DE19606249A1 - Crown cage for ball bearing of high=speed dental drills etc. - Google Patents

Abstract

The crown cage (7) has a cylinder (71), which is made of a thermoplastic resin, with pockets (73) in it containing balls, at preset positions round the cylinder. The cylinder has a first recess (71a) which includes a sprue point during the moulding process. There are also further recesses (71b) for balancing. All the recesses are of the same form. There may be a pair of claws formed on either side of each pocket on the endface of the cylinder, to hold a ball in each pocket. The claws are tapered. The resin may be a polyimide resin to which 5-10% of polytetrafluoroethylene and 10-20% of graphite by weight have been added.

Description

For the present application, the priority of the japani patent applications No. 7-31017 and 8-017770 bean speaks, the disclosure of which is inserted here by this reference is closed.

The invention relates to a crown cage, the egg Ball bearing attached for high speed rotation and a dental handpiece with a sol chen.

In the case of the dental handpiece mentioned, one with reversing a rotary shaft provided at its end with a grindstone bar at high speeds (for example 300,000 to 400,000 rpm.) Rotated. The circumferential speed The grinding stone is therefore selected so high that the Cutting quality improved and the grinding work on the tough can be ended in a short time to give the patient the relieve uncomfortable feeling.  

If a ring or disc groove bearing as a bearing for the dental handpiece or the like is used used a crown cage. In practice it is more common so far wise (see for example the unexamined Japanese patent publication No. 165790/1994) as a crown cage a cage been used, in which by means of a cutting process a bag or the like is formed. This is called Material a cylinder made of a thermosetting resin with heat resistance used to the sterilization work high temperatures (for example 135 ° C) within an Au to resist toclaves. However, since the conventional Chen crown cage cutting work is required increases the number of process steps and thus the manufacturing costs.

To do justice to this situation, one is considered Crown cage for a ball bearing made of a thermoplastic To produce resin as an injection molded part.

To prevent that on the surface of the crown cage, the is composed of molded parts, a sprue cut track that protrudes from the surface of the cage the shape of the crown cage chosen so that in places that correspond to a sprue position, recesses are provided (an area that includes the gate). Other On the one hand, a metal mold is used for the injection molding process used, and since this usually has a sprue, results a recess.

If there is only one recess, the deteriorates Balancing the crown cage. As a result Difficulties of a different kind are to be expected. For example, klap pert the crown cage during high-speed rotation.

The invention has in view of this technical background basically given the task, a crown cage for a ball warehouse with good weight balance as well as a dental  Handpiece with one using a thermopla resin resin as an injection molded crown cage to accomplish.

To solve this task, a crown cage stands out for a ball bearing made of injection molded parts made of thermoplastic Resin is composed of a cylinder has, which during the injection molding on its end face or has a gate at its peripheral surface, a variety of bags to hold balls in predetermined Circumferential division formed on an end face of the cylinder are, a first recess formed in the cylinder, which contains the sprue and a second recess in the Cylinder to correct an imbalance in the Rota tion of the cylinder formed by the first recess is.

If only the first recess is provided to prevent the cage causes a sprue cut track to protrude Circulating an imbalance. This imbalance can al be corrected by the second recess. Of the Weight balance during the rotation of the crown cage, the is obtained as an injection molded part made of thermoplastic resin, is consequently improved. That's why the crown cage rattles not even during the high-speed revolution.

A suitable thermoplastic resin for the crown cage Ball bearing for a dental handpiece is a thermoplastic polyimide resin, from 5 to 10 wt .-% poly tetrafluoroethylene and 10 to 20 wt .-% graphite added are because this improves the abrasion resistance can.

Lubricating oil from the range of liquid paraffins (for example according to ISO VG68) is used for the ball bearing in the dentist Chen handpiece used. In many cases, the lubricating oil but not more than once or twice a month  upset. Consequently, the ball bearing is in almost nothing lubricated condition with very high rotational speeds (for example 400,000 rpm). Even if the Ku gel bearings but used under such severe conditions the cage has sufficient abrasion resistance show, provided it is made of a thermoplastic bottom lyimide resin produced, the said polytetrafluoroethyl len and graphite in the aforementioned mixing ratio are clogged. The cage is also against sterilization at high temperatures in an autoclave or chemical slave resistant. For this reason too, the cage is suitable for use in the dental handpiece.

