Link Ball

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 the smallest possible clearance.

Precautions on Use

Types

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Wear resistance

Features

Structure and Features

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.

Compact Design

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.

Achieves Sphericity of 0.001 mm

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 (Durability Tests with Link Ball Model BL

Alloy

High Strength Aluminum Alloy "A-1 Alloy"

"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.

*The figures shown are target values—these figures are not guaranteed.

● 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

Tensile strength	343 to 392 N/mm²
Tensile yield strength (0.2%)	245 to 294 N/mm²
Compressive strength	490 to 637 N/mm²
Compressive yield strength (0.2%)	294 to 343 N/mm²
Charpy impact	0.098 to 0.196 N･m/mm²
Elongation	2 to 3 %
Hardness	140 to 160 HV

● Physical Properties

Specific gravity	3
Melting point	570℃
Specific heat	793 J/(kg･k)
Linear expansion rate	22×10^-6

High Strength Zinc Alloy

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.

*The figures shown are target values—these figures are not guaranteed.

● Mechanical Properties

Tensile strength	275 to 314 N/mm²
Tensile yield strength (0.2%)	216 to 245 N/mm²
Compressive strength	539 to 686 N/mm²
Compressive yield strength (0.2%)	294 to 343 N/mm²
Fatigue strength	132 N/mm²×10⁷(Schenk bending test)
Charpy impact	0.098 to 0.49N･m/mm²
Elongation	1 to 5 %
Hardness	120 to 145 HV

● Physical Properties

Specific gravity	6.8
Melting point	390℃
Specific heat	460 J/(kg･k)
Linear expansion rate	24×10^-6

● 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

How Load Directions Are Called

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.

Pushing Load and Pulling Load

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.

Model No.	Axial direction	Radial direction
Model BL	X	○
Model BL-A	X	○
Model RBI	○	X

Durability Tests with Link Ball Model BL

Purpose of the Tests

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.

Tested Product, Test Items, Test Conditions and Test Results

Test item	Tested model No.	Test conditions
Test item	Tested model No.	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°			Normal tem- perature

Test item	Test Result					Evaluation
		Sample No.	Change in clearance(μm)		Conditions of the holder, etc.
		Sample No.	Radial direction	Axial direction	Conditions of the holder, etc.
Rotation and rocking durability	THK model BL10D	(1)	26	42	The shank was capable of smoothly rotating after the 1-million cycle test, and capable of continuously operating.	Even in complex link motion, THK model BL10D demonstrated higher durability and wear resistance of the holder than competitor’s product.
	THK model BL10D	(2)	25	40
	compet- itor’s	(1)	Broke in the holder neck after 8,600 cycles		Wear and damage were observed in the holder’s spherical area in approx. 150,000-cycle operation.	The abrasion loss of the competitor’s product immediately before the breakage of the holder was 6 times greater than THK model BL10D (Radial direction).
		(1)	154	60
		(2)	Broke in the holder neck after 8,600r cycles
		(2)	62	20
Lowtemperature rotation durability	THK model BL10D	(1)	63	65	The boot did not show a crack or the like at low tem- perature	This indicates that THK model BL10D is suffi ciently capable of operating in outdoor applications in cold climates.
Lowtemperature rotation durability		(2)	56	59
High temperature rotation durability		(1)	79	84	The boot did not show a crack or the like at low temperature	This indicates that THK model BL10D is suffi ciently capable of operating in hot areas of a truck engine.
High temperature rotation durability		(2)	74	78
Muddy- water rotation durability		(1)	48	51	No muddy-water penetration that may cause wear was observed.	This indicates that THK model BL10D is suffi ciently capable of operating in environments subject to muddy water such as trucks, construction vehicles and agricultural machines since the sealing effect of the boot prevents penetration of muddy water.
		(2)	57	63
		(1)	32	38
		(2)	35	42
Muddy- water rocking durability	compet- itor’s	(1)	240	105	Muddy water penetrated the boot, the spherical area showed chipping and the boot had cuts.	The competitor’s product cannot be used in environments subject to muddy water since chipping or the like may occur in such environments. In addition, wear of the spherical area reached 0.24 mm, 7.4 times greater than THK model BL10D.
Muddy- water rocking durability	compet- itor’s	(2)	246	107

Comprehensive Evaluation

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.