GB1571508A

GB1571508A - Wet blast cleaning

Info

Publication number: GB1571508A
Application number: GB774876A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-02-17
Filing date: 1977-02-17
Publication date: 1980-07-16

Description

(54) WET BLAST CLEANING (71) We, THOMAS WILLIAM KEL SALL, HENRY UNSWORTH AND RAYMOND EVANS, all British Subjects of c/o Cleanstone Co. (Bradford) Limited, Canal Road, Bradford 1. West Yorkshire do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the de-scaling or cleaning of metal surfaces by wet blasting or the application or a jet of abradant in water.

Before the year 1970 it was common practice to remove old paint, rust and corrosion from metal surfaces priort to reprotection by sand blasting. The health hazard arising from the silicous dust producted in the operation then became recognised and the practice was discontinued.

The techniques now used instead are not wholly satisfactory in that one of then, namely wet blasting leads rapidly to further corrosion, whilst the other, dry blasting with copper slag, is expensive in view of the high cost of the abradant.

The object of the invention is to provide an improved method of cleaning metal surfaces.

According to the invention, there is provided a method of cleaning a metal surface comprising applying to the surface a jet comprising an abradent, water and a corrision inhibitor comprising mixed polyphosphates. Preferably the corrosion inhibitor is added to the water before the water is subjected to the pressure of the jet. The concentration of the inhibitor may be in the range of 250g to 1500g and is preferably in the range 300-1000g per 100 gall. water.

Preferably a first stream of sand and air at a pressure greater than atmospheric is formed in a pipe and to this stream is joined a second stream comprising water and inhibitor and having a pressure greater than that of said first stream. The pressures of the first and second streams may be varied so that the pressure of the jet can be varied during the cleaning operation in acordance with the nature of the contamination to be removed. The rate of supply of abradant to the air stream may also be varied for the same purpose.

The invention will be further described with reference to a non-limiting example of a method of working according to the invention.

The metal surface to be cleaned is the exterior surface of a tank which is contaminated by rust and old paint. In order to re-protect the surface it needs to be cleaned of all the old paint and rust down to clean or 'white" metal of a standard of cleanliness in the range SA 2l/2-3 on the Swedish scale.

Moreover, this degree of cleanliness is preferably to be maintained for a sufficiently long period to allow for the application of a protective coat of paint, primer or the like.

A concentrated solution is prepared by dissolving a 500g. briquette of polyphosphate inhibitor in a gallon of water and 3/4 gallon of concentrate is diluted with 100 gallons of water. A quantity of the diluted solution is subjected to a pressure of about 2001b/sq. inch in a suitable pressure vessel.

Air from a compressor producing a pressure of 1001b/sq. inch is admitted above a load of dry sand in an enclosed hopper from which sand is allowed to pass, under the combined influences of gravity and the air pressure, through an exit port into an air pipe carrying a stream of air from the compressor to a flexible rubber pressure hose ending in suitable nozzle. The water containing polyphosphates is admitted to the air stream downstream of where the sand is introduced. Because the pressure of the water is greater than that of the sandladen air, there is no danger of said being blown into the water supply in the event of a blockage occurring in the pressure hose.

A jet of water, polyphosphates, sand and air emerges from the nozzle at high pressure and the jet is applied to the metal surface.

The surface is rapidly cleaned and remains free from further corrosion for several hours.

Depending on the nature and severity of the contamination of the surface a more or less intense cleaning action is required.

Variations can be effected during the cleaning operation by controlling the pressure of the jet in the range 90 to 15 p.s.i. and by controlling the supply of abradant from 5cwt. per hour to zero.

Zero supply of abradant, of course, produces a rinsing effect. In practice, the operator of the nozzle, who is most aware of the nature of the contamination with which he is dealing, may be remote from the apparatus producing the air/abradant and water/inhibitor streams. The first named operator is in such case in telephonic or radio communication with a second operator so as to command such changes as are required. The variation of jet pressure is effected by varying the pressure of the air/or water streams. The variation is abradant supply is effected by means of a valve at the sand hopper exit port.

