上个月，一个做协作机器人关节模组的客户，带着一片齿轮找过来。
尼龙的，齿面已经起毛，齿根有几道细纹。他把件搁在桌上，说了一句："跑了不到四十万次，齿就毛了。你们有没有更耐磨的？"
我没接话，先反问他三个问题：这个齿轮的对偶件是什么材料？齿面算下来 PV 值大概多少？现在是脂润滑还是干跑？
他愣了一下，说前两样没算过。他们只知道自己要的是"更耐磨的料"。
"更耐磨"这三个字，是买不到的。 你要么买更低的摩擦系数，要么买更低的磨损率——这不是一回事，很多场合还互相打架。
还有一句得先纠偏：关节齿轮的寿命终点，很少是"磨到断"，通常是"间隙大到啮合开始错位"。 等它断，说明前面已经错位很久了。
这篇讲三件事：机器人关节齿轮材料被什么约束，自润滑尼龙这条路线的判据怎么定，以及"摩擦系数"和"百万转磨损量"这两个数分别怎么验。
一、关节齿轮的账，要算到百万转之后
先把"百万转"换成能感知的量。
协作机器人一个关节，每天做五千次往复，一年按三百天算，是一百五十万次。做两年，就是三百万次量级。这不是实验室里的加速寿命，是产线上的日常。
关节齿轮和汽车齿轮最大的分别，也在这条上。
汽车齿轮的载荷是脉冲式的——峰值高、次数少；关节齿轮正好相反：载荷不高，但次数极多，而且藏在脂润滑的封闭腔里，温度还不低。
这带来三个后果。
齿面一直在磨。 每次只磨掉极薄一层，累积起来也足够把齿形吃掉。
磨屑出不去。 它留在腔里循环，变成磨粒，反过来加速磨损——这是一个正反馈。
润滑脂会老化、会流失。 所以材料本身的自润滑性必须顶得住，不能把寿命押在"脂一直在"这个假设上。
另有一个容易漏的点：关节齿轮的对偶件通常是钢。 所以这是一个“塑料跑在钢面上”的摩擦副，和塑料对塑料完全是两套账。
尼龙的自润滑，靠的是摩擦中在钢面形成一层转移膜，之后变成"尼龙对尼龙"。膜稳不稳，决定了这个件耐不耐用。 而膜稳不稳，跟吸水状态直接相关——这也是精密关节件要控湿度、要做调湿的原因。
二、六个变量：先问清，再谈牌号
关节齿轮的选型，起点不是翻开牌号表，是问清六个变量。缺一个，后面全是猜。
温度。 关节模组里电机近、减速器远，齿轮的实际温度常见 40–80℃，连续高负载或散热设计不足时会更高。要盯的是长期温度，不是峰值。
载荷与速度。 这两项不能分开报，要合成 PV 值（接触压力 × 线速度）。PV 超限，摩擦热就散不出去，温升随即失控——这是关节齿轮最容易踩的一脚。
介质。 脂润滑还是干跑。脂的基础油与材料相容性要单独确认，有些脂会让件表面发黏、析出，甚至影响齿面尺寸。
寿命。 往复次数以百万计。判据不是"什么时候断"，是"到寿命终点时齿厚掉了多少、间隙涨了多少"。
外观与磨屑。 洁净场景（医疗、食品周边）对磨屑量有额外要求，这会直接排除某些润滑体系。
合规。 涉及析出与挥发的场景，要回到对应标准语境，不自创安全结论。
六个变量里，温度和 PV 是硬门槛，剩下四个决定方案能不能收口。
三、三条自润滑路线的分工
把主流路线并排放，注意看的是"代价"这一列，不是"优点"那一列。
| 路线 | 组成 | 给什么 | 代价 |
|---|
| PA66-GF15 + 固体润滑 | 中低玻纤 + MoS₂ / PTFE / 硅酮 | 刚性、抗蠕变、成本可控 | 玻纤磨蚀对偶钢件；熔接线强度下降 |
| PA66 增韧 + PTFE | 弹性体 + 低摩擦体系 | 抗冲击、噪音低 | 刚性偏低，厚齿承载有限 |
| PA12 + 短纤 | 长碳链 + 少量纤维 | 低吸水、尺寸漂移小、韧性好 | 成本高，耐温上限低 |
三条路线没有"谁更好"，只有"哪个件的哪条账更紧"。
玻纤那一行值得单独说。 玻纤提升刚性、抗蠕变，间接帮到耐磨——但它本身会磨对偶件。 玻璃纤维的硬度与锐边在对磨中像一把微小的锉刀，很多"齿轮磨轴"的案子，根因不是尼龙磨没了，是钢轴被玻纤磨伤了。
PTFE 那一行也有代价。 它把摩擦系数压得很低，但摩擦系数降下来之后，接触面贴合更紧，实际接触应力反而升上去。 换成 PTFE 后对偶件更早划伤的场面，我们见过不止一次。
PA12 那一行的理由是尺寸。 吸水率低一个量级，落到齿上就是"装配时的齿隙和运行半年后的齿隙是同一个值"。代价是耐温——它不适合长期高温工况。
