73 PA66 与 POM：齿轮与滑动件的两个对照方案
一、为什么这两料经常被拿来比
PA66 和 POM 是滑动件与齿轮的两大主流选择：
PA66：强度、韧性、抗冲击——做受力齿轮、传动齿轮。
POM：自润滑、滑爽、磨耗低——做低摩擦齿轮、滑块。
两者都能做齿轮件，但成本、性能、加工完全不同。这一篇把各自的"主场"和"边界"理清。
咖啡机的磨豆器是个好考场。有个客户把 PA66 齿轮与 POM 齿轮各装了一台样机，让客服部门盲听运转声音。POM 那台被评价为更"顺滑"，PA66 那台更"扎实"。
两种感觉都对：POM 摩擦系数低，自润滑，声音干净；PA66 刚性高、韧性足，抗冲击强。
最后方案是混合：主动轮 POM 求静音，从动轮 PA66 求强度，中间的传动轴套用耐磨 PA66。一箱齿轮三种料，各有各的岗位。
工程师说这叫声音分工，账本上叫性能分工，反正不是二选一。
二、化学结构的差异
PA66：聚酰胺，含酰胺基（极性）。
POM：聚甲醛，主链 -CH₂-O- 重复。
差异在于极性：PA66 是极性，吸水性高，本身能形成薄油膜；POM 是非极性，疏水，几乎不吸水。这条极性差异决定了两者所有性能差异的起点。
① PA66 的酰胺基让它能与对偶件形成油膜（吸水后），所以"自带润滑"在中等载荷下是有效的。
② POM 的 -CH₂-O- 主链让它结晶度高、流动性好、磨耗低、POM 自润滑剂容易添加。
③ POM 几乎不吸水——尺寸稳定性远好于 PA66。在尺寸公差敏感的场合，POM 占优。
④ 两者都不耐强酸强碱——但酸对 POM 损害更直接，碱对 PA66 更严重。
三、关键性能对照
| 指标 | PA66 | POM（共聚） | 差异方向 |
|---|
| 拉伸强度（未增强，MPa） | 80-90 | 60-70 | PA66 略高 |
| 弯曲模量（未增强，GPa） | 3.0-3.5 | 2.8-3.2 | 接近 |
| 缺口冲击（kJ/m²） | 5-10 | 6-8 | PA66 略高 |
| 吸水率（23℃ 饱和，%） | 2.0-2.5 | 0.2-0.3 | POM 是 PA66 的 1/10 |
| 摩擦系数（自对偶，干） | 0.3-0.5 | 0.2-0.4 | POM 更低 |
| 磨耗（砂磨，mg） | 10-30 | 5-15 | POM 更低 |
| 连续工作温度上限（℃） | 120-150 | 95-110 | PA66 高一档 |
| 焊接强度 | 中 | 低 | PA66 强 |
| 模具收缩率（%） | 1.2-1.7 | 1.5-2.2 | POM 略高 |
| 注塑流动性 | 中 | 很好 | POM 易灌 |
| 玻纤协同效率 | 高 | 中 | PA66-GF 强 |
| 抗疲劳寿命 | 高 | 中 | PA66 高 |
| 单价（普通级，参考） | 1.0× | 0.9-1.1× | 接近 |
四、POM 胜在何处
① 无需额外润滑的滑动
POM 自润滑性能在低中载荷下显著优于 PA66。在齿轮、滑块、铰链、传动带上，POM 可以在无油状态下长寿命运行。这在以下场合是关键：不能加润滑油的食品机械、医疗器械、洁净室设备。
② 尺寸稳定性
POM 几乎不吸水（0.2-0.3%）。精密齿轮、卡扣对接、薄壁齿轮，POM 三个月后尺寸与首件几乎一致。PA66 在同等条件下尺寸会涨 0.5-1%，可能出公差。
③ 注塑流动性
POM 流动性好于 PA66，薄壁齿轮（≤1mm 壁厚）灌得满。这在复杂齿轮、模数小的精密齿轮上很重要。
④ 加工稳定性
POM 加工温度区间比 PA66 窄但更稳——一旦调好工艺，批次差异小。PA66 受吸水影响，每批料烘干状态不同会有偏差。
五、PA66 胜在何处
① 受力齿轮的高载荷工况
POM 的强度极限在 70 MPa 左右（未增强）。受大载荷时，PA66-GF30 是首选。汽车变速箱、动力总成齿轮、风电齿轮等场景，PA66-GF30 是主流。
② 抗冲击
POM 的缺口冲击比 PA66 低一档。低温下未增韧 POM 偏脆，冬季户外齿轮 PA66 更稳。
