Patent Application
20230304400
The present invention relates to rotatable cutting tools, and more particularly retainers for rotatable cutting tools having controlled hardness.
Rotatable cutting tools are used in a variety of applications and are often used in road milling operations. The rotatable cutting tools often include a bit, a washer, and a retainer. The bit often includes a shank. A retainer is placed around the shank of the bit in order to retain the tool in the holder during operation and protect the holder from wear due to the rotation of the cutting tool. Many technological developments have increased the life of the rotatable cutting tool bits. As the life of the bits have increased, the shank of the rotatable cutting tool bits can become the limiting factor in the life of the bit due to wear experience by the shank during operation of the bit. Several attempts have been made to increase the life of the shank, including body coatings of the shank and plasma transferred arc (PTA) hard-facing of the shank. However, the body coatings do not last long enough and the PTA hard-facing decreases the life of the retainers due to wear and decreases the shank fatigue life. There is a need to increase the life of the shank while also not decreasing the life of the retainers.
The present invention provides rotatable cutting tools with bits and retainers. The retainers surround at least a portion of a shank of the bit. The hardness of the retainers is controlled to selected levels less than the hardness of the shank of the bit. Cutting tools of the present invention address the issues mentioned above by providing cutting tools with retainers having controlled lower hardness than the shank of the cutting tool bit.
An aspect of the present invention is to provide a cutting tool comprising a shank comprising a shank outer surface and a retainer comprising a retainer inner surface at least partially surrounding the shank outer surface. The retainer has a controlled hardness less than a hardness of the shank selected to reduce wear between the shank outer surface and the retainer inner surface.
Another aspect of the present invention is to provide a method of assembling a cutting tool, comprising installing a low hardness retainer around a cutting tool bit shank, wherein the low hardness retainer comprises an inner surface at least partially surrounding an outer surface of the bit shank, and the inner surface has a controlled hardness less than a hardness of the bit shank selected to reduce wear between the bit shank outer surface and the low hardness retainer inner surface.
These and other aspects of the present invention will be more apparent from the following descriptions.
Two different orientations of the washer 300 are illustrated in
The bit shank 160 may be cylindrical in shape. The bit shank 160 may have a shank length Ls measured along the longitudinal axis 500 that is at least 1.00 inches, for example, at least 1.20 inches or at least 1.40 inches. The shank length Ls may be at most 2.50 inches, for example, at most 1.70 inches or at most 1.50 inches. The shank length Ls may range from 1.00 inches to 2.50 inches, for example from 1.40 inches to 1.50 inches. The bit shank 160 may have an outer diameter Ds of at least 0.40 inches, for example, at least 0.60 inches or at least 0.65 inches. The bit shank 160 may have an outer diameter Ds of at most 1.20 inches, for example at most 0.80 inches or at most 0.67 inches. The bit shank 160 outer diameter Ds may range from 0.4 inches to 1.20 inches, for example, from 0.6 inches to 0.8 inches or from 0.65 inches to 0.67 inches.
The retainer 200, as shown in
The retainer inner diameter DR, when installed in a holder, may be at least 0.40 inches, for example, at least 0.60 inches or at least 0.67 inches. The retainer 200 may have an inner diameter DR of at most 1.40 inches, for example, at most 0.90 inches or at most 0.69 inches. The retainer inner diameter DR may range from 0.40 inches to 1.40 inches, for example, from 0.60 inches to 0.90 inches or from 0.67 inches to 0.69 inches.
When the rotatable cutting tool 100 is installed in a holder, and the washer 300′ is in the final position, there may be an average installed gap between the retainer inner surface 220 and the shank outer surface 162. The installed gap may vary after installation as the shank may shift during operation, causing some portions of the shank outer surface 162 to be closer to the retainer inner surface 220 than other portions of the shank outer surface 162. The installed gap may equal half of the difference between the retainer inner diameter DR and the shank outer diameter Ds when the rotatable cutting tool 100 is in the installed position. The installed gap may be at least 0.001 inches, for example, at least 0.003 inches or at least 0.005 inches. The installed gap may be at most 0.100 inches, for example, at most 0.050 inches or at most 0.020 inches. The installed gap may range from 0.001 inches to 0.100 inches, for example, from 0.003 inches to 0.050 inches or from 0.005 inches to 0.020 inches.
