Abstract:
A system and method for sealing a live center is provided. The live center has a spindle disposed, at least in part, within a housing, bearings provide a rolling connection between the spindle and the housing, and a labyrinth seal is mounted to at least one of the spindle and the housing and is configured to reduce an amount of contaminant from entering the housing. A method of sealing a live center is also provided. In some embodiments of the invention, the method includes restricting a fluid path along a spindle, defining the fluid path to have a labyrinth section, providing a drain to the outside of the live center for fluid moving along the path and substantially blocking the path of the resilient seal.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to sealing a live center for use with a lathes, grinders, mills, and other machine tools. More particularly, the present invention relates to sealing the spindle portion of the live center with the housing for both resistance against contaminants entering the live center and retaining lubricating oil or grease within the bearings of the live center. 
   BACKGROUND OF THE INVENTION 
   Machine tools generally hold a work piece at one end with a chuck. Often, the other end of the work piece will be supported, steadied or otherwise contacted by a live or dead center. A dead center is a device that contacts a work piece without rotating. A live center is a device that contacts a work piece and the portion of the center that contacts the work piece rotates along with the work piece. 
   The portion of the live center that rotates along with the work piece is known as a spindle. The spindle is mounted within a housing where the housing of the live center generally does not rotate. Bearings are used to support and facilitate the rotation of the spindle within the housing. Often, it is desirable to provide lubrication for the bearings. In instances where lubrication is used, oil can leak out of the live center or seep along the spindle thus depriving the bearings of lubrication. 
   Accordingly, it is desirable to provide a method and apparatus that substantially seals the oil within the live center so that the oil can provide lubrication for the bearings. 
   Live centers are also hampered by other problems. For example, modern manufacturing techniques include using heavy amounts of coolant, also referred to as cutting fluid, when working on a work piece in a machine tool. The work piece may be constantly subjected to a high-pressure stream or streams of fluid which provide several functions. Among the functions performed are that the coolant keeps the work piece and cutting tool cool, and removes chips and other unwanted material from the area being cut by the cutting tool. 
   The cutting fluid may have in suspension chips or material of the work piece that has been removed by the cutting process. Should some of this fluid and its accompanying material enter the live center, it could potentially interfere with the rotation of the spindle within the live center. For example, chips could jam between the spindle and some other portion of the live center such as the bearings. Also, the chips or material can damage the bearings and bearing races preventing them from operating efficiently or, in the extreme case, jam the spindle from rotating. Alternatively, cutting fluids usually degrade the effectiveness of the lubricant used in the bearings, again creating a variety of problems. 
   Accordingly, it is desirable to provide a method and apparatus which substantially seals the interior of the live center from contaminants such as cutting fluid, chips and other unwanted material from entering the live center. 
   SUMMARY OF THE INVENTION 
   The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect, an apparatus and method is provided that in some embodiments substantially seals the live center to contain lubricating oil within the areas within the live center where the lubricating oil is desired and reduces the amount of the likelihood of the lubricating oil working its way out of the desired areas and depriving the bearings and other moving parts from the benefits of lubrication. 
   In another aspect an apparatus and method is provided that in some embodiments substantially seals the live center from contaminants such as cutting fluid, chips and other unwanted material from entering the live center and potentially interfering with the rotation of the spindle within the housing and/or reducing the effectiveness of the bearings within the live center. 
   In accordance with one embodiment of the present invention, a live center is provided. The live center includes a housing, a spindle disposed, at least in part, within the housing; bearings providing a rolling connection between the spindle and the housing; and a seal mounted to at least one of: the spindle and the housing; and configured to reduce an amount of contaminant from entering into the housing. In some embodiments of the invention, the seal is a labyrinth seal having a shield connected to the spindle and a cover connected to the housing. 
   In accordance with another embodiment of the present invention, the live center is provided. The live center includes a housing; a spindle mounted in the housing; a first seal for impeding contaminant from entering the housing along the spindle; a second seal for impeding contaminant from moving along the spindle; and a third seal for impeding contaminant from moving along the spindle. 
   In accordance with another embodiment of the present invention, a live center is provided. The live center includes a housing; a spindle located in the housing; a first sealing means for impeding fluid from moving along the spindle toward the housing; and a second sealing means for reducing a pressure associated with a contaminant when the contaminant contacts the first sealing means. 
   In accordance with yet another embodiment of the present invention, a method of sealing a live center is provided. The method of sealing the live center includes: restricting a fluid path along a spindle; defining the fluid path to have a labyrinth section; and substantially blocking the path with a resilient seal. 
   There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
   In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
   As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional side view of a live center in accordance with a preferred embodiment of the invention. 
       FIG. 2  is an enlarged side cross-sectional view of a front portion of the live center shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. An embodiment in accordance with the present invention includes a live center having several sealing elements designed and configured to reduce or eliminate contaminants such as cutting fluid, chips and other debris from entering the live center. In some embodiments of the present invention, other sealing means are employed to reduce the amount of lubricant from leaving the bearings within the live center. In some embodiments of the present invention, some of the sealing elements may provide the dual functions of excluding contaminants from entering the live center and retaining lubricant within the live center. 
