GB2159594A

GB2159594A - Screw with flow passage

Info

Publication number: GB2159594A
Application number: GB08513304A
Authority: GB
Inventors: Kurt Stoll; Georg Heid
Original assignee: Festo SE and Co KG
Current assignee: Festo SE and Co KG
Priority date: 1984-06-02
Filing date: 1985-05-28
Publication date: 1985-12-04
Also published as: IT8505170A0; GB8513304D0; IT8505170A1; ES295913Y; ES295913U; IT1186944B; GB2159594B; IT8506998V0; DE3420646A1; DE3420646C2

Abstract

A screw has a longitudinal flow passage for a fluid along the outside of the shank. The shank of the screw has a solid body in the area of the screw axis 11 (8; 9). The passage produced by flattened sections of the shank (8; 9), which interrupt the thread, and by grooves (13) provided in the flattened areas. The shank (8; 9) has an I-cross-section. <IMAGE>

Description

SPECIFICATION Screw with flow passage The invention relates to a screw having a longitudinal flow passage for a fluid along its shank.

Screws of this type are, for instance, used to establish connections in hydraulic or pneumatic systems. Hydraulic or pneumatic components are often provided with connecting bores with a thread for the fluid concerned. At these connecting bores, a connecting piece, distributing element or the like is mounted in a manner to form a seal and secured with a screw of the type referred to.

In order to provide a longitudinal flow path for the fluid along the shank of the screw, hollow screws are used in prior art. In this case, a blind bore originating at the end face of the screw and usually centrally and axially arranged is provided in the shank. The wall of the screw shank has a hole at a suitable point.

The fluid passes throughthe shank in the axial and through the hole in the radial direction, thus being subjected to a sharp deflection.

This involves a high flow resistance. The stability of the tubular.shank is relatively poor.

When the screw is tightened, there is a risk that the head may shear off the shank of the screw at the end of the blind bore. The hole in the side of the shank represents yet another weak point. It must be kept small in order not to affect the stability of the screw; the small cross-section of the opening, on the other hand, results in a high flow resistance. Owing to the stability problems inherent in a tubular screw shank, it has proved impossible to produce screws of this type in one piece by forming, using plastics as a raw material, while complying with the standard size requirements applicable to standardised fluid connections. Trials using a multitude of plastic materials with and without fibre reinforcement have not led to any usable results to date.

The invention aims at providing a screw with a flow passage permitting fluidic improvements, in particular a reduction of flow resistance and a corresponding improvement in throughput, while having higher stability, and capable of being produced, preferably of a plastic material, by forming in a simple and cost-effective way.

According to the present invention there is provided a screw comprising a shank having a solid body, a longitudinal flow passage for a fluid being defined along the shank and being located on an outer side thereof.

The solid body ensures a high degree of stability for the screw. The arrangement of the flow passage along the external surface of the shank permits the maintenance of a large flow cross-section over the entire length and the avoidance of any sharp deflection of the fluid flow. This in turn enables flow resistance to be lowered and throughput to be improved.

The screw can be produced in the sizes commonly found in pressure medium connections using multiple tools by forming processes suitable both for metals and for plastics. This leads to a considerable reduction in manufacturing costs. The notch effects found in prior art are eliminated by the absence of the blind bore and, in particular, of the lateral hole in the screw shank.

Preferably the shank has a substantially circular cross-section, the side of the shank being flattened whereby the cross-section deviates from the circular form over part of its circumference, a screw threaded section being interrupted in the flattened area. The shank may be so flattened as to form two side faces extending at equal distances from the screw axis and parallel to each other.

Preferably also the shank is provided, immediately below a flange-type sealing face at a head of the screw, with a continuous circular groove bordered by a radially projecting shoulder towards the free end of the screw.

A head of the screw may be provided with an external hexagon and a hexagon socket.

This offers great flexibility in handling, in particular with respect to semi- or fully-automatic assembly.

On the following pages, the invention is described in detail with reference to an embodiment illustrated in the drawing, of which Figure 1 shows a side view of the screw, partially cut in a longitudinal centre plane; Figure 2 shows a side view of the screw, turned about its longitudinal axis by 90 , i.e.

viewed in direction II of Fig. 1, partially cut in a longitudinal centre plane; Figure 3 shows a top view of the screw head, viewed in direction Ill of Fig. 1; Figure 4 shows a view of the lower end face of the screw in direction IV of Fig. 2; Figure 5 shows an enlarged section through the screw according to V-V of Fig. 1; and Figure 6 shows a longitudinal section through a connection to illustrate an application for the screw.

