APPLICATION INSIGHT · EUROTECH VACUUM TECHNOLOGIES

Suction cup marks can still appear on glass after protective covers are installed. A cover helps reduce direct contact between the suction cup material and the workpiece, but dust, concentrated contact loads and small movements can still affect the surface. When marks remain, cup size and vacuum level deserve attention alongside cover condition.

In our glass-handling application experience, the correct MTC cover is one part of the solution. Where the machine and workpiece allow it, a larger effective suction area can provide an opportunity to operate at a lower vacuum level while maintaining the required holding performance.

Why marks can remain after fitting suction cup covers

MTC suction cup covers add a protective contact layer over a suitable suction cup. They help address marking associated with direct elastomer contact. They do not isolate the workpiece from every possible contaminant or mechanical effect.

It is useful to separate two mechanisms:

• Material transfer: traces associated with direct contact between the cup compound and the workpiece.
• Particle-related or mechanical marking: contamination compressed at the interface, uneven contact loading, or abrasion when particles move against the surface.

A reduction in rubber-related marks therefore does not prove that all organic and inorganic contamination has been eliminated. For the broader causes, see why vacuum suction cups leave marks on glass .

Dust, local pressure and movement must be considered together

Particles may arrive from the glass, surrounding equipment, storage or previous handling cycles. Incorrect cup sizing or excessive vacuum does not create dust by itself, but an unsuitable contact condition may press existing contamination more firmly against the workpiece.

Hard particles trapped between the cover and the surface can concentrate force over very small areas. If the cup, cover or workpiece then moves slightly, those particles may produce abrasion or scratches. A soft cover cannot make an embedded abrasive particle harmless. Glass manufacturers also warn against particles trapped between coated glass and contact materials during cleaning.

These patterns are inspection clues. Appearance alone cannot establish the cause of a mark.

How a larger suction cup can allow a lower vacuum level

The basic theoretical force normal to the workpiece is:

F_theoretical = Δp × A_effective

Here, Δp is the difference between ambient pressure and pressure inside the cup, and A_effective is its effective suction area. Increasing this area can compensate for a reduction in vacuum pressure difference.

An illustrative comparison

The following calculation uses ideal circular effective diameters. These are calculation assumptions, not the outside diameters or performance ratings of specific EUROTECH products.

Example B has 2.25 times the effective area and 50% less vacuum pressure difference, giving 12.5% more theoretical normal holding force. This illustrates why increasing suitable suction area can create room to reduce vacuum without necessarily reducing theoretical force.

The calculation excludes safety factors, cover effects, leakage, acceleration and shear loading. The percentages describe the ideal calculation only; they do not quantify a reduction in marks, local contact stress or scratching.

Lower vacuum does not directly measure local contact pressure

The effective area used to calculate suction force is different from the actual area where the lip, supporting ribs and covered surfaces touch the glass. Local pressure depends on how force is distributed across those contact points, as well as cover wrinkles, cup stiffness and mechanical preload from the machine.

Consequently, a 50% reduction in vacuum pressure difference does not establish a 50% reduction in pressure at a trapped particle. The proposed benefit is a more suitable distribution of contact loading; the result must be checked on the actual surface.

Simply fitting a larger cup while retaining the same high vacuum also increases theoretical force. Cup size and vacuum should be reviewed as a pair. Available space, glass flatness, cup spacing and the machine mounting arrangement may limit the change. Our flat vacuum suction cup range provides starting points for an application review.

Preserve slip resistance and the required safety margin

Lower local pressure does not automatically mean lower total friction. In a simplified model, the maximum static friction depends on the normal force and the friction coefficient. If total normal force remains similar, enlarging the nominal contact area alone does not necessarily reduce total friction.

For vertical glass handling, friction is also part of what prevents sliding. A cover changes the contact interface, so the friction behaviour of bare rubber should not be assumed to apply to the covered cup.

The larger-area approach may provide additional calculated holding margin when load demand is unchanged. However, the required safety factor remains a design requirement: a higher verified margin must be demonstrated for the complete assembly and worst operating condition. Review suction cup safety factors and dynamic loads before changing the setup.

A practical review when marks persist

1. Document the starting condition. Record the cup and cover, vacuum at the cup, workpiece, orientation, cycle speed and when the mark becomes visible. Photograph the same area under consistent lighting.
2. Restore a clean contact interface. Inspect the glass, cup and cover. Replace contaminated or damaged covers; follow approved cleaning instructions for the specific surface and cover.
3. Check fit and motion. Look for folds, uneven support, excessive approach force, sideways drag and withdrawal before full release. Changing vacuum will not correct excessive mechanical preload.
4. Evaluate cup area and vacuum together. Have the equipment manufacturer or responsible engineer review the covered configuration before an approved, controlled trial. Verify actual vacuum, leakage, build-up time, load distribution and slip resistance throughout the cycle.
5. Inspect the finished result. Compare surface quality over representative repeated cycles and after relevant downstream processes. Record holding performance alongside visible marks, cleaning effort and rejects.

The suction cup size and lifting force calculator can support a preliminary comparison. Final selection needs the actual covered assembly and machine conditions.

Frequently asked questions

Does a remaining mark mean the MTC cover is ineffective?

A remaining mark may have a different cause from the original elastomer-contact mark. Check contamination, cover fit, contact loading and relative movement before deciding which component needs changing.

Should every machine use larger cups and lower vacuum?

No. This is an option to evaluate where space, surface geometry and handling requirements allow it. Larger cups may not fit, seal or share the load correctly on every workpiece.

Can the vacuum setting simply be reduced until the marks disappear?

The acceptable setting must satisfy both surface quality and verified handling performance. The equipment’s operating limits, monitoring thresholds and required safety factor must remain satisfied throughout the cycle.

Technical background

This article combines EUROTECH application experience with an illustrative engineering calculation. General background: OpenStax: friction and normal force ; Pilkington SaniTise handling and cleaning guidance (PDF) . These references explain general mechanisms; they do not establish MTC-specific performance.