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Bushing

A bushing is a type of mechanical component used as a plain bearing or an electrical insulator. In mechanical engineering, it is a cylindrical lining, often functioning as a type of plain bearing, designed to reduce friction and wear between moving parts by providing a replaceable lining for a shaft or hole in machinery.^[1] In electrical engineering, it is an insulating structure that includes a through conductor, providing a passageway for electrical conductors through a grounded barrier while insulating against high voltages.^[2] Typically removable and inserted into a housing, the mechanical bushing constrains relative motion, supports loads, and protects mating surfaces from abrasion while allowing for smooth rotation or sliding.^[3] Mechanical bushings are essential in various engineering applications, from automotive suspensions to industrial equipment, where they offer a cost-effective alternative to more complex rolling-element bearings.^[4] Mechanical bushings come in several types tailored to specific operational needs, including sleeve bushings for basic rotational support, flanged bushings that incorporate an integrated collar to prevent axial movement, and spherical bushings for accommodating misalignment in pivoting joints.^[5] Other variants, such as hydrodynamic bushings, rely on fluid lubrication to generate a supporting film under load, while drill jig bushings provide precise guidance in manufacturing fixtures.^[6] Materials for bushings vary widely to suit environmental and performance demands: common options include sintered bronze or brass for self-lubricating properties, polymers like PTFE (Teflon) for low-friction dry operation, and elastomers such as rubber for vibration damping in suspension systems.^[7] Composite materials combining fibers with resins offer enhanced durability in high-load scenarios.^[4] In practice, mechanical bushings find widespread use across industries, including automotive (e.g., control arm and engine mounts), aerospace (for lightweight pivot points), and heavy machinery (to handle radial and thrust loads).^[8] Selection criteria emphasize factors like load capacity, speed, lubrication requirements, and operating temperature, with maintenance involving periodic inspection for wear to ensure longevity and safety.^[9] Unlike ball bearings, bushings excel in contaminated environments or where space constraints limit rolling elements, though they may require lubrication to minimize heat buildup.^[10]

History

Mechanical Bushings

The use of mechanical bushings, or plain bearings, dates back to ancient civilizations. Evidence from ancient Egypt around 2600 BCE shows cylindrical wooden rollers employed as simple plain bearings to move massive stone blocks for pyramid construction, reducing friction by distributing loads over multiple contact points.^[11] In the Bronze Age, around 2000–1000 BCE, early metal bushings made from bronze emerged in wheeled vehicles and machinery across Mesopotamia and Europe, providing durable sliding surfaces for axles.^[12] During the Industrial Revolution in the 18th and 19th centuries, bushings became integral to steam engines and machinery, with cast iron and bronze variants supporting higher loads in textile mills and locomotives. The 1930s marked a significant advancement with the invention of oil-impregnated sintered bronze bushings, known as Oilite, which embedded lubricant within the porous material for reduced maintenance.^[11] Post-World War II, in 1956, the Glacier Metal Company introduced the first self-lubricating metal-polymer bushings, combining bronze backing with PTFE liners to enable dry operation and extend service life in automotive and industrial applications.^[13] By the late 20th century, composite polymer bushings dominated, offering maintenance-free performance and resistance to contamination, with ongoing innovations in fiber-reinforced materials as of 2025.^[11]

Electrical Bushings

Electrical bushings originated in the early 20th century alongside the growth of high-voltage power systems. The first solid-type bushings, consisting of porcelain insulators with embedded conductors, appeared around 1900 for low- to medium-voltage applications in early transformers and switchgear, limited to about 52 kV due to size and dielectric constraints.^[14] A breakthrough came in 1906 with the development of condenser bushings for a 200 kV high-voltage test transformer, followed by commercial production in 1908 using resin-bonded paper (RBP) with coarse and fine grading to control electric fields and reduce partial discharges.^[14] By the 1940s, oil-impregnated paper (OIP) bushings were introduced around 1944, enabling ratings up to 1,200 kV by using kraft paper saturated with transformer oil for superior insulation in substations and generators.^[15] In 1950, resin-impregnated paper (RIP) bushings emerged, employing epoxy resin with crepe paper for non-flammable, compact designs up to 800 kV, gaining popularity for their environmental safety.^[14] Subsequent decades saw dry-type innovations: silicone rubber on glass-fiber epoxy tubes around 1990, and resin-impregnated synthetic (RIS) bushings using non-woven fabrics from 2010 onward, supporting HVDC applications up to 550 kV with enhanced pollution resistance. As of 2025, hybrid and composite bushings continue to evolve for ultra-high voltages exceeding 1,000 kV, driven by renewable energy integration and grid modernization.^[15]

