SE1250030A1 - Apparatus and method for producing electromagnetic shielding elements - Google Patents

Abstract

The invention relates to a device (100) for applying a material strand to an object, which material strand is intended for the production of an element for electromagnetic shielding. The device (100) comprises a first cylinder (120), which is arranged to accommodate a dispensable first material, a second cylinder (122), which is arranged to accommodate a dispensable second material, and a piston (130, 132) in respectively the first (120) and the second cylinder (122), which pistons (130, 132) are arranged movably in the respective cylinder (120, 122). The device (100) further comprises a drive member having a piston unit (190) for unison displacement of the pistons (130, 132) in order to achieve respectively a first flow of the first material from the first cylinder (120) and a second flow of the second material from the second cylinder (122), a merging unit for merging the first and the second flow into a merged flow in which the first flow flows around the outside of the second flow, and a dispensing nozzle (118) for dispensing the merged flow onto the object in order to achieve the material strand. The invention also relates to a method for applying the material strand.

Description

Magnetic field over the dispensed strand before curing to modify its cross section.

US 6,056,527 discloses an apparatus and method for forming a gasket for electromagnetic interference shielding (EMI). The gasket comprises an electrically conductive liquid polymeric material which, in the uncured state, is expelled from an extruder by means of a pressure expulsion system. To control the expulsion, the pressure can be both positive and negative. However, the gasket in US 6,056,527 is expensive to manufacture and has relatively poor mechanical properties.

The gasket described in document US 5,107,070 has improved mechanical properties. This packing for shielding against magnetic waves comprises a thick support layer with high elasticity and strength and a thin cover layer of a polymeric material containing ferrites and / or magnetites to provide the shielding. The support layer and the cover layer are designed in one piece.

However, there is a need to more precisely adjust the size of these two layers so that an acceptable shielding ability is obtained while the compression forces of the gasket do not become too high.

In addition, the scope should be adjusted so that the material consumption and thus the manufacturing cost of the gasket is lower.

SUMMARY OF THE INVENTION In view of the above, it is thus an object of the present inventive concept to provide a device for applying a material strand comprising two material layers to an object, which material strand is intended for producing an element for electromagnetic shielding, the device allowing a more accurate control of the scope of these two material stocks.

A further object of the present inventive concept is to provide a corresponding method for applying the above material strand to an object. According to a first aspect of the inventive concept, an apparatus is provided for applying a material strand to an object, which material strand is intended for producing an element for electromagnetic shielding. The device comprises a first cylinder which is arranged to accommodate a dispensable first material, a second cylinder which is arranged to accommodate a dispensable second material, and a piston in the first and the second cylinder, respectively, which pistons are movably arranged in the respective cylinder. Furthermore, the device comprises a drive means for unison moving the pistons for producing a first flow of the first material from the first cylinder and a second flow of the second material from the second cylinder, respectively, a joining unit for joining the first and the second flow to a combined flow where the first flow flows externally about the second flow, and a dispensing nozzle for dispensing the combined flow on the object to produce the material string.

By a dispensable material is meant a material which has such a viscosity that it can be dispensed into a string. Furthermore, the material should have such properties that the material string assumes and substantially maintains a cross section with the shape of a horizontal D. The term dispensing on an object refers to dispensing a string in such a way that the string obtains contact with the object along its entire length or point contact with the object. If necessary, a primer can be applied to the object to ensure adhesion between the material strand and the object.

A unison movement of the pistons refers to a joint movement of the pistons, ie. that the pistons follow each other. In other words, their speeds and accelerations are essentially the same.

The first material is preferably an electrically conductive material with an electrical conductivity 01 while the second material is preferably an electrically insulating material. Alternatively, the second material may also be an electrically conductive material with a conductivity O2 which is less than the conductivity G1 of the first material. Since the first flow flows externally about the second flow, the first flow gives rise to an outer material layer of the material strand while the second flow gives rise to an inner material layer of the material strand.

The first and second cylinders preferably have constant cross-sections. These cross-sections are preferably different because the material consumption for each material typically varies. The pistons preferably comprise sealing means for ensuring a tight-fitting contact with the respective cylinder. Due to the constant cross-sections of the cylinders in combination with the unison movement of the pistons, the dispensing ratio and thus the volume ratio between the first and the second material can be controlled more accurately. In particular, the ratio between the thicknesses of the two material layers can thus be controlled more accurately. The dispensed volume from a cylinder during a given time interval is given by the cross-sectional area of the cylinder multiplied by the path of the piston traveled in the direction of the flow outlet of the cylinder during this time interval. From these relations and taking into account the speed at which the dispensing nozzle is moved relative to the object, it can thus be ensured that the outermost material layer does not become too thin by choosing suitable dimensions of the cylinders and pistons. Namely, the outermost material layer must assume a critical thickness in order to allow acceptable shielding.

