Modern technologies for field reconditioning the concrete traverses on the perforations for mushroom head square neck bolts that have used wooden puncture coating

    Concrete traverses that have T13 or T17 standard wooden puncture coating that are still in use on 50 to 60 % of the CFR network, are subjected to dynamic stresses and to the environment (temperature variations, moisture, etc.). All these actions have unwanted effects on the traverses that may be worsened by the improper maintenance of the rail like improper and irregular filling of the orifices, mud on the ballast prisms, weakened links. Such unfavorable actions make the traverse useless over the years and it no longer insures a perfect not between the arils and traverses. The support plates become obsolete and the mushroom-head bolts display 1-2 mm gaps. Trying to wring them in is useless due to the decay of the wooden puncture coatings. The respective decayed area can lead to unwanted broadening of the rails and thus endangering the safety of the travel, imposing speed restrictions. One way to correct this is to replace the coatings with C types – STAS 9528/2-86.
    The replacements can be made on the field, by closing the rails or in RK bases. This particular technique has some execution vices because the geometric measurements of the imprints from the old coatings do not correspond with those STAS 9528/2-86 accept. The minimal accepted tearing force resistance – 6.0 tons is not met. The maximum supported is no more than 4.5 – 5 tons.
    Engineer Anton Vladescu put the basis to a technology that consists in fixing a new mushroom bolt or SB – only screwed on the upper part on M 22 into a SCN silicon mixture – sand-concrete-sulfur.
    Homogenizing the three elements after a certain formula, in normal conditions and melting the resulting mixture in a container prepare the SCN mastic. The optimal melting temperature is 117° C (circa 20 minutes) when the blend reaches a creamed milk thickness. When it reaches this stage it is poured in the orifices of the bolts that were previously cleaned from the old coating and bottom-capped with a 2cm sand cover. In 20 seconds the blend solidifies. During this time, the bolt must be insert in the metal plate orifice. The distance between the rails is made with a special device, positioned every five traverses.
    After a minimum of 15 minutes from pouring the blend, the nuts can be screwed mechanically with a force-couple of 24daNm. The minimal resistance to tearing is now 9.3 tons (when using SB bolts, custom made from B2 SB or B5 SB).
    We will say that the first experimental sectors in which this technique was used in 1973 were on the Medgidia – Tulcea route, in 1974 on the Piatra Olt-Caracal (Vaduleni) route and in 1979 on the Zorleni-Falciu (Murgeni) route – 1000 traverses at a time.
    The method was homologated in 1998 by CN CFR SA and put to use on the 600 route (Barlad - Zorleni – curves of 560 and 580 meter radius) and in 1999 on the Bucharest – Oltenita route – currently developing.
    The main advantages of this technology are given below and the technology brought CN CFR SA dozens of billions annually in savings due to the low costs. We will state two more eloquent such savings: the price of a SCN coating is 700 lei and the price of a C-type wooden coating is 5.500 lei. In addition the mean duration of a SCN reconditioned traverse is 27 years as opposed to three years of the C-type.
    The principal advantages:

  1. Increase in circulation safety – the tearing resistance of a SCN coated SB bolt is 9.3 tons as opposed to 4.5 tons for a c-type wooden device.
  2. The distance between the rails can be adjusted to fit the specifications.
  3. SB bolts can be used.
  4. The life expectancy for this kind of rigging grows from three to 27 years.
  5. The working time for reconditioning is cut to 50%.
  6. The life expectancy for a bolt increases 100% because they are no longer in contact with moisture that accelerates corrosion.
  7. The materials used are less expensive because the bottom no longer has to be insulated with bitumen-white spirt mix to prevent debris from clogging the bottom of the perforation and the cost for a SCN coating is six times less expensive than the C-type.
  8. Increase in the electrical ballast resistance
  9. The metal plate is constantly pressed upon the traverse and can be checked with a dynamometric key.
  10. Speed restrictions are eliminated.
  11. The comfort degree for passengers increases, thus insuring better services.
  12. Maintenance costs related to screwing the bolts drop visibly (30%).
  13. An ecological advantage is that trees are no longer cut to make the wooden coatings only to rot three years later and be replaced.

    14. The SCN mastic can be melted down and the bolt can be replaced easily. It is sufficient only to heat the mixture for 10 minutes and then it can be removed. On orders from CN CFR SA, the Railway Studies and Projects Institute designed a device that was made at SIRCUC Timisoara. The device automates the reconditioning the concrete traverses using this method. Details in a following issue.

    Eng. Emanoil Culda

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