Melt burn

In mountain sports and industrial climbing , melt burn refers to the melting of rope or sling material through a rope running over it under load (for example by lowering it over a sling ).

Situations in which other parts of the rope are constantly rubbing against each other, for example when the rope crosses, or the desired friction with the HMS belay system are not critical , since the resulting frictional heat is quickly dissipated along the continuing rope . It becomes dangerous if one rope always runs over the same place on the other rope or loop and the heat is concentrated there.

Physical explanation

The fibers of the ropes and loops made of polyamide (PA 6.6, trade name nylon ) have a melting temperature of around 260 ° C, which is reached quickly.

The frictional energy converted into heat is calculated (with constant material and constant pressure force) as the product of the rope length running through , the pressure force ( normal force ) and the coefficient of sliding friction : ${\displaystyle \mathbf {S} \,}$ ${\displaystyle \mathbf {F} _{\mathrm {n} }\,}$ ${\displaystyle \mu _{\mathrm {k} }\,}$

${\displaystyle E_{th}=\mathbf {S} \cdot \mu _{\mathrm {k} }\ \cdot \mathbf {F} _{\mathrm {n} }}$.

The pressing force is largely determined by the load hanging on the rope. The speed of the rope run determines the length of the rope in a unit of time ; the time, for its part, how much of the heat energy that has arisen is transported away through heat conduction and rope movement, or how much the temperature in the stationary tissue increases. ${\displaystyle \mathbf {F} _{\mathrm {n} }\,}$ ${\displaystyle \mathbf {S} \,}$

Experiments

Practical tests with the lowering of a load of 80 kg have shown that a 5 mm thick accessory cord sling has melted after a 9 mm rope has passed through a meter, a 10 mm thick sling after about five meters with an 11.5 mm thick rope .

After the lowering process, the loop has a flaw the thickness of the moving rope, the missing material has melted along the rope.

Individual evidence

1. ↑ Pit Schubert : Safety and Risk in Rock and Ice, Volume III: Everything is possible, but really everything. - Bergverlag Rother, Munich, 3rd edition 2013, p. 100, ISBN 978-3-7633-6031-4
2. ↑ Chris Semmel: Climbing - Safety and Equipment. Alpine curriculum 5th - BLV-Verlag, Munich, 3rd revised edition, 2013, ISBN 978-3-8354-1120-3
3. ↑ Kern GmbH: Polyamid 66 (PA 66) , accessed February 25, 2016 [1]
4. ↑ Pit Schubert: Lowering is not abseiling - to burn off the melt when abseiling. In: Berg & Steigen, No. 2/2000, pp. 26–28 ( PDF )