What is surface roughness? How is the roughness standard regulated?

In mechanical processing, surface roughness is an important factor in the requirements for detailed parameters of processing products. For each processing product, depending on the application, the surface roughness requirements will be different. The roughness of the surface has an important effect on the durability and performance of the product. Therefore, learning about what roughness is, surface roughness chart and its importance is extremely necessary.

Table of Contents

What is surface roughness?

The English surface roughness is Suface Roughness. Also known as roughness or surface gloss.

Roughness usually refers to the roughness of the processing product surface. The process of processing the creation of the product that looks with the naked eye can see the gloss, but in fact there are still uneven places. Roughness is a measure of the total number of uneven points on the surface.

It is quantified by the deviation in the direction of the mesong vector of a real surface relative to the gloss requirement. The larger the deviation, the rougher the surface. And conversely, the smaller the deviation, the smoother the surface. The adjustment of roughness depends on the requirements and purpose of the processing product.

What is the finished surface?

The finished surface refers to the process of changing the metal surface including the removal, addition or reshaping. It is a complete structural measure of a product surface defined by three characteristics:

Surface roughness
Roughness
Class and so on.

However, when it comes to surface finishes, it is often interpreted as surface roughness.

Waviness is a warped surface that has a distance greater than the rough surface length.And laying is the direction in which the surface pattern prevails.Machinists often identify layers by the methods used for the surface.

In order to get a good finish surface and high accuracy in metalworking, it is essential to cut at a low chip load level.

Why is surface roughness important?

In friction systems, rough surfaces often wear out faster and have a higher friction coefficient than smooth surfaces. Roughness is a good predictant of the performance of the processing product. Abnormal locations such as convex spots can be the cause of cracks or corrosion.

Extremely important for corrosion and chemical effects.
Aesthetics for processing products.
Affects the adhesion of coatings and paints.
Remove defects on the surface.
Affecting the conductivity/insulation of the product
Increase the abrasion resistance of the product while minimizing the impact of friction.

The lower the roughness, the smoother the surface. However, reducing surface roughness will increase production costs. This leads to a trade-off between the cost of production and the performance of the in-application processing product.

In mold processing, the gloss of the mold is an important factor that determines the fine surface quality of the plastic product. In order for the mold to achieve the required polishing, the surface of the face must be smooth.

Symbols and abbreviations of surface roughness charts

When you learn about roughness? How to read the rough chart, you will see abbreviation symbols such as Ra, Rsk, Rq, Rku, Rz, etc.They are the unit used to measure surface finish.

Ra – Medium surface roughness (μm). Is the absolute average value of profin (hi) in the standard length of L. Often used to assess level 5 to level 11 roughness.

Rmax – Vertical distance from the Top to the lowest bottom position.

Rz – Medium Maximum Height (μm)

The average height of the Rz profile, is also measured in μm. It is the average value of the total absolute values of the top 5 peaks (ti) and the 5 lowest bottoms (ki) in the standard length of L. It is commonly used to assess level 1 to level 5 and levels 13 and 14.

According to TCVN 2511:2007,surface smoothness is divided into 14 levels.

Level 14 is the highest (the smoothest surface) as the following table:

Surface quality	Rough level	Rough parameters		Standard length (mm)
Surface quality	Rough level	Out (μm)	Rz (μm)	Standard length (mm)
Coarse	1	80 – 40	320 – 160	8.0
	2	40 – 20	160 – 80
	3	20 – 10	80 – 40
	4	10 – 5	40 – 20
Semi-chimpanzees	5	5 – 2.5	20 – 10	2.5
	6	2.5 – 1.25	10 – 6.3
	7	1.25 – 0.63	6.3 – 3.2
Star	8	0.63 – 0.32	3.2 – 1.6	0.25
	9	0.32 – 0.16	1.6 – 0.8
	10	0.16 – 0.08	0.8 – 0.4
	11	0.08 – 0.04	0.4 – 0.2
Supernovae	12	0.04 – 0.02	0.2 – 0.1	0.08
	13	0.02 – 0.01	0.1 – 0.05
	14	0.01 – 0.005	0.05 – 0.025

Table 1: Surface smoothness levels

People can take screenshots to make it easier to find when needed.

Related surface roughness standards

Processing accuracy: is the level of accuracy achieved after processing compared to the original requirements in the design that you desire.

In fact the processing accuracy is indicated by the errors in size, deviations in geometric shape, deviations in relative position between the geometric elements of the detail indicated by tolerance.

The processing accuracy is partly expressed in the shape of the microscopic class geometry on the surface of the detail. It is glossiness or surface smoothness, also known as roughness.

Correct level: The correct level is prescribed by the value from small to large according to the degree of size accuracy.

TCVN and ISO are divided into 20 different levels of accuracy, they are numbered in descending order of accuracy of 01, 0, 1, 2, … 15, 16, 17, 18. In it:

– Level 01 ÷ level 1 are super accurate levels.

Level 1 ÷ level 5 are highly accurate levels. These levels apply to the correct details, measuring instruments.

Level 6 ÷ level 11 are the usual levels of accuracy. These levels apply to dockings.

Level 12 ÷ level 18 are low-precision levels. These levels are for free (non-assembled) dimensions.

Processing method	Precision level	Gloss level
External, internal convenience, coarse grates	5	1-3
External convenience, inner convenience, semi-crystal cell	4	4-7
External, internal convenience, chimpanzees	3	7-9
Rough milling	4	1-3
Crystal milling	3	4-5
Drilling, cutting	5	4-6
Rough doa	3	5-7
Doa Chimpanzee	2	8-9
Rough grooming	2a	6-8
Refine	2	9-10
Rough grinding	3a	6-7
Semi-chimpanzee grinding	2	8-9
Grinding chimpanzee	1	9-10
Rough grinding	2	10-12
Clever grinding	1	13-14
Rough grinding	2	6-8
Semi-crystal crushed	1	8-9
Crushed chimpanzee	1	9-11
Tooth stripes, rough teeth milling	4	5-6
Tooth stripes, fine tooth milling	2	6-7
Cavture	2	8

Table 2. Surface accuracy and gloss achieved by processing methods

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