继电器和线圈骨架属于"看着不起眼、出事很严重"的一类件。
它不承大载、不露外观，但它把导线和触点固定在一个精确的位置上。一旦软化变形、爬电击穿或者端子开裂，整机就失效。
选骨架的材料，本质上是在耐温、绝缘、薄壁成型、嵌件强度之间找一个平衡点。
继电器骨架的失效，多数发生在客户看不见的地方。
线圈通电发热，骨架长期处在温升环境里，绝缘电阻缓慢下滑。
一家继电器厂的售后数据里，参数漂移的返修占了投诉的大头。
拆开看，骨架没有变形，没有开裂，只是介电性能悄悄劣化。
这种不声不响的失效，最难防，也最考验选料的前瞻性。
一、线圈温度是第一个变量
骨架紧贴线圈，长期处在绕组温升的环境里。
绝缘等级和温升是对应的：B 级对应约 130℃，F 级约 155℃，H 级约 180℃。这里的温度是长期连续温升，不是短时峰值。
选料第一步不是问"耐多少度"，而是问清楚线圈的绝缘等级和实测温升。
差一档，材料方向就完全不同：130℃ 可以用阻燃增强 PA66，155℃ 往往要用高温体系或 PA46，180℃ 以上通常要看 PA6T、PA9T 或 PPS 这个量级。
还要区分两种温度：绕组内部的温度通常高于外表面，而骨架紧贴绕组。所以测点位置很重要，用外壳温度代替绕组温度，会低估要求。
稳妥的做法是请客户提供绕组实测温升曲线，看稳态值，而不是看某一瞬间的峰值。
二、薄壁加嵌件，是骨架的结构宿命
骨架的典型特征是：壁很薄、尺寸很紧、端子是嵌在里面的。
薄壁件的难点在流动——流程长、壁厚小、还要填满端子周围，材料流动性不够就会出现填充不足或熔接线偏弱。
嵌件的难点在应力——金属端子和塑料的热膨胀不一样，冷却时塑料收缩被金属约束，就在端子周围形成一圈应力集中。
两个难点叠在一起，结果往往是端子附近的微裂。 这类问题在出厂检验时常常看不出来，装机、过炉、或者做几次冷热循环之后才暴露。
对策的顺序是：先给端子加圆角与咬合结构，先试嵌件预热，最后才考虑换料。
还有一个容易被忽略的细节：端子与孔壁之间的塑料厚度。这个厚度决定塑料对金属的约束能力，太薄会被金属"卡"出应力集中，太厚又会让端子松动。
一般建议孔壁厚度与端子直径保持一定比例，同时在孔口留出过渡圆角。这两条是设计规范层面的东西，比选料更早决定成败。
三、爬电距离是骨架的"隐形尺寸"
骨架的几何形状，往往就是产品爬电距离的物理载体。
两个带电部位之间的塑料表面距离，直接决定了产品能承受多高的电压、能过什么等级的安规。
这件事经常被当成纯结构问题，其实是材料与结构一起决定的：同样的距离，高 CTI 材料能承受的电压更高；反过来说，用高 CTI 材料可以把距离做短、产品做小。
新能源平台的继电器电压等级更高，400V 与 800V 平台对骨架的 CTI 与耐电弧要求，比传统 12V、24V 系统严格得多，沿用老牌号往往过不了新测试。
四、材料档次与温度对应
| 长期温升 | 材料方向 | 备注 |
|---|
| 130℃ 以内 | 阻燃增强 PA66 | 成本与工艺最成熟 |
| 约 155℃ | 高温体系 PA66 / PA46 | 需确认长期热老化数据 |
| 180℃ 以上 | PA6T / PA9T / PPS | 工艺窗口差异大，需同步调整 |
注意最后一行：高温尼龙的料温、模温、干燥条件与 PA66 完全不同，换料不换工艺，等于白换。
还有一个选料时经常被问到的问题：能不能用 PPS 替代高温尼龙。两者差别主要在工艺与成本：PPS 吸水率极低、尺寸更稳，但韧性差、成型温度高、对模具要求也高；高温尼龙韧性更好、工艺更接近 PA66、改造成本低。
判断办法是看骨架的形状——薄壁长流程、结构复杂的，高温尼龙更容易做出来；平板型、尺寸要求极稳的，PPS 的优势更明显。
无论选哪个，端子的嵌件方案都要跟着重新算：材料不同，收缩率与热膨胀系数都变了，原来的过盈量不再适用。
还有一条容易被忽略：骨架的存放与调湿。高温尼龙吸湿后尺寸与韧性都会变化，如果客户在装配前才开箱，尺寸可能已经漂了。要不要调湿、什么时候调湿、按什么含水率交货，这些要写进供货协议。
五、骨架最怕的三件事
一是填充不足。 薄壁长流程填不满，端子周围出现缺料。
二是熔接线落在受力或绝缘薄弱位置。 玻纤料熔接线强度低，浇口位置必须避开这些区域。
三是吸水后的尺寸漂移。 骨架的定位尺寸通常很紧，吸湿膨胀会让装配变紧或变松。
这三件事都不是"换一个更好的料"能解决的，要靠浇口设计、模温控制、干燥与后处理一起做。
