POLYCARBONATE PLASTIC & MACHINING

Regarding temperature range, this plastic has a higher continuous use range than some other materials. Polycarbonate holds up to a max temperature range between 107°-147°C (225°-297°F, respectively) before it starts to warp or melt. Among other reasons, designers in aerospace and automotive commonly use this material due to longer exposure to these elevated temperatures. 

Additionally, polycarbonate has great resistance to certain chemicals. It tolerates methanol, ethanol, and bleach among a few others. As a result, machined polycarbonate manifolds are perfect for liquid biopharma applications where alcohols are part of the rinsing process. As having use in medical and biopharma, this material is also available as USP Class VI, which means it passes requirements for blood and skin contact. This is one reason the medical device industry favors it for use in instrumentation.

At 0.375 inches and up in thickness, producers often sell polycarbonate as a machined plate. Depending on the expected end product, the raw material can come either as compressed or extruded. If compressed, the product is clear and has protective masking, best used for optical components. On the other hand, if it has been extruded, it has a rough, translucent look.

When it matters, customers can select from several different tints, including purple and blue. As this material often finds use as part of a protective cover for devices, aesthetics can matter in terms of clarity and protection. Usually, machine-grade polycarbonate plates, rods, and tubes are naturally clear, with either a purple or grey tint depending on the resin. Black is another option as well. Glazing-grade polycarbonate can come as either a clear product or a tinted product, depending on the expected use. These tints include bronze, grey, and smoke.

In sizes greater than 0.375 inches thick, polycarbonate is about15% more expensive than acrylic and 3 times less expensive than Ultem (polyetherimide). Polycarbonate machining for resulting machined parts that need thinner stock, a glazing grade is an inexpensive option.

Machinists usually polish polycarbonate via via vapor polishing or optical machining. However, the polished material is often times softer than acrylic, resulting in lower scratch resistance. Conversely, polycarbonate parts have greater toughness than acrylic parts.

It's important to note that polycarbonate is not inherently UV resistant and requires an addition of a UV stabilizer to avoid yellowing. Any polished polycarbonate medical components that require FDA or USP Class VI certification use a non-UV stabilized material.

Designers may find themselves comparing polycarbonate to acrylic due to their similarities. However, they are different in a number of key ways, including:

• Polycarbonate is much stronger than acrylic.
• Acrylic is not nearly as resilient as polycarbonate.
• Acrylic can be heated and reshaped, while polycarbonate cannot.
• Polycarbonate is more expensive than acrylic.

There are also some limitations to using polycarbonate as a material choice, including:

• The material scratches easily. This can be overcome by using an anti-scratch coating.
• Polycarbonate can expand under heat. Therefore, companies that provide plastic machining services need to fully understand and accommodate for this property. 

When working with this material, here are a few tips to keep in mind:

• Since polycarbonate machined parts wear poorly, do not use these parts in bearing or sliding applications.
• Avoid stress risers. Corner radii reduce the risk of stress cracking and strengthen parts.
• Polycarbonate machined layers are readily bondable, so consider a bonded multilayer manifold to improve performance.
• Heat-staked inserts are important for small threads under #2 or 2 mm, for those applications that require repeated disassembly.
• Consider straight threads over pipe threads, as pipe threads create steady-state stress.
• Machined parts with this type of plastic require annealing after machining, so look for shops that can provide this service.
• Carefully torque threads to avoid stress cracks.
• Do not accept whitish burn marks.
• Polycarbonate machining often forms a tough burr. Therefore, deburring is often necessary, but a smooth, burr-free machined part is possible.

Plastic Machining with Polycarbonate (PC) Plastic transcript