GB2063167A

GB2063167A - Rail for use in the construction of a stencil frame

Info

Publication number: GB2063167A
Application number: GB8035072A
Authority: GB
Original assignee: Svecia Silkscreen Maskiner AB
Current assignee: Svecia Silkscreen Maskiner AB
Priority date: 1979-11-01
Filing date: 1980-10-31
Publication date: 1981-06-03
Also published as: SE7909042L; SE434030B; IT1127917B; FR2468461B1; DE3041012C2; DE3041012A1; IT8050070A0; GB2063167B; JPH02135237U; FR2468461A1; JPS56139989A

Abstract

A rail (11) is suitable for use in the construction of a frame to which a stencil screen (2) is to be secured in position, the frame complete with stencil screen secured in position then being capable of use in a screen printing machine. The rail (11) is hollow and is defined by walls, one of which walls (11a) is profiled so as to define a projection (12). The projection provides surfaces (12a, 12b) which face away from each other and which are capable of cooperation with a holding device (13) for the frame (11). A frame constructed from such rail can be designed in such a way that it can cooperate with a second holding device (3b). <IMAGE>

Description

SPECIFICATION Rail for use in the construction of a stencil frame The present invention relates to a rail of special cross-section and in particular to the type of rail designed to be used in the construction of a frame which is resistant to flexing. A screen or stencil is attached to this frame, and the frame complete with stencil attached may then be used in a screen printing machine and held in position by means of holding devices for the frame which are part of the screen printing machine. The main purpose of this invention is to describe such a rail which may be manufactured in considerable iengths by means of an extrusion process, said rail then being cut to suitable lengths in order to produce the different component parts of the frame. The ends of the component parts of the frame should then be strengthened by welding at the corners.

Rails of the nature and for the purpose indicated above are usually made from perforated and grooved section in order to obtain a structure which is light in weight.

We are already familiar with a number of different rails, all made from perforated and grooved section and intended for use in the construction of a frame which is designed to hold a stencil securely in position. The frame is specially shaped so as to operate in conjunction with the holding device inside a screen printing machine.

The rails for this purpose with which we are already familiar vary in shape depending on the particular problem which it was intended to solve using rail of the section in question. Thus the section of the rail was usually shaped in an effort to facilitate the securing the stencil, the fixing of the stencil to the rail and the fixing of the frame inside the screen printing machine.

Circumstances are known to exist in which the securing and attachment of a stencil to a frame subjects the frame to high stresses. The larger the frame and the stencil, the greater will be the stresses. The forces responsible for these stresses may be divided into two types, namely a) the force which causes the frame to bow inwards towards the centre of the stencil in the same plane as the stencil; b) the force which produces a twisting moment which causes the frame to twist away from the plane of the stencil.

The effects of the stresses referred to above will be noticeable where the frame is made from a rail formed from perforated and grooved section (hollow-section profile), and the effect may even be so great in the case of certain hollow-section profiles that it will impair the correct functioning of the printing process inside the screen printing machine.

Thus a major problem encountered when constructing a frame of low weight from rail of hollow section is to achieve the smallest possible amount of inward bowing of the frame (as in point "a" above), at the same time as it is desirable for the effect produced by the twisting moment upon the frame (as in point "b" above) to be only small and preferably unnoticeable when the stencil is secured in position.

In order to keep down the total weight of the frame and the stencil when secured in position, it is desirable on the one hand for the rail to be of low weight per running metre, and on the other hand to avoid placing such demands on the stability of the assembly that the above disadvantages become noticeable.

One major wish associated with these frames for screen printing machines, particularly in view of the fact that the number of frame formats is extremely limited and is only a few in practice, was that the profile used for the rail should have adequate stiffness for it to be used even with large frames.

It should be noted in this context that the height dimension will usually be identical for all sizes of frame, but that the width may in princple be varied at will, although consideration must of course be given to the weight per running metre and to the anticipated inward bowing in accordance with point "a" above or to the effect of the twisting moment in accordance with point "b" above.

There now follows a description in accordance with the present invention of a rail designed to be used in the construction of a frame to which a stencil may be securely attached. The frame complete with the stencil secured in position may then be used in a screen printing machine, said rail consisting of a hollow-section profile.

What may be regarded as being characteristic of the present invention is the fact that at least one of the walls of the profile shall be formed with a projection. This projection shall exhibit surfaces which face away from each other designed to operate in conjunction with a holding device for the frame.

A further aim of the present invention is for the wail of one profile component to be formed with a projection and so arranged as to face away from the wall of a second profile component also formed with a projection when the two profile components are located one on either side of the stencil.

The projection is formed with two parallel surfaces so arranged as to run parallel with the stencil, but positioned so that both are located on one side (the top side) of the plane of the stencil.

The present invention also describes a possible means of causing the thickness of the wall in the vicinity of the projection to be greater than at other points on the rail. The thickness of the wall in the vicinity of surfaces which face away from each other on the projection is greater than at other points on the rail, although not in the vicinity of the projection.

