Black spots Posted on 14/01/201914/07/2020 by espira_ In this second post we will focus on a very common issue that appears in injection processes: the emergence of black spots in the surface of plastic pieces. These spots are visible in the surface of these pieces and there may be many of them, as well as appear randomly, which hamper processes and threaten their efficiency levels. What are these black spots? They are usually small pieces of dirt or charred material that were dragged from the injection machine’s spindles or cylinders. These are incorporated as visible defects in the final piece. Why are they caused? Contamination of the natural plastic material. Degradation of the plastic, as it is being injected in an excessively high temperature inside the machine for too long. Degradation of previous waste materials that were not cleaned properly and were adhered in the walls of the cylinder or in the spindle. Use of not suitable colorants for the kind of material that is being used. Solutions Use as much non-contaminated material as possible. Conducting a visual inspection of natural chippings is an effective and simple method that can prevent these kinds of problems. Make sure to clean well the residues of the previous material when there are changes of materials in the same machine. We could clean the machine with the same natural material or with products with this purpose that make cleaning tasks and the change of materials easier, as the cleaning masterbatch X-999. With a 10% or 20% dose, we could achieve optimum cleaning levels in the operations involving a change of material.
Information and transparency. Splay marks due to burnings. Posted on 14/01/201914/07/2020 by espira_ This blog on the plastic transformation sector is intended to become a portal of verified information and useful for our customers. In Colortec we are engaged in writing several posts, as a way of transmitting our specialised knowledge and experience in this business. After working closely for more than 25 years with companies from different sectors and sizes, we have gathered the main questions and common patterns when manufacturing our customers’ pieces, ensuring the requested confidentiality by our customers. We believe this may be of great help for other manufacturers and may serve as a guide in design processes and the fix of physical defects of certain pieces. Since our first post, we are going to deal with one of the most frequent physical defects in thermoplastic injection pieces: splay marks. There are many types of splay marks with many possible causes. In this post we will write about splay marks due to burnings. What are splay marks due to burnings? They are caused due to the thermic degradation of plastic or colour concentrate. They appear in form of chalky or brown splay marks over the Surface of the injected piece. What are their main causes? 1st Cause: Excessively high temperature in the injection machine. 2nd Cause: Too much time inside the injection cylinder. 3rd Cause: Low thermic resistance pigments or colorants. 4th Cause: Spindle working at a very high speed. Solutions: Solution to Cause 1: Lower the temperature of the machine’s cylinder, so the temperature of the plastic mass is also lowered. Reduce the injection pressure. It is important to take into consideration if the natural material has been subjected to a drying process before its processing, since prolonged exposures mat degrade the material in advance. Solution to Cause 2: Shortening the times in the cycle may prevent the material to exceed the recommended time spent inside the machine. Solution to Cause 3: Apply masterbatch designed with colorants, pigments or additives with better thermic resistance that may be apt for the material’s temperature processing. Solution to Cause 4: Reduce the spinning speed of the spindle.