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Around 1900, cars and trucks began to share roads with horses and people. They are usually to the right (or to the left in the British Empire, Japan, and Sweden), but there are no lights at intersections to stop the flow in one direction and allow flow in the other. This resulted in the traffic police maintaining order more or less.

The first traffic light in the United States-some say it was in the world-rose in Cleveland in 1912, but I remember the unique traffic light on Fifth Avenue in New York, designed by Joseph H. Freedlander in 1929 and used until 1964 Year. Mercury is the god of speed with winged feet in Roman mythology-Hermes. Mercury and bromine are the only elements that are liquid at room temperature. (Water is a compound, not an element.)

The lights on Fifth Avenue, like most of its predecessors, only show red and green. With this dual-lamp system, red lights up first, then green goes out. This way, if you see red, you will slow down enough time to stop at the intersection.

Yellow Zhongguang was first used in Detroit around 1920 and was borrowed from the railroad. Garrett Morgan obtained the patent for the four-way three-color system in 1923 and licensed it to General Electric, which produced thousands of units.

In addition to the insulation of all wiring, what is the connection with extrusion? stop. This month’s column is about downtime, stopping the extruder for a few minutes or more. Time is important because the system will start cooling immediately (but not always in the feed zone) and will freeze all the plastics in it very quickly unless some heat continues to exist.  

The following content is adapted from my own "Plastic Extrusion Operation Manual", 24th edition (2021). For more information about the manual or to order a copy, or to talk about plastics that are non-toxic and beneficial to our environment and health, please visit my website or call/email me. Contact details are at the end of this article.

Material changes and shutdowns should be planned as much as possible. For material replacement, new materials must be prepared (pre-dried if needed) and a container for the existing contents of the hopper should be provided when needed.

You should match light colors with dark colors. Flowable melts are more viscous, but due to production planning and sales needs, this is not always feasible. Removal of compounds can speed up material replacement and reduce the amount of waste. They are particularly useful between materials that are not compatible with running on large extruders, because the mixed waste is of low value and takes a long time to disassemble.

Most cleaning agents are high-viscosity plastics, some have inorganic fillers added for scrubbing, and are usually highly stable to avoid decomposition. Some cleaning agents have a solvent effect, and one type of cleaning agent will chemically react to depolymerize anything in the system.

In the purification process, temperature is very important. The melt that resists scavenging when cooled may become so soft when it is hot that just changing the temperature can work without using any scavenging. One such non-purge technique relies on the cycle of screw speed.

Can water be purified? The steam may soften and blow out the residue, but water alone is dangerous because the steam may escape from the mold or hopper and scald anyone nearby. Water-saturated filled plastic may be safer.

The screws can be kept full to avoid disintegration on the crushing plate. In this case, use a slide to cut off the flow of the hopper, and run for a few more seconds to clear the first few flights. This will prevent bridging in the throat and sticking to the screw root in the feed zone during cooling and later start-up. When the screw finally stops, keep the barrel cool for a few minutes.

In order to reduce the pollution of decomposing plastic particles, turn off the heater and run the screw at a low speed to reduce the melt temperature and prevent decomposition. Some extruders put nitrogen into the barrel when they are shut down to prevent oxygen from entering the hot reaction zone at the end of the screw.

If you open the machine head to replace the screen while keeping the mold full and in place, be sure to clean the crushing plate and the mating sealing surface carefully.

If the head and mold are clean, please do it quickly as a team. Plastics are more likely to fall off when heated, and the first 10 to 15 minutes are critical to prevent degradation, especially for PVC. After the motor stops, immediately open the head bolts, take out the screen and crushing plate, clean the sealing surface, and other people clean the mold at the same time.

Cleaning metal surfaces may require reheating in an oven or small parts cleaner, such as a fluidized alumina bed, pyrolysis oven, oil bath or salt bath.

When the mold is not in use, use a non-scratch, non-melting cover to protect its lips.

Will the screws come out too? Some extruders never take out the screw and are content with occasional cleaning. Usually, these are large machines that run commodities, and downtime is costly. At the other extreme are UPVC extruders, which take everything apart (almost) every time they stop.

There may be reasons to pull the screw, such as material sticking to the root of the screw or measuring wear. In this case, please empty it as much as possible, and then clean it with washing, wax or woven copper mesh for easier removal and replacement.

Use screw propellers and cranes where needed; avoid using sledgehammers or forklift forks that may damage the equipment. Be prepared to put the screw somewhere and pull it out directly. For small ones, do not use an electric hoist to pull the end up, because the screw may bend.

Most of the screws can be cleaned in the middle of cleaning, still supported by the barrel and at a good working height. Band wrenches are very useful. Some people use brass tools/brushes and braided copper mesh to avoid scratches, which is a good idea on the internal mold surface, but it is not always important on the screw because it depends on the material of the screw surface. There are also screws and mold "soap".

Sometimes, if the temperature of the screw is sufficient for the melt to act as a lubricant, the screw can be returned without cleaning the barrel. It is also easier to heat the barrel due to thermal expansion. However, unless a more stable shutdown purge is used, the old, degraded melt may cause gel and "fisheye" splashes when production is resumed. To clean the barrel mechanically, place a long-axis wire brush on an electric drill, or use a net that is firmly wired or nailed to a broom.

Suck out any loose things. Do not use an air hose to blow the material back into the barrel, as particles may enter the screw seat and prevent full engagement there. Check the area and keep it clean and lubricated.

For all production lines, tracking output per revolution is a good way to "see" wear, even better than measuring it individually, because wear may not matter if the output per revolution does not decrease.

Allan Griff is a senior extrusion engineer. He initially provided technical services for a major resin supplier. Now he has been working independently for many years as a consultant and an expert witness in legal cases, especially as an educator through webinars and seminars. , Both are public and internal, and are now in his new audiovisual version. He wrote "Plastic Extrusion Technology", the first practical extrusion book in the United States, and the "Plastic Extrusion Operation Manual" updated almost every year, available in Spanish, French and English. Learn more on his website www.griffex.com or send an email to [email protected].

Griff said that in the near future, or may never plan to hold live seminars, because his virtual audiovisual seminars are even better than live broadcasts. No need to travel, no need to wait for the live broadcast date, use the same PowerPoint slides, but with audio explanations and written guides. Watch at your own pace; group attendance is offered at a single price, including the right to ask questions and get full answers via email. Call 301/758-7788 or send an email [email protection] for more information.

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