GB2261398A

GB2261398A - Valve spool

Info

Publication number: GB2261398A
Application number: GB9220060A
Authority: GB
Inventors: Kurt Stoll; Herbert Kongeter
Original assignee: Festo SE and Co KG
Current assignee: Festo SE and Co KG
Priority date: 1991-11-16
Filing date: 1992-09-22
Publication date: 1993-05-19
Anticipated expiration: 2012-09-22
Also published as: ITMI922571A1; DE4137805A1; DE4137805C2; GB2261398B; GB9220060D0; IT1256306B; ITMI922571A0

Abstract

A method and a moulding apparatus are provided for producing a valve spool by injection moulding or casting. The valve spool having at least one operative portion or land (12) with an integrally molded annular outer sealing surface (19). To achieve this a liner ring (18) is laid in the mold (1) prior to molding adjacent to each operative portion (12) to be produced, the inner circumferential surface of the ring (18) being shaped in accordance with the desired outer sealing surface (19) and being molded on the operative portion (12). After molding each respective liner ring (18) is removed. The use of liner rings allows a flash-free outer sealing surface on the respective operative portion. <IMAGE>

Description

A Method of producing a Spool for a Valve and an Apparatus for performing

the Method.

The present invention relates to a method of producing a valve spool, in the case of which at least one operative portion or land having in its finished form an external annular, integrally made sealing surface consisting more particularly of synthetic resin, is formed in a mold having at least two parts. The invention furthermore relates to an apparatus for performing the method.

Valve spools, which may be in the form of cylindrical members, are generally of circularly cylindrical form and possess externally a series of axially succeeding annular operative portions or lands which are separated from each other by annular grooves in the spool. In operation such a spool is arranged for sliding movement in a bore in a valve, more particularly in the form of a multi-way valve. Dependent on the position valve ducts open- ing laterally into the bore are separated from each other or connected together in accordance with a given scheme. In order to ensure the proper function of the valve it is necessary to provide-flash-free external sealing surfaces on the periphery of the operative portions, which surfaces are able to provide a precise sealing action on the inner surface of the valve bore.

In order to simplify manufacture the practice has been adopted of producing valve spools by forming in a mold, and more particularly by injection molding. Such a method of the type initially mentioned is described in the German patent publication 3,509,453 C, in which case opera- tive portions consisting of synthetic resin are injection molded onto a spool core body. The flash thereby produced adjacent to the eventual exterior sealing surfaces is later removed by grinding. Such grinding operation is however involved and is responsible for high production costs. Furthermore, such later processing damages or removes the cast skin which is initially produced, something having an unfavorable effect on the length of life and the smooth running properties of the spool.

One object of the present invention is to overcome the above noted disadvantages of the prior art and to provide a method of the type initially mentioned with which a valve spool having a long length of life and free running properties may be produced more simply, more quickly and at a lower price. Furthermore the present invention has the aim of providing an apparatus which is more particularly suitable for performing this method.

1 In order to achieve these and/or other objects appearing from the present specification, claims and drawings, in the present invention a method of the type initially mentioned is so performed that a liner ring is laid in the mold prior to filling the mold adjacent to the respective operative portion or land to be produced and on the uninterrupted inner circumferential surface, which is shaped in accordance with the desired externalsealing surface, the operative portion is produced, and after solidification of the molding material or synthetic resin, the liner ring is removed from the operative portion to free a flash-free outer sealing surface on the respective operative portion.

For this purpose it is possible to use an apparatus which is characterized in that a mold is present which defines a mold cavity which with the exception of parts adjacent to the eventual operative portions to be produced at least substantially corresponds to the outer form of the spool to be produced and which comprises at least two mold parts distributed over the periphery of the mold cavity and able to be moved towards and away from each other and at least one liner ring is able to be arranged removably adjacent to one operative portion to be produced in the mold, said liner ring having a inner circumferential surface which corresponds to the out- line or configuration of an external sealing surface to be molded on the spool to be produced.

It is in this manner that adjacent to the liner rings arranged in the mold the parting zones between the mold parts or halves in abutment with each other are covered over. The entire inner circumferential surface of the respective liner ring is free of crevices so that the operative portion or land molded in a radially outward direction has an outer circumferential surface, which is in contact with the liner ring, free of flash. This circumferential surface is uncovered during the following removal of the respective liner ring taking place more particularly after opening of the mold, so that the finished outer surface is in its finished condition and no further processing of the spool is necessary. The outer sealing surface is consequently directly produced during molding so that no timeconsuming finishing operations are required. Furthermore as a result the "outer skin" remains on the injection molded land unimpaired. The sealing running surface which is eventually utilized during later use of the spool and subjected to a dynamic load is present in the desired final condition right after the end of the molding operation. The removal of the liner rings may be performed without any problems, for instance by pulling off the liner rings in the axial direction. Since owing to their simple structure such rings may be produced in large numbers with high accuracy,--the desired 2 1 valve spools may be manufactured within tight tolerances.

