上个月，一个做协作机器人直线模组的客户，寄来一小段金属丝杠的照片。
照片里是行星滚柱丝杠的螺母外圈，他拿游标卡尺量了三处，说想换成改性尼龙。电话里他问得很直接："你们能不能做 PA66-GF50 的丝杠？减重是不是能到六成？"
我反问他一句："你这个丝杠，长期工作温度大概多少？"电话那头沉默了两秒，说还没测过，是按规格书上的峰值算的。
这段对话我后来想了想，问题不在材料，在他把"丝杠精度"当成了单一指标。丝杠材料能不能从钢换成改性尼龙，得先看清它干的是什么活。
一、丝杠的活，是把"转"变成"走"
行星滚柱丝杠的原理不复杂：螺纹杆转，滚柱在螺纹之间滚动，把旋转运动变成螺母的直线运动。它和滚珠丝杠的区别，是拿滚柱代替滚珠——接触面从"点"变成"线"，单位面积压力小得多，能扛更大的推力。
协作机器人和人形机器人的直线关节，越来越多用这种丝杠做升降和伸缩。它的角色是"把电机的转，变成末端的走"。
这个角色带来一个后果：丝杠的失效，绝大多数不是"断了"，是"走不准了"。
具体是三个地方在变：
导程误差。 螺母每转一圈走的距离，原本是按微米给的。尺寸一变，定位就漂。
温升。 丝杠在封闭腔里转，摩擦热散不出去，件会热胀，导程跟着变。
磨损。 滚柱和螺纹面反复滚压，磨掉一点，间隙就大一点。
所以问"塑料丝杠能不能用"，问法本身偏了。 该问的是：在它的工作温度和寿命内，这个件的导程能不能守住。
二、这个件被什么卡住：六条线
丝杠的工况，比一般结构件麻烦，因为它同时受机械和环境两条线夹击。
温度。 模组里电机近、丝杠远，实际工作温度常见 40–80℃，连续高负载或散热不足时会更高。要盯的是长期温度，不是峰值。
载荷。 推力按牛算，精密直线模组常见几百牛到两千牛量级。这是丝杠最硬的一关——塑料的模量只有钢的一小部分，受载变形直接变成导程误差。
介质。 润滑脂的相容性是硬条件。脂里某些成分会让塑料件表面析出、发黏，甚至影响螺纹尺寸。这一条在样机阶段很少测，到批量才暴露。
寿命。 直线往复以十万到百万次计。判据不是"什么时候断"，是"到寿命终点时导程误差涨了多少"。
外观与洁净。 部分场景（洁净室、医疗、食品周边）对析出和挥发有额外要求，要提前回到对应标准语境。
合规。 涉及食品、医疗接触必须回到 GB 4806.7 / FDA 语境，不自创安全结论。
把这六维摆在一起，结论很清楚：丝杠没有一项能单独达标，它们是耦合的。 温度高一点，热胀多一点，导程就漂；磨损快一点，间隙就大，精度也守不住。
三、塑料能替到哪一步：三条路的边界
从金属换塑料，起点不是挑牌号，是搞清"金属为什么能用"。
钢制丝杠靠三件事吃饭：高模量（不变形）、尺寸不随环境变、表面硬（耐磨）。 换成塑料，前两件都成了问题。
塑料模量比钢低一到两个数量级。补偿办法是加纤维——玻纤和碳纤增强的意义在这。但加水只解决了刚度，解决不了吸水。
把三条主流路线并排放，注意看的是"代价"那一列，不是"优点"：
| 路线 | 组成 | 给什么 | 代价 |
|---|
| 钢制丝杠 | 轴承钢 | 精度、刚性、寿命全在线 | 重、贵、必须持续润滑 |
| PA66-GF50 | 高玻纤 + 耐磨 | 减重约 60%、自润滑、成本低 | 刚性低于钢、耐温上限低 |
| POM 丝杠 | 聚甲醛 | 自润滑好、尺寸稳、便宜 | 强度低、不耐高温 |
三条没有"谁更好"，只有"哪个件的哪条账更紧"。
PA66-GF50 这一行，减重是它最大的卖点。 公开资料里这类方案相对金属能减掉约六成重量——一台协作机器人身上若有好几根丝杠，总减重相当可观。代价是刚性只有钢的一部分，耐温也低一截。
碳纤那行更刚更轻，但导电、贵，靠近电气件要考虑绝缘隔离；各向异性也更明显，翘曲要提前算。
POM 那行自润滑和尺寸稳定性好，但它扛不住大推力，高温工况直接出局。
一句话：丝杠材料选塑料，买的是"轻和自润滑"，不是买"比钢更强"。强度是纤维附赠的，精度才是要另外守的。
四、选型判据表（塑料滚柱的验收页）
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——实际数值必须由具体项目、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 |
|---|