一句话：选路线，先问对偶件能不能承受，再问这个件的温度顶不顶得住。
四、一张判据表：摩擦系数和磨损量分两趟看
把上面的约束落成可核对的指标。下表的门限是方向性建议，不是验收标准——实际数值要由具体项目、具体工况和实测确定。
| 指标 | 方向性门限 | 验证方法 / 标准 | 常见失效 | 通行解法 | 对应助剂体系 |
|---|
| 摩擦系数（对钢，脂润滑） | 0.15 上下，必须标测试条件 | ASTM D1894 / SRV 往复试验 | 扭矩损失、局部温升 | 固体润滑体系 + 对偶件配合 | 润滑剂（内外润滑平衡） |
| 磨损率（质量 / 体积磨耗） | 跑合结束后曲线转平缓 | ASTM D3702 / 台架称重法 | 齿面起毛、齿厚下降 | 固体润滑 + 表面致密化 | 润滑剂 + 耐磨填料 |
| PV 上限 | 常在 1–3 MPa·m/s 量级，须按实测温度修正 | 台架逐级加载 + 红外测温 | 温升失控、软化咬合 | 降 PV 或改结构设计 | 结构决定，不靠助剂 |
| 干湿态尺寸差 | 齿顶圆差异 ≤0.05% | 调湿前后实测 / ISO 294 | 齿隙漂移、回差变大 | 选低吸水基材 + 强制调湿 | 材料本征，不靠助剂 |
| 长期热氧保留率 | 80℃×1000h 后 ≥75% | ISO 527 | 齿面发白、脆化 | 稳定化体系 | 抗氧剂（受阻酚 + 亚磷酸酯） |
| 对偶件磨损 | 钢件表面无犁沟 | 跑合后对偶件表面检查 | 塑件尚好、钢件先废 | 降玻纤含量或改对偶件表面处理 | 偶联剂（界面）+ 润滑剂减摩 |
| 熔接线强度 | 按齿根强度另定门限 | 短射取样 + 拉伸 | 齿根脆断 | 调浇口位置 + 增韧 | 润滑剂过量会拉低此项 |
怎么用这张表：不要逐行打分。先看第 1、2 行，再看第 3 行。 这三行不过，后面的都不用谈——因为关节齿轮的失效是串联的，间隙守不住，疲劳和磨耗的数据就失去意义。
一个提醒：表里"摩擦系数"这一项，测试条件不写清就等于没测。对偶材料、载荷、速度、润滑状态四项缺一，数字就不能比。同一种料换一个对偶件，数值能差出一个档次。
一页纸汇报表（给要向上汇报的人）
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项目：XX 关节齿轮 · 自润滑尼龙路线评估
结论方向：可作为候选路线，能否落地取决于三项前置条件
一、必须守住的三条
1. PV 核算先做完，超限的方案不改设计不动料
2. 脂相容性未确认前，不进入台架
3. 尺寸报告按调湿态出，干态只作过程记录
二、前置条件（任一不满足则建议暂缓）
· 长期工作温度不越过所选体系的持续使用区间
· 有百万转量级台架预算与周期
· 装配同轴度可控（偏载会放大齿面老化）
三、下一步动作
1. 取对偶件实物，标定摩擦副
2. 做 PV 粗算，定加载档
3. 脂浸泡两周后复测尺寸与外观
风险提示：本路线的主要不确定性在长期磨损速率，不在初始强度。
`
五、四个常见的判反
判反一：把摩擦系数低当成耐磨。
这是两件事。一个件可能很滑，但磨得很快；也可能摩擦系数不低，却相当耐用。 磨损率才是"耐磨"的核心，摩擦系数决定的是发热与扭矩损失。
判反二：以为多加点润滑剂就更保险。
恰恰相反——过量即失效。 外润滑加多了会往表面跑，出现喷霜、发白；焊接强度也会跟着掉。润滑剂的作用是让熔体流动和脱模顺畅，不是"越滑越好"。
判反三：拿常温数据推高温表现。
尼龙的耐磨性对温度极其敏感。同一个件，20℃ 能用，80℃ 可能就不行。 PV 上限会随环境温度明显下降，用常温曲线推高温工况，结论一定是错的。
判反四：只算自己磨掉多少，不算对偶件被磨掉多少。
这是关节齿轮最贵的一课。 选耐磨这条路，得同时算两笔账：自己磨掉多少，对方的件又被磨掉多少。玻纤、碳纤增强体系尤其容易把这一项漏掉。
再补一条常被误判的：同一批齿轮，颜色黄得深浅不一。
这通常不是"料不稳定"，而是抗氧剂在混料阶段分散不均。遇到这种情况，先回头查混料与母粒化这两道工序，别急着换料。
六、从干燥到齿形：上机要盯的几件事
