Needle bearing
View Patent ↗The present invention relates to a non-magnetic needle bearing for use in a rotational machine such as, for example, an MRI. The needle bearing may include needles, a cylindrical retainer holding the needles at a predetermined pitch, an outer ring outside of the retainer, and an inner ring inside the retainer. All of the aforementioned may be made of a non-thermoplastic polyimide resin.
1. A needle bearing comprising needles, a cylindrical retainer holding the needles at a predetermined pitch, an outer ring disposed outside the retainer and an inner ring disposed inside the retainer, wherein the outer ring, the inner ring and the needles are made of a first non-thermoplastic polyimide resin comprising a repeating unit represented by the following formula:
wherein R comprises p-phenylene diamine (PPD) units and m-phenylene diamine (MPD) units;
and the retainer is made of a second non-thermoplastic polyimide resin comprising a repeating unit represented by the following formula:
2. The needle bearing of claim 1 , wherein the needle bearing comprises no ceramic or metal.
3. The needle bearing of claim 1 , wherein the second non-thermoplastic polyimide resin further comprises filler.
4. The needle bearing of claim 1 , wherein tensile strength of the first non-thermoplastic polyimide resin is from about 80 to about 250 MPa at 23° C., and the tensile strength of the second non-thermoplastic polyimide resin is from about 45 to about 100 MPa at 23° C.
5. The needle bearing of claim 1 , wherein coefficient of friction (COF) of the first non-thermoplastic polyimide resin is from about 0.07 to about 0.6 at PV=3.4 MPa·m/sec and coefficient of friction (COF) of the second non-thermoplastic polyimide resin is from about 0.01 to about 0.4 at PV=3.4 MPa·m/sec.
6. The needle bearing of claim 1 , wherein flexural strength of the first non-thermoplastic polyimide resin is from about 150 to about 350 MPa at 23° C., and flexural strength of the second non-thermoplastic polyimide resin is from about 60 to about 180 MPa at 23° C.
7. The needle bearing of claim 1 , wherein flexural modulus of the first non-thermoplastic polyimide resin is from about 4500 to about 6900 MPa at 23° C., and flexural modulus of the second non-thermoplastic polyimide resin is from about 2500 to about 4600 MPa at 23° C.
8. A rotational machine comprising at least one needle bearing of claim 1 .
9. The rotational machine of claim 8 , wherein the rotational machine is a magnetic resonance imaging (MRI).
10. The needle bearing of claim 1 , wherein R comprises greater than about 60 to about 85 mole % (PPD) units and about 15 to about 40 mole % m-phenylene diamine (MPD) units.