变速箱齿轮换料，换的往往只是牌号，动的却是整套验证。这篇讲清齿面温度为什么是硬边界、换料后先变的是尺寸不是强度、疲劳与磨损两条线怎么复验，以及换料风险清单与试模排程怎么排。
上个月，一家做变速箱配套件的厂，把一组试验齿轮寄了过来。
用的是快递箱，齿轮之间只垫了一张旧报纸。
电话里他说：「副牌料我们不敢用，可正牌换了个牌号，台架怎么就过不了了？」
他换的是同一条 PA66-GF30 路线上的另一支牌号，性能表看着还高一点。
换完以后出的问题不在齿根，在齿面：跑合两天就出现亮斑，实测温度比原来高八度。
我问他三句：齿面实测温度多少？配对件换没换？齿隙按干态还是湿态算的？
前两样他答得上来，第三样没答。
这三句问话，第九节会回收。
先把这批齿轮的时间线摆出来。
起点是新材料干态数据更好看，项目组认定换料没有风险。
潜伏是跑合头一天，油温比老方案高了三度，被当成正常波动。
爆发是第三天啮合面出亮斑，齿厚减薄几个微米。
结算是拆开测湿态齿隙，已经漂出窗口，预紧也跟着偏了。
变速箱齿轮换料的账，最后常常记在两处：湿态尺寸，和疲劳寿命。
一、六样工况，齿轮这个件四样必须给数
齿轮的载荷不是单一数值，是扭矩、转速、冲击三条线一起走。
扭矩这条要分额定和峰值。急换挡或急加速那一下的瞬时峰值，往往比额定高几倍。
转速这条决定摩擦生热。线速度越高，齿面温度上升越明显。
温度这条是硬边界。齿轮的许用应力随温度上升而下降，不是小幅线性变化，是台阶式下滑。
同一支料，80℃ 时的许用接触应力可能只有常温的一半上下。
而齿面温度等于环境温度加摩擦生热；算的是齿面，不是箱体环境温度。
介质这条是齿轮特有的。齿轮油里的添加剂体系对尼龙有增塑和萃取双重作用。
寿命这条按整车年限倒推，对应的是循环次数，不是单次强度。
外观这条在齿轮上主要看齿面状态：点蚀、亮斑、掉粉。
合规与安全这条要提前分位置：转向、制动相关传动，可靠性要求高于一切，不在这类换料的讨论范围里。
四样数字（额定扭矩、峰值扭矩、齿面温度、循环次数）先问齐，再谈换料。
二、三条路线并列：换的是路线，不是牌号
| 路线 | 适合工况 | 齿面耐温 | 吸湿与尺寸 | 加工窗口 | 适合换自哪里 |
|---|
| PA66-GF30 + 增韧 | 中载中速、座椅与天窗类 | 100–120℃ | 吸水偏高，齿隙要按湿态 | 宽、好做 | 原通用 GF30 |
| PA66-GF30 + 自润滑 | 中载连续运转 | 100–120℃ | 同上 | 中，对润滑体系敏感 | 原含油或 POM 方案 |
| PA46-GF30 | 中高载、热区位置 | 130–150℃ | 吸水更低，尺寸较稳 | 窄，需高料温高模温 | 原高温牌号 |
三条没有谁更好，只有哪条跟你的齿面温度和循环次数兜得住。
一个常见误判是「换高耐温的一档更保险」。
耐温高的那条，吸湿更低、尺寸更稳，代价是加工窗口更窄、韧性偏低。
窗口收窄之后，模具和产线要跟着改；改不动的地方，就是换料后新的风险点。
三、换料后最先变的是尺寸，不是强度
这一点最容易被跳过，因为它不会在打样那天显形。
尼龙吸水都会发生在无定形区，水分子钻进分子链之间，把氢键一个个拆开。
链段变滑，尺寸跟着涨，模量跟着降。
落到齿轮上，就是齿隙漂移。
一个 100 毫米量级的分度圆，尺寸变千分之二三，放到齿隙上就是从「刚好」变成「顶死」或「旷量」。
所以齿轮位有一条纪律：凡走 PA 的齿位，齿隙公差按湿态尺寸校核。
干态算出来的啮合精度，到湿态可能变成干涉。
第二件跟着变的是配对件与润滑。
塑料对钢的磨损低于塑料对塑料，但噪音是另一种表现；配对件一换，摩擦副就换了一副脾气。
润滑脂或齿轮油的牌号也要一起定，脂和料拆开单换，等于把润滑体系拆成两半。
第三件变的是热平衡。
同样的散热量，导热差的材料会把热攒在齿面上。
所以换料之后齿轮箱的散热结构，有时候要跟着调一调。
四、判据表：换料后要复验的是这几项
下表门限是方向性建议，不是验收标准；实际数值必须由你的件、你的工况和实测确定。
| 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 |
|---|
| 齿根弯曲疲劳 | 按循环次数定，不看单次强度 | 齿轮疲劳试验台（循环计数） | 断齿、齿根裂 | 提高疲劳档位 + 齿根圆角 | 增韧剂（疲劳寿命） |
| 齿面接触疲劳 | 按点蚀与磨损速率定门限 | 齿轮试验台 + 齿面复印 | 点蚀、亮斑、磨光 | 自润滑体系 + 齿轮油相容 | 润滑剂（减摩与耐磨） |
| 长期耐热 | 齿面温度×1000h 后性能保持 | ISO 527 / 热老化箱 | 高温软化、齿厚减薄 | 稳定化体系 + 控油温 | 抗氧剂（耐温上限） |