Mechanical Bushings

Definition and Function

A mechanical bushing, also known as a plain bearing or sleeve bearing, is a cylindrical component designed to fit into a bore or opening within a mechanical assembly, providing a low-friction interface between a rotating shaft and a stationary housing.^[16]^[9] It typically consists of a simple sleeve without rolling elements, relying on direct sliding contact, often lubricated to minimize wear and friction.^[6] Bushings are removable and replaceable, allowing for maintenance in applications where precision alignment is critical.^[9] The primary function of a mechanical bushing is to reduce friction and support loads between moving and stationary parts, enabling smooth relative motion such as rotation or linear sliding.^[16] By separating the shaft (journal) from the housing with a thin film of lubricant, bushings accommodate radial loads, distribute stress evenly, and prevent direct metal-to-metal contact that could lead to galling or seizing.^[16] They also provide precise guidance for components, maintaining alignment under dynamic conditions and absorbing minor misalignments or vibrations to enhance system stability.^[9] In addition to load-bearing and friction reduction, bushings protect mating surfaces from wear, corrosion, and environmental damage, thereby extending the service life of machinery.^[9] For instance, in journal bearings, they support the rotor weight while allowing free rotation, often using materials with antifriction linings like PTFE or sintered metals to optimize performance under varying speeds and loads.^[16] This makes bushings essential in low- to moderate-speed applications where high load capacity is prioritized over ultra-high rotational velocities.^[6]

Types

Mechanical bushings are classified into several types based on their structural design and ability to handle specific load directions and installation requirements. These configurations include straight cylindrical forms for basic radial support, variants with added features for axial positioning or load bearing, and specialized designs for enhanced performance in demanding conditions. Each type offers distinct advantages in terms of load capacity, ease of use, and durability, though they may involve trade-offs in complexity or maintenance needs.^[6] Sleeve bushings, also known as straight cylindrical bushings, feature a simple tubular design that primarily accommodates radial loads during rotating, oscillating, or linear movements. They are press-fitted into housings and provide low-friction support for shafts, often using materials like bronze for durability in standard applications. The primary advantage of sleeve bushings is their straightforward, cost-effective construction, which minimizes material use and simplifies integration, though they require precise alignment to avoid uneven wear.^[17]^[6]^[4] Flanged bushings incorporate an integral collar or rim at one end, extending beyond the cylindrical body to facilitate axial positioning and resist thrust loads in addition to radial forces. This design ensures the bushing remains securely located within the assembly, preventing slippage along the shaft axis. Advantages include enhanced stability under combined loads and reduced need for additional retaining components, but the added flange can increase overall size and manufacturing complexity compared to plain sleeves.^[18]^[19]^[17] Split or half bushings consist of two semicircular halves that can be assembled around a shaft without full disassembly of the surrounding machinery, enabling easy installation and replacement in confined spaces. This configuration is particularly useful for retrofitting or maintenance on existing equipment. Key advantages are reduced downtime during servicing and adaptability to irregular shaft conditions, although the split seam may lead to higher wear rates or potential debris ingress if not precisely machined.^[20]^[21]^[22] Thrust bushings are engineered to primarily manage axial loads along the shaft's direction, often featuring a washer-like or shouldered profile to distribute forces evenly and prevent end-play. They differ from radial-focused types by prioritizing linear constraint in one direction while allowing rotation. Benefits include robust performance in applications with predominant pushing or pulling forces and compatibility with high shock loads, but they generally have lower capacity for radial movement unless combined with other designs.^[22]^[23]^[24] Self-lubricating bushings incorporate embedded lubricants to enable maintenance-free operation, reducing the need for external greasing and minimizing contamination risks. Oil-impregnated porous metal types, such as sintered bronze, feature a network of voids filled with oil that releases under load and heat, providing consistent lubrication over time. PTFE-lined composite variants use a thin polytetrafluoroethylene (PTFE) layer on a supportive backing for dry-running low-friction performance. These designs offer advantages like extended service life in inaccessible locations and environmental compatibility, though oil-impregnated versions may lose effectiveness at extreme temperatures, and PTFE linings can be sensitive to high-speed edge loading.^[4]^[25]^[26] Specialized variants address unique operational challenges, such as misalignment or extreme loads. Spherical bushings feature a ball-and-socket-like inner surface that tolerates angular misalignment and deformation, accommodating up to several degrees of offset without binding. This flexibility is advantageous in dynamic assemblies prone to vibration or thermal expansion, but it may introduce slightly higher friction under perfect alignment compared to cylindrical types. Filament-wound bushings employ a helical winding of fibers in a composite matrix to create high-strength, thin-walled structures capable of withstanding heavy static and dynamic loads. Their layered construction provides superior impact resistance and concentricity, though the process limits customization for very small diameters.^[27]^[28]^[29]

