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365 days of lubrication-free continuous operation

Dry-running linear technology in diaper production systems

The output of these highly complex diaper production systems has tripled in recent years without any investment in new machines. This has been made possible firstly by the extremely high system availability and secondly by continual improvements to the production process. The set-up times have also vastly reduced. The necessary flexibility when switching between formats is provided by several products from a comprehensive modular range of linear bearings from igus® GmbH, which covers all requirements. T hese bearings continually stand up to demanding everyday operating conditions.

"A diaper production system in our company has a length of approximately 60 m" reports Thomas Heege, Head of Technology at ONTEX MAYEN GmbH. "Diapers are produced in a ‘one-step process’. That means that we have all the necessary raw materials in the form of rolls or powders. These are merged to produce the end product and packaged in a single process step. ." The Belgium company is the market leader for private label hygiene products and offers a broad range of products for baby, feminine, and adult hygiene. At the Mayen site, eleven systems produce diapers in all shapes and sizes for sale almost worldwide.

A few figures to start

A system produces and packs approximately 1,000 diapers per minute - that equates to approximately 17 diapers per second. The throughput time for each diaper is approximately two seconds. Between six and eight million diapers leave the company premises by truck every day. Diapers differ from one end consumer to the next. Different raw materials, weights, and compositions apply depending on the drug store chain, discount store, or grocery store. One customer wants a particularly white product, another wants a particularly colorful one. "Australian diapers have pictures of kangaroos while in other countries they have comic figures", explains Thomas Heege. "Despite this, the requirements always remain the same. Diapers must essentially be easy to handle, leak-free, and soft on babies’ bottoms!"

The diaper manufacturer has many customers and must therefore be able to guarantee system reliability and flexibility during production and packaging. All changes to orders or sizes give rise to set-up times and adjustments. "Each machine is typically subjected to four size changes per week, which equates to over 200 size changes per year. There are also three product changes, resulting in at least 30 per day", the Head of Technology considers. But the requirements profile is still broader yet. "Our systems run 24 hours a day, seven days a week. That means that they’re used continually for almost 365 days a year. " The high process speed also subjects the systems to high dynamic loads of up to 600 m/min.

Depending on the process, there is usually a warm ambient temperature in the production hall. Despite that, no extreme temperatures occur. Superabsorbent polymers and pulp are processed, which cause a relatively high level of dirt and dust. As superabsorbent polymers also behave similarly to sand, dirt accumulates as a result of friction. "In summary, it can be seen that the systems and the machine components installed in them are subjected to high levels of strain", states Thomas Heege. "Despite this, they have to function with complete reliability under all circumstances." “

Format adjustments to the non-stop conveyor

The diaper production and packaging systems undergo continual improvements. Set-up times like no others are also achieved day in, day out. "We have hundreds of different adjustments for quickly, reliably, and reproducibly retrofitting the systems", explains Thomas Heege. In this regard, drylin® linear bearings from igus® GmbH in Cologne play a key role. Lubrication and maintenance-free, insensitive to dust and dirt, corrosion-free, durable, quiet, and lightweight, they are used as both standard and customer-specific customized solutions in the broadest range of areas.

They predominantly conduct position adjustments, for example in relation to adhesive application points. Depending on the product, the adhesive application head must be reproducibly moved from A to B to C. This can be reliably achieved using linear guides. However, the linear systems also demonstrate their capabilities within the packaging environments and during visual inspections and quality assurance, for example.

First and foremost, various linear units or lead screw modules are used in a broad range of sizes. They are often combined with a lead screw clamp to prevent accidental rotation, position indicators for reliably setting the position, and a handwheel for manual adjustment. There are also clockwise and counterclockwise-rotating trapezoidal lead screw nuts. "We particularly like that special requests are always considered", comments the Head of Technology. "For example, we have created a combined left-hand and right-hand thread on a lead screw so that we can simultaneously adjust two positions around a virtual center." igus® Technical Sales Consultant Markus Schwarz also adds: "A reverse linear movement is used. We jointly created this special customer solution, which is already available in quantities of one or more." “

Special format adjustment lists exist for all size and product changes. If a system undergoes retrofitting, the responsible employees are informed of the applicable parameters. Once retrofitting is complete, the system is fully ready; nothing else has to be readjusted and production can reliably commence.

