High-Quality Nylon Bush Factories & Companies

Unlike metallic bearings that permit very tight running clearances (e.g., 0.001 mm per mm of shaft diameter), polymer bushings require generous operational clearances. The total diametral running clearance ($C_d$) must accommodate three distinct factors: (1) Initial running fit clearance ($C_{fit} \approx 0.003 \cdot d_{shaft}$), (2) Bore collapse resulting from the interference press fit into the housing (typically 80% to 100% of the interference amount $\delta$), and (3) Thermal expansion clearance ($C_{th} = d_{shaft} \cdot \alpha \cdot \Delta T$, where $\alpha$ is the Coefficient of Thermal Expansion, roughly $80 \times 10^{-6}\text{ K}^{-1}$ for MC nylon). A standard practical rule of thumb is a minimum installed bore clearance of 0.004 to 0.005 mm per millimeter of journal diameter, with a mandatory hard floor of 0.25 mm for shafts below 50 mm.

Yes. Polyamides (PA6, PA66, MC Cast Nylon) exhibit excellent hydrocarbon resistance and are completely inert to non-acidic petroleum greases, standard gear oils, hydraulic fluids, and synthetic motor lubricants. Applying an initial smear of lithium-soap or synthetic grease during break-in drastically smooths micro-asperities on the steel pin and doubles operational life. However, caution is required regarding lubricants containing active sulfur compounds, chlorinated extreme-pressure (EP) additives, or concentrated glycol-based brake fluids at elevated temperatures, which can induce slow chemical degradation of the polymer backbone.

Cast monomer nylon (PA6G) is synthesized directly inside liquid casting molds via chemical polymerization at low temperature without high shear pressures. This yields an exceptionally high molecular weight ($M_w > 100,000\text{ g/mol}$) and a high degree of crystalline order (up to 45–50%). It features higher surface hardness, superior compressive strength, greater dimensional stability, and minimal internal molding stresses. Extruded PA66 is manufactured by melting pre-polymerized pellets through an extruder screw under pressure, resulting in lower molecular weight ($M_w \approx 30,000\text{ g/mol}$), slightly lower wear resistance, and higher residual stresses, but higher tensile strength and a slightly higher raw melting point (260°C vs 220°C).

When nylon is submerged in water or operates in relative humidity above 75%, moisture uptake gradually increases until saturation equilibrium (up to 6.0% for PA6). This induces predictable linear swell of approximately 0.25% per 1% of absorbed moisture. Engineers compensate in one of three ways: (1) Machine the installed internal bore diameter with an enlarged allowance equivalent to $\Delta D = D_{nominal} \times 0.015$, (2) Specify low-moisture alternative polymers such as Polyoxymethylene (POM, max 0.8% saturation) or UHMWPE (< 0.01% absorption), or (3) Pre-condition the machined nylon bushings in an elevated warm-water bath (80°C) until dimensional equilibrium is achieved prior to final boring.

The counterface shaft condition dictates whether the wear mechanism remains gentle transfer-film sliding or aggressive micro-cutting abrasive wear. The optimal shaft surface finish is ground and polished to $Ra = 0.2\text{ to }0.4\ \mu\text{m}$ ($8\text{ to }16\ \mu\text{in}$). Shafts rougher than $Ra = 0.8\ \mu\text{m}$ rapidly shave the polymer surface. Conversely, an ultra-mirror finish ($Ra < 0.1\ \mu\text{m}$) prevents the nylon wear particles from depositing the protective polymer transfer film. Shaft surface hardness should ideally exceed 50 HRC (e.g., induction-hardened AISI 1045 or chrome-plated 4140 steel) to eliminate metallic scratching from trapped foreign particulates.

Because plastics have low thermal conductivity and low modulus of elasticity, cutting tools must cut cleanly without rubbing or compressing the stock. Use sharp, unhoned cutting edges (carbide or PCD) with a 15°–20° top rake angle, a 10°–15° front clearance angle, and a small nose radius ($r < 0.4\text{ mm}$). Maintain cutting speeds between 200 and 400 m/min, with moderate continuous feeds (0.15 to 0.35 mm/rev). Avoid shallow, dusting cuts (< 0.25 mm depth) as they induce frictional heat and elastic spring-back; instead, make defined roughing cuts followed by a single final finishing cut with flood coolant or compressed cold air.

During the liquid monomer casting stage, micro-droplets of a specialized liquid lubricant (refined mineral or synthetic ester) are homogenously dispersed and chemically trapped within the polymerizing caprolactam matrix. Because the lubricant is encapsulated at the molecular scale within closed cells, it will not weep, drain, or centrifuge out under gravity or static storage. Under mechanical sliding contact and slight frictional micro-heating, the microscopic lubricant cells on the active surface shear open, depositing a continuous hydrodynamic boundary film. As the bush cools, capillary forces stabilize the film, ensuring permanent lubrication throughout part life.

When periodic flushing or supplemental lubrication is employed, internal groove geometry must avoid sharp stress-concentrating square roots. Use smooth radiused profiles: a standard circular "Figure-8" loop groove, double-spiral, or helical groove with a depth of 2.0 to 3.0 mm and width of 3.0 to 5.0 mm, maintaining full 1.0 mm edge corner radii. Crucially, grease grooves must not break through the outer axial edges of the bush; they should stop 5.0 to 8.0 mm short of each end to prevent contaminant entry and retain the lubricant cushion inside the load zone.

Molybdenum disulfide ($MoS_2$) acts as a nucleating agent during the crystallization phase of cast nylon. The finely dispersed particles trigger the growth of smaller, denser spherulitic crystalline structures throughout the material. This yields a noticeably harder, stiffer bushing with higher load-bearing capacity (compressive modulus increases by 15–20%) and an increased heat distortion temperature. Furthermore, the lamellar slip structure of $MoS_2$ provides dry solid-film lubrication, making black MoS2-filled cast nylon the global industry standard for heavy-load, low-speed outdoor pivot pins such as mining excavator linkages and railway bogies.

While interference press-fitting is standard, thermal cycling or vibration can relax the polymer's radial hoop stress over time. To ensure positive retention across extreme operating temperatures: (1) Utilize flanged bushing geometries clamped axially by a steel retainer plate, (2) Machine an external circumferential retention groove on the bush outer diameter paired with a housing snap ring, (3) Apply mechanical set screws located at the split joint or radial anti-rotation pins, or (4) Apply an anaerobic structural adhesive (such as Loctite 609/680) to clean, degreased surfaces during assembly. Never rely entirely on friction press-fit if service temperatures swing across a range greater than 40°C.