去年冬天，一家做电助力车变速导轮的客户寄来一小袋件，说这批是换料以后打的。
袋子是装链条油的那种自封袋，袋口还沾着油。
里面是六只导轮，外圈齿面磨出了一道台阶，指甲划过去能挂住。
电话里他问得很直接：「换完料以后齿形还是按原图开的，怎么骑了三个月就磨圆了？」
这就是自行车尼龙件换料最常见的开场：外观对得上、尺寸也过检，账却记在别处。
我先问了他三句话。
换的是基材，还是基材连同润滑体系一起换的？
冲击验收做的时候，件是干态的，还是调湿以后的？
低温那一段，验的是零下二十度，还是车间常温？
他停了一下，说头一句答不上来，后两句车间没做过。
这三句问话，第九节会回收。
把这件事拉成时间线，账就清楚了。
起点：新料打出来的导轮外观合格，齿厚和孔径都在公差里，材料单价还比原来低了一截。
潜伏：头两个月没有投诉，骑手只觉得变速手感比原来黏一点，链条油里多了一点细屑。
爆发：第三个月，一批导轮在低温段出现齿顶崩缺和跳档，售后按整车批次退回来。
结算：拆件复测，配方几乎没变；变的是干态低温冲击、调湿后的齿厚，还有润滑体系往表面迁移的速度。
补一处换算：导轮外径只有二十几毫米，齿顶那圈受力更集中，磨掉零点一毫米，啮合侧隙就够让骑手感到跳档。
自行车上的塑料件都不大，但每一件都在户外、在低温里、在几十万次的循环里。
一、换料前，六维工况里至少四样要落成数字
温度这一条要分成三段问，只给一个数是问不准的。
环境温度：长江流域是零下五度到四十度，北方越冬到零下二十五度，出口北欧还要再往下压十度。
日晒温度：深色件夏天正午晒着，表面能到七十度以上，比气温高出一大截。
件自己发的热：链条摩擦位和刹车周边，短时能摸到八十度量级。
低温那一段的分量比高温更重——尼龙最脆的两个条件，一个是干态，一个是低温，两个叠在一起才出事。
载荷这一条要按循环算，不按静态算。
踩踏按八十转每分钟，骑一小时就是四千八百圈；一年按三百小时，是一百四十多万圈。
变速导轮的受载次数比曲柄还高，链条每一节滚过去都要啮合一次。
介质这一条并不只有雨水：还有泥水、链条油、洗车水和汗液，海边骑行还要算盐雾。
泥水最容易被低估——泥浆干在配合面上之后有研磨作用，磨损速率会往上翻。
寿命按整车年限倒推：通勤车按五年，运动车按三年，共享和租赁车按两年算。
里程按每年两千到五千公里计，导轮这类易损件的更换周期，行业里常见口径是三千到五千公里。
外观这一条在彩色件上是硬指标：色牢度、色差、深色件的浮纤，都要在户外跑过再看。
合规这一条要提前分位置：儿童车核边缘锐利度、小零件拉脱力和限用物质，出口件看目的地法规。
这六维里，温度、载荷、介质、寿命四样先问出数字，再谈换哪条料。
连原件的使用温度区间都说不清的，这次换料就是拿一批货去赌。
二、三条路线摆开，不做谁更好的判断
换料不是挑最强的那一个，是把几条路线的代价摊在桌上。
| 路线 | 低温韧性 | 耐候与外观 | 吸水与尺寸 | 常从哪条换过来 |
|---|
| PA66-GF30 + 增韧 + 耐候体系 | 中上 | 深色件好做，浅色件要挑体系 | 吸水中等，尺寸按湿态核 | 通用 PA66-GF30、回料掺混件 |
| PA6-GF30 加矿物混填（成本档） | 中 | 一般，外观件要挑 | 吸水更高，长条件易翘 | 高玻纤 PA66 |
| 自润滑 PA66（导轮、线管用） | 中上 | 看体系，配炭黑更稳 | 中等，齿厚要按湿态核 | 通用 PA66、POM |
| PA11 / PA12 与 POM（不吸水档） | 好 | 好 | 吸水很低，尺寸稳 | 通用 PA66、金属小件 |
四条里没有高下，只有匹配。
玻纤加增韧那条给的是低温韧性，代价是刚性让出去一截。
矿物混填那条把各向异性压下来，长条件不容易翘，代价是抗磨和外观都平平。
PA6 体系在成本上更好看，但吸水率高，尺寸账要按湿态重算一遍。
长碳链和不吸水的那条把尺寸稳住，代价是单价和加工窗口。
为什么低温这一栏要单独列？因为普通弹性体增韧在低温会自己先脆。
它的玻璃化转变温度就压在零下二三十度附近；件一到那个温度，增韧相从软变硬，等于白加。
要在这个温度里干活，得用核壳结构的增韧剂：壳层把应力传开，核层在低温下还留着形变能力。
这不是配方的秘密，是分子结构上的差别。
再补一句：耐候好不好，跟玻纤含量基本无关，跟稳定化体系有关。
所以路线表里"耐候与外观"那一栏，问的不是基材，是这套体系配没配到位。
三、换料以后要重验的那张表
表里的门限只给方向，验收值要由你的件、你的气候区和实测数据来定。
| 指标 | 方向性门限 | 验证方法 / 标准 | 换料后常见失效 | 通行解法 | 对应助剂体系 |
|---|
| 紫外老化保留率 | 氙灯 1000 h 后拉伸保持七成以上 | 氙灯老化 + ISO 4892-2 / ISO 527 | 表面粉化、浅色件褪色 | 稳定化体系按户外档配 | 光稳定剂（受阻胺 + 紫外吸收剂） |
| 低温冲击 | 按冬季装机最低温度定门限 | 低温箱 + ISO 179 | 齿顶崩缺、卡扣开裂 | 核壳增韧体系 + 提高模温 | 增韧剂（核壳结构） |
| 干态冲击 | 干态与调湿态分别留数 | 干态试样 + ISO 179 | 出厂件比用过半年的件脆 | 按干态放行、按湿态复核 | — |