| 湿态齿隙 | 调湿后仍在设计窗口内 | 调湿 + 双啮仪 / 三坐标 | 啮合漂移、噪音变大 | 湿态校核 + 齿形修正 | — |
| 齿轮油相容 | 1000h 浸泡后尺寸与模量可控 | 指定油品浸泡 + 复测 | 溶胀、尺寸漂 | 按实际油品选体系 | 偶联剂（界面稳定） |
| 系统配平 | 装配后偏载与预紧在范围 | 空载跑合 + 电流曲线 | 一侧齿面过载 | 轴心距与预紧复核 | — |
怎么读这张表：先看前两行。
疲劳和磨损这两条是齿轮的主线，也是换料后最容易掉下去的两项。
第三行不是可选项，它决定材料能不能跑到寿命终点。
最后一行是提醒：齿轮系统的失效，很大一部分出在配平上，不在料上。
五、换料后常见的几种失效，和它们真正的原因
失效一：跑合几天后齿面出亮斑。
最常见的误判是「料不够硬，换更高玻纤」。
根因常在装配预紧和轴心距：预紧过大让轴心距偏了零点零几毫米，偏载把一侧齿面顶住。
先复核配平，再谈换料。
失效二：同一批件，齿面黄得不均匀。
这不是料不稳定，常是抗氧剂分散不均，或者稳定化体系的耐温余量不够。
长期 120–150℃ 下，热稳定体系若耐温不够，表面会先变黄，再出现析出物。
看到不匀先查混料与助剂耐温，别急着换基材。
这一条是助剂侧的归因：料没换错，是稳定化体系没跟齿面温度配到位。
失效三：油腔里跑了几百小时后齿厚明显减薄。
根因常是齿轮油里的添加剂对尼龙有增塑与萃取作用，长期浸泡后模量往下走。
定点前要按实际油品做一千小时浸泡对比，数据摆出来再谈方案。
失效四：低温启动时噪音变大。
根因是低温下模量升高，啮合刚性变了，噪声频谱跟着移。
北方冬季路试要专门听一遍，这一项在常温台架上听不出来。
失效五：齿面跑一段时间浮出一层白霜，摸上去发涩，噪音也跟着变大。
根因常在润滑体系过量，析出的润滑剂在齿面结成一圈不匀的膜。
内润滑不足或外润滑偏高，都会让摩擦系数忽高忽低。
查法：先复测摩擦系数，再翻回配方单看润滑剂总量与内外比例。
这一条从助剂侧归因：基材没换错，是润滑体系没跟摩擦副配平。
失效六：同一批齿轮，热机后齿厚减薄的快慢不一致。
根因常是玻纤在齿面的取向不均，跟浇口位置与模温档位有关。
查法：取同一模次的不同件做断面观察，看齿面富玻纤层的厚薄。
先校浇口与模温，再谈换料。
六、加工与验证：疲劳排在强度前面
齿轮的验证和结构件不一样，它先看寿命，再看强度。
验证顺序建议这样排，顺序不能换：
1. 材料级：按齿面温度的耐热保持、按实际油品的浸泡尺寸
2. 工艺窗口：不同模温与保压下打对比件，看熔接线与齿面浮纤
3. 件级：调湿后齿隙、齿根弯曲疲劳、齿面接触疲劳
4. 台架：至少覆盖常温、热机、极限三个温度点
5. 整机：装到实际总成上跑磨合与循环，看油温与噪音
为什么顺序不能换？因为疲劳数据依赖齿面温度和吸湿状态。
状态没锁住就去跑台架，跑出来的寿命只对那一个状态有效。
加工端还有两件事要一起定。
一件是齿形修正。塑料的热膨胀与吸湿膨胀都比金属大，齿形要按工作状态修正。
另一件是干燥与调湿。含水率没控住，前一轮的疲劳数据就不能用。
七、反向：这些位置，齿轮换料先收手
这一段帮你在立项之前止损。
其一，转向、制动相关的传动位置。
这类位置可靠性要求高于一切，改性尼龙不在候选范围。
其二，主传动位置且温度与载荷同时越界。
齿面温度长期越界，靠配方抬上去的峰值顶不住长期连续。
其三，封闭空间、无润滑、持续高负载的位置。
热量出不去，材料没法长期工作，该回到金属。
其四，失效点还没定位的件。
亮斑是配平问题还是材料问题，两件事解法完全不同，先定位再动。
其五，小批量项目且验证预算有限。
齿轮的验证费按轮次算，台架、磨损、蠕变一轮下来不便宜，小批量项目常常算不过账。
把这五条写前面不是劝退，是省时间。
八、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 | 基材与玻纤体系变，齿形可能要修正 | 只换料不修齿形，热态打齿 |
| 干燥 | 按实测含水率定窗口，除湿干燥机必备 | 热风干燥对吸水料基本无效 |
| 调湿 | 关键齿隙按调湿态复测与验收 | 按干态尺寸放行 |
| 料温/模温 | 高耐温体系要更高料温与模温 | 照抄上一支料的档位 |
| 保压/脱模 | 齿根与轮毂位要重定保压 | 齿根内应力集中 |
| 配对件 | 配对件材质与表面一起定 | 只换一个齿轮，摩擦副变了 |
| 齿轮油 | 按实际油品做浸泡对比 | 油和料拆开单换 |
| 验证顺序 | 材料→工艺→件级→台架→整机 | 前一项未过就往下走 |
这张表逐行摊开看，换料前一条条对。
模具这一行，先确认齿形当年是按哪支料的收缩率修正过的。
基材与玻纤体系一变，热态齿形就会跟着走。
