There are a number of different factors that impact the ability of injection molding manufacturers to reach and achieve tight tolerances on finished parts. Learn more about these different factors and how they can play a part in the ability of a manufacturer to meet the demands of today for smaller, more precise parts and components.
EFFECTS OF MOISTURE IN RESIN: WHY IT’S IMPORTANT
Noble is no stranger to what moisture and humidity are capable of. Located in South Louisiana, our team is well versed in everyday adjustments like how to defog a windshield and what fabrics will handle the damp air best. The same attention is taken for our care of materials. Moisture tests are performed on dried material before the press is run to ensure we are meeting the manufacturer’s recommended specifications as each material is unique.
We spoke with our in-house Materials Handler, Shelby Perry, about the importance of getting the moisture levels correct. “Many defects are caused by moisture, air, (and) gasses presented in the resin or mold surface…If the material is not properly dried, the moisture will interact with the polymer during injection.” This can cause any number of part defects, including splay, bubbles, blisters, cracks, or brittleness. “If we see this(splay) happening we want to stop the machine, do another moisture test. If the material is wet then we know we need to stop, and let it dry some more. If it’s not wet, then there is some other issue.”
The purpose of drying materials is to preheat the polymer, remove surface moisture, and remove absorbed moisture. Drying the material can assist in a more stable process. Surface moisture manifests as condensation as material is moved from a cold location to a warm location. Surface moisture is more easily removed with a hot air dryer. Removing any absorbed moisture requires an additional dehumidifying step.
Maintaining and securing the appropriate equipment is the most important first step. With several types of dryers and analyzers on the market, our team has tested the resins commonly used in our facilities and made decisions accordingly. Below is a brief chart comparing different dryers’ pros and cons. “Polyurethane could take six to twelve hours to dry when nylon can take three to four hours to dry. Then it depends on how much material is in the dryer and depends on the type of dryer. But these (pointing to dryer nearby)… they just don’t dry nylon or polyurethane well, you’d have to let it sit in there for days.
While moisture is not always the culprit of part defects, testing your resin is a reliable and easy way to verify where the issue originated. You can see a sample pictured above in the header as it is about to be tested for its moisture content. Testing is crucial when you are changing materials, as each resin has different drying requirements. Depending on the level of moisture in the resin the part may not display any defects, but it may still be compromised. Brittleness, dimensional stability, and poor heat resistance are all possible defects that cannot be confirmed on sight by operators but can be prevented when moisture analysis is conducted.
Bottom line: if you want a stable process and parts that function properly, you must monitor the water content of the resin before processing.
Electric Hot Air Dryer
Passes air through heated coils.
Most common. Easy to maintain and install.
Less efficient than Gas.
Gas Hot Air Dryer
Passes air through heated element.
More efficient than Electric.
Require dedicated gas line; hard to relocate.
Compressed Air Dryer (Speed Dryer)
Uses air from pre-existing air compressor.
Very low risk of over-drying material.
Not recommended for highly hygroscopic material.
Air is both heated and dehumidified.
Capable of operating at a wide range of settings and dehumidifies.
Typically takes 2-4 hours to dry.
Vacuum removes water and volatiles the moment it leaves the pellets; boiling temp.
Can reduce start-up by drying in 1/3 the time compared to Desiccant Dryer.
Requires more skill to operate and lower drying capacity.
Noble has the plastic injection molding automation systems in place to streamline projects for our customers.
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