| 导程误差（温态） | 300 mm 行程内 ≤0.5 μm 量级 | 激光干涉仪实测（温态） | 定位漂、回差大 | 低膨胀基材 + 控温 | 材料本征决定，不靠助剂 |
| 摩擦系数（脂润滑） | 0.15 上下 | ASTM D1894 | 温升、扭矩损失 | 固体润滑体系 | 润滑剂（内外润滑平衡） |
| 百万转磨损量 | <0.01 mm/百万转 量级 | 台架称重法 | 间隙变大、走不准 | 耐磨填料 + 致密化 | 润滑剂 + 耐磨填料 |
| 长期热氧保留率 | 80℃×1000h 后 ≥75% | ISO 527 | 发白、脆化 | 稳定化体系 | 抗氧剂（受阻酚 + 亚磷酸酯） |
| 弯曲模量 | 参考 8–10 GPa（GF50） | ISO 178 | 受载变形、导程变 | 高玻纤增强 | 偶联剂（界面） |
| 脂相容性 | 浸脂后尺寸外观无异常 | 供应商脂样浸泡 | 析出、发黏 | 提前确认脂体系 | 助剂迁移性需评估 |
怎么用这张表：别逐行打分，先看第一行和第二行。这两行过不去，后面不用谈——丝杠的失效是串联的，导程守不住，磨损的数据就失去意义。
一个提醒：表里"导程误差"这一项，很多项目没有现成国标可依。没有标准时，把验证方案写进技术协议，而不是省掉这一项。
五、失效不是"磨没了"：四条真实根因
失效一：导程在头两个月变大，之后稳。
根因通常不是磨损，是吸湿。件在出厂状态（干态或部分调湿）装上去，运行期继续吸湿到平衡，尺寸往一个方向走。两个月后吸湿接近平衡，变化就停了。调湿态交付 + 复测，比换料有效得多。
失效二：表面局部发白，随后掉粉。
根因是热氧老化，而且往往局部——装配偏载导致某几牙长期高温。这时候换更高的抗氧剂档位有用，但根因在装配同轴度，不在料。
失效三：磨下去很快，件本身没坏。
查两件事：一是对偶件（钢螺纹杆）的表面粗糙度与硬度；二是润滑脂是否相容。塑料对钢的摩擦副，磨损常在塑料侧，诱因在钢侧。
失效四：同一批件黄得深浅不一。
这不是"料不稳定"。抗氧剂分散不均的可能性更大——它在混料阶段就没混匀。看到这现象，先查混料工艺与母粒化，别急着换料。
这里有一条要直说的：塑料丝杠的失效排查，先怀疑状态与工艺，最后才怀疑材料。 这和一般结构件反着来——因为精度量级太小，任何状态波动都被放大成"料不行"。
六、上机前这几件事要先定
干燥。 尼龙必烘。含水率超标会在熔融时水解降解，螺纹根部强度直接掉下来。干燥窗口要按实测含水率定，牌号推荐值只当起点——车间湿度、包装受潮、回用料掺入，都会把水分重新带进来。
螺纹的收缩补偿。 螺纹不是圆，各处收缩不一样，玻纤件的取向差异会放大这件事。模具的螺纹补偿要按件做，不能按材料手册的通用收缩率给。
取向与浇口。 玻纤件是各向异性的，流动方向和垂直方向的模量、收缩都不同。丝杠是回转件，浇口位置直接决定圆度和螺纹一致性。
验证顺序。 建议这样排：
1. 尺寸与圆度（调湿后测，干态只做过程记录）
2. 导程误差（装到实际螺纹杆上测，不用替代件）
3. 脂相容性（浸泡后复测尺寸与外观）
4. 台架（跑磨损，中途复测导程）
5. 环境叠加（温度循环 + 湿度循环，最后上整机）
顺序不能换。 前一项不通过就往下走，后面测出来的数据没有解释意义。
打样实录：有客户报来"丝杠精度 0.5 μm"，我们按这个准备留样，结果一看工况才明白——他报的是室温下的导程，没算电机一跑起来腔体升温带来的热膨胀。同样一段 300 mm 行程，温升 30℃ 热胀就能吃掉大半精度余量。后来我们把这件事写进打样确认单：先让客户把"温度区间"说清，再定精度档。
七、边界：什么时候塑料丝杠不该上
这一段可能比前面六段更值钱。
以下四种情况，塑料丝杠这条路不建议推进：
其一，长期工作温度超过 110℃。 PA66 体系在这个区间长期运行的保持数据，公开资料里的支撑不足。这不是改配方能解决的，换体系也难——低吸水和耐高温在尼龙家族里本来就是一对矛盾。
其二，要求导程精度长期优于 ±0.5 μm/300 mm 且高推力。 塑料的模量和热膨胀，决定了它不适合作为超高精度主传动件。这是材料物理层面的边界。
其三，整机的验证资源不足以支撑长周期台架。 丝杠验证不是一次样品测试能收口，要跑到百万次量级、期间多次复测导程。没有这个验证预算，就不要开这个头。