只换料不修齿形，热机跑合时容易打齿。
干燥这一行，齿轮的窗口比结构件更硬，除湿干燥机绕不过去。
上机前实测含水率，把数值记在设备旁边，不靠经验判断。
调湿这一行，关键齿隙按调湿态复测，干态的数只作参考。
按干态尺寸放行，装到总成上就是顶死或者旷量。
料温与模温这一行，高耐温体系要更高的料温与模温。
档位照抄上一支料，齿面的结晶状态会跟着变。
保压与脱模这一行，齿根和轮毂位都要重定保压。
保压给不足，齿根就留下内应力，跑合几天才显形。
配对件这一行，配对件材质与表面处理要一起定。
只换一个齿轮，摩擦副换了脾气，噪音和磨损都要重看。
齿轮油这一行，按实际油品做浸泡对比，别用通用油代做。
油和料拆开单换，等于把润滑体系拆成两半。
验证顺序这一行，材料到工艺到件级到台架到整机。
前一项的数据没出来就往下走，后面每一步都要返工。
九、打样与台架排程（几轮上机、每轮验什么、留样多久）
我们给齿轮换料排的验证，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 3–5 模，只验外观、短射熔接线位置、含水率与关键尺寸。
这一轮先把「料能不能填满齿形」确认掉，留样两件，标注批号与干燥参数。
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。
验调湿后齿隙、齿根弯曲疲劳、齿面接触疲劳；配对件与齿轮油同步送检。
这一轮决定量产参数。留样按批次封存，至少留到量产稳定后三个月。
第三轮·台架与总成：按常温、热机、极限三个温度点跑台架，中途复测齿面温度与齿面状态。
这一轮过了，才建议放量。留样封存周期覆盖首批量产，便于追因。
三轮之间为什么不能跳？因为每一轮的结论都是下一轮的前提。
留样这件事在齿轮上要写进记录，它决定追因能不能落到具体某一轮。
头一轮的留样只服务第二轮，两件足够，标签上写清批号与干燥参数。
这一轮不留样，第二轮出现偏差时就回不到原件上去看。
第二轮定的是量产参数，所以它的留样要跟参数表放在一起。
封存期至少要跟到首批量产结束后的三个月，中途别开箱挪动。
第三轮的留样跨过首批量产，啮合异常时可以直接往回追。
封存条件要避开潮气和油污，标签上注明调湿状态与件重。
一轮留样配一份批记录，追溯才落得下去。
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。
读者常问的三句
问：换料后齿面出亮斑，是换料还是装配的问题？先复核轴心距和预紧，再拆料的问题，顺序反了会白换一次。
问：同一条 PA66-GF30 路线换个牌号，也要重做验证吗？要。玻纤含量、稳定化体系、吸湿速率都可能不同，齿隙和疲劳都要重看。
问：齿轮油要不要跟着换？脂和料是一对，脂换或不换都要做浸泡对比，别把两个变量分开动。
试模与追因三问
问：齿轮的验证要跑几轮台架？按常温、热机、极限三个温度点各跑一轮，中途复测齿面温度，轮次不到不要放量。
问：留样留多久才算够？至少覆盖首批量产后的三个月，并且跟参数表、批记录放在一起，只留件不留记录，价值就有限。
问：副牌料在齿轮上能不能用？先看它偏了哪一项，玻纤含量、稳定化体系还是吸湿速率，偏了多少，再决定要不要重做验证。
回到开篇那三句问话。
问齿面实测温度、问配对件、问齿隙按干态还是湿态算。
这三样答全了，变速箱齿轮换料往哪走基本就定了。
所以副牌料到底能不能用，这一问在齿轮上要先拆成两问：它偏了什么，偏了多少。
换料最贵的从来不是那袋料，是把湿态尺寸、疲劳、油品相容这三件事一起摆上桌面。
When changing transmission gears to a different material, often only the grade is changed, but it involves the validation of the entire set. This article explains why tooth surface temperature is a hard boundary, why dimensions change first rather than strength after changing materials, how to re-verify the two lines of fatigue and wear, as well as how to schedule the material change risk list and trial mold testing.
Last month, a factory that makes transmission components sent over a set of test gears.