     FIG. 1  illustrates the live center  10  in accordance with present invention. As shown in  FIG. 1 , the live center  10  includes a spindle  12 . The spindle  12  is located within the housing  14 . The rear portion of the housing  14  has a taper  16  that is configured to fit and mount in a lathe. The taper  16  shown is known as a number 5 Morse taper (MT). While a live center  10  having a number 5 MT is shown, other tapers or profiles may be used in accordance with the present invention and embodiments of the invention are not limited to that as shown. 
   The rear portion of the spindle  12  is supported by needle bearings  18  which permit the spindle  12  to rotate. The spindle  12  is also supported by ball bearings  20  which also permit the spindle  12  to rotate. Having the two sets of bearings  18  and  20  spaced from each other permit the spindle  12  to be supported and be able to turn. The ball bearings  20  comprise three elements. There is an inner race  22  that contacts the spindle  12 . There are the balls or rollers  24  and the outer race  26 . The outer race  26  contacts the housing  14 . In some embodiments of the invention, ceramic bearings are used. Ceramic bearings are hard and can provide rigidity and reduced friction. In other embodiments of the invention, steel bearings are used. While live center  10  shows needles and ball bearings, other bearing types may be used in accordance with the present invention. Embodiments of the invention are not limited to that as shown. 
   According to some embodiments of the present invention, the ball bearings  20  are lubricated by oil. Oil may be added to the ball bearings  20  by an oil inlet  28 . The oil inlet  28  is covered by a brass washer  30  held in place by a screw  32 . To add oil to the inlet  28 , the screw  32  and the washer  30  is removed and oil may be added. 
   During times of nonuse, the lubricating oil may drip down to the lower set of ball bearings  20  and form a film of oil reserve at the bottom of the housing. Once the spindle  12  starts to turn, the oil will be circulated around the spindle  12  and the ball bearings  20  will form a semi-even layer of oil throughout the ball bearings  20  and provide adequate lubrication. 
   From time to time, oil may work itself out of the area where the ball bearings  20  are. Some embodiments of the present invention have seals to inhibit the leaking lubricating oil out of the live center, and those seals will be discussed in more detail below. Other embodiments of the present invention may use other types of lubrication schemes for the bearings  20 . For example, grease or other lubricants may be used in accordance with the present invention. The discussion of oil being used as a lubricant is meant to be exemplary rather than limiting. 
   According to some embodiments of the present invention, a mid portion of the spindle  12  has threads  34  upon which a tightening nut  36  engages the threads and compresses the bearings  20  against a flange  38  located on the spindle  12 . To the left of the needle bearings  18  are internal threads  37 . Screwed into the treads  37  is a locking screw  39 . The locking screw  39  maintains lubricating oil within the live center while providing access to the needle bearings  18 . 
     FIG. 2  is an enlargement of a front portion of the live center  10  illustrated in  FIG. 1 .  FIG. 2  has been enlarged in order to show detail to provide clarity in explaining an embodiment of the invention. As shown in  FIG. 2 , a spindle  12  is mounted within the housing  14  where the housing  12  contacts the inner races  22  of the bearings  20 . According to some embodiments of the invention, oil is used to lubricate the bearings  20  and creates a fine coat on the inner races  22 , the balls or rollers  24  and the outer races  26  in order to facilitate free movement of the bearings  20 . 
   It is desirable to maintain the oil within the bearings  20  rather than allowing the oil to leak out of the live center  10 . An adaptor  40  is located on the housing  14  and is mounted to the housing  14  by a mounting screw  42 . Among other functions, the adaptor  40  has a channel  44  which houses an O-ring seal  46 . The O-ring seal  46  is made of a resilient material which in some embodiments of the invention may be rubber or any other suitable resilient material. The O-ring  46  is situated in the channel  44  to hinder or impede movement of oil from the bearings  20  along the boundary  48  between the housing  14  and the adaptor  40 . In the unlikely event that a contaminant such as cutting fluid occurs in the boundary  48  between the housing  14  and the adaptor  40 , the O-ring  46  will also hinder movement of that contaminant into the area where the bearings  20  are located. 
   In order to help prevent contaminating fluid such as cutting fluid and chips, and other debris, from entering the live center  10 , a number of features are provided on the embodiment of the invention shown in  FIG. 2 . For example, a labyrinth seal  50  is used. The labyrinth seal  50  includes two parts: a cover  52 , which is mounted to the housing  14  of the live center  10  via a mounting screw  42 . Optionally, as shown, the mounting screw  42  also attaches the adaptor  40  to the housing  14 . In other embodiments of the invention, the shield  54  may be attached in other suitable manners to the housing  14  either directly or via some other element such as the adapter  40  for example. The cover  52  is located close to the spindle  12  and provides a narrow gap  54  between the spindle  12  and the cover  52 . This narrow gap  54  is useful to prevent large contaminants such as chips and other undesirable debris from entering the interior of the live center  10 . The gap is wide enough to permit the spindle  12  to turn while the cover  52  remains stationary attached to the housing  14 . In some embodiments of the invention, the gap  54  is located 0.02 of an inch from the spindle  12 . Other embodiments of the invention may include gaps  54  located other distances away from the spindle  12 . 