其四，用量小到摊不薄模具与验证成本。 这个件要开专用模具、做螺纹补偿、走长周期验证。如果年用量只有几百件，从钱上就不成立。
把这四条写在前头，不是劝退，是省时间。 我见过太多项目在样品阶段很顺，卡在批量验证上，最后整个方案回退——回退的成本，比一开始就不做高得多。
换料风险清单（从金属换到 PA66-GF50，要动的东西）
| 环节 | 要动什么 | 容易漏的点 |
|---|
| 模具 | 螺纹按件做收缩补偿，不能套通用收缩率 | 玻纤取向导致的方向性收缩差 |
| 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 | 按螺纹填充与圆度要求联合调 | 只按牌号推荐值给，不看件 |
| 保压 / 脱模 | 回转件易变形，保压曲线与脱模方式要重定 | 沿用原金属件的工装思路 |
| 调湿 | 强制调湿 + 称重判定 + 复测尺寸 | 按平均壁厚估时间，厚壁处没吸透 |
| 色差 | GF50 件本身颜色深且批次有差 | 外观件的色差标准要提前放宽或另定 |
| 验证顺序 | 尺寸 → 导程 → 脂相容 → 台架 → 环境叠加 | 前一项未过就往下走 |
打样试模排程
| 轮次 | 上机内容 | 每轮验什么 | 留样 |
|---|
| 第一轮 | 螺杆试小样，短射看填充 | 螺纹是否打满、表面浮纤 | 留 3 件，3 个月 |
| 第二轮 | 正式试模，调模温保压 | 圆度、导程（干态） | 留 5 件，6 个月 |
| 第三轮 | 调湿后复测 + 台架初跑 | 导程（温态）、磨损初值 | 留 8 件，12 个月 |
一页纸汇报表（给要向上汇报的人）
`
项目：行星滚柱丝杠 · 材料路线评估
结论方向：PA66-GF50 可作为候选路线，能否落地取决于四项前置条件
一、必须守住的三条
1. 调湿态交付，干态数据不上报告
2. 螺纹按件做收缩补偿，不套通用值
3. 全程无润滑脂相容性数据不进入台架
二、前置条件（任一不满足则建议暂缓）
· 长期工作温度 ≤ 110℃ 量级
· 有百万次量级台架验证预算与周期
· 推力在塑料模量可支撑区间
· 装配同轴度可控（偏载会放大热氧老化）
三、下一步动作
1. 取螺纹杆实物，测实际导程温态漂移
2. 做调湿前后尺寸差，评估件对状态的敏感度
3. 脂相容性浸泡试验（两周起）
风险提示：本路线的主要不确定性在导程精度保持，不在初始强度。
`
读者常问的两句
问：既然 PA66 耐温只有 260℃ 熔点，那靠近电机的丝杠是不是就没戏？
要看实际温度，不要看电机规格。模组的散热路径决定了丝杠的真实温度，很多时候比想象中低。做法是实测——在样机上贴热电偶，跑典型工况，取长时间稳态值。用峰值温度判断会误杀方案，用规格书温度判断会误放。
问：玻纤和碳纤，这个件能不能换？
方向不同。玻纤给的是成本和韧性，碳纤给的是模量和尺寸稳定性。丝杠这类对模量和翘曲都敏感的回转件，碳纤的理由更充分；但碳纤的导电性和成本必须一起考虑。另外换纤维体系等于换一套界面方案，验证要重做，不能只对比样条数据。
结语
行星滚柱丝杠的塑化，说到底是一道精度保持题，不是强度题。
判断链只有三条：
温度定体系 → 吸水率定牌号 → 验证顺序定成败。
三条都定完，"能不能用塑料"这个问题自然就有答案了。
如果你手上正有一个丝杠或直线模组要定料，把三样东西发过来就能给方向：长期工作温度、实际推力量级、年用量量级。
这里做塑料的人多。改性尼龙这个圈子，做丝杠这类精密件的人，挑料比挑设备还细。
我们做的事很具体：把 PA6、PA66、PA46、PA11、PA12、PA6T、PA9T 和尼龙合金这些树脂，改成某个件真正能用的样子；顺带做改性 PPO、PPS 和热塑性弹性体；也经营各大化工巨头的尼龙树脂、副牌料和大包料，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 customer who makes collaborative robot linear modules sent a photo of a small section of a metal screw.
