MACHINERY | PIPE DIES


pressure of the extruder to push it out. Cleaning the body of the die using an air


compressor and brass pliers cools the material enough to increase the melt strength – making it into a single lump rather than a gummy substance that is difficult to remove. The same procedure can be used to clean the body feed ports. This should be followed by brushing with a round brass brush that polishes the surface. The flow area of the 2in (51mm) flange adapter should be cleaned carefully with a brass brush.


Examine all surfaces for irregularities such as burrs and scratches as these must be repaired before reassembly. Most manufacturers recommend a hand polishing stone, followed by stoning with a light application of 600-grit emery cloth – but avoid rounding edges that are intended to be sharp. Flat sealing surfaces can be cleaned in a similar


way. Place the cloth on a clean, flat surface, prefer- ably 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, and require special care and handling to avoid any damage.


Storage and repair Tools should be stored properly in a dry, clean area. A dedicated spot for each tool is best. These areas should have soft surfaces and each instrument should be covered after cleaning. Also, tools should


In the toolbox


Some recommended cleaning tools and materials: n Brass pliers, to grip material and aid in pulling;


n Brass scrapers in different widths – for cleaning flat, exposed surfaces;


n Brass rods – different diameters are good for pushing material out of flow holes;


n Copper gauze for cleaning and polishing exposed round or conical surfaces;


n Compressed air, which is effective at releasing plastic – but take care not to force debris into recesses with compressed air;


n Cleaning solutions may be useful, but always use fresh, clean rags – because used rags often have metal chips embedded in them, which may scratch polished surfaces; and,


n Purging compounds – a wide range is available to purge the extruder screw/barrel of residual polymer.


14 PIPE & PROFILE EXTRUSION | May 2018


be segregated so that they do not come into contact with each other. All tools and instruments should be cleaned thoroughly before storage. When disassembling tools, it is imperative to use purpose-built equipment – which should be available from your supplier. If they are not, ask a reputable tooling house for replacements. The cost of these tools is easily offset by the potential damage caused by improper equipment such as hammers and drifts.


Always follow the guidelines outlined in your


operator’s manual. Individual tools may have specific recommendations, so contact your supplier if anything is unclear. Your supplier understands that optimum performance relies on proper care and maintenance. Here are some useful tips:


n It helps to remove and clean one piece of tooling at a time in order to maintain elevated temperatures; n When cleaning a dual compound crosshead, (plastic and rubber) clean the plastic tooling first and the rubber second; and, n Never use steel tools such as scrapers or screwdrivers because they can scratch the tooling. Tooling maintenance helps ensure a quality


extruded product that meets dimensional specifi- cations, maintains the specified 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 unnecessary costs and these directly affect profitability – and your relationships with customers.


Final reassembly Working from your dedicated tool cart, follow the manufacturer’s instructions for reassembly. Give each component a final wipe with a clean rag before installing. Even the smallest amount of grit, dirt and residual material must always be removed. Use mechanical or manual assistance for heavy and awkward components to avoid unnecessary mishaps. Reapply anti-seize compound to all fasteners if required. Tighten fasteners to manufacturer’s recom- mended specifications, and in the recommended sequence – which should be specified in the manual and is generally in a star pattern. Tighten gradually until the proper torque is achieved to prevent distortion. 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 distribu-


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