Materials

Mechanical bushings are fabricated from a variety of materials selected for their ability to withstand sliding friction, support loads, and resist environmental degradation. The choice depends on factors such as mechanical properties, compatibility with lubrication, and exposure to conditions like corrosion or temperature extremes.^[4]^[30] Metallic materials dominate in applications requiring high durability and load-bearing capacity. Bronze alloys, such as CuSn8 tin bronze, offer superior strength, wear resistance, and corrosion resistance, enabling reliable performance in lubricated or harsh settings.^[4]^[30] Brass provides excellent machinability and inherent anti-friction qualities, facilitating precise fabrication while maintaining moderate strength.^[31]^[30] Steel, often in low-carbon forms, serves as a cost-effective option for low-load scenarios, with potential enhancements through backing layers for improved fatigue resistance.^[31]^[4] Non-metallic materials emphasize reduced weight and friction. Plastics like nylon exhibit low friction coefficients and self-lubricating tendencies, ideal for moderate loads and speeds where noise and vibration must be minimized.^[7]^[31] Composites, typically comprising PTFE layers bonded to metallic backings, combine low wear rates with structural support, promoting self-lubrication in marginal or dry conditions.^[7]^[4] Self-lubricating variants address maintenance challenges in inaccessible areas. Sintered bronze, porous structures impregnated with oil reservoirs, gradually releases lubricant under load to sustain low friction in medium-speed operations.^[4] Solid lubricant-embedded options, such as graphite-infused polymers or bronze plugs, provide dry-running capability with embedded particles that form a transfer film, enhancing endurance in high-temperature or contaminated environments.^[31]^[30] Material selection is guided by operational demands to optimize performance and longevity. High load capacities favor robust metals like bronze, while elevated speeds benefit from low-friction non-metallics such as PTFE composites to minimize heat buildup.^[7]^[30] Environmental factors, including exposure to moisture or chemicals, prioritize corrosion-resistant choices; for instance, bronze's anti-galling properties make it suitable for marine conditions.^[31]^[4] Lubricated versus dry operation further influences decisions, with self-lubricating materials reducing reliance on external oils.^[30]

Design and Manufacturing

The design of mechanical bushings emphasizes precision in fit, load-bearing capacity, and operational performance to minimize wear and ensure reliable sliding contact. Key considerations include clearance ratios, which typically range from 0.001 to 0.003 inches per inch of shaft diameter to accommodate thermal expansion, lubrication film formation, and misalignment without excessive play or binding.^[32] Tolerance standards such as ISO 286 and ANSI B4.1 guide the selection of fits, with common designations like h9 for shaft bores and H7 for housings to achieve clearance or transition fits that balance ease of assembly and functional tightness.^[33] Load and speed calculations rely on the PV factor, defined as the product of specific pressure (P, in psi or N/mm²) and sliding velocity (V, in ft/min or m/s), where P is computed as load divided by the projected bearing area (length × diameter), and V as π × diameter × RPM / 12 for rotational motion.^[34] This factor determines the material's operational limit; for example, bronze bushings often tolerate PV values up to 75,000 psi-ft/min under lubricated conditions, while PTFE composites handle up to 50,000 psi-ft/min in dry environments, guiding designers to select dimensions that keep calculated PV below the material threshold for extended service life.^[35] Manufacturing processes for mechanical bushings vary by material and complexity to achieve the required porosity, strength, and geometry. Machining from bar stock, suitable for metals like bronze or steel, involves cutting the raw material to length, followed by turning or boring on CNC lathes to form precise inner and outer diameters, and finishing with grinding for tight tolerances.^[36] Casting is employed for complex shapes, particularly in bronze alloys, where molten metal (heated to 1,000–1,200°C) is poured into sand or permanent molds, allowed to solidify, then machined to refine bores and surfaces, enabling intricate features like flanges without extensive secondary operations.^[36] Powder metallurgy sintering produces porous self-lubricating types by mixing metal powders (e.g., bronze with graphite), compacting them in dies under high pressure, sintering at temperatures below the melting point (around 800–1,000°C) to bond particles while preserving 20–30% porosity, and impregnating with oil for maintenance-free operation.^[37] For plastic bushings, extrusion forces molten polymers like nylon or PTFE through a die to create continuous profiles, which are then cut to length and machined if needed, offering cost-effective production for corrosion-resistant applications.^[36] Quality control ensures bushings meet performance specifications through targeted finishing and verification steps. Surface finishing, such as honing the bore with abrasive stones, achieves smooth, cross-hatched interiors (typically 0.2–0.8 μm Ra) to retain lubricant and reduce friction, correcting any out-of-roundness from prior machining.^[38] Heat treatment, including quenching and tempering for steel or bronze bushings, enhances hardness (e.g., to 80–90 HRB for wear resistance) while minimizing distortion, often applied post-machining to maintain dimensional stability.^[39] Dimensional accuracy is verified using calipers for ID/OD measurements, plug gauges for go/no-go tolerance checks per ISO 3547-2 (e.g., ID within ±0.05 mm), and three-point micrometers to detect ovality, ensuring fits align with design intent.^[40] A fundamental aspect of bushing design involves calculating frictional torque under sliding contact, derived from Coulomb's law of dry friction, which posits that frictional force opposes motion proportionally to the normal load. For a journal bushing, the torque T is given by