③ 焊接组合件
POM 的焊接强度极差，几乎不能超声波焊。这是 POM 的天然短板。PA66 可以做焊线组合件。
④ 耐温
POM 长期 100℃ 即开始氧化降解（释放甲醛）。PA66 可以到 120-150℃。高温齿轮用 PA66 更安全。
六、两者都不擅长的工况
① 高温 ≥130℃ 长期
PA66 撑不住，POM 也撑不住。要走 PPA / PA46 / PA6T。
② 高精度 + 高载荷
POM 精度够但强度不够；PA66 强度够但精度受吸水影响——这种工况要做后处理（如调湿、定型）+ 玻纤增强 + 高刚性配方，工艺难度大。
③ 强酸强碱
PA66 不耐强酸，POM 不耐强酸——两者都会被腐蚀。
④ 食品级、医疗级
POM 的食品接触级比 PA66 更复杂，POM 的甲醛析出是合规难点。PA66 的食品级配方更稳定。
七、四条混合使用的判断
很多项目里 PA66 与 POM 不是非此即彼，而是一个件里两种料各自负责一块：
① 齿轮 + 轴承座组合
齿轮用 PA66-GF30（受力），轴承座用 POM（自润滑低摩）。这是 PA66 与 POM 最常见的搭配。
② 滑块 + 导轨组合
滑块（动件）用 POM（低摩擦），导轨（静件）用 PA66-GF30（承力）。常见于打印机、办公设备。
③ 同步带轮 + 同步带
POM 自润滑适合做带轮齿。但同步带的承载层与连接件常是 PA66-GF30 编织件。
④ 防水件 + 旋转件
外壳用 PA66（强度），转动件用 POM（自润滑）。洗碗机、洗衣机这样设计。
这种"两料分工"的做法，比"两料纠结选哪一个"要实际。
八、四个延伸判断（齿轮与滑动件对比）
判断一：磨耗低不等于寿命长。POM 磨耗低，但在高温或高载荷下磨耗会急剧升高。真正的"长寿命"要看温度 + 速度 + 载荷的工况组合。
判断二：尺寸稳定不等于精度稳。POM 吸水少，但热膨胀系数高（比 PA66 高一档）。在温度波动大的场合，POM 的热胀冷缩效应比 PA66 大，可能引入新误差。
判断三：低摩擦的"低"是相对值。POM 对钢摩擦系数 0.2-0.4，但加 5% PTFE 可以降到 0.1；加 10% 油可降到 0.05。要看是否还需要额外润滑添加。
判断四：齿轮模数和直径决定能选哪种。模数小（≤0.5）、直径大（≥50mm）的精密齿轮，POM 易灌、薄壁稳定；模数大（≥1）、直径小（≤30mm）的高载荷齿轮，PA66-GF30 强度更稳。
九、边界声明
| 工况 | 建议 |
|---|
| 高载荷齿轮（≥50 MPa 接触应力） | PA66-GF30 |
| 中低载荷自润滑齿轮 | POM（共聚） |
| 精密尺寸齿轮 | POM |
| 焊接组合件 | PA66 |
| 高温 ≥120℃ 齿轮 | PA66-GF30（兼玻纤） |
| 食品级、医疗级 | 走专项 PA66 配方（看目录） |
| 不加润滑油的滑动环境 | POM 或 POM + PTFE |
| 薄壁长流程齿轮 | POM |
| 大模数高功率传动 | PA66-GF30 |
附：两个选型实例
实例一：打印机齿轮组
工况：低载荷（办公环境）；精密模数 0.5；要求无油运行；尺寸稳定。
推演：
低载荷 → POM 即可
无油 → POM 自润滑优于 PA66
精密模数 → POM 流动性好，模具可灌
尺寸稳定 → POM 不吸水
结论：POM（共聚）。
实例二：电动窗帘减速齿轮
工况：间歇载荷（每次运行 10 秒）；模数 0.8；要求 5 年寿命（户外）。
推演：
间歇载荷 → 强度需求中等
户外 → 耐温 / 耐候需求（夏季可达 60℃）
5 年寿命 → 蠕变与老化要稳
结论：PA66-GF30 + UV 稳定剂。POM 在 60℃ 长期户外会缓慢氧化，PA66-GF30 + UV 配方更稳。
行业感：齿轮选型的最大误区，是"用 ABS/PA66/PC 就够了"。 我们见过不少做精密齿轮的项目，因为"我们之前用 PA66，没出过问题"，所以沿用 PA66，结果切到 POM 系工况后出现大量短射、改模半年。齿轮件的核心选择，不是"我喜欢哪个料"，是"这个工况下哪种料的边界条件被打破"。 当我们把 PA66 与 POM 的边界条件列出来，让项目明确"卡在哪一项"，选料就稳定得多。
