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Lock Seamed Tubes Explained

The lock seamed tube is a clean, efficient and low cost process for the generation of tubes from coil stock for a variety of industrial uses.

Perhaps the most significant development driver for the lock seamed (small diameter) tube has been (and continues to be so) is the filtration industry. The requirement to ever more efficiently filter liquids has been driven by the development of increasingly complex and finely toleranced mechanical systems. Where there is a relative movement by either translation or rotation, the provision of a lubricant enhances both the longevity and the efficiency of a mechanical system. The last twenty five years has seen materials technology and the manufacturing processes associated with these materials develop at an unprecedented pace. Correspondingly, the humble filter has been transformed from a relatively simple device to an extremely sophisticated system designed to operate for longer, with greater efficiency at increasingly smaller microscopic levels and at higher pressures. With each requirement offering a natural paradox to the other it is easy to understand at least some the complexities now faced by filtration companies.

A basic filter comprises a number of elements including the core, the filtration media, an outer wrap and casing. It is the purpose of the core and outer wrap (the filter tubes) to support the far more vulnerable filter media and prevent its collapse when it is subjected to the passage of fluids at high operating pressures. To allow this process to take place, not only must both the supporting core and the outer wrap contain holes but also they must retain sufficient strength to prevent collapse. Naturally as operating pressures increase so must the tubes' inherent strength.

The Linear Lock Seamed Tube

In the past, almost entirely, (and indeed for many applications today) the tubes were formed by wrapping a pre-cut steel blank around a circular shaped former and closing it with a linear lock seam. The blanks are invariably cut from coiled stock; this stock material is mostly either ferrous based with coatings or stainless steel, the ultimate application range of the filter dictating the appropriate material selection. Prior to the forming of the filter tube, this coil is de-coiled and fed through a perforating press where the holes or perforations are put into the strip. The strip is then either re-coiled for later use or fed immediately into the tube forming process. The forming process takes the strip and levels or flattens it before it is guillotined or cut-to-length – depending upon the orientation of the strip at the point of guillotining the width of the strip can be used to form either the diameter (in-line set up) or the length (90 degree set-up). The individual, cut blanks are then processed through a bodyformer (Meltog LTM157, BM125 or BM252) where they are formed into filter tubes.

From as far back as the mid-1950's, Meltog has been manufacturing LTM (linear tube machinery) lines. Today there are many examples and many combinations of Meltog linear lock seam filter tube lines in use throughout the world. The process is extremely stable and delivers up an exceptional tube at very high output speeds.

Meltog LTM lines continue to be the first choice for many filter tube applications.

The Spiral Lock Seamed Tube

As material costs have increased, particularly over the last decade, filter tube manufacturers have increasingly looked for ways to mitigate that effect. In tandem with this cost driver is the desire to reduce the environmental impact of all products. We see this effect all around us in our everyday lives from the stronger and safer yet lighter motor vehicles to the knives and forks we use at meal times. The volume of filters produced worldwide is simply staggering, the largest market is automotive, but industrial and pharmaceutical as well as aeronautical applications all use filtration products in vast quantities. A fortunate irony for the filter companies is that a filter is ultimately a sacrificial device – if it isn't then its not working! With a few exceptions, the humble motor car will use between 3 and 10 filters throughout its life. The ability of a filter to be effectively recycled is therefore a most important consideration. One way in which manufacturers have helped to achieve both of these goals is by reducing dramatically the material gauge of the core and outer wrap tubes. In most instances they have achieved this by adopting the spiral tube manufacturing process.

A spiral tube is formed from coil and wrapped in a continuous helix around a former. The joining method is exactly the same as the linear tube counterpart, the lock seam. In forming a lock seam, four material thicknesses are used, as each side to be joined has a hook formed at its edge; in a linear seam this is along its length; however in a spiral tube, the seam is a helix wrapped all the way around the tube. Therefore for a given material gauge, a spiral wound tube would be significantly stronger than its linear counterpart. Filter companies have adopted the natural extension of this process by determining that for a given set of operating criteria, material gauge can be reduced significantly without any detrimental affect on performance. For a single filter this alone would not make a great deal of difference, however with filter companies making batches that extend in to hundreds of thousands – this represents a massive saving and an even bigger boost for the environment.

