GB2152586A

GB2152586A - Piston cylinder assembly with cushioned piston movement

Info

Publication number: GB2152586A
Application number: GB08401098A
Authority: GB
Inventors: Robert William Gronbech; James Colin Inman
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1984-01-14
Filing date: 1984-01-14
Publication date: 1985-08-07
Also published as: GB8401098D0

Abstract

A piston-cylinder assembly is described which comprises a piston-cylinder assembly 1 which is operatively connectable to a hydraulic fluid supply and has a secondary, annular piston-cylinder assembly 4 about the main piston-cylinder assembly 1. The main cylinder 1 and the secondary cylinder 4 communicate through holes 25 on one side of the secondary piston 8, and the secondary cylinder is operatively connected on the other side of the secondary piston 8 to a supply of air under pressure. In use movement of the main piston 2 causes the hydraulic fluid to press on the one side of the secondary piston 8 while the other side of the piston is subject to the pressure of the pressurised air, whereby the movement of the main piston 2 is cushioned. <IMAGE>

Description

SPECIFICATION Piston-cylinder assembly with cushioned piston movement This invention relates to a piston and cylinder assembly, and in particular such assembly in which movement of the piston is cushioned.

A pneumatically operated piston and cylin der unit can provide a degree of cushioning by adjustment of the operating pressure, but this may result in slow response and the need for a larger cylinder to perform a given operation. While a hydraulic cylinder provides a more compact unit for a given performance, there is virtually no cushioning effect as hydraulic fluid is incompressible.

The present invention seeks to provide a piston and cylinder assembly with cushioning that combines the advantages of a pneumatic and a hydraulic cylinder in one unit.

According to the invention there is provided a piston-cylinder assembly comprising: a main piston-cylinder assembly which is operatively connectable to a hydraulic fluid supply; a secondary, annular piston-cylinder assembly about the main piston-cylinder assembly; the main cylinder and the secondary cylinder communicating on one side of the secondary piston, and the secondary cylinder being operatively connectable on the other side of the secondary piston to a supply of air under pressure; so that, in use movement of the main piston can cause the hydraulic fluid to press on the one side of the secondary piston while the other side of the piston is subject to the pressurised air, whereby the movement of the main piston is cushioned.

The invention provides a piston-cylinder unit which allows for pneumatic cushioning of the movement of the main piston while giving the operating advantages of a hydraulic cylinder.

One example of the use of the piston cylinder assembly with these features is in the coiling of strip material when it leaves a rolling mill. The strip material is guided towards a coiling station consisting of a mandrel which may be driven, and a number of wrapper rolls and guide plates. Each wrapper roll is mounted on an arm controlled by a piston and cylinder assembly. The wrapper rolls press the strip against the mandrel for the first few convolutions of the material after which the rolls may be withdrawn as the strip grips the mandrel without any external assistance. However, during these first few turns of strip on to the mandrel, the wrapper rolls hit the bulge which is created over the leading edge of the strip.At this position on the strip, and on each convolution while the wrapper rolls are in an operative position, an impact will occur which results in a marking of the surface of the strip. This section of strip may have to be scrapped or sold as a lower grade product. By providing the cylinders that control the wrapper rolls, with a cushioning arrangement the effect of marking can be minimised on the early convolutions and eliminated at the later stages, before the wrapper rolls are withdrawn.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings, wherein: Figure 1 is a view partly in section of a piston-cylinder assembly in accordance with the preferred embodiment of the present invention; and Figure 2 is a side view of a strip coiling arrangement at the exit side of a rolling mill, incorporating a number of the piston-cylinder assemblies.

Referring to Fig. 1, a piston-cylinder assembly generally, comprises: a main cylinder 1, having a piston 2 and a piston rod 3, and a secondary, annular cylinder 4 mounted about the main cylinder 1. The annular cylinder 4 is constituted by the outer surface 5 of the main cylinder 1 and an annular wall 6 which together define an annular space 7 within which is located an annular piston 8.

The main cylinder 1 is closed at one end by an end cap 9 which has a port 10 for connection to a supply of hydraulic fluid. The secondary, annular cylinder 4 is closed at one end by a generally annular end cap 11 having a flange 20 which mates with the annular wall 6. The end cap 11 and the adjacent outer surface 5 of the main cylinder 1, together define a second annular space 1 2 which is an extension of the first annular space 7. The other end of the secondary cylinder 4 is closed by an end cap 1 3 which has port 1 4 for connection to a supply of air under pressure. The annular piston 8 has a tubular portion 15, with an annular end surface 16, which extends into the second annular space 1 2 of the secondary cylinder 4.The area of the annular end surface 1 6 of the tubular portion 1 5 is selected to be one half of the area of the main piston 1. The annular wall 6 and tubular portion 1 5 together define a third annular space 21 which is closed by the annular piston 8 and flange 20 of end cap 11. Flange 20 has a port 23 connected to a filter unit 24, to communicate the third annular space 21 with the atmosphere. The annular piston 8 has seals 1 7 and 1 8 which engage the outer surface 5 of the main cylinder 1 and the annular wall 6, respectively, and tubular portion 1 5 of the annular cylinder has a seal 1 9 which engages the inside of annular end cap 11.

The main cylinder 1 has an annular series of holes 25 which communicate the main cylinder with the second annular space 1 2 of the secondary cylinder 4, and thereby with the annular, end surface 1 6 of tubular portion 1 5 of annular piston 8.

