Mike,

A bit late in the day to respond but this may interest you. Tasman-Warajay has had some direct experience with this particular problem in the past. The answer is that the wear mechanism in soft loading / hood spoon type chutes is straight sliding abrasion in sized material, and when larger particle are contained within a range of smaller particles (in what could be still termed as free flowing material). Larger particles behaving indepenently are not suitable for this type of system, they should be contained and put on, rather than launched onto, the recieving belt.

Within a transfer system of this type material velocity is typically much higher than a conventional design and in harder materials (i.e. iron as opposed to coal) substantial increases in liner wear rates is the norm. Tasman-Warajay in conjuntion with Dr Jeffory Gates (University of Queensland Materials Performance Dept) undertook an R&D exersize at Finnican Island in Western Australia several years ago to establish the suitability of our transfer system designs in hard rock mining. The results were that they work well, but wear is a major issue. The other thing was that our real life in the field testing results were nothing like the results generated by the accepted laboratory type abrasion tests (i.e. sand and rubber wheel) which Jeff had himself participated in at various stages during his career. (Incidently the department run by Jeff speciallises in liner materials mostly in industrial applications, his personal specialty being bulk white iron castings)

The bottom line is that if you have blockage / bridging problems and this is causing production downtime then a soft-loading transfer will substantially eliminate or help overcome this problem. The down side is that while plant availability is going to increase, so are your liner costs (not a little bit but substantially).

A variety of liners were used in the experiment including Ni-hard 4, Domite, and chromium carbide overlayed plate. The surprising thing was that the various types all performed well in different locations within the transfer system and dreadfully in others. This of course adds a new dimension to the detailed design of the system as well as the expense of carrying a range of replacement items in your stores inventory. Another problem is that due to the geometry in this type of transfer it is nearly impossible to use standard off the shelf liners (More expense and long delivery lead times).

I am not trying to be negative, however I would caution you to be sure that the pain is worth the payback before you start, the first step being undertake some in the field testing. This is as simple as positioning a sample of liner material (or several types) in the material stream (possibly the trajectory from the head pulley) where you can acurately measure velocity, remove it after a measured material throughput and weigh it against its original weight. You will then be able to calculate material loss versus tonnage throughput and depending on the selected thickness, calculate liner changeout fequency and expected cost. After that it becomes a simple current costs verses expected costs and what if any resultant benefit exersize.

The other thing you should be mindful of is that the fundamental design principles of a system of this type are to gather and control the material discharging from a head pulley and then redirect it so that it loads centrally and softly onto the recieving belt at a similar velocity. This means turning the material and you need a certain amount of belt separation to do this (dependant on belt width, velocity, and relationship between the belts). In some cases there is not enough separation to do this and thats that. There are a few tricks that can be done to achieve an acceptable material flowpath in low headroom transfer applications, but after 10 years the best we have been able to achieve is about 8 feet and this is on a small belt.

Given the belt widths you mentioned, the material size and type, and the separation, my response to you if asked to provide a transfer system of the type that we specialise in would be - Sorry we cant help you. If you have been given differing advice, I would suggest that you ask to be shown one that's operating in the field.

Regards Mick

Regards Mick ■