Prepared by Ashik Ahmed

Section Manager Technical Services

Tel.: +880 31 618972~4; Ext.: 2237 (Office)

Email: ashik.rofy@gmail.com, ashik_rofy@yahoo.com,ahmed.ashik@kafcobd.com Mobile: +880 1730059920

 

     

VIBRATION ACCEPTANCE LIMIT FOR FAN /COMPRESSOR/BLOWER

SHOP TEST & SELECTING PROPER BALANCING GRADE FOR A ROTARY

MACHINE.

 

 

PART-I Tuesday, September 17, 2013

VIBRATION ISSUE ON SHOP TEST CONDITION

First of all, we have to go Fan for general purpose Part 7; Specifications for balancing & vibration (ISO 14694:2003).

On page# 09, Balance & vibration application category (BV) is described.

For Kafco case, the fan application category, BV is BV-3.So, the balance quality grade is G6,3.

 

 

The most important for our case is on 8.3, Page:15, ISO 14694; Fan vibration limits for tests in manufacturer's work-shop.

Here is the confusion came for rigidly mounted vs flexibly mounted vibration limit. The flexibly mounted Fan has slightly higher vibration limit. From your pic of site, we understand that the test bench Fan is on flexible mounted condition. As you found vibration 3.5mm/s for thrust end and 3 mm/s for fixed end; the value is well comply with the vibration range.

 

 

Again from Balance and vibration application categories (BV categories) ;table 01,we can find that for BV-3, you have to see ISO 10816-3 also.

From ISO 10816 you can find that 2-K-611 & 2-K-613 are in class III condition having the satisfactory vibration velocity 4.5 mm/s. Both the fans got speed less than 2000 rpm

CLASSIII

2-K-611

RPM 1480 200 KW

2-K-613

RPM 1486 90 KW

Cause they both have flexible Mounting on the Test shop & flexible Drive ( Flexible Coupling).

For KAFCO case all are Flexible Coupling.

If you considered 2-K-614 which is in class IV condition having the satisfactory vibration velocity 4.5~7.1 mm/s.

 

 

CLASS IV2-K-614

FAN RPM 4241

MOTOR RPM 1486 310 KWAs the speed is over 2000 RPM so ,it is in Class IV.Flexible Drive means the Coupling.For KAFCO case 2-K-614 has Flexible Coupling. The Table is given below for your better understanding.

 

 

PART-II Thursday, September 19, 2013

Dear Thank you for your valuable response regarding the FAN BV category. First of all you consider balance & vibration application category BV-4. On ISO14694:2003), page# 09 the BV value is given.

BV-4 came from balance & vibration chart considering the process gas/hazardous gas, balance quality grade G 2.3 & driver power > 37 KW.

 

 

Again from opposite site; Fan for general purpose Part 7; Specifications for balancing & vibration (ISO 14694:2003), on page# 10, Table: 02, Balance quality grade is described. Then, if you consider the fan application category, BV is BV-4; the balance quality grade is G2.5.

Considering BV-4 from ISO 14694 on Table 8.3, Page: 15,; Fan vibration limits for tests in manufacturer's work-shop. The vibration limit is r.m.s 2.8mm/s for flexibly mounted Fan.

Although the peak value is 3.8 mm/s.

So, if you consider

BV-4; the shop test value (3.5 mm/s) is

 

 

found higher than the nominal criteria.

Actually now we are in condition where it is hard to say which will be actual process. If you go through the ISO 1940 table-1 Page #11; Fans are in balance quality grade G 6.3. For balance quality G 2.5; the following equipment's are considered:- • Compressors • Computer drives • Electric motors and generators (of at least 80 mm shaft height), of maximum rated • speeds above 950 r/min • Gas turbines and steam turbines • Machine-tool drives • Textile machines

 

 

So, if you want to proceed with ISO 1940, Fans are in Balance quality grade G 6.3. But the problem is Form our existing 2-K-601 & 2-K-603 test run balancing report which shows the grade is G 2.5.The UIPL specification sheet filled by FSV do also indicate that the grade is G 2.5.

 

 

The balancing report shows that the maximum vibration on test run was 2.1 mm/s with flexible mounting condition .FSV also did mention on that time (26.05.1993) max vibration is 4.5 mm/s. But the reference is not found. (Compatible ISO Standard) That means the residual permissible specific unbalance is 16~17 g.mm/Kg for 1500 RPM.But if we consider Balance quality grade G 6.3 the residual permissible specific unbalance is more 40 g.mm/Kg.So,the tolerance is higher in case of Balance quality grade G 6.3.

 

 

CONCLUSION

So, If we consider G 2.5; we prefer that rotor balancing should be done from the Fan vendor site as it is a new machine. Although we are well capable & has completed successful mass balancing for Fan (2-K-601) we don’t prefer field balancing during the installation to push the vibration level lower.

If you want to proceed with ISO 1940, Fans are in Balance quality grade G 6.3. And considering balance quality grade G 6.3 the vibration value 3.5 mm/s is acceptable from our side.

But as we required balance grade G 2.5 on our Data Sheet (Although it is a over demand for a Fan perspective);we can’t accept the test value vibration of 3.5mm/s.