Relationship Between Peripheral Speed Difference and Processing Effect in Rubber Roll Rice Hullers

Peripheral Speed Difference: The "Soul Parameter" of Rice Hullers

In the working principle of rubber roll rice hullers, the peripheral speed difference between the fast and slow rolls is the key factor generating rubbing force. This speed difference causes paddy between the rolls to receive not only squeezing force but also rubbing force parallel to the roll surface, achieving separation of husk from brown rice. The peripheral speed difference is one of the core determinants of huller process performance.

Working Principle of Peripheral Speed Difference

Basic Mechanical Analysis

When paddy enters the nip between two rolls, it receives two types of forces:

1. Squeezing Force (Normal Pressure)

• Direction: Perpendicular to roll surface
• Source: Compression of paddy by roll gap
• Function: Deforms paddy to create conditions for rubbing

2. Rubbing Force (Shear Force)

• Direction: Parallel to roll surface, consistent with fast roll direction
• Source: Peripheral speed difference between fast and slow rolls
• Function: Creates relative displacement between husk and brown rice for separation

Rubbing force is proportional to speed difference:

F_rubbing ∝ ΔV = V_fast - V_slow

Where:

• ΔV = Peripheral speed difference (m/s)
• V_fast = Fast roll peripheral speed (m/s)
• V_slow = Slow roll peripheral speed (m/s)

Speed Difference and Dehusking Mechanism

Sepparation of husk from brown rice requires overcoming the bonding force between them, which includes:

• Mechanical bonding: Interlocking of surface irregularities between husk and brown rice
• Biological bonding: Tissue connections between glume and caryopsis

The rubbing force destroys these bonds:

1. Squeezing force "bites" the paddy between rolls
2. Speed difference-generated rubbing force moves husk and brown rice in different directions
3. When rubbing force exceeds bonding force, husk tears open, achieving dehusking

Impact of Speed Difference on Process Performance

Relationship with Hulling Rate

Speed difference and hulling rate show positive correlation but not linear:

| Speed Difference | Hulling Rate Performance | Cause Analysis | |-----------------|-------------------------|----------------| | < 1.5 m/s | Low (< 75%) | Insufficient rubbing force, difficult to break husk bonding | | 1.5-2.0 m/s | Medium (75%-85%) | Rubbing force begins to be effective but insufficient | | 2.0-2.5 m/s | Excellent (85%-92%) | Moderate rubbing force, optimal dehusking | | 2.5-3.0 m/s | Very high (> 92%) | Excessive rubbing force, broken rice rate rises sharply | | > 3.0 m/s | No longer increases | Severe broken rice, significant brown rice damage |

Relationship with Broken Rice Rate

Broken rice rate is more sensitive to speed difference:

• Low speed difference (< 1.8 m/s): Low broken rice rate (< 1.5%), but hulling rate not ideal
• Moderate speed difference (2.0-2.5 m/s): Broken rice rate controlled at 1.5%-2.5%, excellent hulling
• High speed difference (> 2.8 m/s): Broken rice rate sharply rises above 4%, poor economics

Relationship with Roll Wear

Higher speed difference accelerates roll wear:

• Each 0.5 m/s increase in speed difference increases roll wear rate by approximately 15%-20%
• Excessive speed difference causes roll surface temperature rise, accelerating rubber aging
• Reasonable speed difference ensures dehusking while extending roll life

Optimal Speed Difference for Different Rice Varieties

Different rice varieties have different husk-brown rice bonding strengths, requiring different optimal speed differences:

| Rice Variety | Husk Characteristics | Recommended Speed Difference | Recommended Fast Roll Speed | |--------------|---------------------|------------------------------|----------------------------| | Japonica | Thin husk, weak bonding | 2.0-2.3 m/s | 14-16 m/s | | Indica | Thick husk, strong bonding | 2.3-2.6 m/s | 15-17 m/s | | Glutinous | Tough husk, difficult to hull | 2.4-2.8 m/s | 15-17 m/s | | Long-grain | Long husk, large rubbing area | 2.2-2.5 m/s | 15-16 m/s | | Short-grain | Short husk, small rubbing area | 1.8-2.2 m/s | 13-15 m/s |

Methods for Setting Speed Difference

Method 1: Setting by Speed Ratio

Most hullers use fixed speed ratios to adjust peripheral speed difference:

Speed Ratio = V_fast / V_slow = n_fast / n_slow

Common speed ratio settings:

| Speed Ratio | Application | Characteristics | |-------------|-------------|-----------------| | 1.2:1 | Easy-to-husk varieties, low broken rice requirement | Gentle rubbing force | | 1.3:1 | Conventional varieties, balanced processing | Most commonly used | | 1.4:1 | Difficult-to-husk varieties, high hulling rate requirement | Strong rubbing force | | 1.5:1 | Special difficult-to-husk varieties | High broken rice risk |

Setting Steps:

1. Determine fast roll speed (based on equipment specifications and variety)
2. Select appropriate speed ratio
3. Calculate slow roll speed: n_slow = n_fast / speed ratio
4. Achieve speed ratio through transmission system (gears or pulleys)

Method 2: Experimental Adjustment Method

For adjustable-speed hullers (such as variable frequency drive), optimal speed difference can be found through testing:

Test Steps:

1. Fix roll gap and feed flow
2. Start from low speed difference (e.g., 1.5 m/s)
3. Increase by 0.2 m/s each time, recording hulling rate and broken rice rate
4. Plot hulling rate vs broken rice rate curve
5. Find the "sweet spot" where hulling rate meets standards and broken rice rate is lowest

Method 3: Adjustment Based on Roll Condition

As rolls wear, optimal speed difference changes:

• New rolls: Rough surface, high friction coefficient, lower speed difference usable
• Normal use period: Standard speed difference setting
• Late wear period: Smooth surface, reduced friction coefficient, appropriately increase speed difference to compensate

Considerations for Speed Difference Setting

1. Comprehensive consideration: Don't only look at hulling rate; must also monitor broken rice rate and roll life
2. Variety adaptability: Adjust speed difference promptly when processing different varieties
3. Seasonal factors: New crop and old crop have different dehusking characteristics requiring fine-tuning
4. Moisture impact: High moisture paddy has tough husks; can appropriately increase speed difference
5. Equipment matching: Speed difference should be coordinated with roll gap and feed flow

Synergy with Other Parameters

Speed difference doesn't exist in isolation and needs coordination with:

| Parameter | Relationship with Speed Difference | Synergy Principle | |-----------|-----------------------------------|-------------------| | Roll Gap | Small gap + Large speed difference = More broken rice | Trade-off between the two | | Feed Flow | Large flow, appropriately reduce speed difference | Avoid excessive squeezing | | Roll Hardness | Hard rolls with large speed difference, soft rolls with small | Hard-soft matching | | Roll Diameter | Large diameter rolls can use smaller speed difference | Large rolls more efficient at rubbing |

Zhejiang Lianggong's Speed Difference Optimization Technology

Zhejiang Lianggong Machinery fully considers speed difference optimization in huller design:

• Precision Transmission System: High gear machining precision, stable speed ratio
• Multiple Speed Ratios Available: Configurations from 1.2:1 to 1.5:1
• Variable Frequency Speed Option: High-end models support fast roll variable frequency speed regulation for stepless adjustment
• Process Guidance: Provides optimal speed difference setting recommendations for different varieties

For detailed technical guidance on speed difference settings, please call 0575-87335525.