干燥。 尼龙必烘。含水率超标会在熔融时水解降解，齿根强度直接掉下来。干燥窗口要拿实测含水率去定，牌号推荐值只能当起点——车间湿度、包装受潮、回用料掺入，都会把水分重新带进来。
熔接线与浇口。 熔接线落在受力齿面上，等于给断裂预埋起点。浇口位置在选料阶段就该一起讨论，因为齿轮的浇口安排往往受限，位置不好避开。
模温与表面质量。 表面越光滑致密，初期跑合越顺。模温不足会造成表面粗糙，跑合阶段磨耗明显偏高。
调湿。 精密关节件要控状态。给客户的尺寸，应当是调湿之后测出来的那一组。
验证顺序。 建议这样排：
1. 材料级：摩擦系数、磨损率、热氧保留率
2. 工艺窗口：不同模温、不同保压打出来的件做对比
3. 件级：齿形、齿厚、间隙，调湿后测
4. 台架：按 PV 档位跑，中途复测齿形
5. 环境叠加：温度循环 + 湿度循环，最后再上整机
顺序不能换。 前一项不通过就往下走，后面测出的数据没有解释意义。
打样实录。 有客户报来"百万转"的需求，我们按档位准备留样，结果一看件才明白：他报的是往复次数，不是转数。一个关节来回一次，齿轮其实转了不止一圈。报错一个量级，验证档位就全错。 后来我们把这件事写进了打样确认单：先让客户把"次数"的口径说清，再定跑多少圈。
七、哪种关节，这条路线该收手
这一段可能比前面六段更值钱。
以下五种情况，关节齿轮走自润滑尼龙这条路不建议推进：
其一，长期工作温度越过所选体系的持续使用区间。 这不是配方能补上的——尼龙家族里，低吸水与耐高温一直互为代价，换体系也只是换一种取舍。
其二，要求长期精度优于 ±0.02 mm。 尼龙吸湿带来的尺寸变化，不是靠配方能压住的。
其三，高 PV 且连续重载。 塑料的承载与散热能力摆在那里，这类工况的失效模式偏向强度与热，塑料很难赢。
其四，没有台架验证的预算和周期。 这个件的验证不会在一次样品测试里收口，得跑到百万次量级，中途反复复测。没有这个预算，就不要开这个头。
其五，年用量小到摊不平模具。 专用模具、齿形补偿、长周期验证，三样都得摊进成本。年用量只有几百件，从钱上就不成立。
把这五条写在前头，不是劝退，是省时间。 样品阶段一路顺、最后卡在批量验证上、整个方案回退的项目，我见过不止一个——回退的代价，通常比当初不做更高。
换料风险清单（从原方案换到自润滑尼龙，要动的东西）
| 环节 | 要动什么 | 容易漏的点 |
|---|
| 模具 | 按新料收缩率重核齿形，必要时修模 | 玻纤含量一变，各向异性跟着变 |
| 干燥 | 按实测含水率定窗口，不是照抄推荐值 | 回用料掺入带入的水分 |
| 料温 / 模温 | 按齿形填充与表面质量联合调 | 只按牌号推荐值给，不看件 |
| 保压与脱模 | 熔接线位置与强度要重定 | 玻纤料熔接线强度下降更陡 |
| 调湿 | 强制调湿 + 称重判定 + 复测尺寸 | 按平均壁厚估时间，厚齿处没吸透 |
| 色差 | 免喷涂件的色板要提前确认 | 固体润滑体系本身颜色偏深 |
| 验证顺序 | 材料级 → 工艺窗口 → 件级 → 台架 → 环境叠加 | 前一项未过就往下走 |
读者追问三则
问：和进口料差在哪？
只讲两件能对照的事：同一指标，看它标没标测试条件；同一件上，看它给没给长期数据。耐磨类指标对条件特别敏感，条件不明的数字不宜直接比。有些件上走国产路线已经比较成熟，有些件目前仍不建议替——具体到你的关节，要看温度、PV 和验证资源三样。
问：玻纤能不能干脆不加？
要想清楚不加玻纤是拿什么换的。不加，刚性、抗蠕变和 PV 上限都会降，代价是齿可能变形、间隙守不住。加，就要接受对偶件磨损这一项。这不是"加或不加"的题，是"对偶件能不能接受"的题。
问：POM 能不能顶这个件？
看工况。POM 尺寸稳、自润滑好、噪音低，但抗冲击偏弱、不适合高载荷。低载荷、高转速的位置它是主流；冲击载荷大的位置，尼龙加增韧更抗打。两个都不足的位置，就该重新想设计。
结语
关节齿轮的自润滑路线，说到底是一道系统账，不是选料题。
判断链只有三条：
温度定体系 → PV 定能不能做 → 验证顺序定成败。
把这三条走完，"这料耐磨不耐磨"这个问题自然就有答案了。
如果你手上正有一个关节齿轮要定料，把三样东西发过来就能给方向：长期工作温度、对偶件材料、循环次数与 PV 估算。