Because of the presence of water, the formation of hazardous sand dust is prevented. Because the sand is relatively cheap it is not necessary to try to recover it after use for re-use. However. other abradants such as copper slag could be used alone or in admixture with sand if required.

The concentration of polyphosphate may be varied according to the quality. for example hardness, of the water and other circumstances. Outside the range of 250g to 1500g of polyphosphate in solid briquette form per 100 gallons of water, however. the inhibitor has been found to be less effective.

Other corrosion inhibitors may be used together with polyphosphates.

Other variations within the scope of the invention include different order to admixture of the components of the jet. and the supply of inhibitor to the jet otherwise than by admixture with water before the water is pressurised.

WHAT WE CLAIM IS: 1. A method of cleaning a metal surface comprising applying to the surface of pressurised fluid jet comprising water, an abradant and a corrosion inhibitor comprising mixed polyphosphates.

2. A method according to Claim 1, wherein the corrosion inhibitor is added to the water before being subjected to the pressure of the jet.

3. A method according to Claim 2, wherein to a first stream of abradant in air at a first pressure greater than atmospheric pressure is added a second stream comprising water and corrosion inhibitor and having a pressure greater than said first pressure.

4. A method according to any one of the precedng claims, wherein the abradant is sand.

5. A method according to any one of the preceding Claims, wherein the corrosion inhibitor is present in the jet in a proportion of between 250g and 1500g per 100 gal. of water.

6. A method according to Claim 5, wherein the proportion lies between 3()0g and 10()0g per 100 gal. of water.

7. A method according to any one of the preceding claims, wherein the pressure of the jet is varied during the cleaning operation.

8. A method according to any one of the preceding claims, wherein the rate of application abradant by the jet is varied during the cleaning operation.

9. A method according to Claim 7 or Claim 8, wherein the variation. respectively of the pressure or of the rate of application, is effected at a location remote from the jet.

10. A method according to Claim 9, wherein an operator of the jet is in telephonic or radio communication with an operator of means for effecting the said variation.

11. A method of cleaning a metal surface substantially as described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. blockage occurring in the pressure hose. A jet of water, polyphosphates, sand and air emerges from the nozzle at high pressure and the jet is applied to the metal surface. The surface is rapidly cleaned and remains free from further corrosion for several hours. Depending on the nature and severity of the contamination of the surface a more or less intense cleaning action is required. Variations can be effected during the cleaning operation by controlling the pressure of the jet in the range 90 to 15 p.s.i. and by controlling the supply of abradant from 5cwt. per hour to zero. Zero supply of abradant, of course, produces a rinsing effect. In practice, the operator of the nozzle, who is most aware of the nature of the contamination with which he is dealing, may be remote from the apparatus producing the air/abradant and water/inhibitor streams. The first named operator is in such case in telephonic or radio communication with a second operator so as to command such changes as are required. The variation of jet pressure is effected by varying the pressure of the air/or water streams. The variation is abradant supply is effected by means of a valve at the sand hopper exit port. Because of the presence of water, the formation of hazardous sand dust is prevented. Because the sand is relatively cheap it is not necessary to try to recover it after use for re-use. However. other abradants such as copper slag could be used alone or in admixture with sand if required. The concentration of polyphosphate may be varied according to the quality. for example hardness, of the water and other circumstances. Outside the range of 250g to 1500g of polyphosphate in solid briquette form per 100 gallons of water, however. the inhibitor has been found to be less effective. Other corrosion inhibitors may be used together with polyphosphates. Other variations within the scope of the invention include different order to admixture of the components of the jet. and the supply of inhibitor to the jet otherwise than by admixture with water before the water is pressurised. WHAT WE CLAIM IS:

1. A method of cleaning a metal surface comprising applying to the surface of pressurised fluid jet comprising water, an abradant and a corrosion inhibitor comprising mixed polyphosphates.

11. A method of cleaning a metal surface substantially as described.