EP2292936A1 - Pneumatic cylinder - Google Patents

Abstract

The cylinder (1) has a cylinder housing (2) and a piston rod (4) comprising a piston element (3). The piston element and the piston rod are supported in an axially movable manner relative to the cylinder housing, where the cylinder housing is made from pressure-free cast polypropylene. A metal cylinder pipe (5) is arranged as a cylinder sleeve for the piston element, in the housing, where the piston element is supported in the sleeve in an axially movable manner. The housing has fastening devices (7) for fastening the cylinder to a welding machine e.g. welding gun.

Description

The invention relates to a pneumatic cylinder according to the preamble of claim 1.

From the German utility model DE 92 07 582 a working cylinder is known which has a housing made of an inner tube and an inner tube surrounding the inner tube radially outer. The outer tube is a plastic tube, which may consist of polyvinyl chloride, a polyacetate or a polyoxymethylene. The outer tube is formed as an extruded part or as an extruding part. In particular, this document teaches the use of a plastic of lower quality in terms of strength for the outer tube, which is not subjected to dynamic loads on the outer tube. The use of the mentioned plastics for the outer tube have only the task of ensuring a diverse contouring of the outer circumference with little effort.

From the EP 12 55 046 B1 is a pressure cylinder, in particular for use in the food industry, in which a cylinder tube is encased by a plastic, wherein the plastic is a transparent material. This should have the purpose of being able to detect any existing position sensors for the piston rod from the outside better. The transparent plastic of the housing contributes nothing or only slightly to the strength and stability of the cylinder. The cylinder tube and two end cylinder cap are by Threaded rods locked together, forming a stable cylinder.

The aforementioned cylinders are not suitable as pneumatic cylinders for use in a welding system, in particular in a portal welding machine or multi-point welding machine, a welding robot or the like. For these applications, known cylinders have a steel tube as a cylinder tube, in which the piston elements and the piston rod are axially displaceable, since such cylinders must be very resistant, especially in terms of mechanical stress. Usually, such welding cylinders are operated at pressures of up to 12 bar and have strokes up to about 180 mm. Such cylinders are used as break points in welding equipment as well as driving spot welding guns which may be stationarily mounted or attached to a robot, e.g. used in the automotive industry. Since the demands in the automotive industry for shortening the production cycle times are getting bigger, this means that the robots with the welding guns have to move faster and faster, especially during idle travel. To get as fast as possible and as soon as possible from a position of a first welding point to a position of a second welding point, the welding guns must be as light as possible. Steel cylinders have a relatively high weight due to the design, so that the associated welding tongs have a correspondingly high weight, which increases the dynamic loading of the robot.

In addition, such steel cylinders are very expensive to manufacture, since, for example, a cylinder tube must be provided at the end with a closure. At the end, this closure is usually welded. The pressure medium supply, In this case, compressed air supply and discharge devices must be provided by means of soldered connection means. Furthermore, it is relatively expensive to attach fasteners for the steel cylinder to this. Usually, holders are welded there, which leads to unwanted heat distortion in the production. From this and also from the soldering results in the production of such a cylinder undesirable stress and undesirable thermal distortion. In order to meet the high demands on the coaxiality and the tight tolerances of a pneumatic cylinder, it is therefore necessary to carry out a tailor-made honing or unwinding after completion of all heat treatments of such a cylinder.

Furthermore, it is usually necessary to also carry out extensive galvanic measures, such as Phosphating be performed to ensure adequate corrosion protection.

The object of the invention is therefore to provide a suitable pneumatic cylinder u.a. for use in welding devices, for example in welding tongs or welding portals, which on the one hand has a reduced weight and, on the other hand, achieves the values of a steel cylinder in terms of component strength under the given boundary conditions. In particular, the number of manufacturing steps and the items required in the production should be significantly reduced.

Furthermore, a pneumatic cylinder is to be specified, which is adaptable in a simple manner in different installation situations and in particular can be arranged closely spaced side by side, so that the distance between two cylinder center axes can be chosen as small as possible. Another object of the invention is to provide a pneumatic cylinder which runs quietly in operation and in particular for installation in a welding / welding tongs in a simple manner an electrical insulation of the cylinder, in particular its piston rod relative to the remaining welding tongs easy.