T = \mu W r

where \mu is the coefficient of friction (typically 0.05–0.2 for lubricated metals), W is the radial load, and r is the shaft radius. This equation arises from integrating the tangential frictional stress \mu P(\theta) over the contact arc, assuming uniform pressure distribution for simplicity, though advanced models account for cosinusoidal pressure variations in partial wraps to yield a steady-state factor approximating 1.25 times the basic product for 90° contact angles.^[41]

Applications

Mechanical bushings are widely used across various industries to support loads, reduce friction, and guide motion in machinery. In automotive applications, they are essential in suspension systems, such as control arms and engine mounts, where they absorb vibrations, handle radial and axial loads, and provide durability in harsh environments.^[8]^[9] In aerospace, bushings serve as lightweight pivot points in landing gear, actuators, and control linkages, accommodating misalignment and shock loads while minimizing weight to meet performance requirements.^[4]^[3] Heavy machinery and industrial equipment utilize bushings for radial and thrust load support in conveyors, pumps, and construction tools, where their ability to operate in contaminated or low-lubrication conditions offers advantages over rolling-element bearings.^[42]^[23] Additional uses include power tools and plumbing fixtures for flanged bushings providing axial support, and dynamically loaded systems like agricultural equipment, where self-lubricating types reduce maintenance needs.^[43]^[44] Selection considers factors like load capacity, speed, and environmental exposure to ensure reliability and longevity.^[9]

Electrical Bushings

Definition and Function

An electrical bushing is an insulating device that allows a conductor to pass through a grounded enclosing structure, such as a transformer tank or switchgear housing, while providing electrical insulation between the conductor and the grounded enclosure.^[45] It typically consists of a central conductor surrounded by layers of insulating material, often encased in a protective housing like porcelain or polymer, to prevent electrical breakdown and ensure safe operation at high voltages.^[46] The primary function of an electrical bushing is to provide dielectric insulation to withstand high voltage stresses, support mechanical loads on the conductor, and seal the enclosure against environmental factors such as moisture, dust, and contaminants.^[47] By insulating the live conductor from the earthed housing, bushings enable the safe transmission of electrical power from internal components to external connections, minimizing the risk of arcing, flashover, or faults. They also facilitate heat dissipation in some designs and allow for monitoring of insulation condition.^[48] Electrical bushings are essential in high-voltage applications where they must handle both electrical and mechanical stresses to maintain system reliability and safety.^[49]

Types and Construction

Electrical bushings are classified primarily by their insulation methods and structural designs, which determine their suitability for various voltage levels and environmental conditions. Porcelain bushings, often used outdoors, feature a solid or compound-filled core encased in a porcelain shell for mechanical strength and electrical insulation. The solid type employs homogeneous porcelain, while compound-filled variants incorporate insulating compounds like oil or resin to enhance dielectric performance in higher voltage applications. These bushings include weather sheds or skirts on the outer surface to increase creepage distance, thereby improving resistance to pollution and surface tracking in contaminated environments.^[50]^[45]^[51] Paper-insulated bushings represent a major category for high-voltage applications, subdivided into oil-impregnated paper (OIP) and resin-impregnated paper (RIP) types. OIP bushings consist of kraft paper wound around a central conductor and impregnated with transformer oil, forming a flexible yet robust insulation core that fills the porcelain or composite housing; this design allows for effective heat dissipation and high dielectric strength. RIP bushings, in contrast, use epoxy resin to impregnate the paper core, resulting in a solid, dry insulation that eliminates oil-related risks such as leaks or flammability, making them ideal for enclosed or seismically active installations. Both incorporate condenser layers—thin conductive foils embedded at intervals within the paper—for uniform voltage grading across the insulation thickness.^[48]^[52]^[53] Resin and epoxy bushings provide compact alternatives, particularly for indoor or space-constrained setups, with cast resin constructions molding epoxy or similar polymers directly around the conductor for seamless insulation. These offer lightweight, non-porous designs resistant to mechanical shock and partial discharges. Hybrid bushings integrate these materials, such as a porcelain or RIP core topped with silicone rubber sheds, combining the rigidity of traditional insulators with the flexibility and hydrophobicity of polymers for enhanced outdoor durability.^[50]^[54]^[53] Key construction elements across these types ensure reliable performance under electrical and thermal stresses. Coaxial capacitors, formed by alternating insulating and conductive layers in condenser designs, enable precise voltage grading by capacitively dividing the potential drop. The capacitance of each layer follows the formula

