Sealing ring disk

A sealing ring disk for a seal at a piston rod with a circular cross-section. The sealing ring disk includes a ring-shaped seal part with a sector-like cut-out as well as a closure part having a main part matched to the cut-out in such a manner that the main part extending in the peripheral direction of the seal part can be inserted into the cut-out in order to assemble the two parts into a single sealing ring disk.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a sealing ring disk for a seal at a piston rod. 
2. Description of the Prior Art 
Dry running piston compressors are machines which require no foreign 
lubrication in the compression part. Such compressors have fixed sealing 
elements past which a piston rod is moved. With such an arrangement, a 
plurality of seal elements are usually arranged pair-wise one after the 
other in series forming a so-called packing. A pair of seal elements 
arranged in a packing in this manner is known from DE-42 01 246 C2. This 
arrangement and design of seal elements has the disadvantage that in each 
case two seal elements are to be placed lying adjacent to one another in 
the direction of motion of the piston in order to fulfil the seal 
function. A known problem of such seals at piston rods is the arising heat 
of friction. Conveying off the heat of friction via the seal elements 
themselves is possible only to a limited extent, since the seal elements 
are usually made of plastic and act thermally nearly as insulators. The 
greatest portion of the heat of friction is thus led off in a clearly less 
efficient manner by the piston rod. The arising heat of friction is thus 
largely responsible for a high degree of wear. Thus, a complicated and 
expensive cooling of the packing containing the sealing elements is often 
required. 
The object of the present invention is to overcome these known 
disadvantages of sealing elements. 
SUMMARY OF THE INVENTION 
The sealing ring disk in accordance with the invention is suitable, in 
particular, for dry running ring piston compressors, with the sealing ring 
disks consisting of a plastic with self-lubricating properties. Such 
sealing ring disks are used e.g. as piston rod seals (stuffing box, 
packing) in which the piston rod is moved past the fixed seal elements. As 
a result of the low heat resistance of polymer sealing materials the heat 
of friction which arises can lead to substantial thermal problems. An 
advantage of the sealing ring disk in accordance with the invention is to 
be seen in the fact that the sealing ring disk can be made relatively thin 
in the direction of the piston rod; and, in comparison with the cited 
state of the art, a single sealing ring disk suffices to ensure the seal 
function instead of the two sealing rings as previously. The relatively 
thin sealing ring disk in accordance with the invention has the advantage 
that an increased heat flow is possible through radiation from the piston 
rod to the metal housing of the packing, since the sealing ring disk that 
acts as an insulator has smaller dimensions, and that the ratio of the 
portion of the piston rod surface not covered over by seal rings to the 
sum of the seal ring contact area is substantially more favorable. A 
further advantage of the sealing ring disk of the invention is to be seen 
in the fact that the radial partition joints known from the current state 
of the art can be dispensed with. For this reason it is no longer 
necessary to use two sealing ring disks lying adjacent to one another, but 
rather the use of a single sealing ring disk suffices. Suitable materials 
for the sealing ring disk are plastics for dry running applications such 
as filled polymers with a matrix of polytetrafluoroethylene (PTFE) or a 
mixture of mechanically solid, high-temperature-resistant and 
wear-resistant modified polymers such as polyetheretherketone (PEEK), 
polyetherketone (PEK) polyimide (PI), polyphenylene sulphide (PPS), 
polybenzimidazole (PBI), polyamidimide (PAI) or even epoxy resin. 
The sealing ring disk in accordance with the invention can be manufactured 
of modified PEEK. This has the advantage that very thin rings can be 
manufactured so that, on the one hand, the piston rod can better transmit 
the heat via radiation to the packing and, on the other hand, a smaller 
frictional area exists between the seal ring and the piston rod, which 
also reduces the heating. Too much heating up of the piston rod can be 
avoided in this manner, which has the advantage that the sealing ring 
disk, which consists of PEEK, is not thermally overloaded, nor does it 
melt.

