MILTON H. MATER, President, Mater Machine Works Inc. Corvallis. Oregon, United States of America
Automation of sawmill operations has awakened much interest among sawmill operators in recent years because it has made an outstanding record in reducing manufacturing costs in such industries as steel, aluminum, plastics and concrete blocks. Can automation be applied as successfully to reducing manufacturing costs in sawmills?
Till recently many sawmill operators believed that automation is so complicated and requires such large capital investment that it can only be applied to very large sawmills. However, the recent development of sawmill automation machinery "packages" has simplified automation and made the investment practical for small- and medium-sized mills.
In many places today one sees mills in this category installing automation log decks, automatic log carriages, automatic edgers, trimmers and similar equipment at a reasonable investment in comparison to gains achieved.
Many sawmill operators have also believed that the single purpose of sawmill automation is to reduce the number of laborers required in the sawmill. Therefore, where the labor costs are low there appears to be little incentive for automating a sawmill. However, the reduction of labor is only one of the many gains made by automation.
Sawmill automation can be defined, for practical purposes, as the control of machines by other machines. For example, if two men are rolling logs on to a log deck and then onto the carriage, it is manual labor. If these men are replaced with a live chain deck, a log stop and loader, and a log turner, and only one man is used on the deck who pushes buttons to control the flow of logs to the carriage, it is mechanization. But, if a machine is installed to control the live deck and stop and loader, so that the logs move towards the carriage automatically, replacing the man who pushed the buttons, it is automation.
Mechanization and automation do not consist merely of installing new machinery. Often new machinery is not required. Mechanization and automation are new ways of thinking. Installing new machinery in a mill does not necessarily save labor or increase efficiency. For instance, if a mill has an old, two-man carriage using a dogger and setter, and if it is replaced with a new two-man carriage, the mill may save maintenance money and manufacture better lumber, but neither productivity nor efficiency will necessarily be increased.
Automation is applied with greatest financial gain in areas where labor costs are highest. The comparison in Table 1, based on American western rates, illustrates this.
TABLE: 1. - COMPARATIVE COSTS, ETC., OF AUTOMATED AND CONVENTIONAL SAWMILLS: UNITED STATES
|
Costs, etc. |
Automated mill A |
Conventional mill B |
|
Capital investment |
$ 260,000 |
$ 150,000 |
|
Depreciation/year on a ten year basis |
$ 26,000 |
$ 15,000 |
|
Number of men on the mill floor |
5 |
10 |
|
Direct labor cost/year at $5,000/man |
$ 25,000 |
$ 50,000 |
|
Total cost/year, Depreciation labor |
$ 51,000 |
$ 65,000 |
|
Cost/thousand, based on 12 million board feet/year production |
$ 4.25 |
$ 5. 42 |
The automated sawmill operates at $14,000 less per year than the conventional mill. It can operate and show a profit when the other mill breaks even or shows a loss. The productivity (the number of board feet produced per man per day) of mill A is 10,000 per man per shift, in mill B it is 5,000 per man per shift.
There are many other gains to be made in applying automation to sawmills. Where manpower is used to load the logs in the mill, roll them onto the carriage turn the logs dog, taper, set out, etc., the entire sawmill must be attuned to the limiting speed and strength of the human muscle. Where machines are used for the physical labor, the men who are placed in the control positions in the modern sawmill - i.e., sawyer, edgerman, trimmerman - can concentrate on making decisions based on their observations and judgment. Meanwhile, the machines do the actual handling and measurement much more accurately and faster than a human being can.
Automation also increases production. In most instances, when men are replaced by machines, not only does the production per man go up, but the total production of the plant increases. As a typical example, when a man was taken off the log carriage at a large western United States mill, the manager reported that within two weeks his production on this headrig jumped from 38,000 per shift to 40,000 per shift. And this increase was made with one man less on his payroll!
Automation also makes for better, more uniform quality. Dimensional quality is more uniform with automation because it depends on repetition, and repetition is something a man does not do well. Setting dimensions accurately demands a man's full attention, both mentally and physically. This is tiring, and the momentary inattention's which occur are wasteful in variations of thickness, width or length. Again, a machine which is steel and copper and electricity and compressed air, cannot be lulled by repetition.
Automation permits dimensional quality control. If a machine is setting too thick, it can be adjusted. Automation eliminates the need for the unskilled type of laborer who merely handle logs or pieces. By replacing these unskilled men with machinery, we limit the type of men employed in the operation to highly skilled, high quality men.
While the simplest method of sawmill automation would appear to be to scrap existing sawmills and start anew, it is obviously impractical to do this. Step-by-step progressive automation has been found to be the practical solution. To shut down and rebuild a sawmill for complete automation operation is usually prohibitive in terms of both time and money.