A further object of the invention is to provide a pneumatic cylinder which is particularly narrow in a transverse direction of the cylinder and can nevertheless apply a compressive / tensile force necessary for operation of welding tongs or other actuating means.

These objects are achieved with a pneumatic cylinder having the features of claim 1. Advantageous embodiments are specified in the subclaims.

According to the invention it has been recognized that the plurality of specific requirements for pneumatic cylinders that are used in welding devices, can be met by selecting a specific plastic for a cylinder housing, wherein a polyamide is selected as the plastic, which is pressure-sealed. Unpressurized pours in the context of the invention is to be understood that the polyamide is not as in the injection molding or extrusion process under pressure is brought into shape, but is poured in a pourable liquid state without applying external pressure in an open mold. Surprisingly, it has been found that the selection of the plastic and the type of processing leads to a particularly strong plastic structure and also to a particularly durable crystalline design of the plastic, so that all application-specific requirements now for the first time by means of a plastic cylinder housing be ensured for the application of the pneumatic cylinder in a welding system.

It has even been found that such a cylinder housing is sufficiently stable in order to work without a metallic inner tube, which forms a bushing for piston elements of the pneumatic cylinder. Of course, it may be appropriate for certain applications that a metal cylinder is arranged as a bushing for the piston element in the cylinder housing.

According to a further preferred embodiment, the cylinder housing is provided in the region of a first end of the cylinder housing with fastening means, which are preferably integrally mounted on the cylinder housing. It is also advisable to unilaterally form the cylinder housing, so that, for example, a bottom piece of the cylinder housing and corresponding fastening devices are integrally formed together with the cylinder housing.

In order to achieve the closest possible packing and the closest possible succession arrangement of several pneumatic cylinders according to the invention, it is recommended to provide the cylinder housing by means of flattenings, so that the closest possible arrangement of the cylinders is ensured next to one another. It is also expedient to provide measuring means in thickened regions of the cylinder housing, by means of which the position of the piston elements or of the piston rod in the interior of the cylinder can be determined. The measuring means may readily be cast in and / or stored in a groove.

At the second end of the cylinder housing this is covered and sealed by means of a, for example metallic closure, wherein the closure on the one hand at a shoulder in the cylinder housing rests and on the other hand is held axially by a so-called Seeger ring. The Seeger ring sits in a groove in the plastic of the cylinder housing.

As a preferred material for the formation of the cylinder housing is a PA12, PA12G or PA6 in question. Appropriately, it makes sense to also produce piston elements or the piston rod from the pressureless cast polyamide. This leads to a further reduction in weight and in particular to a quiet and low-wear running. Furthermore, this embodiment of the piston / piston rods offers the possibility to pour sealing elements in the edge region of the piston in one piece into the pistons and thus to reduce the required assembly costs.

In the pneumatic cylinder according to the invention, it is possible in a simple manner, the housing for forming a multi-cylinder with a plurality, i. To provide two or more cylinder chambers, so that a multi-acting pneumatic cylinder can be achieved. This is particularly easy to achieve in the selected material, since the selected material in the present invention selected processing, namely the pressure casting is very easy to machine and in particular holes for cylinder chambers with a very large stroke in relation to the bore diameter can be easily and accurately produced. Drilling / lifting ratios in the range of up to 1:12 can be produced without any problem.

In the case of the pneumatic cylinder according to the invention, therefore, the cylinder housing is cast in one piece, wherein the casting takes place in such a way that the low-viscosity polyamide has a starter for the polymerization reaction. In this fluid state, the polyamide is poured into an open mold. The polymerization of the plastic then takes place in the mold, that is, the molecular chain formation also takes place in the mold, whereby a very homogeneous and low-stress construction of the casting blank is achieved. This distinguishes the pressure-free casting, for example, from the usual injection molding, where it comes to certain orientations of the already finished molecular chains and in particular in the area of meeting two casting fronts can give weak points, such as on the back of a both sides of the melt flown around the core, the two melt streams again to meet. In injection molding, it may happen that such melt streams no longer bond 100%, since on their surface already on the way a cooling / orientation of the chains has occurred. This problem is known in injection molding as the emergence of a weld line. In contrast, formation of longer molecular chains is observable in the inventive design of the cylinder housing from a pressureless cast polyamide, since a pressing into the mold or pushing through an extrusion die does not occur. After the curing of the polyamide composition in the casting mold, for example, the casting blank can be tempered. This serves for further homogenization and can take in practice, depending on the requirement, about 2 to 6 hours.

