UK replicators succeed with closed loop sprue scrap reclaim
Replicators in Britain are saving money and improving housekeeping by the use of closed loop granulators specially developed by Getecha
BY ALAN SMITH
There are estimated to be 300 Optical Disc injection moulding machines in the UK and a significant development, which has taken place almost unnoticed over the past 18 months and appears set to continue, is that about 60 of these, of various makes, have been equipped with Getecha granulators for the direct reclamation of sprue scrap. Reground material is fed back into the machine hoppers and mixed with each fresh charge of virgin.
Cost savings of the order of £5,000 to £10,000 ($7,500 to $15,000) per annum per machine are reportedly being achieved, resulting in payback periods of about five to nine months. Fears that the admixture of reclaimed material with virgin would adversely and critically affect the quality of the PC melt, and therefore of moulded CDs, have proved groundless.
Extracts from the results of comparative tests carried out by a major replicator confirm this (see Table 1). Yields from the line with closed loop recycling are actually greater than or equal to those for the line without.
Although the granulators installed to date are entirely for CD Audio and CD-ROM production, one replicator has carried out tests to determine their applicability to DVD. Having ascertained that DVD quality can be maintained, this concern now plans to equip its DVD moulding machines with Getecha equipment.
Looked at from other than an immediate standpoint, however, it has to be said that replicators, considered as part of the plastics processing industry, have come late to so-termed 'closed loop' scrap reclamation. This is probably because the complex technicalities of metallizing and other downstream operations, plus an overriding obsession with cycle time reduction, diverted their attention from it.
In fact, there are many plastics conversion processes in which profitability essentially depends upon efficient process scrap reclamation - examples being the manufacture of blow moulded bottles for various liquids, thermoformed trays for food products and polyethylene shopping bags.
Processors in almost every other field apart from optical disc replication have reclaimed their scrap as normal practice for many years and Getecha is one of a number of granulator makers which has developed a wide range of designs to suit different applications.
Early methods of scrap reclamation simply involved collecting 'scrap in' bins at individual machines and taking these when filled to a central department for size reduction in fairly large granulation machines. Then, about 15 years ago, the concept of equipping individual machines with small granulators and directly blending the reclaim with virgin material was introduced.
This method was dubbed 'closed loop' recycling, meaning that the scrap was converted into granular material, known as 'regrind', and directly put through the machine again instead of being taken off line to a centralised reclamation process.
Closed loop reclamation became easier to apply as centralised materials distribution systems and robotic part take-out came into wider use. Centralised distribution, with or without drying, has almost entirely ousted the traditional method of manually filling machine hoppers from sacks, or via a vacuum or flexible spiral conveyor from a container placed by the side of the machine.
With a centralised distribution system, each machine has an automatic hopper level control to call for material replenishment as required and a vacuum valve to govern the flow of each fresh charge of material. If a closed loop granulation system is added, it is not difficult to add a second valve to allow for the delivery of regrind material in the desired proportion relative to virgin.
The first centralised distribution systems were applicable only to large scale moulding operations with at least 20 machines but their application to as few as only four or five machines is now inexpensive and practical. Many optical disc moulding operations are on this scale.
In general industry, the application of take-out robots for part demoulding has taken the place of manual extraction or simple gravity ejection, but neither of these could ever have been considered for disc production in the first place. Robotic part take-out also means robotic sprue scrap take-out and this is its significance in the context of this article.
If replicators have been late to adopt closed loop scrap reclaim, they were well ahead of the rest of the plastics industry in employing robotic part take-out as de rigueur. Closed loop reclaim is applied considerably more easily if the scrap is handled in a controlled manner by a robot rather than falling freely away from the mould in unpredictable directions.
Part and scrap take-out on most disc moulding machines is by a swinging arm robot but on one popular machine, the Krauss Maffei, a robot is not employed with the maker's 'non-opening' mould system. Nonetheless sprue disposal can be described as controlled, inasmuch as the scrap falls from the mould and is consistently directed down a pipe provided for the purpose.