The photo shows the outer ring of the nut of a planetary roller screw. He used a vernier caliper to measure three points and said he wanted to switch to modified nylon. On the phone, he asked very directly: 'Can you make a PA66-GF50 screw? Can the weight reduction reach 60%?'
I retorted to him: 'You lead screw, what is the approximate working temperature for long-term use?' There was a two-second silence on the other end of the phone, and he said it hadn't been measured yet, it's calculated based on the peak value in the specification.
After thinking about this conversation later, I realized the problem wasn't with the material, but that he treated 'screw accuracy' as a single metric. Whether the screw material can be changed from steel to modified nylon depends on clearly understanding what work it is doing.
1. The work of the screw is to turn 'rotation' into 'movement'.
The principle of the planetary roller screw is not complicated: the threaded rod rotates, the rollers roll between the threads, converting rotational motion into the linear motion of the nut. The difference between it and a ball screw is that rollers replace the balls—the contact surface changes from a 'point' to a 'line', which significantly reduces the pressure per unit area and can withstand greater thrust.
Linear joints of collaborative robots and humanoid robots increasingly use this kind of screw for lifting and telescoping. Its role is to "convert the motor's rotation into the movement of the end."
This character brings a consequence: the failure of the lead screw, which in the vast majority of cases is not 'broken,' but 'no longer precise.'
Specifically, there are three places that are changing:
Lead error. The distance the nut moves with each turn was originally given in microns. Once the size changes, the positioning drifts.
