WO1996000138A1

WO1996000138A1 - Shot blast delivery and recovery unit

Info

Publication number: WO1996000138A1
Application number: PCT/CA1995/000386
Authority: WO
Inventors: James Pittman
Original assignee: James Pittman
Priority date: 1994-06-27
Filing date: 1995-06-27
Publication date: 1996-01-04
Also published as: GB9412901D0; AU2782395A

Abstract

A vacuum hood (1) is provided around a blast nozzle (3). Air is drawn from the hood, to a collection apparatus which does not form part of the invention itself, via a collection hose (4). The air collects the blast media and the material removed by the blast media, without allowing escape of same to the environment. Within the hood, the blast nozzle preferably traverses across a path at right angles to the direction of movement of the hood, by virtue of the nozzle being secured to a trunnion (5) which is mounted for travel along a ballscrew (6), the ballscrew being rotated by a motor (7). The direction of rotation of the motor is reversed when the nozzle or trunnion contacts limit switches (8, 8') at opposite ends of travel.

Description

Shot Blast Delivery and Recovery Unit

Technical Field

This invention relates to shot blasting, and in particular to a blast media delivery unit which includes collection and removal of the blast media and of the material removed by the blast media.

There is a growing consciousness regarding health and the environment, and in an attempt to avoid harm to both, the use and handling of shot blast media is now controlled in many jurisdictions.

Traditionally, shot blast cleaning operations were conducted in the open, allowing the sand or other blast media and removed materials to escape to the surrounding environment. Such contamination is undesirable, and accordingly many jurisdictions have now imposed regulations to ensure that the blast media and waste materials are contained. Furthermore, some of the materials which are being removed are considered hazardous, such as lead-based paint, and it is therefore important to ensure that they are contained and collected when removed.

Shot blasting is a time-consuming and labour-intensive process, typically carried out by workers who manually direct a shot-blasting nozzle toward the surface to be cleaned.

There is a need for apparatus which will make shot blasting easier, less time-consuming, and less labour-intensive, while at the same time providing containment and collection of the blast media and removed material. There is also a need for equipment capable of providing a more consistent finish than can be provided by manual means.

Disclosure of Invention Accordingly, it is an object of the invention to provide improved shot blasting apparatus, in order to permit efficient shot blasting combined with containment and collection.

In the invention, a vacuum hood is provided around a blast nozzle. Air is drawn from the hood, to a collection apparatus which does not form part of the invention itself. The air collects the blast media and the material removed by the blast media, without allowing escape of same to the environment. Within the hood, the blast nozzle preferably traverses across a path at right angles to the direction of movement of the hood. Details of the invention will become apparent in the course of the following detailed description.

Brief Description of Drawings

The invention will now be described in greater detail, with reference to the accompanying drawings of the preferred embodiment by way of example, in which: Fig. 1 is a cross-section of the unit, viewed from an angle parallel to the direction of travel. The unit is shown on a horizontal surface in this case;

Fig. 2 is a cross-section corresponding to Fig. 1 , but showing the nozzle traversing;

Fig. 3 is a cross-section of the unit, viewed from an angle at 90 degrees to the direction of travel. The unit is shown on a vertical surface;

Fig. 4 is a close-up cross-section of the seal area; Fig. 5 is an external view of the unit, in which the motor which drives the brush can be seen;

Fig. 6 is another external view, at 90 degrees to Fig. 5; Fig. 7 is a cross-section near the blast hose inlet area; and

Fig. 8 is a cross-section near the ballscrew area.

Best Mode for Carrying Out the Invention

The unit includes a hood 1 that is positionable against a work surface 2. The hood surrounds a blast nozzle 3 that directs blast media at the work surface, such as the side of a ship, factory, bridge, oil tank, or other structure. The blast nozzle is supplied with blast media by conventional means (not illustrated). A vacuum collection system (not illustrated) in connected to the hood via a collection hose 4, to collect and remove the blast media and removed material.

Within the hood, the blast nozzle 3 is secured to a trunnion 5 that travels back and forth along a ballscrew 6, the ballscrew being rotated by an air-driven motor 7. The motor rotates in one direction until the nozzle travels far enough to contact a limit switch 8, and then reverses direction until the nozzle travels far enough to contact a second limit switch 8' and the other end of its travel. In this fashion, the blast nozzle continually traverses from side to side across the path of travel of the hood.

The hood preferably runs on wheels 9, which maintain the desired distance between the blast nozzle and the work surface, to maintain the desired seal pressure and to prevent binding. A primary seal is achieved by four relatively stiff rubber strips 10, which are moveable within channels 11 toward or away from the work surface. An inflatable tube 12, inflated via an inflation valve 13, biases the rubber strips against the work surface. The strips are limited in their movement by bolts 14 passing through elongated slots 15.

A secondary seal is achieved by a flexible rubber skirt 16 that extends outwardly and away from the outer periphery of the hood. The purpose of both seals is to prevent direct escape of blast material and removed material such as might occur if there were no seals whatsoever, due to the inertia of the blast material. However, the seals need not be airtight, and indeed should not be airtight, since it is vital that air be drawn into the hood. Maintaining negative pressure in the hood draws air in through the seals, which not only prevents material from escaping, but also provides some or all of the air required to carry the blast material and removed material away via the collection hose. If desired, air flow into the hood may be augmented by one or more air inlet holes (not shown) through the hood. One or more of the holes may be made adjustable, if desired, to allow more or less air flow.