Slightly to digress, there is a distinction between the adoption of closed loop reclamation applied to CD/DVD general injection moulding, and the newfound trend among UK replicators. In general industry, the desirability of reclaiming scrap per se has never been questioned and closed loop regranulation has been implemented chiefly to improve housekeeping and eliminate labour costs entailed in scrap handling, as well as make fullest possible use of material.
Barriers to its adoption have been that frequent changes of material or colour are the norm in general moulding and that this involves need to clean down the systems at intervals of a few days or even hours. It is most unusual in general moulding for a machine to run with the same material for more than a few weeks and the trend towards shorter runs has become accentuated with the demands of just in time (JIT) moulding.
Conditions are more favourable in disc moulding because the same kind of material is run continuously day in, day out. Where the same applies in other moulding sectors, for example polystyrene jewel cases, hot runner moulds are normally used and no scrap is produced, but such equipment for disc moulding appears to be still in its beta development stages.
Nevertheless the applicability of closed loop scrap reclamation has taken some time to be recognised in the optical disc industry, the first question to be asked being: 'Will yield rates be impaired if a regrind/virgin mixture is used instead of 100 per cent virgin?'
Only practical trials could provide the answer and One to One visited three major UK replicators in August - Universal Music & Logistics, Blackburn DOCdata Ablex in Telford, and EMI Compact Disc (UK), Swindon - to learn of their experiences.
A few other companies turned down the opportunity to co-operate, stating bluntly that they did not wish their customers to know that they recycled their process scrap for fear of being asked for a reduction in price - a sad reflection on the industry.
As already explained, direct reclamation of material is accepted practice in pretty well all other sectors of plastics processing and, if a fair price has been negotiated, it is no business of a customer to question how his suppliers produce good mouldings at the agreed figure.
Another fear expressed by some replicators was that their relations with material suppliers would be prejudiced if they were to recycle PC in-house and consequently need to buy less tonnage. This is unlikely. No supplier of optical PC has a monopoly of the market or could reasonably object when closed loop recycling is so widely practised in other sectors.
Investigations by One to One have not uncovered any objection towards process scrap reclamation by the major PC suppliers. The opposite in fact appears to be the case, one replicator reporting: "Materials manufacturers approve of the use of reclaim at the personal level."
In any event, the scale on which materials companies operate, together with the growth of the overall PC market for optical discs, must enable them to contemplate the effect of an increased trend towards closed loop reclamation with equanimity. They also recognise their environmental responsibilities and are aware of the political advantages to their industry of encouraging recycling by customers.
Unpredicted events have supported the trend towards closed loop reclamation. In Europe, a major Japanese supplier has almost entirely withdrawn from the market, finding this area too competitive and its Far East markets more profitable. (A US supplier which has been hovering in the wings for some time has opportunely jumped in to help make good the shortfall.)
In the US, the rapid increase in DVD sales and the popularity of computer games has caused demand for PC to run ahead of supply and the situation was worsened for a time by the halt in production at a major materials production plant in Texas.
No one can suppose that current stringencies in PC supply can be made good more than fractionally by introducing closed loop scrap reclamation. But there is a certain benefit in recycling a percentage of incoming material tonnage in this way instead of disposing it as scrap to contractors for no recompense, which seems to have been the accepted procedure for many years.
Closed loop reclamation may be said to be the proper way to go about things, improving tidiness and cleanliness around the machine and, as well as material costs, reducing labour requirements involved in handling scrap.
A granulator (sometimes referred to as a 'grinder', which term does not accurately describe how it works) comprises a cutting chamber into which material is directed via a feed throat. In the case of an OD scrap granulator there may be a chute with a circular or rectangular bore attached to the top of the throat through which a piece of sprue scrap drops with each cycle. (This chute may be called a 'hopper' but as it is not used to store a quantity of material it is not a 'hopper' in the usual sense.)
A piece of scrap, comprising the cut-out disc with a length of sprue attached, falls through with each cycle of the machine directly into the cutting chamber (or two pieces down two chutes in the case of twin cavity machines).
