Background of the invention

[0001] The invention relates to an impact device for cleaning of surfaces, particularly heat delivery surfaces, such as boiler faces, convection packets and heat exchangers, the impact device comprising

an anvil;

a body with a first end facing the anvil, and a second end positioned opposite to the first end;

a hammer unit comprising a hammer arranged to be displaceable in the body;

a spring arranged to receive impact energy from the hammer and to transfer impact energy to the anvil, whereby the body is fastened to the anvil, and the impact device comprises means for damping impact force from the anvil to the body. The heat delivery surface may also be a superheater, radiation shields, feed water heaters and air heaters, for example.

[0002] Such an impact device is known from WO 2008/071852.

[0003] An object of the impact device is to free the heat delivery surface from depositions of various kinds agglomerating on the heat delivery surfaces during the use. The depositions should be removed because they prevent the plant or entity which they belong to, for instance a boiler face, from efficiently transferring heat energy, which interferes with the operation of the plant. In the worst case, the deposits may cause a shutdown. Deposits agglomerate for instance because particles present in hot gases agglomerate on the heat delivery surface. The deposits may be, for example, roasted ore concentrate, condensed metallic compounds, soot, ashes, iron oxide, iron sulphides and dirt. The impact devide should be constructed in such a way that it gives a mechanical shock with correct force and frequency so that it will be capable of operating in a desired manner. Information on this is found in publications, and experiments can be carried out to obtain the best results. In this context, reference is made to DE 10 2007 024 286 A1.

[0004] A problem with such impact devices is that their components are subjected to high loads which shorten their service life and cause, in any case, a need for maintenance. Certain components must be exchanged after they have worn down. Disassembling the impact devices and assembling them must, therefore, be as simple as possible - not only for saving time but also for not having to have a shutdown in the plant on which they are mounted.

[0005] When the hammer unit of the impact device is used to strike against the anvil, the body tends to be displaced in a direction opposite to the striking direction of the hammer unit. This recoil loads the components of the impact device. In order to damp the recoil and in order to decrease the load on the components, the impact device may be provided with means that damp the impact force from the anvil to the body. Such means are known from WO 2008/071852. In order for the impact unit to be able to operate in a desired manner, the spring packet (which is arranged to receive impact energy from the hammer and to transfer it to the anvil) should be without clearance and also abut the body. A problem with this known impact device is that it does not comprise means that would guarantee that the spring packet is kept in contact with the anvil. Furthermore, it has a relatively complex construction. The impact device according to WO 2008/071852 is not capable of efficiently damping the force caused by the impact against the body either, and the damping requires that two cylindrical surfaces be displaced in relation to one another, which cannot take place if said surfaces have corroded. Disassembling this known impact device for maintenance is also difficult. Disassembling is required every now and then to carry out necessary maintenance.

Brief description of the invention

[0006] The object of the present invention is to eliminate the problems of the prior art and to achieve an improved, novel impact device which is durable because its components are not subjected to too high accelerations and shocks and which is reliable and can be easily disassembled when required.

[0007] The impact device according to the invention is characterized in that the body is fastened to the anvil by means of an elongated suspension element which is fastened to the anvil by a first end; that

the means for damping impact force from the anvil to the body comprise a spring unit connecting the suspension element to the body flexibly, which allows the body to be displaced in the longitudinal direction of the suspension element;

the hammer device comprises an end facing the anvil; and that the device comprises means for keeping an entity formed of the hammer unit end facing the anvil, the spring and the anvil under compression in a clearance-free manner.

[0008] Preferably, the spring entity comprises at least a planar spring element substantially perpendicular to the longitudinal direction of the suspension element. Such a spring element is easy to provide and it can be easily fastened to the suspension unit and to the body. Preferably, said at least one spring element is fastened to the body by the first end of the body, which faces the anvil. The positioning of the spring element at said end of the body stabilizes the structure.

[0009] Preferably, the suspension element is flexibly fastened to the second end of the body, preferably by means of a second spring, which further stabilizes the structure. Since the fastening is flexible, the effect of harmful impacts and forces on the components of the impact device is minimal.

[0010] Preferably, the suspension element is detachably fastened to the anvil, preferably by means of screw fitting, and the spring unit is detachably fastened to the body in order for the disassembling of the impact device to be as simple as possible. If the impact device comprises said second spring fastened to the second end of the body, it is preferably formed of a planar element perpendicular to the longitudinal direction of the suspension element, and the fastening of the spring is made detachable in view of disassembing.

[0011] Preferred embodiments of the impact device are presented in the attached dependent claims.

