Question

With regards to main transmission shaft flange coupling arrangements:

(a) Sketch a hollow type coupling bolt and the hydraulic head/nut and loading rod which are used to fit it;

(b) Describe how the bolt is fitted;

(c) State the advantage of the hollow coupling bolt as compared to the traditional type of coupling bolt.

Answer 1

Part (a)

Part (b)

A bolt with a diameter slightly larger than the flange coupling bore diameter (D + 0.00025D) is selected.
A push rod (loading rod) is inserted into the hollow coupling bolt, and a hydraulic head is attached.
Hydraulic oil pressure of approximately 30,000 N/m² is applied, causing the bolt to stretch (approximately 0.021mm) and temporarily reduce its diameter by 0.00025D. This allows easy insertion of the bolt into the flange bore.
The bolt is placed inside the bore by hand, and the nut is tightened and nipped up using a spanner.
The hydraulic pressure is then released, allowing the bolt to expand and create a secure interference fit within the bore. This generates a tensile stress of approximately 15.5 tons/m², ensuring a firm grip.
After fitting, the hydraulic assembly (items A, B, and C) is removed, and a protective plastic cap is placed over the bolt head.

Part (c)

The hollow bolt design allows precise control of the bolt load, ensuring optimal tightening and load distribution.
Diametrical re-expansion after hydraulic pressure release ensures a strong interference fit of the shank within the flange bore, reducing the risk of loosening.
Hollow coupling bolts are easier to remove for inspection and maintenance, significantly reducing dismantling and fitting time.
Unlike traditional bolts, hollow coupling bolts minimize wear on the bore, eliminating the need for frequent re-machining.
Replacement of hollow coupling bolts is less frequent, reducing operational downtime and maintenance costs.

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