Meltog is amongst the pioneers of this process, recognising both the importance and application of this technology in the late 1970's. The company's first machine, the STM200 came to market in the early 1980's and since that time a number of companies have emulated the technology but Meltog machinery remains the standard to which all others aspire.

Offering industry beating efficiency in both power consumption and material utilisation, the standard equipment comprises a single compact machine which can be coupled to any feasible combination of coil handling options. All Meltog STM machinery can work with mild steel based coils through to stainless steels and uniquely, all with the same ease of set up and operation.

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The History of the LTM

Long before the application of spiral tube technology, Meltog was manufacturing machinery for the production of filter cores. The late 1950's saw the company take a natural step in applying its technology for linear lock seam container machinery, developed over the previous two decades, to the production of filter (tube) cores. It is perhaps a little known fact that the technology used in the manufacture of decorative containers is analogous to that of the filter tube. Both are formed and held together, in shape, with a mechanical lock which is formed from the product itself, by a feature which is commonly referred to as the “lock seam". Indeed many of the decorative (fancy) cans that one sees on supermarket shelves the world over (biscuit tins, whisk(e)y tins etc.) are probably produced on Meltog equipment. The simplicity and cleanliness of this method of manufacture affords significantly lower capital investment costs, a fully decorated surface (important for fancy can) and less specialist knowledge than other joining methods like a welded seam.

The most significant difference between fancy can machinery and filter tube machinery is the energy requirement during the forming process. Typically a fancy can is formed from pre-printed (decorated) tin plate in thicknesses ranging from 0.20mm (0.008") to 0.3mm (0.012") – in their pre-processed form, these sheets are extremely vulnerable and are handled with the utmost care by the canmaker. However, once formed and seamed to a base or end, the structure becomes very rigid and is therefore able to afford multiple use long after the product originally supplied in it has been consumed. A filter tube on the other hand is formed from a range of materials (from stainless steels through coated steels or aluminium) which can vary from between 0.2mm (0.008") up to 1mm (0.040") in gauge, depending upon the rigours of the intended application. Naturally filter tubes are not decorated but they do have considerably greater inherent strength and rigidity due to a combination of material choice and cross section. The filter tube forming machine is therefore of a more robust construction and is more powerful than its than its decorative counterpart.

Designated as the LTM (Linear Tube Machine) range, Meltog's first machine, the LTM157, was a derivative of its decorative BM157 bodymaker. Although principally the same, this workhorse machine was re-engineered for the rigours of filter tube production. The first such machine available was equipped with a stack feeding system which allowed pre-cut, pre-perforated blanks to be continuously loaded into a magazine hopper thereby affording continuous machine operation.

Although the LTM157 has been mechanically revised several times over the past four decades and now incorporates advanced safety, control and monitoring systems, the standalone LTM157 variant is still available for the high speed, economical production of filter tubes.

In developing the range and to offer the filter manufacturer a larger range of tube diameters, Meltog re-engineered the BM157's larger sibling the BM613. Badged the LTM613 and developed along the same principals as the LTM157, the 1960's saw Meltog offering two variants of standalone filter tube machines covering a diverse range of sizes suited the majority of volume produced, filter applications.

Naturally, the simplicity of the standalone machine required more labour intense processes to be carried out prior to the tube forming process. In particular, the filter blanks would originally come from a plain (slit to width) coil; this coil would be de-coiled and fed through a perforating press (to produce the holes), some times re-coiled thereafter before being decoiled again and cut to length (to produce the blanks), before finally being stacked in magazines in readiness for the LTM. In addressing this issue, the late 1960's saw Meltog integrate into its LTM tubeformers a number of processes and variations within those processes to reduce manning, time and skill. Amongst these features are once only decoiling and strip flattening followed by in-line perforating, in-line cut to length and automatic LTM feeding. In addition the basic LTM machine, no less than 12 variations of this equipment is available and is in use today and linear technology is still the most prevalent production method for tube cores.

The 252 bodyformer, which was developed during the early part of the new millennium, represents the pinnacle of the development of this process.