With reference to Figs. 1 and 3, the screw according to the invention comprises a head 1 of hexagonal shape and having a hexagon socket 2. The screw can be tightened at its hexagon head with a conventional spanner or socket spanner, or alternativelyat its hexagon socket by means of an Allen key. This dual facility is of particular advantage in limited space or for semi- or fully-automatic assembly with the aid of a tightening machine.

As can be seen in Fig. 2, the head 1 is provided with an integral washer 3 projecting radially from the external hexagon. Its underside 4 represents a flange-type sealing face by means of which the screw presses against a sealing ring such as an O-ring. The sealing ring is placed in a circular groove 5 extending round the circumference of a shank section of enlarged diameter. The circular groove 5 is immediately adjacent to the underside 4 of the screw head 1. Towards the free end 6 of the screw, it is bordered by a radially projecting shoulder 7. At the underside of this shoulder 7, the shank diameter is discontinuously reduced, forming an unthreaded neck 8. Adjacent to this neck in the direction towards the free end 6 of the screw, there is a threaded section 9 having a larger diameter than the neck 8 but a smaller diameter than the shoulder 7.

As is most clearly shown by Fig. 5, both the neck 8 and the threaded section 9 of the screw are flattened. As a result of this, the threading is interrupted over part of the circumference of the screw. The threaded section 9 is bordered by two parallel, level side faces 10 arranged symmetrically and at equal distances from the screw axis 11 and oriented parallel to the screw axis 11. Fig. 1, which illustrates one of these side faces 10, shows that the thread runs out at the side face 10.

Beyond the side faces 10, material is missing from the threaded section 9, which would otherwise be fully cylindrical. When inserting the screw into a suitable threaded hole, gaps are formed at the circumference of the screw providing a passage for a fluid such a compressed air or hydraulic fluid.

The shape of the threaded section 9 may be imagined as having been produced by milling or grinding a conventional screw shank, removing two diametrically opposed, identical cylindrical parts having the cross-section of a segment of a circle. The ground or milled surfaces 10 resulting from this process are parallel. This imaginary concept is, however, intended to illustrate the shape of the threaded section 9; the screw according to the inention is preferably manufactured by the forming process.

The unthreaded neck 8 of the screw shank is flattened in a similar manner to the threaded section 9. Fig. 5 shows two level, parallel side faces 12 symmetrically arranged on both sides of the screw axis 11 and extending parallel to the screw axis 11 in the longitudinal direction. The neck 8, too, is therefore not fully cylindrical, lacking the material lying beyond the side faces 12. The neck 8 has the cross-section of a circle from which two diametrically opposed segments of equal size and bordered by parallel secants are missing. The level side faces 12 of the neck 8 are parallel to the side faces 10 of the threaded section 9. In accordance with the smaller diameter of the neck 8, its side faces 12 are offset towards the screw axis 11, lying radially inward of the side faces of the threaded section 9.

When the screw according to the invention is screwed into a suitable threaded hole, the reduced neck diameter relative to the thread diameter results in an annular gap round the neck 8. This gap is widened in the area of the flattened side faces 12. It communicates with the flow passages created on both sides of the threaded section 9 by flattening and permits various connection positions at the circumference of the screw.

The shank of the screw is provided with two grooves 13 in the flattened area, which extend in the longitudinal direction of the screw and increase the flow cross-section along the shank. The grooves 13 are symmetrically arranged on both sides of the screw axis 11.

They are open at the free end 6 of the screw and extend over the entire length of the threaded section 9 and approximately half the axial dimension of the neck 8. As can be seen in Fig. 2, the depth of the grooves 1 3 increases towards the end face 14 of the screw.

The section 17 of the groove 13, which extends along the neck 8, is shallower, its depth remaining approximately constant.

From the step 15 representing the transition between the neck 8 and the threaded section 9, the depth of the grooves 13 increases gradually. At the end face 14 of the screw, the grooves 13 almost reach the screw axis 11, but not quite.

Fig. 4 shows the grooves 13 to have an essentially rectangular profile. Their flanks 16 are level, parallel and oriented at right angles relative to the side faces 10; 12 of the threaded section 9 or the neck 8 respectively (cf. Fig. 5). The root of the groove is divided into two level sections 17, 18, section 17.

which is at the level of the neck 8, being parallel to the side faces 10; 12, i.e. parallel to the screw axis 1 1. Section 18 of the groove root on the other hand, which is at the level of the threaded section 9, extends at an acute angle relative to the screw axis 11.

Between two grooves 13 lying opposite each other, there remains a wedge-shaped web 19.

The end face 14 of the screw has an l-cross- section (cf. Fig. 4). The central supporting element of this profile is represented by the wedge-shaped web 19, while the cross-bars of the I are the cylindrical parts of the threaded section 9, on the exterior of which the thread runs.

