Bearing Housings

SKF

Bearing housings fitted with rolling bearings are economic, replaceable bearing units and require little maintenance.

SKF bearing housings are made of cast iron (certain plummer block housings are available in spheroidal graphite cast iron). The bearing seating of the housings is machined to tolerances such that a loose fit of the bearing outer ring is ensured, and in most cases the seating width is such that the bearing has axial freedom. Thus dimensional inaccuracies, slight positioning errors in mounting and thermal elongation of the shaft can be accommodated in the housing itself. Axial location of the bearing is achieved by employing the location rings specified in the housing tables. The figures in the locating ring designations indicate the approximate width and diameter of the ring. If only one ring is to be used with a bearing having an adapter sleeve, the ring should be positioned on the same side of the bearing as the lock nut; the bearing is then displaced from its central position in the housing by a distance equal to half the locating ring width. If two locating rings are used, one ring should be placed at each side of the bearing. When ordering, the number of locating rings required and their designation(s) should be stated.

SKF bearing housings are always supplied complete with seals. V-ring seals, felt seals (felt strips unless otherwise stated) or labyrinth seals are delivered with the housings as specified in the tables arid need not be ordered separately. V-ring seals are suitable for peripheral speeds of up to 12 m/s and operating temperatures of -40 to +100 deg. C. Felt seals are normally employed for peripheral speeds of up to 4 m/s and temperatures of up to + 100 deg. C. Before using felt strips, they should be soaked in hot cii for a few minutes. Labyrinth seals are universally applicable and not subject to wear.

SKF bearing housings are primarily intended for grease lubrication. In the majority of cases it is sufficient to charge the housings with grease on mounting and to replace this grease periodically when carrying out inspections. Plummer block housings have no provision for relubrication since used grease can be easily replaced once the housing cap has been removed. It shorter relubrication intervals are required a hole may be drilled and tapped to take a grease nipple or Supply line, the position is either marked or indicated by a boss.

For more detailed information regarding sealing arrangements, protective collars and bearing locating rings see cM/0900/PB1 -A

Plummer blocks

Plummer blocks are designed for use with self-aligning ball bearings and spherical roller bearings; the bearing may either have a tapered bore and be mounted on an adapter sleeve or may have a cylindrical bore. The elongated bolt holes in the housing base permit slight adjustments to the position of the plummer block to be made during mounting. The majority of housings are fitted with dowel pins to ensure correct location of the associated caps and bases, which are not interchangeable.

Plummer blocks are designed to accom-modate loads acting at right angles to the base. If the direction of load is not perpendicular to the base care should be taken to see that the housing, cap bolts and holding down bolts have sufficient strength to carry the loads involved. Approximate values for the breaking load for the housings and the yield point for the cap bolts are given in the tables on pages 391 to 393. To obtain the permissible load, the values are divided by a factor selected with regard to safety requirements. For general engineering pur-poses a safety factor of 6 is generally applied for the housings and a factor of 3 for the bolts.

SKF manufacture three different types of plummer block housings: SNA. SN and SD. SNA and SN plummer blocks are designed for use with bearings on adapter sleeves or with cylindrical bore. The housings of SNA plummer blocks are identical for both types of bearings, but are combined with different seals, whereas different housings are used for SN plummer blocks depending on whether the bearing Is to be mounted on an adapter sleeve or has a cylindrical bore. SD plummer blocks are for USS with bearings mounted on adapter sleeves.

Plummer blocks for bearings with adapter sleeve

SNA plummer blocks of series SNA 5 and SNA 6 can be supplied with V-ring seals (suffix TA), felt seals (suffix TC) or a seal set comprising one V-ring seal and one end cover with bonded rubber lip (suffix ATA) as standard. The seal set with end cover should be selected when bearings are to be mounted at the end of a shaft.