FIG. 1a and also FIG. 1h show a ring-shaped seal part 2 which has a 
sector-like cut-out 3 so that the seal part 2 has an opening at this 
position. The seal part 2 has a sealing surface 2a which is oriented 
towards the piston rod 4 and performs a sealing function. FIG. 1g shows a 
section along the line A--A and shows the L-shaped cross-section which the 
seal part 2 has in the present embodiment. The seal part 2 has a main part 
2e which runs out at both ends into the end parts 2c, 2d. From the side 
view of FIG. 1b, it is evident that the two end parts 2c, 2d are made 
thinner than the main part 2e in the direction of a normal or 
perpendicular S to a plane passing through the seal part 2, or in the 
direction of motion of the piston rod 4. FIG. 1c shows a closure part 1 
which has a main part 1e as well as end parts 1g adjoining it at both 
sides which are ring shaped. FIG. 1d shows a side view of the illustration 
in FIG. 1c of the closure part 1 with the closure part having a groove 1a 
in the peripheral direction for receiving a toroidal spring 13. Both the 
seal part 2 and the closure part 1 have resilient properties. FIG. 1e 
shows a sealing ring disk 12 assembled from the closure part 1 and the 
seal part 2. In the process, the closure part 1 was placed onto the seal 
part 2 in such a manner that the closure part 1 lies on the lower part 2f 
of the seal part 2 and that the closure part 1 surrounds the upper part 2g 
of the seal part in the form of a ring. The main part 1e covers the 
cut-out 3 of the seal part 2 and lies on the end parts 2c, 2d in the 
direction of the normal S. The sealing ring disk 12 thereby has a sealing 
function over the entire surface of the piston rod 4. The main part 1e as 
well as the seal part 2 have a clearance S1 in the peripheral direction of 
the seal part 2. The sealing ring disk 12 is advantageously surrounded by 
a toroidal spring or hose spring 13 so that the sealing ring disk 12 is 
under pretension. During the use of the sealing ring disk 12 as a seal 
element the movement of the piston rod 4 leads to wear of the sealing 
surface 2a, which results in the removal of material. The hose spring 13, 
the clearance S1 as well as the resilient properties of the sealing ring 
disk 12 ensure that the seal surface 2a can continue to lie on the surface 
of the piston rod 4. FIG. 1f shows a side view of the sealing ring disk of 
FIG. 1e. 
FIG. 2a shows a further exemplary embodiment of a seal part 2 which has a 
main part 2e that runs out at both ends into the end parts 2c, 2d. The 
seal part 2 is again executed in a ring shape with a sector-like cut-out 
3. Furthermore, the seal part 2 has a support surface 2h for supporting 
the closure part 1 on the side lying opposite to the cut-out 3. FIG. 2b 
shows a side view of the embodiment of a seal part in accordance with FIG. 
2a. As in FIG. 1b the end parts 2c, 2d are also made thinner here than the 
main part 2e in the direction of the normal S. FIG. 2c shows a closure 
part 1 with a main part 1e. FIG. 2d shows a side view of the closure part 
in accordance with FIG. 2c with a recess 1a for the hose spring 13 
extending at the outer surface in the peripheral direction of the closure 
part. The seal part 2 as well as the closure part 1 can be assembled to 
form a sealing ring disk 12 in a manner similar to that shown in FIG. 1e 
so that a seal results along the surface of the piston rod 4. 
FIG. 3a shows a further exemplary embodiment of a sealing ring disk 12. The 
seal part 2 tapers in the radial direction towards the end part 2c, 2d. A 
seal part tapering in this manner has the advantage that the elastic 
properties behave approximately similarly in the peripheral direction. A 
seal part 2 executed in such a manner can be surrounded by a closure part 
as shown in FIG. 1c. In this case, the piston rod 4 would be arranged 
asymmetrically with respect to the periphery of the closure part 1. A 
further possibility is the embodiment of a closure part 1 shown in FIG. 
3a, which likewise has tapering end parts 1g starting from the main part 
1e, with the seal part 2 and the closure part 1 being mutually matched in 
such a manner that the seal part 2 has an axial formation 2i eccentric to 
the piston rod, and that the closure part 1 has an eccentric cut-out 1i 
complementary hereto in such a way that the piston rod 4 lies centrally 
with respect to the entire sealing ring disk 12. FIG. 3b shows a side view 
of the embodiment of a sealing ring disk 12 in accordance with FIG. 3a. 
FIG. 4a shows a further seal part 2 with a main part 2e which runs out at 
both ends into end parts 2c, 2d, with the end parts 2c, 2d again being 
shown thinner with respect to the main part 2e as shown in FIG. 4b. FIG. 
4c shows a closure part 1 which, in the present embodiment, consists only 
of the main part 1e, which has a part if as shown in FIG. 4d. The closure 
part 1e can be inserted into the cut-out 3 of the seal part 2 as shown in 
FIG. 4e, with the closure part 1 being arranged opposite the seal part 2 
extending in the peripheral direction of the seal part 2 and having a 
clearance S1 extending in this direction. FIG. 4f shows a side view of the 
embodiment in accordance with 4e. A recess 1a for receiving a hose spring 
13 can be arranged along the peripheral direction of the seal part 2 as 
well as along the peripheral direction of the main part 1e. The sealing 
ring disk 12 is suitable, in particular, for a seal arrangement for a 
piston rod 4 with a circular cross-section, as shown in FIG. 5. At least 
one sealing chamber 14 which surrounds the piston rod 4 and is formed of 
two chamber rings 5 and is sealingly screwed to the associated cylinder 
space 15 belongs to the fundamental lay-out of a dry running seal 
arrangement or packing 6. It has a two-part sealing ring disk 12 which is 
surrounded by a hose spring 13 and has a closure part 1 as well as a seal 
part 2. The sealing ring disk 12 lies under bias tension with sealing 
surfaces 2a in contact with the piston rod 4.