一个门锁执行器的冬天
起点是汽车门锁执行器齿轮用了 POM，常温测试全部通过。
潜伏期两年，北方冬天零下二十五度，个别车辆解锁异响，售后按个案处理。
爆发在第三个冬天，寒潮集中爆发，解锁卡滞的投诉成批出现。POM 低温下韧性下降，齿面磨损后的间隙被放大。
结算方案：齿轮换低温增韧 PA66 加固体润滑，齿形微调补偿。之后两个冬天平安。
这个案例的结论很干净：常温齿轮比精度，低温齿轮比韧性，温度一变，排序就变。
PA66 与 POM 的齿轮会，三个问题定案。
追问一：最低工作温度多少？ 低温靠近零下二十度，POM 要谨慎。
追问二：润滑条件如何？ 免润滑场合 POM 天然占优，有油脂则差距缩小。
追问三：载荷有没有冲击？ 冲击场合 PA66 的韧性是硬通货。
延伸：四步速判（PA66 vs POM 方向）
四步把齿轮与滑动件选料压缩成可执行判断：
第一步：先标载荷与速度。高载荷（≥50 MPa 接触应力）→ PA66-GF30；中低载荷无润滑环境 → POM（共聚）。
第二步：量焊接与组合。PA66 焊接强度比 POM 高很多。多组件焊接组合件，PA66 优先；纯单体件，POM 优先。
第三步：量自润滑需求。不能加油的工况（POM 自润滑优势）——食品机械、医疗器械、洁净室，POM 占绝对优势。
第四步：测尺寸稳定性。POM 几乎不吸水（0.2-0.3%），精密件 6 个月后尺寸仍准；PA66 吸水 2-2.5%，尺寸会随湿度漂移。
这四条之外还有"两种料分工"的解法：齿轮 + 轴承座组合 → 齿轮 PA66-GF30 + 轴承座 POM。这是最常见的搭配，比纠结"用哪个"更实用。
实战：三步走
第一步：摩擦与强度分开看。POM 摩擦低，PA66 强度高——这两件事不要用"既要又要"的方式做。两个料分工做不同件 是稳的方式。
第二步：齿轮动平衡 + 焊线双测试。高速齿轮必须测动平衡，G2.5 等级以上；焊接齿轮还要测焊线强度。
第三步：长寿命件考虑复合方案。齿轮 PA66-GF30 + 轴承座 POM 是齿轮箱最常见的分工。单一料解决"既要又要"往往出问题。
收尾补一张三问三答。
| 高频问题 | 一句话回答 |
|---|
| 静音优先选谁？ | POM，摩擦系数天生低 |
| 抗冲击选谁？ | PA66，尤其低温有冲击 |
| 尺寸稳定谁好？ | POM，吸水几乎为零 |
| 能混用吗？ | 能，齿系分件各司其职是主流 |
再补一个反向案例。
有个项目把 PA66 齿轮装进了免润滑的精密机构，看中韧性。结果 PA66 吸水后尺寸微涨，侧隙变小，运转半年出现爬行噪声。精密免润滑机构是 POM 的地盘，吸水是 PA66 的天然税，进了别人的主场，优势会变负担。
数字的来历：两三个为什么
POM 为什么自润滑？它的分子链规整、结晶度高，表面能低，与钢对磨时摩擦系数天生小，自己就能跑，不太需要油。齿轮箱里那种干净的运转声，就是低摩擦的直接输出。代价是韧性一般，低温更明显，冲击工况是它的禁区。
低温排序为什么会反转？零下二十度附近，POM 的韧性曲线明显下探，而 PA66 增韧体系的曲线还稳着。常温下 POM 靠低摩擦领先，低温下 PA66 靠韧性反超。温度一变，排序就变——齿轮选型必须先问最低温度，再谈摩擦与噪音。
实操清单：齿轮件立项六动作
主动轮与从动轮分开选材，各司其职
最低工作温度写进验收，寒区项目再加档
免润滑场合先核 PV 值，别只看摩擦系数
冲击工况查韧性曲线，低温段重点看
齿形预留补偿量，吸水与磨损都算进去
每年抽测运转噪音，数据留档对比
齿轮是传动系统里最讲分工的零件。把选材按岗位分配，噪音、寿命、成本三头都能交代。
速判手册：齿轮箱分工速查
| 位置 | 首选 | 理由 |
|---|
| 主动轮（高速） | POM | 低摩擦、低噪音 |
| 从动轮（受冲击） | 增韧 PA66 | 韧性储备 |
