My opinion on the quality of steel barrel curling

My opinion on the quality of steel barrel curling

Luo Weinan

China's accession to the WTO shows that China's economy is an indispensable part of the world economy. It also means that we will face more and stronger competitors. The new economic environment is an environment full of fierce competition. Joining the WTO will bring new opportunities for our economic development, but it will also bring many new and more serious challenges.

The 21st century is the era of the world's new economy, the knowledge economy. The new economy is characterized by knowledge/technology, especially with high technology to improve product quality, increase production and improve economic efficiency. In the past decade or more, reform and opening up have not accelerated the development of China's economy and science and technology. The steel drum manufacturing industry has also achieved great development and progress; the processing technology has been developed from manual (especially in small and medium-sized barrel factories) to machinery-based; tooling equipment has been developed from machinery to mechanical + liquid + gas; The method is developed from manual single machine to part or take part automatically or semi-automatically. The double five layers of steel barrel curling are mainly developed into three layers and seven layers. Thereby, the internal and external quality and production efficiency of the steel drum are stepped up. However, we still have a considerable gap with the advanced level of developed countries. We still do not have the conditions for full competition with them. The leakage of our export steel drums has occurred from time to time. However, we still believe that the new economic environment of the 21st century will undoubtedly bring new development opportunities to our barrel industry like reform and opening up. We have the confidence, determination and ability to meet new challenges. Seize the opportunity to accelerate development and participate in the new round of fierce competition in the world economy.

First, the question is raised

In the new century, the new economy requires our enterprises to "provide the provision of material and spiritual civilization to the society, and to continue, develop, and move into a new era, becoming the mainstay of the social economy in the new era." If a company does not catch up with the new economy in the short period of time - the train of knowledge and technology, then our company has created a lot of glory in the past, and will not go too far to be eliminated, this should not be It is an alarmist, but it should be inevitable. This is what we often call the sense of urgency and anxiety. In view of the above considerations, I will talk about some experiences and opinions from my own practice.

Regardless of the design of any component, equipment and components, the R&D or designer is designed according to its function and purpose according to certain scientific methods. Although we say that the quality and production efficiency of steel drums have reached a new level, there are still no clear explanations and solutions to major quality problems such as crimping. In the articles and monographs on the quality of steel drums, it is only said that “the reasonable and correct curve shape of the joint edge size of the steel ladder semi-finished product (the crimping wheel) must be determined, that is, the reasonable and correct curling The process parameters "," must be grasped according to the contour elements of the wheel groove to correctly determine the shape of the wheel groove, and the groove groove shape can effectively 'control' the objective law of the formation of the crimping structure. Combined with the repeated practice of the test paper profile, Grasp the formation relationship between the groove profile and the hemming structure, in order to guide the design, manufacture, installation and adjustment of the roller, and provide a reliable theoretical basis for finally obtaining a satisfactory crimping structure. "But none of them clearly has a good sealing performance. The formation of the steel drum curl, which structural elements are related to, and the requirements for determining these elements, therefore, the relevant personnel can not make a normative design that meets the requirements of the formation of the curling edge. Due to the different points of view of the developer, the shape after crimping is naturally varied. The double five-layered edge is also the same, and the triple-seven-layered side also has a triangle, a semicircle, a circular scroll, and a trapezoid. Although the curling of various shapes has no obvious advantages and disadvantages, this is the final curling shape formed by the two-roller rolling. The final shape of the crimping does not need to be mandatory for all designers. Appropriate to a design pattern, and the designer must also comply with the most critical: the bottom of the bucket and the barrel are tight: the shape of the head roller groove should be shaped to ensure that the curl is curled by the head wheel The trend of the back layer is to conform to a certain curve and the trajectory of the moving point on the curve, and it must be smooth and wrinkle-free, and should have the same shape and size to ensure that the final formed curl is strongly curled and shaped by two rounds. And rolling, so that the roll not only seals but also forms enough additional stiffness and strength. The phenomenon of open <rolled loose> and over-rolling is also not allowed. Therefore, the quality of the steel barrel bead can only be fully guaranteed if the relevant structural elements are subjected to the necessary specifications and in accordance with the specifications.

