SANVI Trstenik

HIDRAULIKA I PNEUMATIKA

Seals

MATERIALS

 

NITRILE (NBR)
It is suggested for the biggest part of sealing applications and it has a very common use. Nitrile (NBR) is a Butadiene - Acrylo Nitrile (ACN) is a polymer. The percentage of acrylo nitrile in the nitrile compound varies between 30% and 50%. The variation in the percentage of ACN changes the volume, gas permeability, elasticity and compression set of the compound used in mineral oils, grease and fuel. Nitrile is very durable against aliphatic hydrocarbons (i.e. propane, butane, petroleum etc.), mineral oils (lubricants, H, HL, HLP type of hydraulic oils), greases, HFA, HFB, HFC, type hydraulic fluids, vegetal-animal oils, light heating oil and diesel oil. For fuels and industrial fluids, different mixtures are prepared. Our standard nitrile compound is recommended to be used between -30°C and +105°C. For short period of applications, it can be increased to +120°C.

HNBR
It is a kind of elastomer which is made in such a way that a part or complete part of NBR polymer is hydrogenized with double linked Butadien. Vulcanized with Peroxide HNBR has durability against high temperature and oxidation. Having higher temperature resistance and mechanical values than standart NBR compound, HNBR is suggested for the temperature range -30 and +150°C.

SILICONE (MVQ)
Silicon keeps its elasticity between -60°C and 200°C. It is not recommended for dynamic applications. It has a good resistance against ozone, atmosphere and lubricants where as it has a less durability against oxidizing lubricants and some hipoits as well as lubricants of E.P. type.

VITON (FKM-Flourel)
This material under the trade mark Viton or Flourel has durability against all types of greases, lubricants and solvents. And it has a good resistance against many chemicals. It functions very properly in vacuum-systems and in case of applications requiring low gas permeability. Viton keeps its elasticity between -30°C and +225°C.

NEOPRENE (CR)
It has a great resistance to rupture, to tear and to wearing out between the temperatures -45°C and 100°C. It has endurance against flame. Its resistance against mineral oils with high aniline point, silicon oil, grease and alcohole is good. It is also used in applications where endurance for lubricant and atmospheric conditions are required.

POLYURETHANE (PU)
It has a perfect durability against rupture, tear and wearing out in the temperatures between -30°C and 100°C. And it has resistance to atmosphere and ozone. Its resistance to mineral oils, grease and aliphatic hydrocarbon is good. Especially, it is used as shaft stripper and high compressed sealing element.

ETHYLENE-PROPYLENE DIENE RUBBER (EPDM)
The temperature range is -40°C and 145°C. It has resistance against break fluids, steam, phosphate and esther fluids.

STYRENE BUTADIEN RUBBER (SBR)
Between the temperatures -50°C and 100°C its resistance against glycol based brake fluids, inorganic and organic acids and alcohole is good.

NATURAL RUBBER (NR)
It is used between the temperatures -60°C and 100°C and recommended in applications where high flexibility is required.

POLYACETAL (POM)
Among the hydraulic-pneumatic systems it is the most common material used. It has excellent form stability at elevated temperatures up to 80°C. One of the most important features is its low water absorbtion. The temperature range is between -40°C and 140°C. For the quide ring, POM filled with glass is used due to its high contact pressure value.

THERMOPLASTIC POLYESTER ELASTOMER (TPE)

Polyester Elastomers are widely used as backup ring and header ring material with the sealing elements in hydraulic and pneumatic systems due to their chemical structure. It has excellent resistance to hydraulic oils and has high extrusion resistance compared to the other materials. It can be used in temperatures between -40°C to 120°C.

