Release time：2020-01-16 18:44 Browse：
The primary reason elongated screws are prone to deformation after Dacromet coating is related to their high length-to-diameter ratio and the high-temperature sintering stage involved in the Dacromet process.
The core reasons can be summarized in the following table:
| Primary Cause | Contributing Factors | Improvement Direction |
|---|---|---|
| Thermal Stress | The coating requires sintering at high temperatures (typically 220-360°C / 430-680°F). Uneven heating and cooling of the long screw creates internal stresses, leading to warping or twisting. | Optimize sintering profile (e.g., controlled ramp-up/cool-down rates). |
| Uneven Coating & Sagging | During immersion and centrifugation, the coating may apply unevenly due to gravity, creating unbalanced stresses. The screw's high length-to-diameter ratio makes it less rigid, causing it to sag under its own weight when heated to sintering temperature. | Improve coating application (immersion/spinning parameters); use proper fixturing or horizontal support during sintering to prevent sagging. |
| Reduction of Base Metal Strength | The high sintering temperature can slightly anneal the screw, potentially reducing its yield strength, especially if it's a lower-grade steel. This makes it easier for internal stresses to cause deformation. | Ensure the base material has sufficient strength and thermal stability. |
Optimize the Dacromet Process:
Fixturing: Screws should be sintered in a horizontally supported position or on racks to prevent sagging.
Temperature Profile: Use a slow and uniform heating and cooling cycle to minimize thermal gradients and stress.
Coating Application: Optimize dipping and spinning parameters to achieve a perfectly even coating layer.
Screw Design and Material:
If possible, increase the screw's diameter to enhance rigidity.
Specify a material with sufficient strength at the sintering temperature.