Second, the formation of the curl

For crimping, generally, a hemming wheel having two different groove profile shapes is used, and the outer edge of the flange of the barrel body and the bottom cover of the barrel bottom cover is continuous in the order from the outside to the inside ( Rotating) Curling and rolling, so that the material of the crimping material is strongly elastic and plastically deformed along the curve of the tire (commonly known as the sealing flange) according to the shape set by the crimping wheel, and the crimping material of the joint is made. Close together and tightly. Since the bottom cover flange is pre-rolled and glued before the barrel and the bottom cover are overlapped, most of the production plants apply a layer on the flange surface of the inner edge of the bottom cover pre-bead before the cover is closed. Very thin sealant is true, so during the crimping process, when the crimping material is strongly crimped and rolled, the sealant is filled between the layers of the rolls, so that the layers are fully integrated, and the crimping is achieved. Rigidly sealed and required to have sufficient stiffness and strength.

The essence of the crimping process is the process of the barrel body flanging and the bottom cover flange material undergoing the final permanent plastic deformation from the initial elastic deformation under the strong continuous curling and rolling action of the two crimping wheels. Usually the groove profiles of the secondary crimping wheel are composed of several different segments. In order to facilitate the distinction and communication, it is generally customary to call: straight lead-in section A, transition arc section B and working section (the head wheel should be called the coiling working section, and the second wheel should be called the shaping working section) C. Figure 1

Third, the pressure analysis of the crimping process

When the curling begins, the outer edge of the body flange and the bottom cover flange overlaps into the head wheel groove, and the section A and the partial transition arc B are linearly introduced in the wheel groove profile. Under the combined action, the material begins to bend due to side pressure and warp pressure - elastic deformation. If the hemming wheel is removed from the material at this time, the bottom cover flange will return to its original state under the reaction of the internal stress and the flange of the barrel (the result of the material rebound). In the elastic section where the material begins to elastically deform, the amount of deformation depends on the material (the amount of carbon and inversely proportional to the carbon content) and the slope of the straight lead-in section A and the curvature of the partial arc B. The size of the roller; afterwards, as the crimping wheel continues to press down, the contact length of the material with the transition arc increases and extends to the crimping section C. The material is under the control of the groove profile due to the sharpness of the lateral pressure and the radial positive pressure. Increase, causing large bending deformation of the material. At this time, even if the curling wheel is removed to make it out of contact with the material, the material cannot be restored to its original state. At this time, the material also undergoes plastic (permanent) deformation. The fundamental reason for the plastic deformation of the material is that under the strong curling pressure of the crimping wheel, the stress formed inside the material has far exceeded its elastic limit and reached the requirement of plastic deformation of the material. As the head wheel continues to feed, the crimping material is continuously interrupted by the transition arc to the crimping section C. The crimping working section is a key section of whether the crimping can be rolled up according to the number of layers specified by the design, the amount of hook head overlap, and the winding state of the winding layer (Fig. 2). The variation of the radius of curvature of the section and the selection of the minimum radius depend on the material thickness and mechanical properties, and of course the factors such as the radius of curvature of the pre-reel groove profile working section must be taken into account.

Plastic rolling stage

After the curling and rolling of the curling head wheel, the trend of the curling layer, the basic shape and the tightness can be obtained. However, it is not tight enough or incomplete. Some of the crimping materials have not yet been crimped into place, and the shape has not met the design requirements. Therefore, the crimping has not yet formed sufficient additional rigidity and strength. For this purpose, the beading needs two rounds for further strong shaping and rolling, which can be a complete process.

In the initial stage of the second round of pressing, the material that has not been crimped in place is further curled along the deepening section of the lead-in section, and the side pressure PM acts when the rolled outer layer material is pushed to the M point (Fig. 3). The center roll layer will also be further pushed to make the roll hooks more overlapping and closer. When the two wheels continue to press down, the radial pressure P2 will be greater than the shaping component Pm to further roll the wound layer to achieve the full integration and tight requirements of the wound layer.