The V-ring seals Consist of a V-ring and a sheet steel washer, which has been treated to prevent corrosion. The V-ring is mounted on the shaft and seals against the washer, which is mounted in a groove in the housing. The washer has a bonded rubber lip and seals against the housing. The felt seals are ready to mount and consist of oiled felt inserted in a light alloy ring supplied in two halves. These are positioned in the seal grooves in the housing after first inserting a rubber 0-ring (also in halves). This provides adequate sealing between the housing and the ring halves and also prevents the felt seals from rotating.

For exacting operating conditions, the V-ring and felt seals of housings SNA 505 to SNA 518 and SNA 605 to SNA 615 may be supplemented by a light alloy collar (see adjacent illustration), a standard component manufactured by SKF. The collar prevents the seals from becoming damaged and also enhances their sealing effect. The bore diameter tolerance is H10. The collar is designated TSNA B, e.g.: TSNA505B.

If frequent relubrication is required, housings fitted with V-ring seals should be selected (suffix TA). Excess grease can escape from the housing past the up of the V-ring and the risk of hot running because of over-lubrication is reduced. The efficiency o relubrication can be much improved by mounting an extra perforated V-ring inboard of the V-ring seal washer at the side where grease is applied so that grease can Only leave the housing at the opposite side. Housings of series SNA Sand SNA 6 with V-ring seals are therefore available complete with an extra V-ring, grease nipple and splash plate which covers a sector of just over 1800; see adjacent illustration. It should be noted that, where possible, grease should be supplied to housings with these additional features (suffix TAV, e.g. SNA51OTAV) on the side away from the lock nut.

Housings with V-ring seals can be adapted for oil lubrication; see adjacent illustration. It is necessary to drill entry and exit holes for the oil and to supplement the seals. The holes should be drilled one at each side of the bearing so that oil must pass through it. Good sealing is obtained if an extra V-ring is mounted at each side of the housing in an inboard position with its lip against the steel washer: the extra V-rings should be of the perforated type. At peripheral speeds in excess of 7 m/s it may be necessary to locate the V-ring axially. If a wide bearing is used, the steel washer should be turned, for reasons of space, so that its rubber lip faces inwards.

SNA plummet blocks are a development of the SN plummet blocks; the dimensions of both SNA and SN housings follow ISO/P 113 and the housings of series SNA S aria SNA 6 are interchangeable with those of SN Sand SN 6, respectively.

For special purposes where housings of particularly high strength are required, a standard range of housings from size 511-609 is available made of spheroidal graphite cast iron. These housings carry the designation prefix SSNAD, e.g. SSNAD 511 TA. With regard to the strength, please refer to page 391. The foot is solid and without bolt holes. These should be drilled according to the instructions given in the adjacent table. SSNAD and SNA housings are otherwise identical and the same bearings and accessories may be used.

Housing without seals	Dimensions mm
	For two holes		For four holes
Designation	J	N1	J1	J2	N2
SSNAD 511-609	210	18	200	35	15
SSNAD 512-610	210	18	200	35	15
SSNAD 513-611	230	18	220	40	15
SSNAD 515-612	230	18	220	40	15
SSNAD 516-613	260	22	250	50	15
SSNAD 517	260	22	250	50	15
SSNAD 518-615	290	22	280	50	18
SSNAD 529-616	290	22	280	50	18
SSNAD 520-617	320	26	300	60	18
SSNAD 522-619	350	26	320	70	18
SSNAD 524-620	350	26	330	70	18
SSNAD 526	380	28	370	70	22
SSNAD 528	420	35	400	80	26
SSNAD 530	450	35	430	90	26
SSNAD 532	470	35	450	90	26

 

SN plummer blocks of series SN 5 and SN 6 are coupled with felt seals only. End covers for housings to be mounted at shaft ends are available; further details are available on request. For arrangements requiring frequent relubrication, housings with grease valves are available, see adjacent illustration. The housing dimensions are in accordance with ISO/R 113. The bearing seating is machined to tolerance H7.

