Introduction to the Mesh-Belt Normalizing Furnace Factory: How to Handle Mesh-Belt Deviation in a Mesh-Belt Normalizing Furnace?

Guide to Handling Belt Misalignment in Mesh-Belt Annealing Furnaces: Causes, Methods, and Prevention

The mesh belt is the core component of the mesh-belt annealing furnace for conveying workpieces. If it deviates during operation—such as the belt edges drifting off the guide rails or coming into localized friction with the furnace shell or side baffles—it can not only lead to misalignment of the workpiece transport position and uneven heating, but also cause wear and tear or even tearing of the belt edges, potentially resulting in equipment shutdown. To address such issues, it is essential first to accurately identify the root cause of the deviation, then follow a procedure that involves “shutting down the equipment for inspection, making targeted adjustments, and conducting trial runs for verification,” while also implementing routine maintenance to prevent recurrence of belt deviation.

I. First, Identify the Root Cause: The Five Common Causes of Conveyor Belt Misalignment

Web misalignment is not caused by a single factor; it requires a comprehensive investigation that takes into account both the equipment’s design and its operating conditions. The root causes can be categorized into five main types:

1. Installation deviation of the mesh belt: During installation, the centerline of the mesh belt does not coincide with the centerline of the furnace (deviation > 5 mm), or the joints of the mesh belt are unevenly aligned (joint misalignment > 2 mm), which can easily cause the belt to drift to one side due to uneven stress during operation;

2. Axial misalignment of the drive or idler roller: If the axis of the drive roller (which drives the mesh belt) or the idler roller (the tensioning roller at the tail end) is not perpendicular to the direction of belt travel (with a deviation greater than 1°), the linear velocities at the two ends of the roller shaft will differ, causing the mesh belt to drift toward the side with the slower speed.

3. Uneven mesh belt tension: The tension on the two sides of the mesh belt is inconsistent (e.g., one side is under-tensioned while the other is over-tensioned). The side with lower tension is prone to slackening and deviation, which commonly occurs due to improper adjustment of the tensioning device (such as screw-type or weight-driven tensioners) or localized wear.

4. Wear and deformation of roller shafts/ idlers: Uneven surface wear on the drive roller, idler roller, or in-furnace idler rollers (which support the mesh belt)—such as localized pitting or diameter deviations exceeding 3 mm—or bending and deformation of the roller shafts can cause misalignment of the belt’s load-bearing points, leading to belt tracking issues.

5. Uneven workpiece placement and charging: If workpieces accumulate on one side of the mesh belt—e.g., with more than twice as many pieces on one side as the other—or if the workpieces’ center of gravity is off-center, the load on one side of the belt will increase, causing it to drift toward the heavier side. In addition, non-uniform furnace temperatures can lead to differential thermal expansion and contraction in localized areas of the belt, which may also result in slight belt misalignment.

II. Step-by-Step Practical Handling Method for Belt Misalignment

Depending on the underlying cause, targeted corrective measures must be implemented. Before commencing any adjustments, the equipment must first be shut down (by disconnecting the power supply to ensure the mesh belt comes to a complete stop), and then the following troubleshooting and adjustment steps should be followed:

1. Basic Inspection: Quickly Rule Out Simple Deviation Issues

Conduct a visual inspection and address easily resolved causes of misalignment:

Inspect workpiece placement: If workpieces are piled up on one side, clean the mesh belt and reposition the workpieces evenly (ensuring that the load on one side does not exceed 50% of the mesh belt width and that the center of gravity of the workpieces is centered). Run a trial operation for 30 minutes and observe whether the deviation has been alleviated.

Inspect the mesh belt joints: Check for misalignment or looseness at the joint. If the joint is misaligned, remove the joint bolts, realign the mesh belt (ensuring the joint surface is flush and the misalignment does not exceed 1 mm), and then re-tighten the bolts. If the joint is loose, replace any worn bolts or washers to prevent joint movement that could cause belt deviation.

