Lip seals
Introduction
At NMF, we offer a wide range of lip seals, ranging from single or double lip models, made from a variety of high-quality materials. Our lip seals can seal both pressure and rotational speed, depending on the model up to 150 bar or 40 m/sec. A major advantage is the low friction on the shaft, which ensures less wear, lower power loss and longer service life. Models such as the BSB type replace the traditional oil seal and offer up to three times the service life. Many of our products are suitable for ATEX environments and certified for the food industry (EC1935:2004).
Solutions
Our solutions help companies in industries as diverse as food and pharmaceutical, offering excellent performance and cost savings. The design of lip seals contributes to high efficiency and reliability, with customers experiencing extended seal life, as seen in feedback citing an 8-fold increase in service life.
With NMF lip seals, you choose quality, durability and innovative sealing solutions that meet the demands of modern industries.
How does a VR seal work?
A vr lip seal or radial lip seal consists of a rubber diaphragm stretched around a metal support member. On the outside, this sheath acts as a static seal. On the inside, the diaphragm sits on the shaft. The amount of tension and angle of the lip is precisely matched to the shaft. The sealing lip can face either inward or outward. The mounting direction determines the direction from which pressure will act on the seal. Due to the slight preload of the VR seal, there is a low coefficient of friction. As a result, there is little loss of force and energy. In addition, the chance of groove formation in the shaft is minimal.
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Technical explanation of operation of Lip seals
Basics of Lip seals
Lip seals, also known as radial seals, are used to seal the transition between a rotating shaft and a stationary housing component. This is accomplished by a flexible lip that closes tightly around the shaft. The purpose of the seal is to keep lubricants in while keeping external contaminants such as dust and moisture out. The seal lip is usually supported by a spring that provides consistent radial pressure on the shaft.
Materials and Resistance
Lip seals are often manufactured from elastomers such as NBR (nitrile rubber), FKM (fluorinated rubber) or PTFE (polytetrafluoroethylene) for applications requiring higher chemical and temperature resistance. PTFE seals, as shown in the NMF Lip Seal PTFE special brochure, have a low coefficient of friction, are resistant to high temperatures and can be used in corrosive environments. This makes them suitable for applications such as pumps, rotary compressors and mixers.
Pressure and Speed
Lip seals are often exposed to both rotational forces and pressure differentials. Typical seals such as the BSB type can withstand pressures up to 15 bar and speeds up to 40 m/s. These seals are designed to perform at high speeds without excessive wear on the seal lip or shaft. The elasticity of the lip ensures that a constant seal is maintained even with variations in pressure or rotational speed.
Assembly and Maintenance
An important advantage of lip seals, such as the BSB type, is their easy installation. They can be installed without special tools and have the advantage of contacting a different part of the shaft than traditional seals. This reduces the need for shaft overhaul when replacing the seal. The outer wall of the lip seal, made of elastic rubber, adapts to small irregularities in the shaft or housing, ensuring a perfect static seal.
Special Applications
Many lip seals are specifically designed for demanding environments such as ATEX certified zones or hygienic environments in the food and pharmaceutical industries. Lip seals that meet standards such as EC1935:2004 are suitable for food contact and provide a safe sealing solution for equipment that must operate under strict hygiene conditions.
Replacement of Oil Seals
The BSB type, as indicated in the brochures, is a direct replacement for traditional oil seals. It offers longer life, often three times longer than standard oil seals, thanks to the use of high-quality materials and a design that minimizes shaft wear. This reduces overall maintenance costs and increases seal reliability in demanding industrial applications.
Where are VR lip seals used?
Gearboxes
Electric Motors
Pumps
Propeller shaft seals
Vehicles
Spindle seals
Motors
Rotary encoders
Agitators
Household machines
Key features VR lip seal
No hardened shaft or surface treatments of the shaft are required. Available in many different materials and leaves no damage (run-in marks) on the surface.
What materials are VR seals available in?
Due to the universal nature of the VR seal, this seal is manufactured in many different materials. Below are the properties of the most common material types. A comprehensive chemical resistance list can be found here.
NBR (Nitrile-Butadiene-Rubber)
Nitrile-Butadiene-Rubber (NBR) also known as nitrile rubber. This material is suitable for temperatures from -40° to 108° C. And is resistant to lubricating oil, hydraulic oil and water. This material is less suitable for use with acids, solvents and ozone exposure. Well-known brand names are: Krynac® and Nipol®.
FPM/FKM (Fluoropolymer Rubber)
Fluoropolymer Rubber (FPM according to the DIN/ISO system) FKM is the abbreviation for the same material, but according to the American ASTM standard. This material is used when high temperatures -25° to +204° C are involved. FPM also has good performance with many different chemicals and solvents. In dynamic applications, the material is less suitable for alternating direction of rotation (pendulum movements) due to the stick-slip effect. Well known brand names are: Viton®, DAI-EL®, Dyneon®, Tecnoflon®.
EPDM (Ethylene-Propylene-Diene-Monomer)
Ethylene-Propylene-Diene-Monomer (EPDM) O-rings, unlike NBR, are highly UV resistant and resistant to steam, hot water, chemicals and silicone oils. EPDM materials are not resistant to mineral oil-based products such as lubricating oils and motor fuels. The temperature range is between -45°C to +130°C.
