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Keywords: 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 compared with previous years, and the overall quality exists, mainly in the following aspects: the performance of coating film, weld seam, sealing, sterilizing and sealing. This article is only for reference on the comprehensive control of the sealing process in the production process of cans.
First, analyze the influencing factors of double hemming from the principle of sealing
The sealing process of tinplate three-piece cans (or two-piece cans) is accomplished by double-crimping. The double-folding method refers to two roll-sealing rollers with different groove shapes. Through the sequence of two feed movements at the junction of the can body and the can lid, the hooks of the can lid are hooked with the can body flanges. Compaction to achieve the purpose of sealing. Simply put, that is the performance of the first road curling hook, two crimping molding.
In the sealing equipment, the sealing roller, the upper pressure head, and the tray plate are generally referred to as the sealing three elements. The correct groove shape of the roller, the proper position of the indenter and the proper driving force of the tray are the necessary conditions for ensuring a normal roll closure. (See Fig. A1) It is not difficult to see that the three elements of the seal are the basic components of the sealing equipment and are also the basic factors affecting double crimping.
There are mainly the following factors that affect double curl:
1. The right seal pressure
As shown in Figure A1, during the relative rotation of the can body, the roll sealing force P at the junction of the roller groove and the can lid is affected by the radial force Pr, the axial force Pa, and the tangential force Pt in three different directions. The synthesis of force. The function of the head sealing force P(1) mainly includes the bending deformation of the can body and the surrounding material of the cover, and the main compression force of the second winding force P(2) shows the plastic deformation. The calculation of the two roll seal forces is performed through energy conservation and plastic deformation. The general two-volume sealing force is 2 to 3 times the head sealing force.
In the actual operation process, the appropriate winding force is achieved by the proper matching position relationship between the winding roller, the indenter and the support tray (such as the adjustment of the inside and outside clearance of the roller and the indenter, etc.).
2. The physical properties of iron materials
Such as material, hardness, etc., especially relatively small can diameter (such as 202D diameter cans) If tinplate material is thin, high hardness, the difficulty of its sealing requirements will be more, because in this case the double curling process The plastic deformation of the material is smaller and the wrinkles are larger.
3. Empty cans
Different types of tank lid hooks, cans flange to meet the corresponding process requirements, such as poor sealing before welding (>05mm trailing, welding), flanging too small will affect the empty cans Roll sealing performance.
4. Groove groove shape and material requirements
In general, different tank-type sealing rollers have different groove shapes. In general, the grooves of the head rollers are deep and narrow, and the grooves of the two rollers are wide and shallow. At present, the commonly used reeling machines for domestic sealing equipment are medium carbon steels such as 45# and 40Cr, which have a short service life. The output is limited to only 20,000 to 300,000 cans; the more commonly used reeling equipment commonly used reels are generally 4Cr13 and 9Cr18 stainless steels. After vacuum heat treatment, its high hardness, good wear resistance, life up to 10 million cans.
In the three elements of the sealing, the sealing roller is a wearing part, and should be polished or replaced with 1000# or 1200# water-based sandpaper in time depending on the production situation, so as not to affect the process performance of the crimp sealing.
5. Coating coating state
The coating position distribution of the film inside the lid of the can lid is approximately 70% within the hook edge and approximately 30% at the plane. In addition, the film size must meet its own process requirements. Excessive amount of glue can easily form a squeezed glue, and if the amount of glue is too small, no seal packing effect can be achieved.
6. The correct operation and adjustment of the operator
The skilled technical skills and operating level of the operator, as well as the necessary daily maintenance and maintenance, are also factors that affect the double hemming. For example, in the case of a tank type change or the occurrence of a roll seal abnormality that requires necessary adjustments, in addition to replacing necessary components, correct and reasonable adjustments are also critical. Generally, under the proper driving force of the tray, firstly check the width (TC) of the head side (2.20±0.10mm), and then visually measure the tightness of the curl around the lid, and then perform the test after the second curling. Check appearance defects and various dimensional process requirements. Correctly analyze and judge the causes of different defects before making adjustments. Note: (1) Size specifications are measured by anatomical experiments; (2) The first pass is the basis and premise of the second pass. Normally, it is checked at least once a week during normal production.
7. The equipment is in good condition
The integrity of the sealing equipment directly affects the sealing performance of the sealing process, which is related to the correct operation and maintenance of the operator.
