Means for finishing workpieces of irregular shapes

Nov. 20, 1951

H. D. COE, JR., ET AL

2,575,656

MEANS FOR FINISHING WORKPIECES OF IRREGULAR SHAPES

Filed Nov. 26, 1948

<img file="US2575656A_D0001.tif" />

<img file="US2575656A_D0002.tif" />

WITNESSES:

<img file="US2575656A_D0003.tif" />

BY

INVENTORS

Harry D.Coe,Jr.and Joseph B.Oym.

<img file="US2575656A_D0004.tif" />

ATTORNEY

Patented Nov. 20, 1951

2,575,656

UNITED STATES PATENT OFFICE

2,575,656

MEANS FOR FINISHING WORKPIECES OF IRREGULAR SHAPES

Harry D. Coe, Jr., and Joseph B. Dym, Pittsburgh, Pa.

Application November 26,1948, Serial No. 62,102

Claims. (

Our invention relates to methods and means for grinding, sanding, polishing or otherwise finishing irregularly shaped surfaces of workpieces such as turbine blades, hardware, streamlined appliance parts, cams, etc. J

In the manufacture of irregularly shaped bodies it has been a problem to accurately obtain the desired or theoretically correct surface. For instance, with turbine blades of irregular contour, the conventional practice has been to 1 forge or cast the material as close as possible to the desired shape and then improve the finish and correct the shape by hand polishing. The blades are alternately held against an abrasive polishing wheel and checked against profile gages 1 at three points until the desired shape is obtained. This method is not only time consuming, but the attainable accuracy depends only upon the skill and judgment of the operator.

It is an object of our invention to provide meth- 4 ods and means that afford bringing irregular bodies into the desired shape with any desired degree of accuracy and in considerably less time than heretofore required.

Another object of the invention is to greatly ! reduce the skill required for obtaining accurately finished surfaces and to render the accuracy uniform over the whole finished surface. These and other objects of oui· invention will be apparent from the following description. 3

Tn accordance with the invented method, we provide a rigid form block or matrix with an irregular matrix surface that substantially matches the irregular surface to be finished, and we run an abrasive belt with its smooth side over ; the form block while keeping the belt slack. We further hold the workpiece to be finished on the abrasive side of the running belt against the matrix surface of the form block so that, due to the slackness of the belt, the belt adapts itself to the irregular matrix surface. In this manner, the workpiece can be accurately finished merely by holding or forcing it toward the formpiece without requiring special skill and within a period of only a small fraction of the time t necessary for the above-mentioned conventional method.

If the workpiece surface is deeply concave, the belt is run directly over a correspondingly convex form block with the abrasive side out and so I guided that it approaches and leaves the block approximately tangential to the surface at the first and last points of contact respectively. If the surface of the form block or workpiece is sufficiently conical to give the belt the tendency to &lt;

Cl. 51—141) run off the form block, an auxiliary form block of similar shape is provided in reversed relation to the active form block to correct this tendency. If the surface to be finished is convex or a com5 bination of concave and convex, the abrasive belt· is run with no initial, or no appreciable tension and enough slack to adapt itself to the concave matrix surface area of the form block. The larger degree of slack thus required may make it difficult 0 to drive the abrasive belt with belt wheels in the ordinary manner. However, the belt can then be forced against the belt wheels to secure the necessary traction. One way of doing this is to use vacuum on the belt wheels to suck and hold the ;5 running abrasive belt against the wheels. This vacuum method may lead to objectionable noise. According to another and preferred procedure, we run a drive belt together with the abrasive belt over the wheels and keep both belts in face-to20 face contact over a sufficient length to secure the needed traction so that a portion of the abrasive belt can then run free and slack.

The above-mentioned methods, as well as examples of devices suitable for performing these 25 methods, will be understood from the following description of the embodiments illustrated in the drawing, in which:

Figure 1 shows diagrammatically a machine for finishing turbine blades or other workpieces ¢) with deeply concave surfaces,

Fig. 2 shows a top view of the workpiece, abrasive belt and form block of the same machine; and

Fig. 3 is. a diagrammatical illustration of an15 other machine especially designed for finishing convex a slightly convex surface.

The machine illustrated by Figures 1 and 2 is equipped with a drivestand I for a belt driving wheel 2 whose shaft 3 has bearings rigidly to inounted on the stand. The running direction of the driving wheel 2 is indicated by an arrow 4. A backstand 5 of the machine is equipped with an idler wheel 6 whose shaft 7 is journalled in a link structure 8 pivoted at 9 to the stand 5. The (5 link structure 8 is biased by a weight 10 and tends to move the idle wheel away from the driving wheel, thus maintaining the abrasive belt 11 in sufficiently taut condition to secure the necessary traction while permitting the belt to yield and become slack at the place of the form block described presently.

