1. What is the difference between a semi-trailer and a full trailer? What type does Mingsin produce?
A full trailer supports the full weight of its cargo through its own structure. A semi-trailer transfers part of its load to the towing vehicle. Mingsin primarily produces full trailers.
2. Why is the turntable called a "coreless" turntable? What material is it made of? What are the common models? What should be noted before use? What are its advantages? What other steering types exist?
1) The turntable consists of an upper and a lower flange. The mounting surfaces of the flanges are angled, and the mating surfaces are tapered. Ball races are machined into the tapered surfaces to hold the balls. The outer side of the lower flange has a groove. The material is steel.
2) The turntable is made of ductile iron or Masteel (a type of high-quality carbon steel).
3) Common models: ∮600, ∮750, ∮850, ∮1050, ∮1100, ∮1200 (mm).
4) Grease must be added before use.
5) Advantages: simpler manufacturing process, lighter weight, easier installation, high load capacity, strong impact resistance, not prone to fracture or damage, and longer service life.
6) Other steering methods include kingpin steering and universal joint steering, mostly used in automobiles.
3. What is the function of the buffer spring? What is the function of the rubber block?
Buffer spring: When the towing vehicle brakes, it reduces the impact of the rear trailer on the towing vehicle, protecting the drawbar and making it more durable.
Rubber block: Mounted at the four corners of the trailer body. When the side panels are opened, it prevents hard contact between the body and the chassis, avoiding damage.
4. What are the approximate rear tilt angle and left/right tilt angles of a dump trailer?
Rear dump angle: ≥45°. Side dump angle: ≤60°.
5. What types of cargo are high-sided trailers and mesh-side trailers mainly suitable for?
They are mainly suitable for bulky but lightweight goods (e.g., cotton – allowing more volume), and for livestock such as cattle or sheep (preventing them from jumping out).
6. What are the conversion relationships between pound and kilogram, horsepower and kilowatt, foot/inch and meter? How many ways are there to express temperature and how are they converted?
1 lb ≈ 0.453 kg. 1 hp ≈ 0.753 kW. 1 ft = 12 in = 0.3048 m.
Temperature: Celsius (°C), Fahrenheit (°F), Kelvin (K). Conversion: 5(F-50°) = 9(C-10°); K = 273.15 + °C.
7. How do you explain that the towing point of Mingsin's trailers is a "free point"?
Mingsin produces two types of trailers:
- Single-axle trailer: The coupling ring and drawbar are connected by bolts. By changing the relative position, the trailer body can be kept level.
- Tandem-axle trailer: The drawbar is connected to the body by a pin, allowing it to pivot up and down freely to match the height of the towing vehicle.
8. What is the difference between CO welding and ordinary welding? What are the common welding methods? What are the advantages of each, and for which materials are they suitable?
The main difference is the welding wire. Common methods: stick welding (SMAW), TIG (GTAW), MIG/MAG (including CO₂).
- Stick welding (SMAW): Flexible operation, suitable for a wide range of metals, deep penetration. Operator skill-dependent, lower productivity. Suitable for most thicknesses.
- TIG (GTAW): High efficiency, little slag, low distortion, high speed. More hazardous to health (requires protection). Suitable for stainless steel, aluminum, copper.
- CO₂ (MAG): High productivity, low cost, good quality, easy to learn. Higher spatter, poor wind resistance. Suitable for low-carbon steel and low-alloy steel; not suitable for non-ferrous metals.
9. What is the main function of anti-rust paint? What are the main surface treatment methods and their advantages?
Anti-rust paint prevents contact between the workpiece and air, inhibiting rust.
Surface treatment has two stages:
1) Preparation: shot blasting (removes scale and residual stress), grinding (smooths weld points), pickling and phosphating (degreases, cleans, improves corrosion resistance and paint adhesion).
2) Coating:
- Spray painting: attractive appearance, rust resistant.
- Baking paint: brighter, longer-lasting color.
- Galvanizing: best corrosion protection, ideal for areas with high humidity or airborne ions.
- Powder coating: hard, corrosion-resistant, smooth finish.
10. What material is commonly used for Mingsin's leaf springs? What specific material does Mingsin use? What are the advantages of each? What is the purpose of the bushing at the front end of the spring? What are common leaf spring models?
