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‘Spiroflow’ Bulk Bag Filling Machine at PET Processors (UK) L.L.C

30 November 2007

‘Spiroflow’ Bulk Bag Filling Machine contributes to a significant increase in productivity and a reduction in manual handling

Spiroflow Ltd report the success of their bulk bag (FIBC) filling machine at PET Processors (UK) L.L.C. of Dumfries, Scotland (PETUK). The filling machine, supplied by Avery Weigh-Tronix and which was installed last year, has contributed to a significant increase in productivity and a reduction in manual handling.

PET Processors are the acknowledged leaders in batch solid state polymerisation (SSP) and offer a toll processing service to the plastics (polymer) industries. The plant in Dumfries is unique to the UK and was developed from the parent plant in Ohio, USA. The SSP process changes the crystallinity and molecular weight of semi-crystalline thermoplastics, thereby allowing improved processing and, in addition, certain improved physical properties of (Customers’) finished products. Materials processed at the Dumfries plant include PET and some of the derivatives, namely PEN, PBT, PBTE, PTT, PPS, and also Nylons (Poly Amides) A and LCP (liquid crystal polymers) materials. In addition to processing established grades, the plant has the facilities to develop Customers’ experimental grades of speciality polymers too. About 80% of production is material sent in directly by Customers, processed and then returned to them - this is a tolling operation. The remainder comprises polymers sourced on behalf of customers, processed and delivered direct to the end users.

The solid state polymerisation process developed and employed by PET Processors involves processing the polymer in batch rotary reactors, under very carefully controlled temperatures and applied vacuums and, where applicable, under controlled gaseous environments. The polymers are not “melted” but the resultant reaction changes the molecular structure. This is measured as a change in intrinsic viscosity (IV) and differing IV’s will give rise to differing performance of the polymers. The SPP technique employed by PET Processors requires a substantial capital expenditure. Moreover, the operating procedures and controls are critical to ensure the required performance from the product and repeatability between batches.

The SPP process can be applied to processing certain post industrial polymers to return processed polymer to their original or even IV uprated state. This is particularly valuable for improving certain manufacturing first pass efficiencies. PET Processors is a unique and highly efficient organisation operating around the clock, 7 days a week, currently processing over 15,000 tonnes a year.

As part of a major upgrade of their plant, PETUK decided to purchase a new bulk bag filling machine. Given that they have to confirm the weight of processed material in each bulk bag, their first step was to contact Avery Weigh-Tronix, the UK’s leading weighing company and the manufacturer of their weighbridge and a variety of weigh platforms in operation on the site. Avery Weigh-Tronix do not make bulk bag filling machines but, they have worked with Spiroflow over several years, and accordingly a ‘Spiroflow’ Bulk Bag Filling Machine was their number one recommendation.

This recommendation inspired PETUK to place the order with Avery Weigh-Tronix for a Spiroflow machine. Their decision has been well rewarded. The ‘Spiroflow’ Bulk Bag Filling Machine, which was incidentally the lowest priced too, copes admirably not only with the extensive product range which it has to handle, but also with the greater variety of bulk bag sizes and types supplied by PETUK’s Customers.

Whereas the previous bulk bag filling station was fairly inefficient, now aesthetically pleasing and stable 1 tonne bulk bags can be filled to the required weight in less than one minute. That’s also about the time it takes to rig a new bag into position and to remove a filled bag at the end of the cycle. This equates to a filling rate of around 20 bags / hour - a significant increase in productivity.

For filling into bulk bags, processed material is pneumatically conveyed to a high level holding vessel. From here it can pass by gravity or by being pneumatically conveyed through the various internal processing systems before being conveyed back up to a second holding vessel above the ‘Spiroflow’ Bulk Bag Filling Machine. A pneumatically operated slide valve with trickle feed facility controls the flow of material into the filling machine below.

The whole bulk bag filling machine is mounted on a weigh platform, the control for the system is provided by the Avery Weigh-Tronix L336 indicator and tailor-made software was written in-house by Avery Weigh-Tronix’s software engineers to meet the customer’s requirements exactly. The bulk bag support frame is pneumatically lowered for bulk bag rigging and raised for filling to ensure the bag is fully stretched. The integrity of the bulk bag is ensured by it, and its liner, being fully inflated before filling commences. This eliminates any creases that may cause instability or subsequent difficulties during discharge. Displaced air is vented through the annulus which surrounds the filling spout. The bulk bag and its liner are clamped to the filling spout by a split clamp with an over-centre fixing. On this occasion the usual inflatable seal could not be used because of the vast variety of liner and bulk bag types with differing neck diameters. In similar vein, it isn’t possible to use Spiroflow’s automatic bulk bag loop releasing mechanism because there are just too many lifting loop sizes and configurations to make it a practical proposition.

Bulk bags are vibrated as they are filled with the vibration being paused intermittently for weighing. Top up to the target weight is achieved with the inlet valve in its trickle feed position. The vibration technique employed by Spiroflow ensures that it is exerted in the vertical plane only for maximum effect. It is the proper compaction of their contents that ensures Spiroflow filled bulk bags are aesthetically pleasing, are filled to their maximum capacity, are upright and stable - therefore safe to handle.

 Spiroflow adapted their standard filling machine design to accommodate the limited headroom available on site. In addition they positioned the pneumatic cylinders, which raise and lower the bulk bag support frame, to allow for automated removal of filled bulk bags by roller conveyor at a future date.

As Production Supervisor, Iain Steel comments, “The ‘Spiroflow’ Filling Machine frees up plant operators’ time enabling them to concentrate on other, more demanding aspects of the process. It is relatively easy to use and gives us an efficient operation with the big advantage of flexibility. It readily copes with the large variety of bulk bags supplied to us by our Customers”.

Spiroflow are specialists in the conveying and weighing of dry bulk solids. This includes the safe and efficient filling and discharging of bulk bags.

For full details visit their web site at or to discuss a specific application call them on +44 (0)1200 422525. Avery Weigh-Tronix can be found at www.averyweigh-tronix.com or contacted by ‘phone on 0870 90 50061 and PET Processors Operations can be found at www.petuk.com or contacted by ‘phone on 01387 247965.

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