The shank of the screw according to the invention therefore has a solid body in the area of the screw axis 11. The fluid passes along the outside of the shank. It enters through the grooves 13 and the gaps provided at the sides of the shank by flattening and reaches the annular space in the region of the neck 8. The groove openings at the end face 14 communicate with a large flow crosssection, thus avoiding sharp deflections in the flow. The wedge shape of the shank further promotes laminar flow in a particular advantageous fashion. The I-cross-section of the shank ensures high stability.

The screw can therefore be produced by means of a forming process of a plastic ma terial in one piece; it may in particular be injection moulded or cast using multiple tools.

This enables compliance with the dimensional specifications applying to standardised hydraulic or pneumatic connections, whereas only metal screws have been used in the former case until now. The invention therefore permits the replacement of metal by a cheaper plastic material. The advantage of higher stability, of course, also applies to metal screws produced by forming, for instance by aluminium die casting. The flow passage in a screw according to the invention is characterised by a large cross-section varying only to a minor degree over the length of the shank and by a guidance profile promoting laminar flow. This results in a correspondingly high throughput.

Fig. 6 illustrates an application of the screw according to the invention. It shows a fitting 20 having a threaded bore 21 for a fluid such as compressed air or hydraulic fluid. The fitting 20 may in particular be part of a pressure medium distributor or user. A connecting piece 22 is secured to the fitting 20, this connecting piece comprising an annular body 23 and, radially projecting from this, a socket piece 24. The shank of the screw according to the invention extends through the annular body 23. The head 1 rests on a first sealing ring 25 against the top of the annular body 23, a second sealing ring 26 being located between the underside of the annular body 23 and the fitting 20. The threaded section 9 of the screw shank engages the threaded bore 21.When the screw is loose, the annular body 23 can be turned on the fitting 20, thus enabling any orientation of the socket piece 24. When the screw is tightened, the sealing rings 25, 26 are pressed on their seating faces, thus providing a good seal. The fluid passes from the threaded bore 21 through the gaps provided on the outside of the screw shank into the annular space 27 surrounding the neck 8 of the screw shank. The gaps are in part provided by the flattening of the shank described above and in part by the grooves 13. The annular space 27 communicates with a radial passage 28 in the socket piece 24 receiving the fluid.

It is obvious that the application of the screw acording to the invention is not restricted to the L-shaped connecting assembly described above. It is capable of being used for all connecting elements and distributors which have to be secured to threaded bores for the passage of a fluid.

Claims

1. A screw comprising a shank having a solid body, a longitudinal flow passage for a fluid being defined along the shank and being located on an outer side thereof.

2. A screw according to claim 1, wherein the shank has a substantially circular crosssection, the side of the shank being flattened whereby the cross-section deviates from the circular form over part of its circumference, a screw threaded section being interrupted in the flattened area.

3. A screw according to claim 2, wherein the shank is so flattened as to form two side faces extending at equal distances from the screw axis and parallel to each other.

4. A screw according to claim 3, wherein the shank has, in the area of its free end, a threaded section followed, in the direction towards a head, by an unthreaded neck of a reduced diameter relative to the threaded section, and wherein the threaded section and the neck are flattened, forming the parallel side faces which are stepped relative to each other.

5. A screw according to any of claims 2 to 4, wherein the shank is provided with a groove in its flattened area, the groove being open at an end face of the screw and extending in the longitudinal direction thereof.

6. A screw according to claim 5, wherein the depth of the groove increases towards the end face of the screw.

7. A screw according to claim 5 or 6, when dependent on claim 3 or 4, wherein two of the grooves extend symmetrically to a longitudinal centre plane of the screw in its longitudinal direction, flanks of the grooves being straight and extending at right angles to the side faces of the shank, and the roots of the grooves also being straight.

8. A screw according to claim 7, when dependent on claim 4, wherein sections of the grooves extend approximately half-way along the length of the neck.

9. A screw according to claim 6, wherein the end face of the screw has an I crosssection and the body of the shank remaining between the grooves is wedge-shaped.

10. A screw according to any of the preceding claims, wherein the shank is provided, immediately below a flange-type sealing face at a head of the screw, with a continuous circular groove bordered by a radially projecting shoulder towards the free end of the screw.

11. A screw according to any of claims 1 to 9, wherein a head of the screw is provided with an external hexagon and a hexagon socket.

12. A screw according to claim 11, wherein the shank is provided, immediately below a flange-type sealing face at the screw head, with a continuous circular groove bordered by a radially projecting shoulder towards the free end of the screw.

13. A screw according to any of the preceding claims, which is made in one piece by forming and is in particular cast or injection moulded of metal or plastic.

14. A screw substantially as hereinbefore described with reference to the accompanying drawings.

15. Any novel subject matter or combination including novel subject matter herein disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims.