While Alpha Marathon Film Extrusion Technologies Inc. had demonstrated its ability to design and produce conventional multi layer coextrusion dies (concentric spiral type), we were busy in the development of a new modular design, which will carry us beyond today's 5-layer limitation.
The scope was to design and manufacture a modular die system, capable to distribute the molten polymer in a modular concept at very stringent tolerance.
To achieve such tolerance, a new computer software program was developed, to study the flow characteristics and behavior within a model simulation.
Once this program was tested, the rheological results was applied to find the best surface geometry for a plate-type spiral design, When a reasonable level of confidence has been reached and all the variables associated with the polymers and the structures of layers are selected, design begins.
As the die is being designed, full consideration to the mechanical requirements is presented. Design has to address the internal pressure caused by the polymer flow, thermal expansion differentials and the need for true concentricity for precision flow passages, plus total elimination of hang-up areas where polymer degradation may occur.
The die has to be flexible and practical with the ability to accommodate up to eleven/twelve layers in a precise modular concept without compromising shear stress and residence time. This by itself is always the major challenge ahead of us.
Finally, the mechanical design has to consider the practicality and durability of the die in order to withstand the rigors of every day service on the production floor.
After the design and manufacture hurdles were resolved, the ultimate goal is to test the capabilities of this new modular die.
(ADSS) THE NEW STACKABLE DIE SYSTEM
Constant research has resulted in Alpha Dual Spiral System’s new patent pending concept in coextrusion blown film, known as the “Alpha Dual Spiral System” (ADSS). The ADSS will enable processors to take advantage of the improvements brought about from adding layers without adding additional equipment costs. By dividing each individual layer into two separate layers, the enhanced structural and physical properties of each layer material can be taken advantage of. This means that a five-extruder ADSS blown film die would in fact be producing a 10-layer film sheet. As a result, the improvements over a classical die are increased two-fold.
A layer module with two identical spirals flowing in the same direction but at different starting points will improve the gauge variation of the particular layer and the overall gauge uniformity of the layer. This is because any potential high spot in the gauge will correspond to a low spot in the adjacent layer. Upon combining the two layers, the gauge variation in one layer will be cancelled by the other, which also makes a stronger final product with improved flex crack resistance. This, in combination with theADSS’s streamlined temperature mixing flow channels that have a low wetted surface, results in a higher performance die system.
By combing two spirals in one layer module, the complexity of the die does not increase and the cost of the die doesn’t either. The ADSS is the only die on the market that can offer this feature.
The ADSS provides superior streamlining and mixing of melt-flow, temperature isolation and a new standard in die design for simplicity and flexibility to add layers to the die configuration. The low residence time, streamlined Polymer Distribution Modules permit very rapid purging and order changes. Dramatic improvements in line productivity and corresponding reductions in scrap generation are the result.
Conventional dies have cylindrical mandrels for individual layers, each requiring numerous entry and exit ports, and a distribution block. Each passage and component has a corresponding pressure and residence time.
The ADSS has individual zones on each layer module. The polymer distribution system in each module is designed for the type of materials which are to be processed, taking into consideration polymer rheology, flow rate and layer thickness, the purpose of the individual layer within the structure, polymer degradation characteristics and individual layer ratio. A straight bore through the center of all ADSS dies allows various internal bubble cooling methods to be utilized without interfering with polymer flow.
Low height is an added advantage. The horizontal distribution of polymer within the ADSS allows the top of the die to once again become visible, being approximately 3 to 4 feet above the ground.
- A substantial improvement to what was thought as truly modular design. Each layer is
essentially a two-layer die producing two-layer film.
- The entire flow path is highly streamlined and highly polished to eliminate all dead
spots, insuring rapid flushing and eliminating the need to disassemble the die for
- Overall height of the package is substantially lower than conventional dies and feed
blocks thereby allowing easy operator access and effectively increasing nip height.
- Short polymer flow passages decrease residence time, which is of great benefit when
processing degradable materials.
- Outer die lip is adjustable for concentricity with the inner lip.
- All parts electroless nickel-plated. Plating is hardened to a hardness of Rc 60.
- Body heaters provide long life and uniform heat distribution.
- All heater terminals equipped with ceramic safety caps.
- Manufactured from AISI 4340 (DIN W 23.11) machinery steel hardened to 28-32 Rc
- Top and bottom of die are insulated to reduce heat losses.
- Low-pressure die designed for ± 3-5% gauge distribution with 4000-5000 PSI back
- Design features our patented "Flow Mixing Channel" port system to improve thermal
dispersion of polymer flow at entry to spiral section of the die, producing a dramatic
reduction of optical and gauge port lines.
One of the most important advantages of the ADSS system's modular construction is that for the first time, truly effective temperature isolation of material layers can be achieved with ourThermal Isolation technique.
Each layer module is made of a set of distribution plates, which are bolted together as a unit.
Each module is then joined with the others in the die to form a complete die assembly.
Each module has a separate temperature control zone.
Each module is defined by an air gap on both sides of it; including the top or bottom of the die.
Up to 60 degree Celsius temperature differences between adjacent layers are possible
Allows materials with high processing temperatures to be run in any module adjacent to temperature sensitive resins.
Increases run time for temperature sensitive materials.
The patent pending construction of the ADSSallows:
- Modular design allows adding, removing or relocating of layers with minimal effort and
- Future addition of extra layers to keep pace with changing market demands.
- The replacement of modules to handle different structures.
- Taper-lock module design enables ease of die assembly and ensures perfect
concentricity of modules.
- Localized cleaning (if required) of one layer only. Complete die disassembly is not
- Unlimited access to flow passages once disassembled.
- Increased run time for temperature sensitive materials.