Moulds, dies and revives – the Aquapurge treatments
Wednesday, 27 March 2013
Part of the key to an effective mould tool or die is its cleanliness and effectiveness in usage and through production changes.
Leading purging compound developer Aquapurge says that a significant part of its ongoing work is in helping processors overcome bottlenecks and get the best from their investments in tooling.
Using hot runners in moulding, for example, can raise issues and Aquapurge has accordingly developed a wide slate of purging compounds in order to tackle diverse problems.
Aquapurge Technical Director John Steadman points out that ‘the key point for hot runner-based moulding is that the flowability of the polymer is matched to the purging compound. That is why Aquapurge has invested in our moulding machine and spiral flow die in order to evaluate customer materials. These need to be matched so that the customer can run the purging compound in automatic cycle. A ‘too easy’ flowing purging compound will be ineffective for the moulder’s colour changes. If the purging compound is too viscous, short shots may result. Materials may not eject or may stick to the fixed side of the tool. In addition, the purging compound will also get compressed in the hot runner due to the high pressure required to mould a stiff material.
Recent client work has taken Aquapurge into the area of fluorescent colour in polymers. Steadman notes that ‘95% of carbon issues occur in the barrel. However, when you have fluorescent materials - such as those used in the manufacture of ‘magic marker’ pens – these can actually degrade in the tool.’
The Aquapurge solution is partly a simple iteration of moulding shots in order to clear the bulk of specking on colours. Aquapurge then left its Poly Clear HR20 for a two minutes soak mid way through this cycle. ‘This soak was successful in dislodging the carbon from the tool,’ says Steadman, ‘and we recommend it for work with fluorescents.’
Another area of demand for the purging company is colour changing on sheet extrusion. Says Steadman, ‘this can be very difficult especially if plate-out occurs or high levels of pigments are used. Also the purging compound (PC) needs to again be matched to the flow properties of the base material. If it’s too easy flowing, the purging compound won’t get to the edges of the die; if it’s too stiff it will struggle in other ways. In Steadman’s experience a variety of tools and methods are typically needed in order to help cleaning plate-out, including soaking methods.
When it comes to pipe extrusion, die cleanliness and maintenance generally divides into two camps; polyolefins and PVC.
‘Colour removal is typically not the issue when purging with PVC Pipe dies’ says Steadman. ‘Most typically it is carbon build-up - especially with the onset of Calcium Zinc stabilisation systems
To help these problems Aquapurge generally deploys Scrubber Freeze to clear out degraded material. This is a highly-filled Calcium Zinc based, mechanical cleaning compound.
Steadman notes that ‘although most PVC processing dies are designed to be stripped relatively easily for manual cleaning the issue can linger. Basically if the screw and barrel aren’t cleaned then the die will carbonise up earlier. This is because of the autocatalytic effect of PVC degradation; as PVC degrades, it gives off hydrochloric acid and this HCl causes the PVC to degrade. Therefore its standard practice with us that when purging with Scrubber Freeze not only will the die be cleaned but so will the screw and barrel.’
Large bore polyolefin pipe extrusion dies, says Steadman, ‘can be very complex; incorporating many developments, spiral flow, spider, basket, multi-layer and so forth. Compounds of PE 100 present a different order of cleaning difficulty. Steadman recalls that the pressure pipe market consisted of three main solid colours of Black, Blue, Yellow. ‘Really, the only means of colour change then was to have a spare die or to remove the die in use and manually clean it, a process which could take two days.
Legislation has been changed to allow skinned pipes (a natural inner with a skin of colour) or striped pipes, which typically feature a black base material with 4 coloured stripes down the edge. ‘These types of dies still present issues,’ says Steadman, ‘but are a dramatic improvement over the old dies.’ Aquapurge uses its own newly developed Poly Clear HMEX to clean out all die types involved in polyolefin pipe extrusion.
ENDS
NOTES FOR THE EDITOR
Aquapurge has been creating purging compounds for the global plastics processing industry for the past nineteen years. Over 140 compounds have been developed to date. Aquapurge available capacity currently stands at 15,000 tonnes of compound per year.
Aquapurge produces three world-beating purging compound brands and in February 2013 also introduced Poly Clear HMEX to the blow moulding sector. The new Aquapurge material looks like being the company’s most versatile yet.
Aquapurge is well known for its ‘hands on’ work with customers; and for its problem-solving abilities in plastics processing.
Aquapurge views its purging compounds as development partners for its customers in their aims for increasing productivity across plastics processing; Injection moulding, Blow Moulding and Extrusion equipment. Purging with Aquapurge helps its customers to reduce colour changes, and to remove carbon and colour plate-out on plastics processing machinery.
Purging with Aquapurge allows manufacturing customers in plastics processing to become more responsive to their clients; reduce stock and inventory and raise margin and profitability.
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