结论：钢架的寿命取决于涂层完整性，而涂层最先在边角和焊缝失效

钢制车架在成本和强度上有优势，代价是必须处理腐蚀问题。而腐蚀不是均匀发生的——它总是从涂层最薄或最先破损的地方开始，然后向下蔓延。

实际观察下来，最先出问题的位置相当集中：焊缝、切割边缘、螺纹孔、弯折外侧、以及装配时被刮伤的地方。这些位置的共同点是涂层难以均匀覆盖或者容易被破坏。

腐蚀的发生机理

钢的腐蚀需要水和氧同时存在。涂层的作用是隔绝这两者。一旦涂层出现破损，破损处的钢暴露，腐蚀开始；而腐蚀产物体积膨胀，会把周边的涂层顶起，破损面积扩大，形成加速过程。

这个自加速特性意味着：早期的小破损如果不处理，会发展成大面积失效。 所以涂层的完整性比涂层的厚度更重要。

轮椅的使用环境会加速这个过程：雨水、汗液、清洁剂、沿海地区的盐分，都是电解质。护理机构使用的消毒剂也可能对涂层有侵蚀作用。

常见的防腐工艺

工艺 特点 薄弱环节
粉末喷涂 涂层较厚、外观好、成本适中 边角覆盖不均、碰撞易碎裂
电泳涂装 覆盖均匀，能进入缝隙 单独使用时耐候性有限
电泳加喷涂 兼顾覆盖与外观 成本较高
镀锌 有牺牲阳极保护作用 外观受限，成本较高
达克罗等处理 适合紧固件等小件 不适合大件

电泳的价值在于覆盖均匀性。 喷涂靠静电吸附，边角和内腔容易涂不到；电泳是浸入式，能进入缝隙和内腔。对于管件结构的车架，内腔防腐往往被忽略，而潮气会在内腔积聚。

盐雾试验的作用与局限

盐雾试验是评价防腐性能的常用手段：把样品置于盐雾环境中，定期观察腐蚀出现的时间和程度。

它的作用是比较和筛选——不同工艺、不同批次之间比较，能看出谁更好。这个用途是可靠的。

它的局限是与实际寿命的对应关系不确定。 盐雾环境与真实使用环境的腐蚀机理不完全相同，所以「盐雾多少小时」不能直接换算成「实际能用多少年」。把盐雾小时数当作寿命承诺是不恰当的。

另外，盐雾试验通常用平板试片，而实际产品有焊缝、边角、装配损伤。建议用实际产品或包含这些特征的试件做试验，结果才有代表性。

试验设计的建议

用带特征的试件。 包含焊缝、切边、螺纹孔的试件，比平板更能反映真实情况。

做划痕试验。 在涂层上划一道到基材的划痕，看腐蚀从划痕处蔓延的速度。这直接对应实际使用中涂层被刮伤的情形。

结合其他条件。 单纯盐雾之外，可以考虑循环试验（盐雾、干燥、湿热交替），更接近实际的干湿交替环境。

评价指标要明确。 是看起锈时间、锈蚀面积比例、还是划痕处的蔓延宽度，事先定好。

设计上的配合

减少积水部位。 管件要有排水孔，凹陷处要能排水。积水是腐蚀的主要促进因素。

处理内腔。 封闭管件的内腔如果无法防腐，至少要密封防止潮气进入；能做内腔处理的更好。

避免异种金属直接接触。 钢与铝、钢与碳纤维直接接触且有电解质时会形成电偶腐蚀，应当用绝缘垫片隔离。

边角倒圆。 尖锐边角的涂层厚度天然偏薄，倒圆能改善覆盖。

装配防护。 装配过程中的刮伤是涂层破损的常见来源，工装和操作规范上要注意。

售后与使用提示

说明书中可以给出简单的维护建议：定期检查涂层有无破损；发现锈点及时处理；清洁时避免使用侵蚀性清洁剂；沿海地区使用后建议清水冲洗。

「及时处理锈点」这条很实际。 早期的点状锈蚀用简单的补漆就能阻止蔓延，拖到大面积就只能更换部件了。

涂层厚度的均匀性

涂层厚度通常有规定的下限，但实际生产中厚度分布不均匀：平面处厚、边角处薄、内腔可能没有。

检测涂层厚度时，测点选择决定了数据的意义。 只在平面处测，数据好看但不反映薄弱位置；应当在边角、焊缝附近等不利位置也取点。

建议在质量控制中规定测点位置，包含至少一个不利位置，这样厚度数据才有监控价值。

与其他材料的配合

钢制车架上常有其他材料的部件：塑料护板、橡胶塞、铝制配件、织物。这些接触面是腐蚀的高发区，原因是容易积水、难以清洁、可能形成电偶。

设计时应当让这些接触面能排水、能清洁，或者用密封处理隔绝水分。实际售后中，塑料件下方的锈蚀是常见情形，因为水进去出不来。

返修与补漆

生产过程中难免出现涂层破损，需要补漆。补漆的质量通常不如原始工艺——附着力、厚度、耐候性都可能打折。

所以补漆应当有规范：什么程度的破损可以补、用什么材料、怎么处理表面、补后如何检查。大面积破损或者关键部位的破损，应当考虑返工而不是补漆。

加速试验与实际寿命的对应

盐雾试验的小时数与实际使用年限之间，没有普遍适用的换算关系。这个换算取决于实际使用环境——沿海与内陆、户外与室内、是否接触清洁剂，差别很大。

如果确实需要估算实际寿命，比较可行的做法是做对照：把同批次产品分别放在盐雾箱和真实环境中，长期跟踪，建立自己产品的对应关系。这个工作周期长，但得到的数据比套用通用换算可靠得多。

