The manufacturing process of reducers (reducer couplings) mainly depends on the material (metal/plastic), nominal diameter and pressure rating requirements. It is mainly divided into two categories: manufacturing processes for metal reducers and plastic reducers. The production flow, equipment and key control points vary significantly among different processes, which are elaborated as follows:
I. Main Manufacturing Processes for Metal Reducers
(Carbon Steel / Stainless Steel / Alloy Steel)
1. Seamless Hot Extrusion Process
(Core process for high-pressure small-diameter reducers)Application: Seamless reducers (mainly concentric) of DN15~DN300 with PN≥10MPa, mostly made of carbon steel, stainless steel and alloy steel. Production Flow:① Raw Material Preparation: Select seamless steel pipes (outer diameter matching the large end of the reducer) and cut into fixed-length tube blanks (length = developed length of the reducer + allowance).② 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.③ Die Assembly: Fit the heated tube blanks into extrusion dies (inner cavity in conical shape, with a mandrel at the small end).④ Hydraulic Extrusion: Push the blanks through the dies with a 500~2000-ton hydraulic press; the blanks conform to the die cavity under pressure to form a conical reducer blank.⑤ Shaping & Calibration: Put the extruded reducer into a shaping die to correct the taper angle, length and wall thickness uniformity (taper angle tolerance ±1°, length tolerance ±5mm).⑥ Heat Treatment: Anneal carbon steel reducers for stress relief (hold at 600~650℃ for 2 hours); perform solution treatment on stainless steel reducers (heat at 1050℃ followed by water cooling).⑦ Machining: Machine welding bevels at both ends (for butt welding, angle 37.5°±2.5°) and grind surface burrs.⑧ Inspection & Acceptance: Conduct ultrasonic testing (UT) for internal defects, hydrostatic test (1.5 times PN, pressure holding for 30 minutes) and dimensional inspection (diameter, length, wall thickness). Core Advantages: No welds, high pressure resistance, uniform wall thickness, suitable for high-temperature and high-pressure conditions.
2. Stamping & Welding Process
(Mainstream process for medium/low-pressure large-diameter reducers)Application: Reducers (both concentric and eccentric) of DN50~DN600 with PN≤4MPa, mostly made of carbon steel and stainless steel. Production Flow:① Raw Material Cutting: Select hot-rolled steel plates (thickness matching the reducer wall thickness) and cut into sector blanks with a CNC cutting machine according to the developed drawing (single sector for concentric reducers, two asymmetric sectors for eccentric reducers).② Stamping Forming: Heat the sector blanks to 850~900℃, place into stamping dies and press into semi-conical shells with a hydraulic press (one shell for concentric reducers, two asymmetric shells for eccentric reducers).③ Welding Assembly: Fit the two semi-conical shells, perform TIG welding for root pass and arc welding for filling & capping to form a complete conical reducer (flat-bottom alignment shall be ensured for eccentric reducers).④ Weld Inspection: Conduct radiographic testing (RT) or ultrasonic testing (UT) to check weld quality and ensure no cracks or incomplete penetration.⑤ Shaping + Heat Treatment: Correct welding deformation and perform low-temperature annealing for stress relief.⑥ Machining + Finished Product Inspection: Same as the seamless hot extrusion process. Core Advantages: Capable of producing large-diameter and eccentric reducers, lower cost than the seamless extrusion process.
3. Rolling & Welding Process
(Special process for extra-large diameter reducers)Application: Large-diameter reducers of DN≥600 with PN≤1.6MPa (e.g. municipal drainage, mine pipelines), mostly made of carbon steel. Production Flow:① Raw Material Rolling: Select thick steel plates and roll into conical shells with a plate rolling machine (taper realized by adjusting roller spacing).② Longitudinal Seam Welding: Weld shell longitudinal seams (mainly submerged arc welding) and grind welds smooth.③ End Treatment: Cut excess material at both ends to ensure dimensional accuracy.④ Inspection & Acceptance: Visual inspection + low-pressure hydrostatic test; non-destructive testing is not required (low-pressure service). Core Advantages: Customizable extra-large diameter reducers, short production cycle and low cost.
4. Casting Process
(Process for low-pressure cast iron reducers)Application: Cast iron reducers of DN50~DN1200 with PN≤1.6MPa (e.g. drainage in old buildings). Production Flow:① Sand Mould Making: Make reducer sand moulds with quartz sand (including gates and risers).② Melting & Pouring: Melt pig iron to 1150℃ and pour into the mould through the gate; risers are used for slag removal and feeding.③ Cooling & Demolding: Break the sand mould after natural cooling for 24 hours and take out the reducer blank.④ Sand Cleaning & Machining: Remove adhered sand, cut gates/risers and grind burrs.⑤ Hydrostatic Test: Conduct low-pressure water test (0.6MPa, pressure holding for 10 minutes); deliver after passing leakage inspection.
II. Manufacturing Processes for Plastic Reducers
(PVC / PPR / PE)
1. Injection Molding Process
(Core process for PVC/PPR reducers)Application: PVC/PPR reducers (mainly concentric) of DN15~DN100. Production Flow:① Raw Material Drying: Dry PVC/PPR pellets in a dryer until moisture content ≤0.2% (to avoid bubbles during injection molding).② Heating & 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).③ High-Pressure Injection: Inject molten plastic into the reducer injection mould (cavity in conical shape) at high pressure via a screw, holding pressure for 10~15 seconds.④ Cooling & Demolding: Cool the mould with circulating water to below 60℃ and eject the finished reducer.⑤ Trimming & Inspection: Cut gate scraps, inspect dimensions (diameter, wall thickness) and surface quality (no short shots or bubbles), then package for delivery.
2. Hot-Melt Welding Process
(Process for large-diameter PE reducers)Application: PE reducers (mainly eccentric) of DN≥110 for buried gas/water supply pipelines. Production Flow:① Raw Material Preparation: Cut PE pipes into large-end and small-end sections, and expand the large-end section by heating.② 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.③ Welding Reinforcement: Cool after hot-melt welding and inspect weld strength (tensile test).④ Inspection & Acceptance: Conduct dimensional inspection + low-pressure air tightness test to ensure no leakage.
III. Key Quality Control Points
- Wall Thickness Uniformity: Wall thickness deviation ≤±12.5% for seamless extruded reducers; wall thickness at welds ≥ that of base metal for stamped & welded reducers.
- Taper Angle Accuracy: Taper angle tolerance ±1° for concentric reducers; flat-bottom alignment for eccentric reducers (deviation ≤0.5mm).
- Pressure Resistance: Metal reducers shall pass hydrostatic test at 1.5 times PN; plastic reducers shall pass hydrostatic test at 1.25 times PN.
