PT Blog

Five Ways SPC Can Improve Performance

Successful plastics manufacturers and molders have mastered the ability to compete on quality while reducing the inefficiencies and scrap that can create a drag on profitability. For many of these companies, statistical process control (SPC) serves as the framework for continually finding new ways to improve process control, process performance and product quality.

Fundamentally, SPC enables manufacturers to inspect a random output sample from any measurable process and understand what is causing deterministic variations in product, process and quality levels that can be modeled versus completely random factors. This empowers managers to decide whether a given process is producing products with characteristics that fall in a predetermined range. For plastics companies, SPC has proven highly valuable for analyzing deviations in process parameters, temperature, velocity, and machinery attributes that can cause higher scrap rates.

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Running PCR? Optimize Performance & Processability with Stabilizers

Despite countervailing forces such as lower virgin resin prices, strong demand continues for post-consumer recycled (PCR) content in applications such as packaging, pipe and furniture. One reason is the commitment by major brands to address consumer demands for sustainable products and packaging. Also, there are new regulations that encourage the reuse of plastics to support circularity. For instance, in 2022, the UK will introduce a Plastic Packaging Tax to incentivize the incorporation of recycled plastic. Also, the Council of the European Union (EU) adopted a directive in 2019 that introduces upcoming restrictions on certain single-use plastic products. It includes targets for plastic bottles to contain at least 25% recycled content by 2025 and 30% by 2030.

As demand for, and use of, PCR content continues to increase, there has been a renewed focus on the issue of polymer degradation. The properties of PCR content, such as melt flow, color and contamination, are directly related to proper stabilization—either upstream by plastics producers or downstream by recyclers and processors.

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Understanding the Effect of Polymer Viscosity on Melt Temperature

Plastics extrusion has been around for almost 100 years, but despite its extensive history, polymer shear rate/viscosity curves are still not widely used or understood. I was recently asked by an experienced pipe processor why the melt temperature was so high on a new polymer his company was evaluating. They had changed from a fractional-melt-index (0.35 MI) HDPE to a 0.06 MI bimodal HDPE, and were trying to hold the temperature down to accommodate their downstream cooling capacity. They tried drastically reduced barrel temperatures—but not only were they unable to bring the melt temperature down, they overloaded the drive by extracting too much heat from the system.

Basically, the melting and melt-temperature rise in an extruder occur largely by “stretching” any melted polymer contained in the space between the barrel bore and the screw (see illustration). The barrel is heated to help initiate the first melting, but then provides primarily a thermal jacket over that stretching process. The polymer melt sticks rigidly to both the barrel wall and the screw surface (see the highlighted strip in the illustration). The rotating screw then stretches or “shears” the polymer in that space. It’s like the polymer were made up of many tangled rubber bands all attached to the barrel and screw.

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Materials Part 6 of 7: Annealing Tips for Thermoplastic Polyurethanes

Polyurethanes exhibit an incredible range of chemistries and structures that may be unmatched in the world of polymers. While all polyurethanes are fundamentally the product of a reaction between an isocyanate and an alcohol, the exact chemistry of these ingredients can be varied significantly to create a wide range of properties. In addition, altering the ratio of what are referred to as the hard and soft blocks within the structure produces different property balances that are typically indicated by the property of surface hardness, beginning as low as 60 on the Shore A scale and extending up to 75 on the Shore D scale.

Polyurethanes can be chemically crosslinked to form thermosets or they can be thermoplastic. And while these materials are generally considered to be elastomers, rigid urethanes also exist and the mechanical properties of these materials can be further modified with the addition of reinforcing fibers.

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Follow These Purging and Preventive Maintenance Tips for Your Screws and Barrels

In today’s competitive processing environment, every minute counts. Time is money, and faster color and resin changeovers can minimize downtime and reduce scrap and waste to give processors a competitive advantage to optimize current business as well as win new business. Paying close attention to the care and condition of your screw and barrel can yield dividends for processors.

It’s difficult to compensate for the shortcomings of a worn screw or barrel, so maintaining your equipment is vital. The screw and barrel for an extrusion or injection process are often taken for granted. Routine preventive maintenance (PM) is often sacrificed to meet current demand, and while short-term needs are met, the long-term impact of deferring maintenance can be devastating to your business. One means of improving the PM of both screw and barrel is the regular use of a high-quality commercial purging compound (CPC).

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