我们的做法

做盐雾相关试验时，我们建议用带焊缝和切边的试件，或者直接用产品部件，而不只用平板试片。平板试片的数据偏乐观，反映不出实际产品的薄弱位置。

同时建议明确评价指标和判定方式，并在报告中记录腐蚀出现的具体位置。位置信息对改进工艺有直接价值——是边角问题、焊缝问题，还是整体涂层厚度不足，对应的改进方向不同。

有需要可以把防腐工艺方案和结构特征发过来一起设计试验，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，标准信息见标准查询。

English version

Conclusion. Steel frames offer advantages in cost and strength at the price of having to manage corrosion. Corrosion does not occur uniformly: it begins wherever the coating is thinnest or first damaged and spreads from there. In practice the first failures concentrate in particular places, namely welds, cut edges, threaded holes, the outside of bends, and areas scratched during assembly. What these share is that coating either cannot cover them evenly or is easily damaged there.

Mechanism. Steel corrodes where water and oxygen are both present, and the coating's function is to exclude them. Once the coating is breached, exposed steel begins to corrode, and because corrosion products occupy more volume than the metal they consumed, they lift the surrounding coating, enlarging the breach and accelerating the process. That self-accelerating character means a small early breach left untreated develops into large-area failure, so coating integrity matters more than coating thickness. Wheelchair service accelerates it: rain, perspiration, cleaning agents and coastal salt all act as electrolytes, and disinfectants used in care settings may attack the coating.

Common protective processes. Powder coating gives a thick attractive layer at moderate cost but covers edges unevenly and chips on impact. Electrocoating covers evenly and penetrates crevices but has limited weathering resistance on its own. Electrocoat followed by powder combines coverage and appearance at higher cost. Zinc coating adds sacrificial protection but constrains appearance and costs more. Processes such as zinc flake coating suit fasteners and small parts rather than large assemblies.

Electrocoating is valuable for coverage uniformity. Spray processes rely on electrostatic attraction and struggle with edges and internal cavities, whereas immersion reaches crevices and interiors. For tubular frames, internal corrosion protection is often neglected while moisture accumulates inside.

Salt spray testing: use and limits. The test places samples in a salt mist environment and records when and how corrosion appears. Its reliable use is comparison and screening between processes and between batches. Its limitation is that the relationship to service life is uncertain, because salt mist and real service differ in mechanism, so a number of hours cannot be converted into years of service and should not be presented as a life claim.

Salt spray testing also commonly uses flat panels, while real products have welds, edges and assembly damage. Testing actual product or specimens incorporating those features gives results that mean something.

Designing the test. Use specimens with welds, cut edges and threaded holes rather than plain panels. Include a scribe test, scoring through the coating to the substrate and observing how far corrosion spreads from the scribe, which corresponds directly to scratches in service. Consider cyclic testing alternating salt mist, drying and humidity, which approximates real wet-dry cycling better than continuous salt mist. And define the evaluation criterion in advance, whether time to first rust, percentage of rusted area, or creep width from the scribe.

Design measures. Eliminate water traps, providing drain holes in tubes and drainage from recesses, since standing water is a principal accelerator. Address internal cavities, at minimum sealing closed tubes against moisture ingress and preferably treating them. Avoid direct contact between dissimilar metals, since steel against aluminium or carbon composite with an electrolyte present sets up galvanic corrosion, and insulating washers should separate them. Radius sharp edges, where coating is inherently thin. And protect during assembly, since scratches acquired in assembly are a common source of coating damage that fixtures and work instructions can reduce.

Service guidance. The instructions can give simple maintenance advice: inspect the coating periodically, treat rust spots promptly, avoid aggressive cleaning agents, and rinse with fresh water after use in coastal areas. Prompt treatment of rust spots is genuinely practical, since early pitting can be stopped with touch-up paint while a large affected area means replacing the component.

How we handle it. For salt spray work we suggest specimens carrying welds and cut edges, or actual product components, rather than plain panels, because panel data are optimistic and do not reveal where the real product is weak. We also suggest defining the evaluation criterion explicitly and recording where corrosion appeared, since location guides process improvement: edge coverage, weld preparation and overall coating thickness call for different responses.

Send us the protective process and structural details and we will design the test. Phone or WeChat: +86 132 4819 8029.