My solitary experience of belt slitting involved a multi blade scraper receiving a Scandura (knicker elastic) belt which had 'W'd on the brow and emerged from the pulley nips at just the right place for a nice rip. There was no way the scraper was at fault and sabotage was suspected in view of the proximity of the event to the 1985 Miner's Strike in the UK. Several locals were grateful for the chance to pave their garage floors with scrap conveyor belt so all was not lost.

Although anti-rip tackle is automatically considered every time somebody calls for a long belt I have background doubts about the effectiveness. Induction coils embedded in the bottom cover are sat in a wear zone and by a corollary of accurate life cycle costing must eventually be exposed to normal wear which will, should, result in frequent stoppages when exposed coil wires get to the surface. If they work at all it means that your belt is already ripped. Granted the damage limitation helps.

A more frequent scource of damage is excessive misalignment. If the misalignment switches operate regularly then the cause of the trouble is investigated and corrected. There is a valid argument that if training idlers are fitted then there should be no need for misalignment switches. Surely they (switches) would never work in anger. Ho Ho Ho!

For both misalignment and belt riip, prevention is better than cure. Prevention is rather more important in the case of belt rip and makes the fitting of side covers quite plausible. ■

There has been many posts on rip detection devices. I once wrote a paper many moons ago on a the range and effectiveness on the systems available and there was an underlying theme;

> all require a high level of maintenance to ensure they are in working order

> none were effective in all situations

> all required a rip to happen before they reacted so you always lost some belt

> If the rip did not occur in reasonable proximity to where the rip detection system was installed you lost even more belt (very applicable if the rip was caused by an end disc failure of an idler or a head end scraper as most rip devices are installed near or just after the loading point as it is where most rips occurred)

Effective rip detection therefore goes to analysing the root cause not reacting to the event and this means looking at the following:

> If you have high impact and potentially high energy rocks to manage start with designing a very good transfer. Good transfer design means you don't damage the belt at the loading point.

> good quality idlers and regular idler maintenance is essential if you want to eliminate the possibility of an end disc failure

> making sure the belt tracks correctly under all circumstances elimates edge rips particularly on steel cord belts

> Selecting the correct scraper (not segmented blades) as your primary scraper and then ensuring there is a regular maintenance regime.

Rips occur because of poor design or poor housekeeping so look to yourself and your operation before you look to some device that may or may not protect your belt.

Cheers

Colin Benjamin

Gulf Conveyor Systems Pty Ltd

www.conveyorsystemstechnology.com ■

Sir,

we were experiencing the problem while conveying Limestone (size 50 to 75 mm). The cut is because of sharp edges of the limestone and probably due to compaction if the throughput is more. We have put a plate of size 600 mm x 600 mm under the belt with springs underneath and also 2 proxiimity switches. Whenever there is a cut in the centre of the belt, the stones will fall on the belt forcing the proximity switches to act and trip the belt. This solved the problem of the entire belt getting cut.

Regards,

Ravindranath B

Hyderabad, India ■

The best belt penetration detector was one I used many years ago. It involved a simple limit switch some steel eyes, and a length of fishing line.

Basically, the fishing line was anchored at one end and the other end used to hold a limit switch so that the contacts were made. The line was threaded through a series of eyes across the belt width to follow the profile of a troughed belt. This could work in a loading zone with close spaced idlers, or just after the loading zone.

Anything that penetrated the belt would go through and break the fishing line which would open the circuit and cause the conveyor to be stopped.

Very low tech, but simple and reliable. ■

Best way to stop belt rips is to design the transfer chute as if it has to convey scrap iron, swords, rails, grappling irons, roof bolts, nasty sharp things etc.

Then make sure that liner plates cannot swing into the belt when bolt heads are worn off

Cheers

LSL Tekpro ■

Yes Mr Spriggs I agree with you,

Liner plates are one of the major belt slaughters. An incident once happened when the belt was fully loaded with magnetite. A significant length of the belt was cut right through in the middle by a liner plate which fell from the discharge chute. The company lost a lot of money due to the down time, let alone the cost to rectify the problem.

Yes Mr Benjamin you are right good house keeping (regularly inspections and maintenance) can save you a lot of money.

Bonginkosi Benjamin Sokawukile

BBSok… ■