The DMM 8mm hanger and Hilti C50 Resin
The Hanger
The hanger
is produced by DMM in 1mm diameter 316 stainless steel (which is used for
marine applications). It is then formed into a double “P” shape and requires a drilled
hole of 18mm x 75mm deep. Directional loading of the hanger when placed
horizontally is: 25-30 Kn direct pull, 5OKn downward pull.
Wear
on the Hanger
Being made
of 316 stainless steel there
should be very little wear even in constant use, but should a hanger due to wear measure less than 6mm in any one plane then it should be deemed unsafe. This
should be removed by the approved method and another hanger placed in the hole.
Although these hangers have considerable strength basic rigging practices such
as back-ups, V-hangs etc. should still be used.
The Resin
The resin
that will be used to secure the DMM 8mm hanger will be the Hilti C50 resin
which is an Epoxy Acrylate resin which can be used in wet or dry conditions.
One limitation is that the resin cannot be used when the temperature on the day
of application is below -5C. The resin is contained in a double tube, the large
tube is resin the smaller is hardener, both are expelled simultaneously and
mixing occurs in the nozzle. The first 2”
of resin must be discarded as there is a chance that thorough mixing may
not have happened. It an opened tube is not used for some time then the nozzle should be removed and the
thread on the tube is cut back two turns and a clean nozzle screwed on.
(remember to discard the first 2” of
resin)
Gloves should be worn by the persons placing the hangers and using the resin
and the vapors produced should not be breathed
in if possible. Curing time varies with temperature, underground at +5C it is
about four hours but may be longer therefore 24 hours curing time should be
left between placement and use.
The resin is flammable, keep cartridges away from
naked flames (eg. carbide (amps), sparks or direct sunlight. in the event of
fire use a dry extinguisher.
The
Fixing procedure
A)
1.
An 18x75mm hole is drilled in sound rock (a 10mm pilot hole will help to
conserve battery power), the bottom edge of the hole should be spoiled to
except the curve on the hanger. This can be achieved with the drill bit at the
commencement of drilling or with a hammer and chisel after drilling. It is
advised that the four or five holes are drilled first, this will use up one
tube of resin otherwise the resin may cure in the applicator while the next
hole is being drilled.
2.
Excess dust is removed with either a hand-held puffer or the mouth and tube
method.
3.
A small bottle brush is used to remove any remaining dust (this is important in
wet situations where cementing of dust particles occurs which are then
difficult to remove).
4.
Again remove this dust by puffer or by blowing.
5.
The drilled hole should be filled with Hilti C50 resin to about ¾ full, in
tight awkward areas a tube can be fitted to the end of the nozzle.
6.
The DMM hanger is then inserted into the hole with the elongated loop pointing
downwards.
7.
Hangers are to be placed at least 200mm apart eg. V-hangs. On through trip
routes the hangers should be placed about 200mm apart with an angle of 45
degrees between them so that the rope can be threaded through both hangers.
8.
Leave to cure for 24 hours, a label can be placed in well used caves to avoid
premature use.
Roof
and steeply inclined hangs
Follow steps 1-4 as before.
5.
The small dish supplied with the resin should be placed on the applicator, this
should stop any drops of resin coming into contact with the skin.
6.
Using a chisel separate the free end of the hanger slightly.
7.
A small piece of hard plastic is placed around the hanger, this will ensure
that the resin is retained in the hole when the hanger is inserted. The hanger
will have to be held in position until the resin has started to cure (C. 5-10 minutes)
8.
Leave for 24 hours to cure
Safety
DMM
suggest checking for the following indications at potential failure before use:
1.
Reduction in thickness to 6mm in any plane.
2. The surface of the resin breaking away from the rock (indicating possible
internal fracture of the resin or a poor resin bond).
3.
Fracturing of the rock within 200mm of
the hanger
4.
Looseness of the hanger in the rock.
Anchor
siting
It is
suggested that two people experienced in
rigging discuss 1*-following points
before fixing the hangers.
1.
Anchor sites be suitable for SRT,
ladder and pull-through trips.
2. Two resin
anchors for:-
a)
b) Start of traverse if no adequate back up.
c) Rebelays if less than 6m from the pitch head.
3. Anchors should
give a free hang, check for rope rub by holding a krab or maillon just clear of the wall with rope attached. Consider
methods of linking hangers.
4. Anchors need to be reasonably high, this
allows the main belay knot, shared hagers, traverse lines, attachment to belay
device or pulley to be shoulder high. This will minimise fall factors for
anyone fastened on, facilitate SRT rescue and access to and from the head of
the pitch.
5.
Resin anchors need to be at least 200mm (8”) apart to avoid overlapping stress
cones in the rock.
6.
Existing 8mm SD anchors can be left in if they do not compromise the optimum
siting and are not too close to the resin anchors. If the old 8mm SD anchors
are within 150mm (6”) of the resin anchor they are best removed, the hole can
be enlarged to take the resin anchor.
Removal
of the 0MM 8mm hanger
1. Using a 5mm drill bit, drill the resin on
either side of the stainless steel hanger.
2. Place a
bar through the hanger, then rotate the bar and pull the hanger from the rock.
3. Using
an 18mm drill bit drill out the remaining resin from the hole.
4. Blow the
waste resin out of the hole then follow steps 5-8 for the fixing procedure.
Reproduced
with permission of: Les Sykes and P
Ramsden.
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