Processing Methods Overview

<p><br>Successful processing of flexible PVC compounds by injection molding is dependent upon a wide range of variables such as mold design, screw geometry, machine size and shot size. For optimum processing, exact machine conditions will need to be determined by the processor, however the following information will aid the processor in attaining the best possible results. </p> <ul> <li><em>Mold Temperature</em> - inlet water temperature should be between 70 and 100 degrees Fahrenheit. The ejector side should be 10 to 20 degrees colder to help in part removal. </li> <li><em>Stock Temperature</em> - controlled by a combination of heater band settings, screw rpm, and screw back pressure. Consult technical data sheet for recommended temperature. </li> <li><em>Heater Band Settings</em> – to start, set barrel temperatures 20 degrees less than recommended stock temperature. Set nozzle temperature 10 degrees less than recommended stock temperature. </li> <li><em>Screw RPM</em> - a rotation speed of 35 to 50 rpm's should be satisfactory for most applications. </li> <li>Screw Back Pressure - will vary from machine to machine, but generally 60 to 100 PSIG is recommended. </li> <li><em>Injection Speed</em> - s low to moderate for start up; then increase to moderate - fast for production run. </li> <li><em>Injection Pressure</em> - 20% to 40% of the maximum available will yield the best consistency. </li> <li><em>Holding Pressure</em> - usually 50% of the injection pressure. Use just enough to maintain a full part. </li> </ul>

<br /><p>Since flexible vinyl comes in a wide range of hardness and density, the setting of the extruder temperatures will vary greatly. If you have prior experience with a similar flexible vinyl then those temperatures would be a great starting point. If not, refer to the compound's <a href="/MarketsApplications/ProductSearch/tabid/61/Default.aspx?method=Extr" shape="rect">Technical Data Sheet</a> for the recommended stock or melt temperature which will normally be shown as a range. </p> <ul> <li>Take the midpoint of the range and set all barrel, head and die temperatures ten degrees less than the midpoint temperature. </li> <li>Once material is flowing through the extruder, it may be necessary to adjust each temperature zone depending on the aesthetics and output of the material. The most critical zones will be the rear barrel temperature of the feed zone and the temperature of the die. <ul> <li>The <em>feed zone temperature</em> controls the compound sticking to the barrel wall, otherwise known as the bite. Too much bite will lead to overheating of the compound and too little bite will lead to poor output. </li> <li>The <em>die temperature</em> will also influence output and will have an effect on the dimensions of the extrudate. A cold die will restrict flow where as a too-hot die will affect dimensions. </li> </ul> </li> <li>When optimum temperatures are reached, it is known as the <em>temperature profile</em>; temperature profiles vary greatly and include: </li> <li>Straight Profile – a temperature profile with all the same temperatures. </li> <li>Ascending Profile - temperatures that rise from the rear to the die. </li> <li>Inverted Profile - temperatures that decrease from the rear to the die. </li> <li>Hump Profile - a temperature profile with the hottest temperatures in the middle. </li> </ul> <p>All of these temperature profiles may work but finding the right combination for output and aesthetics may take time. </p> <ul> <li>Another controllable setting is the screw RPM. This should be set as high as possible as long as you are producing a consistent quality product. </li> </ul>