| 轴套与垫片 | 耐磨 PA66 | 承压与耐磨兼顾 |
| 密封圈座 | POM | 尺寸稳定 |
分工表看着简单，背后是很多次试错换来的排序。齿轮箱是材料分工的教科书：没有全能料，只有分工好的组合。
再补一个来自售后端的判断技巧：噪音投诉先查温度记录。冬天投诉集中，基本锁定低温韧性不足；夏天投诉集中，多半是热膨胀把侧隙吃掉了，与材料关系不大，与配合公差关系更大。
一张温度时间表，能把售后问题先分到材料或设计两个口袋里，排查方向立刻收敛一半。这个技巧不费钱，但要求售后数据里留温度这一栏——很多团队的数据表里什么都有，偏偏没有温度，这是最值得补的一格。
齿轮件的最后一句忠告：润滑油脂与塑料的相容性要过一遍。有些油脂对 POM 与 PA66 的长期浸泡表现不同，选型时把油脂牌号一起提供给供应商，让相容性测试同批做掉。齿轮箱里的材料从来不是孤立工作的，油脂是第三种材料，别忘了它。
齿轮箱再补一个装配端的细节：压装力。POM 与 PA66 的压入配合过盈量设计不同，POM 刚而硬，过盈大了直接裂；PA66 韧一些，容忍度高一点。装配指导书上把两种料的压装力上限分开写，产线就少了很多"装进去但裂了"的隐性报废。
有客户统计过，这一条改完，齿轮装配报废率从千分之六降到千分之一以下，没有换料，没有加钱，纯粹是把材料的性格写进了作业指导书。
结语
PA66 和 POM 的分工，是"强度齿轮"与"自润滑齿轮"的对照。
PA66 是受力齿轮主场：高强度、抗冲击、焊接、玻纤增强——动力齿轮、传动齿轮、户外齿轮。
POM 是滑动件主场：自润滑、尺寸稳、易灌模——精密齿轮、滑块、薄壁齿轮。
选型的起点不是"哪个更强"，而是"我这个件卡在哪一项"。 卡在强度、冲击、寿命，选 PA66-GF30；卡在自润滑、尺寸、易灌模，选 POM。
73 PA66 and POM: Two Comparative Solutions for Gears and Sliding Components
1. Why these two materials are often compared
PA66 and POM are the two mainstream choices for sliding parts and gears:
PA66: Strength, toughness, impact resistance — used for load-bearing gears and transmission gears.
POM: self-lubricating, smooth, low wear—used for low-friction gears and sliders.
Both can make gear parts, but the cost, performance, and processing are completely different. This article clarifies each one's 'home turf' and 'boundaries'.
The grinder of the coffee machine is a good testing ground. A customer installed a PA66 gear and a POM gear each in a sample machine and had the customer service department do a blind listening test of the operating noise. The POM one was rated as smoother, while the PA66 one was considered more solid.
Both feelings are correct: POM has a low friction coefficient, is self-lubricating, and sounds clean; PA66 is rigid, tough, and impact-resistant.