But a yearly allocation of money for sawmill improvement to be made during an annual shut down is practical and makes good business sense. Step-by-step automation makes sense also because many of the packaged automation machines are being developed gradually for stepwise automation of the mill.
It is important to realize that new machinery, or converting old machinery, is not always the road to automation. Sometimes an inexpensive reshuffling of the existing machinery, or the addition of a few limit switches can replace a man with a machine and improve productivity. Sometimes a combination of one or two new, improved machines, plus a reshuffling of existing equipment and the addition of a few limit switches, gives spectacular improvements.
One mill was able to increase the productivity by 50 percent, take seven men out of the sawmill, and save sufficient space for the addition of a green chain and lumber storage area by changing the line of its lumber flow, reshuffling positions, and adding only two new pieces of equipment, a riderless carriage and an automatic trimmer.
Automation of the front end of an existing mill can readily be accomplished. Packaged machines which can be installed in any mill have been developed for handling logs, from the log pond or dry deck, through the headrig. The modern automated mill does not have a man on the log haul or log deck. The first man usually found in the automated mill is the sawyer, who - by means of remote control - controls those deck functions which require his decision, i.e., log turning for grade carriage loading. All other functions, such as loading the logs onto the log deck, and the actions of the log stop and loader, are performed by automation.
The back end of the sawmill is more difficult to automate in an existing mill. The major difficulty is the lack of adequate waste clearing conveyors. In many existing mills the cost of constructing conveyors is so high that complete automation is not feasible and men must be used just to handle waste material.
Even without new or expensive machinery much efficiency can be gained by following, where possible, the concept of the self-cleaning mill. The general rule applying to automating the back end is: separate the waste material from the lumber pieces as soon as possible. Modern sawmill design calls for leaving the floor under all lumber-carrying rolls and transfers open, so that sawdust and other waste material can fall through into conveyors. In rebuilding a mill for automation it is often possible to follow this practice.
Packaged equipment for automating medium and small sawmills has been developed in recent years, particularly for the front or headrig end of the mill.
Log decks
Logs are heavy and very often awkward to handle. Rolling these logs onto the carriage, dogging them, tapering the log and setting the log forward into the sawline all take a good deal of time and manpower. The process of turning the log after sawing off several pieces and opening a " face ", so that a new " face " can be opened, is also a laborious, dangerous, and 6 job.
In modern sawmills, the function of handling logs is performed with electric motors and machinery and without manpower. Log turners are made in a sufficient variety of types and sizes that they can be installed in almost any sawmill log deck.
The mechanized log deck for carrying the logs to the carriage is often referred to as the " live deck ". It consists of a set of horizontal skids on each of which rides an endless chain. A log stop-and-loader at the carriage end of the deck actually delivers the log to the carriage when the sawyer presses a button. The deck can be automated to roll logs forward automatically as they are required at the carriage.
When a pond is necessary, several varieties of log haul are available which automatically deliver the logs to the log deck.
Log carnage and headrig
The log carriage is equipment which can most readily be automated in most mills - often it is not even necessary to obtain a new carriage. Old carriages in good condition can be automated by attaching packaged conversion kits.
In the automation log carriage, the log is held to the carriage knees by means of compressed air operated dogs. These may be purchased as a " conversion kit " in a steel case which can be attached to the existing knees of most carriages. Different sizes of dogs are available for large, medium or small logs. The dogs operate much more positively and more powerfully than the men which they eliminate.
Setting out is done by the sawyer by remote control from his usual position on the mill floor. He presses buttons for the thickness to be set out. An air, electric, or hydraulic motor on the carriage automatically sets out this thickness. It eliminates the need for a man on the carriage, and also eliminates human error in the thickness setting. These remote controlled setworks can be installed on most types of existing log carriages. Various types of remote controlled tapering devices are available. The latest device is a sliding clutch arrangement which is fitted into the setshaft and is remotely operated to permit one knee to be displaced forward or back with respect to the others.
Air cylinder activated cant kick-off bars and flippers are readily controlled from the sawyer's position.
The compressed air and electricity are carried to the carriage by means of a pair of overhead swinging arms known as a "pantograph".
The bandmill and circular saw husk have undergone changes in recent years to adapt to sawmill automation. A bandmill engineered especially for sawmill automation is built so that the sawyer can control strain, tilt and upper guide positioning by pressing buttons in his kit. The automation bandmill is engineered for a built-in slat bed, a requirement for automation offbearing. The circular saw husk for use in automation is engineered for ready disposal of the waste material from the carriage.
Offbearer
The packaged automation offbearer can be utilized by mills with a waste conveyor from the headsaw, which runs the full length of the mill.
The automation offbearer uses a wide flat belt over the offbearing rolls, which bears away the slabs and pieces of lumber.
