CV554/CV555Rope Switch Replacement

Paraburdoo

Presenter: Phil RohrlachLast Edited : 10 April 2007

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

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.

Single sided Rope Switch

Existing Rope Switch

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.

Effect of Temperature dataEffect of Temperature on Rope Pull Cable and Switch

99.960

99.965

99.970

99.975

99.980

99.985

99.990

99.995

100.000

100.005

100.010

100.015

100.020

100.025

100.030

100.035

100.040

100.045

100.050

100.055

100.060

100.065

1 31 61 91 121 151 181 211 241 271 301 331 361

Month

Rop

e Le

ngth

(m)

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0.011

0.012

0.013

0.014

0.015

0.016

0.017

0.018

0.019

0.020

0.021

Min Cable LengthMax Cable LengthMean Cable LengthSwitch Creep Position (-)Switch Creep Position (+)Mean Switch SetpointMin Trip ZoneMax Trip ZoneMean Switch Movement

July Aug Sept Oct Nov Dec Jan Apr MayMar JuneFeb

Eliminating ‘false’ tripping

Areas ICM have looked at include:

• Switch tolerance• Switch spring balancing• System adjustment• Eliminating Rope expansion• Switch type

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.

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)

Eliminating ‘false’ tripping cont..

3. Rope adjustment• A slotted bracket was proposed, but not used

as it still relied on seasonal maintenance.

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.

Eliminating ‘false’ tripping cont..

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.

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.

Kiepe Centre Balance Switch

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

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

Other Centre Balance Switch eg

• Siemens, Allen Bradley, NHP (all ZS 75S type)

Other Centre Balance Switch eg

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

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

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

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

Installation of Safety System

• E-stop stands• Barricades• Signs