Meaning
Material conditions specified immediately after the injection molding process represent the resin in its unhydrated state. Thermoplastics like polyamides are tested as dry as molded to establish baseline mechanical properties. This designation guarantees that the test specimens have not absorbed environmental moisture.
Properties in this state differ from those in a conditioned state where moisture acts as a plasticizer.
Processing Standard
Polyamides absorb moisture from the atmosphere rapidly upon exiting the mold. Specifying dry as molded values ensures that the material is analyzed before environmental exposure alters the structure. This state is maintained by sealing molded parts in moisture-barrier bags immediately after ejection.
The moisture content must remain below one tenth of a percent to satisfy the dry standard.
Mechanical Behavior
Absence of moisture yields high tensile strength and rigidity in molded nylon components. Under dry as molded conditions, the polymer chains remain closely packed and unshielded by water molecules. This structural arrangement makes the material more brittle than its conditioned counterpart.
Impact resistance increases as moisture is absorbed over time, while stiffness decreases. Component design must account for these changes to ensure that the part does not crack during initial assembly and snap-fit operations.
Quality Control
Accurate testing requires consistent sample preparation to prevent premature moisture absorption. Sealed samples prevent moisture uptake that would otherwise skew laboratory measurements of part dimension and performance. Moulders utilize these dry metrics to verify that the resin met specifications during the production run.
This practice isolates processing performance from post-molding storage conditions.