If a steel tube is used as a bushing for the piston, the steel pipe preferably sits by means of a clearance fit in the cylinder housing, wherein the clearance is achieved on the one hand by machining the bushing and the inner surface of the cylinder housing.

It has been found that if a metal bushing / metal cylinder is used, this end can be open at both ends and the resulting during operation of the pneumatic cylinder by pressurizing axial forces on the bottom portion of the cylinder housing and the closure of the cylinder housing acting forces readily by the cylinder housing itself, so the polyamide plastic can be absorbed.

If the housing has thickened regions or regions with sufficient wall thickness, the connection devices for the supply and removal of the pressurized fluid, in this case compressed air, can be mounted directly in the plastic of the cylinder housing. An additional provision of fittings or the like is no longer necessary. The compressed air supply lines can be screwed directly into the cylinder housing.

It is particularly expedient to form a cylinder package from a plurality of flattened cylinder housings and pneumatic cylinders according to the invention formed therefrom and to provide this cylinder package with, for example, a suitable bundling device. Such a bundling device may for example have a shape guide, so that in each case two adjacent pneumatic cylinders are mechanically connectable by means of positively engaging connecting elements. Such form guides are, for example, a dovetail guide or T-slots.

Overall, in the pneumatic cylinder according to the invention a great advantage is the fact that a variety of primarily conflicting requirements for a pneumatic cylinder for use in a welding system could be met by the selection of the material. In particular, it should be pointed out that welding spatter and welding beads typically occurring in a welding installation during the use of a pneumatic cylinder could not generally damage the cylinder housing in the usual frequency. This resulted in corresponding experiments.

Furthermore, it is of particular advantage that in the production of such a compressed air cylinder, a plurality of steps, in particular a soldering of connection means for the pressure medium lines, welding of corresponding holding devices, phosphating or otherwise galvanic treatment for the purpose of rust protection or / and consuming machining reworks could be omitted to ensure the cylinder tread accuracy. As a result, a significant cost advantage over known cylinder housings made of metal and a considerable simplification of the production of the cylinder is possible.

Furthermore, it is possible in a particularly simple manner to make special shapes and special sizes of the cylinders available to users, since the selected material can be cast free of voids even in large blocks, so that special sizes of cylinders are made available by machining correspondingly cast polyamide blocks can. This is possible in a reasonable cost range, because the selected plastic can be machined easily and accurately.

It is particularly advantageous when using a pneumatic cylinder according to the invention without inner metallic bushing, that the material used has a high self-lubrication property, so that the operation can be done over a long time out with un-lubricated compressed air.

Figur 1:

eine teilweise geschnittene Seitenansicht eines erfindungsgemäßen pneumatischen Zylinders;

Figur 2:

eine Draufsicht auf den Zylinder gemäß Figur 1;

Figur 3:

eine isometrische Ansicht auf einen erfindungsgemäßen Zylinder;

Figur 4:

eine Ansicht eines aus zwei Einzelzylindern gebildeten Zylinderverbund;

Figur 5:

einen Längsschnitt durch eine zweite Ausführungsform des pneumatischen Zylinders in der Ausführungsform als Mehrfachzylinder;

Figur 6:

eine Draufsicht auf den Mehrfachzylinder gemäß Figur 5;

In the following the invention will be explained by way of example with reference to the drawing. Show it:

FIG. 1:

a partially sectioned side view of a pneumatic cylinder according to the invention;

FIG. 2:

a plan view of the cylinder according to FIG. 1 ;

FIG. 3:

an isometric view of a cylinder according to the invention;

FIG. 4:

a view of a cylinder assembly formed from two single cylinders;

