Causes and Non-Disassembly Correction of Bent Extruder Auger Shaft

Maintenance Guide for Brick and Tile Production Equipment

In clay fired brick production lines, the extruder is the core forming equipment, while the auger shaft is one of the most critical transmission components within the extruder. The auger shaft is responsible for transmitting most of the torque generated during operation and for conveying clay materials forward under pressure. Therefore, its operating condition directly affects the forming quality of green bricks as well as the operational stability of the equipment.

During long-term production, due to complex raw material conditions and variations in equipment load, bending or deformation of the auger shaft is a relatively common mechanical problem. If not addressed promptly, it may lead to abnormal equipment operation, mechanical damage, or even production shutdown.

Based on practical maintenance experience in the brick and tile industry, this paper introduces a practical on-site correction method that does not require disassembling the extruder, which is especially suitable for small and medium-sized brick factories with limited maintenance capability.

The auger shaft is a key transmission component inside the extruder and has the following structural characteristics.

• High Torque Transmission

During the extrusion process, the auger shaft continuously transmits mechanical power while pushing the clay material toward the die head.

• Tangential Key Slots

In order to mount the auger blades, the shaft is usually designed with two tangential keyways. Although this structure facilitates blade installation, compared with a solid shaft of the same diameter, its bending strength and torsional strength are relatively reduced.

• Material and Manufacturing Characteristics

In traditional brick machinery manufacturing, due to equipment limitations, many auger shafts do not undergo quenching and tempering heat treatment.

According to general mechanical manufacturing standards, transmission shafts that do not undergo proper heat treatment tend to have lower fatigue resistance and impact strength, which increases the possibility of deformation during long-term operation.

In practical brick production, the bending of the extruder auger shaft is mainly caused by the following factors.

Raw material conditions vary significantly among different brick factories, such as:

• Differences in plasticity index
• Fluctuations in moisture content
• Unstable particle size distribution

These factors cause significant fluctuations in the operating load of the extruder, resulting in periodic alternating torque on the auger shaft.

If the raw material is not properly processed, it may contain:

• Stones
• Metal fragments
• Hard impurities

When these foreign objects enter the extruder, they generate instantaneous impact loads, which may cause bending or even twisting of the auger shaft.

When producing different types of bricks, such as:

• Perforated bricks
• Insulated hollow blocks
• Standard clay bricks

the extrusion pressure varies significantly, which imposes different levels of mechanical load on the auger shaft.

Extruders are typically continuous production equipment. Long-term operation under high load conditions accelerates the fatigue deformation of the auger shaft.

• When the auger shaft becomes bent, the following phenomena usually occur:
• Significant increase in die head oscillation
• Fluctuation in extrusion pressure
• Local friction between the auger and the barrel liner
• Increased vibration and noise of the equipment
• In severe cases, the auger blades may directly collide with the barrel lining, posing a serious threat to equipment safety.

It should be noted that:

Bending of the auger shaft can be corrected, but torsional deformation cannot be repaired without disassembly and replacement.

For brick factories with limited financial resources or maintenance capability, on-site flame straightening can be used to repair the shaft. The specific procedure is as follows.

All auger blades mounted on the shaft must be removed so that the shaft body is completely exposed.

Manually rotate the auger shaft and use a scriber or dial indicator to determine:

• The highest bending point
• The lowest bending point
• The center of the bending position

These locations should be clearly marked.

In most cases, bending occurs near the root of the front bearing.

To prevent damage to the bearings during heating, protective measures should be taken:

• Wrap asbestos rope around the shaft at the bottom of the feed box
• Apply wet clay material outside the asbestos layer

This insulation prevents heat from transferring to the bearing and avoids bearing annealing.

Place the following support tools under the bending position:

• Steel shims
• V-shaped support blocks

This ensures that the bearings will not be damaged during the correction process.

Use an oxy-acetylene flame to heat the bent section of the shaft evenly.

Once the shaft surface reaches a uniform red-hot state, strike the far end of the shaft using an approximately 18-pound hammer to gradually correct the shaft alignment.

During the process, continuously check the shaft alignment with a measuring tool to prevent overcorrection.

After correction, the acceptable tolerance is:

• Auger shaft bending ≤ 1 mm

which is sufficient for normal extruder operation.

Flame straightening may reduce the fatigue strength of the heated area. Therefore, local surface hardening treatment is recommended.

1. Heat the shaft surface using an oxy-acetylene flame
2. Heating temperature: 830–850°C
3. Rapidly cool the heated area with water
4. Utilize the internal heat of the shaft for tempering

During tempering, the surface color typically changes as follows:

• White → Yellow → Blue

When the surface turns blue, immediately cool the shaft with water to stabilize the hardness.

The final hardness of the shaft surface should be:

≤ HRC 30

This level ensures sufficient wear resistance while maintaining material toughness.

For many small and medium-sized brick factories, replacing an auger shaft is costly.

For example:

• Additional costs include transportation, labor, and downtime losses

In many cases, the total economic loss may reach several times the cost of the shaft itself.

Using the on-site correction method can:

• Avoid long production shutdowns
• Reduce maintenance costs
• Improve equipment utilization

Practical experience has proven that on-site flame straightening of a bent extruder auger shaft is an economical, practical, and effective maintenance method.

The technique has several advantages:

• No need to dismantle the equipment
• Short maintenance time
• Low repair cost
• Simple operation

For small and medium-sized brick factories with limited maintenance facilities, this method has high practical value and strong potential for industry promotion.

Through proper equipment maintenance and scientific repair methods, the service life of key extruder components can be significantly extended, ensuring the stable operation of the brick production line.