Packaging technology

Published: 27-02-2012, 13:42

Can seamers

Can seamers are machines that mechanically attach component ends to can bodies in a reliable manner. Around 1900, the sanitary can made its appearance in Europe, where both top and bottom ends were doubleseamed to the can body. The term ‘‘sanitary’’ indicated that solder was not used in the ends being double-seamed, but only on the outside of the can body side seam (1). In 1910 Henry Louis Guenther, inventor and manufacturer, introduced can seamers for double seaming that met the requirements of modern food and beverage processing. His products, which are sold under the trade name of ‘‘Angelus,’’ were so well introduced that they are now used by the largest food, beverage, and can manufacturing companies in the United States as well as abroad (2). Basically, there are two categories of can seamer: In can manufacturing they are called can shop machines, which attach the first end on a three-piece can, and in product filled cans they are called closing machines, which attach the last end on either a two-piece or three-piece can.

THE DOUBLE SEAM

The preservation of canned products requires hermetically sealed cans. The process of creating an airtight closure by attaching the can end component to the can body is called double seaming. This double seam is a metal-to-metal joint formed by mechanically interlocking five layers of metal together: three from the can end and two from the can body (3). These layers are then compressed and ironed tightly to form the hermetic seal (see Figure 1). The can seamer sometimes referred to as a double seamer requires two seaming operations to produce a quality seam formed by the machine’s seaming rolls as the can body and can end are held together by a vertical load applied between the lower lifter and the seaming chuck as the can parts move through the machine. During this seaming cycle the can end and can body meet, and the first-operation seaming roll contacts the can end and begins curling the can end around the can body flange. A second-operation seaming roll follows, which tightens and irons out the seam between the can body and can end forming an airtight hermetic seal between the two parts (see Figure 2).

Double seam made of five layers compressed and ironed tightly to form a hermetic seal
Double seam made of five layers compressed and ironed tightly to form a hermetic seal. Figure 1.
A schematic of the double-seam process
A schematic of the double-seam process. Figure 2.

The double seam is a critical can component for a proper seal. Every angle, radius, and dimension must be correct to ensure a hermetic seal (4). The double seam is defined as follows: ‘‘The curl on the can end containing sealing compound and the flange on the can body are indexed and rolled flat, forming five folds of metal. Sealing compound between folds gives an airtight seal (5).’’

METHOD OF SEAMING

There are two basic seamer designs: can spin and can stand still. Practically all closing machines designed in the early years were of the can stand still type incorporating up to four seaming heads and operation at speeds ranging from 25 to 275 cans per minute. The can-stand-still design is still used extensively and in many cases is a necessity due to the products being closed, such as shortening or some fine powders. In this design the nonrotating can body and can end are assembled between the knockout rod pad and the lower lifter or base plate table. The knockout rod pad keeps the can end firmly in place as the lower lifter (which is synchronized with the knockout pad) raises the can body and can end into the seaming position on the seaming chuck. First operation seaming rolls, which are diametrically opposite each other in a seaming head, revolve around the stationary seaming chuck, and pressure is applied through cam action to form the first operation. After the first operation is completed to the proper thickness, the second-operation seaming rolls, which are diametrically opposite each other, iron out the double seam to the proper thickness. After the seaming operations are completed and the second-operation seaming rolls have been released, the knockout rod follows the seamed can away from the seaming chuck as it is being lowered to the discharge position by the lower lifter (6).

As canning speed requirements increased, can spin or rotating-can-type seamers were developed using a multistation design. Machines with 4 to 18 seaming stations are in use, providing production speeds of 100–2300 cans per minute (see Figure 3). Can ends are automatically separated and mated with the can bodies in the seaming position. The knockout rod pad contacts the can end while the lower lifter, synchronized with the knockout rod pad, lifts the can body and can end into position on the seaming chuck. On thin-walled lightweight cans the machine design incorporates driven seaming chucks and driven lower lifters to prevent can skid or can buckling. One first operation seaming roll actuated by a cam forms the first operation seam. After completion of the first operation seam, the second operation seaming roll actuated by a similar cam action irons out the seam to the proper thickness.

Can seamer
Can seamer. Figure 3.

MACHINE TYPE BY APPLICATION

Can seamers are typically manufactured in five machine types for seaming can ends to can bodies: can shop, atmospheric, mechanical vacuum, steam vacuum, and undercover gassing.

