Because of their geometric shape, delta seals require a higher level of precision from the seal grooves. As a direct result of the manufacturing process and its resulting precision, delta seals are only used for high-pressure autoclaves and high-pressure connections up to a maximum of 2000 mm, whereby the majority are less than 1000 mm.
The following illustration shows the application as a cover gasket. Due to its splined profile, an excellent initial seal is created by the partial plastic deformation of the opposing peaks of the gasket when bolt pre-tensioning force is applied. The radially self-sealing effect arises due to the high internal pressure resulting from the elastic extension of the gasket.
Delta gaskets are not suitable for dealing with intermittent pressures. Additional sealing layers are not practical or necessary. Delta gaskets are generally produced from seamless rings. The sealing material should be softer than the flange material if possible. Care should be taken to ensure adequate creep strength in the material. The gasket is only slightly higher than the sum of the seal groove depths, therefore if the grooves are reworked at any stage a new gasket with greater height will be required.
We produce delta gaskets according to your documentation, from all usual materials. See also the section “Materials commonly used”.
DOUBLE CONE GASKETS
Double cone gaskets are radially compressed like a circular spring by the bolt pre-tensioning force. A pre-tensioning of approximately 1/3 to 1/5 of the test pressure is generally sufficient to achieve the necessary initial seal. So that the gasket does not become overloaded, only a limited amount of clearance should be left between the cover and the gasket.
After pre-tensioning, the gasket will initially have contact inside to the cover. With the application of pressure, it will then spring back by the compressed amount and if there is sufficient internal pressure will expand elastically, so that it offers reliable sealing in all operating conditions due to its optimal design shape.
We would be happy to carry out a cost-efficient check for tracking and to determine the measurements of the double cone gasket as part of our gasket estimate service. The illustration above shows the design principle. The measurements of double-cone gaskets are not standardized.
We can currently supply sealing rings up to Ø 3200 mm. The sealing surfaces are conical surfaces with a sloping angle α. A sloping angle of α = 30° is usual but is not suitable in every case.
There are frequently two or three grooves of a few millimeters wide and a few tenths of a millimeter deep on each conical surface. The grooves fix the enclosed sealing layers into position. The layers provide a better initial sealing behavior.
The sealing layers should be no thicker than 1 mm. Aluminum, copper, nickel, and silver layers from 0.5 mm to 1 mm in thickness have proven successful. If the sealing layers can no longer be produced in one piece from the semi-finished product, they will be welded. The thickness of the welded joint deviates from the layer thickness by between +0.1 mm to -0.05 mm. Profile AR16 has convex sealing surfaces. The convex model has proven particularly reliable where the strains and curvatures of the component vary greatly, where layers of soft metal are not suitable.
COVER PLATE GASKETS
Cup seals are used as self-sealing gaskets, meaning that the sealing force does not come from bolts but from the internal pressure. Therefore, bolts with a smaller cross section can be selected. The entire connection is more compact.
There is a range of profiles in seven different shapes available, with which all sealing problems can be solved. The necessary deformation to conform to the sealing surfaces is achieved with the cover tensioning bolts. When laying out the bolts, attention should also be paid to the weight of the cover and where it is to be installed. Depending on the type of profile and the geometry of the gasket, achieving sufficient deformation will require the correct level of surface pressure and/or the correct internal pressure.
The maximum permitted operating or test pressure can also be estimated from the critical pressure. The selected tolerances and the presence or absence of metal caps or lathed protective caps is of critical importance.