When surrounding at least a portion of the outer diameter Ds of the bit shank 160, the retainer 200 may extend along at least a portion of the shank length Ls. The length of the retainer LR may be less than, equal to, or greater than the shank length Ls. The retainer 200 may have a retainer length LR that is at least 1.0 inches, for example, at least 1.4 inches or at least 1.45 inches. The retainer length LR may be at most 2.0 inches, for example, at most 1.6 inches or at most 1.55 inches. The retainer length LR may range from 1.0 inches to 2.0 inches, for example from 1.45 inches to 1.55 inches.
The retainer 200 includes a retainer gap 230 extending axially along the length of the retainer in a direction parallel with the longitudinal axis 500 from the retainer outer surface 210 to the retainer inner surface 220. The retainer gap 230 may be defined by a gap angle AG.
The retainer 200 may include at least one retainer indent 240, for example two, three, or four retainer indents 240, structured and arranged on the retainer inner surface 220. The retainer indent 240 may extend radially inward from the retainer inner surface 220. The retainer indent 240 may include a curved indent inner surface 242, a flat indent rear surface 244, and an angled or rounded indent front surface 246.
The bit shank 160 may include a radially inwardly extending shank groove 164 for a portion of the shank length Ls away from the bit shank bottom surface 170. The shank groove 164 may have a groove outer diameter DG that is smaller than the shank diameter Ds. The shank groove 164 may be structured and arranged to receive the at least one retainer indent 240. The flat indent rear surface 244 may be structured and arranged to engage the shank groove 164. The flat indent rear surface 244 may engage with the shank groove lower edge 168 when installed around the bit shank 160 such that it prevents the retainer 200 from moving behind the shank groove 164 after installation.
When the washer 300′ is in the final location against the bit body 150, and the retainer 200 expands, coming in contact with the bore of the holder, relative axial movement between the retainer 200 and the bit shank 160 is prevented while still allowing rotational movement between the bit shank 160 and the retainer 200. Axial movement is prevented by the flat indent rear surface 244 that comes in contact with the shank groove lower edge 168 when the bit shank 160 attempts to move in the forward axial direction. During rotational movement of the bit shank 160 in the retainer 200, the shank groove 164 may freely move around the retainer indent 240, allowing the bit shank 160 to rotate within the retainer 200. Therefore, during operation of the rotatable cutting tool 100, the shank 160 may rotate within the retainer 200 while the retainer 200 prevents the bit shank 160 from moving in the axial direction (e.g., forward relative to the retainer 200).
During operation of the rotatable cutting tool 100, the retainer inner surface 220 may engage with the outer surface 162 of the bit shank 160, causing wear. A retainer 200 may usually be made of spring steel with a hardness in the range of 47 to 50 Rockwell Hardness Scale C (HRC) while a bit shank 160 is generally made of steel with a hardness in the range of 45-50 HRC. HRC values may be measured using the standard method described in ASTM standard E0018-20.
In accordance with the present invention, having a retainer 200 with a controlled hardness that is substantially less than the hardness of the bit shank 160 has been found to result in decreased wear of the bit shank 160, as well as minimizing wear of the softer retainer. In conventional pairings of retainers and bit shanks, the hardness of the shanks and retainers are about the same, for example, the hardness of the retainer is in the range of 47 to 50 HRC and the hardness of the bit shank is in the range of 45-50 HRC. However, when the hardness of the bit shank 160 remains in the range of 45 to 50 HRC, for example 47 to 50 HRC, and the hardness of the retainer 200 is decreased to a range of 38 to 44 HRC, for example 39 to 43 HRC or 40 to 42 HRC, then the wear of the bit shank 160 is minimized while also resulting in minimal wear of the retainer 200. The wear of the retainer 200 with a hardness in the range of 38 to 44 HRC, 39 to 43 HRC, or 40 to 42 HRC may be similar to the wear experienced by a retainer 200 with a hardness in the range of 47 to 50 HRC when the bit shank 160 has a hardness in the range of 45-50 HRC. Generally, it would be expected that a decrease in hardness of the retainer 200 would result in increased wear on the retainer 200. However, with these hardness values for the retainer 200 and the bit shank 160, it has been seen that a lower hardness of the retainer 200 can still result in a significant decrease in wear of the bit shank 160 without sacrificing significant additional wear on the retainer 200.
