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ProductsThe products involve multiple fields such as plastics, composite materials, and functional materials, and are applied in areas such as rail transit, special equipment, new energy vehicles, and machinery manufacturing.
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BlogThe products involve multiple fields such as plastics, composite materials, and functional materials, and are applied in areas such as rail transit, special equipment, new energy vehicles, and machinery manufacturing.
Why Do MC Nylon Machined Parts Always End Up with “Sand Holes”? A Clear Explanation of Internal Defects in Cast Nylon (Pores & White Core)
2026-01-26
1. Most “Sand Holes” Are Not Machining Errors
Many workshops experience the same pattern:
Rough machining: normal
Semi-finishing: normal
Final machining near finished size: a hole suddenly appears
Visual inspection and surface turning show no abnormality
The result is full scrap, lost machining time, tooling cost, and delayed delivery
In MC nylon components, these “sand holes” usually indicate internal pores or voids inside the nylon rod.
The machining process does not create these holes—it simply exposes defects that were already present inside the material.
2. Understanding the Terms: Pores, Sand Holes, and White Core
To avoid confusion, it is important to clarify these commonly used terms.
MC Nylon Pores
Internal voids formed when gases or volatile substances are not fully released during cast polymerization. They are typically invisible from the outside.
Sand Holes in Nylon Rods
A workshop term describing the visible hole that appears when machining exposes an internal pore or void.
MC Nylon White Core
A white or opaque region in the center or local area of the rod, often caused by uneven internal structure, temperature gradients, or batch instability.
The main concern is performance inconsistency rather than appearance.
3. Why Do Internal Defects Occur?
MC nylon is produced through in-situ polymerization, meaning internal quality depends heavily on raw materials and process stability. Most defects come from two main sources.
Raw Material and Cleanliness Issues
Excess moisture, impurities, or unstable raw material systems increase the likelihood of pores, inclusions, and white core defects.
Process and Temperature Control Issues
Unstable temperature control, insufficient degassing, or incomplete curing can trap gas inside the material or create uneven internal structure.
As a result, the surface may appear normal while hidden defects remain inside, only to be exposed during deep machining. Larger diameters make these issues more likely and more severe.
4. Move the Risk Forward to the Ordering Stage
Rather than discovering defects during machining, it is far more effective to reduce risk before placing an order.
Before selecting a supplier, consider these five questions:
Are clear quality targets defined (no pores, no white core, no inclusions)?
Is there stable temperature control with defined process checkpoints?
Is any internal defect screening performed beyond visual inspection?
Is batch traceability available (specifications, batch numbers, records)?
Is there a clear responsibility and after-sales handling process if defects occur?
The goal is simple:
do not let final machining become your material inspection process.
5. How We Reduce Scrap Risk
To reduce pore and white core defects in MC nylon, we focus on two key areas.
Source Control
High-quality raw materials, controlled cleanliness, stable temperature control, and batch management improve internal consistency and reduce defect probability.
Pre-Shipment Internal Screening
For critical dimensions or based on customer requirements, internal screening is performed before shipment. This helps ensure that materials delivered are not only visually acceptable, but also suitable for stable and reliable machining.
6. FAQ
Why does the surface look fine, but pores appear during deep machining?
Because most pores and inclusions are located internally and cannot be detected by surface inspection alone.
Does white core always affect strength?
White core indicates structural inconsistency. Its impact depends on the application, but it is best avoided for load-bearing or precision parts.
Are large diameters more risky?
Yes. Larger diameters place higher demands on temperature control, curing, and internal consistency, making supplier capability more critical.
7. Contact Us
To evaluate pore or white-core risk and receive a quotation, please provide:
Diameter, length, and quantity (or drawings)
Application (wear parts, guides, bushings, sliders, etc.)
Critical tolerances and load-bearing areas
Delivery country and city
Photos of the defect location and application details are also helpful for faster evaluation.
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