Temperature rise. When the screw rotates in a closed cavity, the frictional heat cannot dissipate, the part will expand due to heat, and the lead will change accordingly.
Wear. The rollers and threaded surfaces are repeatedly rolled, and as a little is worn away, the clearance becomes slightly larger.
So asking 'Can plastic lead screws be used?' is the wrong way to ask. The question should be: Within its operating temperature and lifespan, can this part maintain its lead accuracy?
2. What is blocking this part: six wires
The working conditions of the lead screw are more complicated than those of general structural parts because it is subjected to the dual pressures of both mechanical and environmental factors.
Temperature. In the module, the motor is nearby and the lead screw is farther away. The actual operating temperature is commonly 40–80°C, and it can be higher under continuous heavy load or insufficient heat dissipation. What needs monitoring is the long-term temperature, not the peak.
Load. Thrust is measured in newtons, and precision linear modules commonly range from several hundred to two thousand newtons. This is the stiffest challenge for lead screws—the modulus of plastic is only a small fraction of that of steel, and deformation under load directly translates into lead error.
Medium. The compatibility of grease is a strict requirement. Some components in the grease can cause deposits and stickiness on the surface of plastic parts, and even affect the dimensions of threads. This issue is rarely tested during the prototype stage and only becomes evident during mass production.
Lifespan. The linear reciprocation counts from hundreds of thousands to millions of times. The criterion is not 'when it breaks,' but 'how much the lead error has increased by the end of its lifespan.'
Appearance and cleanliness. Some scenarios (cleanrooms, medical, food-related) have additional requirements for precipitation and volatilization, and it is necessary to refer back to the corresponding standard context in advance.
Compliance. For food and medical contact, it is necessary to refer back to the context of GB 4806.7 / FDA, and not to create your own safety conclusions.
When you put these six dimensions together, the conclusion is clear: none of the lead screws can meet the standard on their own; they are coupled. With a slightly higher temperature, there is more thermal expansion and the lead drifts; with slightly faster wear, the clearance increases and accuracy cannot be maintained.
3. How far can plastics go: The boundaries of three paths
Switching from metal to plastic, the starting point is not to choose the grade, but to figure out 'why metal can be used'.
Steel lead screws rely on three things to function: high modulus (doesn't deform), dimensions that don't change with the environment, and hard surface (wear-resistant). If replaced with plastic, the first two become problems.
The modulus of plastic is one to two orders of magnitude lower than that of steel. The way to compensate is by adding fibers — this is the significance of glass fiber and carbon fiber reinforcement. But adding water only solves stiffness, it does not solve water absorption.
Place the three main routes side by side, paying attention to the 'cost' column, not the 'advantages' column:
| Route | compose; consist of | Give what | Cost |
|---|
| Steel screw | Bearing steel | Accuracy, rigidity, and lifespan all online | Heavy, expensive, must be continuously lubricated |
| PA66-GF50 | High Glass Fiber Wear-resistant | About 60% weight reduction, self-lubricating, low cost | Lower rigidity than steel, lower maximum temperature tolerance |
| POM lead screw | Polyoxymethylene | Good self-lubrication, stable dimensions, inexpensive | Low strength, not resistant to high temperatures |
The three reconciliations do not have 'which one is better,' only 'which item's account is tighter.'
For the PA66-GF50 line, weight reduction is its biggest selling point. According to public information, this type of solution can reduce about 60% of the weight compared to metal—if a collaborative robot has several lead screws, the total weight reduction is quite substantial. The trade-off is that its rigidity is only a fraction of steel, and its temperature resistance is also lower.
Carbon fiber in that field is stiffer and lighter, but it conducts electricity and is expensive, so insulation and isolation need to be considered near electrical components; its anisotropy is also more pronounced, so warping needs to be calculated in advance.
POM has good self-lubrication and dimensional stability, but it can't withstand high thrust, and it is directly out under high-temperature conditions.
In short: choose plastic for lead screw material if you're after 'lightweight and self-lubricating,' not 'stronger than steel.' Strength comes as a bonus from the fibers; precision is what you need to ensure separately.
