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Rotary seal of PTFE

The rotary seals type RI as the internal sealing version and type RA as the external sealing version are used to seal shafts, axles, rods, pins and rotary glands in rotational and swivel motion applications. They have a proven track record as low-friction components and have been successfully employed over many years. The geometry of the seal enables it to be used for double action duty with both alternating pressurisation and simultaneous differential pressurisation.

The contact surface profile has been designed to ensure reliable use at high pressures and low sliding velocities. Depending on the design and cross section, the contact surface may feature one or two circumferential grooves to enable better transmission of the contact pressure onto the sealed mating surface. Lubricant is stored in the grooves for additionally reducing friction. On the static side, the face for receiving the O-ring serving as the preload element is concave in shape. This increases the contact area while reducing the danger of seal co-rotation. Notches are incorporated in the side faces of the rotary seals to improve the response behaviour with the preload element.

A wide range of different material combinations for the sealing element and appropriate selection of the right material for the preload element ensure effective variability of the system for virtually unlimited use in different applications.

Benefits

  • Outstanding friction behaviour
  • No stick-slip effect, even at low velocities
  • High wear resistance, long service life
  • Very good thermal and chemical resistance
  • Individual size ranges possible
  • Simple groove design
  • Lubricant reservoir

Application ranges

Velocity:up to 1 - 2 m/s
depending on material combination
Temperature:- 60° C to + 200° C
depending on material combination and O-ring material
Pressure:up to 30 MPa (300 bar)
static loads up to 60 MPa (600 bar)
depending on material combination

Installation

The type RI (internal) and type RA (external) rotary seals can be fitted without problem in continuous grooves. To facilitate mounting, it may be advisable to warm the seal in oil at a temperature of approx. 80°C prior to fitting. After fitting the preload and sealing elements, PTFE rotary seals have to be sized. In the case of the externally sealing type RA, this can be done by using the insertion bevel on the cylinder barrel which should have an angle of between 15° and 20° and a length of between 2 mm and 8 mm depending on the as-designed sealing height. The internally sealing type RI has to be deformed into a kidney shape – ensuring that there is no kinking – prior to fitting and then inserted in this form. Once inserted, the seal can be reformed back into its ring shape in the groove. Once the preload and sealing elements have been fitted, the PTFE rotary seal must be sized with a mandrel featuring a bevel of approx. 10°-15° and a length of approx. 30 mm. The piston rod can likewise be used for this sizing operation provided that it has a sufficient insertion bevel. Likewise, a separate sizing sleeve or a sizing pin can be used. It must always be ensured that sharp edges are removed by rounding or bevelling. Thread tips should be covered. Before fitting, ensure that all machining residues such as swarf, chips, dirt and other foreign particles have been removed.

The surface quality of the mating faces being sealed is of decisive importance for the functional reliability and service life of the seal. Where rotary sealing applications are concerned, we recommend that the mating surface exhibit a hardness of approx. 55 HRC with a depth of hardness of at least 0.3 mm. In the case of coated/plated surfaces, it must be ensured that no ablation has taken place. Adequate heat conduction/dissipation must also be ensured by the coating. Unhardened mating surfaces should have a Brinell hardness of at least 1800 N/mm2.

It is important to ensure that there are no ridges, scratches or recesses, nor any concentric or spiral machining marks on the surface. The parameters usually applied for surface description such as Ra, Rz, Rt and Rmax are defined in DIN 4762 and DIN 4768.

In order to properly assess surface quality for sealing applications, the material ratio (bearing curve tp) should also be taken into account. This profile shape parameter is influenced by the machining process applied. The material ratio (Mr) should lie between 50 and 70% as determined at a slice depth of approx. 0.25 x Rz based on a reference percentage of approx. 5%.

Directives

All information and values stated concerning our product portfolio are based on the knowledge optained through a long experience of manufacturing and application.
These figures are for indicative purposes only and may vary (exceed or deceed) according to the particular circumstances. Unknown factors in the applications and practice can considerably change the conditions and reduce and change statements, which may cause the above information to be invalid.
No liability can be accepted for any mistakes or omissions, error and subject to change without prior notice.

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Rotary sealing

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