维护提示 | 737NG碳刹车作动筒漏油

ryn_82 · 发表于 2020-1-2 22:11:06

分享即成长。大家好，欢迎关注阮工频道

2019年11~12月份，河北机队的737NG连续发现了3起刹车组件作动筒漏油，虽然没有造成延误，确实显得很不正常。

一、事件背景

2019年11~12月发生的三起刹车组件作动筒漏油，均为件号2-1740-1的碳刹车组件：

2019年11月18日，B1277飞机鄂尔多斯航后，发现2#刹车榖一作动筒有油迹，清洁后经长时间测试没有渗漏，后续回基地站更换刹车组件。刹车为原始装机件，使用循环：2095
2019年12月4日，B1280飞机佛山航后，发现4#刹车榖一作动筒有油迹，反复刹车测试没有发现渗漏，后续回基地站更换刹车组件。刹车为原始装机件，使用循环：2526
2019年12月26日，B1276飞机鄂尔多斯航后，发现1#刹车榖有2个作动筒有油迹，清洁后经长时间测试没有渗漏，后续回基地站更换刹车组件。刹车为原始装机件，使用循环：1430

典型的漏油照片如下，也比较容易被发现：

看了下，整个大东航737NG，2019年冬季以来，碳刹车作动筒漏油导致拆换的也比较多。

二、原因分析

关于刹车作动筒漏油问题，在之前的文章里提到过：
●737NG飞机冬季常见问题与处理
也是冬季比较常见的问题，厂家也有相应的参考资料：
1. 737NG-FTD-32-12003：Hydraulic Leakage, Messier-Bugatti-Dowty Carbon Brakes
针对的是P/N C20633000 Messier-Bugatti-Dowty (MBD) 的碳刹车：

Background

Prior to 2011, Boeing received very few reports of hydraulic leakage from the MBD carbon brake. However, in mid-2011, Boeing started receiving numerous reports of leakage. The typical number of cycles on the brakes at the time the leakage was discovered was between about 500 and 1500 cycles. Many of the leaky brakes occurred during cold weather operations.

Examination of leaky brakes suggests that the leakage is from the dynamic seal on one or more of the brake's 6 pistons. The part number of the affected seal is A37007.

Testing by MBD has indicated that the rubber compound for the piston dynamic seals may be part (or all) of the root cause of the leakage. As such, they have selected an alternate seal compound for the piston dynamic seal location.
MBD has not found any assembly technique problems in their factory that would explain the leakage, nor have they found any manufacturing anomalies with the metallic parts of the brake (such as seal groove dimensions, etc) that would contribute to leakage.
厂家开始的分析认为是热导致封圈损伤，后续发现是封圈本身的问题，最终的解决措施是推出了改进材料的封圈。
As of April 2012, MBD started receiving an alternate piston dynamic seal, manufactured by the Trelleborg seal company and they have started to supply these improved seals to operators as spare parts.
MBD started to assemble new brakes with the Trelleborg seals, starting in late April 2012. All new brakes with serial number 2489C20633 and on are equipped with the improved Trelleborg seals.
The first new airplane delivered from Boeing with the Trelleborg seals is line number 4134 which delivered in October, 2012.
The new piston dynamic seals are being sold under the same part number (A37007). As a result, operators may wish to make note of the seal manufacturer (shown on the packaging) when procuring or installing seals.
MBD has released the referenced service letter discussing the new Trelleborg seals.

2. 737NG-FTD-32-03013：Hydraulic Leakage at Adjuster Pins on Honeywell Brakes
针对的是目前737NG上使用的件号2612312-1和2612302-1的钢刹车。

Several 737-600/700/800/900 operators whose airplanes are equipped with Honeywell brakes have reported hydraulic fluid leakage at the brake pistons. Examination of the brakes in the shop revealed that the leakage was coming from the adjuster pin seals.
Honeywell attributed this leakage to two root causes:1) Corrosion pits in the nitride surface caused by the protective oxide layer wearing off.2) Seal wear caused by the harder nitride surface and/or a corrosion-roughened surface.

后面主要是改进了作动筒活塞和调节销钉。

3. ISE-32-17-19325：Hydraulic Leakage from Brake Piston End of UTAS(Goodrich) Carbon Brake

针对的是当前737NG上安装的件号2-1740和2-17402-1的碳刹车。

和咱们的情况类似，渗漏主要是由于作动筒活塞封圈损坏导致的。

CMM 32-42-27 Page10006 Fig. 1 item 175, 225 ,250：

【175】68-1510
【225】68-1573
【250】68-1524

虽然目前Goodrich认为热损伤是根本原因。但是，当前我们的标准程序是在主轮放好轮挡后，通知机组松开刹车。
结合漏油都是发生在冬季，所以，个人认为，造成封圈损坏的根本原因，应该和MBD类似，还是封圈在低温下密封性能退化的问题。

三、维护提示

刹车榖检查在AMM TASK 32-41-41-700-802：Main Landing Gear Brake Fast Check (Wheel Installed on the Airplane)
漏油允许标准为：

增压A/B液压系统，全行程“刹车-松刹车”5次，每个刹车上的总渗漏不超过1滴/分钟
缓慢踩刹车到底，刹车脚蹬保持住或设置停留刹车，每个刹车上的总渗漏不超过5滴/分钟

对于有漏油的刹车，每次放行前都必须完成上述检查。并且需要对有污染迹象的刹车进行清洁：

污染迹象包括潮湿或油腻的外观、焦渣堆积或着陆后浓烟。
CMM里使用的清洁剂：

作动筒处使用的是MIL-PRF-680 Type II or III （P-D-680）去油脂清洁剂。
Operators can delay replacement of a leaky brake to help avoid dispatch delays if the leakage is within the limits provided in AMM 32-41-41/601, "Main Landing Gear Brake Fast Check (Wheel Installed on the Airplane)."
Brakes with significant leakage should be removed as soon as possible since fluid leaking on the hot brake components can cause smoke that can be misinterpreted as a fire.
应尽快拆下渗漏的刹车组件，因为热刹车部件上的油液渗漏会导致冒烟，并可能被误认为是着火。

推荐阅读：

完