| 调湿后尺寸 | 齿厚、孔径仍在公差窗口内 | ISO 1110 调湿 + 三坐标 | 啮合侧隙变小、异响 | 按湿态尺寸校核模具 | — |
| 疲劳（啮合与踩踏） | 循环次数按里程折算 | 循环加载 + 缺口试样 | 齿面剥落、根部裂纹 | 降应力集中 + 增韧 | — |
| 耐磨与自润滑 | 五千公里量级的磨损可控 | 台架磨损对比 + 称重 | 齿形磨圆、掉屑 | 表面致密 + 降摩擦 | — |
| 色牢度与色差 | 灰卡等级按外观件要求 | 氙灯后色差 + 灰卡评定 | 彩色件先褪色 | 色粉耐候档前置确认 | — |
| 稳定化余量 | 长期热氧后不发黄、不析出 | 热老化箱 + 外观评定 | 同一批件黄得有深有浅 | 查混料与母粒化 | 抗氧剂（受阻酚 + 亚磷酸酯） |
这张表怎么读：先看头两行。
紫外和低温是自行车件的主线，也是换料后掉得靠前的两项。
第三行不起眼，但冬季的脆断投诉大多出在这里，而它在常温检测里查不出来。
第四行是精密件的老问题：吸湿后的尺寸漂移，往往是因为量测条件没跟材料一起定。
中间三行决定件能用多久，也决定骑手会不会听到异响。
引用标准时把版本年份一并写进规格书，量测方法不一致，两家的数据就没法放在一起比。
四、换料以后最常见的五种失效
失效一：齿顶在低温段崩缺。
多数人先想到"脆就加增韧"，但要看两件事：件是干态还是调湿态，断的时候是常温还是零下。
这一条常从助剂侧归因：增韧体系若用了普通弹性体，它在零下二十度附近自己先进玻璃态，件反而更脆。
等于花了钱，买了个反向效果。
失效二：表面粉化、浅色件褪色。
这不是"料不稳定"，多数是稳定化体系的档位没跟户外走。
紫外线的破坏是两步：紫外先打断分子链，氧再接着进攻。
所以光稳定剂和抗氧剂是配套的两件事，只加一件，另一件的余量就先被耗尽。
失效三：同一批件黄得有深有浅。
根因常见是抗氧剂分散不均，或者挤出造粒那段温度给高了。
方向指向混料与母粒化，不指向基材。
失效四：导轮齿形磨圆、链条里出现细屑。
根因常常不是材料软，是润滑体系往表面走了，表面反而变干。
再加上调湿没做，齿厚按干态放行，装车吸完湿就顶死，侧隙变小，异响和磨耗一起上来。
失效五：彩色踏板用一年就发灰，色号对不上。
根因在色粉的耐候档，不在基材；只对物性表、不对色粉清单，这一栏必掉。
有一句我想单独说。
自行车件出了事，多数人先问"是不是这个料不行"。
但我在现场看到的一半以上，是干燥、调湿和模温三件事没跟着料一起换。
料是顺着工艺走的，工艺没改，换什么料都一样。
五、加工与验证，顺序不能换
自行车件的验证次序，建议按"件在车上怎么坏"倒推着排。
先讲干燥。吸水料含水超标，进料筒就被剪链，件发脆、表面出银纹，而且显形很晚。
我们经手过一类很典型的投诉：同一袋料、同一副模具，这一模好、下一模就脆。
查到最后，配方一个字没动，问题在干燥。
含水率在南方梅雨季最难守，拆包后在车间放几个小时，水分就能回升一截。
我们的做法是上机前用仪器或露点数据确认，不凭手感。
再讲模温。玻纤料最怕模温开低：纤头被冻在件表面，就成了浮纤。
深色件的浮纤是一片一片的发白；紫外再一照，起皮就从纤头那里开始。
模温这一栏，撑的是结晶度和表面状态，这一条在自行车外观件上比在结构件上更要紧。
浮纤常常不是"玻纤加多了"。把模温从八十度提到一百一十五度，同一批料、同一副模具，表面对比件立刻分开。
然后才是调湿。导轮、卡扣这类配合件，必须按调湿态复测和验收。
一件二十几克的导轮，吸到平衡能吸进半克上下的水。
这个量换到一个五十毫米量级的配合面上，尺寸变化是零点一毫米的量级。
在啮合侧隙上，这就是从"刚好"走到"顶死"。
验证次序这样排：
1. 材料级：紫外老化保留率、干态与调湿态冲击
2. 工艺窗口：不同模温与保压下打对比件，看浮纤与关键尺寸
3. 件级：调湿后的齿厚与孔径、疲劳与磨损
4. 台架：低温、常温、盐雾与泥水四组工况
5. 整车：装车跑一个季节，中途复测异响与手感
前一项没过就往下走，后面的数据就没有解释意义。
为什么次序不能换？因为冲击和尺寸都受含水率影响。
状态没锁住就去跑台架，跑出来的寿命只对那一批有效，放量又会漂。
六、边界：这几种位置，自行车件换料先收手
这一段帮你在开工之前止损。
其一，车架、前叉、座管这类主承力结构。
它们要的是刚性和疲劳的综合账，碳纤或铝合金更合适。
其二，花鼓轴心、快拆杆、曲柄、链条这一类。
受的是金属级的应力与冲击，塑料件在这个位置上没有余量。
其三，刹车夹器本体和碟片。涉及制动安全，材料要跟着认证走，改性尼龙不接。
其四，长期泡水、埋在水线下的轴承位。磨损和尺寸两笔账都不划算，该用不锈钢或含油轴承。
其五，零下三十度以下长期骑行的承力件。这个区间要看低温专用体系或长碳链路线，普通玻纤增强体系的数据支撑不足。
其六，失效点还没定位的件。是尺寸问题还是材料问题，解法完全不同，先定位再动料。
把这六条写在前面不是劝退，是省时间。
打样顺、批量卡、整案回退，这笔学费比一开始不换高得多。
七、换料风险清单（从原路线换到这边，要动的东西）
| 环节 | 要动什么 | 容易漏的点 |
|---|
