NQ DCDMA Wireline Core Rod for Geological & Water Conservancy Survey | CGE Drilling

NQ Overshot Assembly is a vertical hole wireline core overshot of Q series. It is manufactured strictly in accordance with international DCDMA standards and matched with NQ wireline drill rods and double-tube inner tube assemblies, serving as the core supporting tool for medium and small borehole diamond wireline core drilling. Featuring mature structure, wide adaptability and reliable fishing performance, it is the mainstream overshot specification with the largest consumption and highest versatility in geological exploration industry.

Application Classification
Q series overshots (BQ/NQ/HQ/PQ) are uniformly designed for vertical boreholes and downward inclined boreholes with an inclination ranging from 35° to 90°. QU series overshots are required for horizontal or low-inclination tunnel boreholes of 0°~35°. The two series adopt structures for different working conditions and cannot be used interchangeably.
As the mainstream medium-small size specification of Q series, the NQ overshot provides a core diameter of 47.5 mm, featuring stable borehole wall and large core recovery. It is applicable for shallow, medium-deep and deep exploration boreholes with a regular maximum working depth of 1500–1800 m, making it the standard specification most widely used in mineral exploration and engineering investigation.

The complete NQ overshot is composed of 12 core components from top to bottom, consistent with international standard assemblies and featuring strong interchangeability:
1. Eye Bolt: Connects the wireline winch and bears the overall lifting load with firm structure and high deformation resistance.
2. Swivel Assembly: Equipped with thrust bearings and grease injection fittings. It can rotate freely during lowering and lifting to effectively prevent wireline twisting and coiling.
3. Jar Tube & Jar Rod Assembly: Delivers vertical mechanical jarring force to quickly release minor tube sticking, core blockage and inner tube jamming downhole.
4. Lock Spring Sleeve & Lock Bushing: Forms a mechanical self-locking structure to limit the opening stroke of lifting dogs and avoid accidental unhooking and inner tube dropping during lifting.
5. Main Compression Spring & Dog Spring: Precisely controls the opening, closing and automatic reset of lifting dogs to guarantee stable and reliable fishing action every time.
6. Ball Position Indicator Mechanism: Generates obvious water pressure signal once the inner tube is fully latched. Operators on the surface can directly confirm successful fishing and avoid empty fishing and repeated operations.
7. Overshot Body & Lifting Dogs: Core load-bearing gripping parts with thickened structure, which firmly engage the spear head of inner tube assembly with strong load capacity and anti-slip performance.
8. Positioning Pins & Spring Pins: Fix the dog assembly for simple disassembly and convenient maintenance, enabling quick inspection and replacement in field operations.
9. Centralizing Guide Section: Automatically centers inside drill rods to maintain high coaxiality and accurately align with inner tube spear head, improving the one-time fishing success rate.
10. Buffer & Shock Absorption Assembly: Effectively absorbs impact force during lowering, protects threads, snap rings and latch structures of inner tube assembly and reduces drill tool loss.

1. Full Wireline Fishing Without Pulling Entire Drill String, Extremely High Drilling Efficiency
The NQ overshot adopts wireline delivery and fishing operation. After coring completion, there is no need to pull out the whole drill rod string. Simply lower the overshot to retrieve the inner tube and extract core samples. It drastically reduces tripping times and auxiliary operation duration, lifting deep-hole drilling efficiency by over 40% and cutting shift costs significantly.
2. Special Stable Gripping Structure for Vertical Holes, Anti-unhooking & Anti-tube-dropping
It adopts symmetric double thickened lifting dogs, which open flexibly under self-weight and achieve firm engagement. Equipped with multi-spring self-locking structure, the dogs stay fully locked throughout lifting to eliminate unhooking and tube dropping risks. The built-in powerful jarring mechanism can rapidly release common downhole faults such as tube jamming, core clogging and adsorption locking, greatly lowering downhole accident rates.
3. High-strength Alloy Material with Superior Wear Resistance & Long Service Life
The main barrel and lifting dogs are made of premium 30CrMnSiA alloy structural steel with integral quenching and tempering heat treatment, delivering high strength and excellent toughness. Key friction and gripping parts are strengthened via carbonitriding treatment, offering great resistance to mud erosion, rock collision and abrasion. It can work stably under both clear water and mud drilling media for long-term operation.
4. Compliant with DCDMA International Standard, Ultra-high Versatility
Fully conforming to DCDMA international standards, it precisely matches NQ wireline drill rods, double-tube inner tubes, latch assemblies and joint accessories from all domestic and overseas brands with 100% interchangeability. Precise fitting tolerances guarantee smooth running without jamming and high coaxiality, compatible with all types of full-hydraulic core drills.
5. Pressure Position Feedback for Safe & Controllable Operation
Standard equipped with ball pressure indicator. Obvious water circuit pressure change occurs once the overshot latches the inner tube, allowing operators to accurately judge fishing status. It effectively prevents empty fishing, misoperation and repeated re-delivery, enhancing construction stability and safety.
6. Modular Structure for Easy Disassembly & Maintenance
All connecting parts adopt standard imperial threads without special locking structures. Wearing parts including springs, lifting dogs and bearings can be disassembled and replaced on site without special tooling. Interchangeable accessories cut inventory costs and support convenient field maintenance.
7. Wide Adaptability as Mainstream NQ Size with High Comprehensive Construction Cost Performance
Located between BQ and HQ specifications, NQ overshot realizes large core sampling volume, stable drilling performance and wide applicable depth range. It serves as the primary specification for geological reconnaissance, metallic mineral exploration, water conservancy & hydropower investigation, highway & railway survey and geotechnical sampling projects, suitable for most medium-deep core drilling works.