C = \frac{\epsilon A}{d}

where \epsilon is the permittivity of the dielectric, A is the effective area of the layer, and d is its thickness; this configuration minimizes field concentrations and prevents breakdowns.^[54]^[48] In OIP variants, expansion bellows integrated into the oil chamber manage thermal expansion by accommodating volume changes in the impregnating fluid, preventing pressure buildup or voids. Sealing against moisture is achieved through robust gaskets, O-rings, and welded joints at interfaces, critical for maintaining insulation integrity in humid or exposed conditions.^[55]^[49]^[54]

Applications

Electrical bushings serve as critical high-voltage terminals in power transformers, enabling the safe connection of internal windings to external grid infrastructure while providing insulation against grounded enclosures. These components are designed to handle extreme electrical stresses, with ratings up to 765 kV, ensuring reliable power transmission in utility-scale systems.^[56]^[57] In switchgear and circuit breakers, bushings function as indoor and outdoor insulators that facilitate busbar connections, isolating high-voltage conductors from earthed metal housings to prevent arcing and faults during operation. This application is essential in substations where space constraints demand compact designs that maintain electrical integrity under varying loads.^[58]^[59] For generators and capacitors in power plants, bushings provide step-up connections that link low-voltage machine outputs to high-voltage transmission lines, supporting efficient energy export while mitigating insulation risks from thermal and mechanical stresses. Resin-impregnated paper (RIP) bushings are particularly suited for oil-free environments in these setups, enhancing safety by eliminating flammable fluids.^[60]^[61]^[62] The primary advantages of electrical bushings in these deployments include their compact form factor, which optimizes space in densely packed substations, and the fire resistance of RIP types, which reduces ignition risks compared to oil-filled alternatives. However, challenges such as seismic qualification are addressed through rigorous testing to withstand vibrations in earthquake-prone areas, ensuring long-term reliability and minimal downtime.^[63]^[62] Specific examples include wall bushings, which enable safe penetration through substation building walls for conductor routing, and potheads, specialized terminations that connect underground high-voltage cables to overhead lines, providing robust insulation at transition points.^[64]

Testing and Maintenance

Testing of electrical bushings involves several diagnostic methods to assess insulation integrity and detect early degradation. Power factor or tan δ measurements evaluate dielectric losses in the insulation, indicating potential degradation due to moisture or aging, typically performed at power frequency or variable frequencies for on-site assessments.^[65]^[66] Partial discharge (PD) detection, standardized under IEC 60270, quantifies apparent charge in picocoulombs to identify localized discharges within the bushing insulation, often using electrical methods for offline or online monitoring.^[67]^[68] For oil-impregnated paper (OIP) bushings, oil analysis examines parameters like dielectric strength, acidity, and moisture content to diagnose contamination or breakdown precursors.^[69]^[70] Performance standards for electrical bushings, such as IEEE Std C57.19.00, outline requirements for design, testing procedures, and acceptance criteria to ensure reliability in power apparatus.^[71] High-potential (hipot) withstand tests apply up to twice the rated line-to-ground voltage to verify insulation strength without breakdown, particularly for solid-core bushings during factory acceptance.^[72]^[73] Maintenance practices focus on routine inspections to prevent failures and extend service life. Visual inspections identify surface cracks, oil leaks, or contamination on porcelain or polymer housings, performed periodically under de-energized conditions.^[74] Thermal imaging detects hot spots indicative of internal faults or loose connections by capturing infrared temperature variations during energized operation.^[75] Replacement is recommended when PD levels exceed 500 pC, signaling significant insulation deterioration that risks catastrophic failure.^[76] Common failure modes in electrical bushings include moisture ingress, which compromises dielectric strength and promotes surface tracking along the insulation interface.^[77] Thermal cycling accelerates aging by causing material expansion and contraction, leading to delamination or void formation in composite layers over time.^[78]

