Comprehensive control on the three-piece can sealing process

Abstract: This paper mainly discusses the various influencing factors of the three-piece can sealing process from the sealing structure and principle, and clarifies how the sealing and quality of various food and beverage cans are comprehensively controlled from the perspective of actual production links and quality control inspection. .
Key words: sealing structure and principle; influencing factors of double crimping; three-level inspection network
The tinplate three-piece cans are currently viewed from the overall market situation, although the overall quality exists, mainly in the performance of the film, weld seam, sealing, sterilization and sealing. This article only talks about the comprehensive control of the sealing process in the production process of empty cans, for reference only.
I. Analysis of the influencing factors of double crimping from the principle of sealing
The sealing process of the tinplate three-piece can (or two-piece can) is done by the double crimping method. The double hemming method refers to two winding rollers with different groove shapes. The two sides of the feeding movement are combined at the joint of the can body and the can lid, so that the hook edge of the can lid is hooked with the can edge of the can body. Press tight to achieve the purpose of sealing. Simply put, the first side of the roll is hooked and the two sides are pressed tightly.
In the sealing device, the winding roller, the upper pressing head and the tray can are generally referred to as three sealing elements. The correct groove shape of the roller, the proper position of the indenter and the appropriate driving force of the tray are necessary to ensure proper sealing. (See Figure A1) It is not difficult to see that the three elements of sealing are the basic components of the sealing equipment, and they are also the basic factors affecting the double crimping.
There are several factors that affect the double crimping:
1. Physical properties of iron materials
Such as material, hardness, etc., especially relatively small can diameter (such as 202D diameter can) If the tinplate material is thin and hard, the sealing requirements will be more difficult, because in this case the process of double crimping The plastic deformation of the material is small, but the wrinkles are larger.
2. Suitable sealing pressure
As shown in Fig. A1, during the rotary motion of the can body, the winding force P of the roller groove at the junction with the can lid is caused by three different directions of radial force Pr, axial force Pa and tangential force Pt. The synthesis of force. The role of the first winding force P(1) is mainly the bending deformation of the material around the can body and the cover. The main compression force of the two winding force P(2) is plastic deformation. The calculation of the two crimping forces is carried out by energy balance and plastic deformation. Generally, the two winding force is 2 to 3 times the head winding force.
In the actual operation process, the proper sealing force is achieved by the proper matching position relationship between the winding roller, the pressing head and the tray tray (such as the adjustment of the inner and outer gaps of the roller and the pressure head).
3. Empty can process
Different cans of can lids and cans must meet the corresponding technical requirements, such as poor welding before sealing (>05mm tailing, welding crack), too large and too small edge will affect the empty can Coiling performance.
4. The groove shape and material requirements of the coiled roller
In general, different can-type closure rollers have different groove shapes. Generally, the grooves of the head roller are deep and narrow, and the grooves of the two rollers are wide and shallow. At present, most of the reeling gears used in domestic sealing equipment are medium carbon steel such as 45# and 40Cr, and the service life is short. The output is limited to 20,000 to 300,000 cans. The coils commonly used in advanced sealing equipment are generally 4Cr13, 9Cr18 and other stainless steel. It is made by vacuum heat treatment and has high hardness and good wear resistance. The service life can reach about 10 million cans.
Among the three elements of sealing, the coiled roller is a wearing part, and should be polished or replaced with 1000# or 1200# water-based sandpaper according to the production situation, so as not to affect the process performance of the crimp sealing.
5. Coating state of the coating
The coating distribution of the inner film of the can lid is about 70% in the hem and about 30% in the plane. In addition, the amount of film should meet its own process requirements. If the amount of glue is too large, it will form an extrusion glue, and the amount of glue will be too small to function as a sealing filler.
6. Operator's correct operation and adjustment
The skilled technical skills and level of operation of the operator, and the necessary routine maintenance and maintenance are also factors that affect the double crimping. For example, when the tank type is changed or the coil seal is abnormal, necessary adjustments are required. In addition to replacing the necessary parts, correct and reasonable adjustment is also critical. Generally, under the appropriate driving force of the tray, first check the width TC of the head side (2.20±0.10mm), and then visually measure the tightness of the curl around the lid. When the two sides are finished, the seal is tested. Check for appearance defects and various dimensional process requirements. Make correct adjustments and judgments for the formation of different defects before making adjustments. Note: (1) The size specification is measured by anatomical experiment; (2) The head side curling is the basis and premise of the two-side crimping, and it is generally checked at least once a week during normal production.

7. The integrity of the equipment
The integrity of the sealing equipment directly affects the sealing performance of the sealing process, which is related to the operator's correct operation and maintenance.
