Making injection molded prototypes is both an art and a science. Parison not being blown defective blow timer, clogged blow lines, or too sharp pinchoffs replace blow timer clean. Top10 injection molding defects and how to fix them. Injection molding machine as for the injection molding machine, several types such as plunger type, plunger preplasticating type, screw preplasticating type and inline screw type, etc. Compression and injection molded sample preparation for hdpe. Top10 injection molding defects and how to fix them tony rogers on june 12, 2015. Obc products for injection molding obc grades designed for injection molding applications are available in a range of densities with melt indices of 5 and 15 g10 min.
Chapter 2 injection moulding process injection moulding is the most widely used polymeric fabrication process. The information is offered solely for your information and is not all. Hdpe plastic granules or pellets are usually available in bulk via railcars or hopper trucks and in semi. The injection moulding troubleshooting guide covers some of the common problems encountered with this process, but is by no means complete. This information is intended to be used only as a guideline for designers and processors of modified thermoplastics for injection molding.
Most importantly, it will help you design solutions to these problems ahead of time. Calculate melt residence time by formula in molding guides. For injection molding, this means there are several items on the mold and press that should be checked before troubleshooting any molding. Solving molding air trap problems definition air traps occur when converging flow fronts surround and trap a bubble of air. Shear rate, for example, is higher in injection molding than in extrusion and rotomolding, by about an order of magnitudea substantial difference, giving high frozenin stress and. Most importantly, it will help you design solutions to these problems. In this video kevin crystal gives an overview of hdpe highdensity polyethylene, surface finished on hdpe injection molded parts, and the properties of this material.
Table 3 is a troubleshooting guide that contains the solution to many common molding problems. Injection machine builders supplying machines to the pet injectionmolded industry are nestal, mechi, formpast, and nissei. Injection molding fractional melt index, high density. Blow molding troubleshooting guide introduction this guide indicates possible causes and corrective actions for problems typically encountered in the blow molding process.
The rapid guide to perfect pet bottles blow molding. Injection molded plastic begins its journey through the part tooling via an. Black spots, brown streaks blisters air entrapment. During polymerization, small molecules called monomers combine to form long polymer chains.
Allow sufficient hold time to cool the part before removing it from the mold. Ppd407b injection molding troubleshooting guide eastman. Highdensity polyethylene hdpe with a melt flow rate less. Injection molding vinyls trouble shooting guide many of the problems encountered while molding pvc have simple solutions. Solve plastic injection moulding problems with this onepage troubleshooting grid. Lower melt temperatures, injection speeds, screw speed and. Injection molding troubleshooting guide brittleness contamination bubbles cont. Implement a quality assurance syste stearate is identifies any trends and allows for develop and publish the quality standards change to become.
Problems can be caused either by defects in the molds, or. Injection moulding troubleshooting guide please note the injection moulding troubleshooting guide covers some of the common problems encountered with this process, but is by no means complete. Because injection mold design and processing is complex, a set. Improper runners or gates mold temperature too low material excessive moisture operator inconsistent cycle machine excessive injection speed or pressure excessive back pressure screw speed too high improper compression ratio of screw. The goal is to correctly identify which problem is actually causing the defect and to. Injection molding troubleshooting guide rtp company. Injection molding reference guide injection molding reference guide. The disadvantages of injection molding such materials included longer cycle times, higher energy costs, and more extensive. Most defects respond to one of a variety of process andor material changes. This is a troubleshooting guide that should be in every operators toolbox or on hisher smartphone or tablet. Molding troubleshooting guide bond readout bond readout is a surface distortion similar to a hump or sink that occurs over a bond line probable cause material process mismatch of compliance between outer panel, inner panel and adhesive incompatible thermal expansion coefficients between the sm and the adhesive. Hangup of molten material in injection barrel or runner system. Machine injection temperature too high injection pressure too low injection forward time too low insufficient material feed improper injection temperature profile excessive injection speed insufficient. The last production of degradable plastics materials in the cylinder, screw, valve adapter maybe curing inside the aggregate hot runner pipe.
If this problem is allowed to continue without fixing the root cause it will very quickly cause damage to the molding surface. This is an excerpt from our new course injection molding fundamentals lesson 1 parts of the machine and operator responsibilities. Increase stock temperature by increasing back pressure andor barrel temperature. Polyethylene pe is widely used in the world today to efficiently protect and transport all types of products. Schematic of thermoplastic injection molding machine. A guide to polyolefin injection molding lyondellbasell. Injection molding calls for the use of manmade synthetic polymers such as polyethylene, abs, and nylon.
For additional troubleshooting information, contact your dow representative. Injection molded plastic begins its journey through the part tooling via an entry section called a gate. Downloadable pdf for troubleshooting injection molding. Ten injection molding defects and how to fix them flow lines, sink marks, voids. Hdpe high density polyethylene is the hardest and stiffest version of this material. The injection moulding troubleshooting guide covers some of the common problems. Injection molding reference guide materials, design, process optimization, troubleshooting and other practical information from the experts at routsis training plastics is a sophisticated and diverse. Troubleshooting guide for blow molding problem possible causes possible solutions 1. But as with any quality problems, knowing how molding defects arise is half. It may be necessary to move the mold to a machine with less injection capacity.
Read the best guides for troubleshooting molding put together by plastics troubleshooting experts. Here are 11 common injection molding defects to watch out for when inspecting. On 125 pages 31 common defects of pet bottles are analyzed and tips given to solve them. It does not have the impact strength of low density, but is more resilient polyethylene is a widely used, inexpensive.
Polyethylene extrusion blow molding process guide formosa plastics corporation, u. Melt temperature too high measure and reduce melt temperature. Troubleshooting guide for injection molding troubleshooting is the art and science of remedying defects after the process has demonstrated the ability to produce acceptable production parts. It can also be used as reference tool for troubleshooting and overcoming. Polyethylene materials solutions for pe products dow inc. Troubleshooting is the art and science of remedying defects after the process has demonstrated the ability to produce acceptable production parts.
Troubleshooting solution guide injection molding machine 1. Injection moulding troubleshooting guide pdf grid author. Cracking when mold opens overpacking hot mold poor drying breakaway too fast needs vacuum break reduce either packing pressure or time. The information contained in these guidelines is provided in good faith and may assist with problem solving and troubleshooting. Troubleshooting tips for injection blow molding used. Close observation of each unsatisfactory condition will usually.
Injection molding involves complex technological and rheological processes that can present possible production challenges. Injection molding defects and solutions moulding defects. Common causes of and steps to prevent vacuum voids in molded parts. If 5 minutes, use smaller shot machine or reduce cycle time. Molding troubleshooters are called upon to resolve problems with the part, mold, machine, or process. Molding troubleshooting guide bond readout bond readout is a surface distortion similar to a hump or sink that occurs over a bond line probable cause material process mismatch of compliance between. Check injection throttle position and if possible, increase its setting. Possible solutionsalter gate position andor increase gate size. Injection molding grades typically have a narrow molecular weight distribution.
Injection pressure should be kept high enough in order to ensure that the pressure value does not drop below the required set point values during the entire cycle. Philosophy of troubleshooting injection molding problems. Transfer molding combines the advantages of injection molding with the ease of compression molding. Thermosets polymers get their strength from a process called polymerization. If problems persist, contact your solvay representative for additional. Shortening the hold time can lead to increases in warpage, sinking marks, ejector pin scars and shrinkage.
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