Conveyed objects are mainly divided into two groups which are box objects and bulk objects.
Types of conveyor differs depends on the types of the conveyed objects.
What is bulk object?
Bulk object suggests objects in pieces, for example sands, stones, etc.
1. About ship bottom shape
In case of conveying bulk objects, to convey them with flat belt is difficult because they have characteristic which is easily spread out. However, belts are commonly kept flat even for bulk object in case of belt conveyors used for belt feeder. Since there are difficulties in conveying objects by belt with flat shape, the belt carrying bulk objects is made to be ship bottom shape. The belts looks ＼＿／ shape in cross section.The shape of ＼＿／ is called ship bottom shape in general. Only belt conveyors with rubber belts are used for conveying bulk objects in general. Resin belts which can convey with bottom shape are also being developed. Since belt conveyor using resin belts can be made as lightweight in its frame etc., they are sometimes preferred to be used in certain location. However, resin belt is not durable and its service life is shorter compered with rubber belt. The reason can be that inflexible and thin resin belt is forced to be formed the ship bottom shape.
There are two ways to hold both of belt moving conveyor forwards and belt conveying objects.
1. To hold by rollers
2. To hold by steel plates. Belt are slid on steel plate. Also called steel plate guide.
Therefore, there are two ways as the above for making ship bottom shape. In case of holding with rollers, belt can be made as ship bottom shape by joining two or three short rollers. Similarly, in case of holding with steel plate, the plate can be bend as ship bottom shape which is ＼＿／ shape. By compering roller and steel plate, durable period of the belts is longer when belts are held with rollers. It is because belt is worn a lot when it is held with steel plate.
Parts of belt that conveying object is called carrier side. Then, parts of belt which is returning is called return side. The way of calling rollers used in each part are “carrier roller” for the carrier side and “return roller” for the return side. This way of calling is common for all other conveyors including belt conveyors.
2. About angle of ship bottom shape, Trough angle
In case of making ship bottom shape, there are three typical angles for the bottom. They are angles of ＼＿ and ＿／. These angles are called trough angles. Of course, they are symmetry and angles are equal. The ship bottom shape described in 1. above can be made by using rollers and also by using steel plates.
Then, how this trough angel can be set up?
For steel plates, the angle can be adjusted freely to any angles by bending the plates. For rollers, there are JIS standards. For belt conveyors using rubber conveyor belts with ship bottom shape, carrier rollers meeting the JIS standard are normally used except for ready-made conveyors. For the ready-made conveyors, rollers of the manufacturer’s own standard are used.
There are two ways for making the ship bottom shape with the carrier rollers, which are using two rollers and using tree rollers. Cross section of belt is ＼／ in case of two rollers and ＼＿／ in case of three. Actually, we produce ones with three rollers in most cases. Bending stress is smaller when three carrier rollers are used. Durable period of belt will be longer as well.
There are three angles for the angle of ship bottom shape, which is also called trough angle. The angles are typically set as the following and they depend on the materials to be conveyed.
1) 20 degrees, object whose specific gravity is large
2) 30 degrees, normal objects
3) 45 degrees, objects whose specific gravity is small
These angles are decided by considering effects to belts by bending and possibility of objects falling to left and right along with the moving direction.
The following picture is about black rubber belt conveyor.
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