SD plummer blocks of series SD 31 TS are designed to take large spherical roller bear-ings or Series 231 C. The housings are fitted with labyrinth rings. These have a clearance titan the chat, but a rubber O-ring inserted between the ring and the shaft ensures that the ring rotates with the shaft and also permits slight axial displacements caused by thermal changes in shaft length. Housings for shaft ends are supplied with an end cover instead of one of the labyrinth rings; further details are available on request. The bearing seating is machine to tolerance H8.

SD plummer blocks can be relubricated. The plug in the lubrication d at in the housing base can b replaced by a grease nipple. The grease penetrates the bearing via the lubrication groove and three holes in the outer ring (VJ33 feature). The housings are also suitable for oil lubrication. Bosses indicate where holes can be drilled in the base and cap for entry and exit of the oil and also to take an oil level gauge and a drain plug. Where circulating oil lubrication is used, the supply may be connected to the lubrication duct in the housing base.

Plummet blocks for bearings with cylindrical bore

SNA plummer blocks of series SNA 2 and SNA 3 are supplied with V-ring seals (suffix TA); those of series SNA 2 up to and including size l8with felt seals (suffix TC). If the housing is to be placed at the end of the shaft, the outer seal may be replaced by an end cover with bonded rubber lip: the designa-tions are given in the housing tables. The V-ring seals comprise a V-ring and a sheet steel washer with protective coating and bonded rubber lip. For housings SNA205 to SNA218 however, the V-ring seals do not include the washer, since the V-ring lips seal directly against the housing, the side faces of the housing being machined. The felt seals consist of felt strips. Regarding oil lubrica-tion please refer to page 386.

SNA plummer blocks are a development of the SN plummet blocks; the dimensions of both SNA and SN housings follow ISOIR 113 and the housings of series SNA 2 and SNA 3 are interchangeable with those of series SN 2 and SN 3, respectively. The SNA housings have much greater strength, however: see pages 391 and 392. Where even greater strength is required. SSNAD housings, described on page 387, can be supplied. The bearing seating is machined to tolerance H8.

SN plummet blocks of series SN 2 and SN 3 are supplied with felt seals only. End covers can be supplied for housings to be mounted at the end of a shaft; further details are available on request. For arrangements

requiring frequent relubrication. housings fitted with a grease valve era available. The housing dimensions are in accordance with ISO/P 113. The bearing seating is machined to tolerance H7.

The spacer sleeves shown in the drawings of plummet blocks for bearings with cylindrical bore are not supplied by SKF.

Housings for bearings with cylindrical bore

The housings of series TVN 2 and TVN 3 ate designed to take self-aligning ball bearings or spherical roller bearings with cylindrical bore. They nave double felt seals. Relubrica-tion is possible if the plug at the side of the housing is replaced by a grease nipple.

TVN housings are supplied either with an end cap (suffix A) or with a cover to take a through shaft (suffix B) The bearing seating is machined to tolerance H7 and the design is such that the bearing outer ring has an axial play oil mm on either side. Bearings can be located by inserting washers of ZW design, see page 487, or a 2 mm wide locating ring (not supplied by SKF). The housings are more frequently used, however, for arrange-ments where the shaft is located in one direction by one bearing and in the opposite direction by a second bearing. In such cases washers or locating rings are not required.

These housings ware originally designed for use on light trucks but may also be used instead of plummer blocks. They are more rigid and can be more heavily loaded than plummer bocks. Data regarding the strength of TVN housings will be supplied on request.

For more detailed information regard-ing sealing arrangements, protective collars and bearing locating rings see cM/0900/PB1 -A

Influence of the direction of loading art the strength of plummet block housings.

Approximate values of the breaking load (P) for the housings, and the yield point (0) for the cap bolts are given in the following tables for different radial directions of loading. When the load acts at an angle of 55 deg. the cap bolts carry no load; Q is always greater than P when the load acts at an angle of 90 deg.

In the axial direction the breaking load is approximately 65 % of P180 deg.

