1.Structure and Feature
1.1 The structure of Pipe conveyor
The position of the head, tail, inlet point, discharging point and pull cord switch of the pipe conveyor is basically the same as that of the ordinary belt conveyor. After the conveyor is fed in the tail transition section, it is gradually encircled into a circular tube to carry out the closed transportation of the material and transfer to the head transition section until unloading.
The pipe conveyor is suitable for the conveying density under various complex terrain conditions of less than 2500kg/m3, and its applicable working environment temperature is -25~40°C, and it can also meet the requirements of heat resistance, cold resistance, waterproof, anti-corrosion, explosion proof, flame retardant and so on. The product can be widely used in power, constructions, chemical industry, mining, metallurgy, wharf, port, coal, grain and other industries. The machine is a new belt conveyor which uses a roller arranged in a hexagonal shape to force the belt to form a circular tube to transport material. With the characteristics of closed transportation, flexible conveying line along the space curve, large conveying inclination angle and long single-machine transportation distance under complex terrain conditions, and it has the characteristics of low construction cost, convenient installation and maintenance, reliable use compared with the ordinary belt conveyors.

1.2 Conveyor Belt
The conveyor belt that can be enclosed into a tube is a special conveyor belt. According to the requirements of different tensions and the like, the conveyor belt can be in the form of a nylon belt and a steel cord belt. The choice of conveyor belt specifications should consider its maximum tension, conveying distance, use conditions and safety factor. The conveyor belt structure should have the following characteristics: 1 in order to make the conveyor belt can be rounded, it needs to have appropriate lateral rigidity to maintain good tubular and sealing; 2 belt body has good elasticity and longitudinal flexibility, so that The belt can be repeatedly subjected to severely bending and shrinkage for a long time; 3 when the tubular belt conveys the material, the belt is stretched, and the covering rubber is exposed to sunlight and wind and rain for a long time. Therefore, the outer covering rubber is required to have high heat resistance. It is resistant to UV rays, flexing and cracking, while the inner cover rubber should have excellent wear resistance.
1.3 Handling capacity（m/h³）
Belt speed(m/s) Pipe Diameter(mm)

Belt speed(m/s)	Pipe Diameter(mm)
	100	150	200	250	300	350	400	450	500	550	600	650	700	750
0.8	17	37	66	118	138
1	21	47	83	148	173	238
1.25	26	59	104	185	216	297	482	585	688
1.6	33	75	132	232	276	380	616	748	881	1060	1238	1428	1618	1808
2.0	42	94	166	296	346	472	770	950	1100	1324	1548	1785	2022	2259
2.5			208	370	432	594	964	1170	1376	1655	1935	2231	2528	2824
3.2				457	543	748	1213	1473	1734	2086	2438	2811	3185	3558
4							1540	1870	2200	3748	3096	3570	4044	4518
5.0											3870	4463	5056	5649

2. Feature and Application
(1)Forced to form a circular tube by six rollers, without the conveyor belt deviation, the pipe conveyor can realize a three-dimensional spiral bending arrangement, and a pipe conveyor can replace a transport system consisting of a number of ordinary belt conveyors, which saves civil engineering and equipment investment, also reduces the point of failure and equipment maintenance and operation costs, pipe conveyors have their own corridors and prevent the impact of rain on the materials, therefore, the use of pipe conveyors based on the trestle can no longer be built, another cost was saved.
(2) the belt is surrounded by a circular tube, which increases the friction coefficient between the material and the tape, so the conveying angle of the pipe conveyor can reach 30 degrees.
(3)The upper and lower hexagon supporting rollers of the pipe conveyor encircles the belt into a round, so the lower branch can reverse transport the materials with different branches.

3 Key points of design
3.1Selection of conveyer belt
There are two kinds of nylon fabric core and steel cord used in the conveyor belt (core layer) used in circular pipe belt conveyor. The length of lap joint on both sides of the conveyor belt is recommended as 1/2 of pipe diameter. The relationship between the belt width and the pipe diameter is B= (PI +1/2) d, and B is the width of the conveyor belt, mm; D is the pipe diameter of the pipe conveyor belt(mm).
3.2Its transmission lines can bypass the buildings, cross the rivers and highways and so on. It can be arranged in any direction in the space according to the curve, which saves the intermediate reload, and can realize a long distance complex transportation material. So pay attention to the following questions.
(1)The pipe conveyor can realize the layout of the space curve transmission line. When there are more curved sections, it is preferable to arrange the number and direction of the curved section symmetrically on both sides of the conveyor, so as to ensure that the tension of the conveyer belt is evenly distributed on its cross section and reduces the distortion.
(2)the length of the transition section of the pipe conveyor depends mainly on the allowable elongation of the conveyor belt. If the transition section is too short, the edge of the conveyor belt will produce a lot of additional stress, making it premature fatigue damage, and even tearing the edge of the conveyor belt when it is serious. If the transition section is too long, it will shorten the seal of the entire transmission line. The length of the transition section depends on the elongation of the conveyor belt and generally takes l=25d.
(3)The pipe conveyor is not suitable for the place of feeding point and unloading point in the middle. If the feeding and unloading points must be set in the middle of the conveying section, the transition section should be added to the flat shape of the conveyor belt, and the feeding device is installed at the feeding point, and the discharging point is directly discharged by the electric or manual plow discharger, and the unloading mode is divided into single side and both sides.
Pipe conveyor has been widely used in China. It is believed that under the drive of World Trade and the increasing awareness of environmental protection in all countries of the world, pipe conveyor will definitely bring high efficiency, energy saving and economic benefits for clients.