Processing Defects of Hostaform POM and Solutions - 1

2026-11-06
Hosatform POM injection molding defects

What is Hostaform POM?

Hostaform is a copolymer acetal resin manufactured by Celanese; it is also known as POM-C. Due to its excellent lubricity, wear resistance, and processability, it is commonly used in applications that require low friction coefficients, such as bearings, valves, gears, and zippers.
Although Hostaform POM offers excellent mechanical properties, its processing still presents numerous challenges. Common processing defects include warpage, sink marks, flash, sliver streaks, bubbles, and dimensional instability. These defects not only affect the appearance of Hostaform POM but also directly impact its performance. This article will provide a detailed overview of the causes of production defects in Hostaform POM and their solutions.

1. Warpage and Dimensional Distortion

Warpage is an extremely common processing defect in the injection molding of Hostaform POM, causing the product to exhibit noticeable warping and dimensional shrinkage after demolding.

The cause of this problem is as follows: Hostaform POM is a highly crystalline engineering plastic. Differences in cooling rates between various parts of the product—such as thick-walled and thin-walled sections—create internal stress, which ultimately leads to warping. This phenomenon is commonly observed in long, flat, and thick-walled products.

Proposed Solution

1. Adjust the molding process by changing the single-stage molding of Hostaform POM to a multi-stage process: the first stage uses a slower flow rate and lower pressure; the second stage uses a faster flow rate and higher pressure to inject 95% of the material; the third stage ensures that sufficient material is left to accommodate dimensional tolerances and maintains pressure at an appropriate temperature and pressure.
2. Optimize the mold temperature to ensure uniform temperature distribution inside the mold cavity.
3. Optimize the product structure to ensure consistent thickness throughout the product
4. Optimize the design and dimensions of the injection gate to ensure melt flowability
5.Consider using low-warpage POM. For complex products, we recommend 👉 Hostaform C9021 GV1/30 glass-fiber-reinforced POM to minimize shrinkage defects in Hostaform POM.
warpage of POM sheet

2. The mold has turned white and has charred residue on it

This is a serious processing defect caused primarily by the formation of formic acid—a byproduct resulting from the reaction between formaldehyde released during the decomposition of Hostaform POM material and oxygen—due to localized overheating of polyoxymethylene (POM) during processing.

This defect is commonly seen when using raw materials of lower purity, as the presence of other materials can cause POM to degrade. We recommend using Hostaform POM C, which offers better temperature resistance

Hostaform C 9021  Hengli HLM90 Yuntianhua Yuncon M90
Heat deflection temperature 1.8 MPa 104℃ 85℃ 95℃
Vicat softening temperature  150℃ - -

Initially, polyformaldehyde products—commonly seen as white or light-colored precipitates, as shown in the figure on the right—can interfere with the product’s venting and demolding; subsequently, formic acid is produced, which is a moderately corrosive substance that can corrode metal molds.

Proposed Solution

1. Lower the barrel temperature to prevent thermal degradation of Hostaform POM material caused by melt temperatures exceeding the recommended range.

2. Reduce the dwell time of Hostaform POM material in the mold

3. Clean the mold promptly to prevent localized material degradation caused by residual material.

4. Check for malfunctions in the temperature control system; older equipment is prone to thermocouple and monitoring system malfunctions.

Whitening and Corrosion in POM Molds

3. Wavy Patterns at the Injection Nozzle

The cause of waviness at the gate location in Hosatform POM products is still due to the high crystallinity of the POM material itself, which leads to material buildup caused by inconsistent cooling rates. This defect primarily occurs at the gate and at the bottom of the gate. There are various causes for this issue, and the following points should be systematically investigated:

1. The injection gate is too small, resulting in excessively high shear rates as the Hostaform POM melt passes through the gate.

2. Melt ejection caused by excessive injection speed

3. Localized cooling caused by a mismatch between the recommended melt temperature for Hostaform POM and the mold temperature

Wavy Defects in POM Injection Molding Gates
References
1. Yuntianhua, "Yuntianhua YUNCON M90 POM technical data sheet", Yuntianhua Co., Ltd
2. Sciencedirect, "Effect of formic acid (HCOOH) on the corrosion protectiveness of magnetite (Fe3O4) at elevated temperature", Maryam Eslami  , Yoon-Seok Choi , Srdjan Nesic , Robert Breining 
3. Ticona, "Hostaform Polyoxymethylene Copolymer (POM)", Celanese company

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