System to improve welds

[RichardWDF]

An item I came across -- I'm curious if such blanket pre-heating techniques have already been in use, or if it could help, on other welding projects:

Railway engineers GrantRail Group Ltd., Doncaster, England, has been awarded a £486,000 ($947,804.80 US) research and development grant to develop a uniform heating system to heat rail tracks during installation and welding when tracks are being replaced. The company believes this method will improve track quality by reducing inconsistent stresses in the railway track. Inconsistent stress in rail tracks can result in buckling and rail breakages, which in severe cases will cause derailments.

GrantRail will work with Sheffield Hallam University and Inditherm, using their patented heating technology that uses conductive polymers. Operating at low voltages — generally 6 to 12 VDC or 24 to 65 VAC — a conductive polymer blanket generates uniform heat output over its entire surface area, from ambient up to 120 degrees C (250 degrees F), as it transmits heat into its surroundings. The blanket’s fabric-like qualities allow it to be fitted over almost any shape. Applications have included patient warming and heat therapy within the medical sector, critical temperature management for industrial processes, accelerated concrete curing in construction, and pitch heating within sports stadia and training grounds.
(Source: The Engineer Online)

[lotechman]

In the shop I am working in we used a reistance heating power supply using nichrome wire run through ceramic chips to form blankets. The heating is conductive. It is OK but easily shorted out if something touches the metal.
We have tried inductive heating using a Miller inverter power supply. The cable we use I find interesting. It is the size of a regular welding cable but really is a relatively small conductor in a water hose carrying coolant. Heating round objects is a mater of simply wrapping it around.
I am amazed at it effectiveness when heating flat surfaces. The rate of heating is much faster than conductive blankets.
I am wondering about effectivenes if the condustive opolymer was carrying a high frequency, high voltage current in order to heat by induction.
The cost of energy is becoming a concern as price rises.

[kbnit]

We use drum heaters. They're commercially available (McMaster-Carr), and relatively cheap. They're a silicone blanket with an electric heater inside, and a varistat to control the temperature. They come with velcro straps, so you can just fit them around the part you're working on, or lay them over a flat part. Since they're relatively still and think, they're not very conformal to intricate geometry. Since they're available in sizes to fit a small 5 gallon pail all the way up to a 55 gallon drum, and temps up to over 200 degrees F, they're a pretty good option for preheating.

[Joshfromsaltlake]

Uh huh.......

120C isn't sufficient for post weld heating and certainly not sufficient for stress relief. (Of course, the people who authorized the grant don't know that.)

Typical postweld heating procedures call for holding at a temperature of 250-300 C for several hours. Stress relieving is typically done in the range of 630-700C.

A ceramic fiber quilt with nichrome wires sewn into it, would be much more logical.

[Joker11]

the way they do it here in arizona is to pour diesel all over the track, they get it burning and heat the rail. Then they weld it. I have seem em do it a bunch. the problem with welded track here is that if the track was not heated prior to welding, and then summer comes, along with 120 degree weather, the track expands, pops the track out of the tie spikes and then the train derails. now they are using concrete spikes. they don't seem to give like wood and i am not sure they have it perfected yet. especially by the number of ties they replace.

[Joker11]

I said concrete spikes by mistake. Should be concrete ties.

Also, there is a crew that runs across and cuts out sections of track in the summer and then replaces sections in winter. That is the craziest thing I have heard. instead of expansion joints, they prefer to do the cut and weld deal. smoother track, no clickity clack. more money.

[DavidSim]

>>I said concrete spikes by mistake. Should be concrete ties<<

This past week I actually went on the GO Train here in the Toronto area with my wife, while we were standing on the platform waiting for the train to arrive I noticed that the ties were all concrete too (at least in the station area.

I guess they have perfected the use of concrete ties, but I would have thought they would crack over time (or when the weather gets really cold like it does here in the winter).

Regards to all.

[shortfuse]

As sort of a side note, if all the railroads start going to concrete ties, then in several years wooden ties will be a thing of the past....as will the retaining walls we build with the old, used ties...can't cut a concrete tie with a chain saw