六、工艺窗口不能照搬
同一台注塑机上，从 PA66 换到 PA6T，需要同时调整料温、模温、射速、保压和干燥条件。
骨架这类薄壁精密件对模温尤其敏感——模温不够，流动与结晶都不理想，尺寸和熔接线一起变差。
"同一个牌号，两家做出来不一样"在骨架上体现得特别明显，因为工艺窗口窄，偏离一点结果就不同。
七、验证清单
送样前建议把这五项测掉：
① 耐压与绝缘电阻，并且要在调湿状态下测。
② CTI，同样要调湿态数据。
③ 球压，确认长期温升下不软化。
④ 端子拉拔力，测嵌件结合强度。
⑤ 冷热循环后复测前四项，看是否有退化。
这五项不复杂，但能覆盖骨架绝大多数失效模式。
骨架的绝缘劣化，机理要讲透。
线圈温升让骨架长期处于八九十度甚至更高。
PA 的介电性能随温度和吸湿双线下滑，两者叠加更明显。
线圈通电还会产生电场，局部放电在薄弱位置慢慢积累损伤。
所以骨架料要看三个温度点的介电数据，而不是常温一个点。
湿热的南方市场，吸湿这条线还要单独加严。
有工厂按销售区域分等级供货，南方市场用低吸湿牌号。
区域化选型听着麻烦，售后数据却非常诚实。
追问一：骨架的绝缘电阻多久测一次？
出厂全测，耐久抽样按批。骨架的介电衰减是慢变量，批次抽测加周期耐久两条线。湿热季节抽测频率加密，南方仓库的骨架料件建议按低吸湿档管理。
追问二：线圈骨架的耐温怎么定级？
按温升加环境温度之和定，留十分之一余量。继电器内腔温度比环境高几十度，骨架等级要按内腔算，不能按环境算。这个差值算错，是骨架选型最常见的错误。
一单参数漂移的追查
某继电器批量参数漂移，返修件拆开骨架完好。最后定位到吸湿：南方仓储三个月，骨架含水率上来，介电常数漂了，线圈电感跟着变。整改是仓储除湿加选低吸湿牌号。参数漂移这种疑难杂症，答案往往在最普通的物理常识里。
骨架选型三看
看温度点的介电数据、看吸湿等级与销售区域匹配、看薄壁流动与成型精度。三看完备，骨架的性能底线就有了。
收一句：继电器是电子系统的哨兵，骨架是哨兵的铠甲。铠甲不响不亮，但哨兵的可靠一半压在它身上。选料时多看一眼温湿双曲线，客户设备就多一分安稳。
继电器骨架还有个延伸话题：信号继电器与功率继电器的分化。信号继电器追求接触可靠，骨架的介电要求极致；功率继电器追求载流，骨架的耐温要求极致。同一个家族，两条技术路线，选料逻辑完全不同。配套厂按路线建两个料单，比一张料单通吃更清晰。行业越细分，料单越要跟着分。把一张万能料单当传家宝的工厂，接不住细分市场的单。
骨架的模具精度也值得一提。骨架是薄壁件，型芯细长，熔体冲刷型芯的偏移直接影响壁厚均匀。壁厚不均的骨架，介电薄弱点就在最薄处。模具的排气、型芯的定位、保压的设定，三个变量决定壁厚均匀度。选料时选流动平稳的牌号，能降低型芯偏移的风险。材料流动的稳定性这个指标不出现在物性表上，却在每一批骨架的实测里现身。它需要靠试产数据说话，需要供应商愿意陪你跑试产。
清单收官
继电器骨架定点资料包：三温度点介电数据、吸湿等级与区域匹配、薄壁试产壁厚均匀度、老化后绝缘复测、与漆或包封料的相容性。骨架虽小，资料包的厚度决定合作的深度。
继电器骨架的包封协同还有个细节。有些继电器工艺是先装骨架再点胶包封，胶的固化收缩把骨架往外拉。骨架与胶的热胀系数差得远，温度循环时交界面的应力反复拉锯。有工厂的骨架在低温段开裂，查出来是胶的配方换了硬胶。包封体系的变更管理，要把骨架复测写进流程。胶和骨架是拴在一根绳上的两只蚂蚱，一头的动作另一头必须知道。
骨架的装配精度也值得一提。动触点簧片压在骨架上，簧片压力长期作用于骨架的薄壁悬臂。悬臂的蠕变让触点压力逐年衰减，继电器的关键参数跟着漂。选料时蠕变模量是骨架的头号指标，比强度更靠前。有继电器厂把触点压力五年衰减值写进选型规范，供应商的蠕变数据因此成为报价必附项。一个参数管一类件，这样的提炼每多一条，供应链就稳一分。
给新入行的采购一个建议：骨架类件的供应商评审，重点看三样——介电测试设备齐全度、温湿双曲线数据完整性、试产配合意愿。三样都是慢功夫，装不出来。骨架件的供应商换了三批才找对的工厂，共同点都是这三样齐备。
继电器骨架还有个自动化装配的新要求。自动化产线对骨架的尺寸一致性要求极高，手动装配时代能容忍的偏差，机械手不容忍。骨架料的成型稳定性因此被提到了新高度。有工厂的自动化改造卡在骨架供料上，尺寸波动让机械手抓取失败率超标。最终靠换稳定牌号加工艺优化解决。自动化浪潮把塑料件的公差要求整体抬高了一档，材料端的响应要跟上。