A gap is left between the headsaw and the offbear-belt. Short slabs, and pieces which cannot bridge this gap fall through into the conveyor. If a circular saw is used, the sawhusk is left open also, so that all sawdust, bark, slivers, etc., fall into the conveyor. If a bandmill is used, then a steel slot bed carries this material off into the gap. Long slabs are carried off by the belt and may be disposed of by several different means.
Edger and edger receiving and outfeed systems
Transferring pieces from the offbear belt or roll-case to the edger feed table automatically is a comparatively simple matter. Lifting transfer chains are installed on skids connecting the offbear system with the edger table. (When an offbear belt is used, it is divided on either side of the transfer chains and extra belt pulleys are built into the system.) The transfer skids are usually raised by an air cylinder.
In high speed mills, automatic setworks are used to position the edger saws instead of the manual levers or handwheels. Automating the edger itself is simply a matter of using power drives to shift the saws, and then using electrical means to control the shifting. In the simplest case, that of a two-saw edger whose saws move toward or away from each other, the handwheel which causes the saw to shift is replaced by an electric motor with a powerful brake built into it. An electrical control unit consisting of cams and limit switches, causes the motor to move the saws to certain widths, such as 4, 5, 6, 8 inches (10, 13, 15, 20 centimeters) etc. The edgerman can override the control unit to obtain other widths. In more complicated edgers, a motor is used to move each saw.
Edger tailing (removing edgings and lumber from behind the machine) is a process that has been difficult to automate. The successful mechanical devices for this purpose are limited to two saw edgers or to two sided edgers which use only two saws acting together on each side. The type of automatic tailing which can be used in less specialized sawmills, must be built into the mill itself.
Trimming
Trimmers come in three varieties: a single saw trimmer cutting pieces on a rollcase as they are stopped by the trimmer operator; two saw trimmers cutting the length as the pieces pass through sidewise, and a multi-saw trimmer cutting to lengths and trimming out defects as the pieces pass through it. Each of these can be automated to reduce the manual labor necessary for trimming, speed up the operation, and give the trimmer-man more time to observe the pieces and make decisions affecting the grade.
The two-saw trimmer is automated by motorizing the saw shifting mechanism. The saws can be moved toward or away from each other by a motor which is controlled by cams and limit switches. In a more advanced type, one saw remains stationary while the other saw moves; this permits the maintenance of a "zero lumber line" through the trimmer.
The multi-saw trimmer is automated by providing limit switches in the trim table which provide for automatic end trimming of the lumber.
Automating a single saw rollcase trimmer consists of providing automatic stops in the rollcase and activating the trim saw by an air or hydraulic cylinder.
As in the other automatic devices, waste conveyors which will carry away the trim ends and sawdust efficiently are essential to the functioning of an automated trimmer.
The lumber-sorting functions
Packaged equipment for automating the lumber sorting function is limited at the present time. Packaged " green chains " are available for lumber sorting by the green chain method, in which the pieces are carried sidewise on a series of endless chains and are pulled lengthwise into lumber piles at right angles to the chain.
Endwise sorting is automated by the so-called " edge sorter ". Lumber is sorted into slots built on rotating rolls or a moving belt, which is raised 10 feet (3 meters) above the floor level. The lumber falls into the slot on one edge and rides lengthwise down the rolls. Each slot ends at its " pocket ", which is merely an open space at the side of the rollcase, sloped down to a set of skids on which the lumber falls. In general, the edge sorting has been used for light and short lumber, up to 16 or 20 feet, with comparatively few sorts, say up to 12.
Automatic stackers are also in a comparatively primitive state of development and are not generally found in any but the largest mills.
The principles applied in building an automation sawmill differ markedly from those used in building an older type of sawmill, geared to the limitation of human muscle and ability. An automation sawmill is not merely one with automation equipment but is engineered for the most efficient layout and flow of logs and lumber. Adequate and correctly built conveyors should be built in so that the mill will be " self-cleaning ".
Many designs of automation mills are available and can be adapted to particular mill conditions.
Sawmills considering a program of progressive automation must consider several important factors:
1. Automation requires labor with a certain degree of skill and training. When installing automation equipment, provision should also be made at the same time to procure or train labor to handle this equipment.2. Automation equipment requires good preventive maintenance. Provision should be made for maintenance of automation equipment at the time of its installation.
3. New ideas and equipment require a transition period. Defects need to be adjusted or mended. It is possible that production may fall short of quotas for a brief period during this transition. Management should prepare beforehand for the transition period in order to get the best co-operation from supervisors and labor.
But sawmill automation has increased the efficiency of sawmilling and enables management to make the greatest utilization of labor, time and raw materials. Progressive automation of sawmills is a satisfactory method for achieving these results.