Further developments and features of the invention will be perceived in the claims.

The method in accordance with the invention and the apparatus in accordance with the invention may be utilized independently of the desired number of operative portions or lands on the spools to be produced. In each case it is merely necessary to modify the number of liner rings to be arranged in the mold prior to introduction of the synthetic resin into the mold. Preferably the apparatus to be employed has suitable means available in order to be able to secure the liner rings in the correct position without any problems. Such means are more particularly in the form of annular receiving recesses in the mold parts, into which the liner rings may be arranged.

The removal of the respectively inserted liner ring from the solidi- fied, i. e. injection molded or possibly cast, spool is preferably performed by pulling it off in the axial direction from the associated spool land. If a plurality of consecutive operative portions are present, the liner rings are preferably pulled in sequence over the sequence of operative portions or lands towards one end. It is furthermore possible to split open a liner ring taken off one operative portion adjacent to one spool land at least at one position on its periphery and then to remove it sideways.

The method and the apparatus are able to be utilized independently of whether a respective operative portion is formed by a layer of material molded or vulcanized on a core body or constitutes some more substantial part of the spool.

Further advantageous developments and convenient forms of the invention will be gathered from the following detailed account of one particularly suitable apparatus in conjunction with the accompanying drawings.

Figure 1 shows a first working embodiment of the apparatus with the mold opened and with the liner rings placed in posi tion, in longitudinal section.

Figure 2 shows the apparatus in accordance with figure 1 with the mold closed after injection molding, also in longitudi nal section.

Figure 3 illustrates the spool after removal from the mold with some of the liner rings still arranged thereon and indi- 3 cating the way in which they are removed, in cross section.

Figure 4 shows the part IV encircled in figure 2 on a greater scale. is a cross section taken through the apparatus in accordance with figure 2 on the section line V-V.

Figure 5 The apparatus utilized in the working embodiment and more particularly illustrated in figures 1, 2 and 5 diagrammatically, possess a mold gen- erally referenced 1 and consisting of two mold parts 2 and 3. They are able to be moved towards each other and away from each other for opening or closing a mold cavity 4 circumferentially enclosed by them, as indicated by the double arrow 5 transversely in relation to the longitudinal direction 6 of the mold. As viewed in the closed condition in accordance with fig- ures 2 and 5 the present mold consisting of two halves 2 and 3 has two mold parting positions 7 and 8 in the peripheral part of the mold cavity 4, such positions of parting being diametrally opposite each other and extending in the longitudinal direction 6. At such positions the two mold parts 2 and 3 adjoin when the mold 1 is closed. It is for this reason not possible to prevent cracks or crevices 9 leading into the mold cavity 4 and, even although they are comparatively small in their dimensions, being responsible for flash on the article produced in the mold.

Departing from the design illustrated it is possible for the mold 1 to consist of more than two mold parts 2 and 3, which adjoin each other in the circumferential direction and/or the longitudinal direction of the mold and define the mold cavity 4.

The method described in the following is for instance intended for the production and finishing of a valve spool 10 illustrated in figure 3. In this respect it is a question of a substantially cylindrical body which has a linear extent, its longitudinal axis being referenced 11. On its periphery it has a plurality of axially succeeding operative portions 12 or lands, in this case 6 thereof, which take the form of annular radial projections extending coaxially in relation to the longitudinal axis 11. Between axially adjacent operative portions 12 there is in each case a waist or a circumferentially extending reduction 13 in diameter. When the valve spool 10 is arranged in the bore of a multi-way valve, not illustrated, the peripheries of the operative portions 12 will run with sealing contact between the outer periphery of the operative portions 12 and the surface of the bore and is, as a result, able in a known manner to connect and disconnect valve ducts with each other fluidwise.