The flows are preferably combined so that they do not substantially mix with each other. The streams can thus flow side by side without substantially mixing with each other. This can be regulated, for example, by adapting the design of the joining unit, such as its axial and radial extent, so that laminar flows are allowed or by adapting the speed of the flows, or in other words, the influence of the drive means on the pistons. By a laminar flow of a liquid is meant a flow in which there is essentially no lateral mixing of the liquid. In other words, there is essentially no turbulence and no vortices in the flow. In the light of the above, the device according to the invention thus allows a more accurate control of the extent of the two material layers. According to one embodiment, the device is intended to be mounted as a superstructure on an already existing dispensing device. According to another embodiment, the device is intended for fixed mounting on a carrier unit.

According to one embodiment, the first and the second cylinder together with the respective piston form a first and a second replaceable cylinder unit. This embodiment enables the cylinder units to be easily replaced as a result of wear, repair, etc. thereof.

According to one embodiment, each cylinder unit is exchangeable for another cylinder unit with a format other than the format of the cylinder unit. The term format includes at least something of cross-sectional shape, cross-sectional area, longitudinal extent or cylinder volume of the cylinder unit. The cross-sectional shape, cross-sectional area or longitudinal extent may refer to the cylinder and / or piston.

The cross-sectional shape can be, for example, circular, oval, triangular, rectangular, etc. The cross-section of the cylinder determines, together with the longitudinal extent of the cylinder, a cylinder volume of the cylinder. An advantage of this embodiment is that the extent of the two material layers to be applied can be easily varied. This means that it is easy to manufacture gaskets of different dimensions with the device according to the invention. In addition, the speed of the dispensing and the total amount of material that can be accommodated in the cylinders can be varied.

According to one embodiment, the first and the second cylinder are connected to a first and a second source of material, respectively, for supplying the first and the second material, respectively. The cylinders are preferably filled with material when the device is out of operation between two dispensing cycles.

Alternatively, the material can be replenished in operation, continuously or sequentially.

According to an embodiment, the device further comprises a decompression unit, which upon activation is arranged to effect a pressure drop in the first and the second material flow. According to a further embodiment, the device further comprises a valve unit for shutting off the first and the second flow, the decompression unit being activatable synchronously with the valve unit. The decompression unit can, for example, be activated in connection with switching off or starting of the device. In one example, the decompression unit comprises a first and a second decompression means related to the first and the second flow, respectively.

Each decompression means in this example comprises a movable core which in operation occupies a specific volume in the channel in which the respective flow flows. In connection with shutdown, the core is moved out of the duct so that it occupies a smaller volume in the duct than the volume in operation. At the same time, the valve units for shutting down are closed. In this way, a pressure drop is obtained in the channel and thus in the material flow. This pressure reduction can thus prevent residual material in the ducts from flowing out after the device has stopped operating. A further advantage is that an uneven distribution of material at the start of operation of the device due to a temporary excess of material in the dispensing nozzle can be avoided. To avoid an uneven distribution of material when returning the core to the position in which it occupies a maximum volume in the duct, it can be slowly re-inserted during operation. The total time period for this reintroduction can be adjustable.

According to one embodiment, the joining unit comprises a first channel for the first material and a second channel for the second material, the second channel opening into the first channel and having such a coaxial extent therein that the first and the second flow, when they meet, are laminar. This meeting can take place where the second channel ends in the first channel. The second flow is preferably centered with respect to the first flow. An advantage of this embodiment is that the laminar flows prevent appreciable mixing of the materials.

According to an embodiment, the device further comprises a moving means for moving the dispensing nozzle relative to the object.

The transfer means may be arranged so that at least one of the dispensing nozzle and the object is movable. Because the dispensing nozzle can be moved relative to the object, a simpler application of the material string to the object is allowed.

According to one embodiment, the dispensing nozzle is integrated with the joining unit. By this embodiment, the flows can be brought together near the outlet of the nozzle so that mixing of the materials due to transport and turbulence can be reduced.

According to one embodiment, the first cylinder has a first cross-sectional area and the second cylinder has a second, cross-sectional area separate from the first cross-sectional area. The different cross-sectional areas mean that the material flows can be different sizes so that different amounts of material of the first and the second kind are dispensed from the nozzle.