Used a courier box, with only an old newspaper placed between the gears.
On the phone he said, 'We dare not use the sub-brand material, but if the main brand just changes the code, why can’t the test bench pass it?'
He switched to another grade on the same PA66-GF30 line, and the performance chart looks slightly higher.
After the replacement, the problem is no longer at the tooth root, but on the tooth surface: bright spots appear after two days of running, and the measured temperature is eight degrees higher than before.
I asked him three questions: What is the actual measured temperature of the tooth surface? Has the mating part been replaced? Is the tooth clearance calculated in a dry state or a wet state?
He was able to answer the first two questions, but not the third.
These three questions will be addressed in verse nine.
First, lay out the timeline for this batch of gears.
The starting point is that the dry-state data of the new material looks better, and the project team determined that changing the material poses no risk.
Lying in wait was the day before the head run, and the oil temperature was three degrees higher than the old plan, which was treated as a normal fluctuation.
The outbreak occurs on the third day, with bright spots appearing on the meshing surface and the tooth thickness reduced by a few microns.
The settlement is to measure the wet-state tooth gap separately, it has already floated out of the window, and the pre-tightening has also shifted accordingly.
The account for changing gearbox gears is often ultimately recorded in two places: wet dimensions and fatigue life.
1. Six operating conditions, for the gear part four items must be provided with numbers
The load on the gear is not a single value; it involves torque, rotational speed, and impact all together.
This torque should be divided into rated and peak values. The instantaneous peak during sudden gear shifts or rapid acceleration is often several times higher than the rated value.
