GB2057924A

GB2057924A - Sodium-filled valves

Info

Publication number: GB2057924A
Application number: GB8028716A
Authority: GB
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1979-09-08
Filing date: 1980-09-05
Publication date: 1981-04-08
Also published as: SE445621B; AT371387B; FR2465147B1; DE2936335A1; ATA436280A; DE2936335C2; GB2057924B; SE8006097L; FR2465147A1; JPS5761883A

Abstract

A sodium filled valve in which residual air in the valve stem is eliminated by evacuating the valve stem after it has been filled with sodium through a filler bore, via a duct or passage which is smaller than the filler bore and then hermetically sealed in vacuo. The duct or passage may be formed in the filler plug, the valve disk or the valve stem wall, and is preferably sealed by electron beam welding, but may in certain cases be sealed by the application of an extension to the valve stem. <IMAGE>

Description

SPECIFICATION Sodium-filled valves This invention relates to a method of manufacturing a sodium-filled valve and in particular a method in which the sodium is introduced into the hollow valve stem through a filler bore and the bore then being ciosed for example, by means of a plug and/or conventional welding or soldering.

The reason for filling valves, more particularly valves for reciprocating engines, with sodium is to obtain better heat dissipation from the valve disc, which is subject to high thermal loading. This improved dissipation is obtained by virtue of the extremely good thermal conductivity of sodium. However, because of the high thermal expansion of sodium, the drilled valve stem cannot be completely filled with sodium, but only to about 80%. The remaining free space in the hollow stem contains atmospheric air which, during valve operation, results in foaming and corrosion of the sodium, and this ieads to unstable thermal conductivity and also impairs heat transfer generally.

One object of this invention is to obviate these disadvantages and to enable the manufacture of sodium-filled valves in such a way that the residual air in the valve stem can be eliminated at minimum cost.

According to this invention we propose a method of manufacturing a sodium-filled valve, comprising introducing sodium into the hollow valve stem through a filler bore and closing the bore, by means of a plug in any suitable manner, wherein the cavity is evacuated via a duct or passage smaller than the filler bore and then hermetically sealed in vacuo.

It is preferred that the said duct or passage is hermetically sealed in vacuo by welding or soldering. Evacuation of the cavity avoids any oxidation of the sodium and hence any ageing. Nor is there any foaming, so that substantially constant heat transfer can be obtained.

In a first embodiment, the duct or passage is situated in the valve disc. Consequently, no thermal or mechanical loading acts on the sealed filler bore either during formation of the duct or passage or thereafter during sealing.

In another embodiment, the duct or passage is in the form of an axial bore in a filler plug. Finally, the duct or passage may be a bore extending through the valve stem wall preferably at an angle to the longitudinal axis of the stem.

In a preferred embodiment of the invention the duct or passage is sealed by electron beam welding, which is a very simple and convenient technique especially since the cavity can be evacuated via the duct or passage when the valve is disposed in the vacuum chamber of the electron beam welding machine in preparation for welding. The electron beam is preferably traversed in a circle around the duct or passage during welding so that the duct or passage collapses and the material fuses to provide a seal without the electron beam passing through the duct or passage and impinging on the sodium inside the cavity. This avoids the risk of vaporizing the sodium which would establish a vapour pressure in the cavity during the sealing of the duct or passage and might result in molten material being squeezed out from the cavity.

It is also advantageous if during drilling and/or sealing of the duct or passage the valve is tilted into a position such that the sodium is remote from the bore. This avoids heating the sodium as far as possible.

For best results, the duct or passage has a cross-section of about 1 mm2.

If desired, the duct or passage may be hermetically sealed by the application of an extension to the valve stem by friction welding, this being carried out in a vacuum bell jar. This embodiment is important inasmuch as a hollow valve stem frequently has to be fitted with a solid end having retaining grooves to secure the valve springs. Solid stem ends of this kind are conventionally fitted to the end of the hollow stem by friction welding or flash butt welding, and this welding operation is advantageously carried out in vacuo so that the valve stem cavity can be evacuated at the same time.

Embodiments of this invention will now be described by way of example with reference to the accompanying drawing of which: Figure 1 is a longitudinal section through a sodium-filled disc valve.

Figure 2 shows a filler plug for a disc valve of the kind shown in Fig. 1 and Figure 3 is a partial longitudinal section through the stem of a modified valve of the general kind shown in Fig. 1.

Fig. 1 shows a valve stem 1, which is drilled and largely filled with sodium. A filler bore 2 is provided at the rear end of the stem and is closed by a plug 3 which is preferably welded at 4 to the stem 1. The cavity in the valve stem 1 is drilled initially by means of a small-diameter bore 6 located centrally in the valve disc 5. This bore 6 (shown in broken lines) is re-closed by electron beam welding.

The filler plug 3 shown in perspective in Fig. 2 illustrates three different ways of providing an evacuating duct. In a first embodiment (solid lines), a small helical groove 32 is formed in the sealing surface of the plug 3. A second embodiment (broken lines) has a small straight groove 31 while a third embodiment has a small central bore extending through the plug 3.

The detail of the valve stem 1 shown in Fig.

3 illustrates another arrangement of an evacu ating passage, in the form of a bore 6a through the wall of the valve stem, the bore being inclined to the longitudinal axis of the valve stem 1.

Claims

1. A method of manufacturing a sodiumfilled valve, comprising introducing sodium into the hollow valve stem through a filler bore and closing the bore by means of a plug in any suitable manner wherein the cavity is evacuated via a duct or passage smaller than the filler bore and then hermetically sealed in vacuo.

2. A method according to claim 1, wherein the duct or passage is situated in the valve disc.

3. A method according to claim 1, wherein the passage of small cross-section is in the form of a straight or helical groove in a sealing surface of the filler plug or the filler bore.

4. A method according to claim 1, wherein the duct or passage comprises an axial bore in a filler plug.

5. A method according to claim 1, wherein the duct of passage is a bore extending through the valve stem wall at an angle to the longitudinal axis of said stem.

6. A method according to claims 1 to 5, wherein the duct or passage is sealed by electron beam welding.

7. A method according to claim 6, wherein the electron beam is passed in the form of a circle around the duct or passage during welding so as to avoid the beam passing there through.

8. A method according to any one of claims 1 to 7, wherein during sealing of the duct or passage the valve is brought into a position such that the sodium is remote from the bore.

9. A method according to any one of claims 1 to 8, wherein the duct or passage has a cross-sectional area of about 1 mm2.

10. A method according to claim 1, wherein the duct or passage is hermetically sealed by the application of an extension to the valve stem by friction welding, this being carried out in a vacuum bell jar.

11. A method of manufacturing a sodium filled valve substantially as hereinbefore described with reference to the accompanying drawings.

1 2. A sodium filled valve when manufactured by the method according to any one of claims 1 to 11.

1 3. A sodium filled valve constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.