These modern day conveyors, generally referred to environmentally friendly conveyors, have been with us in various configurations for over twenty years.
Although offering unique solutions to the everyday problems of transfer tower spillage, pipe conveyors have still to be accepted by the modern plant design engineer.
To assist in understanding the reasons for their general un-acceptance the writer has retraced the development of one of the most common alternative belt conveying options for bulk materials handling.
The system being reviewed is the pipe conveyor, which as its name suggests functions in all basic facets as a conventional belt conveyor, but after being fed and prior to being discharged the belt is formed into a tubular or pipe shape for the vast majority of its journey. (Refer Figure 1).
To develop an historical profile of the advancement of the pipe conveyor the writer analised the installation history of the Japanese Pipe Conveyor (JPC) as contained in their distribution, “Conveyors’ Information of Bridgestone TPE Co., Ltd 2001.
The first pipe conveyor concept was introduced in 1978 by JPC, who, (we were informed), proceeded to obtain Worldwide patents. The basis for the patent was the ability to form a trough belt conveyor into a pipe shape using a unique belt construction and special pipe forming idlers.
Bateman (South Africa) were the first License Partner world wide to be successful in marketing the system outside Japan. With other successful JPC Agents Internationally being Koch (Germany), Noyes (France), Nova (Italy), Dosco (UK), Simplicity (India), Krupp Robins (USA), Young Poony (Korea) and Sistemas (S America).
Worldwide there are approximately 700 pipe conveyors in operation; they have a combined length of 160km with the longest being 5 km pulley centers.
Following is a series of graphs indicating the population details of the most successful pipe conveyor supplier.
The above graphs have some significant features namely:
These findings are quite discouraging to the environmentalists searching for a solution to pollution in materials handling systems, indicating that the pipe conveyor is still not a real competitor to the conventional troughed belt conveyor.
During the period under review the pipe conveyor has been used in less than 1% of the possible applications, indicating that there is a fundamental problem with the acceptance of the pipe conveyor concept.
Considering the development of the longer pipe conveyor installations the following has been documented:
Krupp Robins of the USA have endeavoured to take the Pipe Conveyor to new levels of performance after Bridgestone took over the JPC Company in the early 1990’s. It was only at this time that efforts were made to take the conveyor towards its true potential. An extract from a paper published in Bulk Solids states:
“Jointly Bridgestone and Krupp Robins, Inc. have developed and refined the limited original technology.”
From this combined Krupp Robins / Bridgestone effort, the JPC pipe conveyor was taken over the 5km long barrier in 1994 in Venezuela. Today, numerous pipe conveyor projects of 10 km in length and more are being considered, with capacities exceeding 2 500 tph.
So what actually happened to stunt the original growth of the pipe conveyor concept and where will it go from here?
To answer this question one should continue to follow the pipe conveyor history in the late 1980’s and early 1990’s. At this time the original patents started to expire, providing the opportunity for a new group of technologists to enter the pipe conveyor market.
Unfortunately little or no efforts was made by these new entrants to change the original Technology which, as stated above, had not seen any improvements since its original inception.
Thus the impression was given that little had been done to develop the technology, with suppliers “resting on their lorals, content with royalties from completed projects and spares orders”, was in the opinion of the writer, the reason the pipe conveyor did not take up its rightful position in the belt conveyor market.
This lack of development in the pipe conveyor started to put the pipe conveyor technology beyond the economic viability of most Clients and in some cases the anticipated cost of pipe conveyors was twice that of the conventional conveyor.
The new companies entering the market tried to reverse the so-called ‘demise of the Pipe Conveyor’ however even companies such as Mitsuii, Mitsbishi, Wessehutte, Beumer and Voest Alpine have found it very difficult to remove what was considered to be a high-cost substitute for troughed belt conveyors.
Legitimate attempts to remove this stigma with the statement that “a pipe conveyor is cheaper than a belt conveyor if a transfer point can be eliminated” generally fell on deaf ears. Clients’ opinion was that once they were tied into the pipe conveyor concept, they were tied into one supplier and large spares costs for the life of the plant.
The saviour of the pipe conveyor however is not only the introduction of a new set of technologists introducing competition and new innovation, but also the growing need for an environmental clean up.
We see today that even in the developing world clients requiring international funding are being forced to consider the environmental impact of development, even for the simplest of projects. The onus now being placed on environmental impact has encouraged the newer pipe conveyor suppliers to attempt to remove the shortfalls in the original designs. Some of the improvements include:
Probably the greatest improvement in the pipe conveyor is in the panel and idler layout. The original pipe conveyor design has been reviewed in numerous articles and papers and is shown in the sketch figure 2.