VMQ (Vinyl-Methyl-Polysiloxalane)
Vinyl-Methyl-Polysiloxalane (VMQ) Silicone rubber has excellent aging resistance and is resistant to UV rays, weathering, animal and vegetable oils and fats. Silicone also has a very wide operating temperature range and remains flexible in cold conditions. VMQ is applicable in the food industry. It is not resistant to motor fuels, silicone oils and water vapor with temperatures above 120° C.
HNBR (Hydrogenated Nitrile Butadiene Rubber)
HNBR has very good resistance to hot water and steam, oil resistant even at higher temperatures. For use with: gasoline, also so-called acid gas oil, high alloy oils, cooling water, glycol, acids and alkalis. Not for use with: aromatics, chlorinated hydrocarbons, ketones, esters and ethers, as well as brake fluids. Do not use syntheticoilsor greases, only with mineral components. The temperature range is between -30º and + 150º C. A well-known brand name is: Therbaan®.
Difference between a VR seal and oil seal
Because the membrane of a VR seal is stretched over the support section, it has free room to move. This allows the support section to be enlarged while maintaining flexibility. In the case of an oil seal, the elastomer is glued or vulcanized to the support section. The armor of the vr lip seal allows the seal to withstand pressures up to 150 bar.
VR seals can therefore be used as a replacement for an oil seal. Even if there is groove formation in the shaft. To the right, you will find a version (BSB) specially designed to replace the oil seal 1 to 1. Due to the design of the seal, the seal lip will seal at a different position of the shaft.
What is the allowable working pressure for a standard VR Seal?
Due to the support ring of the sealing lip(s), high pressures can be sealed. The standard version can accommodate pressures up to approx. 15 bar, depending on rotational speed, shaft finish and temperature. For low pressures and relatively large rotational deviations, a low pressure (up to approx. 6 bar) version is available.
VR Seals for high pressure applications
These seals can press seals up to 150 bar at 3,000 rpm through a special construction of the support ring. To withstand the high pressures, there is a gap of only 0.02 mm relative to the shaft diameter. This prevents the elastomeric part of the seal from extruding between the shaft and the support part. The support part is made of plain bearing bronze and also serves as a plain bearing.
VR Seals with metal struts
Most often, the struts are supplied in stainless steel 304. In addition, materials such as aluminum, bronze or acid-resistant stainless steel are available.
VR seals with single sealing lip. What versions are available?
Depending on the arrangement, pressure direction and mounting method, the following single-lip seals are available
.
VR seals with double sealing lips. What versions are available?
Double-lip vr seals are also available in a variety of designs. The arrangement, pressure direction and mounting method are also factors in the choice.
Running surface of a vr lip seal and the surface roughness of the shaft
The surface area of the shaft has a great influence on the degree of density. Especially if the circumferential velocity is high and the medium to be sealed is under pressure. An overly smooth shaft prevents the build-up of a lubricating film between shaft and sealing lip. Less lubrication means wear and heat build-up. A rough shaft causes oil leakage and increased wear of the sealing lip.
The shaft surface roughness is determined by the average tread depth Ra of the machining grooves. For normal operating conditions, the shaft in the area of the sealing lip should have a surface roughness of Ra = 0.6 - 0.8
μm. In high-pressure applications, the surface may have a roughness of Ra 0.4 - 0.6 μm.
What are tolerances of the shaft and housing?
The shaft that is sealed by means of a VR seal is turned off standard with a tolerance h11 the bore in H8.
Running surface of a vr lip seal and the surface roughness of the shaft
The surface area of the shaft has a great influence on the degree of density. Especially if the circumferential velocity is high and the medium to be sealed is under pressure. An overly smooth shaft prevents the build-up of a lubricating film between shaft and sealing lip. Less lubrication means wear and heat build-up. A rough shaft causes oil leakage and increased wear of the sealing lip.
The shaft surface roughness is determined by the average tread depth Ra of the machining grooves. For normal operating conditions, the shaft in the area of the sealing lip should have a surface roughness of Ra = 0.6 - 0.8
μm. In high-pressure applications, the surface may have a roughness of Ra 0.4 - 0.6 μm.
What are tolerances of the shaft and housing?
The shaft that is sealed by means of a VR seal is turned off standard with a tolerance h11 the bore in H8.
VR Lip seal fit with or without grease?
To achieve optimum sealing and minimum wear, lubrication is recommended. A seal with a double lip seal has space between the two sealing lips. This space can be filled with lubricant and serves as a grease depot. As a result, dry running is not a problem. Preferably use mineral oil or silicone grease. Always check for chemical compatibility, though.
Some elastomers, such as Therbaan, have good resistance to dry running. However, lubrication gives a higher service life. Here the lubricant must not contain any synthetic components. Greases with a consistency class NLGI 1 or NLGI 2, according to DIN 51818 are suitable for this purpose.
For EPDM, only silicone-based greases may be used.
VR seal assembly
In addition to good surface roughness and proper tolerance, the correct method of assembly of a lip seal has a major influence on the service life and high quality of the seal. Because the inner diameter of the seal must be stretched during assembly, it is necessary for the shaft to possess a run-up taper. The angle at which the run-up taper must be chamfered is 30°. To facilitate assembly, both the shaft and the sealing lip of the VR seal should be greased. This also ensures that you have good run-in lubrication.
What is the stick-slip effect?
The stick-slip effect results from the rubber sticking to a surface due to lack of lubrication. When there is a transition from standstill to motion, there is high resistance in the first place. Material of the retaining ring affects the degree of the stick-slip effect. The stick-slip effect can damage the rubber and cause leakage.