把料倒进机器之前，齿轮这件事其实已经定了大半——定它的不是牌号选得多准，是干燥、模温、保压这三样有没有跟着一起换。
这类件的选料与试模，可以一起聊。
我们做的事很具体：把 PA6、PA66、PA46、PA11、PA12、PA6T、PA9T 以及尼龙合金这些树脂，调成某个件装上机器后真能用的样子；顺带也做改性 PPO、PPS 与热塑性弹性体。
同时经营各大化工巨头的尼龙树脂、副牌料与大包料，另长期收尼龙原料、水口回料与各类尼龙废料，有正规处置渠道。
配方里的助剂体系按件的工况配——常规助剂常备现货，特殊型号按需配套；你报工况和牌号，料和助剂一次配齐。
Last month, a client who makes collaborative robot joint modules came over with a set of gears.
It's nylon; the tooth surface has already become fuzzy, and there are a few fine lines at the tooth root. He placed the part on the table and said, 'It ran less than 400,000 times, and the teeth are already fuzzy. Do you have anything more wear-resistant?'
I didn't respond immediately, but first asked him three questions: What material is the mating part of this gear? What's the approximate PV value of the gear surface? Is it currently lubricated with grease or running dry?
He was stunned for a moment and said he hadn't counted the first two items. They only knew that what they wanted was 'more wear-resistant material'.
The three words 'more wear-resistant' cannot be bought. You can either buy a lower friction coefficient or a lower wear rate—these are not the same thing, and in many cases, they even conflict with each other.
There is one more thing that needs to be corrected first: the end of the lifespan of a joint gear is rarely 'worn down to break'; it is usually 'the clearance becomes so large that engagement starts to misalign.' If it breaks, it means it has been misaligned for a long time before that.
This article talks about three things: what constrains the material of robot joint gears, how the criteria for the self-lubricating nylon route are determined, and how the two numbers 'coefficient of friction' and 'wear amount per million revolutions' are tested.
