BL and RBI – Khớp cầu nối Link Ball THK

With the Link Ball, a highly accurate bearing steel ball used in the spherical area is first encased in the holder by die cast molding, and then is specially welded with the shank. This unique process enables the mirror surface of the steel ball to be transferred or duplicated on the spherical surface inside the holder to ensure full contact between the ball and the holder. As a result, smooth motion is achieved with a minimum clearance.

Model BL has an adequately firm and yet extremely compact shape because of a highly balanced design. This model is optimal for use in an automobile height sensor or transmission control.

The spherical surface of the shank ball is transferred on the inner surface of the holder while maintaining the sphericity of the bearing steel ball. This allows smooth motion to be achieved with a minimum clearance and provides favorable operability and feel to the link motion.

Two Types of Holder Material

Model BL-A uses the newly developed high-strength aluminum alloy “A-1 Alloy” (see Alloy ), which is light and highly resistant to wear.
Models BL6 and above and model RBI uses the proven high strength zinc alloy (see High Strength Zinc Alloy ).

High Lubricity

The boot contains grease for high lubricity and increased wear resistance.

Large Hexagonal Bolt Seat

The hexagonal bolt seat of the shank has the same dimensions as the seating surface for small hexagon head bolts in accordance with automotive specifications. This prevents the seating surface from sinking and ensures a stable link motion mechanism.

Equipped with a Boot for Protection against Muddy Water

Use of a boot with high trackability in the ball shank prevents muddy water from entering the spherical area even in a muddy environment. Accordingly, types equipped with boots are used also in outdoor applications and automobile parts under the chassis. For details, see the muddy water test data

“A-1 Alloy,” a newly developed high strength aluminum alloy, is an alloy with Al-Zn-Si3 being the main components, is used in the holder of model BL-A. Information on the mechanical properties, physical properties, and wear resistance of materials is presented below.

● Features of the A-1 Alloy

･ Achieves one of the highest strengths among the existing aluminum die cast alloys.
･ Has yield strength approximately twice that of the commonly used aluminum die cast alloy (ADC 12).
･ Has hardness equal to the high strength zinc alloy and achieves high wear resistance.
･ Achieves specific gravity less than a half of the high strength zinc alloy to allow significant weight saving.
･ Highly corrosion resistance and can be used as an automotive part related to wheel control.

● Mechanical Properties

● Physical Properties

Note: The figures shown are target values—these figures are not guaranteed.

The high strength zinc alloy used in the holders of models BL and RBI has been developed as a bearing alloy by mixing Al, Cu, Mg, Be and Ti as well as zinc as the base component. It is excellent in mechanical properties, seizure resistance and wear resistance. Information on mechanical properties, physical properties, and wear resistance is presented below.

● Mechanical Properties

● Physical Properties

● Wear Resistance

The wear resistance of the high strength zinc alloy is superior to that of class-3 brass and class-3 bronze, almost equal to that of class-2 phosphor bronze.

Amsler wear-tester
Test piece rotation speed	185 min-1
Load	392 N
Lubricant	Dynamo oil

Note: The figures shown are target values—these figures are not guaranteed.

Regardless of the shape, the direction of the load applied to the Link Ball is called “axial direction” if it is parallel to the axis of the ball shank, and “radial direction” if it is perpendicular to the axis.

Of the loads applied in the axial direction, the load in the direction of the ball shank being pressed toward the holder is called “pushing load” and the load in the direction of the ball shank being pulled from the holder is called “pulling load.”

● Direction of applied load

The following table shows the load application direction of each model. Avoid using the product in a different load application direction. Failure to do so may damage the product.

The tests were conducted to identify the performance difference between THK Link Ball model BL and an equivalent product of a competitor. As a result, model BL has been used in joints for transmission control units of automobiles, trucks and buses and for steering mechanisms of agricultural tractors.

Test item	Tested model No.	Test conditions
		Applied load	Rotation or rocking angle	Frequency	Total num- ber of rev- olutions or time	Service environ- ment	Load conditions, etc.
Rotation- and- rocking durabil- ity	THK Compar- ison of THK Link Ball model BL10D and compet- itor’s product	±1760N (Radial direction)	Rotation angle: θ=±20° Rocking angle: α=±20°	40 times/min.	1,000,000 cycles	Normal tem- perature
Lowtemperature rotation durability	THK model BL10D only	±1225N (Radial direction)	Rotation angle: θ=±30°	60 times/min.		-30℃	Low-temperature retention time: 280 hours Motion in the rotational direction
High temperature rotation durability						100℃	High temperature retention time: 280 hours Motion in the rotational direction
Muddywater rotation durability						Normal tem- perature
Muddy- water rocking durability	THK Compar– ison of- THK- Link Ball- model- BL10D- and- compet– itor’s- product-		Rocking angle: α=±20°

As a result of comparing THK Link Ball model BL10D and a competitor’s product in representative durability tests, it is demonstrated that model BL10D is superior in strength and wear resistance of the holder and sealability of the boot.These features are achieved through THK’s unique manufacturing process for the holder and the shank, the material used, the structure of upper and lower grease pockets on the spherical area and the development of a highly sealable boot.