FIELD OF THE INVENTION

The present invention concerns a pump for high-density powder transfer.

The pump according to the present invention is designed to be used in systems for high-density powder transfer, and therefore another object of the present invention is a powder transportation system that comprises the pump according to the present invention.

STATE OF THE ART

In the field of powder transportation through conventional Venturi pumps or high-density systems, for example but not only in industrial painting plants, special dedicated pumps make it possible not only to provide the powder to the paint guns, but also to recover and recirculate the so-called “overspray” powders from the painting chamber.

The term “overspray” is meant to indicate the excessive amount of pressurised gas (air), used to transport a certain amount of powder.

A high percentage of gas (air) used substantially increases the speed of the powder itself since the resulting delivery flow would consist mainly of the gas (air) itself.

In the specific case of powder coating, in the spraying step the powder, even if electrostatically charged, tends to rebound on the piece to be painted or worse it goes past the piece itself. This results in the use of a greater number of guns or, alternatively, reduced production speeds with the consequent rising of production costs.

By its nature, overspraying does not give any benefit to the coating process. In fact, it is a burden since it increases the amount of material that must be disposed of, increases the load of the filters, soils the cabin and increases the emission levels into the atmosphere: its reduction, therefore, can only lead to a saving.

In spray painting the recovery and the possibility of reusing the “overspray” powders is one of the greatest problems, the importance of which becomes clearer when it is considered that the legislation that imposes strict limits to the emission into the atmosphere of powders and the control of waste disposal.

In spray painting processes, a significant percentage, from 30 to 70% of powder coating, is in excess and to fall within the emissions limits it is necessary to cut overspray by conveying the excess powder into suitable powder recovery tanks in general adjacent to the painting chamber.

The high-density pumps that the present invention is classified among can therefore be used both to feed the painting product, the powder, to the painting guns by sucking the powder from a feeding tank, and to transfer the powder from the excess powder recovery tank adjacent to the painting chamber to the feeding tank of the powder to the guns.

For the sake of brevity, reference will therefore be made to the pump object of the present invention with the expression “pump for high-density powder transfer”, without, however, thereby wishing to in any way limit the use thereof to only powder transfer operations, instead including among its uses that of feeding a painting gun.

Currently, pumps for high-density powder transfer are known in the state of the art, which use two tanks to process the powder, which operate in a continuous cycle in a two-stroke cycle: while the first tank loads up with powder, the second tank is in the expulsion step. At a subsequent time, the operations in the two tanks reverse, and while the first tank discharges powder the second loads up.

The loading/discharging operations in the two tanks therefore reverse in a continuous cycle according to a time predetermined by the manufacturer of the pump. When using the term pumps for high-density powder transportation, reference is being made to pumps adapted for transporting dry powders, reversing the current gas-powder percentages conventionally required in Venturi pumps, using minimum amounts of gas, a large amount of dense phase powder is transported.

Given the need to process a high flow rate of powders, and therefore given the need to fill the tanks of the pump with a large amount of powder, the known solutions in which the pump foresees a two-stroke cycle that engages two tanks involves excessive powder loading and expulsion times, which translates into pulsed, discontinuous delivery.

The time necessary to discharge the powder from a (loading) tank, is the same necessary for loading the powder in the other (discharging) tank.

Although the cycle is continuous, the powder becomes compacted in the transportation tube and the fact that large amounts of powder are sent, pushed by the pressurised air, causes discontinuous feeding in which two volumes of powder expelled by the pump in two successive steps of the cycle are separated by the presence of air, actually creating a pulsed delivery.

Another drawback of the pumps for high-density powder transfer known from the state of the art is represented by the cleaning system of the pump itself.

Indeed, there is a need in the field to have a deep and complete cleaning of the pump at the time of a change of powder, i.e., for example, in the case in which it is necessary to change the powder to quickly move on to painting with a different colour.

When a change of powder is carried out it is necessary for the pump to be cleaned so as to eliminate any possible residue of the powder used up to that moment.

Pumps known in the state of the art foresee two possible cleaning methods.

According to a first method, pressurised air is introduced into the tanks of the pump from the outside, by means of a dedicated circuit.

This system does not, however, ensure that the cleaning air flow effectively strikes the inner walls of the tanks of the pump, since the air flow is introduced with prevailing axial direction in the tanks of the pump, with the risk that the air flow only tangentially grazes the inner walls of the tanks, which results in very limited cleaning efficiency.

Another drawback of this first cleaning method known in the state of the art concerns the fact that the cleaning air flow, directly mainly axially, undergoes a substantial load loss crossing the tanks of the pump itself. The air, introduced at a pressure of about 6 bar upstream of the powder storage chambers of the pump, finally reaches the ducts of the pump body and of the valves close to the powder introduction and expulsion area with low pressure, and therefore speed. This substantially reduces the cleaning efficiency of the air flow.

Moreover, the fittings between the tanks of the pump and the duct for introducing cleaning air are made of metallic material for sealing purposes, just as the non-return valve provided here is also made of metallic material.

Such metallic materials are therefore in continuous contact with the powder. A second cleaning method known in the state of the art foresees the use of air.

The purpose of the present invention is therefore also that of providing a pump for high-density powder transfer that comprises a self-cleaning device that makes it possible to overcome the drawbacks of known solutions of the state of the art.

SUMMARY OF THE INVENTION

The purpose of the present invention is to avoid the aforementioned drawbacks by providing a pump for high-density powder transfer of the type comprising a main body comprising a valve assembly and a pump body, said valve assembly comprising at least four valves each being configured to selectively close a delivery or powder return duct, said pump body in turn comprising at least four pumping chambers configured to selectively load/discharge powder from/towards the outside, at least one circuit for introducing compressed air in said pumping chambers making a four-stroke pumping cycle.

A further purpose of the present invention is to make a pump for high-density powder transfer, which according to the requirements of the application can be electro-pneumatic or totally pneumatic suitable for use in an ATEX area.

These and other purposes according to the present invention are accomplished by a pump for high-density powder transfer according to claim1.

Further characteristics of the apparatus according to the present invention are the object of the dependent claims.

