# Patent

## Title
Washing machine having balancer

## Abstract

A front loading washing machine including a housing; a water reservoir installed in the housing for containing washing water; a spin tub provided in the water reservoir to hold laundry to be washed, the spin tub having an annular recess and rotating with respect to a horizontal axis of the washing machine; and at least one balancer installed in the annular recess of the spin tub, the balancer comprising an annular shaped race formed of a plastic material.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is continuation application of U.S. application Ser. No. 12/801,952, filed Jul. 2, 2010, now U.S. Pat. No. 7,942,026 which was a continuation of U.S. application Ser. No. 12/659,980, filed Mar. 26, 2010, which issued as U.S. Pat. No. 7,797,970, which was a divisional of U.S. application Ser. No. 11/806,245, filed May 30, 2007, which issued as U.S. Pat. No. 7,743,633, which in turn claims the benefit of Korean Patent Application Nos. 2006-49501 and 2006-49482, both filed on Jun. 1, 2006, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference.


BACKGROUND
1. Field
The present invention relates generally to a washing machine having at least one balancer, and more particularly to a washing machine having at least one balancer that increases durability by reinforcing strength and that is installed on a rotating tub in a convenient way.
2. Description of the Related Art
In general, washing machines do the laundry by spinning a spin tub containing the laundry by driving the spin tub with a driving motor. In a washing process, the spin tub is spun forward and backward at a low speed. In a dehydrating process, the spin tub is spun in one direction at a high speed.
When the spin tub is spun at a high speed in the dehydrating process, if the laundry leans to one side without uniform distribution in the spin tub or if the laundry leans to one side by an abrupt acceleration of the spin tub in the early stage of the dehydrating process, the spin tub undergoes a misalignment between the center of gravity and the center of rotation, which thus causes noise and vibration. The repetition of this phenomenon causes parts, such as a spin tub and its rotating shaft, a driving motor, etc., to break or to undergo a reduced life span.
Particularly, a drum type washing machine has a structure in which the spin tub containing laundry is horizontally disposed, and when the spin tub is spun at a high speed when the laundry is collected on the bottom of the spin tub by gravity in the dehydrating process, the spin tub undergoes a misalignment between the center of gravity and the center of rotation, thus resulting in a high possibility of causing excess noise and vibration.
Thus, the drum type washing machine is typically provided with at least one balancer for maintaining a dynamic balance of the spin tub. A balancer may also be applied to an upright type washing machine in which the spin tub is vertically installed.
An example of a washing machine having ball balancers is disclosed in Korean Patent Publication No. 1999-0038279. The ball balancers of a conventional washing machine include racers installed on the top and the bottom of a spin tub in order to maintain a dynamic balance when the spin tub is spun at a high speed, and steel balls and viscous oil are disposed within the racers to freely move in the racers.
Thus, when the spin tub is spun without maintaining a dynamic balance due to an unbalanced eccentric structure of the spin tub itself and lopsided distribution of the laundry in the spin tub, the steel balls compensate for this imbalance, and thus the spin tub can maintain the dynamic balance.
However, the ball balancers of the conventional washing machine have a structure in which upper and lower plates formed of plastic by injection molding are fused to each other, and a plurality of steel balls are disposed between the fused plates to make a circular motion, so that the ball balancers are continuously supplied with centrifugal force that is generated when the steel balls make a circular motion, and thus are deformed at walls thereof, which reduces the life span of the balancer.
Further, the ball balancers of the conventional washing machine do not have a means for guiding the ball balancers to be installed on the spin tub in place, so that it takes time to assemble the balancers to the spin tub.
