Abstract:
An efficient method of cleaning various workpieces is the so-called wet blasting, by which the workpieces are exposed to a spraying of water with a content of hard macro particles. Optimally, this blasting medium should be recirculated, but this implies noticeable problems with respect to separation of cleaned-off dirt and worn-down blasting particles. The invention provides for a system for processing units enabling these problems to be overcome in a relatively simple manner for achieving a high efficiency and low costs of the combined system.

Description:
This application claims the benefit of Danis Application No. 200 00836 filed May 26, 2000 and PCT/DK01/00371 filed May 28, 2001. 
     BACKGROUND OF THE INVENTION 
     The present invention concerns a plant for the cleaning of new or used metal parts by so-called wet blasting, namely for degreasing and cleaning of relatively small metal items which are suitable for handling in, for example, drum-like cleaning chambers. Such wet-blasting plants, which in a very effective manner work with a mixture of water and cleaning granulate, are known in different configurations, but the plant according to the invention is so special and advantageous that it is not considered necessary to describe the known technique in further detail. 
     In brief, it must be mentioned that the relevant technique is not particularly problematic with regard to the actual main task of executing a spraying of the blasting medium on the items, but rather in arranging this in both an effective and operationally economic manner in a recirculation plant for good utilisation of the blasting medium. Depending on its character and wearing qualities, the blasting medium can be reused over shorter or longer periods. However, it will gradually be worn down to such small grain sizes that this fraction will be ineffective in the recirculation process, and therefore must preferably be separated from the blasting medium, i.e. the mixture of liquid (water) and blasting medium. Moreover, the dirt which is removed from the items by the cleaning should be separated from this medium, and at least from time to time there must be effected a certain addition of new blasting medium in order to keep the plant fully effective. 
     In this connection, a number of part-problems exist which constitute bottlenecks in the overall process, and with the invention it is endeavoured to provide a method and respectively a processing plant which with simple means can ensure an expedient overall function which, by and large, operates in a continuous manner. 
     SUMMARY OF THE INVENTION 
     On this basis, the invention comprises a combination of various procedures which, although separately can be varied within certain frameworks, collectively must be considered as being necessary and adequate for solving the tasks presented. It will herewith be of minor significance for the novelty aspect of the invention whether some of the relevant procedures should be known, in so much as they are new in the overall combination according to the invention. 
     The invention is based on the consideration that an advantageous working procedure can be achieved by dividing the plant into some discrete units for solving part-problems as follows: 
     1) A processing chamber in which on a movable support the items are exposed to a spraying by the blasting medium from an overlying, downwardly-emitting arrangement for this medium; 
     2) An underlying collection tank for the collection of the sprayed-on blasting medium with its content of dirt cleaned from the items, and for precipitation of the heavier particles of the medium therein; 
     3) A transport arrangement such as a worm conveyor for the feeding of the precipitated material up and along an inclined bottom of this tank to an upper bottom outlet. 
     4) A sedimentation tank for receiving the overflow medium from the collection tank for separation of lighter material fractions from the overflow medium via a filter for the draining off of liquid; 
     5) A pump for the sucking of surface liquid from the sedimentation tank for pumping further through a pressure pipe to the medium-spraying arrangement in the processing chamber, and 
     6) An ejector unit inserted in this pressure pipe for the sucking of the concentrated blasting medium from said upper bottom outlet of the collection tank. 
     With this combination, work can be carried out with a continuous two-stage separation of the lighter material fractions, while maintaining high efficiency and good reusability of the fraction of the blasting medium which has not been worn down. 
    
    
     In the following, the invention is explained in more detail with reference to the drawing, in which 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side view of a plant according to the invention, shown during the filling with items, 
     FIG. 2 is a corresponding view shown during cleaning, 
     FIG. 3 shows the same during the emptying of items, 
     FIG. 4 is a detail view of an injector in the plant, 
     FIG. 5 is a detail view of a spraying-in unit for blasting jets, 
     FIG. 6 is a schematic perspective view of a modified processing chamber in the plant, and 
     FIG. 7 is a view of the whole plant seen in perspective. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The main unit in the plant is a cleaning chamber  2  with a front hatch  4  over an opening  6  which can be opened for the introduction and removal of items  8  to be cleaned. These can be placed on a perforated belt  10  which is supported at its side edges against guide disks  12  which guide the belt along an inclined half-circle between reversing rollers  14 , with return run via a roller  16 . When the hatch  4  is closed, a spraying of blasting medium towards the items can be effected from a spray head  18 , cf. FIG. 2, in that the items are dammed-up and agitated by the feeding of the belt  10  in the direction shown by the arrow. Moreover, clean water can be sprayed from a rinsing nozzle  22  down towards the items for cleaning these by rinsing away the blasting medium. 
