Company News & Transmission Industry Updates

1. Overview

A shrink disk (also known as a locking assembly, keyless locking device, or shrink disc) is a mechanical component that creates a keyless friction connection between a shaft and a hub by means of high-strength clamping screws. It complies with Chinese national standard GB/T 28701-2012 and mechanical industry standard JB/T 7934-1999.

Shrink disks are widely used in heavy‑duty industrial applications as an advanced alternative to traditional keyed or splined connections. They are employed to transmit torque and axial loads between shafts and components such as gears, flywheels, pulleys, and couplings. Compared with conventional key joints, shrink disk connections offer superior concentricity, elimination of stress raisers, and easy assembly/disassembly.

2. Working Principle

2.1 Basic Principle

A shrink disk itself does not transmit torque directly. Instead, it works by converting the axial clamping force of tightening screws into a radial clamping pressure. When the screws are tightened, the conical inner ring contracts to grip the shaft, while the outer ring expands to press against the hub bore. This creates a strong interference fit, generating sufficient frictional force to lock the hub securely to the shaft.

In detail:

• The inner ring shrinks inward, clamping the shaft.

• The outer ring expands outward, gripping the hub bore.

The resulting positive pressure produces friction that transmits both torque and axial loads. Under load, the connection relies entirely on the static friction between the mating surfaces.

2.2 Factors Affecting Clamping Performance

The efficiency and reliability of a shrink disk connection depend on:

• Material properties – elastic modulus influences the clamping efficiency.

• Fits and tolerances – proper clearances ensure stable clamping.

• Installation technique – correct tightening procedure is critical.

2.3 Overload Protection

One notable safety feature of shrink disks is their ability to act as a torque limiter. If the applied load exceeds the rated capacity, the friction grip is overcome and the connection slips, thereby disconnecting the drive and protecting the machinery from damage. This dual function – power transmission and overload protection – makes shrink disks highly versatile.

3. Common Types and Configurations

Various designs are available for different applications. The table below summarises the main types:

In addition, types ZJ1 through ZJ19 are covered under GB/T 28701-2012.

4. Installation Procedure

Proper installation is essential for achieving the rated performance and service life. Follow these steps carefully.

4.1 Preparation

Inspection and Cleaning

• Check that shaft and bore dimensions comply with the required tolerances (per GB/T 3177).

• Ensure all mating surfaces are free of dirt, corrosion, and damage.

• Verify that all clamping screws are completely loosened and the shrink disk components are in a free, unloaded state.

Lubrication

• Apply a thin, even coat of light lubricating oil to the cleaned surfaces of the shrink disk and the mating parts.

• Important: Do not use lubricants containing molybdenum disulfide (MoS₂) or other friction‑reducing additives, as these can significantly lower the friction coefficient and reduce the clamping force.

4.2 Step‑by‑Step Installation

Step 1 – Positioning
Insert the loosened shrink disk into the hub bore, ensuring no tilting occurs. Tighten the screws by hand initially. Note that shrink disks are factory‑coated with a rust‑preventive oil, so they can be installed directly.

Step 2 – Graduated Torquing
Use a calibrated torque wrench and tighten the screws in a diagonal, cross‑pattern sequence. Follow the rated torque value (MA) specified for the particular shrink disk model. The standard tightening sequence is:

1. Eliminate gaps – first tighten lightly to remove all clearances between components.

2. Stage 1 – tighten to 1/3 MA in a diagonal, cross‑pattern.

3. Stage 2 – tighten to 1/2 MA in the same cross‑pattern.

4. Stage 3 – tighten to full MA in a diagonal, cross‑pattern.

5. Final check – re‑tighten all screws to MA; if any screw is found loose, repeat the entire sequence.

Some manufacturers recommend an additional pass at 5% above MA to ensure uniform preload.

Why phased tightening?
This method ensures even distribution of clamping force, preventing tilting or uneven loading. The diagonal sequence allows the conical rings to deform uniformly, producing a consistent circumferential contact pressure.

4.3 Important Installation Notes

• Keep the assembly clean; avoid MoS₂‑based lubricants.

• Prevent misalignment or tilting of the connected parts.

• Always close all gaps before starting the torquing sequence.

• For large‑diameter shrink disks, they may self‑tighten during transport – check that they are loose before installation.

5. Disassembly Procedure

Correct disassembly prevents damage to the shrink disk and the mating surfaces.

5.1 Standard Disassembly Steps

Step 1 – Loosen Screws
Turn all clamping screws a few turns counter‑clockwise, but do not remove them completely. Keeping them partially engaged prevents the disk from suddenly springing out.

Step 2 – Insert Jacking Screws
Remove some of the clamping screws (usually the zinc‑plated ones) and replace them with dedicated jacking screws into the threaded holes provided in the front pressure ring.

Step 3 – Release the Clamp
Tighten the jacking screws diagonally until the inner and outer rings separate. Gently tap the jacking screw heads to loosen the disk.

Step 4 – Withdraw the Disk
Grasp the jacking screws and pull the entire shrink disk off the shaft.

5.2 Disassembly Cautions

• Different types may have varying disassembly methods – always refer to the specific design.

• For Type Z1, first loosen the retaining plate screws, then tap the driven component lightly.

• For stubborn, long‑seated disks, specialised tools (e.g., hydraulic pullers) may be needed.

• Avoid brute force to protect shaft and bore surfaces from scoring.

6. Maintenance and Protection

6.1 Rust Prevention

After installation, coat the exposed face of the shrink disk and the screw heads with a rust‑preventive grease. For outdoor or corrosive environments, apply grease periodically and consider adding protective covers.

6.2 Common Problems and Solutions

7. Application Fields

Shrink disks are used across many industries where reliable, adjustable, and maintenance‑friendly shaft connections are required:

• Heavy machinery – crushers, hoists, mining and metallurgical equipment

• Wind power – main shaft to gearbox connections in wind turbines

• General machine tools – CNC machines, lathes, milling machines

• Light industry – packaging, textile, printing, and tobacco machinery

• Power transmission – pulleys, sprockets, gears, timing belt pulleys, impellers, blowers, etc.

In wind energy, the shrink disk is a critical component for connecting the main shaft to the gearbox, and its usage is growing with the renewable energy sector. In underground mining cable cars, shrink disks replace keys and rely solely on friction for load transmission.

8. Key Advantages

Compared with traditional keyed joints, shrink disks offer:

• Simple manufacturing and assembly – no need for high‑precision interference fits; no heating, cooling, or pressing equipment required.

• Easy adjustment – the hub can be positioned and repositioned along the shaft as needed.

• Long service life – friction transmission without relative movement means no wear during normal operation.

• No stress concentration – no keyways, thus higher shaft fatigue strength.

• Overload protection – automatic slippage prevents damage.

• Quick disassembly – simply loosen screws; fully interchangeable.

• Multiple units in series – several shrink disks can be combined to transmit higher torques.

References: GB/T 28701-2012 “ diShrinksks” and JB/T 7934-1999 “Locking assemblies”.