Rice. 1. During the rolling cycle of the vertical roll feed system, the leading edge “bends” in front of the bending rolls. The freshly cut trailing edge is then slipped over the leading edge, positioned and welded to form the rolled shell.
Anyone who works in the metal fabrication industry is likely to be familiar with rolling mills, whether they be pre-nip mills, double-nip three-roll mills, three-roll geometric translational mills, or four-roll mills. Each of them has its limitations and advantages, but they have one thing in common: they roll sheets and plates in a horizontal position.
A lesser known method involves scrolling in the vertical direction. Like other methods, vertical scrolling has its limitations and benefits. These strengths almost always solve at least one of two problems. One of them is the effect of gravity on the workpiece during the rolling process, and the other is the inefficiency of material processing. Improvements can both improve the workflow and ultimately increase the competitiveness of the manufacturer.
Vertical rolling technology is not new. Its roots can be traced back to several custom systems created in the 1970s. By the 1990s, some machine builders were offering vertical rolling mills as a standard product line. This technology has been adopted by various industries, especially in the field of tank building.
Common tanks and containers that are often produced vertically include those used in the food, dairy, wine, brewing, and pharmaceutical industries; API oil storage tanks; welded water tanks for agriculture or water storage. Vertical rolls significantly reduce material handling, often provide better bending quality, and more efficiently handle the next step of assembly, alignment and welding.
Another advantage is shown where the storage capacity of the material is limited. Vertical storage of slabs or slabs requires less space than storing slabs or slabs on a flat surface.
Consider a shop in which large-diameter tank bodies (or “layers”) are rolled on horizontal rolls. After rolling, operators perform spot welding, lower the side frames, and extend the rolled shell. Since the thin shell sags under its own weight, it must be reinforced with stiffeners or stabilizers or rotated to a vertical position.
Such a high volume of operations—feeding planks from horizontal to horizontal rolls only to take them off after rolling and tilt them for stacking—can create all sorts of production problems. Thanks to vertical scrolling, the store eliminates all intermediate processing. Sheets or boards are fed vertically and rolled, secured, then lifted vertically for the next operation. When heaving, the tank hull does not resist gravity, so it does not bend under its own weight.
Some vertical rolling occurs on four-roll machines, especially for smaller tanks (typically less than 8 feet in diameter) that will be shipped downstream and processed vertically. The 4-roll system allows re-rolling to eliminate unbent flats (where the rolls grip the sheet), which is more noticeable on small diameter cores.
In most cases, the vertical rolling of tanks is carried out on three-roll machines with double clamping geometry, fed from metal plates or directly from coils (this method is becoming more common). In these setups, the operator uses a radius gauge or template to measure the radius of the fence. They adjust the bending rollers when they touch the leading edge of the web, and then again as the web continues to feed. As the bobbin continues to enter its tightly wound interior, the springback of the material increases and the operator moves the bobbin to cause more bending to compensate.
The elasticity depends on the properties of the material and the type of coil. The inner diameter (ID) of the coil is important. Other things being equal, the coil is 20 inches. The ID is wound tighter and has more bounce than the same coil wound up to 26 inches. IDENTIFIER.
Figure 2. Vertical scrolling has become an integral part of many tank field installations. When using a crane, the process usually starts on the top floor and works its way down. Notice the only vertical seam on the top layer.
Note, however, that rolling in vertical troughs is very different from rolling thick plate on horizontal rolls. In the latter case, the operators work diligently to ensure that the edges of the sheet match exactly at the end of the rolling cycle. Thick sheets rolled to narrow diameters are less reworkable.
When forming can shells with roll-fed vertical rolls, the operator cannot bring the edges together at the end of the rolling cycle because, of course, the sheet comes directly from the roll. During the rolling process, the sheet has a leading edge, but will not have a trailing edge until it is cut from the roll. In the case of these systems, the roll is rolled into a full circle before the roll is actually bent, and then cut after completion (see Figure 1). The freshly cut trailing edge is then slipped over the leading edge, positioned, and then welded to form a rolled shell.
The pre-bending and re-rolling in most roll-fed machines is inefficient, meaning that they often have breaks at the leading and trailing edges (similar to unbent flats in non-roll-fed rolling). These parts are usually recycled. However, many businesses see scrap as a small price to pay for all the material handling efficiency that vertical rollers provide them with.
However, some businesses want to get the most out of the material they have, so they opt for built-in roller leveler systems. They are similar to the four-roll straighteners on roll handling lines, only turned upside down. Common configurations include 7-roll and 12-roll straighteners that use a combination of take-up, straightener and bending rolls. The straightening machine not only minimizes the dropout of each defective sleeve, but also increases the flexibility of the system, i.e. the system can produce not only rolled parts, but also slabs.
The leveling technique cannot reproduce the results of the leveling systems commonly used in service centers, but it can produce material flat enough to be cut with a laser or plasma. This means manufacturers can use coils for both vertical rolling and slitting.
Imagine that an operator rolling a casing for a section of a can receives an order to send rough metal to a plasma cutting table. After he rolled up the cases and sent them downstream, he set up the system so that the straightening machines were not fed directly into the vertical windrows. Instead, the leveler feeds a flat material that can be cut to length, creating a plasma cutting slab.
After cutting a batch of blanks, the operator reconfigures the system to resume rolling of the sleeves. And because it rolls horizontal material, material variability (including different levels of elasticity) is not a problem.