The crimping is strengthened by two rounds (according to the relevant department, the two-wheel force P2 is about twice the radial force P1 of the head wheel); the shaping and rolling, the crimping material can be fully in place, and at the same time The effect of hardening promotes an increase in stress within the material, promoting stable plastic deformation of the wound layer and sufficient rigidity and strength.

Curve of four or one wheel groove profile

In a long period of time, through a planned and selective (different specifications, different material thickness) to cut and analyze one or two curls, it is considered that the forming principle of the curling is like the crepe paper in daily life. The rolling trend is just like the horizontal projection of the conical spiral (Figure 4). The horizontal projection of the conical spiral is the Archimedes vortex. The theoretical basis for determining the profile of the head winding wheel groove working segment as the Archimedes vortex line is: "A moving point of the curling edge 5 rotates around a certain center, while leaving it according to a certain law, leaving The distance is proportional to the angle of rotation of the moving point. The rotation of this moving point is the Archimedes vortex. Therefore, the C-profile design of the working section of the head wheel groove must conform to the definition of the vortex line, so as to ensure the good overlap between the barrel body hook and the cover hook and the integration of the winding layer; while the two-wheel groove profile is only It needs to be divided into two sections, namely the straight lead-in section A and the shaping section C. The slope of the straight lead-in section is small, about 2/3 of the head wheel; the shape of the working section C is a positive arc. If the slope of the lead-in section of the two-wheel groove is too large, the barrel will be inevitably flashed during the rolling process, and even more, the crimping and breaking will occur. The shape of the segment plays a decisive role in the final shape of the bead, the geometry and the tightness of the bead.

Five, the forming elements of the curling and its determination

How do you achieve the hook overlap, number of layers and final shape requirements after the flange of the barrel and the flange of the bottom cover are sealed? At the time of design, it is necessary to first determine a reasonable combination of the dimensions of the semi-finished material of the steel drum (including the width of the flange of the barrel and the width of the flange of the bottom cover) and the correct shape of the profile of the one or two crimping wheel grooves, that is, a group is reasonably correct. Process parameters. Reasonable refers to the number of layers of the layer specified by the designer, regardless of the thickness of the hook and the cover hook (degrees), whether it is five or seven layers. The degree of overlap can also be obtained by using the overlapping number calculation formula to measure the tightness and strength of the crimping edge. Correctly, whether the first and second crimping wheel groove profiles can smoothly curl the laminated material according to the trend of the rolled layer. Roll-formed and conform to the shape and dimensions specified by the design to ensure that the steel drum is leak-free and has sufficient stiffness and strength.

The curling forming elements mainly include:

1. The width of the edge of the barrel, the corner of the board and the fillet radius of the transition arc;

2. The flange width of the bottom cover of the barrel, the slope of the straight wall of the bottom cover deep section and the fillet radius R of the rounded ends of the straight wall section;

3. The shape and size of each line segment of the first and second crimping wheel groove profiles:

4, pre-roll and spray glue.

The basic relationship between the width of the flange and the bottom flange of the steel barrel and the thickness of the material (Fig. 5)

The calculation formula adopted by the American barrel industry:

Bottom cover flange width: F=19t:

Bucket width: B=0.44F

The calculation formula adopted by the domestic straight side:

Bottom cover flange width: F=23t

Bucket width of the body: B = 0.4lF;

The calculation formula adopted by the author for the triple round curl:

Bottom cover flange width: F=23t

Bucket width: B=O.54F

In the above formula:

T——material thickness, mm

F——Bottom cover flange width, mm

B——the width of the flange of the barrel, mm

In the design of the body flange, not only must there be enough flange width, but also determine the reasonable flange angle, the transition fillet radius and the billet taper of the bucket flange after the flange (circle 6). The purpose of the burring angle is to overcome the side pressure from the leading edge of the beading wheel when the bottom cover flange starts to curl, and to ensure that the flange does not "sit" and pass the two rolls under the combined action of the side pressure and the radial pressure. When pressing, there is no "crushing", and the corner angle is usually 105±5; the radius of the transition arc is the integration of the layer when the flange and the flange are curled, eliminating the gap between the layer and the edge of the barrel. When the apex of the corner is rolled, the flange of the bottom cover is split at the intersection of the curl and the straight wall; the value is usually R=3~5 mm, and the relative bending radius r/t of the material is 2.5~4, the degree of deformation in the rounded area is relatively large, and the variation of the bending half is generally not large, which is convenient for the cooperation with the bottom cover flange. If the value of R is larger, the relative bending radius r/t is larger, and the fourth angle is also increased. The increase of the four corners of the corner will bring a large curvature to the curved rice. At this time, the curl at the beginning of the curling is unfavorable, and even the "reverse" roll of the pre-hem.

Regarding the taper of the flange blanking edge (the inner edge of the flange face), the flange is an elongated type due to the flanged edge or the edge of the flange, and the outer edge of the flange is subjected to tangential pulling. Stretching and thinning must be supplemented by the flow of material, otherwise the outer edge of the flange will be cracked (such defects often occur when the material elongation is between 3 and 5%). Due to the material flow, the material below the flange surface of the barrel is pulled, and the barrel below the flange surface forms a certain taper; generally less than 3? (Fig. 7).

The bottom wall of the bottom cover of the bucket must be tightly matched with the wall of the bucket below the flange surface of the bucket. In the design of the bottom cover, the slope of the straight section of the bottom cover should be 0.052 to 0.061, that is, X=3 to 3.5. The slope. The whole meaning is that the bottom cover and the barrel blank are automatically aligned when the cover is closed, and the finished product is automatically unloaded on the activity tablet; more importantly, the bottom cover is deep and the tight fit of the barrel blank is ensured. At the same time, it is necessary to determine the corner radius R1 and R2 which are reasonable and suitable for the rounded corner of the barrel blank and the rounded corner of the rolled steel ring, so that when the steel drum collides, the bottom cover and the barrel body rise when the pressure drops or the pressure inside the barrel rises. Work together.

In addition to the above, the factors involved in the good sealing and corresponding strength of the steel drum bead are closely related to the radius of curvature of the pre-bead, the amount of glue applied, and the physical and chemical properties of the glue. We have mentioned that the sealing of the crimping edge must rely on the integration of the wound layer and the sufficient overlap of the body hook and the lid hook, and the small gap between the layers of the rolls and the top end of the hook of the hook must be filled with a full sealant. In order to ensure the correct toothing of the body hook and the cover hook and the amount of overlap (the value of the overlap calculation is not less than 0.45%) and the tightness of the center of the curling, the bottom cover flange must be pre-rolled and sprayed in advance. Glue treatment. The groove shape of the pre-reel is exactly the same as the groove structure of the head roller. The difference is only in the size and radius of curvature of each segment, but the curve of the working segment must be a vortex. At the same time, the whole process of pre-rolling is only part of the hemming process to ensure that the pre-hem has sufficient notch width (normally b=1.2~1.5t, Figure 3). The purpose of the pre-rolling is to ensure that the tooth hooks of the body hook and the cover hook overlap and the center of the roll layer is sufficiently tight after rolling, and the wear of the arc of the working wheel of the wheel head wheel and the change of the main body when the head wheel starts to curl are reduced. The force condition, while reducing the splash loss during the glue injection and ensuring that there is enough sealant in the tiny gap of the hook end of the hook.

It is necessary to remind that in order to ensure a very thin sealant between the layers of the rolled edge, a thin seal should be applied to the flange of the bottom cover and the flange of the barrel before the cover is closed. Glue (commonly known as bottom cover glue), its thickness can generally be controlled at 0.12 ~ 0.20 mm (dry glue).

The above is the author's experience and suggestions for improving the quality of steel drums, reducing unqualified losses, improving first-class product rates, enhancing the competitiveness of steel drums, welcoming WTO entry and seeking common development.

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