  1. Can shop. For can manufacturing: this attaches the first end on three-piece cans. 
  2. Atmospheric. For can closing products not requiring removal of oxygen for preservation—that is, soaps, petroleum products, frozen products, and hot products>180°F. 
  3. Mechanical vacuum. Evacuates oxygen from headspace of can for preservation of product at slow speeds—that is, vegetables, specialized powdered products. 
  4. Steam vacuum. Evacuates oxygen from headspace of can with steam for preservation of product at high speeds—that is, fruits, vegetables, soups, fish, meat products, and juices. 
  5. Under-cover gassing. Displaces oxygen in headspace of can with a gas, such as carbon dioxide or nitrogen, to extend shelf life and/or increase internal can pressure for thin-walled aluminum cans—that is, beer and soft drinks. 

Generally, during the process of a modern automated canning operation, cans are filled with a measured amount of product, then transferred from the filler to the can feed table of the seamer. This transfer from the filler to the seamer is critical and must be timed in such a manner to avoid can damage, product spill, or extreme product agitation, thereby rendering a smooth flow of cans and product into the seamer. As the cans move into the seamer, they are sensed by a mechanical, electrical, or optical device that triggers a signal to separate one can end from a stack and feed it in a synchronized rotary manner to an incoming can. Generally, the timing of machine operations is mechanically controlled by cams and there is a dwell period for steam vacuum and undercover gassing applications as stream or gas is injected between the top of the open can and the can end prior to their contact. Filling the headspace of cans with steam or gas displaces the air, preserving the quality of the canned product. After the can parts meet, they move through the seaming cycle of the first and second seaming operations and then the cans are discharged from the machine.

MACHINE SETUP

Can seaming machines are designed to double-seam a given range of can diameters, can heights, and speeds. Can diameters and can heights are expressed in both inches and millimeters, but generally use an industry nominal diameter, such as 200, 202, 206, 207.5, 209, 211, 300, 303, 307, 401, 404, 502, and 603. Industry nominal diameters are defined as follows: The first digit equals inches; the second and third digits equal 1/16 fraction of an inch. For example, a can with a nominal 211 diameter would be the equivalent of 211 16 in. and a can with a nominal 307 diameter would be the equivalent of 3 7 16 in.

It is very important that the machine be setup to the correct specification for the type of can end and can body, diameter of the can end and can body, and material thickness of the end and can body. Important setup procedures include the following:

  1. Checking the fit of seaming chuck to can end. 
  2. Initially installing only the first operation seaming rolls. Remove second-operation seaming rolls if in place. 
  3. Installing seaming chucks and checking that the first operation seaming rolls do not interfere with the seaming chucks when in the seaming position. 
  4. Setting lower lifter assemblies to correct height relationship with can feed table. 
  5. Setting lower lifter spring pressure to proper load with an appropriately calibrated instrument, such as a Dillon force gauge or force cell gauge. 
  6. Setting pin height with an appropriately calibrated instrument, such as a pin height gauge or planer gauge. 
  7. Setting the first operation seaming rolls on each station to a specified seam thickness using a wire gauge of the proper diameter. Run samples of firstoperation seamed cans to verify quality of seam. Visually inspect seam while measuring the seam thickness, seam width, and countersink depth. 
  8. Installing and properly adjusting the second operation seaming rolls to the seaming chucks on all stations to the specified seam thickness. Run samples of the finished second operation seam. Visually inspect the seam while measuring the seam thickness of the finished seam to given specifications using a properly calibrated seam micrometer. Finally, tear down the second operation seam for further inspection. 

KEY FEATURES AND ATTACHMENTS 

Depending on the application and production requirements, can seamers are equipped with features and various attachments to meet the demands of industry processors.

Automatic Stops. For safety reasons, machines are equipped with mechanical, electrical, or optical sensors that cut power to the motor, actuate the clutch release unit, and apply the brake to stop the machine rapidly. These safety devices are located at critical areas on the machine. 

Filler Drive Seamer Safety Clutch. A safety overload clutch is used to protect the can seaming machine in case of a severe can jam or mechanical failure in the filler. In-Motion Timer. This is a timing attachment located between the seamer and filler that synchronizes the transfer of cans from the filler pockets to the seamer feed chain fingers during machine operation.

Can Coding Markers. There are two types of markers—mechanical and ink-jet—used to place the processor’s identification code on can ends. Mechanical markers use type dies that are capable of debossing and embossing identification characters on can ends. Debossing is where the characters are indented into the top of the can end, and embossing is where the characters are raised on the top of the can ends. Mechanical markers are driven by the seamer and have speed limitations up to 1000 cans per minute. They are used primarily on sanitary food cans. Ink-jet markers are not driven by the seamer and use a nozzle assembly device to print droplets of ink to make up characters forming alphanumeric or bar codes. Ink-jet markers apply clear codes to virtually any surface at nearly any production speed, using a programmable controller and software to monitor the ink quality, size, font, and lines of print.

