Yearly maintenance procedures will be different for every injection molding location depending on mold cycle volume. Here are some general guidelines that any molder can use for your hot runners, heaters, leader and ejector pins and more to keep your tooling running efficiently and to prevent unwanted surprises.
1. Check vents for telltale rust or moisture – If you see rust or moisture around a hot runner vent hole, it indicates internal condensation or the possibility that a water line popped off. This moisture causes a short and can be fatal to heaters. When machines are not running 24/7 and are turned off overnight or on weekends, the chances of such condensation increases.
2. Take the time to remind operators not to ‘clear’ nozzle tips from gates – If an operator happens to notice a tiny piece of steel flush with the gate of the mold, it may turn out to be a point-gate needle assembly. ‘Clearing’ this perceived obstruction usually destroys the nozzle tip. To prevent nozzle destruction, verify the tip style of the hot runner system before taking action and assure all operators are well trained to identify the different tip styles they will come in contact with.
3. Lubricate the slide retainers – This is an activity that really should be done once a week if running a 24/7 operation. Year-end is a great opportunity to create a routine maintenance program for lubricating these parts.
4. Cross-check your heater ohm readings – Assuming you checked the ohm readings when your heater was new, this is the time to take a new reading and compare. If the readings are up or down by 10 percent, it is time to start thinking about replacing the heater to ensure it does not fail at a critical time during your production process. If the initial ohm reading was never taken, get a reading now and use that as a baseline for future checks on that heater.
5. Look for signs of wear between leader pins and bushings – Look for scores or scrapes. This damage is due to a lack of grease. If marks are just beginning, you can extend the life of the leader pins and bushings by keeping them well greased. If you find significant wear, it is time to install new parts. Otherwise, cavities and cores may not line-up properly, resulting in unequal wall thickness on your part.
6. Check for water flow – Hookup a hose to the out port and run water through the water line into a bucket. Unclear or colored water may be a sign of rust and poor water flow signifies blockage. Drill out the water lines if these problems are found (or clean with whatever method you typically use). Future problems due to rust and blockage can be prevented by improvements in the plant’s water treatment system.
7. Clean the ejector pins – Over the course of one year, ejector pins will become dirty with gas buildup and film. A good cleaning with mold cleaner every six to12 months is recommended. Once clean, put a light coating of grease on the pins to prevent galling or breakage.
8. Look for nicks in the radius area of your sprue bushings – Nicks are caused by leftover loose, hardened pieces of plastic left in the machine nozzle that cause damage due to clamping force from the injection carriage unit during injection forward. Problems may also occur from a misalignment issue. Look for both possibilities when nicks are found. Replace sprue bushings if damage is bad to prevent a flower pot leak (an old molders term: leakage of plastic between the bushing and the machine nozzle tip).
Following these tips will help you to recognize and prevent potential problems, keeping your molds running at optimal levels. (end)
