Extrusion Asia Edition 2-2020

pressed air; h.) Cleaning solutions may be useful, so remember to use fresh, clean rags (used rags often have metal chips embedded in them, which may scratch polished surfaces); i.) Cleaning oven – for plastic only. Follow manufacturer's re- commendations. If no temperatures are specified do not exceed 850 degrees F (454 degrees C). Don’t quench tooling to cool, as this could affect tooling hardness, concentricity and tolerances. j.) Purging compounds – several are offered to pur- ge the extruder screw/barrel of residual polymer and rubber compounds. Removing Excess Material for Optimum Machining Efficiency Clean parts are critical to extrusion tooling perfor- mance and quality manufacturing. This is especi- ally true for the sealing and locating surfaces – that control uni- formity of the production process. For general maintenance of the tools, before storage or tooling changeover, a thorough cleaning and removal of the excess material assures the preci- sion machining alignments required to produce end products to the precise tolerances. Equipment should be cleaned while it is still hot, since residual polymer and rubber will be easier to re- move. Be sure to follow all MSDS recommendations when heating the tooling. Thermal gloves are used to protect the hands from the heated tooling surfaces. A brass scraper, as well as a brass or copper wool cleaning cloth are recommended be- cause they are soft enough not to scratch the surface. Make Tool Cleaning Easier 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. Cleaning the body feed port using compres- sed 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. Examine all surfaces for any irregularities such as burrs and scratches since these must be repaired before the head is reas- sembled. Most manufacturers recommend using a hand polish- ing 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 sur- faces 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 un- til 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 typical- ly not heat-treated, requiring special care and handling to avoid any damage. Don’t Overlook Repairs Tooling maintenance helps ensure a quality extruded product – one that meets dimensional specifications, maintains the speci- fied minimum tolerance and is economically produced. Dirty, neglected and improperly adjusted tools contribute to excessive compound applications, which in turn complicate maintenance of minimum thickness tolerance. Excess material results in un- necessary costs and these directly affect the profitability of your company and the relationships with your customers. The Important Final Step – Reassembly Working from your dedicated tool cart, follow the manufactur- er’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 re- moved. Use mechanical or manual assistance for heavy and awkward components to avoid unnecessary mishaps. Reapply anti seize compound to all fasteners if required. Tighten fasten- ers to manufacturer’s recommended specifications as well as in the recommended sequence. This fastening sequence should be specified in the manual and is generally in a star pattern. Tighten gradually until the proper torque is achieved to prevent distortion of the tooling. One of a die manufacturer’s main goals is to form a concentric cone as quickly and accurately as possible in the primary section of the die – when the extrudate first emerges from the die's distribution capillaries. A properly designed and manufactured die has even distribution close to the extrudate entrance point, but this effort is negated once the die is adjusted, shifting the extrudate off to one side. An ec- centric cone is formed in the primary area, and a concentric cone exists at only one point in the process, rather than a smooth, continuous flow path with decreasing volume. A pro- perly manufactured and aligned extruded head, along with well-maintained tooling should require little or no adjustment. Another adverse affect of unnecessary die adjustment is the stress introduced to the extrudate caused by unbalanced flow. The net effect is the final product retains memory of this imba- lance and unpredictable die swell occurs. ➠ Guill Tool & Engineering 10 Pike Street, West Warwick, RI 02893, USA www.guill.com 19 Extrusion Asia Edition 2/2020 Guill 812 Three Layer V ersion 03-Rework