The invention is advantageous in the following Details with the aid of a schematically illustrated embodiment example explained in more detail. In the drawings:

Figure 1 is a plan view from below of a crown cage for a ball bearing according to an embodiment of the invention.

Figure 2 is a top plan view of the crown cage;

Fig. 3 is an enlarged sectional view of the crown retainer;

Fig. 4 is a sectional view of the main part of a ball bearing in which the crown cage is installed;

Fig. 5 is a sectional view of the main part of the ball bearing in which the crown cage is to be inserted;

Fig. 6 is a sectional view showing the structure of egg nes dental handpiece in which the Kronenkä fig is used;

FIG. 7A is a schematic end view of an apparatus for loading the fracture strength of the crown retainer agree; and

Fig. 7B is a schematic side view of the device shown in Fig. 7A ge.

In Fig. 6, a dental handpiece can be seen, which contains a crown cage for a ball bearing according to an embodiment of the invention. The dental handpiece has a housing 2, which is arranged in the housing 2 rotating shaft 3 protrudes one end to the outside, one at a part of the housing 2 of the rotary shaft 3 mounted turbine acting fel 4 and a ring or disc groove bearing 5 on which the Housing 2 is fixed so that it rotatably supports the rotary shaft 3 at the sides of the turbine blade 4 .

In the dental handpiece 1 compressed air is supplied to the housing 2 , whereby the turbine blade 4 and the rotating shaft 3 are set in rotation at high speed. Air brushes through the interior of the ball bearing 5 and exerts a cooling effect.

At one, protruding from the housing 2 end of the rotary shaft 3 , a dental drill 31 is formed, and with this dental drill 31 , a hand with a grindstone (not shown) is connected.

Because of the axial movement of the turbine blade 4 , a spacer 6 is provided between it and the ball bearing 4 .

The ball bearing 5 has an inner ring 51 , an outer ring 52 and a plurality of balls 53 which roll between the inner ring 51 and the outer ring 52 . The inner ring 51 and the outer ring 52 are made of a metal of high corrosion resistance, such as stainless steel (such as JIS SUS440C). The ball 53 consists of a ceramic material, which is mainly composed of silicon nitride or SIALON, and is held by a Kronenkä fig 7 , which is inserted into the ball bearing 5 .

As is apparent from FIGS. 1 and 3, the crown retainer 7 is made in accordance with this embodiment, as an injection molded part made of a heat resistant thermoplastic resin, and has a cylinder 71 and pockets 73, which c at a predetermined circumferential pitch on a front surface 71 of the Zylin DERS 71 are provided and are each provided with two claws 72 , which are formed to hold a ball 73 . The resin does not include reinforced fiber such as glass fiber. The reason for this is that the possibility should be excluded that a bare fiber wears off and gets tangled in a track surface on the surface of a pocket.

As the crown cage 7 for a ball bearing for the dental handpiece, a thermoplastic polyimide resin (hereinafter referred to as thermoplastic TPI) is preferably used in the present exemplary embodiment, the polytetrafluoroethylene (hereinafter simply referred to as PTFE) in an amount of 5 to 10% by weight. and graphite is added in an amount of 10 to 20% by weight.

The reason for this is that in recent years dental handpieces for sterilization at high Subjected to temperatures in an autoclave or chemiclaves and the above-mentioned crown cage made of thermoplastic chemical TPI can withstand this sterilization work. Of the Cage for a ball bearing in a dental handpiece has very small dimensions. As a result, the resin must form The cage is outstanding at the time of the shaping Have fluidity. To act as a resin for the shaping of the To be suitable for the cage, it must be releasable from the mold be by moldings in part of the pocket that holds the ball hold in the cage, inevitably from a metal mold are extractable. On the other hand, thermoplastic cal TPI the requirements regarding flowability and mold release properties (generally as design features designated).

As a lubricating oil for the ball bearing in the dental handpiece liquid paraffin series are used (for example,  according to ISO VG68). However, in many cases it will Lubricating oil may not be more than once or twice provided per month. As a result, the ball bearing in an almost not lubricated condition with revolutions very high speed (for example 400,000 rpm.). Even if the ball bearing under this he difficult conditions, the cage can suffice abrasion-resistant, provided that it comes from a thermoplastic polyimide resin is made, the PTFE and Graphite added in the mixing ratio mentioned above are.