| 模具 | 基材与填充体系变，收缩率跟着变，齿厚与孔距要复算 | 只换料不核收缩，啮合侧隙被吃掉 |
| 干燥 | 按实测含水率定窗口，除湿干燥机是前提 | 热风干燥对吸水料基本无效 |
| 调湿 | 配合件按调湿态复测与验收 | 按干态尺寸放行 |
| 料温与模温 | 玻纤体系与增韧体系要更高的模温 | 照抄原来那支料的档位 |
| 保压与脱模 | 齿根与卡扣要重定保压，脱模斜度复核 | 齿根内应力集中，脱模拉白 |
| 色差 | 免喷涂件与彩色件的色板提前确认 | 不同批次基材底色有差 |
| 紫外与色牢度 | 彩色件按目的地气候补验证 | 只测常温物性，不测氙灯后的色差 |
| 验证顺序 | 材料 → 工艺 → 件级 → 台架 → 整车 | 前一项未过就往下走 |
八、打样与试模排程（几轮上机、每轮验什么、留样多久）
给自行车件换料排试模，通常分三轮，轮次之间不跳步。
头一轮·小样比对：用你的原模具打三到五模，只验含水率、外观、短射时的熔接线位置和关键尺寸。
这一轮先确认"料能不能把齿形填满"，留样两件，标注批号与干燥参数，至少留到第二轮结束。
第二轮·工艺窗口与件级：固定料，变模温与保压，打两组对比件。
验调湿后的齿厚与孔径、低温冲击、疲劳与磨损；紫外老化同步送检。
这一轮基本定下量产参数。留样按批次封存，封存期至少到量产稳定后三个月。
第三轮·台架与整车：低温、常温、盐雾与泥水四组工况跑台架，然后装车跑一个季节。
这一轮过了，才建议放量。
三轮为什么不能跳？因为每一轮的结论都是下一轮的前提。
自产这边的配合落在三件事上：配方可以按你的气候区和骑行工况调，打样可以陪着一起摸窗口，小批量多牌号可以并行试。
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。
给采购和技术员用的一页纸
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 踏板本体 | 玻纤增强 + 核壳增韧 | 低温冲击、疲劳 | ISO 179 + 循环加载 | 冬季最低装机温度 |
| 变速导轮 | 自润滑 PA66 | 磨损量、齿厚 | 台架磨损对比 | 里程与链条油种类 |
| 线管与护套 | 低吸水尼龙 | 吸水后尺寸、弯曲疲劳 | 调湿后三坐标 | 走线空间与最小弯曲半径 |
| 水壶架、码表架 | 玻纤增强 + 耐候体系 | 紫外保留率、色牢度 | ISO 4892-2 老化 | 是否外观件与配色 |
| 车筐连接座 | 高韧体系 | 冲击、蠕变 | ISO 179 + 长期载荷 | 最大超载与路况 |
九、几个被反复问到的问题
问：换料以后常温物性对得上，就能放行吗？
答：不够。自行车件的主线是紫外、低温和疲劳，常温那一栏过关，只说明料能打出来。
问：原来的料停产了，配方能照抄吗？
答：能照抄物性，不能照抄工艺。干燥、模温、保压这三样跟着设备和车间走。
问：彩色件一定要加炭黑吗？
答：炭黑是吸收紫外、顺带把颜色做深的一档，浅色件用不了。
浅色件的路子是把光稳定剂的档位配足，再按色粉的耐候档逐支筛选。
问：导轮掺一点回料，能省出来吗？
答：省出来的钱通常会从磨损和跳档上还回去。
回料的分子链断过一截，黏数下降，耐磨和疲劳先掉，批次之间还会不一样。
问：干态和调湿态，到底按哪个放行？
答：装配公差按调湿态算，出厂检测按干态做，两份数都要留。
只留一份，就等于把风险推到装车以后。
问：开头那三句话为什么能定方向？
答：头一句分清了换的是基材还是整套体系，第二句把验收状态问出来，第三句确认低温到底验没验过。
三句答得齐，问题通常已经缩到一两项上。
回到开篇那三句问话。
问基材路线、问验收状态、问低温工况。
这三样答全了，变速导轮这类自行车尼龙件换料往哪走，基本就定了。
自行车上的塑料件都小，账却都不小。
真正贵的从来不是那一袋料的差价，是整车退回来那一批的售后。
最麻烦的询盘是这一句——「换完料以后齿还是那个齿，怎么三个月就磨圆了」。
因为这一句背后，往往同时压着紫外、低温和疲劳三条线，而三条线的验证次序不能换。
我们做改性尼龙造粒，料和助剂一起配；这类件的换料与试模，可以一起聊。
Last winter, a customer who makes electric-assist bike gear guide wheels sent a small bag of parts, saying that this batch was produced after changing the materials.
The bag is a resealable bag used for holding chain oil, and the opening of the bag is still coated with oil.
Inside, there are six guide wheels, and the outer ring's tooth surface has worn into a step, which can catch your nail when you scrape it.