In addition, the ball balancers of the conventional washing machine have a structure in which a racer includes upper and lower plates fused to each other, so that fusion scraps generated during fusion fall down both inwardly and outwardly of the racer. The fusion scraps that fall down inwardly of the racer prevent motion of the balls in the racer, and simultaneously result in generating vibration and noise.
SUMMARY
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a washing machine having at least one balancer that increases durability by reinforcing the strength of the balancer, which is installed on a rotating tub in a rapid and convenient way.
Another object of the present invention is to provide a washing machine having at least one balancer, in which fusion scraps generated by fusion of the balancer are prevented from falling down inward and outward of the balancer.
Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention.
In order to accomplish these objects, according to an aspect of the present invention, there is provided a washing machine having a spin tub to hold laundry to be washed and at least one balancer. The balancer includes first and second housings, the first housing having at least one support for reinforcing a strength of the balancer. The first and second housings have an annular shape and are fused together to form a closed internal space.
Here, the first housing may have the cross section of an approximately “C” shape, and the support protrudes outwardly from at least one of opposite walls of the first housing.
Further, the spin tub may include at least one annular recess corresponding to the balancer such that the balancer is able to be coupled to the spin tub by being fitted within the recess.
Further, the support may protrude from the first housing and comes into contact with a wall of the recess, and guides the balancer to be maintained in the recess in place.
Also, the supports may be continuously formed along and perpendicular to the opposite walls of the first housing.
Further, the supports may be disposed parallel to the opposite walls of the first housing at regular intervals.
Meanwhile, the washing machine may be a drum type washing machine. A front member may be attached to a front end of the spin tub and a rear member may be attached to a rear end of the spin tub. The recesses may be provided at the front and rear members of the spin tub, and the balancers may be coupled to opposite ends of the spin tub at the recesses of the front and rear members.
The foregoing and/or other aspects of the present invention can be achieved by providing a washing machine having at least one balancer. The balancer includes a first housing and a second housing fused to the first housing, and the first and second housings are fused together to form at least one pocket between the first housing and the second housing, the pocket capable of collecting fusion scraps generated during fusion.
Here, the first housing may include protruding fusion ridges protruding from ends of the first housing, and the second housing may include fusion grooves receiving the fusion ridges of the first housing when the first housing and the second housing are fused together.
Further, the first housing may further include inner pocket ridges protruding from the first housing and spaced inwardly apart with respect to the fusion ridges of the first housing.
Further, the second housing may further include outer pocket flanges protruding from the second housing and being situated on outer sides of the fusion grooves when the first housing is fused together with the second housing so the outer pocket flanges are spaced apart from the fusion ridges of the first housing by a predetermined distance, causing an outer pocket to be formed between the fusion ridges and the outer pocket flanges.
Further, the second housing may include guide ridges protruding from the second housing and protruding toward the first housing to closely contact the inner pocket ridges of the first housing when the first and second housings are fused together.
Also, the balancer may further include a plurality of balls disposed within an internal space formed by fusing the first and second housings together, the balls performing a balancing function.
In addition, the washing machine may further include a spin tub disposed horizontally, and the balancers may be installed at front and rear ends of the spin tub.



