Patent Description:
Various types of devices are employed to prepare a floor for refinishing. This includes machines designed to scrape tile and carpet from a floor, polishers, grinders, burnishers and shot blasters. National Flooring Equipment, Inc. of Minneapolis, Minnesota, has been a leading manufacturer and distributor of such equipment for sixty years.

Many concrete floors in commercial building and residential garages are finished with epoxy coatings. Over time resurfacing is required. The original surface must be roughened up to permit the new layer of epoxy to properly adhere to the floor. This step of roughening the floor may be performed using a grinder or a shot blaster.

A shot blaster is designed to blast small metal pellets (shot) onto the floor's surface. Shot blasters typically include a reservoir containing a supply of shot, a mechanism for metering the delivery of the shot, an impeller (referred to as a blast wheel) that provides the force to blast the metered shot at the floor, and plenum attached to a powerful vacuum that collects the used shot, as well as the dust and debris generated by the shot blasting processes. Such a shot blaster is for instance known from <CIT>.

National Flooring Equipment offers a series of shot blasters of different sizes and configurations. These include the National HB5 handheld shot blaster, the National A30 self-propelled shot blaster, and the National A12 ride-on shot blaster. While all the shot blasters offered by National are of high quality and effectively treat the floor, National is continually trying to improve its equipment offerings.

The blast wheel of a shot blaster is enclosed in a blast wheel housing which, in some respects, acts like the barrel of a shotgun used for hunting. The housing contains and directs the shot to the desired location on the floor to be treated. The housing also protects the user of the machine and others in the vicinity of the machine from being struck and injured by shot ejected from the blast wheel.

During use, this house heats up due to friction. Such friction results from the spinning of the blast wheel, the pieces of shot rubbing up against each other as they are blasted toward the floor, and the pieces of shot impacting the surfaces of the housing and the parts contained within the housing, including the blast wheel itself.

The elevated temperatures caused by friction have been known to warp the metal used to form the housing. Also, elevated temperatures within the housing can reduce the life of the blast wheel itself. Even under ideal conditions, the blast wheel must be replaced periodically, typically after less than <NUM> hours of use.

In some cases, the warpage has been so significant that the warped housing makes it more difficult or even impossible to change the blast wheel requiring the housing, itself, be replaced.

Adding heat vents to allow hot gasses to escape from the housing without further modifications to the housing is not an option. This is because shot could also escape through such vents. This would create a mess. This would also damage equipment, fixtures and other objects in the area where the machine is being operated. This could also cause injury to the operator or others in the area. As such, a real need exists to find another way to control the temperature of the blast wheel housing.

The present invention provides various improvements related to heat control and the dissipation of heat that can otherwise damage the components of a shot blaster. The present invention provides a shot blaster according to claim <NUM>.

As noted above, a shot blaster typically includes a housing defining an interior chamber. In the case of the present invention, the housing comprises a mounting plate having an interior surface facing the interior chamber, an exterior surface, and a drive shaft orifice.

A blast wheel is coupled to a drive shaft and positioned within the interior chamber of the housing. The drive shaft extends from the blast wheel through the drive shaft orifice. A bearing is mounted to exterior surface of the mounting plate. The bearing surrounds a portion of the drive shaft and encloses the drive shaft orifice. A first motor is coupled to the drive shaft. This motor turns the drive shaft which, in turn, drives the blast wheel.

A fan may be mounted outside of the interior chamber. The fan is directed to create airflow across the exterior surface of the mounting plate and around the bearing. This fan dissipate heat from the interior of the chamber. More specifically, the air passing over the exterior surface of the mounting plate and around the bearing draws heat away from these structures creating a greater temperature differential that causes heat from inside of the interior chamber to be transmitted to the outside through the mounting plate and bearing.

According to the invention, the housing has at least one wall extending at an angle from the mounting plate adjacent the bearing. Such a wall may be present for various reasons, for example to reinforce the shot blaster assembly or to support other structures. According to the invention, the wall will be positioned between the first motor and the bearing. When so positioned, the wall directs heat generated by the first motor away from the area of the housing immediately adjacent the interior chamber of the housing. The wall, no matter where positioned, includes one or more vents that cooperate with the fan.

The fan has a suction side and a discharge side. The location of the wall will dictate whether the suction side or discharge side of the fan should face the vent(s). When the suction side faces toward the vent(s), air passes through the vents before reaching the fan and being blown by the fan across the mounting plate and around the bearing. This arrangement may be preferred when the wall is not between the motor and the bearing. When the wall is between the motor and the bearing, it may be preferable to position the discharge side of the fan toward the vent(s).

The fan includes a blade and some means to rotate the blade to create airflow. In most cases, the fan will comprise a blade driven by a second motor. However, the blade could also be driven by the first motor without deviating from the invention. For example, the fan could be mounted to the drive shaft to which the blast wheel is mounted or to a separate drive shaft also driven by the first motor. For safety reasons the fan blade will typically reside in an enclosure. The fan blade enclosure does not unduly impede air flow generated by the fan.