In use, hydraulic fluid is supplied to the main cylinder 1 through port 76 in the end cap 78. At the same time, air under pressure is supplied to the secondary cylinder 4 through port 14 in the end cap 1 3 of the cylinder, thereby pressure is applied to the annular piston 8. The third annular space 21 on the unpressurised side of the piston 8 remains connected to atmosphere throughout.

The hydraulic fluid moves the main piston 2 (to the right, in Fig. 1) until movement of the piston is resisted by the force of the workload.

The hydraulic fluid will also pass through the holes 25 into the second annular space 12, where the fluid will bear on the annular end surface 1 6 of the tubular portion 1 5 of annular piston 8. The annular piston 8 will tend to move (to the right as shown in Fig. 1) under the pressure of the hydraulic fluid, but such movement will be resisted by the pressure of air on the annular piston 8. When the movement piston 2 is resisted, the pressure of hydraulic fluid and air acting on either side of the annular piston will come into equilibrium, and the annular piston 8 will stop moving.If the force of the workload increases causing movement of the main piston 2 (to the left as shown in Fig. 1), the hydraulic fluid in the main cylinder will be forced through holes 25 into the second annular space 1 2 of the secondary cylinder 4, and because the air in the secondary cylinder is more compressible than the hydraulic fluid, the movement of the annular piston 8, and thereby the movement of the hydraulic fluid and main piston 2, will be cushioned. Because the surface area of the annular, end surface 1 6 is one half the surface area of the piston 2, a linear movement of piston rod 3 equal to 'Y' results in a displacement equal to '2Y' of the annular piston 4. This is a ratio of approximately 8:1 in the volume of the air compressed in the secondary cylinder 2 against the volume oil displaced in the main cylinder 1.

When the piston 2 is to be retracted the supply of hydraulic fluid is cut off, and a valve (not shown) opened to allow the hydraulic fluid to drain off from the main cylinder. The air pressure in the secondary cylinder will move annular piston (to the left as shown in Fig. 1), thereby exhausting the hydraulic fluid from that cylinder.

An application of the piston-cylinder assembly according to the preferred embodiment of the invention will now be described with reference to Fig. 2, which shows a strip coiler on the exit side of strip mill.

After passing through a rolling mill (not shown) strip material S is fed to a coiling mechanism 26 between driven pinch rolls 27.

The strip is directed by guide plates 28 towards the coiling mandrel 29. In this example three similar wrapper rolls 30, 31 and 32 are mounted for rotation on arms 33, 34 and 35.

Each arm is pivotally mounted on the main frame 36 of the coiling device 26. Piston and cylinder assemblies 38, 40 and 42, as previously described, are pivotally mounted on the main frame 36 and pivotally connected to each of the arms 33, 34 and 35.

When a coil is being started on the mandrel the rolls are moved by the piston and cylinder units to a position that is just clear of the surface of the mandrel by an amount less than the thickness of the strip material. The strip material S passes from the rolling mill between the pinch rolls 27 and through the guide plates 28 to contact the mandrel and the first of the wrapper rolls 30. The leading edge of the strip is made to conform to the outer surface of the mandrel by the wrapper rolls and additional guide plates associated with each roll. These guide plates have been omitted from Fig. 2 for the sake of clarity.

When the leading edge of the strip has made one convolution, the strip that forms the second convolution commences with a bulge B which impacts against each of the rolls in turn as the coil is formed on the mandrel. The impact is transmitted from the roll to the hydraulic cylinder 38, 40 and 42 and the load is directed by way of the hydraulic fluid through the holes 25 in the main cylinder into the second annular space 1 2 where it exerts pressure upon the surface 1 6 of the annular piston 8, as described before. Air is supplied through the port 1 4 to maintain a cushioning pressure within the annulus 7 acting on the surface of the annular piston 8.

The positioning of the wrapper rolls at the commencement of coiling, and during the wrapping operation, may be controlled by a series of pressure transducers as disclosed in our U.K. patent application No. 8330635.

Claims

1. A piston-cylinder assembly comprising: a main piston-cylinder assembly which is operatively connectable to a hydraulic fluid supply; a secondary, annular piston-cylinder assembly about the main piston-cylinder assembly; the main cylinder and the secondary cylinder communicating on one side of the secondary piston, and the secondary cylinder being operatively connectable on the other side of the secondary piston to a supply of air under pressure; so that, in use movement of the main piston can cause the hydraulic fluid to press on the one side of the secondary piston while the other side of the piston is subject to the pressurised air, whereby the movement of the main piston is cushioned.

2. A piston-cylinder assembly as claimed in claim 1, wherein the area of the one side of the secondary piston on which the hydraulic fluid bears is less than the area of the main piston.

3. A piston-cylinder assembly as claimed in claim 2, wherein the area of the side of the secondary piston on which the hydraulic fluid bears is half the area of the main piston.

4. A piston-cylinder assembly as claimed in claim 2 or 3, wherein the secondary annular cylinder has a tubular extension of smaller diameter than a main annular part, and the piston has an annular extension in which extends into the tubular extension, and the main cylinder communicates with the secondary, annular cylinder in the tubular exten sion.

5. A piston-cylinder assembly as claimed in any preceding claim, wherein the main cylinder and the secondary cylinder communicate through an annular series of holes in the main cylinder.

6. A downcoiler incorporating at least one piston-cylinder assembly as claimed in any preceding claim, with the main piston connected to one of the wrapper rolls.

7. A piston-cylinder assembly substantially as herein described with reference to the accompanying drawings.

8. A downcoiler substantially as herein described with reference to the accompanying drawings.