Single-source solutions

The easytube unit is also used in the production systems. This is an ultra-compact modular linear unit for simple adjustment tasks characterized by its simple, effective, and robust structure. A complete system is modularly constructed from just a few components. The outer anodized aluminum tube guides the carriage/s and at the same time protects the trapezoidal threaded spindle and leadscrew nut from external influences. The carriage, torque support, and trapezoidal lead screw nut are all from one cast and made of a special plain bearing high-performance polymer. This guarantees freedom from lubricant as well as a low coefficient of friction and optimal wear pattern. In this application, the jacketed lead screw also has a scale and a handwheel. Markus Schwarz states: "It is a joint system development that has become part of our standard product range and has also been successfully used by a number of other packaging machine manufacturers." “

In addition to further components from the drylin® W construction kit, RJUM linear plain bearings in various sizes substitute recirculating components in several areas. They are based on highly wear-resistant polymers specially designed for linear technology, are extremely robust, low cost, and available from stock within 24 hours.

Something else that makes the diaper manufacturers unique are their material feed cranes. These were designed in-house and carry the heavy rolls of raw material to the machine. Although they are gantry cranes with a height of just 2 m, they move through very high travel ranges. A crane is manually activated by an operator. Hybrid bearings have proven successful in this environment. Modified from the drylin® W range, they offer a combination of gliding and rolling. "We mainly use these bearings for ergonomic reasons", explains Thomas Heege. "Coefficients of friction are minimized. Adjustment and driving power are kept as low as possible so that the material feed can occur seamlessly without any physical exertion by the operator."

Freedom from lubricants

A diaper has to be white. The hygiene policies in the company are correspondingly strict. This includes firstly the personal hygiene of the employees and secondly the components or machine parts used in production and packaging. "As we are also classed as a food processing company, lubricants must be banned to the greatest possible extent", explains Thomas Heege. "The lubricant-free linear bearings enable us to be completely on the safe side." “

The combined production and packaging system focuses on the topic of hygiene. Both areas must be perfectly aligned as expensive periods of downtime otherwise arise. The lubricant-free linear solutions ensure that there is absolutely no risk of the diapers being contaminated at any point of the process. "And if the topic of the FDA ever becomes important, we already have products that are effective in the hygiene and packaging environment", Markus Schwarz highlights.

A team of seven engineers works daily to continually improve the diaper production systems and increase their availability and output. In addition to multiple standard solutions, the company also makes great use of customer-specific developments from igus® GmbH. On important factor here is the advice received, which is usually works seamlessly on site on the machine. "We have had the very best experiences in our work together", confirms Thomas Heege.

"The service lives have continually increased in recent years. We have been able to adapt the systems to the constantly increasing requirements without an exorbitant investment costs. The maintenance and lubricant-free linear products are a key factor in providing us with this flexibility", states Thomas Heege as a final comment. "These are supplemented by the diverse modular system, the extremely quick delivery times, and the non-bureaucratic sample dispatch process. All of these mean that ideas can be quickly implemented!"

Picture of the involved persons

From left: Thomas Heege (Ontex Mayen GmbH), Markus Schwarz, Lars Braun (both igus® GmbH).

 
Picture of the drylin® lead screw module in application.

Center adjustment of a four-line 90° deflection using a drylin® lead screw module SHT-120AWM for non-woven lines. Eight systems are used in total.

 
Lead screw module SHTP-12 with lead screw clamp.

Lead screw module SHTP-12 with lead screw clamp, position indicator, and handwheel enables quick, accurately reproducible format adjustments.

 
Picture of the synchronized height adjustment

The lead screw modules SLW-2080-AWM enable synchronized height adjustment for compressing the packaged diapers in boxes.

 
Picture of the format adjustment of the sensors for monitoring the line center using the drylin®.

Format adjustment of the sensors for monitoring the line center using the drylin® linear unit easytube SET-25. The robust aluminum pipe reliably protects the lead screw.

 
Picture of the inspection camera

Compact format adjustment for aligning the inspection camera using the drylin® lead screw module SHTP-12-AWM.

 
Picture of the material feed crane

Material feed crane. The versatile drylin® W system has also proven effective when adjusting the stocking rolls for non-woven lines: The linear guide WS-20-80 and the hybrid bearing WJRM-01-20 (belt-driven system) optimize the application’s ergonomics.

 
Picture sensor adjustment for the film/foil line center regulation is positioned using the drylin® linear unit

The sensor adjustment for the film/foil line center regulation is positioned using the drylin® linear unit easytube SET-25.

 
Picture of the format adjustment using the drylin® linear unit

Format adjustment of pneumatic cylinders for cleaning-related blow-outs using the drylin® linear unit easytube SET-25.

 
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