A workstand 12 located betwen a drivestand and backstand carries a belt guiding wheel ! 3 and a form block or matrix 14. The form block is ⁵⁵ rigidly attached to the workstand. Its matrix

2,575,656 surface has an irregular shape in order to permit finishing the correspondingly irregular surface of a turbine blade or other workpiece in accordance with the above-described method. The machine, according to Fig. 1 is especially de- 5 signed for finishing workpieces with deeply concave surfaces. In the illustrated embodiment, this surface is assumed to be generally conical so that the form block 14 may cause the abrasive belt IJ to run off the matrix surface. In order to jo prevent this, an auxiliary or compensating form block i 5 is also mounted on the workstand; The compensating form block has about the same shape as the main form block i 4, but is arranged in the reverse direction, i. e., the tapering side of is its surface points to the other side of the belt and hence compensates for the tendency of the belt to run off the form block 14.

Two guides 16 and 17 are provided in order to facilitate placing the workpiece 18 in the proper 20 position on the abrasive side of the belt. When the belt is running and the workpiece i 8 held on the abrasive belt side against the matrix surface of the form block 14, the belt assumes sufficient slackness between the driving wheel and the form 25 block to permit the belt portion at the matrix surface to adapt itself to that surface. As a result, the workpiece surface is finished with the desired accurate shape without requiring special skill and within a period of time much shorter 30 than otherwise required. A water spray nozzle is denoted by 19 and an arrow 20 indicates the feeding direction for the workpiece 18. The arrangement of the form block 14 is preferably such that the belt (( approaches and leaves the 35 block approximately tangential to the matrix and workpiece surface at the first and last point of contact respectively.

The machine illustrated in Fig. 3 has a drivestand 21 for the driving wheel 22. As in the 40 machine of Fig. 1, the bearings for the wheel shaft 23 are rigidly mounted on the stand; The driving direction of the wheel is indicated by an arrow 24. A hackstand 25 carries an idler wheel 26. The shaft 27 is journalled in a struc- 45 ture 28 that is pivoted at 29 to the stand 25 and biased by a weight 30. The abrasive belt 31 Which extends around the drive wheel 22 and idler wheel 26 passes over the matrix surface of a convex form block 34, which is mounted on a 50 workstahd 32. The workstand 32 is also equipped with guides 36 and 37 for the workpiece 38 and with a water spray nozzle 39. In order to permit the belt to adapt itself closely to the concave matrix surface while running over the form block, 55 a larger amount of yielding or slackness is required than with convex matrix surface. Consequently, the traction of the driving wheel may become insufficient to pull the belt over the form block when the workpiece is fed against the block, qq In order to secure the necessary traction, the machine according to Fig. 3 is equipped with an auxiliary rubber belt 40. This belt is endless like the abrasive belt, but has greater length so that it lies in face-to-face relation with the abrasive eg belt on only one side of the wheels but is spaced from the abrasive belt at the other side. In order to maintain the proper spacing and for. keeping the auxiliary traction belt in taut condition, a pressure roller 4i engages the belt 40. The roller 70 4 f is journalled on an arm 42 pivoted at 43 to the workstand 32 and secured in the desired position by means of an adjusting screw 44.

. When the machine is in operation and the workpiece. 38 held on the abrasive side of belt 31 n against the form block 34, the belt portion between the driving wheel 22 and the form block 34 can run with any suitable degree of slackness without reducing the traction below the required amount.

Methods and means, according to the invention, are applicable with advantage for the finishing of a large variety of irregular surfaces, i. e., of surfaces that are neither plane nor straight cylindrical or straight conical and hence cannot readily be shaped by conventional turning, shaping and grinding devices. Aside from the fact that the invention secures a high accuracy and requires less skill, the fabricating method used for bringing the workpiece surface into approximately the desired shape before finishing need not be so closely controlled as is necessary in the conventional procedure, thus lowering the amount of rejects and further reducing the finishing cost. For example, in machines built and operated according to the invention for finishing gas turbine blades, the overall savings afforded by the invention in comparison with the conventional methods amounted to approximately 80%.

The invention also affords a very simple method of forming and redressing the matrix blocks. For such purposes, it is merely necessary to reverse the belt so that its abrasive side runs over the matrix block to be finished or redressed, and to hold a master workpiece on the smooth belt side against the matrix block.

It will be obvious to those skilled in the art after a study of the present disclosure, that devices according to the invention can be modified as respects various design details and components without departing from the essence and features of our invention and within the scope of the claims annexed hereto.