[0012] An essential idea in the invention is that with the suspension element and the spring unit attached to it, it becomes possible to both damp undesired impact force from the anvil to the body and to cause the hammer unit to be directed to achieve a directed and centred impact against the anvil in order to efficiently transfer impact energy to the anvil. Owing to the hammer unit, the spring and the anvil form a clearance-free entity under compression and reduce energy losses, and the efficiency of the device becomes high and, at the same time, wearing of the impact device components is reduced.

[0013] The advantages of the impact device according to the invention involve that the device is capable of efficiently damping undesired impact force and undesired forces so that its maintenance interval and service life will be long. The efficiency and reliability of the impact device are high. The elongated suspension element of the impact device allow a fastening mechanism that is easily accessible and can be easily opened in case the impact device is to be detached from the plant to which it is attached for the purpose of maintenance. The hammer unit of the impact device causes no torque against the anvil, thanks to the hammer unit being suspended by means of the suspension element.

Brief description of the figures

[0014] The invention will now be described in greater detail with the aid of two embodiments, referring to the attached drawing, in which

Figures 1 and 2 show a first embodiment of the impact device in perspective from two different angles;

Figure 3 shows a side view of the impact device in Figure 1 ;

Figure 4 shows a detail of the impact device in Figure 3;

Figure 5 shows damping springs of the impact device, mounted on the body of the impact device;

Figure 6 shows the hammer unit of the impact device in the body;

Figure 7 shows an anvil part in the anvil of the impact device;

Figure 8 shows a side view of a second embodiment of the impact device;

Figure 9 shows a front view of the anvil in the impact device in Figure 8;

Figure 10 shows a section view of the anvil along line X - X in Figure

9;

Figure 11 shows the impact device in Figure 8, seen from its rear end;

Figure 12 shows a front view of a rubber sheet of the impact device in Figure 8;

Figure 13 shows a section view of the ruber sheet along line XIII - XIII in Figure 12; and

Figure 14 shows an enlargement of a suspension element in the embodiment in Figure 8.

Detailed description of the invention

[0015] Figures 1 and 2 show an impact device according to the invention. In Figure 1 , the impact device is fastened to a hammering beam 100 attached to a heat delivery surface (not shown) which is to be cleaned of soot or the like by means of the impact device. Fastening the impact device to the hammering beam 100 is suitably implemented by welding. When the impact device strikes against the hammering beam 100, a shock wave is transferred against the heat delivery surface (not shown) to be cleaned, whereby soot or the like falls off the heat delivery surface.

[0016] The impact device comprises a body 2 and an anvil 1. The body 2 is fastened to the anvil 1 by means of an elongated suspension element 7. The suspension element 7 is fastened to the anvil 1 by its first end 8 by means of screws 10. The suspension element 7 and the body 2 are fastened to one another by means of a spring unit 9 and a spring 30. The spring unit 9 is fastened to the suspension element 7 by means of a fastener 22 and to the body 2 via a flange 20. The fastener 22 is preferably welded to the suspension element 7. The welding seam is, in Figure 4, denoted with reference numeral 101. The spring unit 9 connects the suspension element 7 to the body 2 at an end 3 of the anvil 1 , facing the body, which is best seen in Figure 3. (In Figure 3, the anvil 1 has a shape somewhat different from that in Figure 1 to adapt to the hammering beam 100a that is crosswise in relation to the longitudinal direction of the suspension element 7.) The spring 12 connects the suspension element 7 to a second end 4 of the body 2.

[0017] The spring unit 9 comprises three planar spring elements 13, 14, 12, which are perpendicular to the longitudinal direction of the suspension element 7, see Figure 4. They are at the bottom, by their first ends 15, 16, 11 , connected to the flange 20 via a first support 19, and at the top, by their second ends 17, 18, 105, connected to the fastener 22 via a second support 21. The support 19 is fastened to the flange 20 by means of screw fitting 111. The support 21 is fastened to the fastener 22 by means of screw fitting.

[0018] The spring elements 13, 14, 12 are at a distance from one another such that there is an opening between the adjacent spring elements. Said opening has been provided by placing intermediate washers 106 between the adjacent spring elements. The spring elements 13, 14, 12 surround the suspension element 7, which means that the spring elements take only a little space although they can be dimensioned to give the spring unit a high spring constant, i.e. a rigid spring.

[0019] Figure 5 shows the structure of the spring elements 13, 14, 12, and it can be understood how the elements surround the suspension element 7 when, at the same time, Figure 2 is examined where the suspension element 7 is visible. The spring 30 at the rear end of the body 2 is a planar el- ement perpendicular to the longitudinal direction of the suspension element 7. The spring 30 is fastened to the body by means of screw fitting 102 and also fastened to the suspension element 7 by means of screw fitting, see Figure 2.