Other Types

Drill Bushings

Drill bushings are precision-engineered cylindrical guides, typically made from hardened steel or carbide, that are inserted into jigs or fixtures to accurately direct the path of cutting tools such as drill bits, reamers, or punches during machining operations.^[79]^[80] These devices ensure the tool maintains perpendicularity to the workpiece surface and achieves precise hole locations, with tolerances often reaching 0.0001 inches for inner diameter and concentricity.^[79] The primary types of drill bushings include press-fit (permanent) bushings, which are directly inserted into the jig plate for long-term use; renewable bushings, featuring replaceable liners that allow for easy tool changes or maintenance; and slip bushings, which are loosely fitted for quick alignment and removal in multi-step processes.^[79]^[80] Press-fit variants, such as headless (P/PC) or headed (H/HC) types, provide robust stability under heavy loads, while renewable options like fixed renewable (FM) or slip-fixed (SF) designs incorporate locking mechanisms to secure them during operation.^[80] In metalworking applications, drill bushings are essential components of jigs for repetitive drilling tasks, enabling high-volume production in industries like aerospace and electronics by guiding tools to create precise hole locations.^[81] They support shank-mounted tools in fixtures, preventing misalignment and ensuring consistent results across workpieces without requiring frequent recalibration of the machine.^[80] Key advantages of drill bushings include minimizing tool wander and deflection, which reduces chatter and extends the lifespan of cutting tools by up to 50 times in demanding materials when using carbide variants.^[80] Additionally, they enhance overall machining efficiency by improving hole precision and repeatability, thereby lowering scrap rates in precision manufacturing.^[79] Standardization of drill bushings is governed by ANSI/ASME B94.33, which defines nomenclature, sizes, tolerances, and identification for jig bushings to ensure interoperability across manufacturers.^[82] This standard covers both customary and metric dimensions, with inner diameters available in decimal, fractional, or wire-gauge sizes to match common tool specifications.^[80]

Cable and Grommet Bushings

Cable and grommet bushings serve as protective linings for wires and cables that pass through panels or enclosures, functioning as flexible or rigid inserts—typically constructed from materials like nylon, rubber, or PVC—to shield against abrasion, chafing, and sharp edges at entry points. These components provide essential mechanical protection by distributing stress and preventing damage from repeated flexing or vibration, while also offering strain relief to minimize pulling forces on connections. In low-voltage applications, they overlap with basic electrical insulation but prioritize mechanical safeguarding over high-power conduction.^[83]^[84]^[85] Common types include snap-in grommets, which facilitate quick installation by snapping into pre-cut panel holes and are available in closed designs for single cables or open/close variants for easier insertion; cord grips, often featuring integrated strain relief mechanisms to secure cables against tension and bending; and all-fit bushings, which employ universal sizing with adjustable or multi-stepped interiors to accommodate varying cable diameters without custom fitting. Materials such as nylon 6/6 provide durability and chemical resistance, while rubber options like TPE or EPDM enhance vibration damping.^[83]^[84]^[85] These bushings find widespread use in electronics enclosures to route wiring bundles safely and prevent electrical shorts from edge damage, as well as in automotive wiring harnesses where they endure vibration and environmental exposure to maintain circuit integrity. They enable IP-rated sealing, such as IP67 for dust and water resistance, ensuring protection in harsh conditions like outdoor equipment or vehicle underbodies. Multi-hole designs accommodate cable bundles efficiently, reducing clutter and enhancing assembly modularity in industrial settings.^[83]^[85]^[85] Key features emphasize safety and performance, including flame-retardant properties meeting the UL 94 V-0 standard, which ensures self-extinguishing within 10 seconds of ignition to mitigate fire risks in enclosed spaces. This rating is common in rubber or plastic formulations compliant with RoHS and REACH for eco-friendliness. Additional attributes like pierceable diaphragms in some grommets allow for versatile wire sizing, while overall designs promote easy retrofitting and long-term reliability in dynamic environments.^[86]^[85]^[86]

