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Tandem bearings technical Information
Tandem bearings offer an optimum solution wherever thefollowing requirements apply:
1. small radial design envelope
2. high axial forces
3. long operating life
4. low frictional energy.
Tandem bearings have proven effective principally in gearboxesfor single and twin screw extruders in the rubber and plasticsindustry.
Other possible applications include:
1. deep hole drilling equipment
2. friction welding machines.
Product description
Tandem bearings consist of several axial cylindrical rollerbearings arranged in line, A system of rings and washersmatched to each other ensures that all stages of the tandem bearing are subjected to uniform load at all times irrespective ofthe ratio C/F. The rings and washers are made from hardenedsteel. Tandem bearings are predominantly fitted with standardaxial cylindrical roller and bearing assemblies.
Structure and power flow
Design of bearing arrangements
For the installation of tandem bearings, the adjacent construction must be designed as follows:
1. with preload of one percent of the basic dynamic load rating
2. with radial guidance, for example by means of needle rollerbearings, Figure: Twin screw e xtruder g earbox.
3. without tilting. The adjacent parts must be machined such that no tilting
is transmitted
4. taking account of the spring constants of the tandem bearing,especially when combined with axial bearings of a differentdesign
5. with a mounting fit of f6 for the shaft and F7 for the housing bore, in order to achieve correct functioning of the bearings.
Lubrication
Tandem bearings are always operated with recirculating oil lubrication, Figure Oil outlet, oil inlet, dimensions.
We calculate the oil quantity and oil viscosity in accordance with the data given in thequestionnaire MCT.
Ordering example:
1. Tandem bearing with 6 stages
2. Shaft diameter 4 mm
3. Outside diameter 24 mm
4. Bearing width 105 mm.
Ordering designation:M6CT4*24*105
Oil outlet, oil inlet, dimensions
Multi-Stage Cylindrical Roller Thrust Bearings
Introduction
BRH BEARING
(Tandem Bearings) Multi-stage cylindrical roller bearings (Tandem bearings) have very good characteristics of limited radial space, high axial forces, equal support of all the rows of rollers and long operating life, and is the ideal spindle of parallel
Method of designation
M C T
Tandem Bearings rows
Bore &out diameter
screw extruder.
The tandem bearings provided by our institute has the following types: double rows, three rows, four rows, five rows, six rows and eight rows,
we also provided bearings with shaft and sleeve barrel. Customers can have their own selections according to center distance of screws, space and load . We also accept the orders of other dimensions.
Application of tandem bearings
When using tandem bearings, following recommendations should be adhered :
(1) Preload: 1% of the dynamic basic load rating.
(2) Radial guidance: full complement cylindrical roller bearings .
(3) Eliminate tilting: the supporting parts must be machined to eliminate any tilting.
A: Shaft A2：Sleeeve E:nylon cage
Example:
M6CT2385 (Old:T6AR2385)
Tandem bearing 6-row, d=23 D=85
Tandem bearings are primarily usedwhen reliable support must be provided for high axial forces in a limited radialdesign envelope. A typical application fortandem bearings is the distribution gearin twin screw extruders .Due to the small center distance betweenthe heavily loaded extruder shafts, a tandem bearing is often used in combination with a thrust cylindrical roller bearing having the correspondingload carrying capacity
The combination of two identical tandembearings or two differing tandem bearings is also possibledepending on the design envelope and gear application.
(4) Mounting tolerances: recommended the following mounting tolerances: shaft f6 and housing bore F7.
(5) Lubrication: tandem bearings must always be lubricated by oil circulation .
Tandem Thrust bearings are comprised of “stages” which include precision ground and matched thrust plates and compression sleeves separated by cylindrical roller assemblies. This design enables the Tandem Thrust bearings to provide a solution in a radial restricted envelope. The bearings are available in multiple stages, 2-8 to accommodate your designrequirements. Depending on your preference, these bearings are available in a wide variety of sizes and options as illustrated on the pages to follow.
