Claims
- 1. A centrifugal shotting turbine comprising:
- a pair of parallel spaced flanges having a common central axis perpendicular to the surfaces thereof, each of said flanges having a plurality of radial grooves extending to the outer rim of said flanges on the inside surface thereof;
- a shot delivery device interposed between said flanges and coaxial with said central axis;
- a plurality of bearing pins, one of said pins being located in each of said radial grooves at the end remote from said central axis;
- a plurality of springs, one of said springs being located in each of said radial grooves at the end nearest said central axis;
- a plurality of blades each having a pair of longitudinal fillets extending from opposite edges thereof, the working face of each of said blades having a longitudinal profile which is convex adjacent said delivery device and concave at greater radial distances from said delivery device, the radial fillets on each of said blades fitting into corresponding grooves on said flanges between said bearing pins and said springs, the pressure of said springs securely holding said blades in position between said flanges, said blades being easily replaced and being shaped so as to project shot at a high rate of ejection in a concentrated jet.
- 2. A turbine according to claim 1 wherein each of the grooves in said flanges comprises first and second parts separated by a ledge near the end of said groove remote from said central axis, said first part including a recess containing said bearing pin on one side of said ledge for receiving one end of said fillet and retaining it therein, said second part extending to the rim of said flange on the other side of said ledge to permit the insertion and removal of said blade.
- 3. A turbine according to claim 1, wherein the convex part has a uniform angle of curvature.
- 4. A turbine according to claim 1, wherein the convex part has a variable angle of curvature.
- 5. A turbine according to claim 1, wherein the concave part comprises a zone having a variable angle of curvature.
- 6. A turbine according to claim 1, wherein the concave part comprises a zone having a variable angle of curvature and a zone having a uniform angle of curvature.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 46239 |
Nov 1977 |
BEX |
|
BACKGROUND OF THE INVENTION
This application is a continuation-in-part of copending U.S. Application Ser. No. 962,190 filed Nov. 20th, 1978, now abandoned.
The present invention relates to a shotting turbine. In particular, it relates to a shotting turbine wherein the rate of ejection of the shot and concentration of the jet containing the shot is superior to that of known shotting turbines. Further, in accordance with my invention, the turbine blades, when worn, are easily removed and replaced.
A shotting turbine is used to project shot onto the surface of a metal part so as to give the surface of the part a desired state of roughness. Such turbines, which are conventionally of the centrifugal type, comprise a pair of flanges, a central delivery device which provides a supply of shot, and a plurality of blades or vanes attached to one or both flanges and arranged radially around the delivery device. The effective surfaces of these blades are usually plane and of uniform width, and the method of attachment makes the blades difficult to remove and replace.
The impact of a particle can be expressed in terms of its energy E=(m V.sub.R.sup.2)/2, where m is the mass of the particle, and V.sub.R is the rate of ejection.
The conventional straight blade arrangement projects the shot at a rate of ejection which is directly dependent on the rate of rotation of the turbine. However, in certain cases, this rate is too low to obtain the desired degree of roughness.
For example, rolling-mill rolls are often so hard that the desired degree of roughness cannot be achieved with a straight blade arrangement. Like any machine, the shotting turbine has a limiting speed which cannot be exceeded with safety and without undue wear. The straight blade arrangement limits the rate of ejection of the shot to a value corresponding to the maximum rate of rotation of the turbine.
Moreover, the differential wear of the blades and the flanges often causes imbalances which prevent very high rates of rotation from being effected. As is known, these imbalances are a function of the square of the rate of rotation.
The straight blade arrangement is also disadvantageous because it produces a jet of shot which is spread out both in the direction of movement of the turbine and in the transverse direction. To take a specific example, with a turbine rotating at a speed of 2,500 revolutions per minute and having straight blades with a uniform width of 60 mm, the spreading of the jet gives at a distance of 500 mm from the turbine a jet having an impact length of approximately 793 mm and an impact width of approximately 80 to 90 mm. It has been established that if the central part of the jet produces a uniform roughness on the surface which it touches, the marginal parts of the spread jet contain particles of shot which rebound on the surface to be shot, break down and have an impact effect which is prejudicial to the efficiency of the operation. This spreading of the jet thus appreciably limits the impact force of the jet and is especially troublesome in the shotting of parts which have a curved surface.
The blades of the shotting turbines wear rapidly, primarily as a function of the speed of rotation of the turbine. Accordingly it is necessary to replace them at frequent intervals.
An object of the invention is to provide a shotting turbine having blades profiled so as substantially to improve the rate of ejection of the shot and the concentration of the jet.
Another object of the invention is to provide a shotting turbine having blades which, when worn, can easily and rapidly be replaced.
A higher rate of ejection has definite advantages. In the first place, to obtain the same level of roughness the rate of rotation can be reduced from that required with a lower ejection rate. The rate of rotation of the turbine is an important element since, in a shotting turbine, the differential wear of the blades and flanges brings about troublesome imbalances (vibrations). These imbalances are a direct function of the square of the rate of rotation and are decreased by reducing the rate of rotation. It is important to minimize as much as possible these disruptive forces and an extremely effective means is to reduce the rate of rotation of the turbine.
On the other hand, a higher rate of ejection than is possible with the straight blade arrangement permits higher degrees of roughness to be obtained for the same rate of rotation. In the particular case of rolling-mill rolls, the roll hardnesses achieved at the present state of the art cannot be increased since it would then be impossible to attain the required degree of roughness. Thus, a compromise must be accepted between the desired degree of roughness and the roll hardness, the roll hardness being made as high as possible while still permitting attainment of the required degree of roughness.
For example, with angular shot composed of particles havng an average size of 0.40 mm and with a roll hardness of 730-750 Vickers hardness under a load of 30 kg (HV), the maximum degree of roughness reached is 200 .mu." (CLA: Center Line Average). If the roll hardness is increased by 30 points on the Vickers hardness scale, the maximum possible degree of roughness will be, for example, 170.mu." (CLA).
The improvement in the concentration of the jet of shot brings about a reduction in the spread of the jet, the effect of which is to increase the impact power of the jet for the same delivery of shot.
According to the invention there is provided a centrifugal shotting turbine comprising two parallel spaced flanges having a central axis perpendicular to the surfaces of the flanges. Interposed between the flanges and coaxial with the central axis is a shot delivery device. Also interposed between the flanges are a plurality of blades extending radially outward from the delivery device. Each blade is provided with a pair of longitudinal fillets extending from opposite edges thereof and has a working face with a longitudinal profile that, starting from the delivery device is first convex in shape and then concave.
Each of the flanges is provided with a plurality of radially extending opposite grooves on its inside face which receive the fillets on the turbine blade. Further, each groove contains a bearing pin at its outer end and a spring at its inner end which retain the turbine blade fillets firmly in position while permitting the blades to be easily removed and replaced. A fastening arrangement of this type is disclosed in my Belgian Patent No. 862,932 granted Feb. 15, 1978.
The working face of each blade preferably has a width which decreases progressively from its foot to its head.
US Referenced Citations (12)
Foreign Referenced Citations (5)
| Number |
Date |
Country |
| 862932 |
Feb 1978 |
BEX |
| 834341 |
Mar 1952 |
DEX |
| 559084 |
Feb 1975 |
CHX |
| 518803 |
Mar 1940 |
GBX |
| 743381 |
Jan 1956 |
GBX |
Continuation in Parts (1)
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Number |
Date |
Country |
| Parent |
962190 |
Nov 1978 |
|
Patent Grant
4277965