The present invention thus describes the possibility of providing the profile with points of varying thickness in order by so doing to produce a profile which has greater resistance to lateral flexing, at the same time as it comes within the scope of the description of the invention to give the hollowsection profile increased thickness of material at the top in order to compensate by so doing for the reduced width and to avoid any twisting of the profile due to the tensile forces applied by the stencil.

It has been found that a right angle between the upper and the outer sides of the frame components facilitates their location during welding and cutting to length. This arrangement also facilitates the adjustment to fit the holding device of the printing machine.

It is suggested that the surface should also be ridged or made uneven in some other way so as to provide a better key for the adhesive which is used to secure the stencil to the frame component.

The advantages of a rail in accordance with the present invention are thus firstly that the rail has been given a geometric form such that it provides a high degree of resistance to the inward bowing of the frame component towards the centre of the stencil due to the tensile forces applied to the frame by the stencil, and that at the same time it has been found to provide a structure which will resist the twisting moment imposed by the tensile forces from the stencil to the frame.

It has also been found that the rail profile in accordance with the present invention enables the rail to operate in conjunction with the recently developed holding device for a special frame, said holding device being so designed that on the one hand it is not positioned beneath the stencil and on the other hand it is able to secure the frame component concerned in immediate contact with the stencil and in a plane which is only slightly displaced in relation to the plane of the stencil (so as to reduce the twisting moment), but will also permit the rail to operate in conjunction with other types of holding device designed for older types of frame construction.

What may be regarded as being most characteristic of a rail in accordance with the present invention is indicated in the first paragraph of the following Patent Claim.

A provisional preferred embodiment indicating the significant characteristic features of the present invention is described in greater detail with reference to the attached drawing, in which Figure 1 shows a perspective view of a frame in which a stencil is secured in position; Figure2 shows a horizontal view of the frame in accordance with Figure 1 held in a screen printing machine frame equipped with holding devices and register devices; Figure 3 shows a section Ill - Ill through the frame structure in accordance with Figure 1 in order to illustrate the forces which act upon the frame component with the stencil secured in position; and Figure 4shows a section through a rail in accordance with the present invention.

Figure 1 shows a perspective view of a frame 1, consisting of four components 1 a, 1 b, 1 c and id, in which the frame components 1a and 1c are so arranged as to run parallel with each other and the frame components 1 band id are similarly arranged to run parallel with each other. The frame components are formed from one and the same rail, said rail having a profile of essentially rectangular crosssection with perforations and grooves. The profile of the rail is known as hollow-section profile.

A stencil 2 is secured in position on the rail components la - 1d in such a way that the stencil is placed undertension and is subjected to tensile stresses, whereupon the frame components la - id are permanently attached to the stencil by means of an adhesive. Once the stencil 2 has been secured in position (using an adhesive) on the frame components 1 a - 1 d, the effect of the tensile stresses upon the stencil will cease, said forces being borne by the frame components la - id.

Figure 3 illustrates how the forces to which the stencil 2 is being subjected have a tendency to displace the frame component 1 b to the left. The arrow "F" has been used to show the force which is exerted on the frame component 1 b by the securing in position of the stencil, and the arrow "P" shows the displacement or inward bowing of the frame component 1 b to the position 1 b' (figure 1) produced by the force "F". The force "F" also exerts an effect on the frame component 1 b in the form of a twisting moment "M", which has a tendency to twist the middle portion of the frame component 1 b in such a way that the point 1 b" has a tendency to rise upwards in Figure 3.

The reference designation 3 is used to indicate the holding device which forms part of the screen printing machine, and which consists of a heel 3a, against which the frame components, for example ib, rest together with a threaded screw 3b designed to operate on the upper surface of the frame component 1 b. This holding device is of the old type.

The disadvantage of this holding device is that the component 3a will be located beneath the plane 2' of the stencil 2.

Figure 2 illustrates how a stencil 2, secured in position in a frame 1, must be capable of being registered rapidly in another frame 4, arranged in a screen printing machine. The actual screen printing machine does not appear in the attached drawing for reasons of simplicity. However the frame 4 does exhibit three register devices identified as 5,6 and 7, against which the frame 1 may be adjusted; registering is done with the help of an inflatable hose 8to which compressed air is supplied via a line 9 and a valve 10.

The activation of the flexible hose 8 will force the frame 2 into contact with the register devices 5 - 7.

Figure 4 shows a section through a rail as described in accordance with the present invention operating in conjunction with a different type of holding device to that shown in Figure 3. This holding device for the frame is shaped in such a way that it will not extend beneath the plane 2' of the stencil 2.

Thus the present invention describes a rail 11 designed for use in the construction of a frame, to which frame a stencil 2 may be secured in position.

The frame complete with stencil secured in position may then be used in a screen printing machine. The rail is made from a special hollow-section profile, which is described in more detail below.

The rail in accordance with the present invention consists of a wall 11 a, formed with a projection 12, which is smaller in size than the rest of the wall 11 a.

