Customers today increasingly demand proof of the functionality of custom-designed radial shaft seal rings (oil seals) in special applications. The application of a manufacturer of pumps for diesel engines described below shows how the functionality of radial shaft seal rings in a special application was demonstrated on the test rigs for shaft seals.
Drawing on 50 years of know-how and high-technology testing facilities, Elring Klinger Kunststofftechnik designs customised shaft seals and ensures their functionality in extensive customer-specific test runs.
Shaft seals with a PTFE sealing lip are preferably used to seal rotating shafts. They exhibit outstanding chemical resistance and can also be used in low-lube or dry-running conditions. In a thermal range from -60°C to +200°C radial shaft seal rings are suitable for a broad spectrum of applications. The selection of the PTFE compound in combination with optimal sealing lip design enables very long life cycles in applications like screw compressors or pumps due to outstanding sliding properties. To improve sealing, a hydrodynamic pump-back swirl, which can be achieved either in the sealing lip or the shaft protection sleeve, may be used.
Top performance in extreme situations
Increasingly complex tasks, however, demand top performance in extreme situations by radial shaft seal rings. For example, customers increasingly demand proof of the functionality of custom-designed radial shaft seal rings in special applications. Elring Klinger satisfies these demands through continual developments, which are reflected for example in determining the optimum radial contact force or designing special sealing lip geometries.
In the application of a manufacturer of diesel engines, the specifications cover several pages and numerous application scenarios. The following is an extract from the complex requirements:
- Test runs at 140°C in oil, peripheral speeds of 1,000min⁻¹ up to 8,000⁻¹, stepped increases of the radial shaft offset of up to 0.38mm and angle offset of 0.125mm
- Simulation of static sealing performance with a very thin liquid medium at 140°C and radial offset of 0.285mm
- 500hr of endurance tests at 140°, varying media fill levels, cyclical torque changes and built-in centre offset
Compliance with such extensive specifications poses a particular challenge to a manufacturer of shaft seals.
Test rig for shaft seals
Thanks to its high-tech development facilities Elring Klinger is able to demonstrate the functionality of custom-designed shaft seals for special applications on test rigs for shaft seals.
The illustration shows the test rig set-up between the shaft and the seal installed in the test vessel. An axial shifting of the test vessel creates contact between the shaft and the sealing lip. Depending on the customer’s wish and considering safety rules, the vessel may be filled with special media and tested at different temperatures. For applications under high pressures a precisely balanced spindle bearing is used to absorb the axial forces that occur. The motor can be controlled to enable complex speed cycles to be run. The leakage rates and torques are documented and analysed during the entire test in a PC-controlled process.
Simulation of test conditions
In addition to the standard test conditions, settings to simulate special customer application conditions are possible as well. The design of the test rig allows individually adjustable testing options for the afore mentioned field of application:
- Centre offset (radial, parallel, angular) may be precisely adjusted and quickly modified by shifting or rotating the seal housing using measuring gauges
- Simulation of a vacuum by pressure loading contrary to installation instructions. This makes it possible to test the lifting of the sealing lip
- Simulation of torque variations by increasing and decreasing pressure in specially tested pressure vessels is possible
- Through extensive insulation extreme temperatures can be kept at constant levels
- Special temperature devices enable extreme temperatures of various media to be set
- Precisely adjusted measuring scales allow highly accurate determination of the leakage rate
The testing facilities make it possible to demonstrate that good sealing performance can be achieved with custom-designed radial shaft seal rings. The test runs confirm the function for the special application to the customer. As a result, the customer can reduce extensive field tests, save costs and considerably reduce development cycles.
The following results were confirmed to the pump manufacturer:
- Perfect functioning was demonstrated at high minus and plus temperatures and a shaft run-out of > 0.285mm
- Thanks to optimally designed sealing lips static sealing in the presence of very thin liquid media and different shaft offsets is ensured
- The simulation of the endurance test with various media fill levels, varying speeds and shaft offsets shows optimal functioning of the seal. An assessment of the sealing lip area (sketch of sealing lip) after the test run enables a theoretical service life prediction to be made based on years of experience
In addition to general recommendations such as use at high shaft peripheral speeds of up to more than 30m/s, pressure loads of up to 15bar (short-term) and low-lube conditions, custom-designed radial shaft seal rings can achieve top performance levels even in extreme applications. They include sealing rings with a concentricity of > 0.285mm or lower leakage rate at cyclical speed changes, for example.
Tests can be performed using the following standard parameters:
- Speed: 0⁻¹ – maximum 8,000⁻¹
- Pressure: 0bar – maximum 40bar
- Temperature: -10°C to +140°C
- Diameter: 5mm to 150mm
- Measurement results:
- Torque of the shaft: 0Nm – 10Nm
- Amount of leakage: 0ml – 10ml
The author, Mehmet Cankar, is a member of the technical sales force of Elring Klinger Kunststofftechnik.
