The rope grip mystery.
I have long puzzled over the reason for the installation of two “C” shaped hooks on every bucket carrier. Fig 5.1 (Red arrow)
The reason has finally become obvious, when combining the knowledge of there being upthrust from the haulage rope as the ropeway crossed Causeway Creek and also in the middle of the longer track rope spans. The effect of this on the internal structure of the rope grip was causing failure.
The rope grip is held in the grip slide by the dovetails on either side. The grip can slide up and down within the slide and is kept in either the open or closed position by the square peg which is spring-loaded from the rear, (Fig 5.1 Red Arrow) engaging with either of the two recesses in the back of the grip.
The grip is released from the closed position by operating the handle on the top of the grip, this pushes a pin into the grip which forces the square peg back, disengaging it from the recess allowing the grip to be lifted up the slide. When the lower recess comes opposite the peg, it springs into it, trapping the grip in the upper position.
To release the grip from the upper position, the central button is pushed. This pushes the peg back, disengaging it from the recess, and allowing the grip to fall back to the closed position, whereupon the peg re-engages with the upper recess.
The grip is held in either position by the upper and lower edges of the square peg engaging with the lower edge of the upper recess, and the upper edge of the lower recess. Any wear of these four edges reduces the capacity of them to keep a positive lock in either position.
That would normally not be a problem because the forces acting on the rope grip are on the front fork (Fig 5.6) and the back fork (Fig 5.5) from the rope spider, through the dovetails into the grip slide then to the carrier frame, either pulling the carrier uphill or lowering it downhill. The “Rope Spider” is a device inserted into the strands of the haulage rope to which a sleeve on the outside of the rope is attached. This sleeve has a cone shaped front that can push under the spring loaded back fork of the grip, (Fig 5.7) and then engage with the front fork to push the carrier along. These spiders must have been very strong, strong enough to transfer enough force to the grip and then break the front off the dovetail.
The problem arises when the haulage rope is so tight that it (tries to) lift the carrier off the track rope. This effect happens on the return rope at the lowest point of the valley, the creek crossing. (Fig 5.8), and mid span on the longer spans.
When the damage to the peg and the recess edges is sufficient, the lifting force is enough to push the peg back, disengage it from the lower edge of the upper recess, and force the rope grip into the open position.
So, as the carrier approaches the next tower, the upthrust on the haulage rope becomes down thrust, and the spider slips out of the grip. The carrier then is a free agent and will roll back down the track rope to collide with the following carrier, de-roping the truck and bucket and truck crash to the ground, with the grip in the open position. See Fig 5.9
The effect of the C brackets is to absorb the upthrust of the haulage rope, and eliminate the force pushing up on the grip. Problem solved!
However, this does not explain how there are a number of carriers on the ground with grips open, and C brackets fitted. Something else is de-roping the carriers as well.
The other types of damage to the rope grips, are the breaking of the guide dovetail, either leading or trailing, indicating that a large sudden force was applied to the frame of the carrier, enough for the shock to be transmitted through the spider into the fork of the grip, breaking the dovetail.
A: A leading slide edge broken would indicate that the carrier had been struck from the front, by a runaway carrier traveling backwards downslope. This can happen to a carrier traveling uphill on the outbound rope or the inbound rope. In this case there should be two carriers and buckets at the same site; sometimes more, as it happened more than once. Additional damage can be caused to the wheel truck, as the bucket and carrier are swung away when hit, allowing the trucks to crash together, smashing the truck casting across the hole that supports the wheel bolt. Fig 5.11 and Fig 5.12. The back of the striking truck and the front of the struck truck can be smashed.
B: That the bucket had fouled the tower cross member, or a haulage rope wheel. There are several smashed haul rope wheels across the valley plus some that have been repaired or replaced by standard incline rope rollers. This can happen anywhere and is indicated by the rear carrier arm being severely bent back right at the hook. (Red arrow Fig 5.10)
When the breaking of the leading edge of the grip is caused by the bucket fouling the haul rope crossbar, or the haul rope wheel, the carrier is effectively stopped dead, but the haul rope continues pulling, enough to break the guide.
Our theory for how this can happen, is as follows: –
As a truck crosses over a saddle, the downward force of the haul rope forces it to follow the radius of the saddle plus the rope diameter. (approx. 364+33= 397 mm) for a #1 saddle. If, at the speed the truck is traveling, the natural fall of the bucket on the exit side of the saddle is less than that of the truck, the front pin of the bucket will lift out of the hook at the bottom of the carrier leg. More often than not it will fall back in again as the bucket accelerates downward, and no one is the wiser, but if it doesn’t, trouble follows at the next tower.
An objection to this theory is the presence of the locking fork at the front of every bucket. (Red arrow Fig 5.14). This fork engages with the leg of the carrier to prevent it rotating and discharging its load, until it is manually lifted, so that the bucket can be unloaded. If the peg on the bucket is lifted as the truck passes over a saddle, this fork would act to hold the bucket in alignment until the peg could fall back into the hook. There would need to be some lateral force to displace the peg so that it doesn’t re-engage with the hook, or if the fork was not fully engaged with the leg or was tight and stayed in the disengaged position once it was lifted by the lip of the bucket, its guiding influence would not happen.
An additional measure was adopted to deal with these unintentional disconnects with the haul rope spiders, and that was this simple bracket (Fig 5.13) It has a serious disadvantage in that it could not be put in place until the spider had been engaged in the grip, and the carrier was then moving at 2M/sec. The miner would have to run alongside and clip it on. Tricky!
This bracket (Fig 5.13) hooked under the haulage rope and over the top of the release handle of the grip, guaranteeing that the rope stayed engaged with the grip, whether it was locked down or not.