A second wall 11 b, forming a right angle with the first wall, is designed to hold the stencil 2 in position.

Athird wall 1 1c, forming a right angle with the second wall 11 b, thus faces towards the centre of the stencil 2. A fourth wall 11 d, forming a right angle with both the third wall 1 1c and the first wall 1 1a, is designed to be capable of operating in conjunction with a holding device 3 of familiar construction (Figure 3) and is designed particuiarly for a type rail profile other than that in accordance with the present invention.

In accordance with the present invention at least one of the walls of the profile 11 shall be formed with a projecton 12 and the projection shall exhibit surfaces 12a, which face away from each other, designed to be capable of operating in conjunction with a first profile device 13 for the frame 1. The wall of a first profile component 1 b, formed with a projection, is so arranged as to face away from the wall of a second profile component 1d, formed with a projection, when the two profile components 1 b and 1d are located one on either side of the stencil 2.

The projection 12 is formed with two parallel surfaces 12a and 12b, said surfaces also being arranged so as to run parallel with the plane 2' of the stencil 2, although displaced in such a way that both surfaces of the projection 12 are located on one side of the stencil 2.

The outer surface 11 b' of the second wall 1 1b is ridged so as to provide a better key for a layer of adhesive 2a used to secure the stencil 2 to the frame 11.

The wall thickness in the vicinity of the projection 12 and of the part which is identified as 14 is greater than the wall thickness in other parts of the profile.

The wall thickness in the vicinity of the surfaces 1 2a and 1 2b which face away from each other at the projection and which are identified as 15 and 16 is greater than in other parts of the profile, although not in the vicinity of the projection 12 and the component 14. The third wall 11c may have a thickness which exceeds the thickness of the second 1 1b and fourth 1 1d walls, and is essentially the same as the thickness of the walls 15 and 16.

The wall 11 d, which is located away from the wall 11 b which holds the stencil 2 in position, is designed so as to be capable of operating in conjunction with a second holding device 13fortheframe.

The distance from the wall 11 b designed to hold the stencil 2 in position to the surface 12a closest to the projection 12 is equal to or greater than the thickness of the holding device in the vicinity of the component 13a.

Thus the entire holding device will be located above the plane of the stencil 2.

It may also be seen from Figure 4 that the insides of the walls 11 1 it, 11d are formed with a number of ridges 17, designed partly to stiffen the rail profile and partly to help maintain dimensional stability when the profile is being manufactured for aluminium, magnesium or a similar material by means of an extrusion process.

The invention is not, of course, limited to the typical embodiment described above, but may undergo modification within the context of the following Patent Claim.

Claims

1. A rail designed to form a frame to which a stencil for screen printing can be secured in position in a screen printing machine, said rail having a hollow profile at least one of the walls of which profile is formed with a projection providing surfaces which face away from each other and are capable of cooperation with a holding device for the frame.

2. A rail according to claim 1, wherein the rail comprises a plurality of rail components defining the frame, the wall of one of the profile components with its projection being so arranged as to face away from the wall of a second profile component with its projection when the two profile components are located one on either side of the stencil.

3. A rail according to claim 1 or claim 2, wherein the projection is designed to have two parallel surfaces so arranged as to run parallel with the stencil but positioned so that both are located on the same side of the stencil.

4. A rail according to any one of the preceding claims wherein the outer surface of one of the walls is ridged so as to provide a key for a layer of adhesive.

5. A rail according to any one of the preceding claims wherein the thickness of the wall in the vicinity of the projection is greater than at other points.

6. A rail according to any one of the preceding claims wherein the thickness of the wall portions providing the surfaces which face away from each other is greater than that of other portions of the wall but is less than the thickness of the wall portion of the projection intermediate the said wall portions providing the surfaces.

7. A rail according to any one of the preceding claims wherein the wall which faces away from the wall which is designed to hold the stencil in position, is designed to operate in conjunction with a second holding device for the frame.

8. A rail according to any one of the preceding claims wherein one wall is formed with the projection, which is smaller in size than the rest of the wall, in that a second wall, which forms a right angle with the first wall, is designed to hold the stencil, in that a third wall forms a right angle with the second wall and in that a fourth wall, which forms a right angle with the third wall, is designed to operate in conjunction with a second holding device for the frame.

9. A rail according to any one of the preceding claims wherein the distance from one wall designed to hold the stencil in position to the surface closest to the projection is equai to or greater than the thickness of the holding device at the stencil.

10. A rail according to claim 8, wherein the third wall has a thickness which is greater than the thickness of the second and fourth walls.

11. A hollow rail suitable for the manufacture of a frame for a stencil screen, which rail is defined by walls, one of which walls is profiled so as to provide a projection having a pair of outer surfaces facing away from one another and capable of cooperation with a holding device for holding the frame in a screen printing machine.

12. A rail suitable for the manufacture of a frame for a stencil screen, which rail is substantially as herein described and illustrated with reference to Figure 4 of the accompanying drawings.