After surface processing of parts, tiny peaks and valleys will be produced. The height and spacing of these peaks and valleys are called surface roughness. It is a microscopic geometric shape error, also known as microscopic roughness

friction and wear

Matching properties

corrosive

fatigue strength

Joint surface sealing

surface profile

Sampling length lr

Evaluation length ln

Contour filter

conveyor belt

Contour center line

Surface profile geometry parameters

Contour arithmetic mean deviation Ra

Maximum profile height Rz

Average width of contour unit Rsm

Profile support length ratio Rcr (c)

16% principle

maximum rule

In general, choose from the height parameters Ra and Rz

When Ra is 0.025-6.3μm, the Ra value is preferred (because Ra can fully reflect the characteristics of the surface profile of the part, the measurement method is simple, and the measurement efficiency is high)

When Ra＞6.3μm or Ra＜0.025 μm, Rz can be selected (because this range facilitates the selection of instruments for measuring Rz)

When the part material is soft, Ra is usually measured with a stylus.

On the premise of meeting the functional requirements, a larger roughness value should be used as much as possible

On the same part, the roughness value of the working surface is smaller than the roughness value of the non-working surface

The friction surface has a smaller roughness value than the non-friction surface; rolling friction table The roughness value of the surface is smaller than that of the sliding friction surface

Surfaces with high moving speeds, heavy loads, and important parts subject to alternating loads should have smaller surface roughness values ​​for fillets and grooves.

The precision of joint surfaces, dimensional tolerances and geometric tolerances that require high matching accuracy For surfaces with high requirements, choose a small value for roughness.

For parts with the same tolerance level, the surface roughness of small sizes and shafts is smaller than that of large sizes and holes.

The surface roughness value that requires anti-corrosion, good sealing performance, or beautiful appearance should be small.

Where relevant standards have stipulated surface roughness requirements (such as journals and housing holes that cooperate with rolling bearings, keyways, gear working surfaces, etc.), the surface roughness value should be determined according to the corresponding standards.

Graphical symbol for surface roughness

Marking of surface roughness

How to mark surface roughness requirements on drawings

Assess surface roughness by comparing the measured surface to a roughness template

It is a contact method for measuring surface roughness. Commonly used measuring instruments are electric profilometers

Use the "light section principle" to measure surface roughness. The commonly used instrument is a light section microscope to measure the Rz value, 0.5-60μm