FIELD OF THE INVENTION
The present invention relates to an automatic loader of abrasive sand, particularly for water-jet cutting machines.
Water-jet cutting machines and, more in general, machines that make use of abrasive sand for operation thereof, are usually provided with an own storage tank, into which a supply of abrasive sand is loaded. This is then sent, by pressurised air, into a mini-hopper loading the cutting machine from which the abrasive sand is then drawn automatically for cutting, as required.
The storage tank allows the cutting machine to operate for a predetermined period of time and must hence be periodically reloaded, to allow uninterrupted operation of said machine.
In the current state of the art, the loading of this type of cutting machine servicing thanks is still performed completely by hand by the operator in charge of the cutting machine, using supplies of abrasive sand in 25-kg paper bags, packaged in bulk bags containing 40 bags each and hence weighing around 1 ton.
The bulk bag is positioned by mechanical means as close as possible to the machine or set of machines and then the operator carries the smaller bags on his shoulder all the way from the 1,000-kg bulk bag to the storage tank, then cuts open the bag paper pouring the abrasive into the tank and finally dispose of the paper bag in the waste disposal area.
PROBLEM AND SOLUTION
The current manual procedure for loading storage tanks with abrasive sand, apart from obviously being slow and tiresome, also involves a not negligible cost in terms of even unskilled labour, which must be kept available in order to fill the tanks whereas the workers could be directed more beneficially to more challenging tasks that cannot be automated.
Furthermore, the use of abrasive sand packaged in relatively light bags—essential for manual loading to be possible—also causes a not negligible consumption of resources, both due to the greater cost of the abrasive product supplied in bags in relation to the same product supplied loose within said bulk bags, and due to the management of the bag paper during the bag opening and disposing steps.
The problem underlying this invention is hence to propose a piece of apparatus which allows the automatic loading of said storage tanks of cutting machines, starting from abrasive sand in a loose condition, i.e. not pre-packaged in small bags, thus making it possible to fully eliminate the manual handling of said bags. This object is achieved through an automatic loader having the features defined in Claim 1. The dependent claims define other preferred features of the apparatus of the invention.
BRIEF DESCRIPTION OF THE DRAWING
Further features and advantages of the automatic loading apparatus of the invention will in any case be more clearly apparent from the following detailed description of a preferred embodiment thereof, given purely as a non-limiting example and illustrated in the attached drawing, which shows a diagrammatic, partially sectioned front view of said apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As stated above, the automatic loader for abrasive sand of this invention is intended for servicing a machine tool which makes use of said abrasive sand in its operating cycle, in particular for water-jet cutting machines. The specific type of such a machine tool is not, however, relevant for the operation of the apparatus of the invention and hence in the drawing only the storage tank T for abrasive sand is shown, the outlet U of which is connected—in a manner known per se, and in any case irrelevant for the purposes of the present invention—to the machine tool and the opening E of which is, as per the known art, open outwards for the manual loading of the tank by an operator.
The automatic loading apparatus of the invention comprises in essence a loading chamber 1, positioned above the opening E of the tank T and connected, on one side, to a vacuum pump 2 and, on the other side, to a bulk bag S containing abrasive sand in a loose state. The operation of the vacuum pump 2 is controlled through a processing unit housed in an electrical console 3, according to the operating logic that will be described below. The bulk bag S is arranged inside a sturdy metal frame 4 and is fastened on to the top thereof to hooks 4′ projecting from the upper frame crosspiece through retaining ties 5, so as to prevent it from collapsing as the abrasive sand contained therein is drawn out.
The chamber 1 is connected to the vacuum pump 2 and to the bulk bag S by means of pipes 6 and 7, respectively, preferably made of flexible, abrasion-resistant plastic materials, appropriately reinforced by a wire braid that prevents them from being collapsed when a degree of vacuum is formed therein, as pump 2 is actuated. The pipe 6 is connected at the top of the chamber 1, while the pipe 7 is connected to the side of the chamber 1, in a lower position with respect to the inlet of pipe 6, so as to allow a filter F to be housed in the upper portion of the chamber 1, to prevent any undesired migration to the vacuum pump 2 of the abrasive sand entering the chamber 1 from the pipe 7. The pipe 7 ends with a steel intake nozzle 8, intended to be inserted into the bulk bag S; by preference this nozzle consists of a double-walled pipe, with a plurality of inlet slots formed in each of its side walls. The inner wall of the nozzle 8 is then connected to the pipe 7, while the outer wall of the nozzle 8 forms a protection gap for the inner wall, thus allowing the sand to be sucked into the pipe 7 from a number of entry points—above, below and laterally to the nozzle 8—and hence preventing any possible problem of said nozzle being occluded by the walls of the bulk bag S.
