VAULT // 1925
The Mechanical Features of
Salmon Canning
Early methods employed in can making and canning—modern methods in which rapid-working automatic machines have replaced the former hand methods—present extent of the industry.
Written by M. L. Dodge
OUR PRESENT-DAY SALMON CANNERIES are a mechanical development extending over quite a period of time, the first cannery on the Pacific Coast having been established in 1864, on the Sacramento River, in California. Salmon canning presents many features of interest to the mechanical engineer.
Early Methods
It is interesting to compare early methods with those of the present day. The cans were at first all made by hand with very primitive tools. A square shear operated by a foot treadle cut the sheets of tin into a size for the can “body.” A line was scribed along one end with a tool on the order of a thumb gage. A hand roll rolled the body into a cylinder and it was lapped to the line already mentioned. Then it was tacked with solder at one or two points to hold it in place, then held against a block bolted to a bench with a hand tool, and the remainder of the side seam soldered. At a little later date a form of the exact size of the inside of the can was made and a clamp, operated by a foot lever, held the can body in place while the side seam was soldered.
By this method an expert can maker could solder from 3500 to 4000 can bodies in 10 hours. This was soldering the side seam only. It required a second man to cut the blanks and another to roll them into the cylindrical shape, or three persons to make the 4000 can bodies in 10 hours. Today a machine with two operators can make 150,000 cans every 10 hours.
The ends were made by cutting circular disks from sheets of tin with a rotary shear. The edges of these disks were flanged down in a crude cast-iron die which was operated by a hand screw press.
A 19th-century salmon canning factory in Canada. Photo: Getty
The production line at a salmon canning establishment in Astoria, Ore., circa 1890. Workers are shown packing individual cans with fish. Photo: Getty
In assembling the can, the bottom was slipped over the body and the end of the can rolled about in a pan of powdered rosin. A piece of solder was placed inside and a hot soldering copper curved to the shape of a can was applied outside, and by revolving the can the solder was spread around in the joint. After filling with fish the tops were inserted in the end of the body and soldered by hand around the edge.
The processing, at that time very much of a secret, was simply a case of cooking in water tanks instead of using a retort as at present. The cans, which had a vent hole in the top, were first placed in trays and immersed in boiling fresh water to within perhaps an inch of the top. After they had been cooked for an hour in this manner, they were removed from the water and sealed by a drop of solder put on each vent hole. They were then put into a tank of boiling salt water where a higher temperature was obtained than would be possible with fresh water. After cooking for another hour they were washed by hand with soap and water and a rag, and then painted with red lead and linseed oil.
Such were the primitive methods of can making and canning of the early days.
The First Automatic Can-Body Maker
About 1883 the first automatic body maker was brought into use on the Pacific Coast. This machine turned out lock-seamed can bodies at the rate of 20 a minute. This was improved until a speed of 65 per minute was attained. The Seattle-Astoria Iron Works built its first body machine, still in use, in 1907, at Astoria, Oregon. By this time presses and dies, more on the present-day order, were in use. The tin was fed by hand, however, but the die did its own blanking. An operator on a press could feed on an average about 60 ends a minute.
Can Making Methods
The cans of this period still had soldered ends. However, a steady improvement in mechanical devices for can making has been in progress and at present there is machinery in Seattle that will make cans at the rate of 260, or even faster, per minute, automatically feeding and forming the body from a blank, and lock-seaming and soldering it. Cans manufactured thus are called “sanitary” cans, probably because in the machine-soldered can all the solder is on the outside of the body and the ends are double lock-seamed, with no solder whatever.
The body maker is perhaps the most complicated and particular machine used in the making of cans and requires the most expert mechanical attention. The body itself, before either top or bottom is put on, goes through no less than 13 distinct operations. These operations are as follows:
A woman operates a canning machine at a facility run by tin can manufacturer, the American Can Company in Tampa, Florida, circa 1945. Photo: Getty
A tin can making machine in operation at the Machinery Exhibition in Olympia, London, in October 1912. Photo: Getty
The commercial size of tin plate is first fed to the “trimmer,” which is a series of circular cutters spaced to cut the large sheet into strips of exact width to make the circumference of the can plus the hooks for the lock seam.
Next in order is the “slitter,” which cuts these strips into body blanks of a sufficient width for the height of the can. The body maker feeds these blanks automatically from a stack to the first station where the ends are notched.
The blank is then moved forward to the first folding operation, and then to the second folding operation: these form what are known as the “hooks” for the lock seam. Next a small roller prefluxes the edge of one hook, to ensure the solder’s entering the seam and sweating clear through the joint. Then comes the forming of the body around a “horn.”
This is done by wings swinging down from above and folding the tin around the horn. This horn is a very important part of the machine, for it controls the exact diameter of the finished can. It is a collapsible arrangement with means for expanding to pull the hooks together after the forming wings have overlapped them. The seam is next “bumped,” or flattened out, by a ram from below.
The can has now taken shape and must be soldered. An endless chain with attachment hooks picks the cans off the horn and propels them along a solder horn, first over a fluxing roller and then over a soldering roller, the latter being partly immersed in molten solder. They are next wiped by a wheel composed of muslin disks and similar to a buffing wheel, which takes off the surplus solder. As the cans are still very hot and the solder not set, it is necessary to cool them with an air blast.
A conveyor carries the cans to the “flanger,” where both ends are flanged preparatory to the application of the bottom. Another conveyor takes them from the flanger to the “double seamer,” or closing machine. This machine also has a very important function to perform: it places the bottom on the body and rolls a lock seam. This requires two operations, the first one a sort of tucking the edge of the bottom up under the flange of the body, and the second a flattening-out process to lay the laps of tin tightly together to prevent leaks.
