Risks in Rubber Mixing and Vulcanisation

Rubber production safety: start by understanding the process

In rubber businesses producing parts such as seals, hoses, gaskets and anti-vibration mounts for the automotive supply industry in Bursa, production follows a different chain from plastic injection moulding. Rubber is first mixed with fillers, oils and vulcanisation chemicals, processed on a mill, shaped and then cured under heat and pressure. Rubber production safety encounters a different hazard at each link in this chain:

For similar risks on plastics lines, see our article on extruder and granulation lines; this article focuses on points specific to rubber.

Weighing raw materials and compounding dust

Carbon black, zinc oxide, sulphur and accelerators are usually weighed in powder form. With open weighing, the dust is both inhaled and spread over the bench, the floor and the employee's skin. Rank the measures according to the hierarchy of controls:

• Pre-dispersed or granular form: If possible, use chemicals in pre-dispersed or granular form instead of powder.
• Enclosed weighing and extraction: Install local exhaust ventilation at the weighing station that captures dust at source; empty bags at a bag-emptying station with extraction rather than with an open scoop.
• Sulphur dust: Sulphur is a combustible dust; prevent it from building up, do not use compressed air for cleaning and control ignition sources. For details, see our article on the risk of dust explosions.
• SDS: Post the PPE and storage information from each chemical's safety data sheet in the weighing area.

The Regulation on Health and Safety Measures in Work with Chemical Agents treats substituting a hazardous chemical with a less hazardous one as the priority measure. We plan workplace measurements with authorised laboratories and enter the results into the risk assessment.

The Banbury mixer: feed opening and discharge door

In an internal mixer (often called a "Banbury mixer" on site, after the brand name), two rotors knead the rubber under a ram that comes down from above; the compound drops from the discharge door below onto the mill. Accidents usually happen not during normal production but at the moment of intervention:

1. Reaching into the feed opening: A hand reaching into the opening to push a stuck bag or material can be drawn into the rotor. The feed opening must be guarded so as to prevent access when the ram is raised, and the covers must be interlocked.
2. Unexpected lowering of the ram: Pressure remaining in the hydraulic or pneumatic system can lower the ram even after the power has been isolated. During maintenance, the ram is held with mechanical support and residual pressure is released.
3. Working under the discharge door: Cleaning and maintenance under the door must not be done until the door has been mechanically locked.
4. Hot compound: The discharged compound is hot and gives off fumes; extraction at the discharge point and heat-resistant gloves are needed.

During mixer maintenance, electrical, hydraulic, pneumatic and heating energy are each isolated and locked separately. For the steps, see our article on LOTO lockout and tagout.

Two-roll mill safety

The open two-roll mill is the oldest and most dangerous machine in the rubber sector. The operator feeds, cuts, turns and takes off the compound in strips by hand, all of it right next to two rolls rotating towards each other. The nip point between the rolls can draw in a hand, an arm or a glove within seconds.

For two-roll mill safety, set up the following arrangements on site:

• Body-actuated emergency stop: An emergency stop bar or trip wire that operates without the operator having to reach for it with a hand, when the hand or body approaches the nip point, must be accessible at the front and back of the mill. For the general rules, see our article on the emergency stop button.
• Stopping distance test: The value of the emergency stop depends on how quickly the rolls stop. Check brake performance by testing the emergency stop at the start of each shift and by measuring it at regular intervals, and record the results.
• Reversing: There must be a mechanism to separate or reverse the rolls in the event of entrapment, and employees must know through practice how to use it.
• Feeding method: Material is fed not from the level of the top of the rolls but from a safe height; cutting is done with a knife and with a technique that keeps the hand away from the nip point.
• Clothing: No loose clothing, open sleeves or gloves that could catch in the nip point are worn.
• One person, one control: While someone is working at the mill, no one else must be able to start the machine.

