Radial fit bolts

Radial fit bolts are a special feature used in all types of turbomachinery. They are of increasing importance to users that are both reliability-minded and concerned about life-cycle costs. The radial fit coupling bolt was originally developed for coupling steam turbine shafts by Pilgrim International in Oldham, UK. It is equally useful to coupling other equipment, including, of course, hot gas expander shafts. 

To install the bolt body, it is inserted in the hole through the two flanges with the sleeve in the elearanee position. Hydraulie pressure pushes the sleeve into the final (interferenee) fitted position, and the puller draws the bolt baek into the sleeve. The nut is fitted at one end and the bolt is hydraulieally tensioned with the other nut. The entire proeess takes about 15 min per bolt. 

The eentral body of the bolt has eireumferential grooves, whieh allow lubrieant to flow between the bolt and sleeve. It ean be removed by first removing the nuts and then fitting an oil injeetor into the 

When the bolt is removed and the pressure relaxed, the sleeve eontraets and ean be withdrawn. Normally the bolts and sleeves ean be reused. Only if any maehining of the holes is required, perhaps to mateh an old flange with that of a new replaeement rotor, would sleeves be replaeed, but the same bolts eould be used. 

However, the sleeve is segmented, allowing eonsiderable expansion to turn the eouplings relative to eaeh other, elose the eouplings, and maintain alignment while the radial fit bolts are installed. 

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This chapter discusses the most popular features and controls that are critical to turboexpander operations. Among those discussed are magnetic bearings, squeeze film dampers, radial fit bolts, valve arrangements for FCC expanders, FCC expander load shedding technology, and surge detection and avoidance. 

Source Radial-Fit Bolts Save Millions, " Turbomachinery International, September/October 1995. 

The hydraulieally tensioned, radial-fit bolt (Figure 6-32) replaees the traditional turbine shaft eoupling bolt and is reusable. The main body of the bolt is threaded at eaeh end and has a slight taper on the eenter seetion, whieh engages with the similarly internally tapered sleeve and the two nuts. The bolt is taper-bored at eaeh end to aeeept the puller that is part of the hydraulie tensioning system. 

A number of turbomaehinery users have speeified Pilgrim s CHAT (Coupling Hole Alignment Tool, Figure 6-33), in addition to radial fit bolts. CHAT is a further development of the radial fit bolt, designed to aehieve eoupling hole alignment in the least amount of time and to a toleranee that permits radial bolt assembly. The CHAT tool is based on the same prineiple as the bolt and also uses hydraulie power. 

Figure 6-33. The coupling hole alignment tool (CHAT) has a longitudinally split sleeve for greater expansion. Like the radial fit bolt, it is hydraulically tensioned, but there is no hydraulic separation of core and sleeve.

Depending on the size of the eoupling, up to four CHAT tools might be used to effeet the alignment. Onee enough radial fit bolts are fitted to maintain the alignment, the CHAT tools are removed and the bolting eompleted. 

When the discs are of the shrunk-on design, they are made up individually and stacked onto the shaft by first heating the disc to dilate the bore. They are then allowed to cool and thus attach themselves to the shaft. Keys are normally not used. When the discs are of the stacked design, the discs are equipped with rabbet fit to radially lock the discs to maintain concentricity of assembly. The through-bolts are usually tensioned by stretching hydraulically to a precise value to ensure the mechanical integrity of the assembly. 

A suspended catalyst was removed from a process stream in a pressure filter. After filtration was complete, the remaining liquid was blown out of the filter with steam at a gauge pressure of 30 psi (2 bar). The pressure in the filter was blown off through a vent valve, and the fall in pressure was observ ed on a pressure gauge. The operator then opened the filter for cleaning. The filter door was held closed by eight radial bars, which fitted into U-bolts on the filter body. The bars were withdrawn from the U-bolts by turning a lai ge wheel, fixed to the door. The door could then be withdrawn. 

The top surface contains a radial tee slot into which two tee bolts are fitted. The central spigot locates the slideway for the top slide, which can be rotated and clamped at any angle by means of the tee bolts. Graduations are provided for this purpose. Fig. 9.6. 

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