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### Summary of Bushing Materials
[32]
What material is used for bushings? - SC Industries, Inc.
Common materials include bronze, brass, steel, polymer, and composites. Bronze remains a go-to option due to its wear resistance, while brass offers excellent ...
[33]
How to determine the clearance between the shaft and the bushing?
Jul 17, 2025 · A clearance of around 0.001 - 0.003 inches per inch of shaft diameter is often a good starting point. But as the load and speed increase, you'll ...
[34]
Plain Bearing Bushing Tolerance - viiplus
Plain bearing bushing tolerance is the allowable deviation from specified dimensions, typically for inside (ID) and outside (OD) diameters, ensuring proper fit.Missing: ratios | Show results with:ratios
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Bushing PV Calculations: A Comprehensive Guide - Bronze Lube
Nov 3, 2024 · PV is calculated by multiplying the specific bearing load (p) by the sliding speed (v), with its unit being N/mm² x m/s.
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Bushings and Plain Bearings - Load Capacity and Service Life
The PV value has a considerable influence on the service life of a bushing. The PV value is the product of the specific load (P) and the sliding speed (V). ...Type Of Load · Bushing Velocity · Bushing Operation Intervals
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Plain Bushing Manufacturing Process - Bushing Production - viiplus
This can be done through various methods such as casting (for metals), injection molding (for plastics), or machining (for both metals and plastics). Finishing: ...
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Self-lubricating sintered bearings - Manufacturing Process | AMES
Self-lubricating sintered bearings are manufactured by powder metallurgy technology. A metal powder mixture is pressed in a rigid mould with the negative shape ...
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What is Honing? - Precision Surfacing Solutions
The honing process provides the final sizing and creates the desired finish pattern on the interior of tubing or cylinder bores.
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Steel Heat Treatment: Case vs. Through Hardening Explained
Case hardening enhances the surface hardness of components like pins, bushings, and rollers, providing excellent wear resistance and ensuring the chain's ...
[41]
How To Check The Plain Bushing Dimensions & Size？ - viiplus
Jul 27, 2025 · To verify that the bushings conform to the necessary standards, a pin-gauge test, commonly referred to as the “go/no-go” test, is performed.
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[PDF] Little things that make big differences in bushing friction
This common parameter is defined here as and is calculated by dividing the subtracted moment by the shaft radius and the magnitude of the vector sum of Fx and ...
[43]
[PDF] PAO - Condenser Bushing 25-765 kV Oil-to-Air - GE Vernova
They are designed for use in power transformers and can be installed up to a 45° maximum inclination (up to and including 138 kV) or 30° (161 to 765 kV) off ...
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Power transformer and reactor bushings
Jun 27, 2023 · They are for use as components of liquid-filled transformers and reactors on systems with a nominal voltage of 15–765 kV. 1.2. This Standard ...
[45]
Switchgear Bushings | Polycast
Switchgear bushings are components used in electrical switchgear equipment to connect high voltage electrical conductors to the grounded equipment enclosure ...
[46]
Electrical Bushings Explained - saVRee
Learn about Electrical Bushings! How they work, their components, designs, advantages, disadvantages and applications.Missing: penetrations | Show results with:penetrations
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Generator Bushing Maintenance: Designs & Renovation
Nov 1, 2006 · All generator porcelain bushings are spring loaded to compensate for the variation in thermal expansion of the conductor and porcelain.
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RIG Generator Bushing | Trench Group
A RIG Generator Bushing utilizing resin impregnated paper insulation provide a reliable and safe connection for the generators or electrical machines.
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Hitachi Energy bushings for AC transformers and reactors
Bushings for AC transformers and reactors are designed to minimize partial discharge, reducing the risk of insulation breakdown and increasing the overall ...
[50]
Synthetic Dry Bushings for Application in HV Power Transformers ...
Aug 8, 2025 · Bushings are insulating structures used at all voltage levels for a variety of applications, including in transformers, shunt reactors, ...
[51]
What are the key benefits of using ABB wall bushings in substations?
Jan 23, 2025 · The bushing ensures the electrical connection is insulated and protected from the surrounding environment, preventing electrical leakage and ...
[52]
Pothead - Wikipedia
A pothead is a type of insulated electrical terminal used for transitioning between overhead line and underground high-voltage cable
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Electrical Bushing Types and Their Applications - Putai Electric
Their main function is to provide insulation and mechanical support while preventing electrical faults caused by direct contact between the conductor and ...
[54]
An Expert's Guide to High Voltage Porcelain Bushings - Hewei Power
Sep 2, 2025 · A high voltage porcelain bushing is not just an electrical component; it is a structural member. It must support the weight of the attached ...
[55]
Transformer bushings | Megger
Typical insulation used in a capacitance-graded bushing is oil-impregnated paper (OIP), resin-impregnated paper (RIP), and resin bonded paper (RBP).Missing: method coaxial expansion
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Transformer Bushing Types : RIP Condenser Bushing vs OIP ...
May 10, 2024 · In OIP bushing the core is wound from paper and subsequently treated and impregnated with an insulating liquid, generally transformer oil. The ...
