Painting and sanding

Painting:

is the process of spreading the paint on the surface of the object. Due to the different coatings, there are many coating methods. Common coating methods are: scraping, wiping Coating, brushing, spraying, rolling, dipping and curtain coating, etc.

Basic operation method of painting:

In the actual operation of the coating process, there are actually only two, most of which are sanding and coating. Here I mainly focus on sanding and coating equipment Configuration, theoretical basis and related main requirements as well as steps and methods in actual operation

Sanding: As the saying goes: very paint; three-point sanding, which shows the importance of sanding in painting operations, just sanding below Give some specific instructions

The role of sanding: Generally speaking, sanding has the following functions in coating operations

  1. Remove burrs, oil stains and other surface contaminants on the surface of the white embryo
  2. Reduce the surface roughness of the workpiece, and remove the various processing traces left on the surface during mechanical or manual processing to obtain a smooth and even coating surface< /li>
  3. Enhance the mechanical adhesion of paint
  4. For polishing workpieces, sanding is far beneficial to the smooth progress of the polishing work
  5. Eliminate the rough and uneven raised parts of the seal coating and reduce paint consumption during the seal coating

Methods and advantages and disadvantages of sanding:

The sanding method is generally divided into manual sanding and mechanical sanding:

Manual sanding: general dry sand, wet sand and manual mechanical sand.

  1. Dry sand: generally suitable for hard or brittle surfaces or varnishes, a lot of dust will be generated during the operation, which will affect environmental hygiene
  2. Wet sand: generally used for hand sanding, sanding with water sandpaper or soap, water sanding can reduce sand marks and improve the smoothness of the coating. It saves sandpaper, saves effort and There is no dust floating and will not cause environmental pollution, but the water-sand work piece must wait for the water-milling layer to be completely dry or dry before applying it to the top coat, otherwise it will cause the paint film to self-ify or delamination. In addition, wood with strong moisture absorption is not suitable Water milling, water milling is generally used in paint layer or returning to the workpiece or in the work requiring polishing
  3. Manual mechanical polishing: Large-area construction with electric or pneumatic sand mills can help improve work efficiency, but mechanical sanding is generally only used for white embryos And sanding of the primer

Mechanized sanding

  1. Relying on a belt sander, a large area or curved surface is sanded through a pressure rod or a manual pad. We generally call it hand-pressed sand

The sanding surface is flat and smooth, and the type of sanding belt used for hand-pressing sand is determined according to the process flow

  1. Relying on the sanding machine’s rotation to drive the sanding belt, the flat workpiece passes above or below the sanding belt by the sanding and transfer belt to achieve a large area under the surface Sanding
  2. Edge sanding machine relies on the mold to sand the edge of the part or the linear part, which is only suitable for straight curve or flat sanding li>

Comparison table of sanding requirements for each part

 

Commonly used sandpaper Commonly used sandpaper models Sanding method Functions and requirements
White embryo sanding 180# Hand sand / machine sand Wear thoroughly in the direction of the wood grain, remove burrs or oil stains, check and deal with all quality defects caused or missed in the white embryo processing process, and prepare for painting
Sanding the soil 240# Hand sand / machine sand The residues of the soil filling must be polished clean without leaving any residue. Check for missing or incomplete repairs and repair them in time. The surface of the workpiece is sanded and smooth. Clean
Head degree sanding 320# Hand sand Gently sand in the direction of the wood grain to remove wood hair and particles, not sand
Sanding primer 320# 400# 600# Hand sand / machine sand Sanding of flat primer320#Sandpaper is thoroughly and completely polished to remove oil residue or particles and enhance the adhesion between paint layers(Adhesion)Check Check if there is any defects such as pinholes, dents, etc. and deal with it, and use it for the last time400# or 600#Sand paper, completely and thoroughly polished and smooth, reducing the degree of sand marks to the surface Preparation for painting
Sanding finish 600# 800# 1000# 2000# Hand sand / machine sand For resprayed or repaired workpieces600#or800#sand paper thoroughly, For enhancing mechanical adhesion and polishing workpieces1000#or2000# Sand paper removes particles, increases roughness, and facilitates polishing

 

Causes and solutions for poor sanding

Reason for formation Processing method
Sand marks are too heavy a.Sand paper over-grade sanding, wrong model

b.no sand inspection

c.not completely dry

a.Use the corresponding type of sandpaper for construction

b.Use fine-grade sandpaper to check the sand thoroughly until the sand marks are weakened

c.sand after completely dry

sag point sand The depression after the primer should be filled with soil or primer
Horizontal sanding Not sanding in the direction of the wood grain Use the same type of sandpaper to re-sand along the direction of the wood, and then use fine first-grade sandpaper for sand inspection
Sand wear a.Too much force

b. Repeated sanding

a. White embryo flakes should be refilled with sand, or first sprayed with light yellow primer to fill up, then use pencil and blade to fake the wood grain

b.primer color or topcoat sanding To make up the primer

Incomplete sanding a.the sand is uneven when sanding

b. cut corners when sanding, not sand is good

c.sand leakage

Re-sand all hand sand or machine sand
Collision injury Excessive movements during transportation or operation a.Be sure to handle with care when transporting or operating

b.according to different situations502Glue and wood chips or soil, primer, etc. are repaired and then sprayed again