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) Normal Hangs:

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 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) Main belays for abseil, pulley or belay device.

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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