On the phone, he asked very directly: 'After replacing the material, the teeth were still cut according to the original drawing, so how come they rounded off after just three months of riding?'
This is the most common opening scenario for changing materials of bicycle nylon parts: the appearance matches, the size also passes inspection, but the account is recorded elsewhere.
I first asked him three questions.
Are you replacing just the substrate, or the substrate along with the lubrication system?
When performing the impact acceptance test, is the item in a dry state or after humidity adjustment?
For the low temperature part, is it tested at minus twenty degrees, or at normal workshop temperature?
He paused and said he couldn't answer the first question, and the workshop hadn't done the last two questions.
These three questions will be addressed in verse nine.
If you lay this matter out as a timeline, the accounts will be clear.
Starting point: The guide wheel made from new material has a qualified appearance, and both the tooth thickness and hole diameter are within tolerance. The material unit price is even lower than before.
Lurking: In the first two months there were no complaints, the rider only felt that the shifting was slightly stickier than before, and there were a few fine particles in the chain oil.
Outbreak: In the third month, a batch of guide wheels showed tooth top breakage and skipping in the low-temperature section, and the after-sales department returned them according to the vehicle batch.
Settlement: Re-testing after disassembly, the formula has hardly changed; what has changed are the dry-state low-temperature impact, the tooth thickness after humidity adjustment, and the rate at which the lubrication system migrates to the surface.
A calculation correction: the outer diameter of the guide wheel is only a little over twenty millimeters, and the ring at the tooth top bears more concentrated force. Grinding off 0.1 millimeters is enough to create engagement side play that the rider can feel as shifting jumps.
The plastic parts on the bicycle are all small, but each one is exposed outdoors, in low temperatures, through hundreds of thousands of cycles.