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Technologies | Hitachi Energy
Non-condenser Core Bushings · Porcelain bushings up to 3.6 kV and 6500 A · Porcelain bushings up to 52 kV and 8000 A · Epoxy resin bushings up to 36 kV and 2500 A.Missing: electrical coaxial expansion bellows
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Electrical Bushings Explained - saVRee
### Summary of Electrical Bushings Types and Construction
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[PDF] Diagnostics of HV bushings through oil sampling and analysis
An expansion bellow allows for changes in oil volume under temperature variations, with two electrical switches operating an alarm if oil volume reaches the ...<|separator|>
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[PDF] TESTING AND MAINTENANCE OF HIGH-VOLTAGE BUSHINGS
A. Composite Bushing. - A bushing in which insulation consists of two or more coaxial layers of different insulating materials.Missing: construction expansion
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On-site Health Assessment of 765kV Bushing Insulation using VFTD
Feb 4, 2022 · VFTD is a variable frequency tan delta test for on-site bushing testing, including power frequency, as a pre-installation check.
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IEEE Guide for Diagnostic Field Testing of Electric Power Apparatus
It is measured in terms of dissipation factor (tan ∆) or power factor. When an ac voltage is applied to insulation, current flow occurs in the insulation ...
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IEC 60270:2025
Jun 5, 2025 · IEC 60270:2025 is applicable to the charge-based measurement of partial discharges which occur in electrical apparatus, components or systems.
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[PDF] A Guide for Partial Discharge Measurements on medium voltage ...
IEC 60270 defines partial discharge (PD) measurement, using apparent charge, a measured quantity derived from the PD pulse, measured in picocoulombs.
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Preventive Testing Techniques for OIP Transformer Bushing - NJREC
Sep 26, 2025 · If the bushing oil level abnormally drops, inspect for oil leakage, typically occurring at the bushing cap and end shield. If necessary ...
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[PDF] For the Love of Bushings - Doble Engineering
The results of bushing teardown analysis may result in a bushing replacement plan for similar types, restrict their use and may involve additional maintenance ...
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IEEE C57.19.00 - Power Apparatus Bushings Standard - BSB EDGE
Discover IEEE C57.19.00:2023 for high-voltage bushing standards in liquid-filled transformers & reactors. Ensure compliance with essential testing ...
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https://www.omicronenergy.com/download/file/e5e8a545dfbaebe53f6487fe7f4886a9
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[PDF] EE-03-955 Power Transformer Testing - PDH-PRO
The AC hi-pot test is used to assess transformer windings condition. Hi-pot test is suggested for all voltages, particularly those above 34.5 kV.<|separator|>
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What Maintenance Is Required for Wall Bushings Over Time?
Aug 28, 2025 · Most OIP bushings are equipped with a sight glass or oil level indicator. This must be checked regularly. A low oil level is a critical red flag ...
[71]
https://www.bsbedge.com/standard/ieee-standard-for-general-requirements-and-test-procedure-for-power-apparatus-bushings-ieee-c57-19-00-2023/IEEEC57.19.00-2023
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[PDF] Review of Online Partial Discharge Measurement Practices
... transformer PD testing process across different laboratories so that results can be compared against a pass / fail criterion (e.g. 500pC). Factory testing ...
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Analysis of the Root Causes of Transformer Bushing Failures
Most bushing failures are attributed to moisture ingress, moisture inside a bushing decreases the dielectric strength and life of the insulation, thus ...
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(PDF) Understanding the impacts of moisture and thermal aging on ...
Aug 9, 2025 · This paper first provides a brief description of RVM, PDC and SEC procedures followed by a description of the experimental techniques adopted.
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Understanding Standard Drill Bushings: Comprehensive Guide
### Summary of Drill Bushings from Carr Lane Mfg. Guide
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Drill Bushings: How to Select the Right One - Richconn
Jun 17, 2025 · For drill bushings' inside diameters (ID), B94.33.1 and ANSI/ASME B94.33 standards are followed. IDs can be selected in decimal, fractional, ...
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https://www.researchgate.net/publication/281147199_Analysis_of_the_Root_Causes_of_Transformer_Bushing_Failures
[78]
B94.33 - Jig Bushings - ASME
In stock 21-day returnsThis Standard covers the nomenclature, definitions, types, sizes, tolerances and identification of standard Jig Bushings and Locking Devices. | 1996 | PDF.Missing: advantages | Show results with:advantages
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Different types of cable bushings and their unique advantages
### Summary of Cable Bushings and Grommets
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Grommets, Bushings, Edgings... What Does It All Mean?
### Summary of Grommets and Bushings for Cables
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The ultimate guide to cable management
### Summary of Cable Grommets from "The Ultimate Guide to Cable Management"
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Flame rating UL94V-0 round rubber grommet - ETOL
The UL94V-0 round rubber grommet protects cables from abrasion and meets UL94V-0 standard. It also protects holes from damage.