Patent Application
20090205487
The present invention relates to a pressure cylinder comprising a cylinder space which is bounded by a cylinder housing and in which a fitting piston is axially movable, wherein a piston rod, which is manufactured at least substantially from a composite material of fibres, extends from the piston, which piston rod mainly comprises a layer of core material under a surrounding outer jacket.
Pressure cylinders exist in many shapes and sizes and are usually adapted for a concrete application. Use is usually made here of a metal, in particular stainless steel, as material for the cylinder housing, the piston rod and the piston because of the sturdiness, durability and relatively simple processability of this material, in addition to a relatively favourable raw material price. Metal as basic material for a pressure cylinder does however also have a drawback, this being specifically the relatively high specific weight thereof. The final pressure cylinder will hereby have a considerable overall weight, this being a drawback particularly for applications in which a low weight is aimed for. This is a particular issue on board ships and aircraft, and in hand tools such as for instance rescue tools, wherein from a structural and ergonomic viewpoint the lowest possible weight is sought after.
With a view to lightweight applications, recourse is increasingly being had to composite materials. At a given mechanical strength and loadability, composite materials are significantly lighter than for instance stainless steel. Furthermore, composite materials are generally very highly resistant to corrosion, which makes these materials eminently suitable for use in aggressive environments, such as for instance on board (seagoing) ships.
An example of a pressure cylinder of the type stated in the preamble, in which use is made of a composite material, is known from European patent application EP 239.406. The pressure cylinder described therein comprises a cylinder housing in which a piston with piston rod can move, wherein both the cylinder housing and the piston rod with piston are manufactured from composite material. The piston rod herein comprises an outerjacket of wound composite material fibres having thereunder a laminated layer of core material of alternately straightened and wound fibres
Although a significant weight reduction can be achieved with the known pressure cylinder, it is still far from optimal. The structure of alternately straightened fibres and fibres wound therearound in the layer of core material results in relatively little compactness of the fibres. Particularly in the case of compression strength it has been found in practice that a relatively large amount of material is hereby necessary for the piston rod to be able to guarantee a determined loadability, which results in a greater overall weight and volume, in addition to a higher cost price of course.
The present invention has for its object, among others, to provide a pressure cylinder of the type stated in the preamble, which requires less composite material for the piston rod while the strength remains the same.
In order to achieve the intended object, a pressure cylinder of the type stated in the preamble has the feature according to the invention that at least substantially the fibres of the composite material in the core material are at least almost fully straightened and are oriented at least almost parallel to a longitudinal axis of the piston rod, and that at least substantially the fibres of the composite material in the outer jacket are wound at an angle round the longitudinal axis of the piston rod. By applying substantially only straightened fibres in the layer of core material an extremely compact stacking of the fibres is achieved therein, which manifests itself in a particularly high compression strength. It is hereby possible for a determined loadability to suffice with a significantly thinner layer of core material than in a laminated structure as in the known pressure cylinder. A relatively thin outer jacket of wound fibres herein already provides the piston rod of the pressure cylinder according to the invention with sufficient stability and strength to enable radial stresses to be absorbed. Thus provided is a pressure cylinder with a piston rod of relatively light weight, which can withstand a relatively high pressure load.
A preferred embodiment of the pressure cylinder according to the invention is characterized in that the composite material fibres comprise high strength to weight fibres, in particular carbon fibres. A high strength to weight fibre such as carbon fibre is highly suitable for application in a piston rod according to the invention, because, in addition to a relatively light weight, it also imparts a relatively great strength to the piston rod. A relatively high pressure load can thus be absorbed with additional certainty.
A further preferred embodiment of the pressure cylinder according to the invention is characterized in that the outer jacket comprises a top layer with a practically flat, smooth surface. Such a surface protects the composite material fibres and causes almost no friction damage to parts with which the piston rod is in contact, such as for instance hydraulic sealing means. The outer jacket thus provides a top layer of the piston rod which enhances the durability of the pressure cylinder. With a view hereto, a particular embodiment of the pressure cylinder according to the invention has the feature that the top layer comprises wound fibres and has been subjected to a material-removal process. The piston rod is over-dimensioned and then reduced to the desired diameter, wherein unevenness resulting from the wound fibres disappears.
A further preferred embodiment of the pressure cylinder according to the invention is characterized in that the piston rod is at least substantially constructed around a central tube. Such a tube provides a substrate on which the layer of core material can be arranged in relatively simple manner. A piston rod according to the invention can thus be manufactured relatively quickly and easily.
