In order to optimize extrusion efficiency, quality and overall productivity for medical tubing applications, tooling maintenance is necessary.
The use of a dedicated work cart exclusively reserved and equipped for extruder head maintenance is also recommended. This cart, along with a supply of spare components and hardware is easily justified, especially when examining the potential cost savings that result from well-maintained tools.
It is really important to realize that any misalignment of the tools may be exaggerated in the final product output. Therefore, machining tolerances are held extremely close on today’s multi-lumen and multi-layer medical tubing by utilizing relevant production equipment and processes.
Clean parts, especially with sealing and locating surfaces, are key to product performance and successful end products. These surfaces receive the most care and attention during manufacturing and are the control surfaces that ensure uniformity throughout the tubing. Remember, precision-machined alignments are affected by even a speck of dirt measuring only a few thousandths of an inch. A human hair is about 0.003" (0.08 mm), and since there are many such surfaces in a quality tool, cleanliness is critical.
It is also critical to check the tools for any deformities. Burrs, scratches and scrapes are usually a result of careless handling and/or storage of equipment.
In this example, with an improperly centered tool, a calculated out-of-tolerance area of 0.059 in2 (38 mm2) was derived. When the two surface areas were compared, the calculated material waste was 11.8% of the finished product. The formula is % wall = min. wall thickness, max. wall thickness X 100.
Alternatively, if the % wall can be increased from 80% to 95%, savings of about 12% of total cost can result. Savings will vary depending on the designs.
The quickest way to remove the die is to employ the pressure of the extruder to push it out.
Clean the body by using an air compressor and brass pliers so that the material cools down which increases the melt strength, making it into one-lump versus an elastic, gummy-like substance that is harder to remove. Clean the body feed port using compressed air and brass pliers to simultaneously cool and remove the excess residue from the feed ports. This procedure is followed by brushing with a round brass brush that polishes the surface. The flow area of the 2" (51 mm) flange adapter should be cleaned by carefully using a brass brush.
Most manufacturers recommend using a hand polishing stone to remove the offending burr. Follow stoning with a light application of 600-grit emery cloth if necessary but avoid rounding edges that are intended to be sharp. Flat sealing surfaces can also be cleaned using a stone, followed by a 600-grit emery cloth. Place the cloth on a clean, flat surface, preferably a surface plate, then apply friction in a circular hand motion until the area is clean and even. The parts in question should all be hardened steel alloys and will not be adversely affected using these methods. Inconel, Monel and Hastalloy are typically not heat-treated, requiring special care and handling to avoid any damage.
Working from your dedicated tool cart, follow the manufacturer’s instructions for reassembly. Give each component a final wipe down with a clean rag before installing. Even the smallest amount of grit, dirt and residual material must always be removed. To avoid any unnecessary mishaps, use mechanical or manual assistance for heavy and awkward components.