Discussion on the manufacturing process of metal packaging cans

The traditional production method of Metal Packaging cans is: first, the metal blanks are cut into squares, then the blanks are rolled into cylinders (ie, cylinders), and then the formed longitudinal bonding wires are soldered to form side sealing, one of the cylinders. The ends (ie the bottom of the tank) and the round end caps are mechanically flanged and rolled (ie double crimped seams) to form the can body; the other end is closed after the product has been filled. As the container is composed of three parts: the bottom of the tank, the body of the tank, and the lid of the tank, it is called a three-piece tank. This type of can making method has been largely unchanged for more than 150 years. It has only been greatly improved in terms of automation and processing accuracy. In recent years, the side-sealed weld has been replaced with fusion welding.

In the early 1970s, a new canning principle emerged. According to this principle, the can body and the bottom of the can is a single body, which is stamped and formed from a round flat blank. After the product is sealed, it is a two-piece can. There are two types of molding methods for such cans: stamping - thinning stretching (ie drawing and drawing) and stamping - re-stamping (ie deep drawing). These technologies are not new in themselves. Drawbacks were used to make shells as early as World War I. The difference between canning is the use of ultra-thin metals and the high production speed (the annual output can reach hundreds of millions).

1 Three-piece can manufacturing

The production process is: cutting the coil into rectangular plates with a shearing machine; painting and mounting printing; cutting a length of billet; rolling into a cylinder and welding side seams; repairing the joints and coating; cutting the barrel; forming a recess Slots or corrugations; flanges are pressed at both ends; rolled back; check and code on pallets.

1 cylinder processing. The key process is coil forming and welding side seams. Side sealing methods are soldering, welding and bonding three.

Solder tin solders typically consist of 98% lead and 2% tin. The cylinder forming machine for rolling the flat blank into a cylinder is used in pairs with a side seam sealing machine for soldering. In the cylinder maker, the edge of the slab is cleaned and bent into a hook shape, which facilitates fixing when the cylinder is formed. The barrel is then passed through a side sealer, plus solvent and solder, preheated in the sealing area with a gas torch, heated by a longitudinal soldering roller, the solder is then filled with seams, and then the excess of the solder, mainly in the form of drops The solder is clean.

Welding is the use of self-contained wire electrode principle, the use of resistance welding process. The earlier welding systems used large laps to increase the temperature of the steel to the melting point and weld it at a lower roller pressure. The latest welders use small overlaps (0.3-0.5mm), the metal temperature is just below the melting point, but the pressure of the welding roller must be increased to forge the two overlapping surfaces together.

The weld breaks the original or painted smooth surface of the inner surface so that exposed iron, iron oxide, and tin are present on both sides of the weld. In order to prevent the product from being contaminated and the weld seam from being eroded by the product, in most cases the side seals need to be coated.

Side seals for tanks containing only dry products can be glued. That is, the longitudinal seam is pasted with a nylon belt, and the nylon belt melts and condenses after the cylinder is formed. The advantage is that the original edge can be completely protected but can only be used for TFS because the melting point of tin is close to the melting temperature of the plastic.

2 simplified post processing. Flanges must also be machined at both ends of the Simplified to install the end caps. For processed food cans, the cans may be subjected to external pressure during processing or may be internally vacuumed during storage. In order to increase the strength of the tank, the simplified surface may also need to make ribs. This process is called crimping. In order to increase the production efficiency, the length of the shallow container made of shallow containers is usually two to three cans. At this time, the first procedure is to cut the cylinder. The traditional method is to form the front blank on the cutting machine (notch machine). Make an unbreakable cut. However, the recent development of the tank trim shears developed for two-piece can production.
2 Manufacture of two-piece cans

Both methods of forming two-piece cans are formed using sheet metal forming methods. This method is based on the "fluidity" of the metal exhibited by the rearrangement of the crystal structure under the action of the composite stress, and the material should not break during this process.

1 stamping molding. That is, a punch is used to punch a flat plate into a cylindrical die to deform the flat plate into a cylinder. The diameter of the cup formed after the initial stamping can be reduced by applying a re-punching process. The re-punching process replaces the die with a stamped sleeve and is mounted between the punch and the inner diameter of the cup. The equal area rule determines that the increase in height is accompanied by a decrease in diameter. The re-stamping process can be repeated once more. The book diameter is gradually reduced within a certain limit, and the metal is prevented from breaking.

2 cups of thinning stretch. The stamped cylindrical cup is placed on the punch, and the punch is axially squeezed into a mold. The clearance between the mold and the punch is smaller than the thickness of the cup wall, so that the wall thickness is maintained when the diameter remains unchanged. Thinned. After thinning, the metal volume of the barrel is equal to the metal volume of the cup during thinning and is also equal to the metal volume of the original slab. In the manufacture of the tank, this process is repeated two or three times, and the punch with cup passes through a series of molds one after another through one mold. The most convenient method for installing the stamped forest on the punch is to perform a re-pressing operation before the first thinning.