The aforementioned mixing ratio of PTFE and graphite is preferred because a mixing ratio of PTFE of less than 5% by weight in all components of the crown cage 7 leads to excessive abrasion of the cage and the mixing ratio of PTFE of more than 10% by weight. % leads to low strength of the cage. On the other hand, a mixture ratio of graphite of less than 10% by weight in all components of the crown cage 7 results in unstable friction between the crown cage 7 and the balls 53 , and a mixture ratio of graphite of more than 20% by weight leads to low strength of the crown cage 7 . If only 5 to 10% by weight of PTFE and no graphite is added, the abrasion is unstable, which is not preferred. In addition, the abrasion is excessive, which is again not preferable if only 10 to 20% by weight of graphite and no PTFE is added.

Examples of resins with heat resistance other than TPI are polyphenylene sulfide (hereinafter referred to as PPS), Po lyethersulfide (hereinafter referred to as PES), polyetherni tril (hereinafter referred to as PEN) and polyether ether ketone (hereinafter referred to as PEEK). The resins are for use in cages for ball bearings for all purposes except for ball bearings in dental handpieces. The PES in particular melts easily in methyl chrome,  so that PES can be used for cages that are in an environment can be used without methyl chromium. Because the fluidity of PEN is worse and products with small dimensions PEN are difficult to manufacture, PEN is suitable for cages of a certain size. PEEK is hard and shows no flexi bility. Even if PEEK cannot be used for cages that revolve at very high speeds (300,000 rpm) like this is the case with a cage for a dental handpiece is, this resin can be used for cages that are not rotate at extremely high speeds.

As is clear from Fig. 3, an end 72 a on the side of an opening of the pocket of the claw 72 is designed so that it is thinner than an end on the side of the cylinder 71st This is achieved in that the surface G on its outer diameter and the surface N on its inner diameter water are inclined in succession towards an end face 72 b on the side of the opening of the pocket of the claw 72 . An inclination angle Θ1 of the surface G of the outer diameter is set to approximately 100, for example, while an inclination angle Θ2 of the surface N of the inner diameter is set to approximately 15 °, for example. The reason why the end 72a on the side of the opening of the pocket of the claw 72 is thinner than the end on the side of the cylinder 71 is that the claw 72 is light in weight and the zen exerted on the claw 72 at high speed rotation trifugal force is reduced to restrict the expansion of the claw 72 to the outer ring 52 (in the direction indicated by arrow A), as shown in FIG. 4. In particular, the surface G of the outer diameter of the end 72 a on the side of the opening of the pocket of the claw 72 is therefore inclined, so that this surface G is prevented from coming into contact with the inner diameter of the outer ring 52 when the claw 72 to the outer ring 52 (in the direction indicated by arrow A).

As can be clearly seen in Fig. 1, in the other end face 71 d of the cylinder 71 are a first recess 71 a corresponding to a sprue during molding (ie including the sprue) and a plurality (three in Fig. 1) of second recesses 71 b in the same shape as the first recess 71 a but avoiding correspondence with the sprue (that is avoiding the sprue). The first and second recesses 71 a and 71 b are arranged in a predetermined circumferential division. Furthermore, each of the recesses 71 a and 71 b is provided at an intermediate position between the adjacent pockets 73 .

As clearly shown in Fig. 2, the diameter of the circle C2 falls R1 of the circle C1 that connects the centers of the wall thicknesses of the end faces 72 b on the side of the openings of the pockets of the respective jaws 72, almost to the diameter R2 together, the Connects in the middle of the balls 53 held in the corresponding pockets 73 . The diameter R1 of the circle C1 is a PCD (pitch circle diameter) of the end face 72 b of the opening side of the pockets of the claws 72 , and the diameter R2 of the circle C2 is a pitch circle diameter water balls 53 held in the pockets 73 .