The final plan is a hybrid: the driving gear uses POM for quietness, the driven gear uses PA66 for strength, and the intermediate drive shaft uses wear-resistant PA66. One gearbox has three different materials, each with its own role.
The engineer said this is called sound division of labor, in the ledger it's called performance division of labor, anyway, it's not an either-or choice.
2. Differences in Chemical Structure
PA66: Polyamide, contains amide groups (polar).
POM: Polyoxymethylene, main chain -CH₂-O- repeating.
The difference lies in polarity: PA66 is polar, highly water-absorbent, and can form a thin oil film by itself; POM is non-polar, hydrophobic, and hardly absorbs water. This polarity difference determines the starting point for all the performance differences between the two.
① The amide groups of PA66 allow it to form an oil film with the counterpart (after absorbing water), so its 'self-lubricating' property is effective under moderate loads.
② The -CH₂-O- main chain of POM gives it high crystallinity, good fluidity, low wear, and makes it easy to add POM self-lubricants.
③ POM hardly absorbs water—its dimensional stability is much better than PA66. In situations where dimensional tolerance is critical, POM has the advantage.
④ Neither can withstand strong acids or strong bases — but acids damage POM more directly, while bases are more harmful to PA66.
3. Key Performance Comparison
| Indicator | PA66 | POM (copolymer) | Direction of difference |
|---|
| Tensile Strength (Unreinforced, MPa) | 80-90 | 60-70 | PA66 slightly higher |
| Bending modulus (unreinforced, GPa) | 3.0-3.5 | 2.8-3.2 | approach |
| Notch Impact (kJ/m²) | 5-10 | 6-8 | PA66 slightly higher |
| Water absorption rate (23℃ saturated, %) | 2.0-2.5 | 0.2-0.3 | POM is 1/10 of PA66 |
| Coefficient of friction (self-dual, dry) | 0.3-0.5 | 0.2-0.4 | POM is lower |
| Wear (abrasive wear, mg) | 10-30 | 5-15 | POM is lower |
| Maximum continuous operating temperature (°C) | 120-150 | 95-110 | PA66 high grade |
| Welding strength | middle | Low | PA66 Strong |
| Mold shrinkage rate (%) | 1.2-1.7 | 1.5-2.2 | POM slightly high |
| Injection molding fluidity | middle | Very good | POM Easy Pour |
| Glass Fiber Synergy Efficiency | Tall | middle | PA66-GF Strong |
| Fatigue life | Tall | middle | PA66 High |
| Unit price (standard grade, reference) | 1.0× | 0.9-1.1× | approach |
4. Where POM Excels
① Slide that requires no additional lubrication
The self-lubricating performance of POM is significantly superior to PA66 under low to medium loads. On gears, sliders, hinges, and drive belts, POM can operate for a long time without oil. This is crucial in the following situations: food machinery, medical devices, and cleanroom equipment where lubricating oil cannot be applied.
② Dimensional Stability
POM hardly absorbs water (0.2-0.3%). For precision gears, snap-fit connections, and thin-walled gears, POM dimensions after three months are almost the same as the first piece. Under the same conditions, PA66 dimensions can increase by 0.5-1%, which may cause tolerance issues.
③ Injection Molding Flowability
POM has better flow than PA66, allowing thin-walled gears (≤1mm wall thickness) to be fully filled. This is important for complex gears and precision gears with a small module.
④ Processing Stability
The processing temperature range of POM is narrower than that of PA66 but more stable—once the process is set, batch differences are small. PA66 is affected by moisture absorption, and deviations can occur depending on the drying condition of each batch of material.
5. Where PA66 Excels
① High load conditions of the stressed gear
The strength limit of POM is about 70 MPa (unreinforced). Under heavy loads, PA66-GF30 is the preferred choice. In scenarios such as automotive transmissions, powertrain gears, and wind power gears, PA66-GF30 is mainstream.
② Impact Resistance
The notch impact of POM is one level lower than PA66. Untoughened POM is brittle at low temperatures, while PA66 outdoor gears are more stable in winter.
③ Welded assembly
The welding strength of POM is extremely poor, and it can hardly be ultrasonic welded. This is POM's natural shortcoming. PA66 can be used to make welded joint assemblies.