1. Before changing materials, at least four items in the six-dimensional working conditions must have completed numbers.
The temperature question needs to be divided into three parts; giving only one number is not enough to ask accurately.
Ambient temperature: In the Yangtze River Basin, it ranges from minus 5 degrees to 40 degrees. In northern regions, it can drop to minus 25 degrees during winter, and for exports to Northern Europe, it can be ten degrees lower.
Sun-exposed temperature: Dark-colored items exposed to the sun at noon in summer can reach over seventy degrees on the surface, much higher than the air temperature.
The heat generated by the part itself: the chain friction area and around the brakes, for a short time can reach around eighty degrees.
The portion at low temperature is heavier than at high temperature—nylon is most brittle under two conditions: one is in a dry state, and the other is at low temperature. Problems only occur when the two conditions come together.
This load should be calculated according to cycles, not statically.
Pedaling at eighty revolutions per minute, riding for an hour amounts to 4,800 revolutions; if riding three hundred hours a year, that's over 1.4 million revolutions.
The load frequency of the variable-speed guide wheel is even higher than that of the crank, as each link of the chain must engage once as it rolls by.
This medium doesn’t only include rainwater: there is also muddy water, chain oil, car wash water, and sweat. When cycling by the sea, salt spray also counts.
Mud and water are the easiest to underestimate—after the slurry dries on the surface, it has an abrasive effect, and the wear rate will increase.
Lifespan is calculated backwards based on the total vehicle years: commuter cars are considered five years, sports cars three years, and shared and rental cars two years.
Mileage is calculated at 2,000 to 5,000 kilometers per year. For easily worn parts like guide wheels, the common replacement cycle in the industry is 3,000 to 5,000 kilometers.
Appearance is a strict criterion for colored parts: colorfastness, color difference, and floating fibers on dark-colored parts all need to be checked after being exposed outdoors.
Compliance should be addressed in advance in separate sections: the sharpness of the edges of children's strollers, the pull strength of small parts, and restricted substances. For export items, refer to the regulations of the destination.
Among these six dimensions, ask for the numbers for temperature, load, medium, and lifespan first, then discuss which material to change.
They can't even specify the operating temperature range of the original parts, so this time changing the material is just taking a batch of goods to gamble with.
2. Lay out three routes without making a judgment about which is better
Changing materials is not about choosing the strongest one, but about spreading the costs of several routes on the table.
| Route | Low-temperature toughness | Weather resistance and appearance | Water Absorption and Size | Which one do you usually switch from? |
|---|
| PA66-GF30 Toughened Weather-resistant system | Upper-middle | Dark-colored pieces are easy to make, while light-colored pieces require selecting the system. | Medium water absorption, dimensions based on wet state core | General-purpose PA66-GF30, recycled material blend parts |
| PA6-GF30 with mineral filler (cost range) | middle | Generally, exterior parts need to be selected | Higher water absorption, prone to warping under prolonged conditions | High glass fiber PA66 |
| Self-lubricating PA66 (for guide wheels and wire tubes) | Upper-middle | Look at the system, adding carbon black is more stable | Medium, the thickness of the teeth should be based on the wet state core | General-purpose PA66, POM |
| PA11 / PA12 and POM (non-water-absorbing grade) | Good | Good | Very low water absorption, dimensionally stable | General PA66, small metal parts |
There is no hierarchy in the four lines, only matching.
The fiberglass with added toughening provides low-temperature toughness, but the cost is a reduction in rigidity.
The mineral mixed filler suppresses anisotropy, making it less likely to warp over long conditions, but the trade-off is that both wear resistance and appearance are mediocre.
The PA6 system looks better in terms of cost, but it has a high water absorption rate, so the dimensions need to be recalculated based on the wet state.
The long carbon chain and the one that does not absorb water stabilize the size, at the cost of unit price and processing window.
Why is the low-temperature column listed separately? Because ordinary elastomer toughening will become brittle on its own at low temperatures.
Its glass transition temperature is around minus twenty or thirty degrees; once it reaches that temperature, the toughening phase changes from soft to hard, which is equivalent to adding whiteness.
To work in this temperature, you need a core-shell structured toughening agent: the shell layer spreads the stress, while the core layer still retains deformation ability at low temperatures.
This is not a secret of the recipe, but a difference in molecular structure.
One more thing: whether it is weather-resistant or not basically has nothing to do with the glass fiber content, but is related to the stabilization system.
So in the schedule, the column 'Weather Resistance and Appearance' is not asking about the substrate, but whether this whole system has been properly applied.