骨架的标识管理也值得一提。继电器型号繁多，骨架上要有型号标识，注塑成型时一起做出。标识的清晰度影响下游装配效率，字高深度都有讲究。模具字体的维护周期要列入保养计划，磨损的字迹让产线频频停机。小到一行字，背后都是效率账。
给继电器厂的选型收尾建议：骨架料的评审把成型稳定性放第一，介电数据放第二，价格放第三。成型不稳的料，介电再好也接不住自动化产线的考验。排序对了，定点就快。
结语
继电器骨架选料，判断链是：
先定线圈温升与绝缘等级 → 再定爬电距离与 CTI → 再定薄壁与嵌件的成型方案 → 最后定材料。
顺序对了，选料这一步很短；顺序错了，后面每一环都要为前面买单。
我们站在树脂厂和注塑厂之间。
Relays and coil cores belong to the type of components that 'look insignificant but can cause serious problems if they fail.'
It does not bear heavy loads or show any external appearance, but it keeps the wires and contacts fixed in an exact position. Once it softens and deforms, suffers creepage breakdown, or the terminals crack, the whole device fails.
Choosing the material for the frame is essentially about finding a balance between temperature resistance, insulation, thin-wall forming, and insert strength.
The failure of relay frameworks mostly occurs in areas that are not visible to the customer.
When the coil is energized and generates heat, the framework remains in a temperature-rise environment for a long time, causing the insulation resistance to slowly decrease.
In the after-sales data of a relay factory, repairs due to parameter drift accounted for the majority of complaints.
Upon inspection, the framework has not deformed or cracked; only the dielectric properties have quietly deteriorated.
This kind of silent failure is the hardest to prevent and also the most challenging test of foresight in material selection.
1. Coil temperature is the first variable
The frame is closely attached to the coil, and it is exposed to the winding temperature rise environment for a long time.
Insulation class and temperature rise correspond as follows: Class B corresponds to about 130℃, Class F to about 155℃, and Class H to about 180℃. The temperature here refers to long-term continuous temperature rise, not short-term peaks.