* SSNAD housings have approximately twice the strength

Strength of SN plummer block housing
Housing		Breaking load for the housings *					Yield point for the two cap bolts
Designation P55		P55	P90	P120	P150	P180	Q120	Q150	Q180
--		kN (1kN = 225lbf)					kN (1kN = 225lbf)
SN505	--	70	40	30	30	35	80	45	40
SN506	SN605	80	50	35	30	40	80	45	40
SN507	SN606	90	55	40	35	45	80	45	40
SN508	SN607	100	60	45	40	50	80	45	40
SN509	--	110	65	50	45	55	80	45	40
SN510	SN608	120	70	55	50	60	80	45	40
SN511	SN609	140	85	60	55	70	140	80	70
SN512	SN610	150	90	65	60	75	140	80	70
SN513	SN611	170	100	70	70	85	140	80	70
SN515	SN612	190	110	85	75	95	140	80	70
SN516	SN613	220	130	100	90	110	240	130	120
SN517	--	240	140	110	95	120	240	130	120
SN518	SN615	260	160	120	100	130	240	130	120
--	SN616	280	170	130	110	140	240	130	120
SN520	SN617	340	200	150	140	170	540	300	270
SN522	--	440	260	200	180	220	540	300	270
SN524	--	520	310	230	210	260	540	300	270
SN526	--	620	370	280	250	310	760	420	380
SN528	--	720	430	320	290	360	1000	550	500
SN530	--	860	520	390	340	430	1000	550	500
SN532	--	1100	660	490	440	550	1000	550	500

* Housing series SN2 and SN3 have the same strength as those of series SN5 and SN6, respectively.

Strength of SD plummer block housing
Housing	Breaking load for the housings					Yield point for the four cap bolts
Designation	P55	P90	P120	P150	P180	Q120	Q150	Q180
--	kN (1kN = 225lbf)					kN (1kN = 225lbf)
SD3134	2100	1000	760	680	850	1500	830	750
SD3136	2400	1150	850	760	950	1500	830	750
SD3138	2700	1300	1000	880	1100	2000	1100	1000
SD3140	3200	1600	1150	1050	1300	2000	1100	1000
SD3144	4000	1900	1400	1400	1600	2000	1100	1000
SD3148	4200	2000	1500	1500	1700	3200	1800	1600
SD3152	4700	2300	1700	1700	1900	3200	1800	1600
SD3156	5000	2400	1800	1800	2000	3200	1800	1600
SD3160	6000	2900	2200	2200	2400	3200	1800	1600
SD3164	7000	3400	2500	2500	2800	3200	1800	1600

Shaft dia.		Housing Dimensions										Mass	Designation
da	db	A	A1	H	H1	H2	J	L	N	N1	G
mm		mm										kg	--
130	145	190	130	290	150	50	380	445	35	28	24	28.5	SN226
140	155	205	150	305	150	50	420	500	42	35	30	36.0	SN228
150	165	220	160	325	160	60	450	530	42	35	30	43.0	SN230
160	175	235	160	345	170	60	470	550	42	35	30	49.5	SN232

A marked improvement compared with earlier plummet blocks is that different types of seal can be used. The standard seals supplied by SKF are V-ring and felt seals. They are delivered in special packages to-gether with the housings. Fitting is very simple.

V-ring seals

The V-ring, which is of synthetic rubber, has a thin sealing lip, which functions in an axial direction. The ring also acts as a flinger as it rotates with the shaft. This type of seal can be used with both grease and oil lubrication and is extremely effective under most operating conditions including high speeds.

The V-rings in SNA plummer blocks seal against sheet metal washers with a rust preventive coating and placed in the grooves of the housing. Each washer has a rubber lip bonded around its periphery and which bears against the housing. However, in plummer blocks SNA 205 to SNA 218 the V-rings seal directly against the housing; in this case the side faces of the housings are machined.

SNA plummer blocks with V-ring seals are given the suffix TA, for example SNA 505 TA.