3. The form that needs to be re-verified after changing materials
The thresholds in the table only provide a direction; the acceptance values need to be determined based on your components, your climate zone, and actual measured data.
| Indicator | Directional Threshold | Verification Method / Standard | Common failures after material change | Common solution | Corresponding auxiliary agent system |
|---|
| UV aging retention rate | After 1000 hours of xenon lamp exposure, tensile strength retains more than 70% | Xenon lamp aging ISO 4892-2 / ISO 527 | Surface chalking, fading of light-colored parts | Stabilization system matched according to outdoor grade | Light stabilizers (hindered amine, UV absorbers) |
| Low temperature shock | Set the threshold according to the minimum installation temperature in winter | Low Temperature Box ISO 179 | Tooth top chipping, buckle cracking | Core-shell toughening system Increase mold temperature | Toughening agent (core-shell structure) |
| Dry impact | Residue in dry state and in conditioned state | Dry specimen ISO 179 | Factory-new parts are more brittle than parts that have been used for half a year. | Release according to dry state, recheck according to wet state | — |
| Dimensions after moisture conditioning | Tooth thickness and hole diameter are still within the tolerance window | ISO 1110 Humidity Control Coordinate Measuring Machine | Reduced backlash and abnormal noise | Check the mold according to the wet dimensions | — |
| Fatigue (Meshing and Trampling) | Number of cycles converted based on mileage | Cyclic loading notch specimen | Tooth surface spalling, root cracks | Reduce stress concentration Increase toughness | — |
| Wear-resistant and self-lubricating | Wear controllable at the 5,000-kilometer level | Test Bench Wear Comparison Weighing | Tooth rounding and chipping | Dense surface Reduces friction | — |
| Color Fastness and Color Difference | Gray card level according to appearance part requirements | Chromatic aberration after xenon lamp Gray card evaluation | Colored parts fade first | Pre-confirmation of weather-resistant pigment file | — |
| Stabilization margin | Does not yellow or precipitate after long-term thermal oxidation | Heat Aging Chamber Appearance Evaluation | The same batch of pieces varies in yellow, some deeper and some lighter. | Checking Mixed Material and Pelletizing | Antioxidant (hindered phenol, phosphite) |
How to read this table: first look at the first two rows.
Ultraviolet and low temperature are the main concerns for bicycle parts, and they are also the first two items to deteriorate after material changes.
The third row is inconspicuous, but most complaints about brittle fractures in winter occur here, and it cannot be detected in tests at normal temperature.
The fourth line is an old problem with precision parts: dimensional drift after moisture absorption is often due to the measurement conditions not being set together with the material.
The middle three rows determine how long the component can be used and also determine whether the rider will hear abnormal noises.
When quoting standards, include the version year in the specification. If measurement methods are inconsistent, the data from the two companies cannot be compared together.
4. The Five Most Common Failures After Material Change
Failure 1: The tooth tip breaks off in the low-temperature range.
Most people first think of 'adding toughness when it's brittle,' but you need to consider two things: one is whether it is in a dry state or a conditioned state, and whether it is broken at room temperature or below zero.
This is often attributed to the additives side: if an ordinary elastomer is used in the toughening system, it itself enters the glassy state around minus twenty degrees, making the part even more brittle.
It's like spending money and getting the opposite effect.
Failure 2: Surface chalking, fading of light-colored parts.
This is not 'material instability'; for the most part, it's that the settings of the stabilization system haven't been adjusted for outdoor conditions.
The damage from ultraviolet light occurs in two steps: ultraviolet first breaks the molecular chains, and oxygen then follows to attack.
So light stabilizers and antioxidants are two complementary things; if you only add one, the remaining amount of the other will be exhausted first.
Failure three: Within the same batch of parts, the yellowing varies from deep to light.
The common root cause is uneven dispersion of the antioxidant, or the temperature during extrusion and pelletizing was too high.
The direction points to mixing and masterbatching, not to the substrate.
Failure 4: The sprocket teeth are worn round, and fine debris appears inside the chain.
The root cause is often not that the material is soft, but that the lubrication system moves to the surface, making the surface dry instead.
On top of that, the humidity adjustment wasn't done, the tooth thickness was approved in the dry state, and after loading and absorbing moisture, it jammed, the side clearance decreased, and both abnormal noise and wear occurred.
Failure Five: The colored pedals turn gray after a year, and the color does not match.
The root cause lies in the weather resistance of the pigment, not the substrate; it only affects the physical property surface, not the pigment list, so this column will inevitably be dropped.
There is a sentence I want to say separately.
When something goes wrong with bicycle parts, most people first ask, 'Is it this material's fault?'
But more than half of what I saw on site was that drying, humidity control, and mold temperature were not changed along with the material.
The material follows the process. If the process hasn't changed, it will be the same no matter what material is used.
5. Processing and verification, the order cannot be changed
It is recommended that the verification sequence of bicycle parts be arranged in reverse according to 'how the parts fail on the bike'.
