Sealing Bar Arc-Over: How to Fix Burn Marks and Electrical Shorting in Industrial Vacuum Sealers
Arc-over is one of the more visually obvious faults a commercial chamber sealer can develop, but the burn marks on the sealing element are often the surface indication of an underlying electrical fault that, if not addressed correctly, will recur and damage successive sealing bar replacements. Understanding what causes arc-over, how to distinguish between component-level and board-level faults, and what the correct repair sequence is will determine whether the machine is returned to reliable service or whether it begins a cycle of repeated sealing element failures.
Our workshop in Walvis Bay repairs sealing bar faults on commercial chamber sealers operating across Namibia. Our technicians work in both English and Afrikaans and provide a clear assessment of the fault cause before any components are replaced.
Identifying Arc-Over Damage on Henkelman Jumbo Series Sealing Bars
Arc-over in a chamber sealer sealing bar occurs when electrical current tracks across or through a damaged insulation layer rather than remaining confined to the nichrome resistance wire. The result is a localised high-current discharge that burns the PTFE tape, damages the silicone rubber backing strip, and often scorches the sealing bar body and surrounding chamber surfaces.
On Henkelman Jumbo 30 and Jumbo 42 machines, the sealing bar assembly consists of a nichrome resistance wire held under tension across an aluminium bar, insulated above and below by PTFE tape, and supported by a silicone rubber strip that provides consistent pressure during the seal cycle. When any of these layers is damaged, the insulation system that contains the electrical current during the seal impulse is compromised.
Common causes of initial insulation damage include: PTFE tape that has been cut or abraded by packaging material, silicone rubber that has hardened and cracked through thermal cycling, wire tension that has been set incorrectly and allows the wire to move during the seal impulse, and moisture in the sealing area during the cycle. Any of these conditions creates a path for current to track outside the intended circuit, and arc-over follows.
The visible burn mark identifies where the discharge occurred, but the cause is usually present at a different point in the assembly. A thorough inspection of the full sealing bar, including wire tension, PTFE tape condition along the entire bar length, and silicone backing condition, is required before replacement components are fitted.
Replacing PTFE Tape and Silicone Backing on a Burnt Sealing Element
Once the root cause of the arc-over has been identified and addressed, component replacement follows a consistent procedure. Attempting to replace only the damaged section of PTFE tape is not adequate: once PTFE tape has experienced arc-over damage, the surrounding material has typically been compromised by heat and should be replaced in full.
Remove the damaged assembly: Disconnect the sealing bar from the transformer connection terminals before beginning any disassembly. Release the nichrome wire from its anchor points at each end of the bar, taking note of the original wire routing and tension method.
Clean the bar body: Remove all remnants of burnt PTFE tape, silicone rubber, and carbon deposits from the aluminium bar. The sealing surface must be clean and free of residue before new components are applied. Carbon deposits left on the bar surface create localised hot spots and increase the probability of repeat arc-over.
Inspect the bar body: Check the aluminium bar for deformation or deep scoring from the arc-over event. A bar with significant surface damage may not be recoverable through cleaning and will require replacement.
Fit new silicone rubber backing: Apply a new silicone rubber strip of the correct dimensions and hardness rating. Silicone backing that is too soft compresses unevenly and produces inconsistent seal pressure. Backing that is too firm does not conform to slight packaging irregularities and produces seal voids.
Apply new PTFE tape: Apply a single continuous layer of PTFE tape of the correct width and thickness for the bar format. Overlapping sections or tape with wrinkles creates the same insulation inconsistency that caused the original fault.
Restring the nichrome wire: Install new nichrome wire of the correct gauge and set wire tension according to the manufacturer’s specification for the machine model. Incorrect wire tension is a primary cause of wire movement during the seal impulse, which wears through PTFE tape prematurely.
Seal Wire Tension and Short Circuit Faults: Diagnosis Procedure
If arc-over recurs shortly after a sealing bar has been replaced, the fault is not in the consumable components but in the electrical system delivering current to the sealing element. The impulse transformer and the control system that determines seal time and seal pressure are the areas to investigate.
A transformer that is delivering higher than specified voltage to the sealing element will exceed the thermal rating of the PTFE tape and cause accelerated degradation. A control board fault that produces extended seal time causes the nichrome wire to reach temperatures above design range, which burns through PTFE tape regardless of its initial condition.
Contact resistance at the wire termination points on the sealing bar is another cause of localised heating that does not affect the rest of the bar. If the wire anchor is loose or corroded, resistance at the contact point generates additional heat at that location, which burns the PTFE tape from the inside outward and is difficult to distinguish from arc-over without careful inspection.
A machine that has experienced repeated sealing bar failures should be assessed at the transformer and control board level before another replacement assembly is fitted. Replacing consumable components without identifying the electrical fault that is destroying them is a common error that results in repeated downtime and unnecessary parts cost.
For machines with sealing faults linked to Modified Atmosphere Packaging cycles, gas flush timing can interact with seal cycle timing in ways that affect sealing bar temperature. Our MAP gas flush troubleshooting guide covers gas system faults that may appear as seal quality issues rather than gas system failures.
Our workshop in Walvis Bay carries out sealing bar replacement, transformer testing, and board-level inspection for Henkelman, DZ-series, and other commercial chamber sealer brands. Courier repair is available for customers in Swakopmund, Windhoek, and across Namibia.