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Materials processing and testing
News Release from: Twinshot Technologies | Subject: Rifton Equipment
Edited by the Engineeringtalk Editorial
Team on 06 June 2002
Co-injection produces novel bath chair
Rifton Equipment uses Twinshot Technologies co-injection process to mould the Blue Wave bath chair.
Rifton Equipment uses Twinshot Technologies co-injection process to mould the Blue Wave bath chair This is the first commercial application of a new single-barrel co-injection process developed in-house
This article was originally published on Engineeringtalk on 21 Aug 2001 at 8.00am (UK)
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Co-injection system can be retrofitted too!
Twinshot technology permits the production of multi-material parts with a sandwich construction (co-injection), using a slightly modified standard injection moulding machine
Co-injection moulding process improved further
Twinshot Version II improves on the Twinshot process that permits co-injection moulding of multi-material, by only needing a single screw, with a 2-stage design similar to a vented extruder
It was run on the same single cavity aluminium tooling as the former mono-material version.
Using a foamed core, it runs on a press one-third the size with less warping, sinking and flash.
The microcellular foamed core is 100% post-consumer ABS recovered from electronic housing.
The parts are produced on a conventional press with only 85t of clamp.
The PP seat members are moulded with liquid gas-assist which leaves no vent holes.
Further reading
End-cap for when two nozzles are better than one
Twinshot Technologies has introduced an alternative end cap that puts materials out from two nozzles rather than one.
Stainless performance for for effluent plant
Nature Environmental Solutions (NES) has recently delivered a 100,000-litre continuous biological treatment unit to a large Danish manufacturer.
Radical design for modular helmet
Sheffield-based AME Product Development Solutions has created a modular helmet for Modular Helmet Systems.
This product combines structural support, adjustability and hygiene through extensive use of plastic materials.
A combination of gas-assist and co-injection processes produce parts that are strong and stiff, yet smooth and nonporous.
The ABS side plates combine internal adjustment cogs and external cosmetic covers in the same part.
Twinshot Technologies is a process that permits co-injection moulding of multi-material using two concentric screws within one barrel.
The newly commercialised Twinshot Version II, patent-pending single-barrel co-injection technology does not require two-separate screws.
Plasticising of both components is achieved using a single screw with a two-stage design similar to a vented extruder.
The ratio of materials is controlled externally by starve feeding one or both of the screw stages.
Joel Thomson, inventor of Twinshot, describes the numerous advantages in performance, cost and ease-of-use: "Recovery time is much quicker - even faster than an equivalent conventional screw - because both materials extrude simultaneously.
Independent heat control on the two melting zones is also possible.
Overall cost is reduced because one simple screw replaces two more complex ones".
Other advancements include elimination of the hopper located behind the barrel, making Twinshot Version II retrofitable to all machines regardless of injection piston design.
No new pistons or castings are needed.
No clutch between the drive and the screw is required, thereby eliminating a potential wear component.
No signal or force from the machine is needed to run the process, so any software or control can be used, even old relay controls.
Twinshot Version II can be scaled down to much smaller screws, as low as 20g shot size, and can be installed or removed quickly just like any barrel and screw replacement.
Additionally, previously established Twinshot Technologies advantages over conventional co-injection still apply.
Twinshot is retrofitable to existing presses and works with most conventional molds with no modifications - thereby overcoming the burdens of large capital expense and process complexity that have traditionally made co-injection prohibitive to custom moulders.
A standard injection machine is used with no increase in footprint or power consumption.
There are no mixing manifold or hydraulic nozzle valves to maintain.
There is no pressure loss by directing melt through long distances and around corners resulting in faster clean-out and no dead spots.
The shot size never needs recalculating when material ratio changes, now providing smooth and instantaneous switchover between materials during injection.
"Simplicity and low cost are the distinguishing attributes of the Twinshot system as compared to other commercial co-injection systems", according to co-injection veteran Joseph McRoskey.
Twinshot has been proven to reduce resin costs by 25% or more, dramatically cutting product material costs - the single greatest expense to custom moulders.
Among the many benefits of Twinshot is the ability to encapsulate low-cost materials, including off-spec, regrind, or recycled material.
The system can also be used to produce soft-touch parts in a single moulding operation, encapsulate foamed material to reduce sink, warp, and improve strength-to-weight ratio, and to encapsulate reinforced materials within a cosmetic surface.
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