Shaft taper

Another wheel-to-shaft attachment uses a tapered fit (Figure 5-11, right portion). A center stretch rod constantly pulls each wheel onto the shaft. Should the wheel bore grow, the wheel remains centered and is drawn axially up the shaft taper. The tapered fit reduces galling risk during assembly and disassembly. 

For installation, care should be used to install the hub at the proper location on the shaft taper to provide the interference needed. A jig should be used and allowance made for hub shrinkage on cooling. 

Applications for this alloy has included such items as valve shafts, taper pins, pmnps, fasteners, cables, chains, screens, wire cloth, marine hardware, boat shafting, heat exchanger parts, and springs. 

The Stuckofen or old high bloomery appeared in Germany in ca 1300 AD. This type of furnace was 3—5 m high and enclosed a tapered vertical shaft that was 1—1.2 m in diameter. Small openings near the bottom were provided for no22les (tuyeres, pronounced tweers) that permitted air, suppHed by bellows, to be blown into the furnace. Modem blast furnaces have essentially the same fundamental design. 

A variety of conical refiners were developed that involved modifications of the Jordan refiner. The Hydrafiner, for example, has a short, low taper, high speed rotor, and wide bars (10). The stock is driven through the refiner by an impeller which is fitted to the smaU inlet end of the rotor shaft. The Claflin refiner has a very short, high taper plug. Vanes that fit on the wide end of the plug draw the stock through the unit (11). 

A combination of tapered shaft diameter and increasing pitch is shown in Figure 10a. This allows a length-to-diameter ratio of about 6 1 instead of 3 1. A half pitch screw is used over the tapered diameter. This approach results in an exceUent mass flow pattern provided that the hopper to which it attaches is also designed for mass flow. 

Fig. 10. Mass flow screw feeder designs, (a) Combined tapered shaft and variable pitch screw feeder where A represents a conical shaft and constant pitch (feed section) B, constant shaft and increasing pitch (feed section) and C, constant shaft and constant pitch (conveying section), (b) Stepped shaft screw feeder where A represents a stepped diameter shaft and constant pitch (feed section) and B, constant shaft and constant pitch (conveying section).

Expander-compressor shafts are preferably designed to operate below the first lateral critical speed and torsional resonance. A flame-plated band of aluminum alloy or similarly suitable material is generally applied to the shaft in the area sensed by the vibration probes to preclude erroneous electrical runout readings. This technique has been used on hundreds of expanders, steam turbines, and other turbomachines with complete success. Unless integral with the shaft, expander wheels (disks) are often attached to the shaft on a special tapered profile, with dowel-type keys and keyways. The latter design attempts to avoid the stress concentrations occasionally associated with splines and conventional keyways. It also reduces the cost of manufacture. When used, wheels are sometimes secured to the tapered ends of the shaft by a common center stretch rod which is pre-stressed during assembly. This results in a constant preload on each wheel to ensure proper contact between wheels and shaft at the anticipated extremes of temperature and speed. 

In the tapered labyrinth (Figure 5-5), a fixed labyrinth seals against a tapered shaft. As the shaft moves axially, the clearance of the seal changes. This allows an excess seal gas flow. The resulting venturi effect actually drags the lubricating oil into the process stream. Also, since the tapered shaft seal makes it difficult to provide an effective oil slinger, the problem is compounded. 

Seal gas systems are designed for dry, warm seal gas. However, condensation does occur occasionally. This condensation seems to accelerate erosion in the tapered area of the shaft. The most appropriate corrective action is often to replace the entire shaft. 

Damage to the labyrinth requires replacement of the expander heat barrier or compressor shaft seal. A replacement design (Figure 5-6) uses a replaceable stainless-steel labyrinth mounted on the shaft. Because the seal is not tapered, axial movement of the shaft has little or no measurable effect on seal gas flowrates. Each labyrinth has an integral oil slinger incorporated into the design. Also, each rotating... 

Tapered shaft does not have provisions for oil slinger ring. 

Tapered shaft must be replaced if damaged by wet seal gas or contact with aluminum seal. 

The shaft shall be eapable of transmitting the maximum power at any operating point on the data sheet. The shaft end shall have a j in./ft taper for a hydraulie-fitted eoupling hub (Figure 5-19). 

Figure 5-19. Rotor assembly showing tapered shaft end.

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. 

If the hub removal is necessary, such as required on compressor with non-split seals, a tapered hub fit on the shaft should be used. The removable hubs should have tapped puller holes. The shaft should be keyless with the preferred method of installation and removal by use of hydraulic dilation. Two injection ports 180° apart should be used whether injection is through the shaft or through the hub. Shrink fits should be 2 to 2.5 mil/in. of diameter. API 671 rcL ommends 1,5 mil/in. minimum, but experience indicates the heavier shrink may be required. For the juncture rating calculation, a f ra lion value of. 12 is recommended. 

If keyed tapered shafts are furnished, as may be true with some-installations, particularly for machines under 1,000 hp with small shafts, two keys are recommended. A shrink fit of 1 to 1.5 mil/in... 

Rotary vertical shaft turbine units as shown in Figure 10 and other rotary or reciprocating equipment are other examples. Tapered flocculation may be obtained by varying reel or paddle size on horizontal common shaft units or by varying speed on units with separate shafts and drives. In applications other than coagulation with alum or iron salts, flocculation parameters may be quite different. Lime precipitates are granular and benefit little from prolonged flocculation. 

A shaft rotating at 4000-6000 rev/min carries a primary air fan and an atomizing cup. The cup, typically of about 70-120 mm diameter, is tapered by a few degrees to increase in diameter at the exit. A stationary distributor which projects oil onto the smaller-diameter end of the cup feeds oil to the inner surface. The oil, influenced by centrifugal force, forms a thin film, which passes towards the cup lip. Atomization occurs as the oil leaves this lip. In addition, a primary air supply, normally in the range of 5-12 per cent of stoichiometric (chemically correct) air. 

A variety of mounting configurations are used to attach sprockets to their mating shafts. The most common has a tapered keyway that acts as a wedge when the key is driven in. No setscrews are provided with this type of key installation. 

Compression A rigid compression coupling is comprised of three pieces a compressible core and two encompassing coupling halves that apply force to the core. The core is comprised of a slotted bushing that has been machine bored to fit both ends of the shafts. It also has been taper machined on its external diameter from the center outward... 

Figure 59.16 shows various key shapes square ends, one square end and one round end, rounded ends, plain taper, and gib head taper. The majority of keys are square in cross-section, which are preferred through 41-inch diameter shafts. For bores over 4 inches and thin wall section of hubs, the rectangular (flat) key is used. 

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