4. Selection Criteria Table (Acceptance Page for Plastic Rollers)
Turn the above constraints into verifiable indicators. The thresholds in the table are directional suggestions, not acceptance criteria—the actual values must be determined by the specific project, specific working conditions, and actual measurements.
| Indicator | Directional threshold | Verification Method / Standard | Common Failures | Common solution | Corresponding auxiliary agent system |
|---|
| Lead Error (Thermal Condition) | Within a 300 mm stroke ≤0.5 μm range | Laser Interferometer Measured (Thermal State) | Position drifting, large hysteresis | Low expansion substrate Temperature control | Intrinsic material properties determine it, not relying on additives |
| Coefficient of friction (grease lubrication) | 0.15 up and down | ASTM D1894 | Temperature rise, torque loss | Solid lubrication system | Lubricant (internal and external lubrication balance) |
| Millions of revolutions of wear | <0.01 mm per million rotations magnitude | Test Bench Weighing Method | The gap is getting larger and it doesn't move accurately. | Wear-resistant filler Densification | Lubricant Wear-resistant filler |
| Long-term thermal-oxygen retention rate | After 80℃ × 1000h ≥75% | ISO 527 | Pale and brittle | Stabilization system | Antioxidant (hindered phenol, phosphite) |
| Bending modulus | Reference 8–10 GPa (GF50) | ISO 178 | Deformation under load, lead variation | High glass fiber reinforced | Coupling agent (interface) |
| lipophilicity | No abnormalities in size or appearance after resin impregnation | Vendor lipid soaking | Precipitation, stickiness | Confirm the lipid system in advance | The migration of additives needs to be assessed |
How to use this table: Don’t score row by row; first look at the first and second rows. If these two rows don’t pass, there’s no need to discuss the others—the failure of the lead screw is sequential, and if the lead isn’t maintained, the wear data loses its meaning.
A reminder: For the item 'lead error' in the table, many projects do not have an existing national standard to follow. When there is no standard, include the verification plan in the technical agreement, rather than omitting this item.
5. Failure is not 'worn out': Four real root causes
Failure 1: The pitch increases in the first two months, then stabilizes.
The root cause is usually not wear, but moisture absorption. When the parts are installed in their factory state (dry or partially conditioned), they continue to absorb moisture during operation until they reach equilibrium, causing the dimensions to shift in one direction. After about two months, once moisture absorption nears equilibrium, the changes stop. Delivering parts in a conditioned state and re-testing is much more effective than replacing materials.
Failure 2: The surface becomes locally whitish, followed by powdering.
The root cause is thermal oxygen aging, often localized—partial assembly misload causing prolonged high temperatures in certain teeth. At this point, switching to a higher antioxidant level is useful, but the root cause lies in assembly coaxiality, not in the material.
Failure three: Wears down quickly, but the part itself is not damaged.
Check two things: first, the surface roughness and hardness of the mating parts (steel threaded rods); second, whether the grease is compatible. For a plastic-steel friction pair, wear usually occurs on the plastic side, with the cause on the steel side.
Failure 4: The same batch of items has inconsistent yellowing depth.
This is not 'unstable material.' It's more likely that the antioxidant is unevenly dispersed—it wasn't mixed well during the mixing stage. Seeing this phenomenon, first check the mixing process and masterbatching; don't rush to change the material.
Here is something that needs to be said directly: When troubleshooting plastic lead screw failures, first suspect the condition and process, and only finally suspect the material. This is the opposite of typical structural components—because the precision scale is so small, any fluctuation in condition gets amplified into 'the material is no good'.
6. These few things must be settled before going online
Drying. Nylon must be baked. If the moisture content exceeds the limit, it will hydrolyze and degrade during melting, causing the strength at the root of the threads to drop directly. The drying window should be determined based on the actual measured moisture content, the recommended values for the grade are only a starting point—workshop humidity, packaging dampness, and the addition of recycled material can all reintroduce moisture.