The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, especially when considered in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts:.

This description of the preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. In the description, relative terms such as "lower", "upper", "horizontal", "vertical", "above", "below", "up", "down", "top" and "bottom" as well as derivatives thereof (e.g., "horizontally", "downwardly", "upwardly", etc.) should be construed to refer to the orientation as then described or as shown in the drawings under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as "connected", "connecting", "attached", "attaching" "join" and "joining" are used interchangeably and refer to one structure or surface being secured to another structure or surface or integrally fabricated in one piece, unless expressively described otherwise.

A self-propelled shot blasting machine <NUM> is shown in <FIG>. The machine <NUM> sits on a pair of rear wheels <NUM> and a front drive wheel <NUM>.

Machine <NUM> is driven by an electric motor <NUM> coupled to drive wheel <NUM>. The machine <NUM> has a second motor <NUM> that drives a blast wheel <NUM>.

The machine <NUM> also has a plenum <NUM> incorporating a hopper <NUM> and a housing <NUM> surrounding the blast wheel <NUM>. The plenum <NUM> is coupled to one end of a vacuum tube <NUM> by a fitting (or port) <NUM>. The other end of the vacuum tube <NUM> is coupled to a vacuum (not shown).

Hopper <NUM> is filled with shot prior to use. The vacuum is then energized to create air flow through the vacuum tube <NUM> and plenum <NUM>. The motors <NUM> and <NUM> are then energized. Energizing motor <NUM> causes the blast wheel <NUM> to spin. Shot is metered from hopper <NUM> through a valve into the housing <NUM> where the blast wheel <NUM> is located. The blast wheel <NUM> accelerates the shot toward a spout opening <NUM> at the base of the housing <NUM> adjacent the floor and in an area contained by a suction head <NUM>. As the shot impacts the floor's surface roughening the surface, the shot, together with floor debris and dust, are carried through the plenum <NUM> by the air flow. The dust and debris are carried to the vacuum. The shot is deposited back into the hopper and recycled.

Operation of the two motors <NUM> and <NUM> and the speed and direction of the machine are controlled by ergonomic controller <NUM>.

The housing <NUM> has an interior chamber <NUM> in communication with spout opening <NUM>. The housing <NUM> comprises a mounting plate <NUM> having an interior surface <NUM> facing the interior chamber <NUM>, an exterior surface <NUM>, and a drive shaft orifice <NUM>.

A blast wheel <NUM> is coupled to a drive shaft <NUM> and positioned within the interior chamber <NUM> of the housing <NUM>. The drive shaft <NUM> extends from the blast wheel <NUM> through the drive shaft orifice <NUM>. A bearing <NUM> is mounted to exterior surface <NUM> of the mounting plate <NUM>. The bearing <NUM> surrounds a portion of the drive shaft <NUM> and encloses the drive shaft orifice <NUM>. Motor <NUM> is coupled to the drive shaft <NUM>. Various elements may be employed to couple the drive shaft <NUM> to the motor <NUM>, for example a chain and a pair of sprockets, or a belt and a pair of pullies. In any case, the motor <NUM> turns the drive shaft <NUM> which, in turn, drives the blast. wheel <NUM>.

A fan <NUM> may be mounted outside of the interior chamber <NUM>. The fan is <NUM> directed to create airflow across the exterior surface <NUM> of the mounting plate <NUM> and around the bearing <NUM>. This fan dissipates heat from the interior chamber <NUM>. More specifically, the air passing over the exterior surface <NUM> of the mounting plate <NUM> and around the bearing <NUM> draws heat away from these structures creating a greater temperature differential that causes heat from inside of the interior chamber <NUM> to be transmitted to the outside through the mounting plate <NUM> and bearing <NUM>.

According to the invention, the housing has at least one wall <NUM> extending at an angle from the mounting plate <NUM> adjacent the bearing <NUM>. Such a wall may be present for various reasons for example to reinforce the shot blaster assembly generally or to support specific structures of the assembly. In some cases, the wall <NUM> will be positioned between the motor <NUM> and the bearing <NUM>. When so positioned, the wall <NUM> directs heat generated by the motor <NUM> away from the area of the immediately adjacent the interior chamber <NUM> of the housing <NUM>. The wall <NUM>, no matter where positioned, may include one or more vents <NUM>/<NUM> that cooperate with the fan <NUM>.