According to a second aspect of the inventive concept, a method is provided for applying a material strand to an object, which material strand is intended for producing an element for electromagnetic shielding. The method comprises the steps of: moving in a first and a second piston movably arranged in a first and a second cylinder, the first cylinder being arranged to accommodate a dispensable first material and the second cylinder being arranged to accommodate a dispensable second material, to provide a first flow of the first material from the first cylinder and a second flow of the second material from the second cylinder, respectively, to combine the first and the second flow to provide a combined flow where the first flow flows externally about the second the flow, and dispensing the combined flow on the object to produce the material string.

The method according to the invention essentially exhibits the properties and advantages which have been discussed above in connection with the first aspect, whereby reference is made to the above discussion.

Other objects, features and advantages of the present invention will become apparent from the following detailed description, the appended claims, and the figures.

In general, all terms used in the claims are to be construed in accordance with their usual meaning in the art, unless they are explicitly defined otherwise herein. All references to "an / an / it / it [element, device, component, organ, step, etc." shall be construed openly as a reference to at least one example of said element, device, component, organ, step, etc., unless not explicitly stated otherwise. The steps in any method 10 15 20 25 30 8 described herein need not be performed in exactly the order described, unless explicitly stated.

Brief Description of the Figures Both the above-described and further objects, features and advantages of the present invention will become more apparent from the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, taken in conjunction with the accompanying drawings, in which like reference numerals are used to similar elements, wherein: Fig. 1a illustrates a perspective view of an embodiment of the device according to the present inventive concept.

Fig. 1b illustrates a side view of the embodiment of Fig. 1a.

Fig. 2 illustrates a cross section of the device in Fig. 1a along the line A-A.

Fig. 3 illustrates the lower part of the cross section of Fig. 2 including the dispensing nozzle.

Fig. 4a illustrates a method of applying a string of material to a first object.

Fig. 4b illustrates how the first object in Fig. 4a has been joined to a second object with a shielding seal.

Fig. 5 is a block diagram illustrating a general dispensing device comprising a dispensing unit, a decompression unit and a dispensing nozzle.

Detailed Description of Preferred Embodiments In the following, it will be described how a seal with electromagnetic shielding properties according to the present inventive concept is achieved between two or more objects by means of an explicit embodiment. The intended seal takes the form of a gasket which is produced by applying a string of material containing a liquid, and thus dispensable, sealing material in suitable places in the contact surfaces between the objects. The sealing material comprises a first electrically conductive material and a second electrically insulating material which each have such viscosities that they allow an acceptable dimensional stability of the sealing material. Furthermore, the sealing material can assume an elastic structure and also be formed after suitable treatments as described below.

The first and second materials are preferably made of a silicone rubber, but they can also be made of other elastic materials, such as polyurethane, TPE or the like. The first material further comprises particles with electrical conductivity which are uniformly mixed and oriented in the material according to the desired accuracy. Non-limiting examples of such particulate materials are iron, nickel, cobalt and silver as well as alloys comprising any of these materials. Metal-coated particles such as Ag / Cu, Ag / glass, Ag / Ni, Ag / Al, Ni / C are also conceivable. The content of particles may be 10-80% by weight and preferably 50-70% by weight. The particles advantageously have a diameter in the range 10-200 μm and can have a geometry which is, for example, spherical, flake-shaped or needle-shaped. The particles may also comprise materials with ferrimagnetic or ferromagnetic properties, in which case the particles preferably also comprise an outer layer with substantial electrical conductivity.

Fig. 1a and Fig. 1b generally show a device 100 which is arranged for applying the material strand described above to an object seen in perspective and from the side, respectively. Fig. 2 shows a cross section of the device along the line A-A in Fig. 1a. Fig. 3 shows an enlarged version of the lower part of the cross section in Fig. 2. The device 100 comprises a dispensing unit 102 and a separate material unit 140.

The dispensing unit 102 comprises a first 110 and a second 112 cylinder unit, an air or motor driven drive 114, a joining unit 116 and a dispensing nozzle 118. The nozzle 118 comprises a dispensing needle 230 which is arranged to dispense the material string out of the device 100. 102 connections 150, 152 for material supply to the respective cylinder unit 110, 112 and deaeration valves 160, 162. The deaeration valves 160, 162 can for instance be used to evacuate the device with its constituent components, such as ducts, chambers, etc. from air. The connections 150, 152 are provided with valves 154, 156 for shutting off and switching on the material supply. These valves 154, 156 are operated manually by hand, but according to an alternative embodiment these can be operated automatically, for example by means of an air or motor-driven drive element.