   The other part of the labyrinth seal  50  is the shield  56 . The shield  56  is mounted onto the spindle  12  and in some embodiments of the invention, is press fit onto the spindle  12 . In other embodiments of the invention, the shield  56  may be integral with the spindle  12 . 
   In some embodiments of the invention, the shield and cover  52  are made of steel, however, they can also be made of other materials such as other metals, plastics, or other materials. One advantage of having the cover  52  and the shield  56  being made of steel or stainless steel is that the cover  52  and shield  56  can protect the interior of the live center  10  from heat. Current manufacturing techniques often involve heating a work piece while it is being worked on by a machine tool. In some instances the apparatus used to heat the workpiece can be located near the live center  10  and heat the live center  10 . Because of the relatively high heat capacity of steel, the shield  56  and cover  52 , if made of steel or stainless steel, can absorb a significant amount of heat before the heat enters into the live center. Reducing heat from entering the live center can aid in protecting interior pieces such as the contact seal  66  (discussed more below). 
   The cover  52  and the shield  56  together form a labyrinth path  58  for which the narrow gap  54  is the entrance. The labyrinth path  58  has turns to inhibit the flow or ingress of contaminants into the live center  10 . There is a large chamber  60  which is part of the labyrinth path  58 . As the fluid flows through the labyrinth path  58  at the entrance to the large chamber  60 , the pressure of the contaminating fluid will drop due to the well known phenomenon of pressure drop associated with a fluid expanding into a larger area. Thus, if contaminating fluid is located in the labyrinth  58  before the large chamber  60  will have a higher pressure than contaminating fluid in the labyrinth path  58  and the part of the path after the large chamber  60 . 
   Should fluid continue to flow into the live center  10  along the labyrinth path  58 , it may be drained out of the live center via a drain hole  62 . The drain hole  62  is located in the cover  52  on the bottom portion of the live center  10  so that gravity will encourage any contaminating fluid to flow down and out of the drain hole  62 . While the drain hole  62  is illustrated in the cover  52 , other embodiments of the invention may include a drain hole located in another suitable location or having no drain hole at all. 
   If the contaminant does not flow out of the drain hole  62 , but continues into the live center  10  along the labyrinth path  58 , it will encounter the surface of the spindle  12  on the lip or flange portion  38 . The flange  38  and the adaptor  40  define a narrow channel  64  which will inhibit the flow of contaminants or fluid into the live center  10 . In some embodiments of the invention, the adaptor  40  is spaced about 0.015 of an inch away from the flange  38  on the adaptor  12 , thus providing a narrow passageway  64  for contaminants to flow into the live center  10 . 
   In some embodiments of the invention, the passageway  64  is blocked by a contact seal  66 . The contact seal  66  is set within a bore  68  in the adaptor  40 . The contact seal  66  is made of a resilient material. For example, in some embodiments of the invention, the contact seal  66  is synthetic acrylonitrile-butadine rubber. Seals made of this material have a high elasticity and low friction which is good for high RPM applications. Other suitable seals  66  are made of nitrile. Other seal materials can be used to meet certain application requirements. The contact seal  66  contacts both the adaptor  40  and the spindle  12  at the flange  38 . The contact seal  66  blocks the narrow channel  64  to prevent or hinder contaminants from flowing further into the live center  10 . The contact seal lip  70  is facing the bearings  20 . 
   In some embodiments of the invention, the contact seal  66  provides an additional function of preventing or hindering oil or lubricant from flowing out of the area where the bearings  20  are located and out of the live center  10  along the spindle  12 . In some embodiments of the invention, the contact seal  66  has a seal lip  70  facing in. The contact seal  66  is mounted within the live center  10  on the spindle  12  so that the seal lip  70  is facing the bearings  20  rather than the narrow channel  64 . While the embodiment shown shows the contact seal  66  located between the adaptor  40  and the spindle  12  at the flange section  38 , other embodiments in accordance with the invention may include a contact seal  66  located along the spindle  12  but not necessarily contacting the adaptor  40 , but may contact some other portion of the live center such as the housing  14  or some other structure. The seal may also be of a double lip construction. This design has a sealing (contact) lip and a non-contact protecting lip. 
   Although an example of the sealing system is shown on a live center  10 , it will be appreciated that the sealing system can be used on other items having a similar configuration where a rotating shaft is mounted inside a housing. Also, although the system is useful in the manufacturing industry, it can be used in other industries. The embodiment shown is meant to be exemplary only, and by no means limiting. 
   The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.