Proper melt preparation is critical to the injection molding process. To achieve good melt takes a plasticating screw that is designed and manufactured for your specific needs. Do not settle for anything less. At Md Plastics, we have the experience, technical knowledge and software programs that can provide you with plasticating screws that are optimized for your exact situations. Give us a call today. You may be surprised at what a conversation with us can reveal about potential limitations of your current plasticating screws.
Posi-Melt™ Multipurpose Screw
The perfect choice for processing a variety of materials in the same molding machine
When screw design is considered for a particular polymeric family, the rule of thumb has been: amorphous materials process better with low compression screw designs, while semi-crytalline materials prefer high compression designs. Since semi-crystalline polymers have a sharp melting point and transform quickly between solid and melted state, higher compression designs with shallower metering sections have been the standard preference. But these have a tendancy to over-shear and over-heat amorphous polymers.
The industry standard General Purpose (GP) screw is a square pitch design that has a compression ratio between 2.3-2.7:1 and a 50/25/25 feed/transition/metering ratio. This geometry does an adequate job at best dealing with a broad range of polymer groups, residence times and other processing factors. That being the case, a more advanced design is needed to assure a more uniform, homogoneous melt.
The Posi-Melt™ geometry is a core change to the geomtry of plasticating screws. We have separated the coordinate systems of the root and flight pitch to force the pellets through a channel that changes pressure and velocity while exposing 55-60% more pellets to the heated barrel wall for improved conductive heat transfer. Our advanced design exposes the polymer to changes in velocity and extensional strain. This enables us to lower the volumetric compression for low shear heating while establishing a high “linear depth ratio” between the feed depth and metering depth. The lower volumetric compression works well with amorphous polymers by lowering the shear between the pellets in the transition zone, while the high “linear depth ratio” assures a shallow meter depth for efficient melting of semi-crystalline polymers. The Posi-Melt™ General Purpose Screw has won acclaim from custom molders, resin suppliers and OEMs for its ability to broaden the process window when processing a variety of materials in the same molding machine. It offers significantly better melt preparation, enabling plastic processors the ablity to mold higher quality parts in a wide range of polymers. Improving your process is our goal.
Posi-Melt™ XLA Mixing Screws
The ideal choice when precise color matching is needed or when residence time and swept volume dictate
In order to add a higher degree of homogenization to the melt pool, we developed an especially effective dispursive mixer that works by forcing the polymer to change direction numerous times over a short axial distance. We also add extensional strain by forcing the material to cross over a shallower land multiple times for added shear. A positive pumping angle and major flight OD wiping action assures a low pressure drop for high throughput. It also pressurizes the channels, which promotes quick and effective melt purges during changeovers.
Posi-Melt™ MB Barrier Screws
The optimal solution for achieving maximum pressure and high throughput
Our proprietary MB barrier design forces the polymer between the barrier flight and the inside of the barrel. This causes additional extensional strain to ensure complete melting. We can couple the XLA mixer to the MB barrier for processing a variety of polymer groups, including PP, HDPE, LDPE, PS, PET, ABS as well as many others. All Posi-Melt™ screws are precisely designed to promote the best possible solids conveying and pressurizing so the polymer is transferred properly through the transition and metering zones. Special care is taken to design-in the appropriate leading and trailing edge radii to avoid low-velocity sections in the channel and to maximize pressure. The benefits of Posi-Melt™ screw designs include:
- Quicker color and material changeovers - Posi-Melt™ MB single channel design results in better and quicker purging.
- Lower cost - Posi-Melt™ MB single channel design is less costly to manufacture.
- Complete pressurization throughout for excellent conveying, melting, and pumping.
Posi-Melt™ Extrusion Screws
Solutions for enhancing process stability and throughput
Posi-Melt™ technology is relied upon by extruders around the world. We’ve worked with some of the biggest names in the industry, providing them with solutions that have significantly improved the profitability of their operations. We understand and appreciate the uniqueness of each project. As a result, we spend a great deal of time on the front end of each job communicating with our customers. Every detail is discussed because every detail is important. You can rely on our technical knowledge and expertise to design and manufacture extrusion screws that will improve the reliability of your process and increase production. The end result is greater profitability and a better competitive position in the market you serve.
Posi-Melt™ Screws for Pellet-Fed 3D Printers
Innovative solutions for new and emerging technologies
Md Plastics provides innovative melt preparation and delivery solutions to several OEMs in the additive manufacturing field. Our deep knowledge of how polymers work has resulted in many successful partnerships with manufacturers of pellet-fed 3D printers. This is an exciting field that continues to overcome unique challenges to deliver tremendous value to the plastics world. It’s these challenges that we appreciate most and are dedicated to solving.
Because we sign non-disclosure agreements with all of our additive manufacturing partners, we are unable to share details on our website. If you are interested to learn more, please give us a call.