The rotational speed determines frictional heating. The higher the linear speed, the more significant the temperature rise on the tooth surface.
Temperature is a hard boundary. The allowable stress of the gear decreases as the temperature rises; it is not a slight linear change, but a stepwise drop.
For the same material, the allowable contact stress at 80°C may be only about half of that at room temperature.
The tooth surface temperature equals the ambient temperature plus frictional heat; it is calculated for the tooth surface, not the housing ambient temperature.
This medium is unique to gears. The additive system in gear oil has both plasticizing and extraction effects on nylon.
The lifespan is back-calculated based on the whole vehicle's years, corresponding to the number of cycles, not the intensity of a single instance.
The appearance of this gear mainly depends on the condition of the tooth surface: pitting, bright spots, and powdering.
Compliance and safety should be allocated positions in advance: steering, braking-related transmission, reliability requirements are above all, and are not within the scope of discussion for this kind of material change.
First ask about all four numbers (rated torque, peak torque, gear surface temperature, number of cycles), then discuss material changes.
2. Three routes run in parallel: what is being changed are the routes, not the model numbers.
| Route | Suitable working conditions | Tooth surface temperature resistance | Moisture Absorption and Dimensions | Processing window | Where is it suitable to change from? |
|---|
| PA66-GF30 Toughened | Medium-speed mid-load, seats and sunroof category | 100–120℃ | Water absorption is relatively high, and the tooth clearance should be adjusted in the wet state. | Wide, easy to make | Original General GF30 |
| PA66-GF30 Self-lubricating | Continuous operation under medium load | 100–120℃ | Same as above | Sensitive to the lubrication system | Original oil-containing or POM scheme |
| PA46-GF30 | Medium-high load, hot zone location | 130–150℃ | Lower water absorption, more stable dimensions | Narrow, requiring high material temperature and high mold temperature | Original high-temperature grade |
None of the three is better; it’s only about which one can match the temperature of your tooth surface and the number of cycles.
A common misjudgment is 'switching to a higher temperature-resistant grade is safer'.
The one with high temperature resistance has lower moisture absorption and more stable dimensions, but the cost is a narrower processing window and lower toughness.
After the window narrows, the molds and production lines need to be adjusted accordingly; the places that cannot be adjusted become new risk points after material changes.
3. After changing the material, the first thing to change is the size, not the strength.
This point is the easiest to overlook because it does not show up on the proofing day.
Water absorption in nylon occurs in the amorphous regions, where water molecules penetrate between the molecular chains, breaking the hydrogen bonds one by one.
The chain segment becomes slippery, the size increases accordingly, and the modulus decreases accordingly.
When it falls onto the gears, it causes backlash drift.
A 100 mm level pitch circle, with size variations of two or three thousandths, when placed on the tooth gap, changes from 'just right' to 'jammed' or 'loose'.
So there is a rule for gear positions: for any gear position using PA, the gear clearance tolerance is checked according to the wet-state dimensions.
The meshing accuracy calculated in the dry state may turn into interference when wet.
The second thing to change is the mating parts and lubrication.
Plastic causes less wear on steel than plastic on plastic, but noise is another matter; when one of the mating parts is changed, the friction pair shows a different temperament.
The grade of grease or gear oil also needs to be determined together. Changing the grease and the material separately is equivalent to splitting the lubrication system in half.
The third thing that changed was thermal equilibrium.
With the same amount of heat dissipation, materials with poor thermal conductivity will accumulate heat on the tooth surface.
So after changing the material, the cooling structure of the gearbox sometimes needs to be adjusted accordingly.
4. Criteria Table: These are the items that need to be rechecked after material replacement
The thresholds in the table are directional recommendations, not acceptance standards; the actual values must be determined by your parts, your working conditions, and actual measurements.
