Production Process of "321" And "200" Prefabricated Highway Steel Bridges

（1) Material

1. Material purchase

According to the requirements of construction drawings and materials, the materials should be purchased in large-scale iron and steel production enterprises and large-scale iron and steel enterprises in China, which requires a guarantee of material quality, and can also be sampled to do physical and chemical tests in the operating enterprises.

2. Material test

The materials that arrive in the company's factory should be sampled in accordance with the requirements of the welding procedure assessment report, and physical and chemical tests should be carried out in qualified test units before they can enter the production process

（2) Blanking and processing parts

1. The cutting must be carried out on the laser profile cutting machine according to the regulations in the process card, and should meet the tolerance requirements of the construction drawing or process card.

2. After cutting, shaping, deburring, rust removal, stain removal, and reverse welding of the groove shall be carried out, and stored according to the number for future use.

3. The parts are processed according to the tolerance of the process drawing, and the flat laser cutting machine is used for cutting and processing.

（3) Assembly

1. The assembly of small components, tools, accessories, vertical members, upper and lower chord members, and truss pieces should be carried out on a specially designed and technologically required jig frame.

2. Assembly should be carried out in a sequential process, and the limit support on the jig frame should be accurate and reliable. If there is looseness or deformation, it should be replaced in a timely manner.

（4) Welding

1. Welding should be carried out after the approved welding process review report。

2. The welding of small components, accessories, tools, chords, truss pieces, etc. should be aligned with the welding requirements in the construction drawing, and corresponding welding measures should be taken. The equipment used is an automatic welding robot.

3. Welding method, polarity, welding material, specifications, welding current, arc voltage, and welding speed should be executed according to regulations.

4. The internal and external quality of welding should meet the requirements of the construction drawings.

（5)Hole processing of truss pieces

1. The hole processing of chord members, vertical members, and small and medium-sized square blocks is carried out through punching and drilling according to the process requirements. Punching and turning holes should meet the requirements of the construction drawings.

2. The female and male head holes in the truss piece are drilled and reamed on a fixed drilling machine, and the machining accuracy meets the tolerance requirements of the construction drawing. The equipment is a CNC machining center.

（6)Painting

1. The main accessories of the 321 "steel bridge all adopt shot blasting and rust removal technology. After the shot blasting meets the requirements, the surface dust is blown off with compressed air, and protective treatment layer is applied to the areas without paint.

2. Spray anti rust paint first, reaching the oil film thickness once, and then spray a second coat of military green paint after the paint dries.