Screw-threaded working cylinder

Abstract

A screw-threaded working cylinder includes a tubular cylinder that an end region. The end region has a first thread. The end region has a tapered wall section and the tapered wall section has an axial annular surface. A closure has a second thread and the closure is screwed by the second thread into the first thread in a final mounting position. The closure has a mating axial annular surface. The axial annular surface and the mating axial annular surface are pressed in a positive fitting contact to one another in the final mounting position for defining a pressure contact surface. The pressure contact surface defines a sealing plane, and a surface pressure in an area of the pressure contact surface that causes a deformation of the tubular cylinder and the closure. The deformation occurs within an elastic limit over a range from zero applied pressure to a maximum permissible pressure by a pressure medium for the working cylinder. A piston unit is accommodated in the tubular cylinder.

Claims

1. A screw-threaded working cylinder, comprising: a tubular cylinder having an end region, said end region having a first thread, said end region having a tapered wall section, said tapered wall section having an axial annular surface, a wall thickness of said tapered wall section being at most 60% of a wall thickness of said tubular cylinder; a closure having a second thread, said closure being screwed by said second thread into said first thread in a final mounting position, said closure having a mating axial annular surface; said axial annular surface and said mating axial annular surface being pressed in a positive fitting contact to one another in the final mounting position for defining a pressure contact surface, said pressure contact surface defining a sealing plane, and a surface pressure in an area of said pressure contact surface causing a deformation of said tubular cylinder and said closure, the deformation occurring within an elastic limit over a range from zero applied pressure to a maximum permissible pressure by a pressure medium for the working cylinder; and a piston unit being accommodated in said tubular cylinder.

2. The screw-threaded working cylinder according to claim 1, wherein said closure is provided with a sealing element.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The invention is explained in more detail by the following figures:

(2) FIG. 1 general view of the screw-threaded working cylinder in sectional representation,

(3) FIG. 2 detail view of the screw-threaded working cylinder in sectional representation.

DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows a general view of an embodiment of the screw-threaded working cylinder of the invention. In this embodiment, the tubular cylinder 1 is screwed to a guide closure 2.1 and to a bottom closure 2.2, the tubular cylinder 1 has a first thread 5.1 and 5.2 designed as an internal thread on both sides and the two closures 2.1 and 2.2 each have a second thread 6.1 and 6.2 designed as an external thread. The first threads 5.1 and 5.2 are arranged on both sides in the end regions 4.1, 4.2 of the tubular cylinder.

(5) In addition, a piston unit 3 is accommodated in the tubular cylinder 1 which comprises a piston rod 13 and a piston 12 connected to the piston rod 13 in this embodiment. In order to allow the piston rod 13 to extend during a stroke movement, the guide closure 2.1 has a bore as an axial penetration with a closure inner wall 14.

(6) A wiper 15 and a piston rod seal 16 are provided on the closure inner wall 14 of the guide closure 2.1. The wiper 15 is used in particular to remove dirt from the piston rod 13. The piston rod seal 16 ensures the sealing of the piston rod chamber against the outside atmosphere.

(7) The piston 12 separates the piston rod chamber 19 and the piston chamber 20. The piston rod chamber 19 and the piston chamber 20 are also collectively referred to as working chambers. According to the embodiment of the screw-threaded working cylinder shown, a piston seal 17 is also provided. The piston seal 17 effects the sealing of the working chambers and thus an undesired passing of the pressure medium between the working chambers is prevented. Two guide belts 18 are provided on the piston 12 for its linear guidance and they simultaneously prevent the direct metallic contact with the tubular cylinder 1.

(8) In the following, the coupling of the tubular cylinder 1 with the bottom closure 2.2 is explained in more detail. The construction described and the functional connections explained here apply in the same way to the coupling between the tubular cylinder 1 and the guide closure 2.1.

(9) As especially FIG. 2 shows in an enlarged view of detail A of FIG. 1, the end region 4.2 of the tubular cylinder 1 has a tapered wall section 7. The tapered wall section 7 has a smaller wall thickness than the other sections of the tubular cylinder 1. In the embodiment, the wall thickness of the tapered wall section 7 is about 42% of the wall thickness of the rest of the tubular cylinder 1.

(10) The tapered wall section 7 has an axial annular surface 8, while the bottom closure 2.2 shown here has a mating axial annular surface 9. In the final mounting position, in which the tubular cylinder 1 and the bottom closure 2.2 are screwed together, the axial annular surface 8 and the mating axial annular surface 9 are in positive pressure contact to each other. Thus, a pressure contact surface 10, which acts as a sealing plane, is generated. The sealing plane is designed such that a continuous sealing against the outside atmosphere is guaranteed along the entire pressure contact surface 10.