1. The accounts of the joint gears must be calculated up to a million turns.
First, convert 'million turns' into a perceptible quantity.
A single joint of a collaborative robot moves back and forth five thousand times a day. Calculating with three hundred days a year, that's one and a half million times. Doing this for two years amounts to an order of three million times. This is not laboratory accelerated lifespan; it is the daily routine on the production line.
The biggest difference between bevel gears and car gears also lies in this aspect.
The load on car gears is pulsating—high peaks, few occurrences; joint gears are exactly the opposite: the load is not high, but the occurrences are extremely frequent, and they are hidden in a grease-lubricated sealed cavity, with temperatures that are not low.
This brings three consequences.
The tooth surface is constantly being worn down. Each time only an extremely thin layer is worn away, but accumulated over time it is enough to wear down the tooth profile.
The metal shavings can't get out. They stay circulating in the cavity, turning into abrasive particles, which in turn accelerate wear—this is a positive feedback loop.
Lubricating grease will age and dissipate. Therefore, the material's inherent self-lubricating property must hold up; you cannot base its lifespan on the assumption that 'the grease will always be there.'
Another easy-to-overlook point: the counterpart of the joint gear is usually steel. So this is a 'plastic running on steel' friction pair, which is completely different from plastic-on-plastic.
The self-lubrication of nylon relies on the formation of a transfer film on the steel surface during friction, which then becomes 'nylon on nylon.' Whether the film is stable determines whether the component is durable. And whether the film is stable is directly related to the moisture absorption condition — this is also the reason why precision joint components need to control humidity and undergo moisture adjustment.
2. Six variables: ask clearly first, then discuss the grade
When selecting a gear for joints, the starting point is not to open the brand table, but to clarify six variables. Missing one, everything afterward is just guessing.
Temperature. In the joint module, the motor is nearby and the reducer is farther away. The actual temperature of the gears is commonly 40–80°C, and it can be higher under continuous high load or insufficient heat dissipation design. What needs to be monitored is the long-term temperature, not the peak.
Load and speed. These two cannot be reported separately; they must be combined into a PV value (contact pressure × linear velocity). If the PV limit is exceeded, the frictional heat cannot dissipate, and the temperature rise will immediately spiral out of control—this is the most common pitfall for gear joints.
Medium. Grease lubrication or dry running. The compatibility of the base oil of the grease with the material must be confirmed separately, as some greases can make the surface sticky, precipitate, or even affect the size of the gear surface.
Service life. The number of cycles is measured in millions. The criterion is not "when it breaks," but "how much tooth thickness has worn and how much clearance has increased by the end of its service life."
Appearance and burrs. Clean environments (such as medical and food-related settings) have additional requirements for burr amounts, which directly rules out certain lubrication systems.
Compliance. In scenarios involving precipitation and volatilization, one should refer back to the corresponding standard context and not create safety conclusions on their own.
Among the six variables, temperature and PV are hard thresholds, and the remaining four determine whether the plan can be finalized.
3. The division of three self-lubricating routes
Place the mainstream routes side by side, and pay attention to the 'cost' column, not the 'advantages' column.
| Route | compose | Give what | Cost |
|---|
| PA66-GF15 Solid Lubrication | Medium-low fiberglass MoS₂ / PTFE / Silicone | Rigidity, creep resistance, controllable cost | Glass fiber abrasion on paired steel parts; weld line strength decreases |
| PA66 Toughened PTFE | Elastomer Low-friction system | Impact-resistant, low noise | Low rigidity, limited thick-tooth load capacity |
| PA12 Short Fiber | Long carbon chain, small amount of fiber | Low water absorption, small dimensional drift, good toughness | High cost, low maximum temperature resistance |
There is no 'which is better' among the three routes, only 'which item's which account is tighter'.
The fiberglass industry deserves separate mention. Fiberglass increases rigidity and creep resistance, indirectly helping wear resistance—but it itself can wear down the mating parts. The hardness and sharp edges of glass fibers act like tiny files during wear; in many cases of 'gears wearing down shafts,' the root cause is not that the nylon is worn out, but that the steel shaft has been damaged by the fiberglass.