Automatic Lubrication. Metered amounts of grease and/or oil are automatically delivered by pumps to designated machine areas requiring lubrication while the machine is operating.

Automatic Oil Lubrication Recirculating and Filtration System. This system continually filters water and particles from the recirculating oil. The lubricating oil is pumped and recirculated through the machine, reducing the amount used and the environmental concerns of discarding cycled oil.

Programmable Controller. This provides electrical monitoring of seamer functions and operates auxiliary equipment.

Driven Lower Lifters. Also referred to as driven lower chucks or driven baseplate tables. They accept incoming can bodies or product-filled cans from can infeed devices before being raised by a cam action to meet can ends to be seamed at the make up area. They are gear-driven and rotating in a synchronized design with the seaming chucks to provide stability and enhance can control during the seaming cycle process. Driven lower lifters use a preset spring pressure, which is a vital component in the formation of a double seam.

SEAM TIGHTNESS EVALUATION

Generally, in order to stand the rigors of processing, handling, damage by abuse, and distribution, as well as to ensure product shelf-life, the tightness of the seam is critical and should be evaluated carefully. During the formation of a double seam the proper tightness assures that the sealing compound will fill all the spaces not occupied by metal.

Seam tightness is normally evaluated by the degree of waviness or wrinkle found in the cover hook. This wrinkle is formed by compression of the curled outer edge of the can end as it is folded back under the body flange. By increasing the pressure of the seaming rolls, the wrinkle can be ironed out to a smooth strip; and by loosening the rolls, the wrinkle is increased (7). Wrinkles may be classified by a tightness (wrinkle) rating as shown in Figure 4. A 70% wrinkle rating equates to a 30% wrinkle in the cover hook or 70% of the cover hook is wrinkle-free. Less than 70% tightness is considered too loose. There are other numerical cover wrinkle rating systems used: The Dewey and Almy wrinkle rating uses a 0–10 scale in which absence of wrinkle rates as 0 and a full-width wrinkle rates as 10: another uses a 0–3 rating system. The rating for each end component is based on the worst or deepest wrinkle, because it is at this point or area that the seam is most vulnerable to abuse, leakage, and penetration by bacteria.

Wrinkles are rated by the percentage of tightness
Wrinkles are rated by the percentage of tightness. Figure 4.

In hemming a straight edge of metal, no wrinkles are formed. On curved edges, wrinkling increases as the radius of curvature decreases. For this reason, different wrinkle ratings are specified for small-diameter cans as compared to large-diameter cans (8). A 100% wrinkle rating of a 211 diameter can indicates that the seam may be too tight and should be watched for possible defects such as cutovers, droops, and unhooking. A 100% wrinkle of a 603 diameter can would not necessarily be too tight. With most can seamers using standard seaming roll profiles, the ideal seam almost invariably shows a slight wrinkle, except on 603 diameter and other large-diameter containers.

MEASUREMENT OF PERCENTAGE OVERLAP

The overlap of a double seam is expressed as a percentage of the maximum possible overlap. A minimum percentage of 55% is considered acceptable. The percentage overlap of the seam is established by first measuring the internal seam length, a measurement between the inside of the cover hook and the inside of the body hook, and rating this length as 100. The measured length of the actual overlap is then a portion or percentage of that length calculated (B/A100 = percentage overlap) (see Figure 5).

Overlap measurement
Overlap measurement. Figure 5.

PROFILES OF SEAMS

A properly formed first-operation and second-operation double seam requires the correct adjustments of pressure of the seaming rolls and lower lifter or base plate table. The shape and conformity of the finished seam is determined by the taper and fit of the seaming chuck to the top of the end component and the contoured profile of the seaming rolls. The seaming roll profile is a groove around the circumference of the roll which varies with the diameter of the can to accommodate variations in material, material thickness, cover curl, body flanges, and seam specifications of the user. For any given can diameter, there may be a number of roll profiles, which will properly form the double seam. Firstoperation and second-operation roll profiles are uniquely different. As the first operation seaming roll profile contacts the cover curl, the flange of the can bends over to form the body hook and the edge of the cover tucks underneath to form the cover hook. The second-operation seaming roll profile completes the seam formation by compressing the seam so that the hooks interlock tightly and any metal voids or spaces are filled with the sealing compound.

OTTO L. HECK

RICHARD CABORI

Angelus Sanitary Can Machine

Company, Los Angeles,

California