How do Bushings Work? | The Beginner’s Guide to Bushings

How do bushings work?-Sleeve bearing’s basic introduction

Before we understand how bushings work, let us first have a general understanding of the characteristics of the Sleeve bearing.

From the previous article-Sleeve bearing v.s. Bushing, we learned the following key

points:

  1. sleeve bearing features are high load-carrying capacity, very inexpensive, compact, and lightweight.
  2. Sleeve bearings are characterized by ensuring linear or rotational movement between two parts.
  3. They are used to constrain, guide, or reduce friction in rotary or linear applications.
  4. Sleeve bearings consist of one part that is built up of many types of materials, layered, and combined into a load-carrying system to provide smooth operation and greater durability.
  5. Bushings are also known as sleeve bearings, bushing bearings, plain bearings, self-lubricating bearings, or journal bearings.

How do bushings work?-Factors of sleeve bearing wear

Whether through regular maintenance or the replacement of its companion item, proper installation of a bushing can affect all other components within the drive. Incorrect installation can cause excessive vibrations, increased run-out, or breakage of the mating part, inevitably damaging components and the shaft it engages. At this point, increased downtime and – if the mating shaft is harmed – potentially bigger and costlier issues arise.

Therefore, we should first understand the Factors of sleeve bearing wear before we install the bearings to avoid the following situations.

  1. Abrasive wear. (If the wear is caused by a hard particle rubbing between the lubricated surfaces, it is called three-body wear. Wear caused by an asperity on one surface cutting the other surface is called two-body abrasion.)
  2. Insufficient volume of lubricant.
  3. Overheated lubricant (viscosity at operating temperature cannot support the load causing frictional heat and additional oil thinning.)
  4. Rough surfaces (asperities on the journal cause rubbing.)
  5. Imbalance (improper loading of the support element causing shock loading.)
  6. Journal eccentricity (egg-shaped journal causing rubbing on the high spots.)
  7. Metal fatigue from improper metallurgy.

How do bushings work?-The importance of lubricating grease.

Before installing bushing bearings, we also need to understand the features and functions of lubricating grease.

Generally, self-lubricating bearings work by injecting lubricant into the sliding layer of the bearing. It can be liquid (oil) or solid (graphite, MoS2, lead) depending on the performance of the lubricant under specific conditions (e.g., temperature). 

Through the pores in the sliding layer, lubricant is released to the bearing surface, lubricating it. Whenever the sliding layer wears, the lubricant is not uniformly dispersed throughout the layer, so the performance of the low friction bearing remains the same. Lubricants are usually impregnated on top of the “run-in” surface that provides a low friction bearing performance at start-up, before reaching the bearing surfaces.

Sleeve bearings are normally oil-lubricated but may be lubricated with grease for slow-speed equipment, particularly if they are subject to frequent starts and stops or the bearings may be physically difficult to reach.

Operating under proper speed, surface area, viscosity, and oil volume, a Sleeve bearing can support very heavy loads. The balance between these conditions is important. If the load or the speed changes, the lubricant viscosity must be adjusted to compensate for the change. 

Criteria to consider once you have identified the proper viscosity grade include oxidation stability, corrosion inhibition, wear protection, water, and air separation properties, etc. Because Sleeve bearings can be used in a variety of applications, there is no single set of criteria that should be used. Selection depends on the equipment design and operating conditions.

The type and amount of grease depend on continuous replenishment of the body of grease that is held within the dynamic clearances (empty spaces while the bearing is turning) to maintain effective lubricant condition and hydrodynamic lift. Equipment with poor sealing characteristics may require a heavier body of lubricant and more frequent replenishment cycles.

Under manual (intermittent) relubrication, the volume and the frequency are influenced by operating conditions, grease quality, and available time for the task. Grease selection begins with a consideration of the oil to be used. Heavy oils are used to formulate greases used to manually lubricate plain bearings in high-duty service.

After the proper viscosity oil has been selected, then the soap thickener, oxidation and rust characteristics, worked consistency properties, pumpability (for automatic systems), and load-bearing (EP/AW) properties are considered. For long intervals and very heavy loading, solid additives such as molybdenum disulfide or graphite may be incorporated. The solid additives would serve to mechanically prevent metal contact in mixed film and boundary lubrication conditions.

How to install sleeve bearings? Time to prepare your bushing!

Let us follow these steps for proper installation:

 

  1. First, make sure your shafting is within tolerance. 
  2. Remove all dust, dirt, paint, oil, and grease. (Bushings work through friction and force, so foreign matter on any of these surfaces will inhibit the ability to work correctly.)
  3. Insert the bushing into the component hub and align the bushing’s non-threaded holes to its counterpart’s threaded ones. The threaded holes on the bushing will be utilized during removal. *QD bushings can be mounted two ways, standard or reverse mount.
  4. Insert the bolts through the bushing’s non-threaded hole then thread into your counterpart by hand, leaving the assembly loose.
  5. Install the key onto the shaft and mount assembly as desired. Tighten the setscrew over the key to keep it in place once final drive alignments are complete.
  6. Alternate tightening your bolts gradually until specific torque values are reached. This progressive tightening allows the bushing to seat correctly and squarely.

Thanks for reading “How do bushings work?”

 

If you want to know more models and sizes, please click the following website: https://iskbearing.com/products-catalogue/

 

If you have any questions, please do not hesitate to contact us.

https://iskbearing.com/contact-us/

Taiwan Head Office-JOTA BEARING CO., LTD./ISK BEARING

TEL: +886-3-325-0202

FAX: +886-3-325-9933

E-mail: iskbearing@jota-bearing.com.tw

Address: NO.65, Ln.1434, ChunRi RD.,33051 Taoyuan, Taiwan, R.O.C

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