The document outlines a proposal for replacing existing rope switches at the Paraburdoo conveyor to eliminate nuisance trips and ensure compliance with safety standards. It details the impact of temperature on rope length and the challenges posed by current switch tolerances, while evaluating solutions such as switch type modification and materials with lower expansion coefficients. The proposed approach includes installing Kiepe centre balance switches and necessary components without causing downtime.

1. CV554/CV555
Rope Switch Replacement
Paraburdoo
Presenter: Phil Rohrlach
Last Edited : 10 April 2007

2. Objectives
• Eliminate nuisance trips
• Ensure that the conveyor safety system
complies with Mines Safety and Inspection
Regulations 1995
• Ensure that the conveyor safety system
complies with Australian Standard AS1755
• Renew components to provide a long
maintenance free period in future

3. Nuisance Trips?
• Nuisance trips are primarily caused by ambient
temperature change, which lengthens or shortens
the steel lanyard rope.
• The temperature delta in the Pilbara is up to 45
deg C. Allowing for a steel expansion co-efficient
of 0.013m/m/deg = approx 50mm per 100 metres
• With a spring at the anchor end and an integral
spring in the switch, it means that approx 25mm
of this travel (without considering friction, rope
elasticity etc) will act on the switch.

4. Single sided Rope Switch

5. Existing Rope Switch

6. Nuisance Trips? cont..
• The current switch (ODG) has a tolerance of
about 15mm, as does the NHP Type NTW.
• The switch will trip by 25-15mm = 10mm.
• Therefore, assuming the switch is set up
perfectly, theoretically it is not possible for it not
to trip over the full temperature variation
• Even setting up the switch four times a year into
three ranges – summer, autumn/spring and
winter – may still result in false trips.

7. Effect of Temperature data
Effect of Temperature on Rope Pull Cable and Switch
100.065 0.021
100.060 0.020
100.055 0.019
100.050 0.018
100.045 0.017
100.040 0.016
100.035 0.015
100.030 0.014 Min Cable Length
100.025 0.013 Max Cable Length
Rope Length (m)
100.020 0.012 Mean Cable Length
Switch Creep Position (-)
100.015 0.011
Switch Creep Position (+)
100.010 0.010 Mean Switch Setpoint
100.005 0.009 Min Trip Zone
100.000 0.008 Max Trip Zone
Mean Switch Movement
99.995 0.007
99.990 0.006
99.985 0.005
99.980 0.004
99.975 0.003
99.970 0.002
99.965 0.001
99.960 0.000
July Aug Sept Oct Nov Dec Jan Feb Mar Apr May June
1 31 61 91 121 151 181 211 241 271 301 331 361
Month

8. Eliminating ‘false’ tripping
Areas ICM have looked at include:
• Switch tolerance
• Switch spring balancing
• System adjustment
• Eliminating Rope expansion
• Switch type

9. Eliminating ‘false’ tripping cont..
1. Switch tolerance
• Tripping on a single sided switch (where the
cable length change acts on the switch) can be
reduced by increasing the switch tolerance.
• The limitation is compliance to the AS
(maximum of 300mm lateral pullout to trip)
anywhere in the temperature range. As the
tolerance is increased, pullout distance
increases.

10. Eliminating ‘false’ tripping cont..
2. Switch spring balancing
• The theory was that if the switch end spring
was two stage to become stiffer than the
anchor end, it would resist the temperature
length change, but still allow tripping when the
rope was pulled.
• It worked, but not without exceeding the
AS1755 pullout (230 N)

11. Eliminating ‘false’ tripping cont..
3. Rope adjustment
• A slotted bracket was proposed, but not used
as it still relied on seasonal maintenance.

12. Eliminating ‘false’ tripping cont..
4. Eliminating Rope expansion
• Reducing or eliminating rope expansion is an
obvious factor to look at
• Polymers, resins, kevlars etc have very low
expansion co-efficients (say less than 0.0001
compared to 0.013 for steel) but have high
elasticity and creep (stress relaxation) when
compared to steel.
• Phillystran [modified polyester] quoted up to 7%
length variation at 10% of rated load. Their
10mm rope at 230n (AS pullout limit) would be
approx. 7% loaded.

13. Eliminating ‘false’ tripping cont..

14. Eliminating ‘false’ tripping cont..
• Creep (load relaxation) is also high at part loads.
It seems modified polymer manufacturers like to
quote their maximum load figures, good strength
to weight etc. and how good they are for guy
wires and climbing/rigging equipment.
• Almost no UV resistance of itself (“above rope in
6 mths would be powder”) without jacket.
Therefore, if the jacket is worn through in the
future, the breakages may be as frequent as the
current ‘false’ trips.

15. Eliminating ‘false’ tripping cont..
5. Switch type
• If a ‘centre balance’ type switch is used,
the rope is effectively connected at the
switch, and the expansion is taken up at
the anchor springs each end.

16. Kiepe Centre Balance Switch

17. Kiepe Centre Balance Switch
Some comments about the switch
• Inbuilt detent
• Robustly made
• IP65
• It is currently being tested on site in the
dirtiest place Ed can find

18. Other Centre Balance Switches
• There are many manufactures of centre
balance switches, but without detent. This
means as the rope moves, if there is any
resistance on one side, the switch lever
will easily move to compensate.
• Most of these manufacturers limit the rope
distance to maximum 75 metres, and
Honeywell for eg. down to 30 metres at
40°C

19. Other Centre Balance Switch eg
• Siemens, Allen Bradley, NHP (all ZS 75S
type)

20. Other Centre Balance Switch eg

21. Compliance of Kiepe Switch
• QLD Mines Department has given approvals
• Australian Standards have stated in writing that
they deem the ‘centre-balance’ switch concept
complies. The simultaneous failure of both ropes
are deemed so unlikely as to be neglible.
• The WA Mines Dept states that the relevant
Standards approval is all they require

22. AS1755 Compliance
• Switch indication
• Latching
• Reset
• Breaking/slackening of rope shall activate device
• Pullout force not to exceed 230 N along rope axis
• Pullout (midway) not to exceed 300mm distance and 70 N
• Closed fittings?
• Signs shall be every 30m
• Red rope (should not shall)
• Red actuators (shall)
• Devices signed re purpose

23. ICM Proposal
Our proposal is to:
• Supply and Install Kiepe centre balance
Switches on adaptor brackets
• Supply and Replace ropes, pigtails, anchors
and springs, adjusters etc
• Carry out the work safely without shutdowns

24. ICM Proposal cont..
• The Kiepe centre balance switch is approved by
Kiepe for use with up to 100 metres of rope each
side
• Mounting – use an adaptor bracket that bolts to
existing holes
• Installation – no shutdown will be required by
using portable E-stops at 30 metre spacing
(refer AS1755) as safety system for each 200
metre section while installing

25. Installation of Safety System
• E-stop stands
• Barricades
• Signs