Finally, the chamber 1 is closed off at the bottom by a butterfly valve 9 that is normally kept in the closed position by retaining spring means having a low loading force, so as to open easily under the weight of the sand when the chamber 1 is even only partly loaded. The butterfly valve 9 is also provided with a control micro-switch 10 apt to notify the control unit housed in the electrical console 3 of the open or closed position of said valve.
The operation of the automatic loader of abrasive sand illustrated above is extremely easy and effective and will now be briefly disclosed below.
After having positioned the fixed parts of the apparatus in the configuration described above and having loaded a bulk bag S full of abrasive sand into the frame 4, fastening the ties 5 thereof to the corresponding hooks 4′, the bulk bag S is opened and the nozzle 8 connected to the pipe 7 is inserted into the same. In the drawing the nozzle is shown as fully inserted inside the abrasive sand contained in the bulk bag, but in actual fact it is enough just to insert in the abrasive sand the tip of the nozzle 8, since said tip will penetrate into the bulk bag S due to the suction effect caused by the vacuum pump 2, quickly positioning itself with its lower end at the bottom of said bulk bag.
Before starting up the vacuum pump 2, the control unit housed in the electrical console 3 is set on the values of the specific plant, by adjusting the continued operating time of the vacuum pump, defined as work cycle, based on the internal volume of the chamber 1 and on the suction flow rate of the sand. In other words, the duration of the work cycle is set so as to cause just a partial filling of the chamber 1 in all the various possible working and environmental conditions (temperature, humidity, type of sand etc.).
At the beginning of any work cycle of the vacuum pump 2, a vacuum is first produced inside the chamber 1, and then inside pipe 7 and nozzle 8, which result in drawing in a mixture of air and sand from the bulk bag S. The air entering the loading chamber 1 passes through the filter F and is expelled by the pump 2, while the sand dragged in by the same accumulates on the bottom of the chamber 1. The vacuum maintained in the chamber 1 prevents the butterfly valve 9 from opening even when the weight of abrasive sand acting thereon becomes greater than the loading force of the retaining spring means of said valve. At the end of each work cycle the vacuum pump 2 stops, the butterfly valve opens under the weight of the sand and the sand thus falls by gravity into the tank T. When the chamber 1 has been emptied, the retaining spring means of the butterfly valve 9, no longer contrasted by the weight of the overlying sand, bring the valve 9 back into a closed position and the micro-switch 10 gives the consent to the control unit to automatically start a second work cycle for filling chamber 1. When initially setting the control unit, it is therefore also necessary to set on also the number of successive work cycles that the vacuum pump 2 must perform before stopping and requiring reactivation by the operator. Depending on the operator's requirements and preferences, this number of work cycles can be set as follows:
a—to a finite number of work cycles, for example proportional to the size of the storage tank T of the machine tool or to the consumption of abrasive required per production batch, so that the vacuum pump 2 will stop after filling the tank T completely or, respectively, after loading the amount of abrasive material necessary for one production batch;
b—to an infinite number of work cycles, so that the vacuum pump 2 is switched on automatically each time the butterfly valve 9 is in the closed position. In this case, when the tank T is full, there is no room in the tank T for the sand coming out of the chamber 1 and the sand accumulates therefore in the lower area of the chamber 1, below the butterfly valve 9, which hence remains blocked in the open position, preventing the vacuum pump 2 from starting up again. When the drawing by the machine tool has consumed enough of the sand in the tank T to release the butterfly valve 9, the latter returns to the closed position and allows another work cycle to start.
Obviously, therefore, in the first operating mode the tank T is filled and then emptied alternately, while in the second case it always remains constantly full. Either operating mode can be selected at will by the user, depending on the specific work requirements.
It should be clear from the above description that the apparatus of the present invention has fully achieved the object set above, making it possible to fully remove the burdensome and tiresome manual loading of abrasive sand, to the benefit of the smooth operation of the cutting machines to which the storage tank T is attached, and to the cleanness of the premises, the complete elimination of paper bags to be disposed of and, finally, the lower cost of the abrasive material used when, as stated, this is supplied loose in bulk bags.
It is in any case intended that the apparatus of the invention should not be considered to be limited to the particular arrangement illustrated above, which represents only an exemplifying embodiment thereof, but that a number of variants are possible, all within the ability of a person skilled in the art, without departing from the scope of said invention, as defined by the following claims.