Thread shrinkage compensation. Threads are not circular, and shrinkage varies in different areas. Differences in the orientation of fiberglass parts will amplify this issue. Thread compensation in molds must be done for each part and cannot be based on the general shrinkage rate in the material manual.
Orientation and gate. Glass fiber parts are anisotropic, with different modulus and shrinkage in the flow direction and the perpendicular direction. The screw rod is a rotating part, and the gate location directly determines roundness and thread consistency.
Verification order. It is recommended to arrange it like this:
1. Size and roundness (measured after humidity adjustment, only recorded during the dry state process)
2. Lead error (measure on the actual threaded rod, without using substitutes)
3. Lipid Compatibility (Size and Appearance Re-measured After Soaking)
4. Test rig (run for wear, remeasure lead midway)
5. Environmental stacking (temperature cycling, humidity cycling, finally the complete machine)
The order cannot be changed. If the previous item fails, we move on; the data measured later has no explanatory significance.
Proofing Record: A customer reported a 'screw accuracy of 0.5 μm', so we prepared samples accordingly. But when we looked at the working conditions, we realized—what they reported was the lead at room temperature, without accounting for the thermal expansion caused by the cavity heating up once the motor runs. For the same 300 mm stroke, a 30℃ temperature rise can eat up most of the accuracy margin. Later, we included this issue in the proofing confirmation form: first, have the customer clarify the 'temperature range', then set the accuracy level.
7. Boundaries: When plastic screws should not be used
This section might be more valuable than the previous six sections.
In the following four situations, it is not recommended to pursue the route of plastic lead screws:
First, the long-term operating temperature exceeds 110℃. There is insufficient publicly available data to support the long-term performance of the PA66 system in this range. This cannot be solved by changing the formulation, and switching systems is also difficult — low water absorption and high-temperature resistance are inherently contradictory within the nylon family.
Secondly, it requires the lead accuracy to be consistently better than ±0.5 μm/300 mm and high thrust. The modulus and thermal expansion of plastic determine that it is not suitable as an ultra-precision main transmission component. This is a boundary at the level of material physics.
Third, the verification resources for the entire machine are insufficient to support long-cycle bench testing. Screw verification cannot be completed with a single sample test; it requires running to the scale of millions of cycles, with multiple re-tests of the lead during the process. Without this verification budget, do not start this project.
Fourth, the quantity is too small to justify the cost of making a thin mold and validation. This part requires a dedicated mold, thread compensation, and a long cycle of validation. If the annual usage is only a few hundred pieces, it is not financially feasible.
Writing these four points at the beginning is not to discourage you, but to save time. I have seen too many projects go smoothly during the sample phase, only to get stuck at the mass validation stage, and in the end the entire plan is rolled back—the cost of rolling back is much higher than not doing it from the start.
Material Change Risk List (from metal to PA66-GF50, things that need to be changed)
| link; segment; part | What needs to be moved? | Points that are easy to overlook |
|---|
| Mold | Thread shrinkage compensation is done per piece and cannot use a general shrinkage rate. | Directional shrinkage differences caused by glass fiber orientation |
| Dry | Set the window based on the actual measured moisture content, not by copying the recommended value. | Recycled materials mixed with the water content brought in |
| Material Temperature / Mold Temperature | Joint adjustment according to thread fill and roundness requirements | Only give according to the recommended value by grade, without looking at the pieces |
| Pressure Holding / Demolding | Rotating parts are prone to deformation, and the pressure-holding curve and demolding method need to be redefined. | Follow the tooling approach of the original metal parts |
| Humidity control | Forced humidity adjustment Weight-based determination Re-measure dimensions | Based on the average wall thickness to estimate the time, the thick-walled areas are not fully soaked. |
| Color difference | The GF50 pieces themselves are dark in color and have batch differences | The color difference standards for exterior parts should be relaxed in advance or set separately. |
| Verification order | Size → Lead → Lipid Compatibility → Test Bench → Environmental Superposition | If the previous item fails, just move on. |
Sample Printing and Mold Testing Scheduling
| Round | Computer-based content | What is checked each round? | sample retention |
|---|
| First round | Screw trial small sample, check filling for short shot | Whether the threads are fully engaged and surface fiber fuzz | Keep 3 items for 3 months |
| Second round | Official mold trial, adjust mold temperature and pressure | Roundness, Lead (Dry State) | Keep 5 items for 6 months |
| Round Three | Retest after humidity adjustment Initial test on the test bench | Lead (warm state), initial wear value | Keep 8 items, 12 months |
One-page report form (for people who need to report upwards)
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Project: Planetary Roller Screw · Material Route Evaluation
Conclusion direction: PA66-GF50 can be considered as a candidate route, and whether it can be implemented depends on four prerequisite conditions.