The PTFE line also comes with a cost. It lowers the coefficient of friction, but once the friction coefficient goes down, the contact surfaces fit more tightly, and the actual contact stress actually goes up. We've witnessed more than once scenes where the counterpart gets scratched earlier after switching to PTFE.
The reason for the PA12 line is size. Its water absorption is one order of magnitude lower, so when applied to gears, 'the clearance during assembly and the clearance after half a year of operation are the same.' The trade-off is temperature resistance—it is not suitable for long-term high-temperature conditions.
In a word: when choosing a route, first ask whether the paired component can withstand it, then ask whether this component can handle the temperature.
4. A criterion table: friction coefficient and wear amount are viewed in two rounds
Turn the above constraints into verifiable indicators. The thresholds in the table are directional suggestions, not acceptance criteria—the actual values need to be determined by specific projects, specific working conditions, and actual measurements.
| Indicator | Directional threshold | Verification Method / Standard | Common Failures | Common solution | Corresponding auxiliary agent system |
|---|
| Coefficient of friction (against steel, grease-lubricated) | Around 0.15, testing conditions must be specified | ASTM D1894 / SRV Reciprocating Test | Torque loss, local temperature rise | Solid lubrication system Mating parts fit | Lubricant (internal and external lubrication balance) |
| Wear rate (mass/volume loss) | After the break-in period, the curve levels off | ASTM D3702 / Bench Scale Weighing Method | Tooth surface fuzzing, tooth thickness reduction | Solid lubrication Surface densification | Lubricant Wear-resistant filler |
| PV cap | Often in the range of 1–3 MPa·m/s, must be corrected according to the measured temperature | Stepwise loading on the test rig, infrared temperature measurement | Uncontrolled temperature rise, softened occlusion | Reduce PV or change structural design | Structure determines, does not rely on additives |
| Difference in dimensions between dry and wet states | Addendum modification difference ≤0.05% | Measured before and after humidity adjustment / ISO 294 | Tooth clearance drift, increased hysteresis | Choose low water-absorption substrate Forced humidity adjustment | Intrinsic properties of the material, without relying on additives |
| Long-term thermal-oxygen retention rate | After 80℃ × 1000h ≥75% | ISO 527 | Tooth surface whitening and brittleness | Stabilization system | Antioxidant (hindered phenol, phosphite) |
| Mating part wear | The surface of the steel part has no furrows | Surface inspection of matched parts after running-in | Plastic parts are still good, steel parts are wasted first. | Reduce the glass fiber content or change the surface treatment of the mating part | Coupling agent (interface) Lubricant for friction reduction |
| Weld line strength | Set the threshold according to the root strength of the teeth | Short-shot sampling Stretching | Brittle fracture at the tooth root | Adjust gate location Toughen | Excess lubricant will lower this item |
How to use this table: Do not score row by row. First look at rows 1 and 2, then look at row 3. If these three rows do not pass, there is no need to discuss the others—because the failure of the joint gears is in series, if the clearance cannot be maintained, the data on fatigue and wear become meaningless.
A reminder: Regarding the 'friction coefficient' listed in the table, if the test conditions are not clearly stated, it is equivalent to not having tested it at all. If any of the four factors—counterpart material, load, speed, and lubrication condition—is missing, the numbers cannot be compared. Even for the same material, changing the counterpart can cause the value to differ by an entire level.
One-page report sheet (for people who need to report upwards)
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Project: XX Joint Gear · Self-lubricating Nylon Route Evaluation
Conclusion direction: Can be considered as a candidate route, whether it can be implemented depends on three prerequisites
1. Three Rules That Must Be Followed
1. Complete the PV calculation first; for plans that exceed limits, do not change the design or move materials.
2. Do not enter the test bench before lipid compatibility is confirmed
3. The size report is given in the conditioned state, with the dry state recorded only for process documentation.
2. Precondition (It is recommended to postpone if any are not met)
· The long-term operating temperature does not exceed the continuous use range of the selected system
· A test bench budget and cycle at the million-level turnover scale
· Assembly coaxiality is controllable (eccentric load will accelerate gear surface aging)
3. Next Steps
1. Take the actual paired component and calibrate the friction pair
2. Do a rough calculation of PV and determine the load level
3. Retest the size and appearance after soaking in fat for two weeks
Risk reminder: The main uncertainty of this route lies in the long-term wear rate, not in the initial strength.