If the crown cage 7 at a high speed of, for example, 400,000 rpm. revolves around, and only the first recess 71 a, which avoids a gate cut track, there is an unbalanced deflection from the crown cage 7 due to the first recess 71 a. With the invention, however, any imbalance caused by the first recess 71 a is corrected by the second recesses 71 b, so that the balance when turning can be improved. In particular, blind second recesses 71 b of the same shape as the first recess 71 a are provided, and these recesses are formed in a predetermined circumferential direction in the other end face 71 d of the cylinder 71 , whereby the weight balance during the rotation of the injection molding process Crown cage 7 is improved from thermoplastic resin. As a result, the crown cage 7 does not flutter in the centrifugal direction when rotating at high speed.

The diameter R1 of the circle C1, which connects the centers of the wall thickness of the end faces 72 b on the side of the openings of the pockets of the respective claws 72 , and the diameter R2 of the circle C2, which the centers of the pockets 73 held in the corresponding Balls 73 connects almost collapse. When inserting the crown cage 7 into the ball bearing 5 , as shown in Fig. 5, therefore, the end face 72 b comes to rest on the side of the opening of the pocket of the claw 72 on the ball 53 , whereby no bending forces in the direction of the crown cage 7 to the outer ring 52 (in the direction indicated by arrow X) and to the inner ring 51 (in the direction indicated by arrow Y). For this reason, the end face 72 b on the side of the opening of the Ta claw 72 , which rests on the ball 53 , not to the outside diameter or the inside diameter of the ball 53 , so that the ball 53 in the smoothest way in the pocket 73 can be held. The crown cage 7 can therefore be inserted smoothly into the ball bearing 5 .

The present invention is not limited to the above-described embodiment. Although in the described embodiment, the surface G of the outer diameter and the surface N of the inner diameter at the end 72 a on the side of the opening of the pocket of the claw 72 are inclined so that the end 72 a on the side of the opening of the pocket of the claw 72 is thinner than the end on the side of the cylinder 71 , it is also possible to incline only one or the other surface G or N of the end 72 a of the side of the opening of the pocket of the claw 72 .

In the exemplary embodiment explained above, the first and the second recesses 71 a and 71 b are formed in a predetermined circumferential division on the other end face 71 d of the cylinder 71 ; but the recesses 71 a and 71 b can also be formed in a predetermined circumferential division on the inner circumferential surface or on the outer circumferential surface of the cylinder 71 . In any case, the sprue decides on the location where the first recess 71 a is to be seen, and the second recesses 71 b are determined on the basis of the first recess 71 a. Specifically, if the gate is on the other end face 71 d of the cylinder 71 , preferably both recesses 71 a and 71 b are also provided in the other end face 71 d of the cylinder 71 . On the other hand, if the gate is on the inner peripheral surface (or the outer peripheral surface) of the cylinder 71 , the two recesses 71 a and 71 b should preferably also be arranged on the inner peripheral surface (or the outer peripheral surface) of the cylinder 71 . If the equilibrium is ensured during the rotation of the crown cage 7 , the first recess 71 a or the second recesses 71 b can also be provided on the other end face 71 d and the peripheral surface of the cylinder 71 , or vice versa. Furthermore, the sizes of the recesses 71 a and 71 b can differ, provided that the balance is ensured during the rotation of the crown cage 7 .

The embodiment of the invention was explained here in connection with an example in which the crown cage 7 is used in a ball bearing for a dental handpiece. But it can also be used in a ball bearing for high speed rotation of a machine tool or the like.

Needless to say that different con structural changes and corrections within the scope of the claims of the present invention can be made.  

attempt

There is a crown cage for a ball bearing for a dental handpiece of the same shape as shown in Fig. 1 made by injection molding from thermoplastic TPI to prepare experimental examples 1 and 2 and comparative examples 1 to 5, in which the content of PTFE and graphite to different Values is set as shown in Table 1.

With the cages from the corresponding examples, Ver search carried out under the following conditions in order to belle 1 to achieve the results shown.

Table I

Test conditions

Initial values of the breaking strengths of cages H are determined in each example so that two jigs 8 and 9 attached to projecting portions 81 and 91 are pulled up and down, respectively, as indicated by the arrows in Figs. 7A and 7B .