POLYTETRAFLUOROETHYLENE-PTFE

This material is known as Teflon, the trademark of DUPONT Company. PTFE material does have the lowest coefficient of friction. Due to the low friction coefficient and high wear resistance, it is able to work on poorly lubricating conditions as well as high sliding speeds. PTFE can be used in temperatures between -200˚C to +260˚C. It has very good resistance to all chemicals except alkaline metals, high pressure-temperature chlorotriflour and basic floorings. Hardness and elasticity make the material to be used widely in hydraulic applications. Depending onto the application; glass, graphite, carbon, MoS2 and bronze filled PTFE can be used to increase mechanical and physical properties. The influence of the hydraulic media, the behavior in contact with the counter surface and the form stability depending on the operating temperature are the important properties when selecting the PTFE compound among the others.

POLYAMIDE-PA

This material is known as Nylon 6. It can be used in temperatures between -30°C to +120°C, for short period of applications this can be increased up to +140°C. Polyamide is able to work on poorly lubricating conditions and does have high wear resistance. It is commonly used as guiding elements in hydraulic and pneumatic systems. Special additives can increase the mechanical and physical properties of the material depending on the application.

POLYOXYMETHYLENE - POLYACETAL (POM)

It has excellent form stability between temperatures -40°C to +100°C, for short period of applications this can be increase up to +140°C. It is commonly used as guide and backup rings in hydraulic and pneumatic systems. It is being safely used in mineral oils, HFA and HFB type of oils. For the guide ring, glass filled POM is used due to its high contact pressure value.

 

 

STORAGE CONDITIONS

 

During storage rubber and plastic parts may be exposed to chemical and physical changes. This could be caused by combined factors.

• Oxygen
• Ozone
• Direct sun light
• High temperature
• Ultra-violet rays
• Humidity
• Dirth and chemical affects

Stored in good conditions, rubber and plastic products can keep their chemical and physical features in long periods.

Enviroment, moisture and temperature
Ideal temperature is between 5°C and 25°C and moisture rate should be about 60%. Less temperature rates do not result in technical changes, but before assembly, the temperature for seal is advised to be 20-25°C. In addition to those direct heat contacts are not recommended.

Dirt
It may change the mechanical features of products. Therefore, the environment should be cleaned before assembly and during storage.

Light and ultra-violet rays
Recommended storage conditions are the rooms protected from fleurasant lambs, ultra-violet rays,
powerful light sources and direct sun lights. Red or orange colour lights are adviced.

Oxygen and ozone
They are oxidizing agents. What is suitable for seals is to store them by packing up with polyetilen (PE) materials. Ozone is especially a destroying agent and so there should not be electrical equipments with high voltages such as motors, etc.

Deformation
Deformation should be avoided during storage. Rubber parts and thermo-plastic seals should be kept away from coersive forces and squeezing because they cause a rapid change in mechanical features and endurance against agents in nature.

Contact with grease and hydraulic liquids
Any contact with solvents, oils and other liquids should be avoided.

Contact with metals
Some metals (i.e. manganez and copper) may harm some seal types, therefore, contacting directly with metals or their alloys should be avoided.

 

GENERAL ASSEMBLAGE INFORMATION

 

There appears a lot of problems because of incorrect assemblage of hydraulic and pneumatic sealing elements. It is vital that assemblage rules should be obeyed in order to make successful applications in hydraulic and pneumatic cylinders.


1- It is very important that the entire system and the fitting area should be cleaned out. There should not be any
    dirt and foreign particles in the area (for example, chip).

2- Before fitting, the measures of housing and the seal, radii, the chamfer and the surface quality must be checked 
    and cleaned out. The burrs on sharp edges are very dangerous.
 
3- The cleanliness of the sealing elements should be checked.
 
4- All the sealing elements should be installed after being oiled with system oil. Oiling with grease should be avoided.
 
5- Installation tools with sharp edges should not be used.
 
6- Uncontrolled heating of sealing elements before fitting is ruther dangerous.

7- While testing the cylinder after fitting, there should not be out of specified measures of pressure, temperature,
     linear velocity etc. given in our catoloque. 
 
8- In case of carrying out final procedures (ie. Painting), the heat over 80¡C should be avoided.