8. Use of can lid (easy opening or bottom lid)
In theory, the easy-open lid or bottom lid produced by different manufacturers should have interchangeability with the indenter. However, in fact, there are many domestic production lines for can lids, and there are still some differences between the sizes and specifications of can lid products produced, which are mainly reflected in the height of can lids and hooks. Other dimensional deviations are not large, as shown in Figure A2 (details) See GB/17590-1998 54) So in the actual use of the process should pay attention to the following aspects: (1) easy to open the lid or degree of cover material is better, not only have a certain tensile strength, but also have a certain degree of flexibility (2) structural dimensions (mainly hook-side diameter D1 hook height H and countersunk head C); (3) sealant dry amount; (4) breaking force (open-loop easy-opening cover EOE ≥ 1.3kgF, full Open cover FOE ≥ 15kgF); (5) Easy to open the lid, the bottom cover and the pressure head with the tightness should be appropriate (the former can be slightly rotated with each other, the latter is relatively tight); (6) empty cans before production cover down Or after the sterilization of the solid tank, appropriate amount of liquid paraffin or vegetable oil should be applied to the curling area to prevent mechanical abrasion and rust.
Second, from the sealing structure to see double curling process requirements
The appearance requirements of the easy-open-cap three-piece can sealing process are mainly expressed in: (1) The double-folding is to be uniform and smooth, with no obvious oil stains and damage on the surface; (2) The curled portion must not have slip seals, false rolls, and crimps. Cracks, double lines, squeezed glue and other defects; specifications and size requirements are mainly expressed in: (1) different cans of the curling size including curl width, curling thickness, high curling, body hook, cover hook; to comply with the appropriate Process size requirements, (2) overlap length and overlap rate, tightness, seam cover hook integrity rate.
The double-seam sealing structure can be sampled by a can edge cutter, and the hook state of the body hook BH and the lid lid hook CH can be clearly seen on the projector.
Then, how to obtain good sealing structure and normal crimping in the process of empty can production or solid can filling? From the quality control requirements, we must pay attention to and satisfy the following points:
1. The three-point dimensions (W, T, H) should be uniform when the side seals are dissected, and the deviations of the internal dimensions (BH, CH) must not exceed the given values. (Note: The external dimensions must have sufficient hemmed width W and a reasonable T value. At the same time, considering the increase in W at the time of debugging, the overlap rate OL% will decrease by 7% to 8%.)
2. Connect the length OL and the overlap ratio OL%. OL ≥ 0.95 ~ 12mm, OL% ≥ 60% ~ 75% when storing aluminum alloy easy to open the lid; OL ≥ 100mm, OL% ≥ 50% when sealing the bottom of the tin can or easy to open the lid. OL and OL% are available in three methods: calculation method, projector arbitration method, and lookup table method (see the provisions of GB/T14251-93).
3. Roughness WR% and tightness TR%. The tightness of the sealing structure is an important indicator of the can sealing performance. It is usually assessed by visually measuring the degree of wrinkle on the inside of the cover hook during visual anatomy experiments. As shown in Figure A4, the WR% is 0% to 20% I (normal). , 25% to 50% II degree (relatively loose), 60% to 100% III grade (unqualified) three grades, that is, the corresponding TR%≥75% (TR%≥60% of sealed aluminum alloy easy to open lid, seal plating Tin plate bottom cover or easy to open cover TR ≥ 50%).
4. Sew cover hook integrity rate JR%. Weld seam outside the curling cover hook caused by the lack of effective hanging hook caused by the inner lip, generally meet the OL, OL% and TR% of the conditions, JR% not otherwise required (visual measurement JR% ≥ 65% can be. )
With reference to the relevant calculation formula and parameters: (1) T = 3tC + 2tB + G (G take 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 length of overlap, the numerator is the actual overlap length); (4) the upper gap UC <0.4mm, the lower gap LC ≤ 0.25mm.
Third, the necessity and importance of establishing a three-level inspection network
The production of tinplate three-piece cans is a pipeline operation, and the problems that occur in each production process will directly affect the normal operation of the next process. Therefore, in order to obtain a good crimp seal quality, quality control checks must be performed between processes to eliminate problems before each production stage so as not to flow into finished products.
The three-level inspection network is the production self-inspection of this process, the quality of each process before and after the inspection, and the quality inspection during the production process. The establishment of a three-level inspection network ensures product quality. The sealing quality cannot be separated from the three-level inspection network.
In the finished product quality inspection process, sealing quality as an important indicator of total quality inspection, under the conditions of the external process to meet the requirements, mainly pay attention to the seam slippery seal, chipping, squeeze plastic, flanging gap, card cans, etc. .
2. Sealing structure and size requirements.
3. Sealing requirements. Empty tank pressure 0.15MPa pressure 1min no leakage, tank expansion and deformation, if the real tank high-temperature sterilization (121 °C / 20 ~ 30min) under pressure relief tank does not rise and leakage.
In short, through the analysis of the above aspects, we have a preliminary understanding of the quality and comprehensive control of the sealing process. We can make timely and accurate analysis and judgment when there are different defects in the crimp quality.
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