Item 1171
OTHER: Mechanics -
Bearing - Crossed Roller
Crossed Cylindrical Roller Bearings
Note:
It appears that SKF no longer produces this bearing.
For Technical Information:
See;
SKF general catalogue, p.402
Equivalent Bearing Loads:
(approximate value) (from SKF general catalogue, p.402)Dynamic:
P = Fr + 0.45 * Fa + (4 * M / (d + D)) when Fa / (Fr + (4 * M / (d + D))) <= 1.5
P = 0.67 (Fr + Fa ) + ((4 * M) / (d + D)) when Fa / (Fr + (4 * M / (d + D))) > 1.5
Static:
P0 = Fr + 0.44 * Fa + (4 * M / D + D)
where;
Sources and other Outside Information:
Quote from ZNL Precision Bearings PVT. Ltd., India:
|
REF: PBPL/120303/2 |
Visit Our website : www.znlbearings.com |
Date: |
12th March,03 |
|||||||
|
Name: |
jackson.dave@shaw.ca |
Delivery Terms: |
FOB, MUMBAI (ADD 5% FOR CIF) |
|||||||
|
Address: |
Brand : |
ZNL/Your registered or NEUTRAL |
||||||||
|
City: |
Country: |
Dispatch : |
90 to 120 days. |
|||||||
|
Phone: |
Packaging: |
Each one box. |
||||||||
|
Pos. |
Bearing No. |
Quantity |
Price USD/Pc. |
Total USD. |
||||||
|
Minimum Order Quantity |
||||||||||
|
1. |
MMXC 1922 |
12 |
37.530 |
450.36 |
||||||
|
2. |
MMXC 1022 |
12 |
52.560 |
630.72 |
||||||
|
3. |
MMXC 1924 |
12 |
39.510 |
474.12 |
||||||
|
4. |
MMXC 1024 |
12 |
54.180 |
650.16 |
||||||
|
5. |
MMXC 1926 |
12 |
55.260 |
663.12 |
||||||
|
6. |
MMXC 1930 |
12 |
66.600 |
799.20 |
||||||
NASA Tech Brief:
Crowned races have been proposed for crossed roller bearings. Crowning of the races is expected to reduce scuffing of the cylindrical rollers. Crowning of the races is expected to be especially beneficial in bearings made of polymers (instead of metals) to reduce weight.
The crossed-roller bearing design is the roller equivalent of the x-type ball bearing design. In a crossed-roller bearing, the races are conical surfaces at angles of 45° to the axis of rotation. The advantages and disadvantages of the ball and crossed-roller designs are complementary: In comparison with ball bearings, roller bearings can withstand greater loads. On the other hand, roller bearings are more susceptible to scuffing, which is caused by a kinematic mismatch between tangential roller speeds at the inner and outer diameters of the races.
In a crossed-roller bearing with crowned races (see figure), the contact area, and thus the amount of scuffing, would be reduced (relative to that of conical races) to a value near that of ball bearings. The crown radius is a free design parameter that can be chosen, along with other parameters, in consideration of the bearing material(s) and the loads that must be borne in a given application.
One might ask why it would be preferable to crown the races instead of crowning the rollers. The reason is a practical one: Unlike in the case of steel bearing balls, it is difficult to fabricate polymeric bearing balls or polymeric crowned rollers with sufficient precision to ensure sharing of loads as needed for long bearing life. On the other hand, cylindrical crowned rollers of sufficient precision can be fabricated easily by centerless grinding in conventional machines.
This work was done by Donald Bickler of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Mechanics category.
NPO-30203
Have a US citizen obtain this report.
Is there a local company that can do high quality centerless grinding?
The following is available to a US citizen or resident only
Jun-2002 issue, page #72
Crowned Races for Crossed Roller Bearings
TSP is available for downloading as a PDF document NPO30203 (206.47 KB).
- Click here to download this item now.
- Click here to request further follow-up or contact assistance for this item only.
Postings on Eng-Tips Forum:
Reply on Eng-Tec from dimondjim re my request for suppliers:
Rotek Inc. 330-562-4000 makes cross roller bearings. They do not appear to produce this type of bearing. I have sent them an e-mail asking if they do and if not, who does.
Timken Co. [TKR] in Canton Ohio makes tapered cross roller bearings. They do not appear to produce this type of bearing. I have sent them an e-mail asking if they do and if not, who does.
________________________________
2nd post on Eng-Tec from dimondjim re my request for suppliers:
I worked for both companies and they both make cross roller bearings. I just retired from Rotek and we have made many for tunnel boring application. They were not crowned rollers but crown relieved rollers. For continuous duty or high speeds a cage is needed in the design. For slower applications plastic spacers are used and if very slow no spacers or cage is used maximizing the static capacity of these. Some of the cross roller designs have had 2 rollers in the thrust direction and then 1 roller in the opposing direction installed around the bearing. I have seen 3 roller to 1 also in catalogues. Rotek makes large bearings that bolt on to structures. Most of the cross roller designs have been changed to the 3-roller design if space permits. Harvey Sable or Mark Gonczy from Rotek should be able to help you. You may tell them that Jim Geisey referred you to them. If you are talking about small bearings i.e. under 12 inch diameters, Rotek does not make that product line. Feel free to call me at home as well. 330 678 0226.
Timken makes tapered cross roller designs and most of their rollers are crowned as far as I know. Who did you talk to about these? I think crown relieved may be an alternative to full crown.
From the article that you suggest, are your talking about polymer rather than steel. If so you are correct. Neither Timken nor Rotek make plastic bearings. What is your application?
I think SKF was sued many years ago and dropped that product line. These were bolt on bearings that replaced ball bearings. Cross roller bearing demand very rigid mountings and very flat surfaces to ensure full load support.
________________________________
3rd post on Eng-Tec from dimondjim re my request for suppliers:
I do not know to whom you spoke but both companies make cross roller bearings. Rotek rollers are crowned relieved to reduce the end stresses. I think Timken still puts a full crown on the tapered rollers but am not certain about the tapered cross rollers. If you mean that neither make polymeric bearings, you are correct. Rotek just finished a large tapered xr bearing inner and outer races for a large cross roller bearing for Timken. Rotek does not make tiny bearing i.e. under 12 inches. Plastic has so little load carrying ability, that we never seriously considered these for any heavy-duty application.
As to crowning the raceways, it would be very difficult to gage or machine these, fine turning might be an option.
________________________________
Another post on Eng-Tec from AHRBearing re my request for suppliers:
Can you advise on the magnitude of the moments? I've had experience on helicopter bearing design and I can appreciate what your after. I know of a company in Germany that could do it but it would depend on the loads and the target unit weight your after.
Crossed Taper Roller Bearings
Note:
XXX
Sources and other Outside Information:
SKF:
http://www.skf.com/portal/skf/home/products?newlink=1_21_7 From talking to Cris at SKF, it appears that they do not or no longer produce these bearings, and the smallest was 8" ID. He said that they might be producing some for specific customers.Timken crossed taper roller bearings;
Are too large.TXR (crossed roller bearing)
Back to top | SynchroLite Home Page | UniCopter Home Page
Last Revised: October 10, 2005