(11) By tightening the screw connection, a surface pressure is produced in the area of the pressure contact surface 10 in the final mounting position, which results in an axial deformation of both the tubular cylinder 1 and the bottom closure 2.2. The load on the tubular cylinder 1, in particular on the tapered wall section 7, and on the bottom closure 2.2 combined with the surface pressure is set in such a way that in all operating conditions, i.e. with or without pressure application of the pressure medium, the deformation remains within the elastic limits of the materials used. The deformation of the coupling partners at changing operating pressures takes place exclusively in the elasticity range. As the functionality of the screw-threaded working cylinder is not restricted by irreversible plastic deformations, it can be used in the long term and is less susceptible to faults.

(12) As FIG. 2 also shows, an additional sealing element 11 is provided in the embodiment in the bottom closure 2.2, which is designed as a ring-shaped elastic seal and is only used as an additional securing measure in special applications.

(13) Some of the advantages achieved are mathematically demonstrated in the following by means of the embodiment, and practical values were used for the underlying parameters.

(14) The steel grade S35 N, which has an elastic limit R.sub.0.2, also referred to as 0.2% proof stress, of 355 N/mm.sup.2, was chosen as the material for the calculation basis both for the tubular cylinder 1 and for the closures 2.1 and 2.2.

(15) In this example, the diameter D.sub.K of the piston 12 was determined to be 75 mm. The wall thickness s of the tubular cylinder 1 is 6 mm, whereas the reduced wall thickness a in the area of the tapered wall section 7 is 2.5 mm.

(16) The following mathematical relationships apply to the calculation of the forces acting on the annular surfaces 8; 9:
F.sub.red=(D.sub.K+s)**a*R.sub.0.2=(75+6)**2.5*355=225,841 N
F.sub.max=(D.sub.K+s)**s*R.sub.0.2=(75+6)**6*355=542,019 N

(17) Here, F.sub.red indicates the force to be applied when using a reduced wall thickness of 2.5 mm and F.sub.max indicates the force required without using a tapered wall section 7 and thus for a wall thickness of 6 mm. The result is a reduced force F.sub.red of 225,841 N and a maximum force F.sub.max of 542,019 N.

(18) Thus, with a constant wall thickness of 6 mm along the entire tubular cylinder 1, an approximately 2.4-fold force application would be necessary to reach the elastic region of the material to the same extent as it is the case with the use of a tapered wall section 7 with a wall thickness of 2.5 mm.

(19) Due to the lower force F.sub.red, which is necessary to achieve the surface pressure required for sealing when using a screw-threaded working cylinder according to the invention, a reduced thread length I.sub.red can be used, for example.

(20) $l_{\mathrm{red}}=\frac{F_{\mathrm{red}}*P}{d_G**H*p_{\mathrm{zul}}}=\frac{225.841*1,5}{77,026**0,812*177,5}=9,71\mathrm{mm}$

(21) Here, P stands for the thread pitch, d.sub.G for the flank diameter of the thread, p.sub.zul for the permissible flank pressure for the thread and H for the thread depth are as the projected flank of the thread. The permissible flank pressure p.sub.zul is calculated as follows:
p.sub.zul=R.sub.0.2*0.5=355*0.5=177.5 N/mm.sup.2

(22) According to an analogous calculation, the thread length l.sub.max results for the non-reduced axial annular surface 8:

(23) $l_{\max }=\frac{F_{\mathrm{red}}*P}{d_G**0,812*p_{\mathrm{zul}}}=\frac{542.019*1,5}{77,026**0,812*177,5}=23,31\mathrm{mm}$

(24) Thus, the resulting difference between the thread lengths l.sub.max and l.sub.red is 13.6 mm. The shorter thread length achieved reduces the amount of material usage, the size and the production time of the screw-threaded working cylinder.

(25) In addition, energy is also saved in the assembly and manufacture of the screw-threaded working cylinder. The subsequent calculation illustrates this advantage by calculating the torques M.sub.red for a force at the level of F.sub.red and M.sub.max for a force at the level of F.sub.max:
M.sub.red=F.sub.red*d.sub.G*0.5*tan(+)=225,841*77.026*0.5*tan(0.36+2.86)
M.sub.red=489,329 Nmm490 Nm
M.sub.max.sup.=F.sub.inax*d.sub.G*0.5*tan(+)=542,019*77.026*0.5*tan(0.36+2.86)
M.sub.max=1,174,391 Nmm1175 Nm

(26) Here, x denotes the helix angle of the thread and (Rho) the friction angle according to the formula tan()=0.05.

(27) The difference from M.sub.red to M.sub.max denotes the savings achieved in the torque required during the assembly of the screw-threaded working cylinder. In addition, energy and time are saved correspondingly in the manufacturing process.

LIST OF REFERENCE NUMERALS

(28) 1 tubular cylinder 2.1 guide closure 2.2 bottom closure 3 piston unit 4 end region 5 first thread 6 second thread 7 tapered wall section 8 axial annular surface 9 mating axial annular surface 10 pressure contact surface 11 sealing element 12 piston 13 piston rod 14 closure inner wall 15 wiper 16 piston rod seal 17 piston seal 18 guide belt 19 piston rod chamber 20 piston chamber