8. Use of can lid (easy lid or bottom lid)
In theory, the easy-opening or bottom cover produced by different manufacturers should have interchangeability with the indenter. However, in fact, there are many domestic production lines for can ends. The size specifications of the canned products produced are still different from the international regulations. The main performance is in the height of the cans and the height of the hooks. The other dimensions are not much different, as shown in Figure A2. See GB/17590-1998 54) Therefore, pay attention to the following aspects in the actual use process: (1) The material of the easy open cover or the cover should be good, both have certain tensile strength and certain flexibility. (2) structural size (mainly hook outer diameter D1 hook height H and countersunk head C); (3) sealant dry amount; (4) breaking force (pull ring easy opening cover EOE ≥ 1.3kgF, full Open cover FOE ≥ 15kgF); (5) easy to open the cover, the bottom cover and the pressure head should be tightly fitted (the former can be slightly rotated with each other, the latter is relatively tight); (6) before the production of empty cans Or after the actual tank sterilization, it is advisable to apply a proper amount of liquid paraffin or vegetable oil to the curling part to prevent mechanical abrasion and rust.
Second, the process requirements of the double crimping from the sealing structure
The appearance requirements of the easy-opening three-piece can sealing process are mainly as follows: (1) The double-rolled edge should be even and smooth, and the surface has no obvious oil stains and damage; (2) The curled portion must not have a sliding seal, a false roll or a curled edge. Defects such as splitting, double-line, and extrusion; the size requirements are mainly as follows: (1) The crimping dimensions of different can types include the width of the bead, the thickness of the bead, the height of the bead, the hook of the body, and the hook of the cover; Process size requirements, (2) overlap length and overlap ratio, tightness, seam cover hook integrity.
The double-edged sealing structure can be sampled by a can edge cutter, and the hook state of the body hook BH of the can body and the lid hook CH of the can lid can be clearly seen on the projector. Its five-layer structure is shown in Figure A3 (Seal structure diagram)
So, how do you get a good sealing structure and normal curling during empty can production or solid can filling? From the quality control requirements, we must pay attention to and meet the following points:
1. The three-point size (W, T, H) of the edge sealing anatomy should be uniform and the internal dimensions (BH, CH) should not exceed the given value. (Note: The external dimensions must have sufficient curl width W, reasonable T value, and at the same time consider the factor of OL% reduction of 7% to 8% for every 0.1 mm increase in W.)
2. Connect the length OL and the lap rate OL%. When the aluminum alloy is easy to open, OL ≥ 0.95 ~ 12mm, OL% ≥ 60% ~ 75%; OL ≥ 100mm when the bottom of the horse can be opened or easy to open, OL% ≥ 50%. OL and OL% can be used in three methods: calculation method, projector arbitration method, and table lookup method (see GB/T14251-93).
3. Grain WR% and tightness TR%. The tightness of the sealing structure is an important indicator of the sealing requirements of the can. It is usually evaluated by the degree of wrinkles on the inside of the lid when visually anatomically experimenting, as shown in Figure A4, WR% is 0% to 20% I (normal). , 25% to 50% II degree (relatively loose), 60% to 100% grade III (unqualified) level 3, that is, the corresponding TR% ≥ 75% (sealing aluminum alloy easy open cover TR% ≥ 60%, sealing plating The bottom cover of the tin sheet or the easy opening cover TR ≥ 50%).
4. Sewing hook completeness rate JR%. Refers to the fact that the outer edge of the weld seam is not formed by the effective inner hook due to the inner drip lip. Generally, under the condition of satisfying OL, OL% and TR%, JR% is not required (visually JR%≥65%). )
With reference to the calculation formula and parameters: (1) T = 3tC + 2tB + G (G takes 0.15 ~ 0.25mm); (2) OL = BH + CH + 1.1tC-w; (3) OL% = BH + CH + 1.1tC-w / w (2.6tC +1 .1tB) × 100% (the denominator is the theoretical splicing length, the numerator is the actual splicing length); (4) the upper gap UC < 0.4 mm, and the lower gap LC ≤ 0.25 mm.
Third, the necessity and importance of establishing a three-level inspection network
The production of the three-piece cans of tinplate is the assembly line operation, and the problems in each production process will directly affect the normal operation of the next process. Therefore, in order to obtain a good quality of the crimping seal, quality control inspection must be carried out between the various processes to eliminate the problem before the production process, so as not to flow into the finished product.
The three-level inspection network is the production self-inspection of this process, the quality inspection of the front and back processes and the quality sampling in the production process. A three-level inspection network has been established to ensure product quality. Sealing quality is inseparable from the three-level inspection network.
In the quality inspection process of the finished product, the sealing quality is an important indicator of the overall quality inspection. Under the conditions of the external process, the main attention is to the sealing, chipping, extrusion, cuffing, card, etc. .
2. Sealing structure and size requirements.
3. Sealing requirements. The empty pressure inside the empty tank is 0.15MPa and the pressure is kept for 1min without leakage, rising tank and deformation. If the real tank is sterilized by high temperature (121°C/20~30min), the tank will not rise and leak.
In short, through the analysis of the above aspects, we have a preliminary understanding of the quality and comprehensive control of the sealing process. When there are different defects in the quality of the crimping, we can make timely and accurate analysis and judgment.