| Indicator | Directional Threshold | Verification Method / Standard | Common failures after material change | Common solution | Corresponding auxiliary agent system |
|---|
| Tooth root bending fatigue | Determined by the number of cycles, not by the intensity of a single session | Gear Fatigue Test Bench (Cycle Count) | Broken teeth, cracked tooth roots | Increase fatigue level Tooth root fillet | Toughening agent (fatigue life) |
| Tooth surface contact fatigue | Set threshold according to pitting and wear rate | Gear Test Stand Gear Surface Copying | Pitting, bright spots, polishing | Self-lubricating system Gear oil compatible | Lubricant (Friction Reduction and Wear Resistance) |
| Long-term heat resistance | Tooth surface temperature × performance retention after 1000 hours | ISO 527 / Heat Aging Chamber | High-temperature softening, tooth thickness reduction | Stabilization system Oil temperature control | Antioxidant (Maximum Temperature Limit) |
| Wet interproximal space | Still within the design window after humidity adjustment | Humidity Control Double Gear Instrument / Three Coordinate | Meshing drift, increased noise | Wet state verification Tooth profile correction | — |
| Gear oil compatibility | Dimensions and modulus controllable after 1000h soaking | Soak in specified oil and retest | Swelling, dimensional drift | Select the system according to the actual oil type | Coupling agent (interface stabilizer) |
| System Balancing | Eccentric load after assembly and preloading within range | No-load run-in current curve | Overload on one side of the tooth surface | Center Distance and Preload Review | — |
How to read this table: first look at the first two rows.
Fatigue and wear are the main lines of the gear, and they are also the two items most likely to be lost after material replacement.
The third line is not optional; it determines whether the material can reach the end of its lifespan.
The last line is a reminder: the failure of the gear system is largely due to balancing, not the material.
5. Several common failures after material replacement and their real causes
Failure 1: Bright spots appear on the tooth surface after a few days of running in.
The most common misjudgment is 'the material isn't hard enough, switch to higher-grade fiberglass.'
The root cause often lies in assembly preload and shaft center distance: excessive preload shifts the shaft center distance by a few hundredths of a millimeter, causing one side of the gear teeth to be pressed.
First review the balancing, then discuss changing the materials.
Failure 2: In the same batch of parts, the gear surface turns yellow unevenly.
This is not due to unstable material; it is often because the antioxidant is unevenly dispersed, or the thermal margin of the stabilization system is insufficient.
Under long-term exposure at 120–150°C, if a thermally stable system cannot withstand the temperature, its surface will first turn yellow, and then precipitates will appear.
If you notice unevenness, first check the temperature resistance of the mixed material and additives, don't rush to change the substrate.
This one is the additive side's attribution: the material wasn't changed incorrectly; it's that the stabilization system wasn't matched to the tooth surface temperature.
Failure three: After running in the oil cavity for several hundred hours, the gear thickness has significantly decreased.
The root cause is often that the additives in gear oil have a plasticizing and extracting effect on nylon, and prolonged soaking causes the modulus to decrease.
Before setting the point, a thousand-hour soaking comparison should be done according to the actual fuel, and the plan can be discussed once the data is laid out.
Failure 4: Noise increases during low-temperature startup.
The root cause is the increase in modulus at low temperatures, which changes the meshing stiffness, causing the noise spectrum to shift.
The road test in the northern winter needs to be listened to specifically, as this item cannot be detected on a test bench at normal temperature.
Failure five: After running for a while, the tooth surface develops a layer of white frost, feels rough to the touch, and the noise also increases.
The root cause often lies in the excessive amount of lubricant in the lubrication system, causing the precipitated lubricant to form an uneven ring of film on the gear surface.
Insufficient internal lubrication or excessive external lubrication can both cause the friction coefficient to fluctuate.
Investigation method: First, retest the friction coefficient, then look back at the formula sheet to check the total amount of lubricant and the internal-to-external ratio.
This one can be attributed to the additive side: the substrate wasn't changed incorrectly; it's that the lubrication system wasn't balanced with the friction pair.
Failure Six: For the same batch of gears, the rate of tooth thickness reduction after heating is inconsistent.
The root cause is often the uneven orientation of the glass fibers on the tooth surface, which is related to the gate location and mold temperature settings.
Inspection method: Take different parts from the same mold batch for cross-sectional observation to check the thickness of the glass fiber-rich layer on the tooth surface.
First check the gate and mold temperature, then discuss material change.
6. Processing and Verification: Fatigue comes before strength
The verification of gears is different from that of structural components; it first considers lifespan, then strength.