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features and advantages of the present invention will be more apparent from the following detailed description of the embodiments, taken in conjunction with the accompanying drawings, in which
FIG. 1 is a sectional view illustrating a schematic structure of a washing machine according to the present invention;
FIG. 2 is a perspective view illustrating balancers according to the present invention, in which the balancers are disassembled from a spin tub;
FIG. 3 is a perspective view illustrating a balancer according to a first embodiment of the present invention;
FIG. 4 is an enlarged view illustrating section A of FIG. 1 in order to show the sectional structure of a balancer according to a first embodiment of the present invention;
FIG. 5 is a perspective view illustrating a balancer according to a second embodiment of the present invention;
FIG. 6 is an enlarged view illustrating the sectional structure of a balancer according to the second embodiment of the present invention;
FIG. 7 is a perspective view illustrating a disassembled balancer according to a third embodiment of the present invention;
FIG. 8 is a perspective view illustrating an assembled balancer according to the third embodiment of the present invention;
FIG. 9 is a partially enlarged view of FIG. 7; and
FIG. 10 is a sectional view taken line A-A of FIG. 8.



DETAILED DESCRIPTION OF THE EMBODIMENTS
Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.
Hereinafter, exemplary embodiments of the present invention will be described with reference to the attached drawings.
FIG. 1 is a sectional view illustrating the schematic structure of a washing machine according to the present invention.
As illustrated in FIG. 1, a washing machine according to the present invention includes a housing 1 forming an external structure of the washing machine, a water reservoir 2 installed in the housing 1 and containing washing water, a spin tub 10 disposed rotatably in the water reservoir 2 which allows laundry to be placed in and washed therein, and a door 4 hinged to an open front of the housing 1.
The water reservoir 2 has a feed pipe 5 and a detergent feeder 6 both disposed above the water reservoir 2 in order to supply washing water and detergent to the water reservoir 2, and a drain pipe 7 installed therebelow in order to drain the washing water contained in the water reservoir 2 to the outside of the housing 1 when the laundry is completely done.
The spin tub 10 has a rotating shaft 8 disposed at the rear thereof so as to extend through the rear of the water reservoir 2, and a driving motor 9, with which the rotating shaft 8 is coupled, installed on a rear outer side thereof. Therefore, when the driving motor 9 is driven, the rotating shaft 8 is rotated together with the spin tub 10.
The spin tub 10 is provided with a plurality of dehydrating holes 10a at a periphery thereof so as to allow the water contained in the water reservoir 2 to flow into the spin tub 10 together with the detergent to wash the laundry in a washing cycle, and to allow the water to be drained to the outside of the housing 1 through a drain pipe 7 in a dehydrating cycle.
The spin tub 10 has a plurality of lifters 10b disposed longitudinally therein. Thereby, as the spin tub 10 rotates at a low speed in the washing cycle, the laundry submerged in the water is raised up from the bottom of the spin tub 10 and then is lowered to the bottom of the spin tub 10, so that the laundry can be effectively washed.
Thus, in the washing cycle, the rotating shaft 8 alternately rotates forward and backward by of the driving of the driving motor 9 to spin the spin tub 10 at a low speed, so that the laundry is washed. In the dehydrating cycle, the rotating shaft 8 rotates in one direction to spin the spin tub 10 at a high speed, so that the laundry is dehydrated.
When spun at a high speed in the dehydrating process, the spin tub 10 itself may undergo misalignment between the center of gravity and the center of rotation, or the laundry may lean to one side without uniform distribution in the spin tub 10. In this case, the spin tub 10 does not maintain a dynamic balance.
In order to prevent this dynamic imbalance to allow the spin tub 10 to be spun at a high speed with the center of gravity and the center of rotation thereof matched with each other, the spin tub 10 is provided with balancers 20 or 30 according to a first or a second embodiment of the present invention (wherein only the balancer 20 according to a first embodiment is shown in FIGS. 1-4) at front and rear ends thereof. The structure of the balancers 20 and 30 according to the first and second embodiments of the present invention will be described with reference to FIGS. 2 through 6.
FIG. 2 is a perspective view illustrating balancers according to the present invention, in which the balancers are disassembled from a spin tub.
As illustrated in FIG. 2, the spin tub 10 includes a cylindrical body 11 that has open front and rear parts and is provided with the dehydrating holes 10a and lifters 10b, a front member 12 that is coupled to the open front part of the body 11 and is provided with an opening 14 permitting the laundry to be placed within or removed from the body 11, and a rear member 13 that is coupled to the open rear part of the body 11 and with the rotating shaft 8 (see FIG. 1) for spinning the spin tub 10.
The front member 12 is provided, at an edge thereof, with an annular recess 15 that has the cross section of an approximately “C” shape and is open to the front of the front member 12 in order to hold any one of the balancers 20. Similarly, the rear member 13 is provided, at an edge thereof, with an annular recess 15 (not shown) that is open to the rear of the front member 12 in order to hold the other of the balancers 20.
The front and rear members 12 and 13 are fitted into and coupled to the front or rear edges of the body 11 in a screwed fashion or in any other fashion that allows the front and rear members 12 and 13 to be maintained to the body 11 of the spin tub 10.
