grade 3, except that the bars are pickled to remove scale and oxide. This improves the surface of the sheet.

In the class of loose-rolled sheets are included:

1. Auto-body sheets. The bars are pickled to remove oxide scale and cinders. The sheets are loose rolled, the "rough downs" are pickled, box annealed, pickled, given one or two cold passes, reannealed, and stretcher leveled. For a sheet of extra deep drawing quality the heat treatment is given in a normalizing-annealing furnace instead of box-annealing furnace. Normalizing restores the grain structure required for satisfactory working under certain conditions. The other treatments for this grade of sheet are the same as for the preceding grade. For hood and fender stock the bars are pickled. Sheets are hot rolled, and the "rough downs" pickled, annealed, pickled, full cold rolled, reannealed, and stretcher leveled.

2. Steel-furniture sheets. These receive practically the same treatments as auto-body sheets.

Other commercial grades, mostly heavy-gage sheets, are produced on the jobbing mill or the continuous mill."

Classification of sheets.-With respect to size, sheets are classified according to weight per square foot and thickness in fractions of an inch. The weight and thickness of sheets of specified gage are shown below. As a rule sheet mills do not roll thinner than No. 30 gage. Sheets thicker than one-eighth inch seldom are rolled on a sheet mill but are reduced on a jobbing mill.

Analysis of Productivity, by Departments

TABLE 3 gives the detailed data from which the labor productivity averages are derived. The significance of these figures is commented on in the text statements separately for each department.

TABLE 3.-AVERAGE LABOR PRODUCTIVITY, TOTAL HOURS OF LABOR, AND TOTAL PRODUCTION IN STANDARD SHEET MILLS, BY DEPARTMENTS, 1925 TO 1929