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 Purpose

    Type 4-68centrifugal fan (below calls fan) is a kind of low and middle pressure fan, it has a wide service range, flat pressure curve, facilitate to install and repair, and low in price. In the current, there are multitude of items for fan, Type 4-68 is still ”a firm rock in mainstream ” of fan, it undertakes the ventilation of general factories, warehouses, high buildings and subways etc. and often appears on the main occasion such as Beijing Subway, it can output or input gas, but the gas handled by fan must be air or other gas which is non-inflammable, non-volatile, non-explosive, non-corrosive to steel and harmless to the people, visco-material shouldn’t be contained in the gas. Dust and hard particle content in the gas is not greater than 150 mg/m3, the gas temperature shall not exceed 80℃.

Type

In normal condition, type 4-68 centrifugal fan has 13 different sizes and 18 varieties, they are 2.8A, 3.2A, 3.6A, 4A, 4.5A, 5.6A, 6A, 6C, 6D, 8C, 8D, 10C, 10D, 12D, 16B, 20B. One of them can be made of two types rotation i.e. right and left, viewing from one end of the motor, it is called as clockwise fan if the impeller rotates clockwise, and symbolized with “right”, on the contrary, it is called as counter clockwise fan if the impeller rotates counter clockwise, and symbolized with “left”. The outlet position of the fan can be expressed from the outlet angle of the casing, among them, No. 2.8～6A is made of a kind of angle 0°, user can change the angle according to the requirement, without note when ordering.

 

Special note:

1.Adjustment of angles for No. 2..8A outlet is 0°～225°, the interval is 45°;

2.Adjustment of angles for No. 3.2A～6A, 6C, 6D outlets is 0°～225°, the interval is 22.5°;

3.Adjutment of angles for No. 8D～10C, D outlets is 0°～180°, the interval is 45°;

4.Adjustment of angles for No. 12C, D outlets is 0°～180°, the interval is 15°;

5.No. 16B, 20B outlets can be made three kinds of angles which are 0°,90°,180°and can not be adjusted, note when ordering.

6.The mentioned outlet angles is the customary doing of the fan trade, if they can’t meet your specific environment and condition, our factory can manufacture satisfactory angles for you, if this situation occurs the installation dimension behind the manual may be changed, users should take notice.

There are 4 driving modes: A,B, C, D:

• Shaft disc of fan is installed on motor shaft by keyway, i.e. motor directly connecting;  

B—Cantilever bearing unit, belt driving, pulley is in the middle of two bearings;

C—Cantilever bearing unit, belt driving, but the pulley is outside the bearing;

D—Cantilever bearing unit, coupling directly driving.

In the fan trade customary doing, type 4-68 No. 2.8～5 take mode A, No. 6 takes modes A, C and D, No. 8～12 take modes C and D, No. 16, 20 take only mode B.

Generally these driving modes can meet users operating requirement, if they can’t meet your requirement, our factory has ability to design and manufacture satisfactory fan for you.

Structure

The fan mainly consists of impeller, casing, inlet and driving unit, but No. 2.8～6A is mode A driving, and without driving unit.

Impeller—it is the key part of the fan, its material and contour can determine the wind pressure, flow rate, power consumption, noise and service life. The impeller consists of 10 backward wing blades, a curved front disc and flat rear disc, they are made up of steel plate, 16 Mn stainless steel or glass fiber reinforced plastics according to the various purpose and medium, the impeller shall be balanced statically and dynamically, over speed running test is carried out, and thus it has smooth running and the aerodynamic performance is good.

Casing—it shall be made two kinds of different types, among them: No. 2.8～12 casing is made in integral type, it can not be disintegrated. No.16～20 casing is made in three-open type, besides the casing is divided into two parts along the split horizontal level, the upper casing is vertically divided into two parts again along the centerline, and they are fixed by bolts, and thus facilitate to disassembly, repair and move. It is welded with normal iron plate or stainless steel, or machined with glass fiber reinforced plastics according to the purpose of the fan, however technology, price and schedule are also different.

Inlet—the inlet is manufactured as an integral type, the section which is parallel to the shaft is curved forms and gas is allowed into the impeller smoothly with a little loss, the inlet is generally fixed on the side of the fan with bolts. Radial and axial clearances between inlet and impeller are too small, friction can be caused between them, and when the clearances are too big, air leakage can be caused between them, please keep the design dimensions.