As one cycle, the cages are left in an autoclave under high pressure flow at a temperature of 135 ° C for five minutes and then in dry air at a temperature of 180 ° C for ten minutes, drying the cages. This is repeated in 500 cycles to examine the deterioration in the strength of the cages for each example. The breaking strengths of the cages taken from the autoclave are determined with the jigs 8 and 9 for each example, and then the breaking strengths of the cages taken from the autoclave are compared with the initial values of the breaking strengths of the cages H by the extent find out the deterioration of their strengths.

The degree of abrasion is also used in ball bearings Crown cages for each example after a permanent Tested under a predetermined condition (300 hours the operating time at which a process of 15 seconds Be powered under 120 gf load and 15 seconds without operation an oil supply every 30 minutes, is repeated). also the torque before and after the durability test tries to change it before and after this ver try to establish. If a big change in torque is perceived, the coefficient of friction becomes larger and the friction is more unstable.

Test results

The results of the experiment in experimental examples 1 and 2 prove that the one made of thermoplastic TPI Crown cage, the 5 to 10 wt .-% PTFE and 10 to 20 wt .-% Graphite added was not easily handled by the autoclave is influenced and has superior durability.  

On the other hand, the results of the experiment at Ver same example 1 that with a PTFE content of less than 5% by weight of the abrasion increases even if the Gra phit content is in the preferred range, so that this Kro cage does not show excellent durability.

The test results for comparative example 2 prove that in the event that the PTFE content is 10% by weight increases, the strength decreases even if the graphite stop is in the preferred range, so that this crowns cage does not show great durability.

The test results in comparative example 3 prove that with a graphite content lower than 10% by weight, the Rei exercise becomes unstable even when the PTFE content in the preferred area, so this crown cage again does not show great durability.

The test results for comparative example 4 prove that with a graphite content greater than 20% by weight, the starch decreases even if the PTFE content in the preferred Be is rich. This crown cage also shows no outstanding Durability.

Claims (6)

1. Crown cage for a ball bearing, which is composed of injection molded parts from a thermoplastic resin, characterized by

• - A cylinder ( 71 ) which has a sprue on the end face or the peripheral surface thereof during the injection molding process;
• - A plurality of pockets for receiving Ku gels ( 73 ) which are formed in a predetermined circumferential division on an end face ( 71 c) of the cylinder ( 71 );
• - A first recess ( 71 a) which is formed in the cylinder ( 71 ) and includes the sprue; and
• - A second recess ( 71 b) which is formed in the cylinder ( 71 ) for correcting an imbalance caused by the first recess ( 71 a) during the rotation of the cylinder ( 71 ).

2. Crown cage for a ball bearing according to claim 1, characterized in that both recesses ( 71 a, 71 b) have the same shape and are provided at a predetermined circumferential division. 3. Crown cage for a ball bearing according to claim 1 or 2, characterized in that from both sides of the pocket ( 73 ) a pair of claws ( 72 ) on one end face ( 71 c) of the cylinder ( 71 ) is formed, the one in hold each of the pockets ( 73 ) held ball ( 53 ) and that each of the claws ( 72 ) is formed in a tapered shape. 4. Crown cage for a ball bearing according to one of claims 1 to 3, characterized in that on one end face ( 71 c) of the cylinder ( 71 ) from both sides of the pocket ( 73 ) a pair of claws ( 72 ) for holding the in each the pockets ( 73 ) held ball ( 53 ) is formed that the diameter (R1) of a circle (C1) connecting the centers of the wall thicknesses of the end faces on the side of the openings of the pockets of the corresponding claws ( 72 ), and Diameter (R2) of a circle (C2), which connects the centers of the corresponding pockets ( 73 ) held balls ( 53 ), almost coincide. 5. Crown cage for a ball bearing according to one of claims 1 to 4, characterized in that the thermoplastic resin is a thermoplastic polyimide resin, 5 to 10 wt .-% Polytetrafluoroethylene and 10 to 20 wt .-% graphite adds. 6. Dental handpiece, characterized by

• - A ball bearing ( 5 ) with a crown cage ( 7 ) for a ball bearing according to claim 5;
• - A housing ( 2 ) which supports the ball bearing ( 5 );
• - A rotary shaft ( 3 ) which is rotatably supported by the ball bearing ( 5 ); and
• - A on the rotary shaft ( 3 ) attached turbine blade ( 4 ).