- iglide® Plastic Bushings: p x v value, Lubrication

Table 1.3: Heat conductivity values of shaft or housing materials

Material	Thermal Conductivity [W/m x k]
Steel	46
Aluminum	204
Cast iron	58
V2A	16
Ceramic	1,4
Plastic	0,24

Figure 1.9: Correction factor for the p x v value

Picture 1.9: Testing the properties of plastic bushings

Table 1.4: Adjustment of the permitted p x v value through lubrication

Lubrication	Correction factor
Dry operation	1
In the installation	1.3
Persistent, fat	2
Persistent, water	4
Persistent, oil	5

p x v value

For plastic bushings, the product is given a new value depending on the specific load (p) and the surface speed (v). The p x v value can be considered a measure of the frictional heat and can be used as an analytical tool to answer questions concerning the proper application of a plastic bushing. For this purpose, the actual p x v value is a function of the shaft material of the ambient temperature and the operating time.

Permitted p x v value

Present is

K1, K2	Constant for heat dissipation
	(K1 = 0.5, K2 = 0.042)
s	Plastic bushing wall thickness (inch)
b1	Plastic bushing length (inch)
μ	Coefficient of friction
λs	Heat conductivity of the shaft
λk	Heat conductivity of the plastic bushing
ΔT	(T_a - T _u)
T_u	Ambient temperature
T_a	Max. ambient temperature

Correction factor

The tolerated p x v value can be increased in intermittent operation if the plastic bushing temperature never reaches its maximum limit because of the short operating times. Tests have shown that this is true for operating times below 10 minutes. An important qualifier here is the ratio of the operating time and pause intervals. Long pauses make a greater contribution to re-cooling.
The different curves in Figure 1.9 represent different ratios ("3 times" means that the pause lasts 3 times longer than the operating time).

Lubrication

Although iglide® plastic bushings are designed to run dry, they are compatible with standard lubricants. A single lubrication during installation improves the start-up behavior and coefficient of friction, thus reducing the frictional heat. The permissible loads for plastic bushings can also be increased by using lubrication. Table 1.4 shows the correction factors for the p x v value when using lubrication.