The first step in material selection is not to ask 'how much temperature it can withstand,' but to clarify the insulation class of the coil and the actual measured temperature rise.
Just one grade difference, and the material direction is completely different: at 130℃, flame-retardant reinforced PA66 can be used; at 155℃, a high-temperature system or PA46 is often needed; above 180℃, usually PA6T, PA9T, or PPS at this level must be considered.
It is also necessary to distinguish between two types of temperatures: the temperature inside the winding is usually higher than the surface, while the frame is in close contact with the winding. Therefore, the location of the measurement point is very important; using the casing temperature instead of the winding temperature will underestimate the requirements.
A prudent approach is to ask the customer to provide the measured temperature rise curve of the winding, looking at the steady-state value rather than the peak value at a particular moment.
2. Thin walls with inserts are the structural destiny of the framework.
The typical characteristics of the skeleton are: the walls are very thin, the dimensions are very tight, and the terminals are embedded inside.
The difficulty with thin-walled parts lies in the flow — the process is long, the wall is thin, and the area around the terminals must also be filled. If the material's fluidity is insufficient, it will result in incomplete filling or weak weld lines.
The difficulty with inserts lies in stress—the metal terminals and plastic have different thermal expansions, and when cooling, the plastic shrinkage is constrained by the metal, forming a ring of stress concentration around the terminals.
When two difficulties overlap, the result is often microcracks near the terminals. This type of problem is often not detectable during factory inspection and only becomes apparent after installation, soldering, or several thermal cycles.
The sequence of countermeasures is: first add fillets and interlocking structures to the terminals, then try preheating the inserts, and only finally consider changing the material.
There is another detail that is easily overlooked: the thickness of the plastic between the terminal and the hole wall. This thickness determines the plastic's ability to constrain the metal; if it is too thin, the metal will 'bite' and cause stress concentration, and if it is too thick, it will make the terminal loose.
It is generally recommended that the thickness of the hole wall be kept in a certain ratio to the diameter of the terminal, while leaving a transition fillet at the hole opening. These two points are related to design standards and are decided earlier than material selection in determining success or failure.
3. The creepage distance is the "invisible dimension" of the framework
The geometric shape of the skeleton is often the physical carrier of the product's creepage distance.
The distance of the plastic surface between two charged parts directly determines how high a voltage the product can withstand and what level of safety standard it can meet.
This matter is often regarded purely as a structural problem, but in fact it is determined by both materials and structure: for the same distance, high CTI materials can withstand higher voltage; conversely, using high CTI materials allows the distance to be shortened and the product to be made smaller.
The relay voltage levels of new energy platforms are higher. The CTI and arc resistance requirements for the frameworks of 400V and 800V platforms are much stricter than traditional 12V and 24V systems, and using old brands often cannot pass the new tests.
4. Correspondence Between Material Grades and Temperature
| Long-term temperature rise | Material direction | Remarks |
|---|
| Within 130℃ | Flame-retardant reinforced PA66 | The cost and technology are the most mature |
| About 155℃ | High-temperature system PA66 / PA46 | Need to confirm long-term thermal aging data |
| Above 180℃ | PA6T / PA9T / PPS | The process window varies greatly and needs to be adjusted simultaneously. |
Pay attention to the last line: the material temperature, mold temperature, and drying conditions for high-temperature nylon are completely different from PA66; changing the material without changing the process is equivalent to changing for nothing.
There is another question that is often asked when selecting materials: whether PPS can replace high-temperature nylon. The main differences between the two are in process and cost: PPS has extremely low water absorption and more stable dimensions, but it has poor toughness, high molding temperature, and high requirements for molds; high-temperature nylon has better toughness, the process is closer to PA66, and the modification cost is low.
The way to judge is by looking at the shape of the framework — for thin-walled, long-process, complex structures, high-temperature nylon is easier to use; for flat types with extremely stable size requirements, PPS has more obvious advantages.
No matter which one is chosen, the terminal insert scheme must be recalculated: with different materials, both the shrinkage rate and the thermal expansion coefficient change, and the original interference fit is no longer applicable.