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The History of the STM

For over 25 years Meltog has produced the STM (Spiral Tube Machine) range of machines. In the early 1980's, the original the STM200 revolutionised the production of filter tube cores delivering to the industry a level of versatility that had hitherto been unachievable. Not least the massive increase in the strength of the cores, the process's stability, and the equipment's compact footprint and reduced tooling inventory brought immediate bottom line improvements to the user. The Meltog system's unique tube cut off system remains to this day unrivalled in terms of quality, with consistent burr free tubes and process capability tolerances being easily exceeded.

The 1990's saw the introduction of the STM125; similar in appearance to its older sibling, this machine offered a reduced diameter capability in return for increased production speeds and a lower capital investment cost.

Both machines can be found in OEM, first and second tier, and aftermarket filter companies throughout the world.

The turn of the new millennium saw both machines fully re-engineered. Named the “Smart STM®" range, the machinery offers full backward tooling capability but with significant speed improvements, improved tooling geometry, reduced set-up times with industry leading repeatability and further process reliability. In another industry first, the re-engineering of the machine's drive system and with the increased frame stability an overall reduction in power consumption was achieved. Today the Meltog Smart STM range remains amongst the most efficient machine of its type on the market.

Being committed to continuous innovation, in 2004 Meltog unveiled the Smart STM125fc. Based upon the size capacities of the standard Smart STM125, the fc variant added a flying cut capability, raising outputs over the standard variant for short tubes by at least 2.5 times. A tube which therefore would have been produced at 30 per minute is produced at 75 parts per minute. Although featuring a number of innovative systems, the operators benefited from the continued simplicity and familiarity of the Meltog control system. Though perhaps the most unique feature, is the fc's dynamic tube measuring system; rather than relying on pre-determined, theoretical algorithms, the 'fc' measures tube length in real time, thereby compensating for both variations in material characteristics and operator setting. The result is a quality which is comparable to the benchmark, standard Smart STM125 /200, with a considerably enhanced output - a unique feat upon flying cut machines.

Today the Smart STM125's and STM200's set the standards by which others are judged. No range of machines can offer the diameter range, strip width and gauge ranges together with the ability to produce either single or double louver piercing in-line from plain strip. All STM 125/200's can produce tubes from plain, pre-perforated or expanded strip in materials ranging from tin plate to aluminised and zinc based materials up to stainless steel; all with industry leading quality.

The latest spiral tube machine innovation from Meltog is the STM75. This competitively priced machine addresses the high volume short length tube market and caters for tube diameters between 25mm (1") and 75mm (3") in a variety of materials with gauges between 0.2mm (0.008") and 0.4mm (0.016"). Only one standard strip width is offered; 47.2mm (1.858"), but as is expected from a Meltog STM a variety of material specifications (i.e. tin-plate or stainless etc) and types (plain, pre-perf or in-line louver) are all available to the user. Tool changeovers are again straight forward and rapid with a cast-iron repeatability. Despite the STM75 being the highest output machine in the Meltog range, it still retains excellent 'green' credentials as it requires the least power of all variants on offer. A derivation of Meltog's tube cut off principle is included on the machine ensuring the end user with a high quality 'best in class' result.

“STM" is a brand of Meltog.

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Comparison Between Linear Lock Seam and Spiral Lock Seam

Linear Lock Seamed Tubes Cell Characteristics

  • High output, typically rates from 60 up to 120 tubes per minute can be achieved
  • Exceptional tube quality both in roundness across the entire tube length as well as diametric
  • characteristics and overall length consistency.
  • Economical process for tube lengths up to 300mm and diameters up to 200mm
  • Low capital investment costs (excluding perforating press)
  • Corrugating option for increased tube strength or reduced material consumption

Spiral Lock Seamed Tubes Cell Characteristics

  • Highly flexible
  • Low capital investment cost
  • Minimal footprint
  • Economical operational costs
  • Outputs from 10 to over 100 tubes per minute
  • In process pierce and louver – up to 25% open areas
  • Stainless, tin plate, aluminised and zintec steels
  • Plain, pre-perforated or expanded mesh strip
  • Rapid set up /changeover
  • Standard diameters from 25mm to 200mm – infinite length
  • Inherent strength

As an alternative to providing pre-perforated tube; both processes can operate with expanded or plain strip – the former can provide a significant open area for maximum fluid flow (a typical application would be an air filter), the trade off being a reduction in strength; the latter can be used to form a plain tube if required.

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