Common materials: 65Mn and 60Si2Mn.
- 60Si2Mn: good elasticity and bending resistance.
- 65Mn: lower cost.
The bushing is wear-resistant, easy to replace, and increases spring life.
Common models: 7C-1T, 7C-3T, 7C-5T, 7C-5T Heavy Duty (tandem springs count as a set; the number indicates the load capacity per set in tonnes).
11. Why are some trailers called "tripod live-drawbar" trailers? What is the significance and benefit?
The tripod draw-bar is very sturdy, easy to hitch/unhitch, and allows more cargo to be loaded in a container, saving shipping costs.
12. Why does Mingsin use "agricultural tires" on its trailers?
Mingsin's vehicles are often used in agricultural fields and mountainous areas with poor roads, mud, or no roads. The tires need high load capacity, intermittent operation, and resistance to aging, wear, and cracking. Agricultural tires meet these requirements. The drawback is thick rubber and poor heat dissipation, so they cannot be used at high speeds.
13. What terrain is a single-axle trailer suitable for? Compare advantages and disadvantages with tandem-axle trailers.
Single-axle: suitable for rough, steep terrain. Advantages: smaller turning radius, better off-road ability, fuel economy.
Tandem-axle: suitable for flat terrain; provides a smoother ride.
14. What do the model numbers of hydraulic cylinders mean? How to select a cylinder for a given vehicle?
The first letter(s) indicate the type of hydraulic cylinder. The following numbers indicate bore diameter, rod diameter, and stroke. Others indicate connection type and accessories.
Example: HSGL01-80/45E-1201-925X118
- HSC: engineering hydraulic cylinder
- L: external thread connection
- 80: bore (mm)
- 45: rod diameter (mm)
- E: pressure rating 16 MPa
- 1201: cylinder head earring with bushing, rod end internal thread, no cushioning, internal thread port connection
- 925: stroke (mm)
- 118: mounting distance (mm)
15. Briefly explain the principle of a three-way dump trailer and its advantages.
Principle: A hydraulic cylinder is mounted centrally under the body. For rear dumping, the pins at the front ends of the body are removed, the cylinder extends, and the chassis tilts backward. For side dumping, the pins on the opposite side are removed, the cylinder extends, and the chassis tilts to the other side.
Advantages: Dumping can be done in tight spaces without moving the vehicle, and you have more choices of dumping direction.
16. What is the purpose of the reverse pin? What is the purpose of the guard rail?
Reverse pin: Mounted on the turntable frame. It prevents the turntable from rotating, ensuring straight-line movement and enabling reversing without unwanted steering.
Guard rail: Prevents people or animals from going under the wheels, avoiding injury.
17. What materials are used for rims? How to match a rim to a tire model? How to interpret offset, pitch circle diameter, and center bore?
Rim materials: section steel or malleable iron.
Tire-rim matching examples:
- 6.50-16 → 5.50-16 rim
- 7.50-16 → 6.00G-16
- 7.00-16 → 5.50F-16
- 8.25-16 → 6.50H
- 9.00-16 → 7.00T
- 10.0-20 → 7.50V
- Offset: distance between the rim's mounting face and the tire's center plane.
- Pitch circle diameter (PCD): diameter of the circle passing through the center of the wheel bolt holes.
- Center bore: diameter of the center hole in the rim.
18. Briefly describe common brake types, how they work, and why they are used.
Types: air brake, hydraulic brake, electric brake, surge (overrun) brake, disc brake. All operate by expanding brake shoes against a drum (except disc brakes).
1) Surge brake: Movement of the drawbar actuates a camshaft that rotates the cam, pushing the brake shoes against the drum.
2) Air brake (service): High-pressure air from the tow vehicle's compressor enters the brake chamber, pushing a rod that rotates the cam and expands the shoes.
3) Air-release (spring) brake: Uses a special valve to exhaust air from the service brake, allowing a spring to apply the brakes.
4) Electric brake: An electromagnet actuates the brake shoes inside the drum.
5) Hydraulic brake: Brake fluid actuates the camshaft.
6) Parking brake (manual): A spring pulls the actuating rod to rotate the cam and apply the shoes.
