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WEIGH FEEDER FK

UNIQUE BELT DRIVE Weigh belt feeder with a unique design giving minimal belt tension over the weighing zone producing accurate weighing from 5 to 20,000 kg/h. Sideways movement of the belt is locked, preventing errors due to build up of material.

MODULAR CONSTRUCTION Modular construction of the stand, conveyor frame and enclosure, gives optional feed to the left or right, in painted or stainless steel, with or without enclosure.

SERVICE FRIENDLY The conveyor frame extends sideways on runners to enable easy service and maintenance. The enclosure has few recesses and crevices. Two belt scrapers are fitted at the output end of the belt.

WEIGH FEEDER TYPE FK

PRINCIPAL DESIGN OF THE WEIGH FEEDER The upper side of the weigh belt feeder is divided into three zones. See figure below. One loading zone, which in most applications is provided with a hopper. Below this zone a load plate is situated. The next zone is the weighing area under which a weighing plate is situated. The third zone is the feed out part at the end of the belt.

LOADING AREA

LOAD PLATE

WEIGHING AREA

TRACTOR DRIVE

FEED OUT

WEIGHING PLATE

The belt is provided with series of holes along the sides. Between the loading and weighing zones are toothed drive wheels. These teeth drive both the upper and return strands of the belt. Because the belt is driven by both the upper and return strand it is prevented from sideways travel.

The material is drawn out from the hopper and is delivered over the weighing zone where the belt tension is negligible. The roller at the output end is spring mounted to give a small controlled belt tension. DESCRIPTION OF CONSTRUCTION The construction of the weigh feeder consists of two main parts, the conveyer and the stand. The conveyor has a frame with two transverse tubes, which slide on shafts attached to the frame of the stand. Also on the stand is the drive gear. The toothed wheels are driven from the inner side via a joint coupling, making the conveyor frame easily withdrawn for cleaning. Along the belt sides are adjustable side skirts. At the drive wheels are devices for pressing the belt against the driving teeth. The side skirts are removed sideways if the belt requires replacing. Belt scrapers for both sides of the belt are situated at the out put end. These are V shaped and placed in front of each other. The lower one is part of a cradle construction formed as a weight loaded tilt (collecting) plate from which the waste falls at the output end. Before the belt is removed the complete scraper device is easily lifted off its pivots and removed. Also the waste from the inside of the belt is discharged onto the tilted collecting plate.

Brackets pressing on the upper and return strands of the belt Toothed drive wheels

Weigh plate

Fine adjustment (vertical) of the load plate

Side skirts attached to the frame

Drive shaft bearings corrosion protected

Roller suspended with parallel springs giving frictionless movement

Load plate

Belt tension adjuster

Load cell measuring the load on the weigh plate

Belt scrapers for both sides of belt

Counter weight

FRONT VIEW

Extension arms (used for maintenance)

Support bracket

Gate valve Hopper

Connection box

Side skirt (shown in maintenance position)

Frame unit shown in withdrawn maintenance position

Loading point Drive

pivots for the belt scraper

Drive shaft coupling

CONSTRUCTION

APPLICATIONS FEEDING OUT FROM BINS AND GRAVIMETRIC DOSING The weigh belt feeder is intended for feed out and dosing of bulk materials such as powder and granulates. See Fig. 1. The material is drawn out from a bin situated above the weigh feeder and the feed rate is controlled by changing the belt speed. By using different software in the instrumentation a constant feed rate - or ratio control could be obtained.

SYSTEM T 2

MEASURING THROUGHPUT SYSTEM T 2

A third application area is as a conveyor belt scale. See Fig. 3. In this case no control of the flow rate is actual, the instrument indicates the flow rate and totals the amount of material conveyed, the belt speed is mainly constant.

SYSTEM T 2

CONTROLLED MASS FLOW AND GRAVIMETRIC Material which can not be drawn out from a bin or are fluidising, are usually fed onto the belt by a screw or vane feeder. See Fig. 2. The dosing is achieved by controlling the speed of revolution of the feeder shaft, which is controlled by the weigh feeder instrumentation. Thereby the same control is achieved as above.

THEORY

BELT TENSION WITH A CONVENTIONAL FEEDER

BELT TENSION - THE PRINCIPAL PROBLEM WHEN WEIGHING WITH BELT CONVEYORS When the rollers at the weighing area are not exactly aligned, the load sensed is influenced by the belt tension. If the central roller [see Figure below] is below the surrounding rollers, the belt tension S and the material/belt load P causes a lifting force p. The roller load sensed becomes P p and thus smaller then the real value. Usually the belt tension S must be about ten times the load P to avoid belt slip, making alignment of the rollers critical. p

S

S.E.G INSTRUMENT AB

The Figure below shows that weighing is done where the belt tension is maximum at the area marked. To drive the belt the tension “So” is required. To draw the hopper material out requires an additional force Sm. The belt friction against the weighing plate gives a total Sf. Their values change from idling to full load as marked by - and +. The difference of the two states illustrates the large change of the belt tension over the weighing area. Sf+

Sm+

SfSm-

So

M

S BELT TENSION FOR THE WEIGH FEEDER TYPE FK

P-p Thus imperfect alignment , dirt on rollers and varying belt tension generally causes the dominant belt weighing errors. A low, constant belt tension is always desirable. At low belt tension [see Figure below] the belt tare weight distributes evenly on all of the rollers and the lifting force p is reduced.

S

p

The force Sm here arises between the hopper and the driving wheels making the weighing zone unaffected by this force. Besides the tension force “So” need not be bigger then the friction force Sf, because due to the tractor feed the belt cannot slip. The belt tension at the weighing zone is negligible and thus the weighing insensitive to misalignment and dirt.

Sm+

S

Sm-

S.E.G INSTRUMENT AB

M

Sf So

P-p

S-E-G INSTRUMENT AB Box 111 43 S-16111 Bromma SWEDEN

Tel: +46-8-764 74 00

Fax +46-8-764 75 00

Internet: www.s-e-g.com