Welded. When steel is heated up, it expands. When it cools, it contracts. This is just a physical property of the material that must be accounted for. When laying CWR, it must be heated past the maximum expected temperature for the area it is being laid down in, and then spiked down. When it cools, it contracts and is under tension, so that when it expands it has room to expand in. What happens, especially with older CWR is the rail wasn’t heated hot enough when it was laid down, when the sun shines down and the temp gets hot, the rail tries to expand (length wise mostly) but doesn’t have enough room, so starts to push on itself until it bows out to the side… and you get a sun kink! Now that being said, sun kinks can and do happen in jointed rail for the same reason the rail get shot and tries to expand but can’t. However, due to the nature of extra space in the joints this is far less common. Now one thing that happens with jointed is replacing a section of CWR with jointed, and not heating the rail before inserting the new rail. This video explains perfectly a CWR repair done the wrong way:

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The solution to this is to lay an oil covered rope along the rail, light it on fire, let the rail expand then bolt the new rail in place. This can be seen here, where a CWR repair is done the right way:

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Matt F
Moscow ID