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5. Four Common Contradictions
Mistake One: Mistaking a low friction coefficient for wear resistance.
These are two different things. One may be very smooth, but wear down quickly; it may also have a high coefficient of friction, yet be quite durable. Wear rate is the core of 'wear resistance,' while the coefficient of friction determines heat generation and torque loss.
Incorrect thinking number two: believing that adding more lubricant makes it safer.
On the contrary—excess leads to failure. If too much external lubricant is applied, it will move to the surface, causing frosting and whitening; the welding strength will also decrease. The purpose of a lubricant is to enable smooth flow of the melt and easy demolding, not 'the more slippery, the better'.
Counterargument three: Using room temperature data to infer high-temperature performance.
The wear resistance of nylon is extremely sensitive to temperature. The same part may work at 20℃, but might fail at 80℃. The PV limit will significantly decrease with ambient temperature, and using a room temperature curve to predict high-temperature conditions will definitely lead to incorrect conclusions.
Judgment 4: Only count how much you have worn down yourself, not how much has been worn down on the mating part.
This is the most expensive lesson for gear joints. Choosing the path of wear resistance requires calculating two sets of numbers at the same time: how much you wear down, and how much of the other party's parts are worn down. Glass fiber and carbon fiber reinforced systems are particularly prone to overlooking this item.
Here’s another common misjudgment: gears from the same batch, with varying shades of yellow.
This is usually not 'unstable material', but rather uneven dispersion of the antioxidant during the mixing stage. When this happens, first go back and check the mixing and masterbatching processes, and don't rush to change the material.
6. From Drying to Tooth Shape: A Few Things to Watch When Using the Machine
Drying. Nylon must be baked. If the moisture content exceeds the standard, it will hydrolyze and degrade during melting, and the root strength of the teeth will drop directly. The drying window should be determined based on the measured moisture content; the grade recommended value can only be taken as a starting point — workshop humidity, packaging moisture, and the addition of recycled materials can all reintroduce moisture.
Weld lines and gates. When weld lines fall on the load-bearing tooth surface, it is equivalent to pre-embedding a starting point for fracture. The gate location should be discussed together during the material selection stage, because the placement of gates for gears is often limited and it is difficult to avoid unfavorable positions.
Mold temperature and surface quality. The smoother and denser the surface, the smoother the initial running-in. Insufficient mold temperature can cause surface roughness, and wear during the running-in phase will be noticeably higher.
Humidity control. Precision joint parts need to have their condition controlled. The dimensions given to the customer should be the set measured after humidity adjustment.
Verification order. It is recommended to arrange it like this:
1. Material level: friction coefficient, wear rate, thermal-oxidative retention rate
2. Process window: Compare parts produced under different mold temperatures and different holding pressures
3. Part level: tooth profile, tooth thickness, clearance, measured after humidity adjustment
4. Test bench: Run according to the PV gear, re-measure the tooth profile midway
5. Environmental stacking: temperature cycling, humidity cycling, and finally assembling the whole machine
The order cannot be changed. If the previous item fails, we move on, and the data measured afterwards has no explanatory significance.
Proofing Record. A customer requested a 'million rotations,' and we prepared samples according to the tiers. But when we looked at the parts, we realized: they were reporting the number of reciprocations, not rotations. One joint moving back and forth once actually makes the gear rotate more than a full turn. Reporting the wrong order of magnitude messed up the verification tiers. Later, we included this in the proofing confirmation form: let the customer clarify what they mean by 'number of times' before deciding how many rotations to run.
7. For which joint should this route be stopped
This section might be more valuable than the previous six sections.
In the following five situations, it is not recommended to pursue the self-lubricating nylon path for joint gears:
First, the long-term working temperature exceeds the continuous use range of the selected system. This is not something that can be compensated for with the formulation—within the nylon family, low water absorption and high-temperature resistance have always been a trade-off, and changing the system only changes the type of compromise.
Secondly, it requires long-term accuracy better than ±0.02 mm. The dimensional changes caused by nylon moisture absorption cannot be suppressed by formulation.
