Coefficient of linear expansion

In this page we will explain the coefficient of linear expansion.

What is linear expansion coefficient?

The coefficient of linear expansion is the rate at which an object changes or expands in length due to an increase in temperature.

Therefore, it can be said that materials with large coefficients of linear expansion tend to change in length due to temperature rise.

What is the difference from the coefficient of thermal expansion?

In some cases, the coefficient of linear expansion is called the coefficient of thermal expansion, and they are almost synonymous.

In the case of the coefficient of thermal expansion, it is sometimes expressed as the “volumetric expansion coefficient,” which is the rate at which the volume of an object expands.

Formula for coefficient of linear expansion

The coefficient of linear expansion can be obtained from the ratio of the amount of deformation ΔL due to a temperature change of 1°C and the length L before deformation.

The calculation formula is as follows.

• Coefficient of linear expansion α＝(ΔL/L)×(1/ΔT)

Unit of coefficient of linear expansion

The unit of coefficient of linear expansion is expressed as one of the following.

• 1/℃
• 1/K

“℃” is the unit of Celsius temperature, and “K” is the unit of absolute temperature, read as “Kelvin”.

Even if the unit of coefficient of linear expansion is converted from “1/°C” to “1/K”, the value will be the same.

Coefficient of linear expansion of main materials

The linear expansion coefficients of commonly used materials are as follows.

Coefficient of linear expansion of metal

Material		Coefficient of linear expansion(10-6/℃)
aluminum	A2017	23.6
	A5052	23.8
	A5056	24.3
	A7075	23.6
structureal steel	SS400	11.7
carbon steel	S45C	12.1
	S50C	11.7
	S55C	11.7
tool steel	SKS3	12.2
	SKD11	12.0
stainless steel	SUS303	17.3
	SUS304	17.3
	SUS430	10.4
coppere	C1100	17.7
	C1020	17.7
brass	C2801	20.8
	C3604	20.5
	C2700	20.3
titanium		6.3~8.4
magnesium	AZ31	26.8
	AZ91	27.2
molybden		5.2
tungsten		4.4
inconel		11.5～13.3
potassium		85
gold		14.2
silver		18.9
lron		11.8
lead		28.9
nickel		13.4
platinum		8.8
magnesium		24.8
prehardened steel		11.5
nichrome		18
duralumin		23
platinum		8.9

Linear expansion coefficient of resin

Material		Coefficient of linear expansion(10-6/℃)
MC nylon	MC801	80
6 nylon	6N	72
Duracon, Polyacetal	POM	81～85
polypropylene	PP	58～100
polyethylene	PE	120～140
Polycarbonate	PC	66
polyethylene terephthalateート	PET	65
acrylic	PMMA	50～90
vinyl chloride	PVC	50～100
Acrylonitrile・Butadiene・Styrene	ABS	65～95
Teflon	PTFE	70～100
polybutylene terephthalate	PBT	25～95
polyether ether ketone	PEEK	25～50
Polyphenylene sulfide	PPS	49
polyamide imide	PAI	30.6
polyvinylidene fluoride	PVDF	160
paper bake	cloth bake
	paper bake	160
Epoxy Glass		60～60.5
Polystyrene		34-210
Polymethyl Methacrylate		80

Linear expansion coefficient of other materials

Material	Linear expansion coefficient(10-6/℃)
silicon	2.6
diamond	1.0
zirconia	5.4
graphite	3.1
boron	4.7
granite	4-10
marble	3〜15
common grass	8-10
pyrex glass	2.8

If you have any questions about precision machining, please contact TDC

At our company, in order to suppress thermal expansion, we polish so as not to generate frictional heat as much as possible. In addition, we take measures to prevent the measurement results from being affected by temperature acclimatization before measurement.

Precise polishing is possible not only for the above materials, but also for various materials such as metals, resins, ceramics, and crystal materials. If you have any questions regarding the selection of materials, please feel free to contact us.

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