The fan <NUM> has a suction side and a discharge side. The location of the wall <NUM> will dictate whether the suction side or discharge side of the fan <NUM> should face the vent(s) <NUM>. When the suction side faces toward the vent(s) <NUM>, air passes through the vents <NUM> before reaching the fan <NUM> and being blown by the fan <NUM> across the mounting plate <NUM> and around the bearing <NUM>. This arrangement may be preferred when the wall is not between the motor and the bearing. When the wall <NUM> is between the motor <NUM> and the bearing <NUM>, it may be preferable to position the discharge side of the fan <NUM> toward the vent(s)<NUM>.

The fan <NUM> includes a blade <NUM> and some means to rotate the blade to create airflow. In most cases, the fan <NUM> will comprise a blade driven by an additional motor. However, the blade could also be driven by motor <NUM> without deviating from the invention. For example, the fan <NUM> could be mounted to the drive shaft <NUM> to which the blast wheel <NUM> is mounted or to a separate drive shaft also driven by the motor <NUM>. For safety reasons the fan blade will typically reside in an enclosure <NUM> that does not unduly impede air flow generated with the fan.

<FIG> shows an alternative embodiment of the present invention. This embodiment includes modifications to the blast wheel. housing <NUM>. Specifically, vents <NUM> and <NUM> have been added to the exterior walls of the blast wheel housing to provide air flow through the interior chamber <NUM> of the blast wheel housing <NUM>. The blast wheel housing has been further modified to include a liner <NUM> between the blast wheel <NUM> and the vents <NUM> and <NUM>.

The liner <NUM> may be an imperforate metal sheet. When this is the case, only the region of the interior chamber <NUM> of blast wheel housing <NUM> between the liner <NUM> and the vents <NUM>/<NUM> is directly vented. Heat generated in other parts of the interior chamber <NUM> is dissipated via conduction through the liner <NUM> and then carried out of the housing <NUM> by air flow through vents <NUM>/<NUM>. This airflow may be enhanced by employing a fan <NUM>. Fan <NUM> is shown positioned within the interior chamber <NUM> of blast wheel housing <NUM> adjacent vent <NUM>. The liner <NUM> separates the fan <NUM> from the blast wheel <NUM>. As such, the liner <NUM> isolates and protects the fan <NUM> (and the vents <NUM>/<NUM>. ) from shot flying off the blast wheel <NUM>. The fan <NUM> could also be mounted outside of the housing <NUM> adjacent one of the vents <NUM>/<NUM> to make assembly easier.

For even greater air flow through the housing <NUM>, the liner <NUM> may be semi-permeable. Specifically, the liner <NUM> may be formed as a mesh with pores large enough to permit air to pass through the liner <NUM> and small enough to prevent shot or other particles flying off the blast wheel from passing through the liner <NUM>.

As noted above and shown in <FIG>, the blast wheel housing <NUM> is part of (or at least in fluid communication with) the plenum <NUM>. The plenum <NUM> is coupled to a vacuum tube <NUM> which is attached to a vacuum (not shown). When the vents <NUM>/<NUM> are provided, the liner is semi-permeable and the vacuum is energized, the vacuum will draw air in through the vents <NUM>/<NUM>, the liner <NUM>, and the rest of the interior chamber <NUM>. This air will exit the interior chamber <NUM> through the spout opening <NUM>. The fan <NUM> may again be provided to enhance such air flow through the interior chamber and out the spout opening <NUM>.

The embodiments shown in <FIG> and <FIG> may, of course, be combined to enhance cooling and heat dissipation from the interior chamber.

Claim 1:
A shot blaster comprising:
a. a housing (<NUM>) defining an interior chamber (<NUM>), said housing (<NUM>) comprising a mounting plate (<NUM>), said mounting plate (<NUM>) comprising an interior surface (<NUM>) facing the interior chamber (<NUM>), an exterior surface (<NUM>), and a drive shaft orifice (<NUM>);
b. a blast wheel (<NUM>) coupled to a drive shaft (<NUM>), said blast wheel (<NUM>) positioned within the interior chamber (<NUM>) of the housing (<NUM>) and said drive shaft (<NUM>) extending from the blast wheel (<NUM>) through the drive shaft orifice (<NUM>);
c. a bearing (<NUM>) mounted to the exterior surface (<NUM>) of the mounting plate (<NUM>), surrounding a portion of the drive shaft (<NUM>), and closing the drive shaft orifice (<NUM>), wherein the housing (<NUM>) comprises a wall (<NUM>) extending at an angle to the mounting plate (<NUM>) and adjacent the bearing (<NUM>);
d. a first motor (<NUM>) coupled to the drive shaft (<NUM>); and
e. characterised in that said wall (<NUM>) is between the first motor (<NUM>) and the bearing (<NUM>) and the shot blaster further comprises at least one first vent extending through said wall (<NUM>) and adapted to provide airflow through said wall (<NUM>) and configured to provide a flow path for air moving across the exterior surface (<NUM>) of the housing (<NUM>) which is configured to conduct heat from the interior chamber (<NUM>) of housing (<NUM>).