The vulcanising press: closing, heat and steam

In seal and mount production, moulds are cured between heated platens in hydraulic presses. The vulcanising press carries three separate risks:

• Closing area: If the press closes while the operator is placing a part in the mould or removing a part from it, crushing occurs. The closing movement must start only after the hands have left the danger zone, through two-hand control, a light curtain or an interlocked guard. For the general principles, see our article on press safety.
• Hot platens and moulds: Contact burns are common during part removal, mould cleaning and mould changes. If moulds are to be changed before they have cooled, this is done with heat-resistant gloves, suitable lifting equipment and written instructions.
• Steam and pressure: In steam-heated presses and autoclaves, the lines and vessels are under pressure. The autoclave door must have an interlock that prevents it from being opened while there is pressure inside.

Annex III of the Regulation on Work Equipment requires periodic inspection of presses and pressure vessels at least once a year, unless a standard or the manufacturer provides for a shorter interval. Clarify with the authorised person who will carry out the inspection which inspection group your vulcanising presses and autoclaves fall into.

Rubber fumes and skin exposure

During vulcanisation, especially when the mould opens, a cloud of fumes rises above the press. Rubber fumes are not a single substance but a complex mixture formed by heating rubber and its additives. Nitrosamines can form from some accelerators. The International Agency for Research on Cancer (IARC) classifies work in the rubber manufacturing industry in the group of agents carcinogenic to humans (Group 1). The fumes should therefore be managed not as a "smell" but as an exposure:

1. Extraction at source: Install a hood or edge extraction over the press, close to the point where the mould opens; verify with a smoke test that the extraction really captures the fumes.
2. Working position: Set up a part-removal arrangement in which the operator does not put their head into the fumes when the mould opens.
3. Substitution: Assess with the compound development team a move to accelerator systems with a lower tendency to form nitrosamines.
4. Measurement: We plan workplace measurements with authorised laboratories and enter the results into the risk assessment.
5. Skin: Accelerators and some additives can cause allergic contact dermatitis. Plan suitable glove selection and hand care as in our article on occupational dermatitis.

If solvent-based adhesive is used between layers in hose production, fire and solvent vapour are assessed separately. At periodic examinations of employees exposed to fumes and dust, the workplace physician monitors respiratory and skin findings; we plan the necessary tests with authorised healthcare providers.

Points specific to hose and seal lines

• Mandrel and braiding machines: There is an entrapment risk when the hose core is pulled and at the rotating bobbins of wire braiding machines; rotating parts must be inside interlocked guards.
• Continuous vulcanisation lines: On hot air, microwave or salt bath lines used for profile seals, the risks of hot surfaces and a hot environment stand out.
• Cryogenic deflashing: At deflashing machines working with liquid nitrogen, oxygen can be depleted in enclosed or poorly ventilated rooms. The room must be monitored with an oxygen detector, and machine maintenance must follow the confined space procedure.
• Manual deflashing: Reduce knife injuries with cut-resistant gloves and guarded cutters.

At Bursa Sistemer OSGB, we carry out risk assessment machine by machine at rubber and plastics businesses in Bursa and the surrounding provinces, and under our OHS specialist service we plan on-site monitoring of these checks. For the general risks of the sector, see our chemicals and plastics page.

Frequently Asked Questions

What is the most effective measure on a two-roll mill?

An emergency stop arrangement that operates without the operator having to reach for it with a hand when the hand or body approaches the nip point, and a brake that stops the rolls quickly. Test the emergency stop at the start of each shift, measure the stopping distance regularly and teach the feeding technique through practical training.

Are rubber fumes harmful?

Yes, they are an exposure that needs to be managed. Vulcanisation fumes are a complex mixture, and IARC classifies work in the rubber manufacturing industry as carcinogenic. Local exhaust ventilation above the press, a suitable working position and workplace measurement are the basic measures.

Is a vocational training certificate mandatory in rubber production?

Yes, if your workplace is in the hazardous or very hazardous class. Row 61 of Annex 1 of the vocational training regulation covers all work in the rubber industry, from compound preparation to shaped products. An employee without a certificate must not be employed in this work.

How are burns at the vulcanising press prevented?

Use hand tools for part removal and mould cleaning, provide heat-resistant gloves and carry out mould changes with written instructions. Mark hot surfaces and give employees a practical demonstration of first aid for burns.