4 The operative portions 12 consist of a synthetic resin material, such material being more particularly a polymer or an elastomer. The operative portions are produced by injection molding in the above noted mold 1, there being the particular feature that in the working embodiment they are in- jected or vulcanized on a reinforcing spool core 14. The spool core 14 is practically a spool skeleton, which in the working embodiment consists of metal and more preferably of brass. As also illustrated in figure 1, the core is a basic body 15 which is substantially cylindrical 15 if one ignores the operative portions, which body at the operative portions 12 has radially outwardly projecting annular flanges 16.

Reverting to the mold 1 it is to be mentioned that the mold cavity 4 defined by it corresponds to the outer periphery of the valve spool 10 to be produced with the exception of the part adjacent to the operative portions 12 to be made. In those parts in which the valve spool 10 is to have operative portions 12, receiving recesses or other suitable means are provided, which render possible positioning of liner rings 18 in the mold cavity 4. The liner rings 18 belong to the above noted apparatus and it is a question of separate items, which are more particularly designed in the form of inserts and may be arranged in the mold cavity 1 as shown in figures 1 and 2 so that they may be removed again.

In order to render it possible for a respective operative portion 12 to fulfill its sealing function and to freely run, it must have a so- called external sealing surface 19 (figure 5) on the radially outwardly facing outer surface, which extends circumferentially in relation to the longitu dinal axis 10. This sealing surface 19 will later make contact with the inner surface of the valve bore and should be free of flash or the like irregularities. The invention provides for the manufacture of a valve spool, in the case of which such flash and irregularities are not even allowed to appear at all on the other sealing surface 19.

In this respect the liner rings 18 play a substantial part. They are preferably produced of metal, more particularly brass. They have at least one holding section 20, which serves for anchoring them in a receiving recess 17 and in the case of the working embodiment is constituted by prac tically the entire ring body. As considered in the closed condition of the mold 1 each respective liner ring 18 has moved radially to be practically completely within the associated receiving recess 17. The breadth of the ring and the receiving recess is in the working embodiment substantially equal to the breadth of the outer sealing surface 19 to be produced.

The uninterrupted annular inner circumferential surface 21, which in the condition fitted in the mold is centered on the longitudinal axis 11 of the spool 10 to be produced, is shaped in accordance with the configuration of the respective desired outer sealing surface 19. This is to be more particularly well seen from the enlarged view of figure 4. For instance in this case the radial inner circumferential surface 21 is so shaped that the liner ring 18 has in this zone two axially consecutive coaxially extending recesses 22 so that between them a circumferential bead is formed and at each axial end there is a respective circumferentially extending annular edge 23 which projects radially inwards.

In order to perform the method the first step is to open the mold 1 by moving apart the two mold parts 2 and 3 as indicated by the double arrow 5. As a result the mold cavity 4 becomes accessible, in whose inner wall surface the receiving recesses 10 are set. In the opened condition there is a division up of the wall of the mold cavity so that a circumferential section 24 and 24' (figure 5) is associated with one respective receiving recess 17.

Now one of the liner rings 18 is arranged in each of the receiving recesses 17 arranged adjacent to the operative section 12 to be produced. This is preferably performed by inserting all liner rings 18 in the circumferential section 24 of one of the mold parts 3. Then after this the mold cavity 1 is closed so that the ring sections, which have so far not been anchored fit into the circumferential sections 24' of the other mold part 2. All liner rings 18 are as a result fixed and axially locked in sequence with a set axial spacing coaxially in relation to the spool 10 within the mold cavity 4.

The next step is for the synthetic resin to be introduced into the mold cavity 4 which is closed on all sides, suitable input openings being indicated in figures 1 and 2. The synthetic resin fills up the mold cavity 4, it moving outwards radially onto the inner circumferential surface 21 of the liner rings 18. It is in this manner that a respective operative sec- tion 12 is produced with a radially, circumferentially extending outer surface shape corresponding to the inner circumferential surface 21.

After solidification of the synthetic resin the mold 1 is opened and the spool 10 is removed therefrom. In this respect the liner rings 18 are normally still coaxially locked on the operative sections 12, but however they may be removed without any problems so that the outer periphery of the operative sections 12 is uncovered, which in each case constitutes a flashfree outer surface 19, for which no finishing operations are necessary. During introduction of the synthetic resin into the mold the liner rings 18 will have covered over the mold parting junctions 7 and 8 also present at the operative portions 12 to be produced and prevent them from communicat- 6 Z7 ing with the mold cavity and the spool to be manufactured. Therefore formation of flash adjacent to the outer sealing surface 19 is avoided. Adjacent to the side of the liner rings 18 flash is produced on the spool 10 but in no way causes interference as regards the eventual sealing function and if necessary may be left in place. The production of mold parting plane flash is for this reason prevented adjacent to the eventual dynamic sealing surfaces.