Driving unit—it consists of shaft, bearing box, rolling bearing, belt pulley or coupling.

Performance

The Performance of the fan is symbolized by flow, total pressure, speed, power, efficiency and Parameters etc.. there are certain conversional relations between these parameters, the relation can be shown by performance curve, mathematical formula and form mode etc;

Q—Flow rate        m3/h;        H—total pressure            Pa;

N—Shaft power      kW          η—total pressure efficiency

ηm—mechanical efficiency %        r—specific gravity          kg/m3

n—speed            r/min;        t—temperature             ℃

where:

with footnote 2 symbolizes the known parameter,

with footnote 1 symbolizes the unknown parameter.

The performance of the fan normally indicates the performance under the standard state. When the operating condition is inconsistent with standard state, at this moment the Performance must be converted into the performance under the standard state. The so-called standard slate indicates: atmospheric pressure P=101325 Pa, acceleration of gravity g=9.8m/sec2, air density ρ=0.1223kg·sec2/m4, atmospheric temperature t=20℃, the required power N=10-3η-1·K·Q·H, the relative humidity &=50%

A、D、C driving efficiency value

driving mode	Mechanical efficiencyηm
A motor driving D coupling driving C belt driving	1.00 0.98 0.95

 

 

 

Selection of value k

motor power (kW)	value k
below  0.5 >0.5～1 >1～2 >2～5 >5	1.5 1.4 1.3 1.3 1.15

 

Adjustment of Flow rate

The phenomenon of flow excess or insufficient often occurs in operation, there are many reasons in occurring such phenomenon. If the phenomenon of flow rate sometimes great and sometimes little occurs during operation, the main reason is due to resistance in pipe net sometimes strong and sometimes weak. If it is gradually reduced through a long period or suddenly reduced within a short time, the main reason is that the fan passage or pipe net is pl ed. The phenomenon of flow excess or insufficient will occur during normal running after installing, the main reason is as follows:

1.The actual and theoretic values k of resistance in pipe net is widely different. It was known normal pipe net characteristic equation H=KQ2, where: k is the coefficient of resistance, if the actual value k is less than the theoretic value k, the flow rate increases; vice versa, flow rate decreases, see Fig. 1 (b)

2.The effect of fan total pressure deviation △p have not been considered during selecting. when the actual total pressure of fan is a positive deviation, the flow rate increases, and when it is a negative deviation, the flow rate decreases, see fig 1 (a).

Fig.1  Pipe net characteristic curve

The flow rate excess or in sufficient occurred after fan newly installing and putting into operation, one of the following methods can be used to eliminate:

(1) Flow rate can be adjusted by damper.

(2) Increasing or decreasing the speed of the fan.

(3) Changeover a higher or lower pressure fan.

(4) Changeover pipe net to reduce the coefficient  k of resistance.

It must be pointed out: flow rate is normally adjusted by damper, but when the actual flow rate is much greater than the required, it wastes power, it is not economical, if the condition permits reducing fan speed or changing-over a lower pressure fan is normally used.

When the damper is full open, the flow rate is still insufficient, at this moment, the damper has lost its function, so try to reduce the resistance coefficient of pipe net, or increase the speed of the fan, or change-over a higher pressure fan, but the fan driven by motor and coupling can not be normally changed the speed, only the fan driven by belt, the speed can be increased and decreased by the means of changing the size of belt pulley diameter, the max. speed must be lower than the performance and optional part table required.

Note:

(1) No. 10,12,16 and 20 is converted according to the non-dimensional performance of No. 10 model.

(2) No. 5, 6 and 8 is converted according to the non-dimensional performance of No. 5 model.

(3) No. 5 below is determined by the actual testing sample fan performance.

The dimensional formula which converted by non-dimensional performance curve is :

Total pressure          (Pa)     

Flow rate 

Power     (kW)

Where:

D—outer diameter of impeller (m)  μ—linear velocity of impeller outer circle (m/s)  ρ—air density (kg/m3)

The required power is equal to shaft power plus mechanical loss and motor storing quantity.

Installation and Operation

First, prepare attachment and tools before installation, then, check every parts of the fan, impeller, casing , shaft and bearing etc. should be inspected carefully, if damages are found, repair should be carried out, and then clean inside of the bearing box with kerosene.

