No. 625 /12
Ref C25/12
Date: 17 August 2012
To: All Branches
Dear Colleagues,
Lightweight Delivery Trolley (LWT) - Handle Unclipping Issue
A CWU Safety Representative has identified an issue encountered at Huddersfield DO
in connection with difficulty unclipping of the LWT handle on some units. An example LWT with the 'stiff to open' problem concerned was supplied from Huddersfield DO to Royal Mail Central Engineering at Swindon along with another unit not presenting the same problem. The asset number of the sample LWT supplied with the problem was 390 00009465 09 and the asset number of the sample LWT that did not display the 'stiff to open' problem was 390 00016046 10.
An Engineering Review was carried out whereby the component parts - the Handle Outer Mouldings and the Clip Mouldings were examined along with the force required to separate them or unclip them and comparisons made with the original checks undertaken during acceptance testing and the acceptance criteria.
The force required to unclip the example problematic trolley along with a trolley from a later production batch were assessed to determine if the force to unclip still meet the acceptance criteria. The testing determined that the average force required to unclip the problem LWT did not now meet the acceptance criteria.
The clip moulding was removed from the Huddersfield sample and placed in a beaker of hot water (circa mid 90 degrees centigrade) for 10 minutes and then refitted to the LWT, the force to unclip was then retested and it was well within the acceptance criteria.
The clip moulding and the outer handle moulding are both injection moulded parts whose features are determined by the mould tool used to manufacture them.
Over time the mould tool may become worn, so affecting the features but this typically manifests after manufacturing in the 100,000s and at this stage we are below 50,000 LWT units produced.
The asset numbers for the sample from Huddersfield indicating that it was produced in 2009 or very early 2010 with non problematic sample being from a 2011 production run. All trolleys have been stored with the pull handle in the clipped position for a significant period of time. The material that the clip moulding is manufactured form is an unreinforced polyamide (nylon) which will exhibit age hardening, a thermo reversible process. The immersion of the clip in hot water reverses the age hardening.
In normal use the process of clipping and unclipping the handle prevents the clip moulding from hardening in a shape that locks it firmly to the handle outer
moulding.
Royal Mail Central Engineering Recommendations
1. Light Weight Trolleys identified as being "stiff" to open should initially be subjected to a series of unclipping and clipping activities.
2. Light Weight Trolleys that continue to be "stiff" should have the clip moulding removed and immersed in hot water (between 90 and 100 degrees centigrade)
for 10 minutes, to thermo reverse the age hardening. If this is required Engineering will produce an instruction sheet.
3. The User Instructions should be reviewed and an appropriate additional process for managing the unclipping of "stiff" to open trolleys included.
This information is being circulated in order to assist Delivery Office Units deploying New Delivery Methods in case this problem is experienced.
It has also been recommended that the process of storage and distribution be investigated in order that the oldest LWT units are distributed from storage to
DOs first (first in - first out process) as the "new" trolleys supplied to Huddersfield were manufactured nearly three years ago.
Attachment: Light Weight Delivery Trolley Huddersfield Delivery Office - Handle Unclipping Issue Report & Recommendations.
Our thanks to Mick Gledhill ASR for raising this issue.
Yours sincerely
Dave Joyce
National Health, Safety & Environment Officer