As used herein, the terms “low hardness” and “lower hardness” when referring to the retainer 200 means the retainer 200 has a controlled hardness less than the hardness of the bit shank 160 in which the retainer 200 is installed. In some non-limiting embodiments or aspects, the bit shank 160 may be at least 1 HRC harder than the retainer 200, for example, at least 2 HRC, at least 3 HRC, at least 4 HRC, at least 5 HRC, at least 8 HRC, or at least 11 HRC harder than the retainer 200. The bit shank 160 may range from 2 to 11 HRC harder than the retainer 200, for example, from 4 to 9 HRC harder or from 6 to 7 HRC harder than the retainer 200.
The hardness of the retainer 200 may be decreased by tempering and/or heat treating the retainer 200 at elevated temperatures and selected times, which can be determined by those skilled in the art without undue experimentation. The tempering of the retainer 200 may occur after initial hardening of the retainer 200. A retainer 200 may be tempered once, twice, or more in order to obtain the desired hardness.
In some non-limiting embodiments or aspects, the retainer 200 may include a steel, such as a spring steel. For example, the retainer 200 may include 1070 grade spring steel, or other spring steals, such as 1050, 1060, 65Mn, and/or the like. The 1070 grade spring steel may include carbon in the range of 0.65%-0.75% by weight and manganese in the range of 0.60%-0.90% by weight. The 1070 grade spring steel may also include sulfur in the range of 0% to 0.050% by weight and/or phosphorous in the range of 0% to 0.040% by weight. A majority of the balance of the composition by weight may include iron. The bit shank 160 may include known steels, such as 4140, and/or the like.
In some non-limiting embodiments or aspects, the retainer 200 may include 65Mn steel. The 65Mn steel may include carbon in the range of 0.62% to 0.70% by weight, silicon in the range of 0.17% to 0.37% by weight, manganese in the range of 0.90% to 1.20% by weight, phosphorous in the range of 0% to 0.035% by weight, and sulfur about in the range of 0% to 0.035% by weight. The 65Mn steel may also include chromium in the range of 0%-0.25% by weight, nickel in the range of 0%-0.25% by weight, and/or copper in the range of 0%-0.25% by weight. A majority of the balance of the composition by weight may include iron.
The retainer 200 may be made of the same or a different material than the bit shank 160. The bit shank 160 may be made of the same or different material than the bit body 150. The retainer 200 may be composed entirely or mostly of a spring steel, such as 1070 grade spring steel or 65Mn steel. The retainer 200 may have a majority of the composition having the same hardness. At least 85% of the retainer 200 may have hardness in the range of 39 to 43 HRC, for example, at least 90% or at least 95% of the retainer may have a hardness in the range of 39 to 43 HRC. The retainer 200 may be able to achieve the hardness of 39 to 43 HRC without the use of any cladding, coating, and/or hard facing of the retainer inner surface 220. In some non-limiting embodiments or aspects, the entire cross-sectional area of the retainer 200 may be a constant hardness, e.g., the same hardness. The entire cross-sectional area of the bit shank 160 may be a constant hardness, e.g., the same hardness.
A radial thickness of the retainer 200 may be defined between the retainer outer surface 210 and the retainer inner surface 220. The hardness of the retainer 200 may be substantially constant throughout the radial thickness of the retainer 200 in the radial direction. A radial thickness of the bit shank 160 may be defined by the shank outer surface 162. The hardness of the shank 162 may be substantially constant throughout the radial thickness of the bit shank 160.
Illustrating the invention is the following example that is not to be construed as limiting the invention to their details.
Bit shank and retainer hardness, as well as wear characteristics, were measured on assemblies including standard bit shanks and standard retainers, in comparison with standard bit shanks and lower hardness retainers of the present invention. In addition, retainer wear characteristics were measured on assemblies including standard retainers and bit shanks having PTA hard-facing.
