Information concerning the application of asbestos-free gasket materials

Technical information TI 3.1.002 09

For a safe  handling and right mounting of our sealants stands this information to your disposal.
To your advice, we give you on agreement also gladly one of our application-technicians to your disposal.   

Please order our technical information regularly. The technical informations are adapted on the newest stand regularly.
The in each case current piece of information is available to your disposal at our homepage..

CONTENT:

Interpretation of the sealing-connection 

1.1 flange-qualities 
Flange-surfaces have influence on the dense-effect 
-> look at the roughness of the flange 

1.2 Thickness of the seal 
The thickness of the seal is to adapt on the Compressive strength of the material 
-        for asbestos free seals it it is possible to reduce the sealing thickness

1.3 maximum use-temperatures of asbestos-free sealing sheets 
-> look at the temperature-borders 

1.4 the optimal surface pressure  
The optimal surface-compression is dependent on many parameters 
-> look at the minimum and maximum-values for the surface-compression 

1.5 Pressure and temperature-limits 
The maximum pressure is dependent on Temperature, seal-geometry and flange-condition 
-> Maximum-values for Pressure in dependence of the Temperature 

2. Handling of the seal 
2.1 Thightening of the seal 
FA-seals brittle often under higher temperatures. 
The seals should be tightened before the first opening

2.2 the surface-coating-system OBS 
sealings with no anti-adhesive surface stick to the flange 
-> Use sealings with surface-coating, then however don’t use additional lubricants or pastes

2.3 self-adhesive sealings
For difficult montage-cases 

1. Interpretation of the sealing-connection 

1.1 flange-qualities 

Thin seals have more compressive strength as thick seals. The seals should be therefore preferably thin.
With given Compressibility of the sealing, rough dense-surfaces necessitate thick seals to prevent
surface-leakage in order to achieve an optimal bracing of the seal in the surface (illustration 1).   

Illustration 1: minimum-seal-thickness for Centellen^®-Materiale as function of the rough-depth and of the surface-compression 

1.2     Thickness of the seal

With corresponding rough-depth of the seal-surface, the right surface-compression and with reserves at that screw-strengths,
the seal-thickness can be reduced with the exchange from asbestos-containing against asbestos-free seals
- at least in the upper thickness-area -. 

As plates are standard in the strengths 0,3 mm, 0,5 mm, 0,8 mm, 1,0 mm, 1,5 mm, 2,0 mm, 3,0 mm up to 4,0 mm available;
on wish, also plates until 6,0 mm can be manufactured. Exception: DSL 3670 only can be delivered from 0.8 mm.
Following formats are available as standard-measurements:

1000 x 1500 mm       1500 x 1500 mm       1500 x 3000 mm

The Compressive strength of the seal higher with bigger width/thickness relation of a seal. Provided it is possible,
the seal-width should be increased therefore. 

Table 1: recommended seal-thickness 

1.3     maximum use-temperatures of asbestos-free sealing sheets

In all Centellen^®-Types and in HD 3822 the aramide fibre is used as reinforcement firbre.. Because of the sensibility of the aramide fibres
at hydrolisis mediums is the maximum use temperature in steam lower than in water-free surroundigs. 

DSL 3670, especially made for steam, and UDP 3620, made for high temperature and high pressure can be used at higher steam temperatures.

sheet 2:            maximum temperatures for asbestos free sealing sheets

Look at relations between temperature and Pressure (look at  1.5)!

As a rule of thumb there can be mentioned that thin seals with a large relation between wide and thickness can be used at higher temperatures
than thick seals o seals with a small relationship between wide and theickness (looak at 1.4)

1.4     The optimum surface pressure for the preconditioning of the seal, _<-opt

The formula to get the neccesary best surface pressure for the preconditioning s_opt depends on the following factors:

*    a minimum pressure _<-min, to stick the seal at the flange and to close the pores of the seal and

*    the part of the inner pressure m·p,  m is a constant factor for the relation of inner pressure and surface pressure.

_<-opt  =  _<-min + m · p

for liquids:

_<-opt     = 10 + 3 · p  Centellen^®-materials
_<-opt     = 15 + 3 · p   DSL 3670
_<-opt     = 20 + 3 · p   UDP 3620
_<-opt     = 20 + 3 · p  Europil^® WS 3640

for gases:

_<-opt     = 20 + 4 · p   Centellen^®-Materials
_<-opt     = 25 + 4 · p  DSL 3670
_<-opt     = 30 + 4 · p  UDP 3620
_<-opt     = 30 + 4 · p  Europil^® WS 3640

p          :     Innerpressure to be sealed                                                             [N/mm²] (1 N/mm² » 10 bar)
m         :     relation between surface and inner pressure                                 [-]
_<-opt           :     optimized surface pressure for preconditioning                            [N/mm²]
_<-min          :     minimum pressure for preconditioning                                          [N/mm²]

The dependency of the surface pressure from the inner pressure and the nominal diameter of the seals at a smooth flange
(dimensions according to DIN 2690) as shown in picture 2.

The seal has to be covered with the minimum pressure -  _<-min – also at very low inner pressure -, to close the pores
and to guarantee that the seal fits to the flange cover and to hold seal by the flange.

A lot of studies have shown, that the leakage of the seal is lower, if the seal got strong pressure. This lower leakage even
exists if the pressure will come down later.  

picture 2:          surface pressure for Centellen^®-Materials -> DIN 2690 as a  function of inner pressure (at gases)

                                                                            inner pressure (bar)

We learn, that the seal should get a strong pressure, but you have to look at the maximum surface pressure combined with the maximum operating temperature. For the operating situation you should try to get the following value _<-B for the surface pressure:

_<-B  =  m · p

table 3: Maximum surface pressure at operating conditions _<-BO

1.5     Limits for pressure and temperature

The shown values for maximum temperature and maximum pressure should not occur simultanesously !

It is not possible to create a simple pressure/temperature formula for the limits of each material.
The reason is the dependancy on diverse parameters e.g. the absolutely thickness, the relationship of
wide- and thickness and the relationship of diameter and wideness of the seal, the roughness of the surface
to be sealed and the surface pressure. At a pressure of 40 bar seals according to DIN 2690 20 up to 150 
have a relationship of wideness/thickness of the seal from 8 up to 14 and a diameter/thickness relationship from 2,7 up to 7.
The widenesses are from 16 up to 28 mm.

1.6     Tightening of the seal

For the use of the seal at pressures more than 16 bar we recommend to tight the seals in cold state. When it is possible you can tighten the seals after a few hours again, but not before a time of 30 minutes and not after a time of 60 minutes after first use. If you tighten the seal at any later time the seal may brake.

1.7     The surface covering system OBS

Table 4:     Standard versions of surface coverings

On your desire we can deliver the seals with an one side anti-adhesive-coating ore with an anti-adhesive-coating on both sides.
The following surface coverings are possible:

Table 5:           possible versions of surface coverings

For your individual order please give us the above mentioned marking added after the material name.

Example:          Centellen^®-HD WS 3822, graphite-covered on one side:
                          ->  Centellen^®-HD WS 3822 G 1

2.3     Self adhesive seals

Very difficult mounting conditions can be solved at using self adhesive seals. All Hecker^® materials can be
delivered with an self adhesive foil.