Koyo NAXK12Z combined needle roller and thrust ball bearing, 12 x 21 x 23 mm

These Koyo NAXK.Z combined needle roller bearings incorporate a radial needle roller bearing without an inner ring and a thrust ball bearing in one unitized package, with a machined outer ring. They are an effective alternative to separate radial and thrust bearings in terms of cost, handling and packaging, and they take radial and axial loads together.

The NAXK series is the thrust ball version of the Koyo combined bearing, and the NAXR series has the same dimensions with a cylindrical roller thrust component for higher axial capacity.

In the designation, the Z suffix means the thrust washer is retained with a dust cap.

The range has 11 sizes with a needle roller complement bore of 10 to 50 mm. Koyo bearings are made by JTEKT Corporation.

Where this product is used

• Industrial applications
• Machine tools
• Automotive transmissions

Features

• Radial needle roller bearing and thrust ball bearing in one unitized package
• Machined outer ring, supplied without an inner ring; matching JR inner rings are listed for each size
• Radial dynamic load rating C 7.5 to 30.2 kN and thrust dynamic load rating Ca 10.4 to 29 kN
• Thrust static load rating C0a 14 to 75.4 kN
• Oil lubrication speed rating 4,300 to 9,500 min-1
• Dust cap retains the thrust washer

Key specifications

Available sizes

Selecting the right option

Choose the size from the shaft diameter, which is the needle roller complement bore Fw, then check the outside diameter D, the width C and the thrust washer outside diameter Da against the housing space. Each size lists a matching JR inner ring for use where the shaft cannot be hardened and ground.

Slippage can occur if the axial load is too light and the speed is high, particularly with inadequate lubrication. The minimum axial load is C0a/2200 kN, where C0a is the thrust static load rating in kN.

Fitting and use

Combined bearings can be used with or without matching inner rings. Without an inner ring, the radial internal clearance is smaller, because the needle roller and cage assembly runs directly on the shaft, so the shaft should be hardened and ground as a raceway. Where the shaft cannot meet the raceway requirements, use a standard inner ring.

Simple through-bored housings are adequate. The suggested housing tolerance is K6 (M6 for a tighter fit) when the load is stationary relative to the housing, and M6 (N6 for a tighter fit) when the load rotates relative to the housing. The suggested shaft tolerance with an inner ring is k6 for shafts over 10 mm up to 40 mm and m6 for shafts over 40 mm up to 70 mm when the load is stationary relative to the housing, and g6 for all diameters when the load rotates. Without an inner ring, use h6 for a stationary load and f6 for a rotating load.

The shaft-piloted thrust washer must be supported over at least half of its width. When pressing the bearing into a housing with a tight fit, relatively high press-in forces may brinell the thrust raceways, so install it with uniform, continuous pressure against the installation tool and avoid sudden impact. At times it may be desirable to heat the housing before mounting.

Where the axial loads are relatively high and the application allows oil lubrication, consider the NAXK and NAXR types with oil. Bearings with a dust cap can use oil, although their design makes them better suited to grease. Bearings are shipped with a corrosion-preventive compound that is not a lubricant, and they can be used with oil or grease without removing it. It can be advisable to remove the compound before packing the bearing with a suitable grease, to get the best grease performance.

The needle roller complement bore tolerance of the unmounted bearing is F6, the shaft-piloted washer bore tolerance is E7, and the thrust component thickness C1 tolerance is +0 to -0.200 mm. Other tolerances follow the normal class for metric series radial bearings and standard thrust bearings.

Related products

Also available from Koyo: the Koyo JR metric inner ring range, the Koyo NAXK range and the Koyo NAXR range.