The process flow of reducers varies according to materials (metal/plastic) and manufacturing processes (seamless extrusion, stamping and welding, injection molding). It can be mainly divided into two categories: process flow for metal reducers and process flow for plastic reducers. The detailed steps of each mainstream process (from raw materials to finished products) are as follows:
I. Core Process Flow for Metal Reducers
1. Seamless Hot Extrusion Process
(For high-pressure small-diameter seamless reducers)Application: Carbon steel, stainless steel and alloy steel concentric reducers of DN15~DN300 with PN≥10MPa Full process steps:
- Raw material acceptance and cutting
- Raw material: Seamless steel pipe (outer diameter matching the large end of the reducer), with material quality certificates (chemical composition, mechanical properties) inspected.
- Cutting: Cut into fixed-length tube blanks by CNC cutting machine (length = developed length of reducer + machining allowance), with flat and burr-free end faces.
- Heating treatment
- Put tube blanks into a medium-frequency heating furnace and heat to plastic forming temperature (950~1050℃ for carbon steel, 1100~1200℃ for stainless steel).
- Hold for 10~20 minutes to ensure uniform temperature inside and outside the blanks (to avoid cracking during extrusion).
- Hot extrusion forming
- Feed heated blanks into a hydraulic press, fit into conical dies (inner cavity in the shape of a reducer), with a mandrel positioning the small-end diameter.
- The hydraulic press pushes the blanks through the dies at a pressure of 500~2000 tons, and the blanks conform to the die cavity to form a conical reducer blank.
- Shaping and correction
- Place the blank into a shaping die to correct the taper angle (tolerance ±1°), length (tolerance ±5mm) and wall thickness uniformity.
- Cut off excess material at both ends to ensure accurate diameters of the large and small ends.
- Heat treatment
- Carbon steel reducers: Annealing (holding at 600~650℃ for 2 hours, furnace cooling) to relieve extrusion stress.
- Stainless steel reducers: Solution treatment (heating at 1050℃ followed by water cooling) to improve corrosion resistance.
- Alloy steel reducers: Normalizing + tempering to enhance high-temperature strength.
- Machining
- Machine welding bevels at both ends (for butt welding: angle 37.5°±2.5°, root face 1~2mm).
- Grind surface oxide scale and burrs to ensure surface roughness Ra≤12.5μm.
- Quality inspection
- Dimensional inspection: Measure diameter, length and wall thickness with calipers/total station, and check wall thickness uniformity with ultrasonic thickness gauge.
- Non-destructive testing: Ultrasonic testing (UT) for internal defects; radiographic testing (RT) added for high-pressure reducers.
- Pressure test: Hydrostatic test (1.5 times PN, pressure holding for 30 minutes, no leakage or deformation).
- Material re-inspection: Verify material grade with a spectrometer.
- Finished product packaging and marking
- Spray anti-rust paint (carbon steel), pickling and passivation (stainless steel).
- Print markings including model (e.g. DN200×DN150 PN4.0), material and batch number.
- Waterproof packaging with inspection reports attached.
2. Stamping and Welding Process
(For medium/low-pressure large-diameter reducers, including eccentric types)Application: Carbon steel and stainless steel concentric/eccentric reducers of DN50~DN600 with PN≤4MPa Full process steps:
- Raw material cutting
- Raw material: Hot-rolled steel plate (thickness matching the reducer wall thickness), cut into sector blanks according to developed drawings (one sector for concentric, two asymmetric sectors for eccentric).
- Stamping forming
- Heat blanks to 850~900℃, place into stamping dies, and press into semi-conical shells with a hydraulic press.
- For eccentric reducers, ensure the flat-bottom sides are aligned after assembling the two shells.
- Welding assembly
- After shell assembly, perform TIG welding for root pass (to ensure full penetration) and arc welding for filling and capping.
- Remove slag after welding and grind weld reinforcement (0~3mm).
- Weld inspection
- Radiographic testing (RT) or ultrasonic testing (UT) for weld defects, and penetrant testing (PT) for surface cracks.
- Subsequent steps: Same as the seamless hot extrusion process: shaping and correction → heat treatment → machining → quality inspection → finished product packaging.
3. Rolling and Welding Process
(For extra-large diameter low-pressure reducers)Application: Carbon steel reducers of DN≥600 with PN≤1.6MPa Full process steps:
- Steel plate rolling: Put thick steel plates into a plate rolling machine, adjust roller spacing to roll into a conical shell (to realize diameter gradual change).
- Longitudinal seam welding: Weld shell longitudinal seams by submerged arc welding and grind welds.
- End treatment: Cut excess material at both ends to ensure diameter accuracy.
- Low-pressure test: Hydrostatic test (1.5 times PN, pressure holding for 30 minutes).
- Packaging and delivery: Direct marking and packaging without complicated heat treatment.
II. Core Process Flow for Plastic Reducers
1. Injection Molding Process
(For small-diameter PVC/PPR reducers)Application: PVC/PPR concentric reducers of DN15~DN100 Full process steps:
- Raw material drying: Dry PVC/PPR pellets in a dryer at 80~100℃ for 2~4 hours, with moisture content ≤0.2% (to prevent bubbles in injection molding).
- Heating and melting: Feed dried pellets into the barrel of an injection molding machine and heat to melting state (160~180℃ for PVC, 200~220℃ for PPR).
- High-pressure injection: Inject molten plastic into the reducer mold cavity under high pressure via a screw, holding pressure for 10~15 seconds.
- Cooling and demolding: Cool the mold with circulating water to below 60℃, eject the finished product and cut off gate scraps.
- Quality inspection: Dimensional inspection (diameter, wall thickness) and appearance inspection (no shortage, bubbles or cracks).
- Packaging and delivery: Pack qualified products into cartons marked with model and material.
2. Hot-Melt Welding Process
(For large-diameter PE eccentric reducers for buried gas/water supply pipelines)Application: PE eccentric reducers of DN≥110 Full process steps:
- Raw material preparation: Cut PE pipes into large-end and small-end sections, and expand the large-end section by heating.
- Conical transition section fabrication: Thermoform PE sheets into conical transition sections, and butt-weld both ends with large-end and small-end sections by hot-melt (temperature 200~220℃).
- Cooling and solidification: Cool naturally for 30 minutes after welding to ensure weld strength.
- Inspection and acceptance: Dimensional inspection and air tightness test (0.1MPa, pressure holding for 24 hours without leakage).
- Packaging and transportation: Wrap with protective film to prevent scratches during transportation.
III. Core Quality Control Nodes in the Whole Process
- Raw material stage: Material re-inspection (spectral/chemical analysis) to eliminate unqualified materials.
- Forming stage: Temperature and pressure control (hot extrusion/injection molding), weld quality (welding procedure).
- Inspection stage: Dimensional tolerance, non-destructive testing, pressure test (core acceptance items).
- Finished product stage: Clear marking and adequate protection (anti-rust/anti-scratch).
