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(From the archive of ”bulk solids handling", article published in Vol. 35 (2015) No. 4 , ©2015 bulk-online.com)

Fig. 1: Pipe conveyor installation (Picture: © CKit Engineering)

Pipe conveyors were initially designed by a Japanese conveyor company in the late 1970’s as an innovative solution to enclosed conveyor system solutions. In 1990 the bulk material industry received approval to freely use this technology. This allowed for large leaps in technology, making pipe conveyors a more effective way of conveying bulk material. However this did not last as pipe conveyors are perceived to be more expensive and difficult to maintain. In the following sections it will be shown that pipe conveyor solutions are not only viable but more effective then troughed belts in many respects.

Description of Mechanisms

Fig. 2: Pipe conveyor forming

Pipe conveyors are simply troughed conveyors which form an enclosed pipe. This is achieved by increasing transition idler angles and eventually six roll idler configurations on a specified diameter. The transition distance at the tail and head end of the conveyor is responsible for gradually shaping the belt. This change in shape from trough to pipe has had far reaching effects on the design and equipment used in bulk material conveyance.

Pipe Conveyors: Advantages

Fig. 3: Gantry- and Trestle-type conveyor structures

Pipe conveyors provide effective solutions for a variety of problems faced in the industry, this includes

• Spillage free transportation of material is obtained due to the enclosed belt.
• Material build-up on idlers is reduced, decreasing maintenance, as no material is spilled during transit.
• Pipe conveyors fit into narrow areas and save space in congested areas. This is possible due to a circular belt profile, allowing the gantry width to be reduced.
• Can negotiate tight horizontal and vertical curves because the material is enclosed within the pipe and cross belt slip is reduced by the idler configuration.
• Greater rate of elevation is obtained due to the increased contact between belt and material.
• Has better belt edge damage control, due to improved belt training.
• Weather resistance to wind and rain is improved as the material is enclosed, therefore gantry does not require covers.
• Ecologically/environmentally friendly as it is able to pass around sensitive areas and negotiate remote terrain.

Disadvantages

The formation of the pipe conveyor does not come without its disadvantages; however these often become negligible in light of the large improvements to that the pipe provides.

• Pipe conveyors have larger power requirements due to the large additional amount of idlers
• Larger belt widths are required to form a pipe diameter capable of conveying the same material as a troughed conveyor (considering both belts run at the same speed)
• Overloading and over-sized particles are more likely to cause problems in the system. This is because of the limited space available within the closed pipe compared to open troughs of standard systems.
• Due to the completely enclosed arrangement of the belt and idlers maintenance and removal of the belt is more difficult.

Comparison between Pipe and Troughed Conveyors

Carry Capacity

Table 1 shows the carrying capacity of pipe and conventional conveyors. This example allows for 70% fill factor and a belt speed of 4 m/s for a material density of 1000 kg/m³.From this we find that the belt width of pipe conveyors is far larger than that of conventional conveyors for the same tonnage. This must be carefully considered when choosing between pipe and troughed conveyors because of the cost of belting.

Route Layout

From the analysis in Fig. 4 we find that the pipe conveyor allows for fewer transfer points because it is capable of negotiating tighter curves and inclines. The increase in horizontal and vertical curves further increases the power requirement. Conventional conveyors will require large inclines to feed into the following transfer increasing the power requirements. From this we see that depending on the route, length and curves either pipe or conventional conveyors will be used.

Fig. 4: Pipe conveyor concept

Fig. 5: Route comparison

Power Requirements

The basic power comparison (Table 2) was carried out for a conveyor running 2000 t/h at 4 m/s. The route includes multiple horizontal curves with 5000 m radius.

We expect the power consumption of the pipe conveyor to be higher due to added idler friction and large belt mass. This does not make the troughed conveyor a better solution; it simply shows the difference in supplied power.

Structural Components

Above we noticed that to carry a similar amount of material on a pipe required a wider belt than that of conventional conveyors (Table 3). Below we see that the required belt grade/rating for pipe conveyors are lower than that of the conventional conveyor (Table 4). The tension within the belt in order to pull the belt is distributed across the belt, for this reason the rating of the belt is lower for pipe conveyors because a wider belt it used.

Idler spacing is to be kept lower for pipe conveyors in order to maintain the shape of the pipe. This drastically increases the number of idlers and brackets (Table 5), which in turn has significant effects on the cost of the conveyor.

Pipe Conveyor Theory

Pipe Conveyor Calculations

Belt Tension

Belt tension calculation for pipe conveyors is carried out in the same fashion as troughed conveyors. Two major properties of the belt to consider is what provides the tensile strength of the belt (reinforcement of a carcase) and the belt resistance to surface damage (i.e. elastomeric cover grade). Belt selection considerations include:

• The belt strength must be sufficient to transmit the power across the span of the conveyor.
• The belt carcase must be able to support the material duty, conform to the idler configuration when empty (troughability) and allow for enough flexibility to wrap around pulleys.
• The quality of the belt cover must be suitable to withstand the physical and chemical effects of the material being conveyed. This includes abrasion, temperature of material and corrosive effects.

In order to calculate the power requirements and choose a suitable belt for the conveyor; calculation of the belt tension is required. Factors to be considered are

• Friction factors of the system such as belting material and pulley construction.
• Material and belt mass per unit length.
• Conveyor profile with regards to ho­rizontal and vertical curves.
• Conveyor configuration with regards to idler spacing and pulley configuration.