THE SPIDERS OR ROPE KNOTS
The only detail that I have of these is from a publication called “Aerial or Wire Rope Tramways – Their Construction and Management” by A. J Wallis-Tayler C.E. printed in 1898.
The knots were a cast sleeve slid along the rope to the required position, then kept in place by whitemetal being poured into a cavity formed by driving a tapered pin through the knot, and removal of the hemp rope core. Fig 5.15. However, the wear marks on the restored grip do not indicate that such a knot was used at Katoomba. They had to have a tapered leading edge to push the rear spring-loaded grip fork up allowing it into the grip. The rigid front fork then does all the work transferring the load through the grip, through the grip slide to the carrier cross arm. My proposal is that a spider was used that was inserted in between the rope strands, and the internal taper in the knot was pulled up against it then maybe a tapered pin driven through to hold it in place. More research is being done on this question.
This must have been a very laborious process, because every knot had to be slid along the length of the rope to its position. I think as a practical solution, with a length of rope weighing 9 tons, that the rope would have been installed in shorter lengths and spliced together.
THE TENSION PIT
Two Archaeological studies have been done on the Tension Pit, the last in September of 2017, from which a report was prepared by Fiona Leslie of Niche Environment and Heritage.
A large number of items were excavated, recorded and re-buried. The hoped for finding of the tension weights in the bottom of the pit did not eventuate, apparently, they had been recovered for their lead content. However, from the size of the weight cradles, and from calculations of the weight necessary to provide the correct tension, we should be able to estimate the number of weights used.
The pit is 31 feet long 6 feet wide and 9 feet 3 inches deep. The gauge of the ropeway was 6’7¾” or 2025 mm. The pit contained 4 tension weight cradles, suspended on chains, which passed over four chain profile wheels. (Fig 5.17 – Red Arrow) and 5.18)
The enormous length of the hold down bolt shows how big the timbers were that the tension pit supports were made from.
Over the top of the pit was erected a timber frame which supported the transfer rails for the trucks to run on, (Fig 5.19 – Red Arrow) once they had come off the ropes, and the four chain wheels. The top edge of the pit was lined with timber to try to control soil from falling into the pit. The rest of the pit was unlined, the whole pit being dug into a talus slope, the walls consist of fractured sandstone.
The Transfer rails were not horizontal as they were at Gladstone, but sloping up to the North, to allow for the haul rope angle.
In the pit were 4 cradles tensioning the ends of four track ropes, two inbound 33mm dia. 13/12/6/1 and two outbound 25mm dia. 12/6/1.
The two ropes coming from the top of the cliff, where the unloading station was located, only needed a small amount of tension weight, as their job was to keep sufficient tension in the lower spans between towers, to keep the buckets from fouling the ground, and to maintain the correct angle of entry for the ropes into the transfer rails. The two cradles for the inbound and outbound ropes coming from the mine had to carry sufficient weight to equal and slightly exceed the horizontal load of the ropes for the entire distance to the bottom of the valley at the creek crossing.
The largest, about three and a half tonnes, (140x½ cwt weights ) would be the inbound rope, and its cradle would be the Northernmost in the pit. Next at about 2.1 tonnes would be the outbound rope to the mine.
At the Southern end of the pit, the inbound rope to the clifftop, would need 1 ton, and the next inline, the outbound rope from the clifftop would only need ½ ton.
One hundred and forty ½ cwt weights would make 2 ½ layers in a box 5’ square and would only need to be 18” deep.
The tension pit at Gladstone was 12 feet deep, but the Katoomba pit was shallower, at 2.8M or 9’ 3”. The Gladstone pit was in the middle of a long horizontal series of towers, whereas the Katoomba pit is in the middle of a long downslope, and the extra height at the Northern end keeps to a minimum the required vertical travel of the tension weights. As a bucket passes between towers on a horizontal rope the tension increase at centre span is much larger than that on an inclined rope, and the amount of rope that needed to be paid out into the span to maintain the minimum tension is much greater.
However, the Katoomba System was very unusual. At the Northern or unloading end, the inbound and outbound track ropes were securely anchored using these anchor bolts Fig 5.20 and 5.21.
The siting of the tension station was governed by the breaking strain of the track ropes, having to maintain the safety factor of 2:1. The tension in the track rope at the top of the cliff due to the weight of the length of rope hanging down the slope and the weights in the pit cannot exceed this value of 50% of the breaking strain of each rope. A 251 metre fall in 860 metres.
So, Schulze was forced to site the tension station about half-way to the creek from the top of the cliff. This created a huge problem as to what to do with the rest of the distance. He only had one tension station to re-use from Gladstone. Ideally, he should have put in another tension station where the ropeway crossed the creek, but he just had to “fudge” it. The two track ropes were anchored at the mine end, reached all the way to the creek, approx. 1,660 metres, with a fall of 271 metres, then uphill to the tension station a further 780 metres with a rise of 193 metres. All he could do was to let the tension weights for these ropes sit on the bottom of the pit with just enough weight to balance the downslope pull to the creek and a little bit more, just in case there was some disaster, such as a tree falling across the line, so that any damage wouldn’t be terminal. The Southern end just had to look after itself, and any excess sag that developed from expansion or rope stretch would just result in a bigger sag over the creek.
This then created a haulage rope problem at the creek crossing, about which, more later.
Recovered items from the Tension Pit.
From one of the four wooden boxes that held the tension weights, we have recovered the following: –
1: T4 – A piece of wood 16” x 8” x 1 ½” identified by John T Ford (BSc, MA) as Eucalyptus sp. – grey ironbark group
83 x 4” nails
1 Rope grip- no front plate – handle prised open
2 Square headed coach screws 4” and 6”
1 nail 5”
1 piece of 2mm wire 8”
1 bent 3/8” rod bent.
2: T2 – 47 x 4” nails 4 pieces of wood enclosing nails