The balancers 20, which are installed in the recesses 15 of the front and rear members 12 and 13, have an annular shape and are filled therein with a plurality of metal balls 21 performing a balancing function and a viscous fluid (not shown) capable of adjusting a speed of motion of the balls 21.
Now, the structure of the balancers 20 and 30 according to the first and second embodiments of the present invention will be described with reference to FIGS. 3 through 6.
FIG. 3 is a perspective view illustrating a balancer according to a first embodiment of the present invention, and FIG. 4 is an enlarged view illustrating part A of FIG. 1 in order to show the sectional structure of a balancer according to a first embodiment of the present invention.
As illustrated in FIGS. 3 and 4, a balancer 20 according to a first embodiment of the present invention has an annular shape and includes first and second housings 22 and 23 that are fused to define a closed internal space 20a. 
The first housing 22 has first and second walls 22a and 22b facing each other, and a third wall 22c connecting ends of the first and second walls 22a and 22b, and thus has a cross section of an approximately “C” shape. The second housing 23 has opposite edges that protrude toward the first housing 22 and that are coupled to corresponding opposite ends 22d of the first housing 22 by heat fusion.
The opposite ends 22d of the first housing 22 protrude outward from the first and second walls 22a and 22b of the first housing 22, and the edges of the second housing 23 are sized to cover the ends 22d of the first housing 22.
Thus, when the balancer 20 is fitted into the recess 15 of the front member 12 of the spin tub 10, the first and second walls 22a and 22b are spaced apart from a wall of the recess 15 because of the ends and edges of the first and second housings 22 and 23 which protrude outward from the first and second walls 22a and 22b. Further, because the first and second walls 22a and 22b are relatively thin, the first and second walls 22a and 22b are raised outward when centrifugal force is applied thereto by the plurality of balls 21 that move in the internal space 20a of the balancer 20 in order to perform the balancing function.
In this manner, the plurality of balls 21 make a circular motion in the balancer 20, so that the first and second walls 22a and 22b are deformed by the centrifugal force applied to the first and second walls 22a and 22b of the first housing 22. In order to prevent this deformation, the second housing 22 is provided with supports 24 according to a first embodiment of the present invention.
The supports 24 protrude from and perpendicular to the first and second walls 22a and 22b of the first housing 22 which are opposite each other, and may be continued along an outer surface of the first housing 22, thereby having an overall annular shape.
The supports 24 have a length such that they extend from the first housing 22 to contact the wall of the recess 15. Hence, the first and second walls 22a and 22b are further increased in strength, and additionally function to guide the balancer 20 so as to be maintained in the recess 15 in place.
Here, when the plurality of balls 21 make a circular motion in the first housing 22, the centrifugal force acts in the direction moving away from the center of rotation of the spin tub 10. Hence, the centrifugal force acts on the first wall 22a to a stronger level when viewed in FIG. 4. Thus, the supports 24 may be formed only on the first wall 22a. 
In the balancer 20 according to the first embodiment of the present invention, when the first and second housings 22 and 23 are fused together and fitted into the recess 15 of the spin tub 10, the supports 24 are maintained in place while positioned along the wall of the recess 15. Finally, the balancer 20 is coupled and fixed to the front member 12 of the spin tub 10 by screws (not shown) or in any other fashion that allows the balancer 20 to be coupled to the front member 12.
Although not illustrated in detail, the balancer 20 is similarly installed on the rear member 13 of the spin tub 10.
The ends 22d of the first housing 22 include fusion ridges 42a that protrude toward the second housing 23. The fusion ridges 42a are inserted within fusion grooves 43a of the second housing 23.
FIGS. 5 and 6 correspond to FIGS. 3 and 4, and illustrate a balancer 30 according to a second embodiment of the present invention.
The balancer 30 according to the second embodiment of the present invention has an annular shape and includes first and second housings 32 and 33 that are fused together forming an internal space 30a therebetween in which a plurality of balls 31 are disposed. The balancer 30 according to the second embodiment of the present invention is similar to that of balancer 20 according to the first embodiment of the present invention, except the structure of supports 34 of balancer 30 is different from that of the structure of the supports 24 of balancer 20.
As illustrated in FIGS. 5 and 6, the supports 34 according to the second embodiment of the present invention protrude parallel to first and second walls 32a and 32b of a first housing 32 which are opposite each other, and the supports 34 are disposed at regular intervals along the first and second walls 32a and 32b. The first housing 32 further includes a third wall 32c. Ends 22d of the first housing 32 extend from an end of the first and second walls 32a and 32b. 
Similar to the supports 24 according to the first embodiment, the supports 34 of the second embodiment have a length such that the supports 34 extend from the first housing 32 to contact the wall of the recess 15. The surfaces of the supports 34 thereby abut portions of the front member 12. Hence, the first and second walls 32a and 32b are further increased in strength, and additionally function to guide the balancer 30 so as to be maintained in the recess 15 in place.