Equations are formulated to calculate the effects of each of the above considerations:

where:

where:

where:

Power Requirements

The power requirements for pipe conveyors are calculated in the same manner as troughed conveyors. We find that for a straight inclined conveyor the power requirements for the troughed belt are lower than that of the pipe. The additional power is as a result of forming the belt and increased friction between the belt and idler sets. When considering curved profiles, power consumption increase as a result of changing the horizontal direction of material within the pipe.Power requirements increase with the number of transfer points; this is due to the increased power to raise the conveyor to the required height for transfer to the next conveyor. Pipe conveyors require fewer transfers as they are capable of negotiating tighter curves (smaller radius). For this reason pipe conveyors gain an advantage of lower power consumption when conventional troughed conveyors would require many transfer points.

where:s = belt speed

Conveyor Profile

Due to the enclosed pipe profile and 6 idler support configurations, pipe conveyors are capable of negotiating tighter curves, with a smaller radius. When tilting the frame on horizontal curves, material is safe within the pipe reducing spillage at these points. This also has its shortfall in that the greater change in direction causes a larger tension in the belt and power requirement of the drive.

Fig. 6: Pipe conveyor curve

Fig. 7: Pipe forming and opening equipment

A comparison of troughed and pipe conveyor routes is shown in the corresponding section above.

Idler Design and Mounting

The idler configuration maintains the shape of the belt and provides support for the belting over the profile. The bottom three idlers support the load and the top three to keep the pipe form. For this reason, idler configuration for pipe conveyors has been the subject of many discussions over the years. Major concerns are:

• Large friction between the belt and id­lers increases power demand and wear.
• Belt training to reduce pipe rotation which allowing leaks in the pipe.
• Idler and support structure alignment to ensure minimal belt wear and friction.

Fig. 8: Issues with six idlers on two sides (left) and on one side (right)

Idler configurations consist of two sets of three idlers in a hexagonal shape. Originally Idlers were all placed on one side of the support panel, this caused idler interference and belt edge wear. To ensure this does not happen, Ckit proposed the new Idler configurations which are discussed in the last section.

Fig. 9: Older idler panel design

Belt Training Procedure

Belt training is important to pipe conveyors in order to prevent belt fouling with the structure, chute work etc. This will result in permanent damage to the structure and belt. Furthermore belt alignment is used to keep the overlap in the belt at the vertical top of the pipe form. This is done to reduce spillage, as seen in Fig. 10.

Fig. 10: Belt training (a and b) and idler adjustment for belt training (c)

Belt training is to be carried out for three conditions, no-load, partial-load and full-load. Training of the belt is done by one person to reduce redundancies and duplication.The testing procedure is as follows

2. Station personnel along the length of the conveyor to monitor the pipe rotation.
4. Station personnel at the head and tail end to monitor the pipe forming
6. The belt overlap is monitored with reference to the structure , making sure it does not rotate more than 20° clockwise or anti-clockwise
8. If the belt rotation is greater than 20° belt training is required.

The procedure for belt training is as follows:

2. Training of the belt is carried out by one person to reduce redundancies and duplication of idler adjustments.
4. Training the belt requires the responsible person to rotate and position the bottom idler of the configuration.
6. Training of the belt begins at the tail end of the conveyor.
8. First adjustment is to the tail pulley, then loading and transition section, and along the carry side to the head end pulley.
10. Once at the head-end section, training follows the belt through the take-up, drive and head pulley.
12. Training is complete once the return belt has been adjusted.

Effects of Idler Support Structure Alignment

Fig. 11: Tilted idler resistance sketch

Idler support structures have a large impact on the running of pipe conveyors and can be the difference between success and failure of a project. Correct mounting of the idlers result in lower power consumption and less wear on equipment. From experiences in India of poor erection of idler support structures we find that further resistance is added through tilt resistance (T_t). This model is currently being analysed by our team in order to minimize its effects. The model is based on the prerequisites presented in Figs. 11 and 12.

Fig. 12: Tilted idler resistance calculation

As material flows through horizontal curves, we find that the change in direction of the material increases the required power. This is based on the analysis according to Fig. 13.

Fig. 13: Added tension due to curve

Ckit Contributions to Pipe Conveyors

Idler Mounting

Ckit has developed idler brackets mounting whereby one set of three idlers is on the front of the bracket and one set of three is at the back of the bracket. This reduces belt pinching between idlers which cause belt edge damage. This also reduces the interference between idlers, which often occurs when mounted on a single side.The mounting of the idlers has also been modified to decrease its mass while maintaining rigidity; this reduces the load bearing pressure on the trestles. This reduction has a major effect on the trestle and footprint design. The smaller frames allow it to be easily mounted within the triangular gantry area (Fig. 14).

Fig. 14: New light weight idler panel design

Triangular Gantry

To reduce the mass of the gantry, the cross-section was changed to a triangle, this allowed for less steelwork with the same rigidity (Fig. 15).

Fig. 15: Triangular gantry construction

Maintenance Trolley

Ckit designed and developed self-propelled maintenance trolley has been a revolutionary design for conveyor technology. It allows for maintenance personnel to easily perform inspections and maintenance on damaged idlers and related structures (Fig. 16).

Fig. 16: Maintenance trolley

The trolley is large enough to carry all equipment and spares, making maintenance quicker and therefore reducing downtime. The trolley is driven via hydraulic motors and is supplied with a power generator to carry out maintenance where required.

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