④ Temperature Resistance
POM begins to oxidatively degrade (releasing formaldehyde) at 100℃ over the long term. PA66 can withstand 120-150℃. PA66 is safer for high-temperature gears.
6. Operating conditions that neither of them is good at
① High temperature ≥130℃ long-term
PA66 can't hold up, and POM can't hold up either. We need to go with PPA / PA46 / PA6T.
② High precision High load
POM has sufficient precision but insufficient strength; PA66 has sufficient strength but its precision is affected by moisture absorption — this situation requires post-processing (such as humidity conditioning and molding) with glass fiber reinforcement and high-rigidity formulations, making the process difficult.
③ Strong acids and strong bases
PA66 is not resistant to strong acids, POM is not resistant to strong acids — both will be corroded.
④ Food grade, medical grade
The food contact grade of POM is more complex than PA66, and the formaldehyde release from POM is a compliance challenge. The food-grade formulation of PA66 is more stable.
7. Judgment on the Combined Use of Four Articles
In many projects, PA66 and POM are not mutually exclusive; instead, both materials are used in one part, each responsible for a specific section:
① Gear and bearing housing assembly
Gears use PA66-GF30 (for load-bearing), and bearing housings use POM (self-lubricating with low friction). This is the most common combination of PA66 and POM.
② Slider and Guide Rail Assembly
The slider (moving part) uses POM (low friction), and the guide rail (static part) uses PA66-GF30 (load-bearing). Commonly found in printers and office equipment.
③ Synchronous pulley Synchronous belt
POM is self-lubricating and suitable for making pulley teeth. However, the load-bearing layer and connectors of timing belts are often made of PA66-GF30 woven materials.
④ Waterproof parts Rotating parts
The casing is made of PA66 (for strength), and the moving parts are made of POM (self-lubricating). Designed like a dishwasher or washing machine.
This approach of 'dividing the work between two materials' is more practical than 'struggling to choose between the two materials'.
VIII. Four Extended Judgments (Comparison between Gears and Sliding Components)
Judgment 1: Low wear does not equal long life. POM has low wear, but under high temperature or high load, wear can increase dramatically. True 'long life' depends on the combination of temperature, speed, and load conditions.
Judgment Two: Dimensional stability does not equal precision stability. POM absorbs little water, but has a high coefficient of thermal expansion (one level higher than PA66). In environments with large temperature fluctuations, the thermal expansion and contraction effect of POM is greater than that of PA66, which may introduce new errors.
Judgment Three: The 'low' in low friction is a relative value. POM has a friction coefficient of 0.2-0.4 against steel, but adding 5% PTFE can reduce it to 0.1; adding 10% oil can reduce it to 0.05. It depends on whether additional lubrication is still needed.
Judgment Four: The gear module and diameter determine which type can be selected. Precision gears with a small module (≤0.5) and a large diameter (≥50mm) are easy to mold with POM and have stable thin walls; high-load gears with a large module (≥1) and a small diameter (≤30mm) are more reliably strong with PA66-GF30.
IX. Boundary Statement
| Operating condition | Suggestion |
|---|
| High-load gears (≥50 MPa contact stress) | PA66-GF30 |
| Medium and low load self-lubricating gears | POM (copolymer) |
| Precision dimension gear | POM |
| Welded assembly | PA66 |
| High temperature ≥120℃ gear | PA66-GF30 (also with glass fiber) |
| Food grade, medical grade | Use a specialized PA66 formulation (see catalog) |
| Sliding environment without lubrication | POM or POM PTFE |
| Thin-walled long-process gear | POM |
| Large module high power transmission | PA66-GF30 |
Appendix: Two selection examples
Example 1: Printer Gear Assembly
Operating conditions: low load (office environment); precision module 0.5; requires oil-free operation; dimensional stability.
Deduction:
Low load → POM is fine
Oil-free → POM self-lubricating is better than PA66
Precision modulus → POM has good fluidity, and the mold can be filled
Dimensional stability → POM does not absorb water
Conclusion: POM (copolymer).
Example 2: Electric Curtain Reduction Gear
Operating conditions: intermittent load (10 seconds per operation); module 0.8; required 5-year lifespan (outdoor).