[0020] Figure 6 shows that the body 2 is positioned in the hammer unit comprising a hammer 5 and an impact part 25. Since the impact part 25 is between the hammer 5 and the anvil 1 , it may be called an intermediate part. The hammer 5 is displaceable in the longitudinal direction of the body 2. The impact part 25 is arranged to abut an anvil part 24 when the impact device is mounted for use (cf. Figures 1 and 2). The contact force is generated by a spring 103. The contact force, which corresponds to the prestressing force, is typically 500 to 1 000 N. The anvil part 24, in turn, abuts a spring 6 arranged to transfer impact energy to an anvil body 23. The spring 6 is formed of two cup springs 26, 27. The anvil 1 abuts, via the spring 6 and the anvil part 24, the impact part 25 with a counterforce F corresponding to the prestressing force of the spring 103. The anvil part 24 comprises a groove 28 arranged to fit into the inner circle of the cup spring 27 such that the anvil part 24 is kept supported in place in the cup spring 27, see Figures 6 and 7. The cup springs 26, 27 are, in turn, supported against the anvil body 23. The spring 103 is arranged to keep the hammer 5 in contact with the impact part 25 also when a prestressing force generated by the spring unit 9 and of a desired magnitude (e.g. 500 to 1 000 N) to maintain correct operation of the impact device affects the impact part 25.

[0021] The arrangement described allows the entity formed of the hammer unit, the spring 6 and the anvil 1 to be kept under compression in a clearance-fee manner, and the end of the impact part 25 that faces the anvil part 24, the spring 6 and the anvil body 23 to be under compression in a clear- lance-free manner during the impact. Thanks to this, no high frequencies with energy losses are generated during the impact. The hammer 5 and the impact part 25 are guided well in the body 2 that forms a cylinder. Thanks to this, an air cushion of a uniform thickness is formed between the impact surface, i.e. between the hammer 5 and the impact part 25. The air gap prevents metallic contact between the hammer 5 and the impact part 25 during the impact. Hereby, no high detrimental frequencies are generated at this location either but energy losses and the efficiency are improved. The body 2 is, in turn, directed straigth and centred towards the anvil 1 , which involves that also the impact part 25 becomes directed straight and centred towards the anvil. Further, since the anvil body 24 comprises a convex surface facing the facing end of the impact part 25 and having a large radius, the hammer unit always generates a straight and centred impact against the anvil body 24. Also this improves the efficiency of the device.

[0022] The hammer unit and the hammer 5 have central boring 107 into which air or other gas can be conveyed under pressure. At the end of the boring 107, there is a valve 108 for conveying air in. The hammer 5 is provided with a bevelling 109.

[0023] In the following, the operation of the impact device is described.

[0024] If air or other gas is conveyed into the boring 107, the hammer 5 is displaced to the right, owing to the bevelling 109 in the hammer 5, and a gas chamber is formed between the impact part 25 and the hammer 5, see Figure 6. The spring 103 exerts a counterforce against the displacement of the hammer 5 to the right. A connection 110 allows the air to be quickly let out of the boring 107 and the gas chamber to the chamber 113. The mechanism comprises a pipe 114, in which a valve 115 is formed. The valve 115 opens for instance when the pressure in the pipe 114 and the boring 107 is reduced. Then, excess air can flow out of the chamber 113 to the surroundings via a filter 116. Owing to the filter 116, no dirt is formed in the device. When the air is let out of the boring 107 and the gas chamber, the hammer 5 strikes against the impact part 25, which, in turn, gives impact energy to the anvil part 24, which, in turn, transfers impact energy via the spring 6 - i.e. not directly - to the anvil body 23. The impact of the hammer 5 generates in the anvil body 23 a frequency that is dependent on the mass of the movable hammer unit and the spring constant of the spring 6. The spring constanct affects the contact time and the frequency; a lower spring constant results in a longer contact time and a lower frequency. The mass of the hammer may suitably be 8 kg, for example. The frequency may suitably be 1 000 Hz if the hammer 5 is at a distance from the impact part 25.

[0025] At the moment when the air is let out of the chamber and the boring 107, the body 2 is sligthly displaced in a direction that is opposite to the direction the hammer 5 assumes due to the spring 103 that moves the hammer to the left towards the impact part. Owing to the spring unit 9 that allows flexible suspension of the suspension element 7 to the body 2, the suspension element 7 is kept in place at that moment when the air is let out of the chamber. At the moment when the hammer 5 strikes against the impact part 25, the body 2 has already moved back somewhat, i.e. in the direction towards the anvil 1 , but not so far back that the body would have assumed its original position before letting the air out. Owing to the spring unit 9 (and the spring 30), the suspension element 7 is displaced at the moment when the hammer 5 strikes against the impact part 25 backwards from its original position, and efficient damping of recoil energy is achieved from the anvil 1 to the body 2.