Next, the construction of a balancer 40 according to a third embodiment of the present invention will be described with reference to FIGS. 7 through 10.
FIGS. 7 and 8 are perspective views illustrating disassembled and assembled balancers according to the third embodiment of the present invention, FIG. 9 is a partially enlarged view of FIG. 7, and FIG. 10 is a sectional view taken along line A-A of FIG. 8.
As illustrated in FIGS. 7 and 8, a balancer 40 includes a first housing 42 having an annular shape and a second housing 43 having an annular shape that is fused to the first housing 42, thereby forming an annular housing corresponding to the recess 15 (see FIG. 2) of the spin tub 10. The first and second housings 42 and 43 may be, for example, formed of synthetic resin, such as plastic by injection molding.
As illustrated in FIG. 9, the first housing 42 has a cross section of an approximately “C” shape, includes fusion ridges 42a protruding to the second housing 43 at opposite ends thereof which are coupled with the second housing 43, and inner pocket ridges 42b protruding to the second housing 43 spaced inwardly apart from the fusion ridges 42a. 
The second housing 43 has a first surface 431 facing the first housing 42 and a second surface 432 opposite to the first surface 431. The second housing 43, which is coupled to opposite ends of the first housing 42 in order to form a closed internal space 40a for holding a plurality of balls 41 and a viscous fluid, includes fusion grooves 43a recessed along edges thereof so as to correspond to the fusion ridges 42a, outer pocket flanges 43b and guide ridges 43c. The outer pocket flanges protrude to the first housing 42 on outer sides of the fusion grooves 43a so as to be spaced apart from the fusion ridges 42a of the first housing 42 by a predetermined distance. The guide ridges 43c protrude from the first surface 431 to the first housing 42 on inner sides of the fusion grooves 43a and closely contact the inner pocket ridges 42b of the first housing 42. Grooves 433 are formed on the second surface 432 at positions corresponding to the guide ridges 43c, respectively. As shown in FIG. 9, the grooves 433 extend in a circumferential direction of the balancer 40. Each of the grooves 433 includes an inclination surface 434 that is inclined toward a bottom thereof. Meanwhile, the first surface 431 of the second housing 43 includes a portion 435 that protrudes toward the first housing 42. The guide ridges 43c protrudes from the protruding portion 435 of the first surface 431 toward the first housing 42.
The guide ridges 43c of the second housing 43 move in contact with the inner pocket ridges 42b of the first housing 42 when the second housing 43 is fitted into the first housing 42, to thereby guide the fusion ridges 42a of the first housing 42 to be fitted into the fusion grooves 43a of the second housing 43 rapidly and precisely.
Thus, when the fusion ridges 42a of the first housing 42 are fitted into the fusion grooves 43a of the second housing 43 in order to fuse the first housing 42 with the second housing 43, as shown in FIG. 10, an inner pocket 40b having a predetermined spacing is formed between the fusion ridges 42a and inner pocket ridges 42b, and an outer pocket 40c having a predetermined spacing is formed between the fusion ridges 42a and the outer pocket flanges 43b. 
In this state, when heat is generated between the fusion ridges 42a of the first housing 42 and the fusion grooves 43a of the second housing 43, the fusion ridges 42a and the fusion grooves 43a are firmly fused with each other. At fusion, fusion scraps that are generated by heat and fall down inward of the first housing 42 are collected in the inner pocket 40b, so that the scraps are not introduced into the internal space 40a of the balancer 40 in which the balls 41 move. Fusion scraps falling down outward of the first housing 42 are collected in the outer pocket 40c, and thus are prevented from falling down outward of the balancer 40.
In the embodiments, the balancers 20, 30 and 40 have been described to be installed on a drum type washing machine by way of example, but it is apparent that the balancers can be applied to an upright type washing machine having a structure in which a spin tub is vertically installed.
As described above in detail, the washing machine according to the embodiments of the present invention has a high-strength structure in which at least one balancer is provided with at least one support protruding outward from the wall thereof, so that, although the strong centrifugal force acts on the wall of the balancer due to a plurality of balls making a circular motion in the balancer, the wall of the balancer is not deformed. Thus, the plurality of balls can make a smooth circular motion without causing excess vibration and noise, and thus increasing the durability and life span of the balancer.
Further, the washing machine according to the embodiments of the present invention has a structure in which the balancer can be rapidly and exactly positioned in the recess of the spin tub by the supports, so that an assembly time of the balance can be reduced.
In addition, the washing machine according to the present invention has a structure in which fusion scraps generated when the balancer is fused are collected in a plurality of pockets, and thus are prevented from falling down inward and outward of the balancer, so that the internal space of the balancer, in which a plurality of balls are filled and move in a circular motion, has a smooth surface without the addition of fusion scraps. As a result, the balls are able to move more smoothly, and excess noise and vibration are minimized. The balancer may have a clear outer surface to provide a fine appearance without the fusion scraps, so that it can be exactly coupled to the spin tub without obstruction caused by the fusion scraps.
Although a few embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims and their equivalents.

