Sleeves – not what they used to be

Since those pioneering days, Polysleeve – operating from premises adjacent to Polyflex headquarters in Pinetown, KZN – has grown rapidly, and today sells sleeves and adapters throughout South Africa and exports to other African countries. The two companies are entirely complementary and use their joint expertise to understand printers’ needs and to deliver a complete package.  

All this is explained by Polysleeve manager, Graham Mortlock, who also emphasises the ability to provide both in-the-round (ITR) and seamless sleeves. The former are locally manufactured while the latter are imported from suppliers such as DuPont.  

As part of its commitment to the flexo fraternity, Polysleeve offers a free audit of sleeve libraries, helping printers to assess the sleeve component of their printing process. 

‘Before the advent of Polysleeve, South African printers didn’t have an opportunity to consult hands-on sleeve experts in this way,’ Graham claims. ‘Now we can help them to identify shortfalls in their usage/storage and handling. Also as part of the audit, we identify problematic and possibly redundant sleeves. These on-site audits consist of a visual identification and evaluation of the sleeve library, but we also offer off-site tests (at our factory) to check sleeve dimensions, including outer diameter measurements, roundness and inner core evaluation. Through rigorous R&D, we’ve maintained a competitive edge by complying with standards set by our European counterparts, including safety measures such as ESD (electrostatic discharge).’

The current scenario

So what has changed in recent times? What are the latest trends?

‘Imported sleeves have become less “over engineered”. Exotic materials such as carbon fibre and Kevlar are used less frequently,’ Graham replies. ‘A typical imported sleeve now has a polyurethane outer shell, with a variety of fillers (weight savers) underneath. Below that layer, 90% of sleeves are fairly similar – a foam layer sandwiched between two glass fibre layers,’ he continues.

‘In addition, we’re now seeing the inclusion of a “cap layer” at the ends of imported sleeves – something we’ve always included since Polysleeve’s inception!’

Essentially, this ‘cap layer’ prevents exposed sleeve ends suffering damage when sleeves are roughly handled (as they often are in practice).

‘A damaged end can result in a sleeve getting stuck on the press; and removing a stuck sleeve isn’t easy. I’ve seen cases of stuck sleeves having to be cut off the mandrels,’ Graham relates.

Damage can also occur when a sleeve is loaded on to the mandrel. As the operator slides the sleeve on, it’s pushed until it hits the locating pin and then rotated in order to locate on to the pin. This rotating manoeuvre is unavoidable, but with continuous sleeve changeovers the sleeve’s sidewall and core can be damaged.

‘Recently, sleeve manufacturers have been looking for economical ways to prevent such damage,’ Graham explains further. ‘Our sleeves hold out well because of our solid end caps, but we’ve seen core damage, even though we use a stainless steel locating slot. We now offer a sleeve with a full metal ring incorporating the locating slot and we’ve supplied one customer with this ring on all new sleeves ordered this year. We’re closely monitoring performance to ascertain viability of the ring and longevity of the sleeve end, before we commence production and offer this as standard.’

Trend to variable repeat sleeves?

Another trend on which Graham remarks is that local printers prefer VRS (Variable Repeat Sleeve). ‘At first,’ he says, ‘the use of adapters with thin light sleeves was appealing because of the ease of use and low weight of the product. But slowly I noticed printers choosing the thicker VRS as opposed to a thin sleeve adapter combination.’

Having studied this trend, Graham reckons it’s obvious that the VRS, being bulky and robust, has a longer life expectancy.

‘However, generally speaking, it depends on regular jobs being run on a specific press. For common repeats used on different products, it makes sense to have an easy changeover with a thin sleeve but if the repeat change is more than the diameter provided by an adapter then a VRS per repeat can save changeover time – being one sleeve versus a sleeve plus adapter,’ he adds.

Another issue is sleeve handling and storage. In Graham’s view the best case scenario is that all sleeves should be stacked upright  (not horizontally) and should be regularly cleaned of excess ink and oil. ‘A major concern is the inner tube that should always be as clean as possible,’ he warns. ‘It not, residue builds up and the sleeve eventually becomes too tight to put on to a mandrel.’

He suggests, also, a regular check to ensure

1.  air pressure is maintained at 6 bar;

2.  air holes are clear of any obstructions; and

3.  there are no sharp edges on any mandrel, mounting mandrel or sleeve storage holder.

‘A sleeve must slide on to the mandrel relatively easily. If more than one person is needed to manoeuvre it, undoubtedly one of these three points is to blame. The third point is a particular No! No! A sharp edge can cause scratches to the inner core. If the core eventually ruptures, you can throw the sleeve away,’ Graham remarks.

As a footnote, Graham mentions the latest Fischer & Krecke presses that use an RFID chip system embedded into the sleeve. Through this chip, the press is able to identify each sleeve and what plate it carries. ‘We have been approved to install these chips into our sleeves,’ he proudly relates, ‘and we’re in the process of negotiating with a manufacturer of a machine that inserts these chips. We’re very close to finalising the purchase,’ he promises.

It seems, therefore, that a further chapter could soon be added to this sleeve saga in the not-too-distant future.