[0026] The displacements of the body 2 and the suspension element 7 described involve that the impact device is not subjected to detrimental, great impact and acceleration forces in the operation of the impact device.

[0027] When the body 2 and the flange 20 are displaced to the right in relation to the suspension element 7 in this way, a traction force is generated in the spring element 13 of the spring unit 9, and a compression force is generated in the spring element 14, which is illustrated by the arrows in Figure 4. In the spring element 12 in the middle, both traction forces and compression forces may be generated in such a way that on one side of the spring element, traction forces are generated, and on the opposite side, compression forces are generated.

[0028] When the impact device needs to be dismounted for maintenance, it is sufficient to remove the screw fitting 10 with which the suspension element 7 is fastened to the anvil body 23 and to remove the screw fitting 11 by which the support 19 is fastened to the flange 20 as well as the screw fitting 102 by which the spring 30 is fastened to the flange 4 of the body 2.

[0029] Figure 8 shows a second embodiment of the invention. Figure 8 uses reference numerals that correspond to those in Figures 1 to 7 for corresponding components. The embodiment in Figure 8 differs from the embodiment in Figure 1 primarily in that the spring unit has a different structure and in that the suspension element is different. Further, the shape of the anvil is different from that in Figure 1.

[0030] In the embodiment according to Figure 8, the body 2' is fastened to the anvil 1' by a plurality of elongated suspension elements in the form of eight studs 7a' to 7f whose first ends 8a', 8e', 8f are fastened to the anvil 1'. The studs 7a' to 7f comprise, at their end that faces the anvil 1', threads 10a', 10e', 10f, and the anvil 1' comprises eight holes 31a' to 31f with threads for receiving the studs. The anvil 1' comprises a round plate with a through-hole for receiving the hammering beam 100'. The hammering beam 100' is welded to the anvil. The part of the hammering beam 100' that is, in Figure 8, positioned on the right side of the round plate of the anvil 1 ' and that abuts the spring 6' can be said to form a part of the anvil 1 ' because the hammer unit 5' strikes against said part.

[0031] The spring unit for damping impact force from the anvil V to the body 2' is formed of eight screw springs 9a' to 9f arranged around the end of the studs 7a' to 7f that faces the body 2'. The screw springs 9a' to 9f abut, by their first end, the flange 20' at the end 3' of the body 2' facing the anvil 1 ', and abut, by their opposite end, nuts 111a' to 1 11 ', which fasten the anvil 1' to the flange 20', and abut the flange 20'.

[0032] The impact device in Figure 8 comprises four rubber sheets 32' (or elastomeric sheets) in the form of a sheet packet that abuts, by its one end, the flange 20' and abuts shoulders 32' in the studs 7a', see Figure 14. The rubber sheets 32' have a corresponding hole 40' for the studs, see Figure 12, which shows a separate rubber sheet 32'. The hardness of the rubber sheets 32' is preferably 90 Shore, and their task is to damp vibrations. The number of rubber sheets 32' may vary. Figure 13 shows a section view according to line XIII to XIII in Figure 12.

[0033] The components of the impact device within the body 2' correspond to those in the embodiment according to Figures 1 and 6.

[0034] In the embodiment in Figure 8, the suspension element is symmetrically with regard to the impact device. Thanks to this, the impact effect becomes symmetric in operation, which means that there is no need to construct the device with heavy components but the device can be made light. Further, there is the advantage that components which are easy to manufacture can be used; the springs may be standard components. The number of springs 9a' to 9f in the spring unit may vary.

[0035] The invention has been described above only with reference to two preferred embodiments. Therefore, it is to be noted that the invention can be, with regard to its details, implemented in a plurality of ways within the scope of the attached claims. Thus, the means for keeping the entity comprising the hammer unit, the spring and the anvil under compression in a clearance-free manner may vary. Instead of a spring 103, 103', prestressing can be generated by means of pressurized air or other gas. The mechanism with which the hammer unit strikes against the anvil may vary; the hammer of the hammer unit does not have to be displaceable by means of spring force but the displacement may be provided for example by pressurized air, hydraulically or magnetically, by gravitation, blasting or explosion. The structure of the hammer unit may vary, as may the structure of the anvil. Instead of cup springs, it is feasible to have springs of elastomeric material. The impact device is suitable for cleaning surfaces other than heat delivery surfaces. Thus, it may be used for cleaning gas pipes and gas pipe apparatuses.