Two-bearing housings
Home / Products / Rolling Mill Bearings / Two-bearing housings / SKF Two-bearing housingsTwo-bearing housings – PD series
SKF two-bearing housings were originally developed for fan shafts with an overhung impeller, but are also suitable for other applications with similar shaft arrangements. Compared to the conventional shaft arrangement where two self-aligning bearings are mounted in separate pillow (plummer) block housings, two-bearing housings provide several advantages including improved running accuracy and quieter operation.
PD two-bearing housings can also be supplied as ready-to-mount units.
Standard housing design
PD two-bearing housings are non-split housings with two bearing seats(→ fig.1). They consist of a housing body and two covers that are bolted to the body with either four or six bolts. The housings have four holes drilled into the feet for attachment bolts.
PD housings are available in three series,each similar in their external design, but accommodating different bearing arrangements:
• PDN series, for normal radial and axial loads
• PDP series,for predominant or alternating axial loads
• PDR series,for heavy radial and normal axial loads
Features and benefits
PD housings have the following features and benefits:
Compact design
The bearings are incorporated in one housing,which saves space.
Smooth running
The two bearing seats are concentric. Since bearing misalignment is avoided , rigid bearings can be used. The resulting stiff arrangement provides a high degree of running accuracy and enables high speeds.
Quiet operation
The accurate alignment of the rigid bearings in one housing enables quiet operation. For units with the designation PDNB , a wave spring washer in the smaller housing range further reduces noise levels ·
Available as units
PD housings can also be supplied as units ,complete with bearings and shaft. These ready-to
-mount units are assembled and greased at the factory, saving time and reducing the risk
of contaminating or damaging the bearings during assembly.
Easy handling
Large housings have two eye bolts for safe and easy handling.
Housing material
PD two-bearing housings and their covers are made of grey cast iron.
Housing variants
In addition to standard design PD housings ,the following variants are available on request：
• housings for oil bath or circulating oil lubrication systems
• housings for vertical shaft arrangements
For additional information contact the NEWORLD application engineering service.
Sealing solutions
PD two-bearing housings are designed for two sealing solutions:
• a V-ring seal , for housings in the PDN 2 and PDP Series (→ fig . 2)
• a felt strip and a V-ring seal , for housings in the PDN 3 and PDR Series (→ fig. 3)
Design considerations
Shaft-bearing combinations
PD two-bearing housings accommodate bearings on a cylindrical seat on stepped shafts.
Standard bearing arrangements
PD two-bearing housings can accommodate different bearing arrangements , depending on the series.
Housings in the PDN Series
The bearing arrangement for housings in the PDN Series comprises：
• two single row deep groove ball bearings in the 62 series for housings in the PDN 2 series (→ fig . 4)
• two single row deep groove ball bearings in the 63 series for housings in the PDN 3 series (→ fig . 5)
Housings in the PDP Series
The bearing arrangement for housings in the PDP Series comprises (→ fig . 6):
• a single row cylindrical roller bearing in the NU 22 ECP Series , in the non -locating bearing position
• a pair of universally matchable single row angular contact ball bearings in the 72 series , mounted back-
to -back in the locating bearing position
This bearing arrangement accommodates axial loads in both directions and can support heavier
loads than bearings in PDN Series housings. Housings in the PDP Series can also accommodate
other bearing combinations ·
Housings in the PDR Series
The bearing arrangementfor housings in the PDR Series comprises (→ fig . 7):
• a single row cylindrical roller bearing in the NU 3 ECP Series , in the non -locating bearing position
• a cylindrical roller bearing in the NU 3 ECP series im combination with a single row deep groove ball
bearing in the 63 series (with C3 clearance) , in the locating bearing position.
The deep groove ball bearing acts as a pure thrust bearing , accommodating the axial loads in both
directions and is mounted with radial clearance in the housing. To prevent the outer ring from turning ,
an 0 -ring is inserted in a groove im the cover that abuts the outer ring. The bearings support heavier
radial loads than bearings in both PDN and PDP Series housings.
Non-standard bearing arrangements
Housings in the PDN Series are designed to accommodate two deep groove ball bearings. For special applications , the housings can be fitted with various combinations of deep groove ball bearings , angular contact ball bearings , cylindrical roller bearings and spherical roller bearings.
NEWORLD Can supply the following combinations , available as assembled units (→ fig. 8):
• PDNA .DD Units , incorporating a deep groove ba lbearing in the non -locating bearing position
and a pair of universally matchable angular contact ball bearings , mounted back-to -back , in the
locating bearing position. Smaller housings accommodate axial loads in only one direction , while
larger housings can withstand axial loads in both directions (a)
• PDND Units , incorporating an NJ design cylindrical roller bearing on each end to form a cross
located ( " floating " ) bearing arrangement (b)
• PDNE Units , an NJ design cylindrical roller bearing and a deep groove ba lbearing to form a cross
located ( " floating " ) bearing arrangement(c)
• PDNF .DD Units , incorporating an NJ design cylindrical roller bearing and a pair of universally
matchable angular contact ball bearings , mounted back-to -back , to form a cross-located
( " floating " )bearing arrangement(d)
• PDNL Units , incorporating a spherical roller bearing on each end to form a cross- located
( " floating " ) bearing arrangement(e)
Bearing arrangements
Typically, PD two -bearing housings accommodate a locating and a n on -locating bearing. In some
applications,however both bearings are used to locate the shaft axially, each in one direction· This is
called a cross-located ( " foating " )bearing arrangement.
Load carrying capacity
PD two-bearing housings are imtended for loads acting perpendiculary toward the Support surface. If the
housing is supported over its four feet and the loads are purely perpendicular, loads are limited ony by the
bearings. Housings in the PDN Series that have bearings preloaded with a wave spring washer
accommodate axial loads in one direction only.
Scope of delivery
Unsplit Plummer block housing units are ideally ordered as complete units. The housing body, shaft, seals and rolling bearings are then included in the scope of delivery. It is also possible, however, to order the housing body (with seals), the shaft and the rolling bearings separately.
