Plastic Tube Manufacturing in Water Treatment and Pharmaceutical Industries

From car-seats for children to the computer keys we type with, plastic plays an everyday role in our lives. But beyond its use in common objects, it also serves as an essential component in the manufacturing and materials handling sectors. Plastic tubes, in particular, are responsible for a multitude of functions in a vast array of industries, including pharmaceutical and waste water treatment and clean water handling applications. Because plastic tubing is so versatile and is available in varying compositions, the manner in which tubing is used in different industry sectors can differ.

Plastic Tubing in Water Treatment Applications

In plastic tubing applications for waste water and water treatment applications, there or four common kinds of plastic tubing used: acrylic (Plexiglass), polycarbonate, vinyl, and polyethylene. Within the plant, tubing is typically used during chemical operations that meet the plastic’s temperature and corrosion requirements. To connect and join tubing, the ends are fused together using heat or solvent-cement. In both processes, the tube-ends are first melted down until they are soft and malleable, then pressed together. With solvent-cement, a solvent is used to slightly dissolve the plastic tube-ends, and the ends are pressed together. The plastic ends then harden to each other, creating a strong joint. When heat is used, the tube-ends are simple pressed against a hot plate until they become molten, then pressed against each other. As they cool and harden, the tubes join to one another.

When it comes to handling water, polyethylene (and also polyvinyl chloride and polybutane) is the preferred material for plastic tubing. Because the interior of plastic tubing is so smooth, friction loss is lower than with other kinds of tubing materials, such as metal. Additionally, plastic is lightweight, making it easy to install. However, it’s important to avoid using plastic around gasoline, oil, or any form of industrial solvent, as these can both degrade the plastic and potentially contaminate the water. In cases where plastic tubing is used to carry drinking water, the tubing must adhere to NSF international regulations. Approved tubing will bear an NSF seal on the exterior.

Plastic Tubing in Pharmaceutical Applications

Much like the tubes that handle drinking water, tubing applications for pharmaceutical applications must also meet certain standards, and are manufactured with sensitive applications in mind. For applications that use plastic tubes to move pharmaceutical liquids, there are typically two types of tubing available: single layer and laminated. Single layer tubing does not feature true barrier traits, despite the presence of a coating. Laminate tubing, on the other hand, features a barrier layer within the composite structure of the laminate.

In tube manufacturing there are two different steps. The first step involves the manufacture of the tube itself, referred to as a sleeve. The second step involves attaching the threaded end of the tube, also called the head. The process by which a tube is attached to its head entails one of two methods: the Downs or Strahm manufacturing method is typically used.

In order to generate a plastic sleeve (to manufacture a single-layer tube), LDPE plastic is fed into an extruder and passed through a die. The result is a 12 to 20 mm thick (wall-thickness) tube, which is ready to be coated. The tube is then cooled via a chilled mandel, which helps expedite hardening and also cuts the tubing into designated lengths. Next, the newly formed sleeve is coated to enhance moisture resistance and other desired properties.

When the sleeve is complete, heading can begin. The Strahm method of heading depends on extrusion and injection molding to connect the threaded ending to the end of a tube. The Downs method, the more common of the two, uses compression to mold the head onto the tube.