A further preferred embodiment of the pressure cylinder according to the invention is characterized in that, along at least a part of a length thereof, the tube at least comprises a cavity which is open at least at a proximal end of the piston rod. The cavity in the tube results in a weight-saving and thus provides an extra-light piston rod, and moreover provides a fixing option at the proximal end.
A further preferred embodiment of the pressure cylinder according to the invention is characterized in that the piston rod is connected to the piston via an insert, wherein a distal end of the insert protrudes fittingly into the cavity in the proximal end of the piston rod, and a proximal end of the insert is durably connected to the piston. Because the piston rod and piston do not form an integral whole, the piston rod and piston can be manufactured separately of each other and from different material. The two components can hereby be optimally adapted to the conditions to which they are exposed. The piston can thus for instance be manufactured from a metal so as to bear a heavy pressure load. The insert provides a durable connection between the piston rod and piston.
A further preferred embodiment of the pressure cylinder according to the invention is characterized in that the insert comprises at least one injection channel which extends between an injection opening at the proximal end of the insert and an outflow opening which opens into a slit between an outer wall of the distal end of the insert and an inner wall of the proximal end of the piston rod. An adhesive can be injected through such an injection channel, and then flow via the outflow opening into the slit so as to fill the free space there. The insert can thus be firmly adhered to the piston rod with the adhesive.
A particular embodiment of the pressure cylinder according to the invention is characterized in that a seal which hermetically seals the slit is arranged on either side of the outflow opening, between the outer wall of the insert and the inner wall of the outer end. Such seals prevent the adhesive running out of the slit into the cavity of the piston rod. The adhesive will thus substantially fill the space in the slit between the seals.
A further particular embodiment of the pressure cylinder according to the invention has the feature that the seal comprises a sealing ring and that a groove is formed in the outer wall of the insert on either side of the outflow opening for receiving the sealing ring therein. Such a sealing ring completely seals the slit around the insert. The groove provides a. fitting space in which the sealing ring remains in place. The insert with sealing rings can thus be placed in relatively simple manner in the cavity of the piston rod.
A further particular embodiment of the pressure cylinder according to the invention has the feature that the insert comprises at least one evacuation channel in open communication with the injection channel, and that the evacuation channel extends between an inlet opening at the position of the slit between the insert and the proximal end of the piston rod and an evacuation opening on a free surface of the proximal end of the insert. Such an evacuation channel provides a free egress for air and the adhesive. An injected adhesive under pressure will expel the air present in the slit and itself eventually exit via the outflow opening. It is thus relatively easy to determine when the piston rod and the insert are wholly glued to each other.
A further preferred embodiment of the pressure cylinder according to the invention is characterized in that the piston comprises at least one injection channel and at least one evacuation channel having respectively an injection opening and an outflow opening on a free surface of the piston, and that the injection channel and the evacuation channel are in open mutual communication via a gap present between the piston and the piston rod with insert. Through such an injection channel an adhesive can be injected and flow into the gap in order to fill it. The adhesive can flow out via the evacuation channel. It is thus relatively easily possible to determine when the piston is wholly glued to the piston rod and the insert. This prevents a liquid, such as a hydraulic liquid, entering between the piston and the piston rod.
A further preferred embodiment of the pressure cylinder according to the invention is characterized in that the piston is screwed onto the insert. A relatively rapid and relatively simple, yet durable, connection is provided by screwing the piston onto the insert. A further preferred embodiment of the pressure cylinder according to the invention is characterized in that the piston and the insert are manufactured from metal, in particular from high-grade aluminium, more in particular from anodized high-grade aluminium. An insert of anodized high-grade aluminium is highly resistant to the forces acting thereon at a relatively high pressure, and is corrosion-resistant. It thus provides a reliable connection between piston rod and piston.
The invention also relates to a method for manufacturing a piston rod from at least substantially composite material from composite material fibres, the method according to the invention being characterized in that fibres saturated with a binder are pulled through a die and in straightened form are formed into a layer of core material, that fibres saturated with binder are wound at an angle around the layer of core material to form a surrounding outer jacket, and that, after being formed, the layer of core material and the outer jacket are cured. Pulling the fibres through a die allows a layer of core material to be manufactured which comprises a relatively high content of fibres oriented and straightened along a longitudinal axis. By winding fibres therearound, a piston rod is obtained which is moreover able to absorb the radial forces released during a pressure load. The binder binds the fibres to each other and provides strength and cohesion to the layer and jacket after curing. With such a method a relatively strong piston rod is thus obtained, which at a relatively low weight can withstand a relatively high pressure load.