It is recommended to arrange the verification in this order; the order cannot be changed:
1. Material grade: according to the heat resistance of the tooth surface temperature, and the soaking size based on the actual oil
2. Process window: Compare parts under different mold temperatures and holding pressures to observe the weld lines and fiber floating on the tooth surface
3. Component level: tooth gap after moisture adjustment, root bending fatigue, tooth surface contact fatigue
4. Test bench: covering at least three temperature points—ambient, hot engine, and extreme
5. Complete machine: Install on the actual assembly for break-in and cycling, and check oil temperature and noise
Why can't the order be changed? Because fatigue data depends on the tooth surface temperature and moisture absorption state.
If the state is not locked, running the test rig will only make the lifespan applicable to that particular state.
There are two more things to decide at the processing end.
One is tooth profile correction. The thermal expansion and moisture absorption expansion of plastic are both greater than those of metal, so the tooth profile must be corrected according to the working conditions.
Another issue is drying and humidity control. If the moisture content is not controlled, the fatigue data from the previous round cannot be used.
7. Reverse: At these positions, the gear should stop feeding material first
This section helps you cut your losses before starting a project.
First, the transmission positions related to steering and braking.
The reliability requirements for this type of position are above everything else; modified nylon is not within the candidate range.
Secondly, the main drive position and temperature simultaneously exceed the limits along with the load.
The tooth surface temperature exceeds the limit for a long time, and the peak raised by the formulation cannot withstand long-term continuous operation.
Third, enclosed spaces, lack of lubrication, and positions under continuous high load.
Heat can't escape, the material can't work long-term, it needs to go back to metal.
Fourth, parts whose failure points have not yet been located.
Is the bright spot a balancing issue or a material issue? The solutions for these two are completely different. Locate first, then act.
Fifth, small-batch projects with limited verification budgets.
The verification fee for gears is calculated per round, and a full cycle of bench testing, wear, and creep is not cheap. Small-batch projects often can't make the numbers work.
Putting these five points at the beginning is not to discourage, but to save time.
8. Material Change Risk List (From the original route to this one, things that need to be moved)
| link; segment; part | What do you want to move? | Points that are easy to overlook |
|---|
| Mold | If the substrate and fiberglass system change, the tooth shape may need to be adjusted. | Only replace the material without repairing the tooth shape, cutting teeth in a hot state |
| Dry | Set the window according to the actual measured moisture content; a dehumidifying dryer is essential. | Hot air drying is basically ineffective for water-absorbing materials |
| Humidity control | Key gear clearance remeasured and accepted according to the adjusted humidity state | Release according to dry-state dimensions |
| Material Temperature / Mold Temperature | High heat-resistant systems require higher material temperature and mold temperature | Copy the gear setting from the previous batch |
| Pressure Holding / Demolding | The tooth root and wheel hub position need to be re-pressurized | Stress concentration at the tooth root |
| Pairing part | The material of the matching parts is determined along with the surface | Just changed one gear, the friction pair has changed |
| gear oil | Soak comparison based on actual oil products | Change oil and parts separately |
| Verification order | Material → Process → Component Level → Test Bench → Complete Machine | If the previous item fails, just move on. |
Looking at this table row by row, everything matched item by item before the material change.
In the mold industry, first confirm which material's shrinkage rate the tooth profile was adjusted for in that year.
When the substrate and fiberglass system change, the hot-state tooth profile will follow accordingly.
Only replace the material without repairing the tooth profile, which can easily cause tooth clash during break-in on a hot machine.
In the drying industry, the gear windows are harder than the structural parts, and the dehumidifying dryer can't get around them.
Measure the moisture content before using the machine, and record the value next to the equipment, rather than relying on experience to judge.
In the field of humidity adjustment, the key tooth gaps should be re-measured under humidity-adjusted conditions, and the dry state values are only for reference.
Released according to the dry state dimensions; when installed on the assembly, it either bottoms out or has clearance.
In terms of material temperature and mold temperature, high heat-resistant systems require higher material and mold temperatures.
The gear position follows the previous batch, and the crystalline state of the tooth surface will change accordingly.
In the process of holding pressure and demolding, both the tooth root and the hub position need to have the pressure recalibrated.
If the holding pressure is insufficient, residual stress will remain at the root of the teeth, and it will take a few days of running-in for it to become apparent.
For the row of paired parts, the material and surface treatment of the paired parts should be decided together.
