Why do rail grinder trains work at night?

Why the track has to be closed

• Flying swarf and sparks. Grinding removes metal as hot chips and dust. The extraction system on a 12-head unit moves around 5000 m³/h of air, but nothing is allowed to reach a live track or a passenger environment.
• No tolerance for a stopped machine. A grinding train works at 7-12 km/h and cannot get out of the way. Once the sequence of passes has started, the possession has to run to completion or the profile is left part-ground.
• Electrical isolation. Overhead line equipment is switched off and earthed before anyone works near the rail head, which on an electrified route means no traffic at all.
• Surface temperature control. Acceptance requires the ground surface to sit below 130 °C within 30 s. A cool, stable night environment makes that easier to hold than a hot afternoon of continuous traffic.

Where the machine cannot get a window at all, the industry uses different equipment. High-speed passive grinding cars work at 60-80 km/h and do not need the line closed, and portable grinders are used for turnouts and spot defects. The trade-offs are set out in portable rail grinder versus full-size grinding train.

What actually fits into a night possession

Inside a metro or urban system the window is tighter still, and internal-combustion machines are restricted or prohibited in tunnels, enclosed stations and elevated sections. That is why battery-powered units have become the default for urban rail grinding work.

What it costs the operator

Because the window is short, the productivity figure that matters is pass-kilometres per possession, not metres per hour. A stone that stops cutting part-way through the sequence wastes the whole window, and a stone that has to be changed mid-possession wastes time that cannot be recovered. That is why wheel life is specified as a hard number — for the GMC-96B class the requirement is a stone life of not less than 50 km under Q/CR 1-2014, verified by a burst test at 5700 rpm for 30 seconds, a static balance coefficient of 0.4 and a contact pressure of at least 10 kN.

At Liuzhou, Molaton stones consumed 20-30 mm over the campaign where imported reference stones consumed 43.5-59 mm — roughly twice the wear resistance over the same pass-kilometres, which directly reduces how many nights the job takes. On the Hefei-Wuhan high-speed line the same wheels averaged 214.22 pass-km each at 4.28 pass-km/mm against 3.27 for the reference, with no continuous blueing. The commercial side of window planning — how many nights a section needs and what it costs — is analysed in rail grinding cost per kilometre.

RailwayCare has manufactured rail grinding wheels since 2004, was the first dedicated producer in China, drafted industry standard JB/T 11431 and holds ISO 9001, ISO 45001 and CRCC certification. The products used on these night campaigns are listed under Molaton on the railway grinding wheel page.