3 punch cupping manufacturing. The manufacturing process of cupping and cupping is generally as follows: unfolding a common strip coil; Xu lubricant; blanking and cupping; re-punching; thinning and stretching of the sidewall of the cup; bottom forming; Simplified cutting at the correct height; cleaning and handling . For dry beverage cans, exterior coating, printing, inner surface coating, flange formation and closing of open ends are also required. For food cans, external coating, open-end flange molding, cylinder crimping, and inner surface coating or can end during cleaning are fabricated on pre-coated panels on multi-die presses. There are ripples (ribs) to take internal and external pressure. The final process here is the crimping to form a double crimp seam (see Figure 1). Place filler on the final seal to act as a sealing gasket.

Figure 1 double curl sealing
1-End cap crimped and folded over the flange of the cylinder 2- Seal packing 3 - Sealing overlap amount 4 - Tube 5 - End cap

4 deep-impregnated tank manufacturing. The steps for making a deep-flush can are as follows: the thin strip coil is cut into a vortex-like sheet; the sheet is coated and finished (also can be coated with a coil); the blank blank is blanked and the cup is washed; Or two times, depending on the size of the tank); Forming of the bottom of the tank; Edge trimming to the correct width; Inspection and sterilization.

Like the punching process, a multi-die punching machine is used to load and unload a wide roll of sheet material or plate and punch it into shallow cups.

Shallow cups are gradually reduced in diameter and height by once and twice re-pressing. When the final punching is stopped to a certain extent, a flange is left on the can, like all other sheet metal forming processes. Irregular edges are cut off and the bottom of the tank is machined to the desired shape.

3, processing equipment

The main equipment for can making processing includes various press forming machines, shear blanking machines and other auxiliary equipment. There are many kinds of these devices and it is impossible to introduce them. In view of the fact that the modern can making industry adopts the features of automated production, this chapter only takes the composition of the canning and cupping production line (Figure 2) as an example to give a brief explanation.

Figure 2 composition of the cupping production line
l-Extruder 2 - Checking and Lubricant Coating Equipment 3 - Single Liner Stretching Machine (Simplified) 5 - Cutting Machine
6-tank cleaning machine 7 - External surface coating equipment 8 - Box furnace 9 - Full equipment 10 - Box furnace 11 Noodle - flange forming machine
12-Inspection Machine 13 - Internal Sprayer 14 - Curing Oven 15 - Local Secondary Spray 16 - Curing Oven

Sheet rolls are transported by the transporter to the unwinder (draft stand). The decoiler typically has two arms, one arm facing the sheet roll carrier and the other arm feeding the press. The roll can be replaced by the swivel arm. Sheet rolls are passed through lubricant coating equipment, coated on both sides with a lubricant, and passed over a pair of rubber rollers to remove excess lubricant. On older production lines, the lubricant is formulated to a correct concentration and then held in a In the container, add it to the lubricant tank as needed. In newer production lines, an external circulation system is generally used, which can perform temperature control, continuously filter and maintain constant lubricating oil quality.

The cup press is a specially designed double action press which first punches down several round blanks and then punches the round blank into a shallow cup shape. Both actions are completed in one journey.

The function of the cup wall ironing machine is to convert the cup into a cylinder with a properly distributed sidewall thickness and to turn the cup bottom into a design shape that resists internal pressure during use. Here, the cup is re-punched and left on the punch, and then passes through three thinning draw rings in order to thin the cup wall. At the end of the journey enter the auxiliary press, forming a round arch and a cup bottom. At the beginning of the return journey, the spring ejector rod unloads the can body from the punch by means of the compressed air sent from the punching tube, and the can is sent out of the machine by the conveyor belt.

Each cup wall thinning deep drawing machine works in conjunction with a trimming machine. Edge trimmer has two types of guide rail and roller. The rotary frame of the rail edge trimmer is equipped with a plurality of cores, and the can edge is cut between the rotating core and the stationary rail. On a roller type edge trimmer, one end of the can is fed between two rollers and rotates around its own axis. The two rollers pick up each other to complete the trimming action.

After the cans are cut at a fixed height, the cans are opened downwards and turned upside down on a mesh conveyor belt. They are transported in large quantities to a series of cleaning chambers equipped with spray nozzles, and are pressed and thinned with detergent. The lubricant used is washed off and finally rinsed in ion-free water to ensure no smearing and drying.

A flange molding machine closes the mouth of the beverage can and flanges, while the food can is formed by crimping and flanges. In order to avoid the metal axial surface roughness caused by thin drawing, the flange molding generally adopts spinning process. The constriction of the top of the beverage can can be retracted with a mold after spinning the flange.