Characteristics
Universal Seal Piston Rings were developed specifically to be totally interchangeable
with the TFE piston rings currently available, and to provide a product which
can be more readily installed on the pistons and provide longer field service
life. Polyurethane Piston Rings manufactured from Unithane 460D material with
and outer wear layer containing a concentration of Molybdenum Disulfide (MSO2).
The purpose being: to provide a low friction surface during the initial break-in
period of the hydraulic cylinder. Series 77 Piston Rings can be manufactured
from alternate materials to meet specific design requirements.
Series No. 77 – Piston Rings provide many advantages as seals.
1. Unithane piston rings expand readily to fit over the major piston diameter
and recover quickly to permit immediate installation of the piston into the
cylinder bore. No expensive expanding arbors or re-sizing dies are required.
This results in a reduction of assembly time and eases field replacement.
2. The Superior cut strength of Unithane 460 D material in combination with
an ultimate elongation of 430% insures that fewer rings are scrapped during
assembly. This also helps to avoid cylinder rework by elimination damaged rings
which being installed on the piston.
3. Unithane piston rings resist field failures attributed to minor scoring
or galling of the cylinder bore which will cause rapid failure of piston rings
made from other less abrasion and cut materials.
4. The inherent elastic memory exhibited by Unithane piston rings insures
instantaneous response to rapidly varying system pressures and eliminates the
objectionable compression set or “cold flow” characteristic commonly
associated with TFE materials.
Unithane piston rings will operate effectively in hydraulic cylinders with
pressures up to 3000 PSI and with radial clearances as great as .008 inches.
The cylinder bore should be finished not to exceed 20 RMS for maximum service
life although somewhat higher limits can be accepted depending on pressure
and frequency of cycling.
The standard bore diameter and the corresponding groove diameter for normal
application of Unithane piston rings is as shown on page 2. These recommendations
conform to ANSIB93.32-1973 and NFPA STD T3.19.18-1973 Groove Dimensions for
Fluid Power Radial Compression Type Piston Rings. Oversize or undersize cylinder
bore diameters from -.020 to +.025 can readily be accommodated provided that
an equivalent adjustment is made in the groove diameter. In extreme oversize
conditions beyond +.025 the groove diameter may need to be increased slightly
more than a matching equivalent and a 90 durometer O ring may be substituted
for the normal 70 durometer to help maintain sufficient circumferential contact
between the piston ring and the cylinder bore.
Material
- TYPE: Unithane 460D, Liquid Cast Polyurethane
- HARDNESS: Durometer 60D
- FLUID COMPATABLILITY: See ‘Material Specifications’, Technical
Bulletin US-96
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