Third, high PV and continuous heavy loading. Plastic's load-bearing and heat dissipation capacity is obvious, and failure modes in these conditions are biased toward strength and heat, making it hard for plastic to win.
Fourth, no bench validation budget and cycle. Validation of this part won't be finished in a single sample test; it must run to the million-times scale and be repeatedly tested midway. Without this budget, don't start this venture.
Fifth, annual usage is so small that molds can't be evenly spread. Special molds, tooth profile compensation, long-cycle validation—all three must be factored into costs. Annual usage is only a few hundred pieces, so it's not feasible financially.
Writing these five points upfront is not to discourage them, but to save time. I've seen more than one project where the sample phase went smoothly but eventually got stuck on batch validation, with the entire solution rollback—the cost of rollbacks is usually higher than not doing it at all.
Material Change Risk List (Switching from the original plan to self-lubricating nylon, items to be moved)
| Steps | What to Move | Points Prone to Leakage |
|---|
| Molds | Heavy core tooth profiles according to shrinkage rate of new material, mold modifications if necessary | Changes in glass fiber content cause anisotropy to change accordingly |
| Drying | Set the window based on actual measured moisture content, not just copy recommended values | Reused material mixed in with added moisture |
| Material temperature / mold temperature | Adjust according to the combination of tooth profile, filling, and surface quality | Only follow the recommended grade value, without checking the parts |
| holding pressure and demolding | Position and strength of the welding line must be re-determined | Greater drop in strength of the fiberglass welding line |
| Humidity adjustment | Forced humidity adjustment + weighing determination + re-measurement of dimensions | Estimated time based on average wall thickness, thickness teeth not fully absorbed |
| Color difference | Color palettes for non-sprayed parts must be confirmed in advance | Solid lubrication system color is relatively dark |
| Verification sequence | Material-level → Process window → Piece-level → Bench → Environment overlay | Skipped the previous item and proceeded |
Reader's three follow-up questions
Question: What's the difference from imported materials?
I'll only talk about two things you can compare: for the same measure, check if it marks the test conditions; For the same item, see if it provides long-term data. Wear resistance indicators are especially sensitive to conditions; if the numbers are unclear, it's best not to compare directly. Some parts have already matured toward domestic production, while others are still not recommended for replacement—when it comes to your joints, it depends on temperature, PV, and verification resources.
Question: Can you simply skip adding fiberglass?
You need to think clearly: what exactly are you getting in exchange for fiberglass? If you don't add it, rigidity, creep resistance, and PV limits will all decrease, but the cost is that the teeth may deform and gaps can't be held. If you do, you have to accept wear on the paired parts. This is not a question of "add or not," but whether the dual part is acceptable.
Question: Can POM support this part?
It depends on the working conditions. POM has stable dimensions, good self-lubrication, and low noise, but weak impact resistance and is not suitable for high loads. Low loads and high rotational speeds are mainstream; For areas with high impact loads, nylon with toughening is more durable. Areas lacking both need to be redesigned.
Conclusion
The self-lubricating route for joint gears is, ultimately, a system issue, not a material selection issue.
There are only three judgment chains:
Temperature determines the system→ PV can be done, → verification sequence determines success or failure.
Once you complete these three points, the question of "Is this material wear-resistant?" naturally have an answer.
If you have a joint gear to be preserved, send over three items and you can give directions: long-term operating temperature, counterpart material, cycle count, and PV estimation.
Before pouring the material into the machine, the gears are already mostly decided—it's not about how accurately the grade is chosen, but whether drying, mold temperature, and holding pressure are all replaced together.
You can discuss material selection and mold testing for these types of parts together.
What we do is very specific: mixing resins like PA6, PA66, PA46, PA11, PA12, PA6T, PA9T, and nylon alloys into a condition that can actually be used in machines when installed; We also produce modified PPO, PPS, and thermoplastic elastomers.
We also handle nylon resins, sub-brand materials, and bulk materials for major chemical giants, and we also regularly collect nylon raw materials, sprue recycling, and various nylon scraps, with proper disposal channels.
The additive system in the formula is tailored to the working conditions of each piece—regular additives are always in stock, special models are matched as needed; You specify the working conditions and grade, and the materials and additives are all prepared in one go