Felt seals

The felt seal is a simple but adequate seal which can be used with grease lubrication and at peripheral speeds of up to some 4 m/s. Plummer blocks of series SNA 5 and SNA 6 are obtainable with split felt seals consisting of oiled felt incorporated in a light alloy ring in two pieces. These are pressed into the housing grooves after first inserting rubber strings, which serve both as an effective seal between the housing and the light alloy ring and also to prevent this from rotating. Plummer blocks SNA 205 to SNA 218 may also be supplied with felt seals but they comprise loose felt strips that are fitted directly in the grooves, i.e. they have no metal backing.

SNA plummer blocks with felt seals are given the suffix TO, for sample SNA 505 TO.

Supplementary sealing components

Protective collars

Where operating conditions are severe, the V-ring and felt seals of plummet blocks SNA 505 to SNA 518 and SNA 605 to SNA 615 may be supplemented by a light alloy collar, a standard component available from SKF. The collar protects the seals against damage and also im-proves the sealing effect. The bore diameter tolerance is H10.

The protective collars are designated TSNA (000) B, for example TSNA 505 B.

End covers

If the bearing is mounted at the end of a shaft, the bore at the outer side of the housing should be closed by means of a special cover. The end covers, which are supplied separately in packages, are designated ASNA followed by the number of the housing, for example ASNA 506-605. Plummer blocks of the series most frequently used, SNA 5 and SNA 6, are available with a seal set comprising one end. cover and one V-ring seal and are then given the suffix ATA, for example SNA 505 ATA.

Special seals for plummer blocks of type SNA

Essential manufacturing data

In TSP 6020, "Plummet blocks of type SNA", some types of special seal are shown on page 5, and the related application dimensions of the housings are given in the table section. This leaflet gives the dimensions required for the manufacture of the seals, which are easily made from tubular material.

Illustrated on this page are two seals for extremely severe operating conditions, a labyrinth seal and a combined V-ring and gap seal equipped with a nipple for lubricating the V-ring. The table gives the dimensions necessary to ensure that the seals fit the housings; other dimensions may be varied. However, in view of the manufacturing tolerances, the bearing internal clearance and inevitable misalignment, sufficient radial clearance in the labyrinth must be ensured.

The labyrinth seal, type TS, shown on this page, is recommended in cases where SKF standard seals cannot be used for one reason or another, for instance if they do not match the diameter of the shaft. Depending on the radial space available for the collar, the (a) or (b) design should be chosen.

x 2 design a design b

Locating rings

The bearing seating in the housings is sufficiently wide to allow axial freedom for any bearing. A bearing which is to locate the shaft should therefore be fixed in position by means of one or more locating rings. If this bearing is mounted on an adapter sleeve, the locating rings should be placed as follows:

1 ring - on the same side as the sleeve nut
2 rings - one on each side of the bearing
3 rings - two on the same side as the sleeve nut
4 rings - two on each side of the bearing

1. Suffix TA to housing e.g. SNA 520 TA, indicates supplied with two V-ring seals and washers.
2. Suffix TC to housing e.g. SNA 520 TC, indicates supplied with two felt seals and light alloy rings.
3. Suffix ATA e.g. SNA 520 ATA, indicates supplied with one V-ring seal and washer and one end cover.
4. For polyurethane protective collars see standard No. CM/0900/PB1B. When calling up these parts the material must be stated since SKF also supply light alloy collars with corresponding part nos.
5. Locating ring designation indicates width and o/dia e.g. 10/370 = 10 wide x 370 o/dia.
6. For details of labyrinth seals and 0-rings see standard No. CM/0900/PB1A.
7. For Teconite seals see drawing No. 2156428.

References

SKF - General Catalogue 3000 IIE/GB666 11 - July 1978.
SKF - SNA Plummer Blocks Ref. No. TSP 6020.
SKF - Special Seals for SNA Plummer Blocks Ref. No. TSP 6021
SKF - Drawing No. 2156428.