Let's talk about drying first. If the moisture-absorbing material exceeds the moisture limit, the feed tube will be chain-cut, the parts become brittle, silver streaks appear on the surface, and defects become visible very late.
We have handled a very typical type of complaint: the same bag of material, the same mold, one mold turn out fine, the next one is brittle.
After checking to the end, the formula wasn't changed at all; the problem was in the drying.
Moisture content is hardest to maintain during the plum rainy season in the south. After opening the package and leaving it in the workshop for a few hours, the moisture can recover to some extent.
Our approach is to confirm with instruments or dew point data before going online, not based on touch.
Let's talk about mold temperature again. Fiberglass materials are most afraid of a low mold temperature: the fiber ends get frozen on the surface of the part, turning into floating fibers.
The floating fibers of the dark-colored parts are turning white piece by piece; after another exposure to ultraviolet light, the peeling starts from the fiber tips.
The mold temperature column supports crystallinity and surface condition, and this is more important for bicycle exterior parts than for structural parts.
The floating fibers are often not due to "too much fiberglass." Raising the mold temperature from 80 degrees to 115 degrees caused the same batch of material, with the same mold, to immediately separate on the surface comparison pieces.
Then comes humidity adjustment. Matching parts such as guide wheels and buckles must be re-measured and accepted according to the humidity-adjusted state.
A guide wheel weighing over twenty grams can absorb about half a gram of water when balanced.
When this quantity is transferred to a mating surface of the fifty-millimeter scale, the dimensional change is on the order of 0.1 millimeters.
On the meshing clearance, this is moving from 'just right' to 'fully tight'.
The verification order is arranged as follows:
1. Material Level: UV aging retention rate, impact in dry and conditioned states
2. Process window: Compare parts molded under different mold temperatures and holding pressures, and check for floating fibers and key dimensions
3. Component Level: Tooth thickness and aperture after humidity adjustment, fatigue and wear
4. Test Bench: Four working conditions of low temperature, normal temperature, salt spray, and muddy water
5. Complete Vehicle: Run the vehicle for one season after loading, and re-test for abnormal noises and handling during the period
If the previous item fails, moving on means the subsequent data has no explanatory value.
Why can't the order be changed? Because both impact and size are affected by moisture content.
If the state isn't locked, running the test bench will only make the lifespan valid for that batch, and it will drift again when mass produced.
6. Boundary: In these positions, stop changing bicycle parts first
This section helps you cut your losses before starting work.
First, main load-bearing structures such as the frame, front fork, and seat tube.
What they need is a comprehensive account of rigidity and fatigue; carbon fiber or aluminum alloy is more suitable.
Secondly, things like the hub axle, quick-release lever, crank, and chain.
It is subjected to metal-level stress and impact, and the plastic part has no margin in this position.
Third, the brake caliper body and disc. Involving braking safety, the materials must follow certification, modified nylon is not acceptable.
Fourth, bearing positions that are soaked in water for a long time or buried below the waterline. Both wear and size considerations are not cost-effective; stainless steel or oil-containing bearings should be used.
Fifth, load-bearing components for long-term riding below minus thirty degrees. In this range, one should consider low-temperature specialized systems or long carbon chain routes, as ordinary glass fiber reinforced systems lack sufficient data support.
Sixth, parts whose failure points have not yet been identified. Whether it is a dimensional issue or a material issue, the solutions are completely different. Identify the problem first before handling the material.
Putting these six points at the front is not to discourage, but to save time.
Proofing orders, batch cards, and full case rollbacks—this tuition fee is much higher than if it hadn't changed from the start.
7. Material Change Risk List (From the original route to this one, things that need to be moved)
| link; segment; part | What needs to be moved? | Points that are easy to overlook |
|---|
| Mold | If the substrate and filling system change, the shrinkage rate changes accordingly, and the tooth thickness and pore spacing need to be recalculated. | Only the material is changed without checking shrinkage, and the meshing side clearance is consumed |
| Dry | Determine the window based on the actual measured moisture content, with the dehumidifying dryer as a prerequisite | Hot air drying is basically ineffective for water-absorbing materials |
| Humidity control | Coordinate parts to be retested and accepted under conditioned moisture state | Release according to dry-state dimensions |
| Material Temperature and Mold Temperature | The glass fiber system and the toughening system require higher mold temperatures. | Copy the gear settings of the original material |
| Pressure Holding and Demolding | The tooth root and snap fit need to have pressure retention redefined, and the draft angle for demolding needs to be reviewed | Stress concentration at the root of the tooth, whitening when demolded |
| Color difference | Advance confirmation of color samples for uncoated parts and colored parts | There are differences in the base color of different batches of substrate |
| Ultraviolet and Color Fastness | Colorful items require climate-based inspection according to the destination | Only test the properties at normal temperature, do not test the color difference after xenon lamp exposure |
| Verification order | Material → Process → Component level → Test bench → Complete vehicle | If the previous item fails, just move on. |
8. Proofing and trial mold scheduling (number of machine runs, what is inspected each round, how long samples are kept)
Replacing materials and testing molds for bicycle parts is usually done in three rounds, without skipping steps between rounds.