In all retainer sets, the bit shanks of the standard retainer sets were made of 4140 type steel. In the case of the PTA hard-facing bit shanks, the 4140 type steel was coated with a standard PTA hard-facing material. The hardness values of the standard bit shanks (without PTA hard-facing) were measured to be between 45 and 50 HRC, measured by ASTM standard E0018-20.
In all retainer sets, the retainers were made of 1070 spring steel. The standard retainers had hardness values measured to be between 47 and 50 HRC, measured by ASTM standard E0018-20. The lower hardness retainers were produced by tempering standard hardened retainers at elevated temperatures for sufficient time to reduce hardness to desired levels of between 39 and 43 HRC.
Wear tests were conducted for assemblies with standard shanks and standard retainers, standard shanks and lower hardness retainers, and PTA hard-facing shanks and standard retainers. Approximately 60 rotatable cutting tools for each of the different types of assemblies, totaling 180 rotatable cutting tools, were installed into holders which were attached to blocks on a rotating cutting drum installed in a standard road milling machine. The blocks were arranged in a 15 millimeter spacing pattern as commonly used in the road construction industry. The machine, equipped with rotatable cutting tools including tools of standard retainers, tools with lower hardness retainers, and tools with hard facing on the shank with standard retainers, was then run for 4 days milling approximately 2 inches of asphalt from the road surface. Each day the machine was run for approximately 9 hours. During operation the cutting drum rotated at approximately 110 rpm and cool water was constantly sprayed on the tools as the drum rotated. The cutting speed of the machine was approximately 115 feet per minute. At the end of the four days all of the tools were removed from the holders and the wear of the shanks and retainers on a portion of the tools was measured. The total asphalt cut was 43,579 yd2.
The standard and lower hardness retainer sets were measured to determine the amount of wear of the components. The measurement of the amount of wear was conducted by measuring diameters of the bit shanks before and after milling, and by measuring radial thicknesses of the standard retainers and lower hardness retainers before and after milling, using standard measuring equipment such as digital calipers and micrometers. For the bit shanks, wear testing was conducted at the upper portions and the lower portions of the bit shanks. The amount of wear is measured in terms of inches of material removed from the outer diameters of the bit shanks and inner diameters of the retainers.
Results of the wear testing are shown in
When the average hardness of the shank is between 45-50 HRC and the average hardness of the retainer is decreased to between 39-43 HRC, the average wear of the upper portion of the bit shank is 0.0154 inches of material loss after the 4 days of testing. The average wear of the lower portion of the bit shank is about 0.0084 inches of material loss after the 4 days of testing.
As can be seen in
Also shown in
The data in this example demonstrate that when the hardness of the retainer is decreased from 47-50 HRC to 39-43 HRC, average shank wear is decreased both in the upper portion and the lower portion of the bit shank. However, the average wear of the retainer remains about the same despite the decrease in the retainer hardness. The data also demonstrates that using wear protection on the shank with a standard retainer causes a significant increase in material loss of the retainer, thus causing a significant decrease in the life of the retainers.
As used herein, “including,” “containing” and like terms are understood in the context of this application to be synonymous with “comprising” and are therefore open-ended and do not exclude the presence of additional undescribed or unrecited elements, materials, phases or method steps. As used herein, “consisting of” is understood in the context of this application to exclude the presence of any unspecified element, material, phase or method step. As used herein, “consisting essentially of” is understood in the context of this application to include the specified elements, materials, phases, or method steps, where applicable, and to also include any unspecified elements, materials, phases, or method steps that do not materially affect the basic or novel characteristics of the invention.
For purposes of the description above, it is to be understood that the invention may assume various alternative variations and step sequences except where expressly specified to the contrary. Moreover, all numbers expressing, for example, quantities of ingredients used in the specification and claims, are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
It should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.
In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances. In this application, the articles “a,” “an,” and “the” include plural referents unless expressly and unequivocally limited to one referent.
In this application, the use of “horizontal”, “vertical”, “positive” and “negative” are used as relative terms and it is understood that during use the d rotatable cutting tool may have different orientations.
Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.