The dispensing unit 102 also includes decompression units 170, 172 and flow valves 164 and 166, or equivalent shut-off valve units 164, 166, which are arranged to turn on or off the first and second flows, respectively. The lateral unit 140 includes two material sources 141 and 142 for storing dispensable materials. The ll / lateral source 141 stores a first material in the form of an electrically conductive material and the material source 142 stores a second material in the form of an electrically insulating material. In a non-limiting example, the first material has a resistivity of between 1 and 200 m 2 cm.

According to an alternative embodiment, the second material consists of an electrically conductive material with a resistivity which is higher than the resistivity of the first material. The lateral sources 141, 142 can advantageously be provided with explosion protection. The material feeding from the material sources takes place by means of an air-powered feeding device (not shown) which is connected to air connections 143, 144 on the material unit 140. This type of feeding is well known to the person skilled in the art and will not be described in more detail. Alternatively, the material feed can be driven with a motor-driven feeding device.

Outlets 145, 146 of the material sources 141, 142 are connected to the connections 150, 152 on the dispensing unit 102 for material supply via the hoses 180, 182. Note that in Fig. 1a and Fig. 1b the hose 180 is connected to the connection 150 while the hose 182 is disconnected from connection 152.

The material unit 140 can thus be located at a distance from the dispensing unit 102, which among other things allows mounting of the dispensing unit 102 on small machines. According to an alternative embodiment, the material unit and the dispensing unit are mounted together. The first 110 and the second 112 cylinder unit comprise a first 120 and a second 122 cylinder, respectively, i.e. a cylindrical cavity in which pistons 130, 132 are movably arranged, as shown in Fig. 2. The pistons 130, 132 are driven in the vertical direction by a common piston unit 190 which is connected to the drive means 114. Furthermore, the first 110 and the second 112 comprise the cylinder unit a first 192 and a second 194 mixer or mixing device, respectively. The purpose of these mixers is to mix the respective materials to an acceptable degree and to counteract air formation in the components that can give rise to defective gaskets.

The connections 150, 152 are connected to channels 121, 123 which in turn are connected to the cylinders 120, 122. By connected is meant that flows of dispensable materials between the connections 150, 152 and the cylinders 120, 122 are allowed. These connections thus allow filling of materials in the cylinders 120, 122 from the connections 150, 152 via the channels 121, 123.

Further, the channels 121 and 123 are connected to channels 124, 126, 128 and 125, 127, 129, 210, respectively, which are included in the dispensing unit 102.

The decompression units 170, 172 comprise decompression cores 174, 176 which are arranged upstream of a point for merging the first and the second flow. According to an alternative embodiment, the decompression cores are arranged downstream of the point for merging the first and the second flow. The cores 174, 176 can accommodate a variable volume in the channels 126 and 127. More specifically, the decompression cores 174, 176 can be moved in the horizontal direction (see Fig. 2) so that their tips can be inserted in and out of the channels 126, 127.

The decompression cores 174, 176 are driven by a pneumatic drive element, but other drive elements are equally conceivable. The lateral unit 140 and the dispensing unit 102 are controlled by means of a control unit (not shown). In particular, this control unit is arranged to control the drive means 114. Furthermore, the control unit is arranged to control the flow valves 164, 166 and the decompression units 170, 172 and their cooperation.

The control unit may also be arranged to control the material supply to the cylinders 120, 122 by controlling the air supply to the air connections 143, 144, to control the valves 154, 156, and to control the opening and closing of the vent valves 160, 162.

The dispensing unit 102 is thus arranged to feed the first material from the cylinder 120 in a first flow through the channels 121, 124, 126, 128 to a joining chamber 220 included in the joining unit 116 and to feed the second material from the cylinder 122 in a second flow through the channels 123, 125, 127, 129, 210 to the joining chamber 220. In the joining chamber 220, the first and second flows are joined to a joined flow in which the two flows are not mixed.

The dimensions of the channels 128 and 129, 210 are such that the flows are laminar.

The joined flow flows from the joining chamber 220 to a needle channel 232 included in the dispensing needle 230. Note that according to the present embodiment, the dispensing nozzle 118, and thus the needle channel 232, is integrated with the joining chamber 220. Alternatively, however, this nozzle may be located outside the joining chamber.