Deduction:
Intermittent load → Medium strength requirement
Outdoor → Temperature / weather resistance requirements (up to 60°C in summer)
5-year lifespan → Creep and aging need to be stable
Conclusion: PA66-GF30 UV stabilizer. POM will slowly oxidize during long-term outdoor exposure at 60℃, while PA66-GF30 UV formulation is more stable.
Industry insight: The biggest misconception in gear material selection is thinking 'using ABS/PA66/PC is enough.' We have seen many precision gear projects that continued using PA66 simply because 'we used PA66 before and never had problems,' only to encounter a lot of short shots and half a year of mold modifications when switching to POM. The core of gear material selection is not 'which material I like,' but 'under this working condition, which material's boundary conditions are being exceeded.' When we list the boundary conditions of PA66 versus POM and make the project team clearly see 'where it is getting stuck,' the material selection becomes much more stable.
A winter of a door lock actuator
The starting point is that the gear of the car door lock actuator uses POM, and all tests at room temperature passed.
Incubation period of two years, northern winter temperatures of minus twenty-five degrees, occasional vehicles making abnormal noises when unlocked, after-sales service handles on a case-by-case basis.
The outbreak occurred in the third winter, with cold waves erupting in concentration and a batch of complaints about jammed cards appearing. The toughness of POM decreases at low temperatures, and the gaps on the worn tooth surfaces are amplified.
Settlement plan: Replace the gears with low-temperature toughened PA66 reinforced with solid lubricant, and fine-tune the gear profile for compensation. Then two winters passed safely.
The conclusion of this case is very clear: at normal temperature, gears are measured by accuracy; at low temperature, gears are measured by toughness. When the temperature changes, the ranking changes.
The gears of PA66 and POM meet, and three issues are finalized.
Follow-up question 1: What is the minimum working temperature? At low temperatures close to minus twenty degrees, caution is needed with POM.
Follow-up Question 2: What are the lubrication conditions? In non-lubricated situations, natural POM is superior; with grease, the gap narrows.
Follow-up Question 3: Does the load have an impact? In impact situations, the toughness of PA66 is hard currency.
Extension: Four-step quick judgment (PA66 vs POM direction)
Four steps to condense the selection of gears and sliding parts into executable judgments:
Step 1: First mark the load and speed. High load (≥50 MPa contact stress) → PA66-GF30; medium to low load in non-lubricated environment → POM (copolymer).
Step 2: Measure welding and assembly. The welding strength of PA66 is much higher than that of POM. For multi-component welded assemblies, PA66 is preferred; for single-component parts, POM is preferred.
Step 3: Assess self-lubrication requirements. Conditions where oiling is not possible (POM's self-lubricating advantage) — food machinery, medical devices, clean rooms, where POM has an absolute advantage.
Step 4: Measure dimensional stability. POM absorbs almost no water (0.2-0.3%), and the dimensions of precision parts remain accurate after 6 months; PA66 absorbs 2-2.5% water, and its dimensions will drift with humidity.
Besides these four methods, there are also the 'two-material division' solutions: gear and bearing housing combination → gear PA66-GF30, bearing housing POM. This is the most common pairing and is more practical than worrying about 'which one to use'.
Practical Combat: Three Steps
Step 1: Consider friction and strength separately. POM has low friction, PA66 has high strength—don't try to achieve both at the same time. It's safer to have the two materials handle different parts.
Step 2: Gear Dynamic Balancing Dual testing of weld lines. High-speed gears must undergo dynamic balancing with a grade of G2.5 or higher; welded gears also need to be tested for weld line strength.
Step 3: Consider composite solutions for long-life components. Gear PA66-GF30 and bearing housing POM are the most common division in gearboxes. Using a single material to achieve 'both requirements' often causes problems.
Finish off with one more sheet of three questions and three answers.
| Frequently Asked Questions | Answer in one sentence |
|---|
| Who should be prioritized for mute? | POM naturally has a low coefficient of friction |
| Who to choose for impact resistance? | PA66, especially has impact at low temperatures |
| Who has good dimensional stability? | POM, water absorption is almost zero |
| Can they be used interchangeably? | Yes, the gear system components each perform their own duties, which is mainstream. |
Add another reverse case.
