1680 North Main Street
Orange, CA 92867
Phone: (714) 283-2032
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CRT has the ability to mold Tensile, Flex, Izod & Heat Deflection specimens, along with Compression Molding, and 2-roll milling capabilities to better control the outcome of test results. CRT documents all profiles, including dying time & temperature, barrel & mold temps, cycle times, pressure, etc. This information is used for quality control for future tests, which is for continuing resins from established customers. CRT is the first laboratory accredited by the National Sanitation Foundation (NSF) for the purpose of providing them with Injection Molded test specimens (type-I tensiles).
CRT started molding in 1980 when it was noted that the test specimens coming from outside labs or customers where either out of tolerance or had excessive flash. CRT has over 20 years experience in injection molding & extrusion of a wide variety of filled and unfilled polymers. CRT has internal capabilities of Injection Molding and Extrusion of all polymer blends and feels that its extensive knowledge of these polymers, may aid you in current on the floor problems. Many molders call CRT to verify if molding, drying, etc. are at optimum prior to going into production. Other manufactures, rely on CRT to pre-qualify extrusion compounds on out 1Ó lab extruder. This method assures that if a new compound is formulated, that all thermal & physical property measurements meet specifications. CRT can customize a project for your specific application and with in-house testing available, we can assure that the materials will be evaluated for compliance.
As we look into specific molding problems, below are some possible solutions may be used as an aid in producing quality molded parts.
Keep in mind that up to 65% of product rejections are directly related to Injection Molding profiles, and that up to 20% can be from the Mold. When a defect occurs, the molding profiles must be reviewed (assuming that materials are in spec).
Described below, are problem and solution categories that may help to determine if quality parts are being produced.
In an Injection Screw that's molding at a low compression ratio for the resin being used, causing the polymer molecule-chain not to form correctly. The result is a weak molecular bond, hence brittle parts. De-lamination can be a result of this, because the skin on the part will not molecularly bond .
The technician must take a compression reading to identify and record the ratio. This should be performed once every six months (depending on the usage). Most Alloy blends are very sensitive to shear/compression and detailed attention must be incorporated on these materials. Most suppliers will have the compression-ratio of the material they supplied. Excessive dwell (residence) time is of great concern, especially with engineered polymer grades. The barrel-to-shot ratio must be kept at a minimum. Too much dwell time will cause crystallization of the molecules and other problems, thus resulting in breach of quality.
Most molders use tool assembly lubricant to break in a new or revised mold (tool). When this is applied, one must take note that too much lube on any of the knock-outs or adjacent areas may leach in to the molded part during production. This is seen in very transparent parts when just a small amount of lube exists. The parts clarity is compromised and usually blamed on the material. In other areas of the Molding machine itself, leaks tend to haunt most molders and waiting for production to slow down may cause even more serious problems. The oil leakage from the machine may come in contact with the molded parts ejecting from the tool. This can cause serious down-time delays if not properly corrected. One should consider that if a seal has been leaking for a while, then breaks down during production, the production time is increased, thus not meeting the deadline.
These problems can always be avoided, with proper supervision from the foreman and corrective action. The leaks must be addressed immediately and a pre-production run must be initiated to confirm that the leak was properly corrected (if time allows)
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With molds and all of their intricate slide, pins, etc., it is important to lubricate all areas that see movement. Once the pins, cams, lifters, etc., have been lubricated, it will usually have a service life 10 times that of non-lubricated tools. This preventative action must be applied to achieve full production output. This will also save the molder considerable down-time and undo spent money to fix the problem.
These problems can always be avoided by only using what's required to eject the part(s) and to properly lubricate the internals of the tool. On too many occasions, the molder used excessive amount of mold release, which causes rejections due to surface appearance, brittleness, or surface-plating.
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Most molders use re-grind at a certain percentage, if not 100%. This can cause many problems, especially if Fiber Reinforced materials are being produced. When the Virgin material comes in to the shop and the matrix contains 30% Glass-Fiber, the molder will usually use a 20% re-grind to the virgin material. When doing this, one must take note of when they started to use the re-grind, because if not properly calculated, you could end up producing a part with up 100% re-grind, hence brittle parts (which some molders consider contamination) A sloppy workshop can also contribute to contamination and if not properly cleaned and maintained will cause production problems and/or rejections.
Most of these problems cans be regulated if not completely eliminated by implementing policies to ensure the effectiveness of the workshop area and the employees. When using re-grind materials (depending on how critical the application is), one must take note to log down the re-grind input and replace with Virgin material. When Glass Fibers are at issue, the fibers break down during the first heat history, and if profiles are not set to optimum performance, would increase the chances of the fibers being crushed even more during production, hence brittle parts A sloppy workshop is always very difficult to work in. This can be avoided by not eating or drinking around the machine during production. Also, when the floor-boy cleans the shop, the excessive dust and dirt will travel into gaylords, drums, boxes, hoppers, etc., and contaminate the area. This can be avoided by placing all lids and covers on the materials to ensure they don't get contaminated, in addition to labeling all materials and the containers.
When a part becomes discolored or distorted, the common problem lies in the residence time (or dwell-time). When the material stays in the barrel too long, the Base Resin, colors and/or stabilizers start to degrade and will turn the part a darker color. Take for instance the Carbon Black Antioxidant; if the material is too hot or sees excessive dwell time, the Carbon Black will sometimes burn-off at the nozzle, hence a material containing 2% CB at the start of the run, may only contain 1% in the molded part. This material is now out-of-spec and cannot be used for its intended purpose(s).
Heat Sensitive material or materials containing heat sensitive anti-oxidants, will require a barrel ratio of 2-1 or even 1-1 (optimum). For best results, the barrel should be depleted for every shot. This will ensure that the material(s) are not degrading during production.
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In general, a hot mold will keep the material at the molten stage much longer, which but doing so, builds the molecular chain of the material(s). This results in a very dense material, which appears darker due to its density. However, a cold mold will cause loss of color consistency because the mold cools the material too quickly, resulting in a less denser part, with a lighter appearance.
The mold temperature should be adjusted within the suppliers specifications for that material and cycle times. Be aware that the color will change slightly whenever the profiles are manipulated. One should note all profiles and mold temperatures for optimum parts appearance and use for future reference.
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In general, the supplier will provide information regarding the materials profiles and production cycles. When this information is supplied, the molder should take careful consideration that the profiles can always be enhanced (if trial tested). If an operator is causing late or early gate openings or closings, the cycle time shifts and becomes inconsistent. When the barrel heating zones start to compensate for the heat loss, it causes both hot & cold spots in the material being injected. This results in color shifts and other related problems with the material, which could be rejected at a later date.
All operators should be aware of the material they are molding, in addition to the floor-boys. Use examples, conduct mini-seminars (in-house) to fully verse them in the materials they mold with. This will only enhance the quality from start to finish and part rejections may be explained easier and faster than if these plans weren't initiated.
CRT Laboratories custom tailors Injection Molding Quality Control Programs for your specific application and/or product. CRT will conduct seminars at your facility to better enhance your in-house Quality Control Methods for ultimate control over molded parts. CRT has given seminars at several Medical firms (with Melt Flow & DSC), which greatly improves the internal (online) Quality Control process to better enhance their quality system.
Should you need additional information about CRT Laboratories' Injection Molding testing capabilities please contact us via our RFQ Form or call us at (714) 283-2032.