The following points must be noted during installation:

1. Lubricating oil or mechanical oil should be coated on the joint surface in order to prevent rust.

2. When the bolt is screwed in the joint surface, if there are setting dowels, doweling the joint surface first, and then tighten the bolt.

3. Pay attention to check the casing and any tools or goods should not be dropped and remained inside the casing.

Requirements of installation:

1. During installation, prohibit children, old people, disabled person and the persons who has difficulty getting about a bit on the installing site to surround and watch.

2. Install the fan first and then switch on power supply.

3. During installation, the weight of air duct should not added on the casing of the fan.

4. Correct the dimensions between the impeller and the inlet according to the drawing, keep the horizontality of the shaft.

5. When installing the inlet pipe, the bolt of inlet is directly used to connect pipe, at this time the inlet is fixed by three countersunk screws.

6. During installing No. 6 D～No. 12 D, the coaxality of fan shaft and motor shaft and the parallelism of both ends of coupling are measured by dial gage and feeler gage. The permissive coaxial error is 0.05 mm. The permissive parallelism error of coupling is 0.1mm.

7. Turn the rotor with hand or lever after installation to check whether it is over tight or touched with stationary components.

8. After installing the motor, install the belt pulley or coupling guard, if the inlet is not connected to the inlet pipe, the protective net or other safety device is also added (provided by user himself). Other parts of the fan are fixed according to the drawing.

Because of the flow rate Q, total pressure H, the shaft speed n, and shaft power N having the specific relations:

Thus, without changing the motor capacity, the shaft speed can not change, otherwise, the motor may be damaged by overload.

The motor power used by fan indicates under the specific operating condition, shaft power plus mechanical loss and storing quantity, but not the required power when the outlet full open, if the outlet or inlet of fan without connecting pipe or without outside resistance, the motor can not be put into operation. For the safety, a valve should be installed in the inlet and outlet pipes of the fan, close the valve when motor start up, the valve is slowly open after running, until reached the specific operating condition, and pay attention to the current if exceeds the rated value.

Maintenance

1. Don’t allow fan with trouble running.

2. Maintenance of fan can only be carried out during shut-down of fan.

3. Don’t freely change the maintenance person, specific person operating and repair the fan is preferred.

4. When the fan is repaired, the motor switch must be monitored or locked.

5. Regularly remove dust, contamination and the foreign materials and prevent rust.

6. Inspect the thermometer and oil indicator regularly.

7. Except replacing the lubricant after overall, replace the lubricating oil periodically.

List of troubles and causes

Troubles	causes
Severe vibration of bearing box	1.The shaft of fan is not parallel with that of motor; the coupling is misalignment. 2.friction between casing or inlet and impeller. 3.The foundation is not rigid enough or firm enough. 4.loosing of rivets in impeller or deformation of impeller. 5.Loose matching of shaft with impeller main disc. 6.Loosing of the bolts which connect casing and bearing with support, bearing with its cover. 7.Installation of fan inlet and outlet ducts is improper, which causes vibration. 8.The rotor is unbalance.
High temperature-rise of bearing	1.Severe vibration of bearing box. 2.Lubricant is poor in quality, deteriorated, mixed with dust, sand, contamination and etc. 3.Connection of bearing box cover and pedestal is over tight or Loose. 4.Fixing position between shaft and rolling bearing is slant, the front and back bearing are out of alignment. 5.wornout of rolling bearing.
Over current and high temperature-rise in motor	1.Gate or damper in the inlet and outlet pipes are not closed when starting-up. 2.Flow rate exceeds the specific value or air duct leaks. 3.Air density delivered by fan is over strong or contain visco-materials. 4.Input voltage of motor is low or is cut out in a single phase. 5.Coupling connecting is out of alignment the belt is too tight or the clearance is not uniform. 6.Influence caused by severe vibration of bearing box. 7.Influence caused by fan in parallel operation condition is worse or trouble happened.
Belt sliding	Two belts are not in the center line. The belt slides down from a small belt pulley.
Bet chattering	The distance of two belt pulleys is too short or the belt is too long.

Huashide(shandong)fan Co.Ltd

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Add:kunmingrod.linyi.P.R.china

E-mail:17853928877@163.com

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Tel: 17853928877