News-HowStrawsAreMade

HOW STRAWS ARE MADE

Proudly Australian, Austraw manufacture several of it’s straw lines here in Brisbane. A very interesting process – we thought you might like to know how this is done.

Below is an excerpt from http://www.madehow.com/ detailing the process.

Straws are made from a formulated blend of plastic resin, colorants, and other additives.

Polypropylene is a resin made by polymerizing, or stringing together, molecules of a propylene gas. When a very large number of these molecules are chemically hooked together they form this solid plastic material. This resin is light-weight, has fair abrasion resistance, good dimensional stability, and good surface hardness. A key attribute of this plastic is that it is safe for contact with food and beverage.

Colorants can be added to the plastic to give the straws an aesthetically pleasing appearance. These pigments are typically supplied in powdered form, and a very small amount is required to impart bright colours.

The Manufacturing Process

Plastic compounding

  • 1 The polypropylene resin must first be mixed with the plasticizers, colorants, antioxidants, stabilizers, and fillers. These materials, in powder form, are dumped into the hopper of an extrusion compounder that mixes, melts, and forms beads of the blended plastic. The powders are mixed together and melted as they travel down the barrel of the extruder. Special feeder screws are used to push the powder along its path. The molten plastic mixture is squeezed out through a series of small holes at the other end of the extruder. The holes shape the plastic into thin strands about 0.125 inch (0.3175 cm) in diameter. One compounding method ejects these strands into cooling water where a series of rotating knives cut them into short pellets. The pellet shape is preferred for subsequent moulding operations because pellets are easier to move than a fine powder. These pellets are then collected and dried; they may be further blended or coated with other additives before packaging. The finished plastic pellets are stored until they are ready to be moulded into straws.

Straw extrusion

  • 2 The pellets are transferred to another extrusion moulder. The second extruder is fitted with a different type of die, which produces a hollow tube shape. The pellets are dumped in a hopper on one end of the machine and are forced through a long channel by a screw mechanism. This screw is turned in the barrel with power supplied by a motor operating through a gear reducer. As the screw rotates, it moves the resin down the barrel. As the resin travels down the heated channel, it melts and becomes more flowable. To ensure good movement and heat transfer, the screw fits within the barrel with only a few thousands of an inch clearance. It is machined from a solid steel rod, and the surfaces almost touching the barrel are hardened to resist wear. By the time the resin reaches the end of the barrel, it is completely melted and can be easily forced out through the opening in the die.
  • 3 The resin exits the die in a long string in the shape of a straw. It is then moved along by a piece of equipment known as a puller which helps maintain the shape of the straw as it is moved through the rest of the manufacturing process. In some processes, it is necessary to pull the straw through special sizing plates to better control the diameter. Eventually, this elongated tube is directed through a cooling stage—usually a water bath. Some operations run the plastic over a chilled metal rod, called a mandrel, which freezes the internal dimension of the straw to that of the rod. Ultimately, the long tubes are cut to the proper length by a knife assembly.

Read more: http://www.madehow.com/Volume-4/Drinking-Straw.html#ixzz3mLC8Ssie