FIG. 5:

a longitudinal section through a second embodiment of the pneumatic cylinder in the embodiment as a multi-cylinder;

FIG. 6:

a plan view of the multiple cylinder according to FIG. 5 ;

A pneumatic cylinder 1 according to the invention FIGS. 1 to 4 has a cylinder housing 2, in which at least one piston element 3 are mounted axially displaceably together with a piston rod 4. In the cylinder housing 2 sits as a bushing for the piston member 3, a metal cylinder tube 5. In the region of a first end 6 of the cylinder housing 2, the cylinder housing 2 has fastening means 7, which together with a bottom piece 8, the cylinder housing 2 close at one end. The cylinder housing 2, the bottom piece 8 and the fastening device 7 are integrally formed. At the opposite second end 9 of the cylinder housing 2, the cylinder housing is open. In the region of the second end 9 closes a closure, in particular a metal closure 10, the cylinder chamber of the cylinder housing 2. The closure 10 is supported on one side, for example, front side of the metal cylinder 5 from. Nevertheless, corresponding shoulder can also be present in the interior of the cylinder housing 2, against which the closure 10 is set. Other end is the closure 10 by means of a securing ring 11, in particular one Seeger ring, which sits in a corresponding groove 12 in the cylinder housing 2, set. The closure 10 has a passage opening 13 for the piston rod 4. From the second, open end 9 ago extends in the cylinder housing 2, a further groove 14, into which engages a projection 15 of the closure 10, so that the closure 10 with respect to. The cylinder housing 2 is rotatably mounted. The passage opening 13 has at least one straight boundary 16, which corresponds to a corresponding flat side 17 of the piston rod 4 and thus the piston rod 4 rotationally fixed with respect to. The cylinder housing 2 is fixed.

In the region of the first end 6 and / or in the region of the free cylinder wall of the cylinder housing 2 supply / discharge means 18 are provided for pressurized fluid, in particular for compressed air.

The cylinder housing 2 of the pneumatic cylinder 1 according to the invention is formed from a non-pressure cast polyamide and consists in particular of a PA6, PA12 or PA12G.

In a preferred manner, the cylinder housing 2 flats 19a, 19b, which are arranged approximately opposite and parallel to each other. In the region of the flats 19a, 19b, mold guides 20 may be provided, for example a dovetail guide, so that adjacently arranged pneumatic cylinders 1 can be connected to one another by means of a suitably shaped connecting element in the manner of a plug-in block 21 corresponding to the mold guides 20.

By providing the flats 19a, 19b, the cylinder housing 2 has thickened portions 22a, 22b in which more convenient Manner measuring means (not shown) for determining the position of the piston 3 with respect to. The cylinder housing 2 are poured.

FIG. 4 shows an example of a composite of two pneumatic cylinders 1 according to the invention, which are assembled by means of a plug 21.

According to a particular embodiment of the invention ( FIGS. 5 and 6 ), the pneumatic cylinder according to the invention is designed as a multiple cylinder with an integrally formed cylinder housing 2. In the integrally formed cylinder housing 2 sits a plurality, in particular three cylinder bores 30, which each serve to receive at least one piston element 3 and a piston rod 4. The cylinder bores 30 are used either for receiving a metal cylinder tube 5 or store directly, without the interposition of a metal cylinder tube 5, the piston rods / piston element unit axially displaceable. Conveniently, the cylinder bores 30 are connected to each other by means of a communicating line, so that all three cylinder bores 30 can be uniformly acted upon by pressurized fluid by pressurizing means 18. By such an arrangement, which can be easily formed, in particular with a cylinder housing 2 from a non-pressure molded polyamide, particularly narrow multi-cylinder are possible, which allow a high compressive force at a small width b.

In this case, it is particularly possible to form cylinder bores 30 whose diameter / length ratio d / l is particularly small. In particular, diameter-length ratios of 1: 8 to 1:12 in comparison to cylinder housings made of metal are particularly easy to produce, since the inventively selected unpressurized polyamide resin can be machined particularly easily and even with such unfavorable diameter / length ratios still sufficient manufacturing accuracy can be achieved.