Features and Benefits
1.Minimal Backing Support Requirements 2.Space Saving Design
3.Matched Precision Ground Rollers 4.Machined Brass Roller Riding Retainer 5.Precision Ground Inner and Plates
5.Precision Ground Inner and Outer Compression Sleeves
Tandem Bearings in Twin Screw Extruder Gearboxes
4.Bearing Selection
BRH BEARINGS
Modern twin screw extruder gearboxes with a high power density such as those used in the processing of thermoplastic materials are machine elements that must provide a high degree of reliability in operation. The tandem bearingssupplied by a well-known rolling bearing manufacturer have been used in harsh environments fordecades. In spite of increasing demands placed on these bearings, like the
requirements for deep foundation drilling equipment or friction welding machines, these products have proven themselves as reliablemachine elements. These tandem bearings represent an excellent solution for applications requiringa small radial design envelope,high axial forces and long life.
1.Tandem Bearing Design
Tandem bearings consist of several coaxially arranged thrust cylindrical roller and cage assemblies. Two, three or four thrust cylindrical roller and cage assemblies can be used, corresponding to product designations M2CT.., M3CT.. andM4CT.. respectively. Six row and eight row tandem bearings (M6CT.. and M8CT..) are also available. These products consist of two triple row and two four row tandem bearings respectively.
The special elastic system of matched rings and washers made from hardened rolling bearing steel ensures that there is an equal load on all rows regardless of the magnitude of the axial load.
2.Tandem Bearing Operation
To meet the requirement that all rows support equal portions of the axial forces from the extruder screw regardless of the load ratio C/P, the shaft sleeves and housing sleeves are specially designed so that the same deflection is achieved for each row. The geometry of the rings thus plays an important role in providing the optimum flow of power in the bearing. The shape of shaft washers and housing washers primarily effects the load distribution on the length of the cylindrical rollers. The design of shaft and housing washers allows both components to receive the same polysymmetric deformation. Although the washers underload are subject to elastic deformation,both raceways nonetheless remain almost parallel to each other. Rolling element tilting or edge loading on the rolling elements, which lead to reduced service life, can thus be eliminated.In addition to the equal deflection on each row mentioned above, in the case of six row and eight row tandem bearings the load distribution between the three row and four row tandem bearings must be achieved corresponding to their load carrying capacity. This can be done by matching the shaft sleeve and the housing sleeve.
Three pieces of information are necessary when selecting a suitable tandem bearing:
– the maximum possible bearing OD
– the desired calculated rating life under operating load and speed
– the maximum screw pressure.
The maximum possible bearing OD results from the intermeshing of two screws in the case of twin screw extruders. In the process, the crest dia- meter of one screw contacts the root diameter of the other screw. The re- sulting tight center distance and the output shaft near the tandem bearing limit the radial design space. The length of a tandem bearing is normally not a crucial factor in bearing selection. For this limited envelope, tandem bearings are available in the 31.5 to 900 mm OD range.
The required calculated rating life under operating load and speed is gen- erally between 20,000 and 40,000 hours for extruder gearboxes. Smaller gearboxes such as those used in extruders for laboratory applications have shorter life requirements. Here, a value of 5,000 hours is sufficient.
Another factor to consider in bearing selection is the maximum screw pressure. Due to the deformation of the components and the resulting stresses, a maximum permissible axial load Fa max may not be exceeded. The value for Fa max, the dynamic load rating C as well as the static load rating C0 can usually be found in the tandem bearing delivery drawing.
The value Fa max refers to the permissible strain on the components (rings, washers,etc.). For this reason, the maximum screw pressure should be known. On the other hand, the dynamic and static load ratings refer to the entire rolling element set. Since the value for Fa max is always lower than C0, the static load rating C0 is not relevant for the selection of a tandem bearing. We can provide gearbox manufacturers with a tandem bearing data sheet so that all relevant data can be recorded precisely. This allows the optimum bearing solution to be recommended.
4.Mounting Tandem Bearings
Tandem bearings are mounted with a loose F7 fit for the housing and f6 for the tandem bearing shaft. A loose fit is necessary to allow the axial shifting (deflection) of the washers, rings and sleeves. The seating surface of the adjacent structure (housing and shaft) should be designed to have a perpendicularity tolerance to DIN ISO 1101 and qualities IT4 to IT7(depending on the diameter range).
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