The cutting chamber is cylindrical and has a horizontal central rotor driven through a reduction gearbox by an electric motor, and on the rotor are three knife blades 100mm long disposed axially and equidistantly. There is a close clearance between these rotating blades and two fixed knives arranged one on each side of the chamber and scrap is cut as the rotating knives pass the fixed knives. Minimum dust is created as the rotation speed is relatively low. Getecha has determined an optimum speed of 160 rpm. Noise level is inaudible above that of an hydraulic moulding machine.
In the lower part of the cutting chamber is a curved perforated screen through which the cut fragments of scrap fall into a collection box. The moving blades sweep over the perforations, pushing the regranulate through. Any pieces too large to go through the perforations are subject to further cuts until reduced to the required size. Regranulated scrap is evacuated from the collection box via a vacuum pipe.
The diameter of the screen holes determines the size of the reclaimed material, which is matched to that of virgin so that a homogeneous blend can be produced. The Getecha granulator has a special feature to assist this. An ordinary granulator has screen holes drilled radially but disc scrap is of such a shape that the sprues would tend to fall through the holes, disc uppermost, without being cut.
The holes are therefore drilled at an obtuse angle to the radius so that this tendency is greatly diminished, it being more difficult for the sprue to fall straight through. Various angles for these holes were tested before the most effective was found.
Getecha, a specialist maker of granulators based near Frankfurt/Main, Germany, has made closed loop machines for general moulding for many years. When several UK replicators first decided to look into the feasibility of using such equipment some 18 months ago, Warminster-based Getecha UK, headed by Andy Gibbens, supplied its standard model, the RS185, for trials and subsequently about 60 of these have been installed.
The German parent and the UK subsidiary have since undertaken a considerable amount of development work in conjunction with users, culminating in the introduction of the CDRS100 machine specifically designed for the optical disc industry. The figures in the model designations refer to the rotor diameters inmm. The CDRS100 therefore has a smaller rotor and cutting chamber than the RS185 and is overall a more compact design whilst remaining adequately sized for its task.
Another major difference is that the CDRS100 is made entirely in stainless steel, minimising the likelihood of undesirable contamination of reclaimed material. Other modifications relate to matching the granulator to suit different types of moulding machine.
With the Netstal Discjet 600, which has no well space beneath the mould area, the granulator is placed on the same side of the machine as the robot take-out and at the end of the base of the clamping unit. Instead of a chute, a 45mm bore flexible PU tube is provided from the feed throat of the granulator to the aperture in the machine guarding through which the robot swings to deposit the disc on to the downstream conveyor. On its return, the robot halts briefly opposite the mouth of this tube and the sprue is blown down it.
For the Toolex machine, another three-tiebar design but which has an overhanging clamping unit with free space beneath, the caster wheel mounted granulator is disposed on the floor at the clamping end of the machine.
A 45° angled chute of suitable length is provided for the granulator such that its opening is directly below the mould and sprue scrap falls down this directly into the cutting chamber.
This arrangement is broadly similar to that for the Krauss Maffei machine, a four-tiebar design with an overhanging clamping unit and, as standard, a vertical tube under the mould space for sprue disposal. The granulator is placed at the end of the machine such that the chute inlet is directly beneath the tube.
In either of these two applications, a pneumatically operated flap can be fitted to close the inlet to the granulator automatically when the moulding machine is shut down for stamper changing. Opening the gate or injection carriage retraction initiates flap closure to obviate the risk of foreign material being introduced.
As well as these types of machine, granulators have been applied to Sumitomo and Netstal N60 models. Adaptation of the Getecha unit to other makes of machine should present no difficulty.
The reclaimed material in the collection chamber of the granulator is evacuated each time that a fresh charge of virgin material is delivered. Granulators have so far been applied at customers using Motan, Piovan, Lanco and Colortronic conveying and drying systems. A dual mixing valve is fitted to the material inlet of the vacuum hopper loader on the machine. One branch of the valve is for the virgin material from the drier and the other the regrind from the granulator.