There's one more point that's easily overlooked: the storage and humidity adjustment of the skeleton. The size and toughness of high-temperature nylon will change after absorbing moisture, and if the customer only unpacks it before assembly, the dimensions may have already shifted. Whether to adjust humidity, when to adjust it, and at what moisture content to deliver should all be written into the supply agreement.
5. The three things a skeleton fears the most
First, there is insufficient filling. The long thin-walled process cannot be completely filled, resulting in material shortages around the terminals.
Secondly, the weld line falls on a stressed or weak insulation area. The strength of the weld line in fiberglass materials is low, so the gate location must avoid these areas.
Third is the dimensional drift after water absorption. The positioning dimensions of the framework are usually very tight, and moisture-induced expansion can make the assembly tighter or looser.
None of these three issues can be solved simply by 'changing to better material'; it requires a combination of gate design, mold temperature control, drying, and post-processing.
6. The process window cannot be copied directly
On the same injection molding machine, when switching from PA66 to PA6T, it is necessary to adjust the material temperature, mold temperature, injection speed, holding pressure, and drying conditions simultaneously.
Thin-walled precision parts like skeletons are particularly sensitive to mold temperature—if the mold temperature is insufficient, both flow and crystallization are suboptimal, and the dimensions deteriorate along with the weld lines.
"The same grade, but two manufacturers produce different results" is particularly evident in the framework, because the process window is narrow, and even a slight deviation leads to different outcomes.
7. Verification Checklist
It is recommended to test these five items before sending the sample:
① Voltage resistance and insulation resistance, and they should be measured in a humidity-controlled state.
② CTI also needs to adjust the wet-state data.
③ Ball pressure, confirm that it does not soften under long-term temperature rise.
④ Terminal pull-out force, used to measure the bonding strength of the insert.
⑤ After thermal cycling, retest the first four items to see if there is any degradation.
These five items are not complicated, but they can cover the vast majority of failure modes of the framework.
The insulation deterioration of the skeleton should be thoroughly explained in terms of mechanism.
The coil temperature rise keeps the skeleton at 80 or 90 degrees or even higher for a long time.
PA dielectric performance declines with both temperature and moisture absorption lines, making the overlap even more pronounced.
When the coil is energized, it generates an electric field, and partial discharge slowly accumulates damage at weak points.
So the skeleton material should be based on the dielectric data at three temperature points, not just one point at room temperature.
In the hot and humid southern market, the moisture absorption line must be strictly enhanced.
Some factories supply by sales region, but the southern market uses low moisture absorption grades.
Regional selection sounds troublesome, but the after-sales data is very honest.
Follow-up question 1: How often should the insulation resistance of the skeleton be measured?
Factory full testing, durability sampling by batch. The dielectric decay of the skeleton is a slow variable; batch sampling and periodic durability are two lines. During hot and humid seasons, the frequency of sampling is increased; skeleton materials in southern warehouses are recommended to be managed at low moisture absorption levels.
Follow-up question 2: How is the temperature resistance of coil skeleton graded?
Set it as the sum of temperature rise and ambient temperature, leaving a one-tenth margin. If the relay's internal cavity temperature is tens of degrees higher than the ambient temperature, the skeleton grade should be calculated according to the internal cavity, not by the environment. This difference is a miscalculated error and is the most common error in skeleton selection.
Tracking parameter drift in a single order
A relay batch has parameter drift, rework parts disassembled and the skeleton is intact. Finally, the focus is on moisture absorption: after three months of storage in the south, the skeleton moisture content increased, the dielectric constant drifted, and the coil inductance changed accordingly. Rectification involves dehumidifying the warehouse and selecting a low moisture-absorbing grade. For difficult problems like parameter drift, the answer often lies in the most basic physical knowledge.
Three looks at skeleton selection
Check the temperature point dielectric data, see the moisture absorption level matches the sales area, and check thin-wall flow and forming accuracy. Third, check completely, and the bottom line of the skeleton performance is clear.
To conclude: The relay is the sentinel of the electronic system, the skeleton is the armor of the sentinel. Armor may not be loud or flashy, but half of the sentinel's reliability rests on it. When selecting materials, one more look at the temperature and humidity hyperbola makes the client's equipment more stable.