There was a project that put PA66 gears into a lubrication-free precision mechanism, attracted by its toughness. As a result, PA66 swelled slightly after absorbing water, reducing backlash, and after half a year of operation, crawling noise appeared. Precision lubrication-free mechanisms are the territory of POM, and water absorption is a natural disadvantage of PA66. Entering someone else's main field turns an advantage into a burden.
The Origin of Numbers: Why Two and Three
Why is POM self-lubricating? Its molecular chains are orderly, it has a high degree of crystallinity, and low surface energy, so its friction coefficient against steel is naturally low. It can move on its own and doesn’t need much oil. The clean running sound in a gearbox is the direct result of low friction. The trade-off is that its toughness is average, more noticeable at low temperatures, and impact conditions are its no-go zone.
Why does the ranking reverse at low temperatures? Around minus twenty degrees, the toughness curve of POM drops significantly, while the curve of the PA66 toughened system remains stable. At room temperature, POM leads due to low friction, but at low temperatures, PA66 overtakes thanks to its toughness. When the temperature changes, the ranking changes—the first question in gear selection must be the lowest temperature, before discussing friction and noise.
Practical Checklist: Six Actions for Gear Project Initiation
The driving wheel and the driven wheel are made of different materials, each performing its own function.
The minimum working temperature is written into the acceptance; for cold region projects, an additional grade is added.
For non-lubricated situations, first check the PV value; don't just look at the friction coefficient.
Check the toughness curve under impact conditions, with a focus on the low-temperature section
Tooth profile relief allowance, including both water absorption and wear
Conduct random tests of operational noise every year, and keep data records for comparison
Gears are the parts in the transmission system that are most specialized in division of labor. By assigning materials according to their roles, noise, lifespan, and cost can all be accounted for.
Quick Reference Manual: Gearbox Division Quick Lookup
| Position | first choice | Reason |
|---|
| Drive wheels (high-speed) | POM | Low friction, low noise |
| Driven wheel (impact-receiving) | Toughened PA66 | Resilience Reserve |
| Bushing and gasket | Wear-resistant PA66 | Both pressure-resistant and wear-resistant |
| Seal ring seat | POM | Dimensional stability |
The task allocation table looks simple, but behind it is a sequence achieved through many trials and errors. The gearbox is a textbook example of material division: there is no all-purpose material, only a well-divided combination.
Here's another judgment tip from the after-sales side: for noise complaints, first check the temperature records. If complaints are concentrated in winter, it basically points to insufficient low-temperature toughness; if complaints are concentrated in summer, it's mostly because thermal expansion has eaten up the side clearance, which is less related to the material and more related to the fitting tolerances.
A temperature timetable can first sort after-sales issues into two categories: materials or design, immediately narrowing down the investigation direction by half. This technique doesn't cost money, but it requires that the after-sales data include a temperature column—many teams' data sheets have everything, except temperature, which is the most worthwhile field to add.
The final piece of advice for gear components: check the compatibility of lubricating grease with plastics. Some greases behave differently when POM and PA66 are soaked long-term, so provide the grease grade to the supplier during selection, and have the compatibility test done in the same batch. The materials in the gearbox never work in isolation; grease is the third material, don’t forget it.
Add another assembly-end detail for the gearbox: press-fit force. The interference fit design differs between POM and PA66: POM is rigid and hard, and if the interference is too large, it cracks directly; PA66 is more tough and has a higher tolerance. In the assembly manual, the upper limits of the press-fit force for the two materials are written separately, which reduces a lot of 'inserted but cracked' hidden scrap on the production line.
Some customers have counted that after this change, the scrap rate for gear assembly dropped from six per thousand to less than one per thousand, without changing the material, without spending extra money, purely by writing the character of the material into the work instruction.
Conclusion
The division of labor between PA66 and POM is the contrast between 'high-strength gears' and 'self-lubricating gears'.
PA66 is the main field for load-bearing gears: high strength, impact resistance, weldability, glass fiber reinforcement—power gears, transmission gears, outdoor gears.
POM is the home field of sliding parts: self-lubricating, dimensionally stable, easy to mold — precision gears, sliders, thin-walled gears.
The starting point for choosing a material is not 'which is stronger,' but 'which aspect is my part stuck on.' If it's stuck on strength, impact, or durability, choose PA66-GF30; if it's stuck on self-lubrication, dimensions, or ease of molding, choose POM.