The device 100 is in operation during different operating cycles, i.e. time periods between start-ups and downtime. At the end of a first duty cycle, the decrompression units 170, 172 prevent the material flow, and thus the material strand, from becoming uneven. These irregularities of the material strand give rise to an uneven element for electromagnetic shielding. More specifically, the units 170, 172 are activated at the same time as the flow valves 164, 166 turn off the flows, during which activation the decompression cores 174, 176 are moved out of the channels 126 and 127 and give rise to a pressure reduction in the respective channel and thus the inflows. This pressure reduction prevents the respective material flow from continuing to flow out of the nozzle 118 after the supply of the flow has ceased.

After the first duty cycle is completed, there is typically an excess of residual material at the outlet of the needle channel 232 which can give rise to an uneven distribution of material at the start of a subsequent second duty cycle. However, the pressure reduction described above means that the excess can be sucked into the needle channel 232 and thus counteracts this uneven distribution at the start of the second cycle.

According to the present embodiment, the decompression cores 174, 176 return during operation slowly to the positions at which they occupy a maximum volume in the channels 126, 127. The slower the return, the less uneven the material flow out of the nozzle. In this way, an uneven distribution of the material from the nozzle can be effectively counteracted.

After dispensing, the material string can undergo further treatment processes.

In one example, the material strand is treated in a process during which it assumes an elastic structure in which it is not dispensable. This process may include, for example, some or all of curing, vulcanization, heating, chemical exposure to external substances, treatment with UV light, etc.

Furthermore, the material strand can be processed in a process during which it is formed to assume a desired cross-sectional shape. The forming of the material strand can take place, for example, by applying a mold to the dispensed material strand. Alternatively, when at least one of the first and second materials comprises a magnetic material, the forming may be by subjecting the string of material to a magnetic field. The flux density of the magnetic field has such a spatial distribution that a desired shape of the material strand is assumed.

In the following, a method of applying a material strand to a first and a second object will be described with reference to Fig. 4a and Fig. 4b. The purpose is to obtain a seal between these objects which are thereby shielded from electromagnetic radiation.

Fig. 4a shows a first object 410 in the form of a box with a bottom surface 414 formed in one piece with its walls 416, 418. This object is made of material with electromagnetic shielding properties such as metal or metallized plastic. Furthermore, the first object 410 comprises an edge 412 around its opening. The first object 410 is arranged to accommodate sensitive electronic equipment which, in order to function acceptably in a radiation-exposed environment, needs to be shielded from this electromagnetic radiation. Optionally, the first object 410 may include electronic connections which, for simplicity, are not shown.

The first object 410 is mounted on a fixed surface while the nozzle 118 is movably mounted relative to the first object 410. The movement of the nozzle 118 advantageously takes place automatically by means of a moving device which is for instance operated by a numerically controlled operation.

As shown in Fig. 4a, a string of material 430 is applied to the edges 412 of the first object 410 by moving the nozzle 118 over and along these edges 412 while the device 100 dispenses the combined flow described above from the dispensing nozzle 118. In a non-limiting example is the thickness of the outermost electrical material layer between 0.3 mm and 0.4 mm. In the figure, the nozzle 118 moves momentarily in a direction R. The speed of the nozzle 118 may vary during the dispensing but is preferably constant. The speed is preferably between 100-6000 mm / min.

After the material strand 430 has been applied to the edges 412, it is treated so that it assumes an elastic structure as described above and thus forms an element for electromagnetic shielding. Prior to that, the material strand can also undergo a deformation to reduce the compression force required to obtain an acceptable electrical contact between the first 410 and the second object 420.

The second object 420 is then applied with a compression force against the first object 410. More specifically, the second object 420 is arranged on top of the first object 410. This object can also be made of metal or metallized plastic. More specifically, for each edge portion of the first object 410 there is a corresponding portion of the second object 420. Between each pair of portions there is the element which thus provides an electromagnetic shielding contact between the objects and which also acts as an environmental seal which prevents the ingress of e.g. and dust.

It will be appreciated that the decompression unit may be isolated from the present invention and thus may also be used in dispensing devices intended for other types of dispensing. In particular, two cylinders with two separate material flows or a mixing device are not specifically needed. Fig. 5 is a block diagram illustrating a general dispensing device 500 including a dispensing unit 510, a decompression unit 520 and a dispensing nozzle 530.

The dispensing unit 510 is arranged to deliver at least one flow of a dispensable material from its outlet 512. Each material may be conductive or insulating. The delivery can take place, for example, by storing each material in a cylinder and by a piston discharging the material as described above. In particular, the dispensing unit 510 is arranged to dispense by means of a piston a flow of material stored in a single cylinder.

