US 3591989 A
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United States Patent  Inventor Jorgen Granlie Enkoping, Sweden [21 Appl. No. 798,955
[22} Filed Feb. 13, 1969  Patented July 13,1971
 Assignee Aktiebolaget Bahco Stockholm, Sweden  Priority Feb. 20, 1968  Sweden  HAND GRINDING MACHINES 5 Claims, 2 Drawing Figs.
 11.8. C1 511/268, 51/170 PT  Int. Cl B241) 55/04,
 Field of Search 51/170, 266, 268
 References Cited UNITED STATES PATENTS 2,452,268 10/1948 Schumann 51/266 X 2,462,710 2/1949 Ballinger 51/268 X Primary ExaminerJames L. Jones, Jr. Attorneyl-larry Cohen ABSTRACT: A grinding machine wherein a grinding wheel is rotated by a compressed air-driven motor and wherein sound dampening means is formed in a dust shield which surrounds part of the periphery of the grinding wheel and has an air-outlet passage formed between two peripherally extending parts of the dust shield.
PATENIEI] JUL 1 3 I97! sum 1 BF 2 fllullllllllll I m i ii HAND GRINDING MACHINES The present invention is concerned with an improvement in hand grinding machines of the type which consists of a motor driven by air under pressure and a grinding wheel rotated by said motor and partly surrounded about its periphery by a dust shield.
Persons using conventional machines of this type are constantly subjected to discomfit in the form of disturbing noise emanating from the machine whilst it is in operation. The noise is mainly caused by the air departing from the pneumatic motor and although perhaps only at times by the departing mixture of air and oil, or by turbulence and oil splashes caused by the air flow. A further discomfit is in the form of dust from the wheel and the article being ground.
The object of the present in vention is to eliminate or at least reducethe efiect of one or more of these causes of discomftt. This object is achieved by means of the present invention, which mainly characterized in that the dust shield consists of an outer and an inner wall which between them form a chamber having one or more outlet openings situated at the periphery of the grinding wheel and adapted to direct the outgoing air away from the motor side of the machine in a free flow substantially parallel to the line of the axis of rotation of the grinding wheel, and in that the chamber is connected by one or more supply passages to the air outlet of the motor, to lead away air leaving the motor, via said chamber.
Thus the main characterizing features of the invention provide for a considerable reduction of the sound level, by causing the outgoing air to pass through a sound-dampening chamber. This arrangement also affords the possibility of conducting the air away from the machine in such a manner that the operator need not come into contact with the departing flow of air, which can be used, in the form of an air curtain, as a dust-conducting extension of the shield. This further development is explained more precisely in the depending claims. An embodiment of the invention will now be described in more detail with reference to the following drawings, in which FIG. 1 is a partially cut away side view of a hand grinding machine provided with a sound damping chamber, and in which the departing air is passed from the machine axially, while FIG. 2 shows in perspective the end of the same machine bearing the grinding wheel, and in which the grinding wheel and its attachment means have been removed and the shield partly cut away, to expose the structure of the invention. The illustrated grinding machine has a motor ll operated by air under pressure and mounted in the body of the machine. The air is lead away from the motor, through an annular passage 2 which is formed by the space between a shaft 3 and a tubular member 4 surrounding said shaft. The shaft connects the motor 1 to a grinding wheel 5 which is detachably affixed to the shaft by hub plates 6, keyed to the end of the shaft in a conventional manner.
The grinding wheel 5 is surrounded about half its periphery by a casing 7, the shield, which in a known manner serves as a safety plate, and shields half the grinding wheel axially on the motor side of the machine. In accordance with the concept of the invention, the casing 7 consists of an outer wall 8 and an inner wall 9, which between them form a chamber 10. The outgoing air is passed to the chamber from the passage 2, through an opening 11 in the tubular position 4 and a tubular connector 12 detachably connected therewith and surrounding the end of said portion, while at the same time said connector forms an element which partially defines the chamber and which is connected to both walls of thecasing to support the same.
The outer wall 8 in the proximity of the connector 12 is in the form of a half, frustoconical casing, located concentrical with the shaft 3, while the inner wall within a corresponding area comprises a flat, half-ring, placed in a plane perpendicular to the shaft 3. The two walls meet at a radial distance from the shaft 3 which is somewhat greater than the outer diameter of the grinding wheel 5, and are bent axially at this point; away from the motor side of the machine, so that their terminating portions which peripherally enclose the grinding wheel form substantially two casing halves. The inner one of these halves, i.e. that which forms part of the wall 9, is corrugated to form ridges I3 which abut and are suitably fixed to the inside of the outer casing half, which forms part of the wall 8. In this way there is formed in the circumferential space between the ridges ejection passages 14, defined by the inner and outer wall. As a result of orientating the corrugation so that the ridges extend parallel with the shaft 3, the ejection passages 14 cause the exhaust air to leave the machine in a corresponding direction, so that a curtain of air is formed outside the free edge of the casing.
The arrangement thus provides a means, in the form of chamber 10, for dampening the sound created by the exhaust air, a means of leading away the air in a direction in which it does not cause discomfit to the operator, and a means of improving the shielding effect of the casing, by generating a curtain of air which leads the grinding dust away from the machine.
The invention is not restricted to the shown and described embodiments, but can be varied within the scope of the following claims.
1. An improvement in hand grinding machines of the type which consists of a motor driven by air under pressure and a grinding wheel rotated by said motor and partly surrounded about its periphery by a dust shield, the improvement being characterized in that the dust shield consists of an outer end and an inner wall which between them form a chamber having one or more outlet openings situated at the periphery of the grinding wheel and adapted to direct the outgoing air away from the motor side of he machine in a free flow substantially parallel to the line of the axis of rotation of the grinding wheel; and in that the chamber is connected by one or more supply passages to the air outlet of the motor, to lead away air leaving the motor; via said chamber, said chamber being disposed on the motor side of the grinding wheel and presenting in a section behind the line of the rotary axis of the grinding wheel a substantially triangular profile, with one corner situated at a radial distance from the line of the rotation axis of said wheel which is greater than the outer radius of the wheel and defined along adjacent sides by the outer and the inner wall and along the opposing side by a part of the machine body enclosing the shaft connecting the motor and the grinding wheel.
2. The improvement of claim 1, wherein the portion of the shield surrounding a part of the periphery of the grinding wheel presents both the outer and the inner wall, the walls being adapted to form therebetween a substantially continuous gap or series of openings, which comprise the outlet opening or openings from the chamber.
3. The improvement of claim 2, wherein the inner wall within said portion of the shield is corrugated in a wayto present ridges against the outer wall, said ridges abutting and preferably affixed to said outer wall, and wherein the inner and outer wall form between them, in the spaces between the ridges the outlet openings from the chamber in the form of passages, which impart to the outgoing air a direction of movement substantially parallel to the line of the rotary axis of the grinding wheel.
4. The improvement of claim- 1, wherein the supply passage to the chamber is a tube which surrounds the shaft connecting the motor and grinding wheel with a clearance sufficient to allow passage of the air, and wherein at least one opening in the part of the machine body surrounding said shaft communicates with the chamber.
5. The improvement of claim 4, wherein the tube nearest the grinding wheel is composed of two separable parts, of which one, in the form of an external sleeve, extends somewhat along the inner tube in an axial direction and is securely connected to the radial inner edges of the walls of the shield thereby to support said shield and form the inner of the defining walls of the chamber, while the inner tube extends up to the motor and is connected with its casing.