First round · Sample comparison: Use your original mold to make three to five samples, only checking moisture content, appearance, weld lines during short shots, and key dimensions.
This round should first confirm whether the 'material can fill the teeth', keep two samples, mark the batch number and drying parameters, and keep them at least until the end of the second round.
Second Round · Process Window and Part Level: fix the material, change mold temperature and holding pressure, make two sets of comparison parts.
Check the tooth thickness after humidity adjustment along with the aperture, low-temperature impact, fatigue, and wear; UV aging samples should be submitted for inspection simultaneously.
This round basically sets the mass production parameters. Samples are sealed and stored by batch, with a storage period of at least three months after mass production stabilizes.
Round 3 · Test bench and complete vehicle: Run the test bench under four conditions - low temperature, normal temperature, salt spray, and mud and water, then install on the vehicle and run for one season.
Only after this round is over is it recommended to increase the volume.
Why can't three rounds skip? Because the conclusion of each round is the premise of the next round.
The cooperation on our self-produced side focuses on three things: the formula can be adjusted according to your climate zone and riding conditions, sampling can be done together to find the optimal window, and small-batch trials with multiple grades can be conducted in parallel.
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.
A one-page document for purchasers and technicians
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions that need to be confirmed first |
|---|
| Pedal body | Glass fiber reinforced Core-shell toughening | Low-temperature shock, fatigue | ISO 179 Cyclic Loading | Minimum installation temperature in winter |
| Variable speed guide pulley | Self-lubricating PA66 | Wear amount, tooth thickness | Test Bench Wear Comparison | Mileage and types of chain oil |
| Conduit and sheath | Low water absorption nylon | Dimensions after water absorption, bending fatigue | Coordinate measuring machine after humidity adjustment | Routing Space and Minimum Bend Radius |
| Water bottle cage, computer mount | Glass fiber reinforced weather-resistant system | UV retention rate, color fastness | ISO 4892-2 Aging | Whether the exterior parts match the color scheme |
| Bicycle Basket Mount | High-toughness system | Impact, creep | ISO 179 Long-term load | Maximum Overload and Road Conditions |
9. Several Frequently Asked Questions
Question: After changing the material, if the room temperature properties match, can it be approved?
Answer: Not enough. The main stress tests for bicycle parts are ultraviolet, low temperature, and fatigue. Passing the room temperature column only indicates that the material can be produced.
Question: The original material has been discontinued. Can the formula be copied exactly?
Answer: You can copy the material properties, but you cannot copy the process. Drying, mold temperature, and holding pressure should follow the equipment and workshop conditions.
Question: Is it necessary to add carbon black to colored parts?
Answer: Carbon black absorbs ultraviolet light and also deepens the color, so it can't be used for light-colored parts.
The approach for light-colored pieces is to fully adjust the levels of the light stabilizer, and then screen each piece according to the weather resistance grade of the pigment.
Question: If a little recycled material is mixed into the guide wheel, can it save costs?
Answer: The money saved usually gets spent back on wear and gear skipping.
If the molecular chain in the recycled material breaks, viscosity decreases, wear resistance and fatigue drop first, and batches will also differ.
Question: Between dry and humidity conditioning, which release should be used?
Answer: Assembly tolerances are calculated according to humidity condition, factory inspection is done as dry state, and both copies must be retained.
Keeping only one copy means pushing the risk to after loading.
Question: Why do the first three sentences set the direction?
Answer: The first sentence clarifies whether the base material is replaced or the entire system; the second asks about acceptance status; the third confirms whether low-temperature testing has been conducted.
If you answer all three sentences together, the question usually narrows down to one or two items.
Back to the three questions at the beginning.
Ask about the base material route, acceptance status, and low-temperature operating conditions.
If you answer all three, the direction for replacing nylon parts like shift guide wheels is basically settled.
The plastic parts on the bike are all small, but the bill is big.
The real price difference is never the price difference per bag of material, but the after-sales service for the batch returned from the whole bike.
The most troublesome inquiry is this sentence—"After replacing the material, the teeth are still the same, how come they are rounded in just three months?"
Because behind this sentence often lies three lines simultaneously: ultraviolet, low temperature, and fatigue, and the verification order of these three lines cannot be changed.
We do modified nylon pelletizing, mixing material and additives together; For these parts, material change and mold trial can be discussed together