This original design had 6 idlers on one side of the panel and this often resulted in the belt getting trapped between the idlers, often causing major belt damage.
Today more and more suppliers are moving to the convention of placing three idlers on either side of the panel. This approach has reduced the possibility of trapping the belt as the edge of the belt between the idlers idler roll length can be increased to cause an overlap of the roll edges, thus minimizing the opportunity for the belt to get trapped between the rolls (refer figure 3 below).
This concept, however it does have a deficiency in that a “nip” point is created between the belt and the roll requiring more stringent safety precautions being employed at the installation.
The design of the panel is also under extensive review because the present designs are generally wasteful in terms of steelwork utilization. A paper written by Ralph M Horak and published in Bulk Solids Handling October 1997 shows some of the alternative designs being considered for panel and idler support, (See sketch figure 4).
Another example of a totally innovative solution was put forward in a paper by S. Hinterholzer, F Kessler and K Grabner again published in Bulk Solids Handling November 2001, (an artists impression of the concept is shown in figure 5).
Yet another concept has also been successfully used by ConveyorKit on a number of pipe conveyors in India is shown in figure 6.
“The Uni Idler Panel”, is being developed to offer automatic idler changing without having to compress the pipe shape. (This development is specifically for future high-tension steel cord conveyor belt applications).
The review of the panel layout also resulted in a change of the belt training method employed. Early systems used spacers between the idler roll and frame to adjust the idlers. Alternatively a spring clip arrangement allowed the idler to be adjusted relative to the panel. All the idlers on the panel were able to be adjusted making accurate belt training and specifically repeatability almost impossible.
This resulted in maintenance personnel declaring many pipe conveyors to be ‘untrainable’ which served only to further damage the credibility of the pipe conveyor concept.
Today there are a number of new belt training methods being proposed. Basically the training concept is identical to that of conventional belt training methods of angling / rotating the idler across the belt.
One of the simplest methods consisting of a single, adjustable idler placed in the direction of maximum belt load, (usually on the bottom of the panel set).
Typically this concept is shown in figure 7 below and as can be seen that by simply rotating the idler in the horizontal plain the pipe belt rotates accordingly.
Another criticism of the pipe conveyor has been the greater power absorbed per ton of material conveyed. This disadvantage was primarily caused by the selection of the idler diameter and idler spacing on pipe conveyors.
Historically the idler diameters were selected in the 60 mm to 80 mm range primarily due to the congestion of the six idlers on one side of the panel. A secondary reason has been the fact that the majority of conveyors were considered to be in the low capacity / length range, with smaller idler loads.
Mr L.K. Nordell of Conveyor Dynamics Inc. presented a paper which supported by his field measurements proved that the power drawn by a conveyor is related to the idler diameter and the resulting indentation of the belt cover by the idler.
It has been proven that the power absorbed is a function of idler roll diameter, represented by the equation:
Power reduction = 1-(d1/d2)2/3 Where d1 and d2 represent the minor and major roll diameters respectively.
This is a significant finding when one considers the large number of idlers used on a pipe conveyor installation. Therefore the use of larger roll diameters (>114mm), for most installations is now commonplace.
Historically the belt selection has been considered the critical component for an installation to be deemed a success or failure. Belt selection is very difficult with many companies trying to offer what is considered to be the correct belt for the particular application.
In the development of the pipe conveyor belt construction it was identified that the belt needed what is termed longitudinal flexural rigidity, to maintain the pipe form and edge flexibility to form the overlap and subsequent sealing.
In essence this should not be too difficult to achieve however today there are very few successful suppliers of pipe conveyor belting. Coupled to this is the fact that in almost all cases these vendors import the belt into the country of use, at a prohibitive cost and often to the detriment of the project.
In conclusion the writer would like to suggest that the invention of the pipe conveyor is one of the truly great inventions in the bulk materials handling industry.
The introduction of a number of new companies offering the technology has also dramatically improved the cost effectiveness of the pipe conveyor in comparison to conventional belt conveyors and at the same time, encouraged ongoing improvements in the development of the technology.
It can now be comfortably proved that the pipe conveyor will be more cost effective, friendlier to the environment and a safer installation in comparison to almost all other conveying types.
When country specific local conveyor belt vendors come to realize the true potential of the market for pipe conveyors and start to compete with their international competitors, we will then see pipe conveyors being considered as the only option to solving materials handling problems.