Just changing one gear changes the temperament of the friction pair, so noise and wear need to be closely reconsidered.
In the gear oil industry, when conducting soaking comparisons, use the actual oil product instead of using general-purpose oil as a substitute.
Separating the oil and additives for individual replacement is equivalent to splitting the lubrication system in half.
The verification sequence is this line: from materials to process to component level to test bench to complete machine.
If the previous step's data hasn't come out, moving forward means every subsequent step will have to be redone.
9. Proofing and Test Stand Scheduling (number of machine runs, what is checked each round, how long samples are kept)
The verification for changing the material of the gears is usually divided into three rounds, and there is no skipping between the rounds.
First round · Sample comparison: Use your original mold to produce 3–5 samples, only checking appearance, short shot weld line position, moisture content, and key dimensions.
In this round, first confirm whether the material can fill the tooth shape, keep two samples, and mark the batch number and drying parameters.
Second round · Process window and part level: fix the material, change mold temperature and holding pressure, make two sets of comparison parts.
After verification and adjustment of humidity, check for tooth clearance, root bending fatigue, and tooth surface contact fatigue; paired parts are sent for inspection along with gear oil.
This round determines the mass production parameters. Samples are sealed by batch and kept for at least three months after mass production stabilizes.
Third round: Test rigs and assemblies: Run the test rigs at three temperature points – ambient, hot, and extreme – and retest the tooth surface temperature and condition midway.
Only after this round is completed is it recommended to increase the volume. Keeping samples sealed and stored covers the first batch of mass production, making it easier to trace the cause.
Why can't you skip between the three rounds? Because the conclusion of each round is the premise of the next round.
The matter of sample retention must be recorded in the gears, as it determines whether the cause tracking can be assigned to a specific round.
The samples from the first round are only for the second round, two pieces are enough, and the label should clearly indicate the batch number and drying parameters.
If we don't keep a sample this round, when deviations appear in the second round, we won't be able to go back to the original item to check.
The second round is about setting mass production parameters, so its sample retention should be kept together with the parameter sheet.
The storage period must last at least three months after the end of the first batch of mass production, and the box should not be opened or moved in the meantime.
The third round of sample retention surpasses the first batch of mass production, and when meshing abnormalities occur, it can be traced back directly.
The storage conditions should avoid moisture and oil contamination, and the label should indicate the humidity status and the weight of the item.
Each sample should be matched with a batch record, only then can it be traced.
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 materials and auxiliaries are prepared together at once.
Three questions readers often ask
Q: After changing the material, bright spots appear on the tooth surface. Is it a problem with the material change or assembly? First, recheck the shaft center distance and preload, then disassemble the material if there's a problem. Doing it in the wrong order will result in a wasted material change.
Q: If we change the grade of the same PA66-GF30 material, do we need to redo the validation? A: Yes. The glass fiber content, stabilization system, and moisture absorption rate may all differ, so both tooth clearance and fatigue need to be reexamined.
Q: Do we need to change the gear oil as well? Grease and oil come as a pair. Whether you change the grease or not, you need to do a soaking comparison, and don't change the two variables separately.
Three Questions on Mold Testing and Cause Tracking
Q: How many bench test cycles are required for gear verification? Run one cycle at each of three temperature points: normal temperature, hot engine, and extreme. Re-measure the tooth surface temperature in the middle. Do not increase the volume if the number of cycles is not reached.
Q: How long should samples be kept to be sufficient? At least covering the first three months after mass production, and kept together with the parameter sheets and batch records. Keeping only the items without the records has limited value.
Q: Can secondary grade material be used on gears? First, check which aspect it deviates in—glass fiber content, stabilization system, or moisture absorption rate—and by how much, then decide whether re-validation is needed.
Back to the three questions at the beginning.
Ask for the measured temperature of the tooth surface, ask about the mating parts, and ask whether the tooth clearance is calculated in dry or wet conditions.
If you answer all three of these, it basically determines where the transmission gear change material will go.
So whether the sub-brand material can be used or not, this question about the gear must first be broken down into two questions: what is it off, and by how much.
The most expensive part of changing materials is never the bag of material itself, but putting wet-state dimensions, fatigue, and oil compatibility all on the table together.
