Text version of the page

− 40 °C as they lose theirelasticity.The organic solvents normally used to clean rolling bearings such as white spirit ortrichlorethane do not affect cage properties, nor do dilute alkaline cleaners (e.g. soda) ifthey are at room temperature and the periodduring which they are in contact is short.The chlorofluorocarbons or ammonia usedin refrigeration do not attack polyamide. In vacuum, polyamide cages become brittlebecause they become dehydrated.Steel cages The majority of SKF needle roller bearingsare fitted with pressed cages of steel or sheet steel. These cages have relatively highstrength and weigh little. They take up little space in the bearing and therefore allowadequate lubricant supply to the roller/race-way contacts. The sheet steel cages are produced fromdeep drawing strip or tube. The joints are welded. To reduce friction and wear theymay be hardened and surface treated.The steel cages are produced from mildsteel tube and have profiled surfaces.Steel cages can be used at operatingtemperatures up to 300 °C. They are not af-fected by the mineral or synthetic oil-basedlubricants normally used for rolling bearings,nor by the organic solvents used to cleanbearings. There is a risk of corrosion wherewater is present. temperature. Brief periods at up to 20 °Cabove the recommended maximum tem- peratures can be tolerated provided they are interspersed with longer periods at operat- ing temperatures below the recommended values, and provided the maximum operat- ing temperature for the lubricant is not ex- ceeded. When operating temperatures are constantly above 120 °C, bearings fitted with metallic cages must be used. Polyamide cages are also unsuitable for operating tem- peratures below

Needle roller bearings (4703 /IE) - 5564 2

Table 7

Permissible operating temperatures for cages ofglass fibre reinforced polyamide 6,6 with various bearing lubricantsLubricantPermissible operating temperature
1) –°C Mineral oils Oils without EP additivese.g. machine oils, hydraulic oils120EP oilse.g. industrial and automotive gearbox oils110EP oilse.g. rear axle and differential gear oils (automotive), hypoid gear oils100 Polyglycols, poly- α -olefins120Diesters, silicones110GreasesLithium base Synthetic oils
2) , polyurea, bentonite, calcium complex120
1) 2) Measured on the outside surface of the outer ring For sodium and calcium base greases and other bear-ing greases with a maximum operating temperature below 120 °C, the maximum temperature for the poly- amide cage is the same as the maximum operating temperature for the grease; otherwise the permissible maximum operating temperature is 120 °C

23