In most areas of industrial and structural manufacturing, manufacturers are looking to increase the number of factory floors to simplify on-site fabrication and assembly. However, this rule does not apply when it comes to the manufacture of large storage tanks and similar large structures, mainly because such work involves incredible difficulties in handling materials.
The roll-fed vertical swath used on site simplifies material handling and optimizes the entire tank fabrication process (see fig. 2). It is much easier to transport rolls of metal to the job site than to roll a series of huge profiles in the workshop. In addition, on-site rolling means that even the largest diameter tanks can be produced with just one vertical weld.
Having an on-site equalizer provides more flexibility for site operations. It is a common choice for on-site tank fabrication, where the added functionality allows manufacturers to use straightened coils to fabricate tank decks or tank bottoms on-site, eliminating transport between the shop and construction site.
Rice. 3. Some vertical rolls integrated into the on-site tank production system. The jack lifts the previously rolled course up without the use of a crane.
Some on-site operations integrate vertical swaths into a larger system, including cutting and welding units combined with unique jacks, eliminating the need for on-site cranes (see Figure 3).
The entire reservoir is built from top to bottom, but the process starts from scratch. Here’s how it works: The roll or sheet is fed through vertical rollers just a few inches from where the tank wall should be. The wall is then fed into guides that carry the sheet as it passes around the entire circumference of the tank. The vertical roll is stopped, the ends are cut off, stabbed and a single vertical seam is welded. Then the elements of the ribs are welded to the shell. Next, the jack raises the rolled shell up. Repeat the process for the next cake below.
Circumferential welds were made between the two rolled sections, and then the tank roof was fabricated on site – although the structure remained close to the ground, only the top two shells were fabricated. Once the roof is complete, jacks lift the entire structure in preparation for the next shell, and the process continues—all without a crane.
When the operation reaches its lowest level, slabs come into play. Some field tank manufacturers use plates that are 3/8 to 1 inch thick, and in some cases even heavier. Of course, the sheets are not supplied in rolls and are limited in length, so these lower sections will have several vertical welds connecting the sections of the rolled sheet. In any case, using vertical machines on site, the slabs can be unloaded in one go and rolled on site for direct use in tank construction.
This tank building system is an example of material handling efficiency achieved (at least in part) by vertical rolling. Of course, like any other method, vertical scrolling is not suitable for every application. Its applicability depends on the processing efficiency it creates.
Assume a manufacturer installs a no-feed vertical swath for a variety of applications, most of which are small diameter casings that require pre-bending (bending the leading and trailing edges of the workpiece to minimize unbent flat surfaces). These works are theoretically possible on vertical rolls, but pre-bending in the vertical direction is much more difficult. In most cases, vertical rolling of large quantities, requiring pre-bending, is inefficient.
In addition to material handling issues, manufacturers have integrated vertical scrolling to avoid gravity (again, to avoid flexing large unsupported shells). However, if the operation only involves rolling a sheet strong enough to retain its shape during the entire rolling process, there is no point in rolling that sheet vertically.
Also, asymmetrical jobs (ovals and other unusual shapes) are usually best formed on horizontal swaths, with top support if desired. In these cases, the supports not only prevent sagging due to gravity, they guide the workpiece during the rolling cycle and help maintain the asymmetrical shape of the workpiece. The complexity of manipulating such work vertically can negate all the benefits of vertical scrolling.
The same idea applies to cone rolling. Rotating cones rely on friction between rollers and pressure differential from one end of the roller to the other. Roll the cone vertically and gravity will add complexity. There may be exceptions, but for all intents and purposes, a vertically scrolling cone is impractical.
The use of a three-roll machine with translational geometry in a vertical position is also usually impractical. In these machines, the two bottom rolls move side to side in either direction, while the top roll is adjustable up and down. These adjustments allow the machines to bend complex geometries and roll material of various thicknesses. In most cases, these benefits are not increased by vertical scrolling.
When choosing sheet rolls, it is important to conduct a careful and thorough research and take into account the intended production use of the machine. Vertical swaths have more limited functionality than traditional horizontal swaths, but offer key advantages when it comes to proper application.
Vertical plate rolling machines generally have more fundamental design, performance and design features than horizontal plate rolling machines. In addition, the rolls are often too large for the application, eliminating the need to include the crown (and the barrel or hourglass effect that occurs in the workpiece when the crown is not properly adjusted for the job being done). When used in conjunction with unwinders, they form thin material for entire workshop tanks, typically up to 21’6″ in diameter. The top layer of a much larger diameter field-installed tank may have only one vertical weld instead of three or more plates.
Again, the greatest advantage of vertical rolling is in situations where the tank or vessel needs to be built upright due to the effect of gravity on thinner materials (up to 1/4″ or 5/16″ for example). Horizontal production will require the use of reinforcing rings or stabilizing rings to fix the round shape of the rolled parts.
The real advantage of vertical rollers lies in the efficiency of material handling. The less manipulation you need to make with the body, the less likely it is to be damaged and reworked. Consider the high demand for stainless steel tanks in the pharmaceutical industry, which is busier than ever. Rough handling can lead to cosmetic problems or worse, damage to the passivation layer and product contamination. Vertical rolls work in tandem with cutting, welding and finishing systems to reduce the chance of manipulation and contamination. When this happens, producers can benefit from it.
FABRICATOR is North America’s leading steel fabrication and forming magazine. The magazine publishes news, technical articles and success stories that enable manufacturers to do their job more efficiently. FABRICATOR has been in the industry since 1970.
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Post time: May-07-2023