This material can, for example, be conductive.

The dispensed material flows in channels 540, 542 to the dispensing nozzle 530 from which they are discharged in the form of material strands as described above.

The decompression unit 520 is arranged to effect, upon activation, a pressure drop in the material flow or the material flows described above. Furthermore, the decompression unit 520 may comprise one or more decompression cores 541 which are movably mounted in or between the channels 540, 542. The decompression unit 520 may thus occupy a variable volume in these channels 540, 542. The decompression units 520 may be of the type described above with reference to to the embodiment shown in Figs. 1-3.

Thus, in accordance with this aspect different from the invention, a device for applying a material strand to an object, which material strand is intended for producing an element for electromagnetic shielding, could comprise a dispensing unit 510 for delivering a flow of a dispensable material, a dispensing nozzle 530 for dispensing the delivered flow onto said object to produce said material string, and a decompression unit 520 which upon actuation is arranged to provide a pressure drop in the delivered flow. 16 In a concluding example, the dispensing device 500 l may in particular adopt the embodiment included in the left (or alternatively the right) part of the dispensing unit 102 illustrated in Fig. 2, i.e. comprising a cylinder, a piston, a mixer, a decompression unit, and a dispensing nozzle.

The invention has mainly been described above with reference to a few embodiments. However, embodiments other than those described above are equally possible within the scope of the invention, as defined by the appended claims, as will be readily appreciated by one skilled in the art.

Claims (11)

10 15 20 25 30 17 REQUIREMENTS An apparatus (100) for applying a strand of material to an object, the strand of material for producing an electromagnetic shielding element, comprising a first cylinder (120) arranged to accommodate a dispensable first material, a second cylinder (122 ) arranged to accommodate a dispensable second material, a piston (130, 132) in the first and the second cylinder, respectively, which pistons are movably arranged in the respective cylinder (120, 122), a drive means (114) for unison movement of said pistons (130, 132) for providing a first flow of the first material from the first cylinder (120) and a second flow of the second material from the second cylinder (122), respectively, a joining unit (116) for joining the first and the second flow to a combined flow where the first flow flows externally about the second flow, and a dispensing nozzle (118) for dispensing the combined flow on said object t for producing said material strand. The device of claim 1, wherein the first (120) and second (122) cylinders together with the respective pistons (130, 132) form a first and a second replaceable cylinder unit (110, 112). The device of claim 2, wherein each cylinder unit (110, 112) is interchangeable with another cylinder unit having a format other than the format of the cylinder unit (110, 112), the format comprising at least one of the cross-sectional shape, cross-sectional area, length or cylinder volume of the cylinder unit. 10 15 20 25 30 18 Device according to any one of the preceding claims, wherein the first (120) and the second (122) cylinder are connected to a first (141) and a second (142) material source, respectively, for supplying the first and the second material, respectively. Device according to any one of the preceding claims, further comprising a decompression unit (170, 172), which upon actuation is arranged to effect a pressure drop in the first and the second material flow. The apparatus of claim 5, further comprising a valve unit (164, 166) for shutting off the first and second flows, the decompression unit (170, 172) being activatable synchronously with said valve unit (164, 166). An apparatus according to any one of the preceding claims, wherein the joining unit (116) comprises a first channel (128) for the first material and a second channel (210) for the second material, the second channel (210) opening into the first channel (128) and has such a coaxial extent in it that the first and second flows, when they meet, are laminar. An apparatus according to any one of the preceding claims, further comprising a moving means for moving the dispensing nozzle (118) relative to the object Device according to any one of the preceding claims, wherein the dispensing nozzle (118) is integrated with the joining unit (116). Device according to any one of the preceding claims, wherein the first cylinder (120) has a first cross-sectional area and the second cylinder (122) has a second cross-sectional area separate from the first cross-sectional area. A method of applying a string of material to an object, the string of material intended to produce an element for electromagnetic shielding, the method comprising the steps of: moving in unison a first (130) and a second (132) piston movably arranged in a first (120) and a second (122) cylinder, respectively, the first cylinder (120) being arranged to accommodate a dispensable first material and the second cylinder (122) being arranged to accommodate a dispensable second material, in order to provide a first flow of the first material from the first cylinder (120) and a second flow of the second material from the second cylinder (122), respectively, to combine the first and the second flow to provide a combined flow where the first flow flows externally about the second the flow, and dispensing the combined flow on said object to provide said material string.