Inspect the tensioning device: Verify that the tensioning mechanism (e.g., the lead screws on both sides of the idler roller) is symmetrical. If the extension length of one lead screw exceeds that of the other by more than 10 mm, use a wrench to adjust the lead screw—rotate it clockwise to increase tension and counterclockwise to decrease it—until the tension on both sides is equal. After adjustment, press down on both sides of the mesh belt with your hand to check for any difference in tension; the deviation should be no greater than 10%.

2. Core Adjustment: Handling Roller Shaft and Installation Deviations

If the deviation persists after basic inspection, the roller shaft position and mesh belt installation condition must be carefully adjusted:

Adjust the axes of the drive and driven rollers

First, measure the perpendicularity between the roller shaft axis and the web travel direction: place a square against the end face of the roller shaft and the furnace side wall (or guide rail). If the gap between the square and the roller shaft end face exceeds 0.5 mm, loosen the mounting bolts on the bearing housings at both ends of the roller shaft (e.g., on the bearing housings on both sides of the drive roller), gently shift the bearing housing by 1–2 mm at a time, and recheck with the square after each adjustment until the perpendicularity deviation is ≤0.2 mm.

If the mesh belt drifts to the left, it indicates that the linear speed on the left side of the drive roller is lower (the roller’s axis is offset to the left). In this case, slightly adjust the left bearing housing of the drive roller to the right, or the right bearing housing to the left (conversely, if the belt drifts to the right, make the opposite adjustment). After making the adjustment, run the equipment on a trial basis for 1 hour. If the direction of drift changes, make an opposing fine adjustment until the deviation between the mesh belt’s centerline and the furnace body’s centerline is ≤3 mm.

Repair or replace worn roller shafts / idler rollers

Use calipers to measure the diameter of the roller shafts (e.g., the diameters at both ends of the drive rollers). If the diameter deviation exceeds 3 mm, or if there are obvious depressions or wear on the surface, the roller shaft must be removed and replaced with a new shaft of the same model, ensuring that the material is identical to the original shaft—for example, heat-resistant steel 310S. If the idler rollers are worn, a batch inspection of the in-furnace idler rollers shall be conducted (sampling one out of every ten), with worn idlers being replaced. During installation, ensure that the axis of each idler roller is perpendicular to the running direction of the mesh belt and that the spacing between idlers is uniform (with a deviation no greater than 5 mm).

Correcting Installation Deviations of the Conveyor Belt

If the deviation between the centerline of the mesh belt and the furnace centerline exceeds 5 mm, loosen the mesh-belt tensioning device and shift the mesh belt in the direction opposite to the deviation (e.g., if the mesh belt is deviating to the left, shift the entire belt 5–10 mm to the right). During this adjustment, two operators must work in tandem, simultaneously pushing at both ends of the mesh belt to prevent twisting. After the adjustment, re-tension the mesh belt, use a tape measure to verify the distances between both sides of the mesh belt and the furnace guide rails (the deviation must be ≤3 mm), and then conduct a trial run for verification.

3. Special Treatment: Addressing Thermal Expansion and Contraction and Local Wear

To address belt misalignment caused by uneven furnace temperatures or localized wear of the mesh belt, special measures must be implemented:

Thermal expansion and contraction-induced misalignment: If misalignment occurs in winter or during the initial startup phase (due to low furnace temperature and uneven shrinkage of the mesh belt), first raise the furnace temperature to 200–300°C and preheat for 30 minutes to ensure uniform thermal expansion of the mesh belt, then make fine adjustments to the tensioning device to balance the tension on both sides. If high summer temperatures cause localized expansion and subsequent misalignment, appropriately reduce the tension (to prevent excessive stretching of the mesh belt) while also checking the furnace ventilation to ensure uniform temperature distribution (temperature difference ≤20°C).

Localized wear-induced misalignment: If one edge of the mesh belt is severely worn (e.g., wear width > 5 mm), resulting in unequal tension on the two sides, the worn section must be trimmed (ensuring that the belt width still meets the workpiece conveying requirements) or the locally worn segment must be replaced (with careful alignment at the joint to ensure a smooth, flush connection). If the wear is severe (with a high risk of belt breakage), the entire belt should be replaced with a new one that matches the original model in terms of material, mesh size, and width.