结论：常温合格不代表冬天合格

塑料材料有一个共同特性：温度降低时，材料从韧性状态转向脆性状态，冲击强度明显下降。 转变发生的温度区间因材料而异，有的材料在零下十几度就明显脆化，有的要更低。

这意味着一个实际问题：产品在常温下通过了冲击或跌落测试，在冬季户外使用时仍可能开裂。 而这类失效往往发生在使用者最需要产品可靠的时候。

脆化的机理

简单说，塑料的韧性来自分子链的运动能力。温度降低时分子链运动受限，材料无法通过形变吸收能量，冲击时就直接断裂而不是变形。

几个相关的特点：

转变不是突变，而是一个区间。 在转变区间内，性能随温度快速变化。

加载速度有影响。 加载越快，表现出的脆性越明显。所以冲击比慢速加载更能暴露问题。

缺口敏感性增加。 低温下材料对缺口、尖角、划痕更敏感，应力集中处更容易起裂。

老化会使情况变差。 紫外线照射、化学侵蚀会使材料进一步脆化，老化后的低温性能比新品差。

受影响的部件

部件 后果 风险等级
脚踏板与脚踏支架 断裂，使用者足部失去支撑 高
扶手与扶手支架 断裂，影响转移安全 高
卡扣与锁定件 失效，部件意外脱开 高
轮毂盖与装饰件 破损，主要影响外观 低
控制器外壳 开裂，内部进水 中
手推圈涂层 开裂脱落 中

