About the comprehensive control of the sealing technology of tinplate cans

First, analyze the influencing factors of double hemming from the principle of sealing

The sealing process of tinplate cans is completed by the double crimping method. The double hemming method refers to two roll-sealing rollers with different groove shapes. Through a sequence of two feed movements, the can ends are joined to the can body flanges at the junction of the can body and the can lid. , Pressing, so as to achieve the purpose of sealing. In simple terms, the first channel is crimped and the second crimped.

In the sealing equipment, the roll seal roller and the top pressure head support tray are often referred to as the seal three elements. The correct groove shape of the roller, the reasonable position of the indenter and the proper driving force of the tray are the necessary conditions to ensure a normal enveloping. (See Figure 1) 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 physical properties of tinplate materials

Such as material, hardness, etc., especially relatively small can diameter (such as 202 diameter cans). If the material of the tinplate is thin and its hardness is high, the difficulty of the denser requirement will be greater, because in this case, the plastic deformation of the material during the double curling process will be smaller, and the wrinkles will be larger.

2, the appropriate seal pressure

As shown in Fig. A1, during the rotating motion 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 P1 is mainly the bending deformation of the can body and the surrounding material of the cover. The compression of the second roll sealing force P2 is mainly manifested as plastic deformation. The calculation of the two rolling forces is performed by 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 roll-sealing force is achieved by properly matching the positional relationship between the roll-sealing roller, the indenter and the support tray (such as the adjustment of the inside and outside clearance of the roller and the indenter, etc.).

3, empty tank process size

Different pot-shaped can ends and flanges of the cans must meet the corresponding process requirements, such as bad welding before sealing (>0.5mm tailing, welding cracks), too large and small flanging can affect the empty cans. Roll sealing performance.

4、Roller shape and material requirements of roll sealing roller

In general, the 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, and the output is limited to only 2-30000 cans; the more commonly used reeling equipment commonly used reels are generally 4Cr13, 9Cr18, etc. After vacuum heat treatment, its high hardness, good wear resistance, long life, can make about 10 million cans.

In the three elements of sealing, the sealing roller is a wearing part. It should be polished or replaced with 1 000# or 1 200# water-based sandpaper in time depending on the production conditions so as not to affect the process performance of the crimp sealing.

5, the coating coating state

The correct coating position distribution of the inner film of the can ends is about 70% inside the hook and about 30% at the plane. In addition, the amount of plastic modulus must meet its own process requirements. Excessively large amounts of glue tend to form squeezing gums. When the amount of glue is too small, the effect of sealing packing cannot be achieved.

6, the operator's correct operation and adjustment

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, when a can type or a roll seal abnormality needs to be changed, the correct and reasonable adjustments other than the replacement of necessary components are also critical. In general, under the proper driving force of the tray, firstly check the width Tc (2.20±0.10mm) of the head-side width, and then visually measure the tightness of the curl around the lid, and then perform the test after two rounds of crimping. 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 integrity of the equipment

The intactness 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, the use of the lid (easy to open or bottom cover)

In theory, the bottom cover produced by different manufacturers should have interchangeability with the indenter. However, in fact, there are many domestic can lid production lines, and there are still certain differences between the sizes of can lid products produced and the international regulations, which are mainly reflected in the height of can lids and hooks, and other dimensional deviations are not as shown in Fig. 2.

Therefore, in the actual use of the process should pay attention to the following aspects: (1) the bottom cover material is better, not only a certain tensile strength, but also have a certain degree of flexibility; (2) structure size; (3) sealant dry amount (4) breaking force; (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 relative to each other, the latter is relatively tight); (6) empty can production drop cover Before or after sterilization, apply a suitable amount of liquid paraffin or vegetable oil to the curling area to prevent mechanical abrasion and rust.

Second, from the sealing structure to see the double curling process requirements

The appearance requirements of the tinplate can sealing process mainly include: (1) The double curl must be even and smooth, with no obvious oil stains and damage on the surface; (2) The curled area must not have slip seals, false rolls, crimps, double Defects such as wire and squeezed glue; specification and size requirements are mainly expressed in: (1) The crimp size of different cans must meet the corresponding process size requirements; (2) overlap length and overlap ratio, tightness, seam cover hook Complete rate.

The double-seam sealing structure can be sampled by a can edge cutter, and the hook of the body hook BH and the can lid CH can be clearly seen on the projector. Its five-layer structure is shown in Figure 3.

Then, how to obtain a good sealing structure and normal crimping in the production process of empty cans or solid cans? From the quality control requirements, we must pay attention to and satisfy the following points:

1, W, T, H

The three-point dimensions (W, T, H) must be uniform in the crimping and closing anatomy experiment, and the deviation of the internal dimensions (BH, CH) must not exceed the given value.

2, overlap length OL and overlap rate OL%.

When the aluminum alloy is easy to open, OL≥0.95mmm～1.2mm, OL%≥60%～75%, and OL≥1.00mm, OL%≥50% when the tinplate is closed or easy to open. OL and OL% are available in three methods: calculation method, projector sizing method, and look-up table method.

3, wrinkle degree WR% and tightness TR%.

The tightness of the sealing structure is an important indicator of can sealing performance. It is usually assessed by measuring the degree of wrinkle in the cover hook during visual anatomical experiments. As shown in Figure 4, the WR% is 0% to 20% of the level I, 25 ~ 50% II degree, 60% ~ 100% III grade III, that is, the corresponding TR% ≥ 75%.

4, the joint cover hook integrity rate JR%.

Refers to the fact that the outer edge of the finger-weld cover hook is formed due to the lack of an effective cover hook. Generally, under the conditions of OL, OL% and TR%, JR% is not required.

Third, the necessity and importance of establishing a three-level inspection network

The production of tin cans and cans for pipelines is an assembly line operation. Problems in each production stage will directly affect the normal operation of the next process. Therefore, in order to obtain a good seal quality, quality control inspections must be performed between processes to eliminate the problems in the production process so as not to flow into the finished product.

The three-level inspection network is the production self-inspection of the process, the quality of each process before and after the process, 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 quality inspection process of the finished product, the sealing quality is an important indicator of total quality inspection. Under the condition of satisfying the external process dimensions, the main attention should be paid to: 1. Slipping, chipping, squeezing, flanging, and notching Cans, etc.; 2, sealing structure and size requirements; 3, sealing requirements. Empty tank air pressure 0.15Mpa pressure 1min no leakage, tank and deformation, if the real tank can not rise under high temperature sterilization pressure relief and leakage.

In short, through the above analysis, 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 crimping quality.