With a pneumatic multiple cylinder according to the FIGS. 5 to 7 In particular, it is possible to achieve high pressure forces, although the width b of the cylinder housing is very low compared to the height h. By coupling the respective piston rods outside the cylinder housing, it is possible in a simple manner to achieve high pressure forces, since all pistons act in parallel. The resulting surfaces of the individual pistons are relatively small and can be made round in cross-section, so that there is a reduced sealing problem compared to an oval or otherwise freely shaped piston. In particular, cylinders according to the FIGS. 5 to 7 be arranged very tightly nested. This makes it possible, for example, to realize welding tongs or welding portals with particularly narrow dot patterns. In the field of welding tongs, such a narrow-built cylinder can often be reduced accessibility problems such as those caused by an excessively large welding tongs, for example in the body shop.

LIST OF REFERENCE NUMBERS

1

pneumatic cylinder

2

cylinder housing

3

piston element

4

piston rod

5

Metal cylinder tube

6

First end

7

fastening devices

8th

breech

9

Second end

10

shutter

11

circlip

12

groove

13

Through opening

14

groove

15

head Start

16

limit

17

flat side

18

Druckmittelzuführ - / - removal device

19a, 19b

flats

20

form guide

21

plug Stein

30

bore

Claims (15)

Pneumatic cylinder, in particular for use in a welding device, eg a spot welding gun or a spot welding portal, with a cylinder housing (2) and a piston rod (4) having at least one piston element (3), wherein the piston element (3) and the piston rod (4) are relative to the cylinder housing (2) are mounted axially displaceable, characterized in that the cylinder housing (2) is formed from a non-pressure molded polyamide. Pneumatic cylinder according to claim 1, characterized in that in the cylinder housing (2) a metal cylinder tube (5) is arranged as a bushing for the piston element (3), in which the piston element (3) is mounted axially displaceable. Pneumatic cylinder according to claim 1 or 2, characterized in that the cylinder housing (2) in the region of a first end (6) of the cylinder housing (2) fastening means (7) for securing the pneumatic cylinder (1) to a welding device, such as a welding gun or a Welding portal and the fastening device (7) and the cylinder housing (2) are integrally formed. Pneumatic cylinder according to one of the preceding claims, characterized in that the cylinder housing (2) along its longitudinal extent at least one flattening (19a, 19b). Pneumatic cylinder according to one of the preceding claims, characterized in that in thickened regions of the cylinder housing (2) measuring means, in particular position sensors are cast or inserted into a groove. Pneumatic cylinder according to one of the preceding claims, characterized in that the cylinder housing (2) has mold guides (20), so that in each case two adjacent pneumatic cylinders (1) are mechanically connectable by means of positively engaging connecting means (21). Pneumatic cylinder according to one of the preceding claims, characterized in that the cylinder housing (2) is closed at the other end with a closure (10) which bears on one side on a projection / shoulder or on the front side of the metal cylinder tube (5) and on the other side by means of a snap ring (11 ) is fixed, which sits in a groove (12) in the cylinder housing (2) and axially fixes the closure (10) against the shoulder. Pneumatic cylinder according to one of the preceding claims, characterized in that the cylinder housing (2) for forming a multi-cylinder has at least two cylinder chambers (30). Pneumatic cylinder according to one of the preceding claims, characterized in that the non-pressure cast polyamide is a PA12, a PA12G or a PA6. Pneumatic cylinder according to one of the preceding claims, characterized in that at least one piston element (3) and / or the piston rod (4) is formed from a non-pressure molded polyamide, in particular from the same material as the cylinder housing (2) is formed. Pneumatic cylinder according to one of the preceding claims, characterized in that sealing elements of the piston elements (3) are formed integrally with the piston (3). Pneumatic cylinder according to one of the preceding claims, characterized in that the sealing elements is designed as a soft lip seal. Pneumatic cylinder according to one of the preceding claims, characterized in that the sealing elements are cast at least partially into the piston elements (3). Welding device comprising at least one pneumatic cylinder according to one of claims 1 to 13. Welding device according to claim 14, characterized in that the welding device is a welding gun, a portal welding machine or a multi-point welding system.

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