## Claims

1. A drum type washing machine, comprising:
a housing;
a water reservoir installed in the housing to contain washing water;
a spin tub provided in the water reservoir to hold laundry to be washed; and
a ball balancer coupled to the spin tub to compensate for a dynamic imbalance during rotation thereof, the ball balancer comprising an annular-shaped race having a closed internal space in which a plurality of balls and viscous fluid are accommodated, the annular-shaped race including a first plastic member and a second plastic member joined to each other to define the closed internal space, the first plastic member having a U-shaped cross-section and the second plastic member adapted to cover an open side of the U-shaped cross-section of the first plastic member, the second plastic member having a first surface facing the first plastic member and a second surface opposite to the first surface,
wherein the U-shaped cross-section of the first plastic member is defined in part by side walls, each of the side walls including an engaging portion to engage with a portion of the second plastic member,
wherein the engaging portion includes a fusion ridge adapted to be inserted within a fusion groove provided at the second plastic member and an inner pocket ridge which is spaced apart from the fusion ridge and configured to create a space to receive fusion scraps falling inward off the fusion ridge to prevent the fusion scraps from being introduced into the closed internal space of the ball balancer, the inner pocket ridge adapted to engage with a guide ridge of the second plastic member, and
wherein the guide ridge of second plastic member protrudes from the first surface at an inner side of the fusion groove toward the first plastic member, and a groove is formed on the second surface at a position corresponding to the guide ridge.

2. The drum type washing machine of claim 1, wherein the groove extends in a circumferential direction of the annular-shaped race.

3. The drum type washing machine of claim 1, wherein the groove includes an inclination surface that is inclined toward a bottom of the groove.

4. The drum type washing machine of claim 1, wherein the first surface of the second plastic member includes a portion that protrudes toward the first plastic member.

5. The drum type washing machine of claim 1, wherein the second plastic member further includes an outer pocket flange protruding from an outer side of the fusion groove, the outer pocket flange including a surface which physically contacts the spin tub when the ball balancer is coupled thereto, and
wherein the ball balancer is coupled to the spin tub such that the open side of the U-shaped cross-section of the first plastic member faces in a direction different from a direction of gravity.

6. A drum type washing machine, comprising:
a housing;
a spin tub to hold laundry to be washed, the spin tub rotating with respect to a horizontal axis of the washing machine; and
a ball balancer coupled to the spin tub to compensate for a dynamic imbalance during rotation thereof, the ball balancer comprising a first plastic member and a second plastic member joined to each other to define a closed internal space in which a plurality of balls and viscous fluid are accommodated, the first plastic member including a first side wall, a second side wall and a connecting wall between the first side wall and the second side wall, the first plastic member having an open side opposite to the connecting wall, and the second plastic member adapted to cover the open side of the first plastic member, the second plastic member having a first surface facing the first plastic member and a second surface opposite to the first surface,
wherein the first side wall includes a first engaging portion to engage with a first portion of the second plastic member, the second side wall includes a second engaging portion to engage with a second portion of the second plastic member, the first engaging portion includes a first fusion ridge and an inner pocket ridge which is spaced apart from the first fusion ridge and configured to create a space to receive fusion scraps falling inward off the fusion ridge to prevent the fusion scraps from being introduced into the closed internal space of the ball balancer, and the second plastic member includes a first fusion groove and a guide ridge formed on the first surface to receive the first fusion ridge and engage the inner pocket ridge, respectively, and a groove formed on the second surface, the groove corresponding to the guide ridge.

7. The drum type washing machine of claim 6, wherein the first side wall, the second side wall and the connecting wall form a three-sided annular-shaped structure having the open side.

8. The drum type washing machine of claim 7, wherein the three-sided annular-shaped structure has a U-shaped cross-section with a first rounded corner between the first side wall and the connecting wall and a second rounded corner between the second side wall and the connecting wall.

9. The drum type washing machine of claim 6, wherein the first side wall is located most distant from a center of rotation of the annular-shaped race, and the second side wall is located closest to the center of rotation of the annular-shaped race.

10. The drum type washing machine of claim 6, wherein the second side wall is located most distant from a center of rotation of the annular-shaped race, and the first side wall is located closest to the center of rotation of the annular-shaped race.

11. The drum type washing machine of claim 6, wherein the second engaging portion includes a second fusion ridge.

12. The drum type washing machine of claim 11, wherein the second plastic member includes a second fusion groove adapted to receive the second fusion ridge.

13. The drum type washing machine of claim 6, wherein the groove extends in a circumferential direction of the ball balancer.

14. The drum type washing machine of claim 6, wherein the first surface of the second plastic member includes a portion that protrudes toward the first plastic member.

15. The drum type washing machine of claim 6, wherein the second plastic member further includes an outer pocket flange protruding from an outer side of the first fusion groove, the outer pocket flange including a surface which physically contacts the spin tub when the ball balancer is coupled thereto.