US Patent: 2,396,505
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| Grinding
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Patentee:
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| Clarence Gumper (exact or similar names) - West Haven, New Haven County, CT |
| Manufacturer: |
| Not known to have been produced |
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Patent Dates:
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| Applied: |
Jun. 22, 1943 |
| Granted: |
Mar. 12, 1946 |
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Joel Havens
"Vintage Machinery" entry for Bridgeport Safety Emery Wheel Co.
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Description: |
| Abstract: Many times it is desired to grind cylindrical articles so as to finish or partially finish the external or peripheral surface thereof, or to reduce the article to a desired diameter. In the grinding of rubber and rubber like articles, great difficulty has long been encountered, for with such articles an excessive amount of heat is developed not only by the friction produced between the grinding wheel and the article but also by the energy consumed as a result of the progressive distortion or displacement of the relatively soft material by the grinding wheel as the latter is traveled along the rotating article to be ground. This excessive amount of heat results in burning or partially melting the article and causes the grinding wheel to deteriorate rapidly, requiring it to be frequently dressed and permitting its use for only a relatively short time. In addition to developing excessive heat, the drawing or distortion of the material of the article in the direction of the cut produces a hump which, becoming excessive, suddenly passes under the wheel. This causes the wheel and article to chatter leaving undesirable, rough and uneven surfaces on the article as evidenced by a discernible pattern produced on the surface thereof. Another difficulty has been that in grinding interrupted or broken cylindrical surfaces such as a disk with projections very much like gear teeth, it frequently occurred that although the grinding wheel was properly adjusted for successfully performing the operation on a number of pieces, it was not infrequent that the grinding wheel would bite into the projections and knock or rip them off, thus spoiling the piece. This happens most frequently when the article is made of a harder or less resilient rubber or rubber-like composition. It has been the practice heretofore to employ a wheel of reasonable width considering the amount of material to be removed from the article to be ground and the ability of the wheel to withstand the centrifugal force tending to disintegrate it at the high speeds at which such wheels are unnecessarily operated. It has been thought that the use of a narrower wheel, to reduce the operative width of the grinding Wheel and thus the number of abrasive grits which may be operative on the article to be ground at one time, would result in a slower and less efficient grinding operation, and this is probably true with regard to conventional grinding wheels. The use of a narrower wheel did not solve the problem, for it left the surface of the article patterned by rough uneven surfaces. However, the difficulties above referred to have been solved by the present invention by providing a grinding wheel of essentially the same width as conventional grinding wheels used for the same purpose, but having its grinding surface interrupted or divided by a space so as to form two (or more in the event that more than one space is provided) grinding surfaces to be presented seriatim to the article to be ground as the work progresses. I have found that when the grinding wheel is so divided, notwithstanding the fact that both surfaces operate in the same plane, the leading grinding surface removes the larger quantity of material to be ground off during the traverse of the work by the grinding wheel, and does so without excessive drawing of the material being ground, and that whatever stress is present in the material, as a result of the grinding operation by the leading grinding surface, it is relieved at the space between the two grinding sections so that the material resumes its normal position, leaving to the second grinding surface the comparatively light work of finish grinding, that is to say, smoothing off the chatter marks caused by the first grinding surface; and that the material after the second grinding surface has passed over it is comparatively smooth and free of any irregularities such as an objectionable pattern of chatter marks. I have found that the dividing groove may be quite narrow without reducing the efficacious operation of the wheel. For instance, I have found that with a 10" diameter wheel having a width from edge to edge of 1", the groove may be only wide to obtain the desired results as above stated. The groove may have any desired depth depending upon the amount which the wheel may be worn or dressed off before it is discarded and depending upon the strength of the bonding medium in the wheel to resist disintegration of the narrowed wheel sections due to the centrifugal force developed at the high speeds at which such grinding wheels are used. 'With the particular composition which I employ which has a Bakelite base, I have found that the groove in a 10" wheel such as above described may be at least 1" deep. In the operation of the wheel of the present invention, when taking a cut of the same depth as would be done with a conventional wheel and which would then result in excessive overheating not only of the article being ground but also of the wheel and driving motor, it has been found unexpectedly that the temperature of the article being ground has not been substantially or excessively raised nor does the motor operate at a temperature higher than any other electric motor developing its full power. Likewise, the wheel is not excessively hot. In fact, the temperature of the article, the grinding wheel and the motor is such that the article being ground and the motor may be touched by the hand without danger of burning, an act which would be extremely dangerous with a conventional grinding wheel. I do not have any definite or conclusive understanding as to the reason for the development of so little heat with the use of the wheel of the present invention. I simply know it to be a fact. One theory advanced is that since the distortion and displacement of the material being ground is relieved when the space between the two grinding surfaces is reached, less useless work is performed with the resulting development of less heat. The grinding wheel is usually employed in connection with a blower system which sucks in fresh air as well as the dust from the grinding operation. In view of this, another theory for the reduction of operating temperatures and thus the prolonging of the life of the wheel and the reduction of spoilage of the articles being ground, is that the work of grinding off the material is distributed between two grinding portions of the wheel which rotate in an atmosphere of continuously fresh air and having a groove between them radiate their heat more rapidly. However, experiments have not established either theory conclusively, and it may be that the reasons for the improved results obtained by the use of the wheel of the present invention is a combination of those above suggested and possibly some others as yet unknown. The present invention may be applied in various sorts of ways to existing or conventional wheels and to wheels of various shapes and sizes, so long as the leading and trailing grinding surfaces operate in substantially the same plane. Claims: 1. The method of grinding rubber-like articles which includes the steps of adjusting a rotating grinding Wheel to take a cut of desired depth in a rotating article; feeding the wheel along the article, the article being relieved of grinding stress at a place between leading and trailing sections of the wheel which have a straight-line contact with a tangential plane. 2. The method of grinding rubber-like articles which includes the steps of rotating an article contacting the article with a grinding wheel having a straight line contact with a tangential plane parallel to the axis of rotation of the article to take a cut of desired depth while feeding the wheel along the article, the article being relieved from contact with the wheel intermediate the edges of the wheel, and again immediately contacting the wheel with the article as the wheel travels there along. 3. The method of grinding rubber-like articles with a wheel having a straight line contact with a tangential plane which includes the steps of contacting the work with a leading section of the wheel to take a desired out while feeding the wheel along the article; and contacting the article with a trailing section of the wheel which is in substantially the same plane of contact as the leading section and spaced from the latter by a gap, the article opposite the gap being relieved of grinding pressure from the wheel. 4. The method of grinding rubber-like articles with a wheel having a straight line contact in a tangential plane which includes the steps of taking a full depth cut with the leading section of the wheel while feeding the wheel along the article, and finish-cutting the surface with a trailing section of the wheel, the article being relieved of grinding pressure immediately after the first cut by the leading section of the whee |
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