Which brake is used depends on the configuration of the towing vehicle.
19. What do overall dimensions refer to? What do body dimensions refer to?
Overall dimensions: the maximum length, height, and width of the entire trailer. They determine the vehicle's maneuverability (e.g., for a warehouse with limited space).
Body dimensions: the length, width, and height of the four side panels that form the cargo box.
20. How many types of tire tread patterns are there? For what conditions is each used?
- Herringbone (chevron): drive wheels.
- Diagonal (zigzag): good water drainage, prevents sideslip.
- Water groove: high-speed performance, low rolling resistance.
General classification:
1) Longitudinal grooves: good handling, low rolling resistance, low noise, good water drainage, resistant to lateral slip.
2) Transverse grooves: good driving force, braking force, traction, wear resistance.
3) Combined grooves: advantages of both longitudinal and transverse.
4) Block tread: good driving and braking force.
5) Off-road tread: designed for dry/wet, rough, muddy, or sandy conditions.
21. What is the main purpose of the front marker pole on a trailer?
1) Height indication: shows that the load must not exceed the pole's height.
2) Prevents cargo from shifting forward and causing danger during braking.
22. What are the common tail light colors and their meanings? What colors are in Mingsin's common 7-core cable?
(Note: The original numbering jumps – answered as written)
Tail light colors: red (running light), yellow (fog light or turn signal), white (reverse light or license plate light).
7-core spiral cable colors: black (ground), yellow, red (brake), green, blue, brown, white (illumination).
23. (Actually question 24 in original – renumbered here for clarity) What is the main purpose of the front and rear corner reinforcements?
They reinforce the body, and also provide mounting points for rubber buffers and foot steps.
24. (Original 25) Why are drop-side posts (stanchions) used on long trailers?
Long side panels tend to deform and become heavy to operate. Stanchions allow a long side panel to be divided into two or more sections, reducing deformation and making it easier to open.
25. (Original 26) How many types of reflective devices are there? Where should they be placed on a trailer?
Three types: reflective tape, reflective light, reflective strip. Colors: red, yellow, white. They should be placed on the rear and sides of the body in visible positions to reflect light and warn other vehicles, preventing collisions.
26. (Original 27) Why use a reducing air line coupler?
It allows quick, secure, and durable connection.
27. (Original 28) If required, what lights should a trailer be equipped with?
Running lights, reverse lights, turn signals, license plate light, brake lights, hazard lights, fog lights, clearance lights.
28. (Original 29) What are common hydraulic fitting models?
M22×1.5, M20×1.5.
29. (Original 30) Why are some side panels flat and others ribbed (dimpled)?
Both have advantages. Flat panels can use thicker steel if needed. Ribbed panels are more attractive and have higher strength and bending resistance.
30. (Original 31) Why are locknuts (prevailing torque nuts) used in some places?
On connections subject to relative motion, ordinary nuts can easily loosen. Locknuts prevent this, greatly improving safety and reliability.
31. (Original 32) What are the main components of an axle? What is the typical axle structure and material? What bearings are used?
Components: axle tube, wheel hub, spindle (stub axle), brake shoes, brake drum, bearings, camshaft, eccentric shaft, bearing cap, connecting spring. Bearings: tapered roller bearings.
Typical structure: Axle tube is seamless steel pipe (16Mn). Spindles are made of 45# round steel, hot-assembled and welded to the tube.
32. (Original 33) What is the difference between calcium grease and lithium grease? When should each be used?
Calcium grease: suitable for normal temperatures and low speeds; good water resistance. Temperature range: -10°C to 60°C.
Lithium grease: suitable for high speeds and high temperatures; good water resistance and rust prevention. Range: -20°C to 120°C.
33. (Original 34) Under what conditions is a galvanized trailer suitable?
High temperature, humid, rainy, or areas with high airborne ion content.
34. (Original 35) What are the features of Mingsin's cotton trailer?
It uses high side panels for greater volume. Its main advantage is the linkage-operated self-unloading side doors, which greatly improve unloading efficiency for cotton.
35. (Original 36) How to interpret the markings on a tire?
Example: 8.25-16. 8.25 = section width (8.25 × 25.4 = 209.55 mm). 16 = rim diameter (16 × 25.4 = 406.4 mm).