Relay Framework has an extended topic: the differentiation between signal relays and power relays. Signal relays pursue reliable contact, while the skeleton requires the ultimate in dielectric; Power relays pursue current carrying and the skeleton demands extreme temperature resistance. Within the same family, two technical routes have completely different material selection logic. Supporting factories build two material lists according to the route, which is clearer than covering everything in one list. The more segmented the industry, the more the material list must be divided. Factories that treat a universal material list as a family heirloom cannot take orders from a niche market. The mold precision of
skeleton is also worth mentioning. The skeleton is a thin-walled part, and the core is slender; the melt erodes the core and its offset directly affects wall thickness uniformity. For a skeleton with uneven wall thickness, the dielectric weak point is at the thinnest point. Mold venting, core positioning, and holding pressure setting determine wall thickness uniformity. When selecting materials, choose grades with stable flow to reduce the risk of core misalignment. Material flow stability is not an indicator on physical property tables, but it appears in the actual tests of every batch of skeletons. It needs trial production data to speak for itself, and suppliers need to be willing to accompany you through trial production.
List End
Relay Framework Fixed Point Data Package: Three temperature point dielectric data, moisture absorption level and area matching, thin-wall trial production wall thickness uniformity, insulation retesting after aging, compatibility with paint or encapsulation materials. Although the skeleton is small, the thickness of the data package determines the depth of cooperation.
There is another detail in the encapsulation collaboration of the relay skeleton. Some relay processes install the skeleton first and then apply glue for encapsulation; the adhesive cures and shrinks to pull the skeleton outward. The thermal expansion coefficient between the skeleton and the glue is very different, and the stress at the interface during temperature cycling repeatedly pulls and tugs at the interface. Some factories have skeleton cracks during low-temperature periods, and it is found that the glue formula has been replaced with hard glue. Change management of the encapsulation system requires skeleton re-testing into the process. The glue and skeleton are like two grasshoppers tied to the same rope; the movement of one end must be known at the other. The assembly precision of the
skeleton is also worth mentioning. The moving contact spring presses against the skeleton, and the spring pressure acts long-term on the thin-walled cantilever of the skeleton. The creep of the cantilever causes contact pressure to decay year by year, causing key relay parameters to drift along with it. When selecting materials, creep modulus is the number one indicator for the skeleton, even ahead of strength. Some relay factories include five-year contact pressure attenuation values in their selection specifications, making supplier creep data a mandatory item in the quotation. One parameter controls one class of parts; with each additional refinement, the supply chain stabilizes.
Advice for New Procurement Professionals: When evaluating skeleton components, focus on three key factors—completeness of dielectric testing equipment, completeness of temperature and humidity hyperbola data, and willingness to cooperate in trial production. All three are slow processes and can't be assembled. It took three batches of suppliers to find the right factory for frame parts, and the common point is that all three are present.
Relay Components also have a new requirement for automated assembly. Automated production lines demand extremely high dimensional consistency for the skeleton; deviations tolerated in the manual assembly era are not tolerated by robotic arms. As a result, the molding stability of skeleton materials has been elevated to a new level. Some factories have automated modifications stuck on skeleton feeding, causing dimensional fluctuations to cause excessive failure rates in robotic arm grasping. Ultimately, this is resolved by switching to stable grades and process optimization. The automation wave has raised the tolerance requirements for plastic parts by a notch, and the material side must keep up.
Skeleton marking management is also worth mentioning. There are many relay models, and the skeleton must have model markings and be made together during injection molding. The clarity of the labels affects downstream assembly efficiency, and the height and depth of the text are all carefully considered. Maintenance cycles for mold fonts must be included in the maintenance plan, and worn letters cause frequent shutdowns on the production line. Even a single line of text is behind the efficiency account.
's final advice for relay manufacturers: When evaluating skeleton materials, prioritize molding stability first, dielectric data second, and price third. Materials with unstable molding won't withstand the test of automated production lines no matter how good the dielectric is. If the order is right, the selection process will be faster.
Conclusion
Relay skeleton material selection, the judgment chain is:
First determine coil temperature rise and insulation grade→ then set creepage distance and CTI →, then decide on thin-walled and insert forming schemes→ finally decide on materials.
The order is correct, the material selection step is very short; If the order is wrong, every subsequent step must pay for the previous one.
We stand between the resin plant and the injection molding plant