A brush 17 is mounted within the hood, and is driven by a second air motor 18. The brush is intended to clean the surface and to stir up any settled blast media and removed material, so that it can be carried away by the airstream to the collection system. Preferably, the brush is mounted horizontally, along whichever side of the hood will be the lowest, so that when blast media and removed material settle by gravity towards the bottom of the hood, the brush stirs it up. The brush may be made adjustable, or may be self-adjusting, such as via spring-loaded mounts (not illustrated). Smaller hoods than the one illustrated in the drawings have higher air flow velocities, in general, and therefore all blast media may be carried away without the need for a revolving brush.

The collection hose 4, for a similar reason, is also preferably positioned on the lower side of the hood, to take advantage of gravity. This assumes that the apparatus is being used on a vertical or substantially vertical surface, for which it is particularly well adapted. For work on a horizontal surface, other than a ceiling, gravity obviously does not come into play, and there is no obviously preferred location for the brush and collection hose.

As mentioned, the brush is driven by a second air motor. However, as an alternative, the brush could be driven via a friction wheel which engages the work surface, such that the friction wheel rotates as the hood advances. A gearbox would connect the friction wheel to the brush, at any desirable speed ratio, such as 1 :5.

Preferably, the blast nozzle protrudes into the blasting hood through an air tight rubber seal and secondary floating seal, provided by a pleated rubber membrane 19 for example. The portion of the blast nozzle behind these seals is connected to a coupling mounted on a ballscrew assembly. This coupling can hold the blast nozzle in a fixed position, or allow the nozzle to swivel on a single axis at an angle of between 30 and 150 degrees relative to the ball screw. Optional throwing plates will allow the nozzle to traverse perpendicular to the ball screw and cut an arc at the end of each traverse. The plates come into contact with the coupling, forcing it to rotate as the ball screw continues turning, so that the nozzle pivots outwardly in the arc.

In order to achieve a system which effectively carries away the blast media and removed material, there are a number of criteria which must be taken into account. These criteria are quite empirical, and inevitably a certain amount of tinkering is required in order to produce the optimum performance for any given hood size, blast rate, etc., but nevertheless it is important to understand the principles, so that if performance does not appear to be optimum, appropriate adjustments can be made.

Those criteria are as follows. First of all, the job dictates certain requirements, i.e. the size of the job and the type of finish to be removed will determine what blast media, blast pressure, target distance and blast flow rate (blast cfm) should be provided. There are thus two major control parameters, namely the size, shape and surface to be cleaned, and the finish required. These parameters will control the selection of the hood size, blast media, blast nozzle (diameter and configuration), blast pressure and target distance. In turn, these combined factors will determine the blast rate in CFM. The uniformity of the structure will determine a minimum leakage rate around the seals. The sum of the leak rate and the blast CFM should never exceed 75% of the vacuum CFM (capacity), to ensure that negative pressure is constantly maintained within the blast hood. Typically the drawn CFM falls in the range of 50 to 350 CFM depending on the detailed variables and parameters just mentioned. Higher CFM is required on large hoods, in the event of poor seals, or with blast media with high bulk density and coarse grade. The nozzle traverse rate can be set between 4 and 60 cycles per minute and is tuned to provide the finish required. Should the surface vary considerably, the traverse rate can be remotely increased or decreased. The hood is generally winched at an advance speed of from 6 inches to 48 inches per minute. This speed can also be increased or decreased remotely. It should be noted that although external propulsion such as a winch is contemplated, self-propulsion could also be employed via any normal means, such as an internal winch, or driven wheels.

The invention provides full containment and collection of the blast media and removed material, with little or no escape to the environment.

The above description relates to the preferred embodiment by way of example only. It should be appreciated that there are a number of obvious variations to the invention, and such variations are considered to be within the scope of the invention as defined by the following claims, whether or not expressly described or referred to above.

For example, it should be apparent that the nozzle could be reciprocated by any other conventional reciprocation means. The ballscrew and limit switch arrangement is just one example. Other means could include a cam, a piston, a rack-and-pinion arrangement, or any other conventional means.

It should also be appreciated that the scale of the apparatus can be varied widely, from units such as the one described above (on a larger or smaller scale), down to smaller manually-operated units, which may or may not include traversing of the nozzle. In smaller units, where the seal is likely to be too good to allow sufficient airflow, auxiliary air openings, such as a number of holes through the hood, may be provided.

Industrial Applicability

The invention provides a blast media delivery unit which includes collection and removal of the blast media and of the material removed by the blast media.

Claims

Claims:

1. A shot blast media delivery and recovery unit, comprising a shot blast nozzle (3) connected to a supply of shot blast media for directing said shot blast media towards a work surface (2), characterized by a hood (1) surrounding said nozzle, open towards said work surface, and vacuum collection means (4) connected to said hood to remove blast media and removed material from within said hood.

2. A unit as in claim 1 , further characterized by said shot blast nozzle (3) being mounted within said hood for traversing across the direction of intended movement of said hood.

3. A unit as in claim 2, further characterized by said traversing being by virtue of said nozzle being secured to a trunnion (5) which is mounted for travel along a ballscrew (6), said ballscrew being rotated by a motor (7), the direction of rotation of said motor being reversed when said nozzle or trunnion contacts limit switches (8, 8¹) at opposite ends of travel.

4. A unit as in claim 1 , further characterized by a rotatable brush (17) within said hood, to stir up any settling blast media and removed material.