Foreign tire: 400/60-15.5. 400 = width (mm). 60 = aspect ratio (height = 400 × 0.6 = 240 mm). 15.5 = rim diameter (393.7 mm). Overall theoretical height = 240×2 + 393.7 = 873.7 mm. 14PR = ply rating (higher = stronger, more durable). R or Z = radial. D = steel cord. Also load index, speed symbol. Other designations: PC (passenger car), LT (light truck), TB (truck/bus), AG (agricultural), OTR (off-the-road), ID (industrial), AC (aircraft), MC (motorcycle).
36. (Original 37) What are the advantages of the different paints Mingsin commonly uses?
- Spray paint: good adhesion, wide application, fast drying.
- Baking paint: high surface gloss, attractive.
- Galvanizing: long-term rust protection.
- Silver paint: silver color, relatively rust-resistant, attractive.
Paint composition: oils, resins, pigments, thinners, and additives (driers, curing agents, plasticizers, anti-moisture agents).
37. (Original 38) How are high-strength bolts distinguished from ordinary bolts?
High-strength bolts: grade above 8.8, material 35# or 45# steel, quenched and tempered.
Ordinary bolts: grade below 6.8, material Q235.
38. (Original 39) What kind of transport is a flatbed trailer suitable for? How does the tandem-axle suspension work?
Flatbed trailers are good for short-distance, yard-to-yard transport with easy loading/unloading. Also suitable for irregularly shaped or oversized cargo, mobile power stations, lighting towers, etc.
Tandem-axle suspension: By adjusting the position of the front and rear axles, the body remains relatively level, providing a good shock-absorbing effect.
39. (Original 40) What are the advantages of torsion axles?
Attractive appearance, higher grade, lower ride height, suitable for highway speeds, saves leaf springs, good ride comfort.
40. (Original 41) What is the principle of the hand-cranked landing leg? Why do some legs have casters?
The crank turns bevel gears, which turn a threaded screw to raise or lower the leg.
Casters allow the leg to be moved by pushing rather than lifting, making it easy to reposition.
41. (Original 42) What is the principle of a manual hydraulic pump? Why design it that way?
Manual operation of a piston pump builds pressure to extend a hydraulic cylinder. This design is used when the towing vehicle has no hydraulic take-off – it’s a backup system.
42. (Original 43) What is the purpose of the safety chains?
They act as a backup connection between the towing vehicle and the trailer, preventing separation if the main coupling fails.
43. (Original 44) What are the main uses of a tool trailer?
A generic term. Examples: ramp trailer (with rear ramps for wheeled or tracked vehicles), enclosed (tilt) trailer (weatherproof, suitable for tools, cooking gear, fishing equipment).
44. (Original 45) What are the advantages of LED lights? What is the typical system voltage?
LEDs: attractive, energy-saving, waterproof, fast response, safe, reliable. If one LED fails, the light still works. Typical voltage: 12V.
45. (Original 46) What is the production process and packaging method for agricultural trailers?
Production process:
1) Cutting, bending, drilling, punching, shaping →
2) Cleaning (removing scale, burrs, flash, oxide scale, rust, chips, oil) →
3) Riveting, welding →
4) Finishing (straightening) →
5) Coating (anti-rust primer and topcoat).
Packaging: Vulnerable parts (side panels) wrapped in foam paper. Small parts packed in woven bags (one bag per trailer). Other parts without packaging, unless otherwise specified.
46. (Original 47) What is the national standard for agricultural trailer production in China? How is rated load capacity determined?
Standard: GB/T4330-2003. Load capacity is calculated based on the volume of the cargo box.
47. (Original 48) What are the main components of an agricultural trailer?
Main components: upper and lower chassis, drawbar, running gear, electrical system, brake system, side panels. Dump trailers also have a hydraulic system.
48. (Original 49) Definition of track width, wheelbase, and loading floor height?
Track width (per axle): distance between the centerlines of the two tires on the same axle.
Wheelbase: distance between the centers of the front and rear axles when parallel.
Loading floor height: vertical distance from the trailer floor to the ground.
49. (Original 50) What is the HS code for agricultural trailers?
HS code: 8716200000.
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