高风险的三类有一个共同点：它们都是承力或安全相关的部件。 这些位置用塑料时，低温性能应当验证，不能只看常温数据。

测试的做法

试样状态。 在目标低温下充分平衡，时间要足够让试样芯部也达到温度。这一步做不到位，测出来的是表层低温、内部常温的混合状态。

测试温度。 按产品的预期使用地区确定。北方冬季户外的实际温度可能比想象中低，建议留余量。

加载方式。 优先做冲击，因为冲击最能暴露脆性。可以做摆锤冲击、跌落冲击，或者整机的低温跌落。

在低温下测试还是取出后测试。 应当在低温下进行，取出后温度回升很快，几十秒就会有明显变化。

含缺口的试样。 因为低温下缺口敏感性增加，含缺口的试验更接近实际（实际部件上总有圆角、开孔、分型线）。

整机验证。 部件级测试之外，建议做整机的低温跌落或低温运行，因为装配状态下的应力分布与单件不同。

选材与设计上的应对

选材层面： 选择低温性能较好的材料类别；对关键部件考虑增韧改性的牌号；确认供应商提供的低温数据是在什么条件下测的。

设计层面： 避免尖锐内角，用足够大的圆角；避免壁厚突变；开孔位置避开受力路径；关键部件考虑增加壁厚或加强筋；以及对高风险部件考虑用金属替代。

验证层面： 关键部件做低温冲击验证；整机做低温跌落；老化后再做一次低温验证。

最后一条容易被跳过，但很重要。 新品的低温性能和老化两年后的低温性能可能差别明显，而产品的使用周期通常远超两年。

说明书上的处理

如果产品有低温使用的限制，应当在说明书中明确：

使用温度范围；低温下的注意事项；存放温度范围；以及从低温环境进入室内时的处理（可能产生冷凝水）。

但要注意：说明书的限制不能替代设计上的解决。 如果产品在当地正常的冬季温度下就不可靠，写进说明书并不解决问题——使用者仍然要在冬天用它。

低温对其他材料的影响

除了塑料件，低温还会影响产品的其他部分，测试时可以一并考虑：

电池。 低温下容量明显下降，放电能力减弱。电动轮椅在冬天的续航缩短是普遍现象，建议测量并在资料中说明。

润滑。 润滑脂在低温下变稠，转动阻力增加，手动轮椅推起来更费力。

橡胶与弹性体。 轮胎变硬，抓地力下降；密封件变硬，密封性能可能下降。

液晶显示。 低温下响应变慢甚至无法显示。

金属。 多数常用金属在这个温度范围内影响不大，但焊缝和某些牌号仍需注意。

整机的低温验证比单纯的塑料件测试更有价值，因为它反映的是产品在冬季的整体可用性。

数据怎么用在产品资料里

低温测试的数据可以用在几个地方：

说明书的使用温度范围。 基于实测而不是估计。

冬季使用的提示。 比如续航会缩短多少、需要注意什么。

面向北方市场的销售材料。 有数据支撑的低温性能是实质卖点。

设计改进的依据。 哪个部件先出问题，就改哪个。

第二项对使用者最有帮助。 明确告知冬天续航会缩短，比让使用者自己发现要好——后者容易被理解成产品质量问题。

测试温度怎么定

常被问到的问题是测试温度取多少合适。建议的考虑因素：

目标销售区域的历史低温记录。 而不是平均气温。

产品的存放场景。 户外、车库、未供暖的房间，温度可能低于室外。

运输环节。 冬季运输中产品可能经历比使用时更低的温度。

留余量。 在上述基础上再留一档余量。

按平均气温定温度是常见的偏差，因为失效恰恰发生在极端低温的那几天。

我们的做法

做低温相关测试时，我们会特别注意两点：试样的温度平衡是否充分，以及测试是否在低温环境下进行。 这两点做不到位，数据会偏乐观，而偏乐观的数据比没有数据更危险。

对于面向北方市场或者有户外使用场景的产品，我们建议把低温冲击纳入常规测试范围，并对承力的塑料件单独验证。这部分增加的成本有限，但对应的是明确的安全风险。

有需要可以把材料信息和使用地区发过来一起确定测试温度和项目，或者直接联系：132 4819 8029。检测能力见服务介绍，产品分类见手动轮椅检测与电动轮椅检测，案例见案例。

English version

Conclusion. Plastics share a common characteristic: as temperature falls, the material moves from a tough to a brittle state and impact strength drops markedly. The transition range varies by material, with some embrittling noticeably below around minus ten degrees and others requiring colder conditions. The practical consequence is that a product passing impact or drop testing at ambient may still crack when used outdoors in winter, and such failures tend to occur exactly when the user most needs the product to hold.

Mechanism. Toughness in plastics comes from the mobility of the molecular chains. As temperature falls, chain mobility is restricted, the material cannot absorb energy by deforming, and an impact breaks it rather than deforming it. Several features follow. The transition is a range rather than a step, and within it properties change rapidly with temperature. Loading rate matters, with faster loading revealing brittleness more clearly, so impact exposes the problem better than slow loading. Notch sensitivity increases, making the material more susceptible at notches, sharp corners and scratches where stress concentrates. And ageing makes matters worse, since ultraviolet exposure and chemical attack embrittle the material further, so low-temperature performance after ageing is poorer than when new.

Components affected. Footplates and footrest supports carry a high risk, since fracture leaves the user's feet unsupported. Armrests and their supports carry a high risk, since fracture affects transfer safety. Buckles and locking components carry a high risk, since failure allows parts to separate unexpectedly. Hub caps and trim carry low risk, affecting appearance. Controller housings carry moderate risk, since cracking admits water. And handrim coatings carry moderate risk through cracking and detachment. The three high-risk categories share a feature: all are load-bearing or safety-related. Where plastic is used in those positions, low-temperature performance should be verified rather than inferred from ambient data.

How to test. Condition specimens fully at the target temperature, allowing enough time for the core to reach it; done inadequately, what is measured is a cold surface over an ambient interior. Set the test temperature from the product's intended region, bearing in mind that actual winter outdoor temperatures in northern areas can be lower than expected, so leave margin. Prefer impact loading, since impact exposes brittleness best, whether by pendulum, drop impact or whole-product drop at low temperature. Test in the cold rather than after removal, since specimens warm quickly and change noticeably within tens of seconds. Include notched specimens, since notch sensitivity rises in the cold and notched tests are closer to reality, actual parts always having radii, holes and parting lines. And verify the whole product as well as components, since stress distribution in an assembly differs from that in a single part.

Material and design responses. On material: choose categories with better low-temperature performance, consider toughened grades for critical parts, and check the conditions under which supplier low-temperature data were obtained. On design: avoid sharp internal corners in favour of generous radii, avoid abrupt changes in wall thickness, keep holes off load paths, consider added thickness or ribbing on critical parts, and consider metal for high-risk components. On verification: low-temperature impact testing of critical parts, whole-product low-temperature drop, and repeat low-temperature verification after ageing. The last is easily skipped and matters, since low-temperature performance when new and after two years of ageing can differ markedly while service life is usually far longer than two years.

What to say in the instructions. Where the product has low-temperature limitations, state the operating temperature range, precautions in cold conditions, the storage temperature range, and how to handle moving from a cold environment indoors, where condensation may form. Note, though, that an instruction limitation does not substitute for a design solution. If the product is unreliable at ordinary local winter temperatures, writing it into the instructions solves nothing, because users still have to use it in winter.

How we handle it. In low-temperature testing we pay particular attention to two things: whether specimen conditioning is adequate, and whether testing takes place in the cold. Failing either produces optimistic data, and optimistic data are more dangerous than none. For products aimed at northern markets or used outdoors we suggest bringing low-temperature impact into the routine programme and verifying load-bearing plastic parts individually. The added cost is limited and the risk addressed is a clear safety one.

Send us the material information and intended region and we will set the test temperature and items. Phone or WeChat: +86 132 4819 8029.