Polycarbonate is one of the most popular plastics when it comes to machined parts. Specifically, many manufacturers use it in medical equipment and in vitro equipment. Known for its clarity and toughness, polycarbonate machined parts offer a myriad of uses for designers.
Polycarbonate is available in many shapes and forms and experts create it using multiple manufacturing processes.
For applications below 0.375-inches thick, glazing-grade polycarbonate (or window grade) is often the best option. Glazing-grade is a low-cost extruded product that ships with a protective masking. It is available in several tints since manufacturers often use the plastic as part of a protective cover for devices where looks matter.
At 0.375 inches and up in thickness, polycarbonate is sold as a machined plate. If compressed, the product is clear and has protective masking. On the other hand, if it has been extruded, it has a rough, translucent look. Both types have either a purple or grey tint. However, machined optical parts are also available without color.
Both rod and tube polycarbonate are extruded products. Rods are ground to size, leaving a non-clear finish. Manufacturers deliver tubes in protective sleeves and are window glass clear.
Cost of Polycarbonate
In sizes greater than 0.375 inches thick, polycarbonate is about 15 percent more expensive than acrylic and three times less expensive than Ultem (polyetherimide). For machined parts that need thinner stock, a glazing grade is an inexpensive option.
Machine-grade polycarbonate plates, rods, and tubes are naturally clear, with either a purple or grey tint depending on the resin. Black is also readily available. Glazing-grade polycarbonate is a clear product and tinted product; the tints include bronze, grey, and smoke.
Polycarbonate is known for its toughness and impact resistance, so it is often used in bullet-proof glass applications. However, this does not mean that the plastic resists stress cracking or crazing. Since it is an amorphous material, it suffers from steady-state stress; mechanical stress or certain chemicals will cause cracking or crazing. A common example of this is with fasteners which may stress crack when overly tightened.
This plastic has a higher continuous use temperature than acrylic. For polycarbonate, that temperature is 225 degrees Fahrenheit, whereas acrylic is 150 degrees Fahrenheit.
In addition to a higher continuous use temperature than acrylic, polycarbonate has better chemical resistance. It tolerates methanol, ethanol, and bleach. As a result, machined manifolds made with this plastic are perfect for liquid biopharma applications where alcohols are part of the rinsing process.
It is also available as a USP Class VI material, which means it is suitable for blood and skin contact. This is one reason the medical device industry favors it for use in instrumentation.
Polycarbonate Machining Tips
- 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.
Benefits of Polycarbonate
- Polycarbonate machined parts are translucent in appearance but can easily return to clear via a vapor-polishing process.
- This plastic is quite dimensionally stable; close tolerances are possible.
- It has a higher continuous use temperature than acrylic.
- It is available as a USP Class VI material.
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