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Bore and Key Shaft Services

Years ago, there was considerably huge concern in applying devices that were already standardized. This is commonly referred as to the dimension of shaft keys. But there are tendencies that designers tend to forget and that would be some of the essential factors that do exist. This page would show you the things to consider that would include shaft boring and shaft keying.

Bore and key shaft are commonly used with any of the following:

  • Manufacturing
  • Railroad
  • Industrial
  • Food and Beverage Manufacturing

These materials are very useful with the abovementioned sectors that need it the most. With that, there are just some certain things that one needs to know about the material in order to have the quality at its finest.

Key material

For the key material, you need to see to that you choose a key material with the same strength and hardness as the hub or shaft. This is mainly to avoid key failures due to overload.

Couplings for connecting shafts can be placed in two categories:

  • Keyed
  • Keyless

The fits of couplings can be categorized as well as:

  • Clearance
  • Interference

Keyed arrangement may have either a clearance or interference fit while keyless coupling arrangement will always have an interference fit.

Shaft boring vs. Shaft keying

Shaft boring is commonly known in the industrial field as digging a vertical or near –vertical tunnel from the top down, where there is originally no access to the bottom. On the other hand, shaft keying mainly focuses a machine element which is the key that is used to connect a rotating machine element to a shaft. This is to preclude the relative rotation amid the two parts that may enable torque transmission. In order for the key to function, it must have a keyway and a keyseat. This is a slot and pocket where the key fits.

For modern couplings, particularly those made from alloy steels, usually have shorter hubs. They are typically considered to be equal to, or only slightly longer than the shaft diameter.

In this case, key stress is about 50% higher than shaft stress. This would seem to appear to have a requirement that the key material is 50% stronger than that of the hub; however, because part of the torque is transmitted through friction between the shaft and hub bore, the key material needs to be as robust as the shaft material. Key stock is available from most steel suppliers in various grades of steel, including alloy steel.

Key geometry and fit

If the key is not properly fitted, it can cause costly maintenance problems or even machine failures. So before installing a hub for a drive component, you have to make sure that the key has the correct shape and dimensions. The key fits properly as follows:

  • Sliding (not the clearance) should fit in the hub keyway.
  • Tight in the shaft keyway.
  • Key length spreads inward from the shaft end (never beyond) to beyond the hub end, by at least the rounded portion of the key.
  • Clearance should fit radially — a small clearance between the top of the key and bottom of the hub keyway.

The proper fit of the key ensures that the hub can’t rotate, even slightly, on the shaft for this may lead to damage. As damage to these contact surfaces occurs, clearance develops between them, and the key will ultimately shear.

A sliding fit between the key and hub keyway is highly suggested for ease of assembly and disassembly and can cause a hub to split. To guarantee that the hub seats properly on its shaft, you have to provide some clearance between the key and the bottom of the hub keyway. In the case of a coupling hub, the mentioned clearance delivers an opening through which water or destructive gases can enter the coupling, causing damage to its internal surfaces. To seal this opening against contaminants, you have to apply a room temperature vulcanizing (RTV) sealant on top of the key before installing the hub.

So you wouldn’t have to deal with the fillet radii in the keyway, the corners of a key must be chamfered. While on the other hand, too large a chamfer decreases the area of contact between the key and the sides of the keyway. Under load, and mostly during shock loads, these smaller contact surfaces are more easily dented.

A loose – fitting key, permits forces produced by torque to roll the key, causing high edge loadings between the key and keyway. Such edge loading can crop the key. Tapered keys are sometimes used instead of setscrews. This is in order to hold hubs from sliding on their shafts. If driven in too far, they cause poor hub – to shaft contact; if not driven far enough, they will allow sliding between hub and shaft. Sadly, there is no way to know and check if tapered keys are properly installed. For these reasons, one should avoid using tapered keys for coupling applications.

Design and Manufacturing

Keyed shafts that obtain a square end key is probable to damage the shaft when transmitting torque. This is because the corner of the key will create a high contact stress in the shaft, this then can cause it to fail. In order to escape such failures, use only keys with rounded ends.

The transmission of torque over a key must occur over the full length of the hub, or else twisting movements can befall between the hub and shaft. These movements cause shaft fretting (surface damage caused by small alternating motions), which leads to exhaustion failure. If a key has a round end, the only way to transmit torque over the full length of the hub is to spread the key beyond the hub, by at least its rounded portion. And although the end of the key is rounded (as it should be), the key transmits torque only over its straight portion.

Another factor that affects the system balance is the relationship between the key and hub length. Given that a void between the rounded end of the key and the end of the hub keyway, it will cause the system to be out of balance. This situation can cause vibration especially at the high speeds normally encountered in electrical motor operation.

While a key that spreads beyond the hub also causes imbalance. If a balanced coupling is necessary, you will have to use a notched key. As a rule – of thumb, a coupling should always be balanced if it is going to be mounted on the shaft of a motor with a balanced rotor.

The most known and common encountered error in key manufacturing is the use of key steel which is considered to be softer than the shaft. Always bear in mind that the key material and hardness should be similar to that of the shaft or hub.

Our services

There may be other shaft boring companies and shaft keying companies that may offer and explain to you what bore and keys are and its importance, however, here with us, you won’t only get such knowledge about how these materials work, and what they do, we will also be able to offer and provide you a quality service there is. If you have a shaft that gets worn out, messed up, stripped or just needs to be replaced, you can always give us a call for we can do the manufacturing process and make it running again.

We have an efficient, effective and high – quality service that is incomparable than that of other companies.

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