     The blasting medium is fed in a circuit, namely down through the perforated belt  10  to an underlying blasting medium tank  24 , and from here via an ejector  25  and a pump  28  back to the spray head  18 . 
     When the items  8  have been cleaned and rinsed, the hatch  4  can be opened again, FIG. 3, and the items can then be emptied into a mobile receiving bin  30  by reversing the belt  10 . 
     In the blasting medium tank  24 , which is held filled with water with an upper overflow pipe  32  to a combined sedimentation and filter unit  26 , the blasting medium itself will normally precipitate, and in order to hold the blasting medium suitably mixed with water it has been found advantageous to arrange a controlled feeding of the material to a discharge pipe  29  to the ejector  25 , preferably by use of an inclined worm conveyor  34  above an inclined bottom surface in this tank. During the process, or the successive processes, the blasting medium will be subject to a certain wearing down, whereby as mentioned below there will occur a continuous separation of worn-down and herewith ineffective blasting material in the filter unit  26 . On the other hand, supplementary blasting medium must be added to the circuit, preferably to the tank  24 , for maintaining an effective concentration of blasting medium. Since there will be turbulence in the sullied water in the tank  24 , it can not be detected visually or in another direct manner to what degree of filling the blasting medium arises in the tank, whereby great uncertainty arises with regard to the necessary dosing-in of new blasting medium. 
     With the invention, this problem is solved by introducing a detection of that turning moment with which the drive motor indicated at  36  for the worm conveyor  34  influences this worm conveyor, in that the drive moment will naturally vary with the degree of viscosity of the contents of the tank. Relevant variations in the drive moment can be registered in a purely electrical manner in the power consumption of the drive motor, but with the invention a more mechanical solution to the problem is preferred, namely a contact registration of a swinging-out of the gear motor  36  which drives the worm  34 . This motor is suspended hanging out in a radial manner from the core of the worm  34  outside the tank  24 , and it will thus be able to swing out from its purely hanging-down position. Such a swinging-out will be dependent on how great a resistance to movement the worm  34  is exposed during its rotation, and on this basis it is possible to arrange a simple contact indication depending on whether the gear motor swings up to a high position as an indication that the blasting medium mixture is now suitably filled with blasting medium, or respectively to a low position in which an addition of new blasting medium will be called for. 
     In the filter module  26  there are placed a series of vertical plates which damp the turbulence in this chamber, and hereby make possible a sinking down of an appreciable part of the dirt which is added to the water by the cleaning of the items. The dirt sinks down to an inclined conveyor  38  which leads it out for collection in a refuse tray  40 , and which at the same time can serve to drain water from the material. 
     The water which is transferred to the filter unit  26  via the overflow pipe  32  will typically contain both cleaned-off dirt and particles of worn-down blasting medium, and the discharge water which is led through a pipe  42  to the pump  28  will thus be more or less free of larger particles. It is this water which from the pump  28  is brought through a pipe  44  to the ejector  25  for suction of the water-mixed blasting medium through the pipe  29 , and pressing forward of this hydraulic blasting medium through a pipe  46  to the spray head  18 . 
     This spray head  18  is preferably configured as shown in FIG. 5, namely as a vane rotor  48  which from the axially-supplied water can throw this out over the whole breadth of the processing area inside the main chamber. 
     In FIG. 6 it is indicated that for the support of larger processing items, use can be made of a rotating support disk or basket in the chamber  2 , driven in any suitable manner and including reversing operation. The spray head  18  can be used unchanged, even though it works mainly with a slinging-out of the blasting medium in a rectangular stream which is narrower than the diameter of the support disk. 
     FIG. 7 shows a practical configuration of the plant, including with special regard to a possible upper arrangement for the movement of the cover plate  4 . It must be noted that work can possibly be carried out with several filter modules  26 , and that various modifications can be introduced such as the building together of the filter unit  26  and the pump  28 .