In the case of the configuration of the liner ring illustrated in figure 4 as described above, there is adjacent to each respective operative section 12 a circumferentially extending sealing surface, which has two circumferentially extending sealing humps 26 and 26' or beads arranged one after the other in the axial direction, between which there is a coaxial annular recess or groove.

It will be apparent that for the production of a spool 10 having a plurality of operative sections 12 arranged in an axial sequence a plurality of sealing rings 18 are utilized, which are arranged in the mold 1 prior to the molding operation in a coaxial manner in accordance with the axial spacing of the desired operative section 12.

The spool 10 to be produced may consist completely of the same syn- thetic resin which is able to flow and is also utilized for the production of the operative sections 12. However it is preferred to provide a spool core which in the finished condition is in the center of the spool and which has a stiffening effect and is molded or injected onto the synthetic resin material constituting the respective operative section 17. In this respect the method sometimes referred to as "vulcanizing coating" may be utilized.

If the finished spool 10 is to have a spool core 14, then prior to introduction of the synthetic resin into the mold a suitable basic body as above noted is manufactured in some suitable manner and like the liner rings 18 is arranged in the mold which has been suitably prepared. It is an advantage if the basic body is provided with centering heads 27, more particularly adjacent to the two ends thereof, which so take up positions in corresponding bays 28 in the mold cavity that there is an exact coaxial alignment of the basic body 15 in relation to the liner rings 18 surrounding it with radial play. The annular flanges 16 then in this case assume positions which are at least substantially in the same radial plane as the respective associated liner ring 18.

The following molding operation is by and large the same as that described above, the molding material at the same time surrounding the basic body 15 in the circumferential direction so that the body is embedded 7 in the molding material. The configuration of the mold cavity 4 is preferably so selected that the parts of the basic body between the operative sections 12 are as well surrounded by a layer of molding material integral with the operative sections 12 while maintaining the necessary waists 13.

It will be clear that in case of need individual sections 15 of the basic body may be left without any casing.

In all cases the removal of a liner ring 18 from the associated operative section 12 is conveniently so performed that after the molding operation and after removing the spool 10 from the mold it is drawn off in the axial direction 11 from this operative section 12. This drawing off operation is practically not hindered at all by the operative section 12 consisting more particularly of a soft synthetic resin material. As shown in figure 3 two liner rings 18' and 18' ' already drawn off are to be seen, whose previous positions are shown in broken lines at 30, the arrows 31 indicating the direction of pulling off.

If a_ liner ring 18 drawn off the associated operative section 12 comes into a position adjacent to a waist between two operative sections 12 or lands, as is the case with the liner ring 18'' in figure 3, there are basically two possibilities in order to completely remove the ring. As one possibility the liner ring 18' and 18'' may be pulled off further in the draw off direction 31 over the next operative sections 12. As the other possibility the liner ring 18 and 18' ' may be opened at least at one position on its circumference and then be removed transversely in relation to the longitudinal direction 11 from the waist 13. In this respect it is for instance possible to open out the liner ring 18' ' at a point over some extent of the periphery which is at least equal to the thickness of the spool at the waist 13. Any ring opening having a smaller dimension may be opened, for instance by twisting the opened ring. The simplest method is to open or split the liner ring 18 and 18' ', which is adjacent to a waist, at two points on its periphery so that there are then two ring parts which are readily removed.

It will be clear that the materials for the liner rings 18 and the molded structure coming into contact therewith should be so matched that on molding there is an at least substantial avoidance of adhesion and later pulling off is possible without any difficulty. In case of need it is also possible for the inner circumferential surface 21 to be pretreated, for instance by being coated with a demolding agent preventing adhesion. It is important that on removing a liner ring 18 from the operative section 12 its circumferential surface constituting the outer sealing surface 19 is not damaged.

8 Since in the case of the method in accordance with the invention the zone, constituting the outer sealing surface 19, of the operative section 12 is not subjected to the danger of an abrasive finishing treatment, there is as a result a high quality and gapless sealing surface. The production of a spool 10 is limited to only a few working steps. Owing to the simple production of the liner rings 18, which may even be able to be used again, both the method and also the apparatus for performing the method are relatively cheap. Since the liner rings 18 have a simple configuration, their inner circumferential surface may be produced within very tight tolerances, something that is not without its effect on the quality of the cast sealing surface 19 so that there are no tolerance problems in the production of the spools.