A further method according to the invention is characterized in that the layer of core material is manufactured in segments. By manufacturing the core material in segments use can be made of a relatively simple die with a relatively small number of spools from which the composite material fibres are drawn. Such a method thus provides a relatively practical production process.
A further method according to the invention is characterized in that a top layer of at an angle wound fibres is ground smooth and to size. A method is thus provided which makes the top layer of the piston rod fitting and smooth, whereby objects with which the piston rod is in contact, such as sealing O-rings, sustain no friction damage, or hardly any.
A further method according to the invention is characterized in that the core material is glued onto a central tube. Glueing of the core material, in particular core material segments, to an underlying tube is relatively simple. Such a method thus provides for relatively easy manufacture of the piston rod. A further method according to the invention is characterized in that the piston rod is connected to a piston by an insert which is glued to the piston rod at a first end and is connected to the piston at a second end. The piston and piston rod are thus durably connected to each other.
A particular method according to the invention is characterized in that at least one piston rod is severed from a rod of greater length. With such a method one or more piston rods of the correct length can be manufactured quickly and relatively easily from a rod of greater length. Production costs will hereby be lower.
The invention will now be further elucidated with reference to a number of exemplary embodiments and an accompanying drawing. In the drawing:
The figures are otherwise purely schematic and not drawn to scale. Some dimensions in particular may be exaggerated to a greater or lesser extent for the sake of clarity. Corresponding parts are designated in the figures as far as possible with the same reference numeral.
An exemplary embodiment of a piston rod for use in a pressure cylinder according to the invention is shown in longitudinal section in
Piston rod 1 is constructed mainly from a layer of core material 3, which is glued to tube 2. Within the scope of the present invention “mainly” is understood to mean that the layer of core material forms at least 50% of the piston rod. According to the invention this layer of core material consists substantially, if not completely, of straightened fibres of a composite material. In this example the layer of core material 3 comprises a composite material of a high percentage of carbon fibres which are saturated with resin and which are manufactured in segments 4 by pulling the fibres with resin through a die and curing them. With this “pultrusion process” a higher percentage of composite material fibres in the core material can be obtained compared to the winding of fibres, whereby the strength and rigidity of the layer increases, with the result that the layer of core material can bear a relatively high percentage of the total compression-strength of the piston. The resin used here is an epoxy resin, although a polyester, polyurethane, phenol or vinyl ester resin can also be used.
An outer jacket 5 is wound round the layer of core material 3. Outer jacket 5 comprises a layer of composite material of wound carbon fibres and epoxy resin, but may also comprise other high strength to weight fibres. The carbon fibres are wound round core material 3 at an angle of between 60° and 89° relative to the pultruded fibres so as thus to form a very strong layer which prevents buckling of the fibres under pressure.
Outer jacket 5 comprises a top layer 6 of ground glass fibres, although these can also be carbon or other types of fibre which are relatively hard and can be ground. Piston rod 1 can thus be ground smooth and to size, whereby wear to sealing rings and penetration of a liquid, such as for instance a hydraulic liquid, are prevented. In the cavity (not shown) of tube 2 lies a part of a metal insert 10 with a part of an injection channel 11 in the centre thereof. An adhesive can be injected therethrough so as to thus adhere insert 10 to the piston rod.
As further shown in
As further shown in
The cavity of the piston rod is sealed on both sides by insert 10 and closing part 20, whereby the penetration of a liquid, for instance the hydraulic liquid, is prevented.
An exemplary embodiment of an insert for use in a pressure cylinder according to the invention is shown in
As further shown in longitudinal section in
An exemplary embodiment of a piston for use in a pressure cylinder according to the invention is shown in
As further shown in longitudinal section in
Although the invention has been further elucidated on the basis of only a single exemplary embodiment, it will be apparent that the invention is by no means limited thereto. On the contrary, many variations and embodiments are still possible within the scope of the invention for the person with ordinary skill in the art. The piston and piston rod can thus for instance form an integral whole so as to wholly preclude penetration of a liquid. It is otherwise noted here that, when reference is made in the application to a pressure cylinder, this is also understood to mean cylinders which exert a tensile force on a connected apparatus by means of a pressure applied in the cylinder space.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1031911 | May 2006 | NL | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/NL2007/050252 | 5/30/2007 | WO | 00 | 4/30/2009 |
