Can custom engineering improve slitter rewinder performance?

UK: Ball lock ensures precise control

LIKE MANY sectors, the converting industry was hit hard by the global financial crisis of recent years. Indeed, studies carried out by industry leading bodies reflect the harsh realities of the decline in the economy, highlighting negative changes in financial indicators, such as widespread decreases in pre-tax profitability and diminishing order sizes.

In uncertain market conditions, it is vital that converters continue to control costs, maintain operating margins and deliver even higher standards of customer service. Although there are many factors that contribute to success, from a manufacturing viewpoint the ability to ensure that production systems function reliably and at optimum levels of performance is critical.

This is especially true of slitters and rewinders, which often run for extended periods and have to operate at fast speeds, while ensuring precise control of web tension, with high levels of accuracy and repeatability. Key to their reliable operation is the performance of component parts, such as the ball locks used to locate and hold rolls of material on winding and rewinding shafts. Indeed, ball locks, although sometimes taken for granted, are vital elements in keeping slitters and rewinders functioning consistently and without error.

Accordingly, a new generation of integrated ball locks has been developed in recent years to help maintain accurate web tension, accommodate variations in core dimensions, minimise cardboard dust and make loading and unloading faster and simpler. Combined, these improvements translate to enhanced productivity and, ultimately, profitability, something that is vital for converting companies during this time of post recession recovery.

One example of this new technology in practice is an innovative engineering solution, custom designed and built by Dawson Shanahan, that is helping a leading manufacturer of advanced slitters and rewinders to improve the performance of its latest secondary systems used in plastics, paper and board applications in the converting, packaging and labelling sectors. Indeed, Dawson Shanahan developed a ball lock mechanism that ensures precise control of web tension, minimises dust from cardboard cores and reduces both lead times and component costs.

Each of these secondary slitters and rewinders typically incorporate a series of shafts onto which uncut roll materials wound on cardboard cores are loaded. Each web of material is threaded through the machine onto rewind shafts, prior to being slit at speeds of up to 1000m/min along the length of the web into various widths and then rewound onto smaller cores for subsequent use.

On both the loading and discharge sides of each machine the cores are sized to fit longitudinally as precisely as possible on the unwind and rewind shafts. However, the nature of the cardboard materials inevitably means that there are considerable variations in dimensional tolerances, while the need to be able to slide cores on and off shafts means that a mechanism is required to clamp each core firmly in place to maintain precise web tension.

To achieve this, ball lock devices, especially sprung loaded ball bearings, are fitted to each shaft. Previously, the company had been constructing ball locks in house from externally sourced components. However, this process was relatively time consuming, as the production team had to source multiple parts, ensure that individually they met quality standards and then construct and test each mechanism before it could be mounted on a rewind shaft. Additionally, it meant that the company had to hold and manage stocks of components, which again took time and drew the engineers away from their primary function of producing finished machines.

The solution developed by Dawson Shanahan has replaced the older design of ball lock with a simpler yet more efficient system, which uses a sequence of custom built units fitted along the length of each rewind shaft. Each ball block incorporates precision engineered inner and outer steel shells, through which spring loaded ball bearings protrude to form a clamping mechanism that operates against the inner surface of each cardboard core. Pressure is applied to each ball bearing assembly by means of pneumatically activated bladders running along the length of each rewind shaft, enabling clamping pressure, and therefore web tension, to be accurately set and regulated.

Depending on the width of the machine, there can be up to 128 ball locks on each pair of rewind shafts, which are normally either three or six inches in diameter. Although simple in construction, the system is proving to be extremely efficient and reliable. Perhaps most importantly, as Dawson Shanahan supplied complete ball lock assemblies, built and tested for quick installation, this meant that the company no longer needed to assemble units in house. This enabled them to realise significant savings in both production costs and lead times, as the need to hold stock was eliminated, while overall levels of quality also improved.

Similarly, Dawson Shanahan also worked closely with the company to develop a new design of slot profile. This helped them to improve the functionality of the rewind shafts with the new slot profile ensuring that each ball bearing assembly stays correctly aligned, while making it easier to retract the ball locks for loading and unloading. For its customers, this helps to minimise dust and debris from the cardboard cores and improves speed of handling and productivity.

Accordingly, the latest generation of ball lock components have been developed in order to achieve speed, efficiency and effectiveness, having been engineered to cope with the handling of large material rolls, while also being simple to install, competitively priced and able to function for long periods with minimal maintenance. As a result, this has a significant impact on overall operating performance of slitting and rewinding machines, increasing their productivity and profitability to help converting companies develop a competitive edge in the marketplace.


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