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Claims

1 A method of producing a valve spool with at least one operative portion having an annular external sealing surface, wherein-the spool is formed in a mold having at least two parts, a liner ring being positioned in the mold adjacent to the intended location of the respective operative portion, and having an uninterrupted inner circumferential surface which is shaped to be complementary to the desired profile of the external sealing surface, moldable material then being introduced into the mold cavity to produce the or each operative portion, and, after solidification of the moldable material, the liner ring being removed from the operative portion to free a.flash-free outer sealing surface thereon.

2. A method as claimed in claim 1, wherein, for the production of a spool having a plurality of axially succeeding operative portions, a plurality of liner rings are utilized, which are arranged coaxially in the mold, in accordance with the axial spacing of the desired operative portions, prior to forming in the mold.

3. A method as claimed in claim 1 or claim 2, wherein the sealing surface exposed after removal of a respec- tive liner ring is in a condition such that it does not have to be treated and more particularly to be given any finishing treatment.

4. A method as claimed in any one of the preceding claims, wherein the closed condition of the mold each respective liner ring adjacent to the outer sealing surface to be produced covers over positions of parting of the mold between the parts of the mold.

5. A method as claimed in any one of the preceding claims, wherein after forming the material in the mold each respective liner ring is removed by drawing off in the axial direction of the spool from the respective operative portion on the spool.

6. A method as claimed in claim 5, wherein, in the case of a spool having a plurality of operative portions, each respective liner ring is drawn off the respective operative portion associated therewith during molding, over the adjacent operative portions from the spool.

7. A method as claimed in claim 6, wherein, in the case of a spool having 2 plurality of operative portions, each respective liner ring is drawn off the respective operative portion associated therewith during molding and is split in an axial part between two operative portions at least at one position on the periphery, whereby to be removed to a side.

B. A method as claimed in any one of the preceding claims, wherein the liner rings are inserted in receiving recesses formed in the mold prior to closing of the mold.

9. A method as claimed in any one of the preceding claims, wherein, by suitable matching of the materials of the operative portions to be produced and of the associated liner ring adhesion between the operative portion and the liner ring is prevented during molding.

10. A method as claimed in any of claims 1 to 8, wherein by provision of a demolding agent or demolding layer adhesion between the operative portion and the liner ring is prevented during molding.

11 11. A method as claimed in any one of the preceding claims, wherein prior to moulding in addition to the liner rings a basic body constituting the spool core is so introduced into the that it is surrounded by the inserted liner rings, more particularly so as to leave a radial clearance and so that during the following molding operation the basic body is enveloped along at least a part of the length thereof by the molding material serving to produce the operative portions.

12. An apparatus for producing a valve spool with at least one operative portion having an annular external sealing surface, the apparatus comprising a mold which defines a mold cavity, the latter, with the exception of those parts adjacent to the intended location of the or each operative portion, being substantially complementary in shape to the desired profile of the spool to be produced, at least two mold parts distributed over the periphery of the mold cavity and movable towards and away from each other, and at least one liner ring which is able to be removably arranged adjacent to the intended location of the operative portion in the mold, the liner ring having an inner circumferential surface which is complementary to the desired profile of the external sealing surface to be produced on the spool.

13. An apparatus as claimed in claim 12, wherein, in the closed condition of the mold, in the inner wall surface of the mold for each liner ring an annularreceiving recess is constituted which, adjacent to abutting or adjoining parts of the mold, has parting positions, the latter, with the liner ring inserted, being covered over with respect to the outer sealing surface to be produced.

14. An apparatus as claimed in claim 12 or 13, 12 i wherein, adjacent to a radial inner circumferential surface corresponding to the eventual outer sealing surface, at least one liner ring has two axially spaced coaxially and peripherally extending recesses in such a manner that the sealing surface prdouced on molding has two sealing humps following each other in the axial direction.

15. An apparatus as claimed in any one of the claims 12 to 14, wherein at least one liner ring consists of metal and more particularly of brass.

16. An apparatus as claimed in claim 15, wherein said at least one liner ring consists of brass.

17. A method of producing a valve spool substantially as described hereinbefore with reference to the accompanying drawings.

18. An apparatus for prdocuding a valve spool substantially as described hereinbefore with reference to the accompanying drawings.

19. Any novel subject matter or combination including novel subject matter disclosed in the foregoing Specification or Claims and/or shown in the drawings, whether or not within the scope of or relating to the same invention as any of the preceding Claims.

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