1. Three Rules That Must Be Followed
1. Delivered in a humidified state, dry data is not reported
2. The threads are compensated for shrinkage individually, not using a common value.
3. Full-process data without grease compatibility will not enter the test stand
2. Precondition (It is recommended to postpone if any are not met)
· Long-term operating temperature ≤ 110℃ range
· Budget and schedule for test bench verification at the scale of millions of cycles
· Thrust in the range supported by the plastic modulus
· Assembly coaxiality is controllable (eccentric loading can amplify thermal-oxidative aging)
3. Next Steps
1. Take the actual threaded rod and measure the actual lead under thermal drift.
2. Dimensional differences before and after moisture conditioning, assess the sensitivity of the part to the condition
3. Lipid compatibility soaking test (starting from two weeks)
Risk reminder: The main uncertainty of this route lies in maintaining lead accuracy, not in the initial intensity.
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Two questions readers often ask
Question: Since PA66 has a heat resistance of only 260°C melting point, does that mean the screw near the motor is out of the question?
You should look at the actual temperature, not the motor specifications. The module's heat dissipation path determines the actual temperature of the lead screw, which is often lower than expected. The approach is to measure it directly—attach thermocouples to the prototype, run typical operating conditions, and take the long-term steady-state values. Using peak temperature to make judgments may unnecessarily discard solutions, and using the rated temperature from the datasheet may lead to incorrect acceptance.
Question: Can this part be replaced with fiberglass or carbon fiber?
The directions are different. Glass fiber provides cost-efficiency and toughness, while carbon fiber provides modulus and dimensional stability. For rotating components like lead screws, which are sensitive to modulus and warping, carbon fiber is more justified; however, its conductivity and cost must also be taken into account. Additionally, changing the fiber system is equivalent to changing a whole set of interface solutions, so verification must be redone, and you cannot just compare spline data.
Conclusion
The plasticization of planetary roller screws, after all, is a question of maintaining precision, not strength.
There are only three judgment chains:
Temperature determines the system → Water absorption determines the grade → Verification sequence determines success or failure.
Once all three are set, the question of 'whether you can use plastic' naturally has an answer.
If you have a lead screw or linear module on hand that you need to specify materials for, just send over three things and we can give guidance: long-term operating temperature, actual pushing force magnitude, and annual usage quantity.
There are many people making plastics here. In the modified nylon circle, those who make precision parts like screws are even more meticulous about selecting materials than selecting equipment.
What we do is very specific: we transform resins like PA6, PA66, PA46, PA11, PA12, PA6T, PA9T, and nylon alloys into forms that can actually be used in certain parts; we also modify PPO, PPS, and thermoplastic elastomers; in addition, we deal in nylon resins, secondary materials, and bulk materials from major chemical companies, and we have long-term operations collecting nylon raw materials, sprues, and various nylon waste, with proper disposal channels.
The auxiliary system in the formula is matched according to the working conditions per item — conventional auxiliaries are kept in stock, and special models are matched as needed; you report the working conditions and grade, and the material and auxiliaries are prepared together at once.