These valves operate alternately to avoid layering of the two materials and ensure homogeneous mixing, which is assisted by the swirling cyclonic flow. The required charge of virgin is delivered and the reclaim valve is opened for total time which is generously adequate to completely empty the collection box.
This ensures that there is no residual material in the collection box which may absorb moisture from the atmosphere. Reclaim is returned to the machine while still warm and no additional drying is necessary for it to be as dry as the virgin material. If the moulding machine is shut down for a stamper change or servicing, the contents of the granulator collection box can be evacuated and returned to the central drying system for redrying.
Filtration of reclaimed material is important and affects yield rates because finer particles are a likely cause of black specks in disc mouldings. Using a 530 micron filter in the hopper loader, one replicator achieved 95 to 96 per cent yield rates with a virgin/regrind blend but changing to a 1,200 micron filter improved the rate to 98 per cent. The finer filter did not allow smaller particles to be extracted.
Yield rates are often therefore better for virgin/regrind blends than for pure virgin when larger filters are fitted. Loss of material in the form of extracted dust is of the order of 600 to 1,000 g per machine per week and thus negligible.
Christine Rosenberger, technical director of Getecha, said that five CDRS100 machines were out on test in Germany with as many replicators, also one in France and another in Luxembourg. Chuck Thiele, who has newly set up Getecha Inc in Kalamazoo, Michigan, is to send five units for trials in CD production and later DVD with five US replicators.
He reported 'tremendous interest' at REPLItech Miami in June this year, where he took eighty inquiries. The raw material shortage in the US was critical and interest shown by GE and Bayer was encouraging, added Thiele, who was formerly with Motan.
Universal Music & Logistics, Blackburn
The first production Getecha CDRS100 granulator has been installed at Universal on a Netstal Discjet, part of a Singulus Skyline, and the company has decided to buy a second granulator shortly. Evaluation has shown no deterioration in either product quality or yield as the result of introducing regrind material directly into the moulding process. Yields are currently averaging 97 per cent at a cycle time of about 3.5 seconds.
Trevor Burke, senior project engineer, said: "The cost reduction through using regrind means that the granulator will pay for itself relatively quickly, and in addition the problems of collecting and storing scrap sprues are eliminated."
The plant operates a total of 21 injection moulding machines and it is intended to investigate the feasibility of equipping older machines with Getecha granulators in the near future.
DOCdata Ablex, Telford
"Addition of reclaim material definitely does not impair yield," said Andy Martin, senior engineer, DOCdata Ablex. The company uses 1.5 tonnes of GE Lexan high flow PC per day to make 100,000 CDs. Extracts from a Schenk scanner report are given in Table 2.
The company aims for a minimum yield of 95 per cent but had noted an immediate improvement in yield per tonne when Getecha equipment was introduced on its three Leybold Speedline dual lines with four Krauss Maffei and two Netstal machines. An Arburg mono line is also employed.
At the time of One to One's visit, DOCdata was in the throes of taking in a First Light dual-line with two Toolex machines and four Leybold mono lines with Arburg horizontal machines from its Battersea site, an outcome of the takeover by the Dutch parent. Other equipment was being transferred to France. Once this machinery had been assimilated, it was the intention to install more Getecha units.
EMI Compact Disc (UK), Swindon
Incentives to equip 24 Toolex MD100 machines in 12 duo lines with closed loop reclaim equipment were the effects of Health & Safety legislation and a desire to achieve environmental improvements from reuse, as against incurring landfill or other transport costs to other reclamation companies. Treading on sprues was likened to walking on ball bearings.
EMI performed the installation of the granulators itself, carrying out the work between 11 pm shutdown on Fridays and the same time the following Sunday. Six machines were converted in the first phase, another six in the second and finally the remaining 12.
"We were achieving 97 to 98 per cent yield rates before introducing the Getecha granulators," reported Paul Buck, project engineer. "We now obtain similar rates with the use of these. There was a slight drop in yield at first but this was because of unfamiliarity with the equipment.
"Material savings are equivalent to one bulk delivery of about 19.8 tonnes of PC a year," Buck added.
Table 3 shows EMI's comparative yield rates for a typical machine with Getecha equipment.