A pressure of about 200 pounds is required to roll the second operation tight. The rollers are diametrically opposed and are operated by a toggle. A chuck fits the depression in the can end, forming a solid support for the seam during the rolling operation. After the cans have been tested for leaks, they are ready for the canner.
The can end which has just been put on the can in the double seamer requires quite an outlay for machinery for its manufacture. To avoid waste of tin plate, a scroll shear is employed to cut strips for the automatic press. To cut straight strips and then punch round disks out of them obviously creates a waste in the form of a triangular-shaped piece between each two holes and the edge of the strip. The scroll shear takes advantage of a staggered layout of holes, thus reducing the waste to a minimum.
These strips are stacked in the hopper of the press and are fed automatically to the die. A modern press will make ends for a tall 1-lb. salmon can at the rate of 250 per minute. A strip of tin is taken from the hopper and placed on the feed bar, which moves it along intermittently under the die. When all the ends are cut from this strip, the scrap that is left is thrown out at one side, while another strip is picked out of the hopper and placed on the feed bar. One strip follows another closely; there are no idle strokes of the press.
The ends, after being dropped out of the die, slide down a chute into a “curler,” which is simply a revolving disk or ring with a groove in its edge and a stationary segment outside of this, with a corresponding groove on its inside edge, the space between the two being sufficient to accommodate the diameter of the end. The end sliding down the chute from the press is guided in between the revolving disk on one side and the end of the segment on the other side. The revolving action of the disk rolls the end around the segment and throws it out at the discharge end. This turns the edge under slightly, making it possible to stack the ends without their sticking together.
From the curler the ends must go through the compound-applying machine, which places a thin coating of rubber compound inside the edge. This compound forms a gasket in the seam when the end is rolled on to the body. After applying the compound, which is in liquid form, the ends pass through a drying process before they can be handled or boxed for shipping.
Modern Canning Methods
Improvements in can making have been accompanied by corresponding improvement in handling and canning methods. Power boats with winches handle fish traps and dump the fish by the ton into scows or into fish tanks in the trap tender for transportation to the cannery where they are handled by a modern elevator. The modern fish-cleaning machine trims, washes, and scores the fish in a more thorough manner than was usually done by hand, and the man with the butcher knife has been replaced by the “fish cutter,” an endless chain carrying sectional buckets or fingers past revolving circular knives that cut the fish to proper length for a can.
Hand filling is practically a thing of the past. The first machine filler was built by Mathias Jensen, of Astoria, in 1875, and operated at a speed of about 20 cans per minute. With refinements of design the present Jensen filler, while employing the principles of the original, is a very quiet, smooth-running machine, capable of filling from 80 to 100 cans per minute, and putting a measured amount of salt in each can besides.
As an example of refinement in design may be cited the cam that operates the plunger on the can filler. For several years the usual method of making this cam was to rough-mill it to approximate shape, place it on a machine, and chip and file the surface to a fair contact with the roller. The roller pin did not point to the center of the shaft, and the cam had a long travel and mostly on one side of the center line. By redesign of the lever carrying the roller and its bearing bracket, equalizing the travel on each side of the center, and making the axis of pin radial with the cam, it is possible now to mill the cam to such a degree of accuracy that hand fitting, which formerly consumed from two to four days, is no longer necessary.
A tin can factory worker. Photo: Getty
Quality control team inspects the quality in a canned fish factory. Photo: Getty
From the filler the cans of fish are carried on a chain or belt over a “mending” table, where small pieces of fish may be placed in cans to fill up any space that may be left by the filler. They then go to the “clincher” where the cover is put on and the edge crimped over the flange of the can body enough to keep it in place and yet allow the air to escape as the can is heated in the exhaust box.
The clincher has developed in the past few years from an intermittent-motion squeezing arrangement to a continuous rotary rolling process of almost unlimited speed, and its efficiency is shown by the fact that this machine has been in practical use now for five years with no changes in design.
From the clincher the can passes to the “exhaust box,” whose function is to heat the contents of the can to about 200 °F and drive out all the air possible prior to sealing the top on. It consists of either a series of disks with gear teeth on the edges and a sort of figure-eight guide, or a chain arrangement to take the cans back and forth through the box, keeping them in a bath of steam for from 12 to 15 minutes.
Leaving the exhaust box, the next step is to double-seam the cover on. This is called the closing operation. The closing machine may well be called the most important machine in the cannery, for upon its work depends the whole success of the pack. The manufacturer of the cans, if the canneryman buys his cans, will guarantee to make good all claims for spoilage due to leaky cans for any amount greater than five cans in every 1000, provided the leak occurs in the side seam or the end put on when the can is manufactured. If there is anything wrong, however, with the end that the canner puts on, it is the canner’s loss.
The present double seamer has not undergone so much redesign as has most of the other canning equipment, due to the fact that the original designer of the machine was a finished mechanical engineer. Small refinements have been added in the past few years to take care of a demand for increased speed. Some bearing sizes have been increased, and safety devices added.
The remainder of the canning operations are not of so much importance from a mechanical standpoint, as they are simply cooking, washing, inspecting, labeling, and shipping processes.
To give an idea of the size of the industry at present, it may be said that there were 188 canneries in the states of Washington and Oregon and the Territory of Alaska in operation for the season of 1924. Their total output was approximately six and a quarter million cases, which, at 48 one-pound cans to the case, represents a sales value of $44,000,000. Of this number over five million cases were put up in Alaska.
M. L. Dodge was chief engineer at Seattle-Astoria Iron Works in Seattle. He presented this work before the ASME Western Washington Local Section on Feb. 20, 1925.
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