Brazing Alloys and Fluxes

Brazing is a reliable, simple and safe method of joining metal components. However, brazing alloys and fluxes contain elements, which, if overheated, produce fumes, which may be harmful or dangerous to health. Special care should be taken not to overheat cadmium containing brazing alloys, as inhalation of cadmium oxide fume can be particularly harmful.

Brazing should be carried out in a well-ventilated area with operators positioned so that any fume generated will not be inhaled. The installation of local extraction is being increasingly recommended, particularly when brazing with cadmium containing alloys.

Apart from fume hazards, flux can be moderately irritating to the skin and prolonged contact should be avoided.

It must be said, however, that with correct brazing practice and adequate ventilation the Health and Safety risks are minimal.

Many of the recommendations in this data sheet are common sense, It is important that management, safety officers and individual brazing operators make themselves fully conversant with all of these safety precautions and so minimise the chance of accidents occurring.

General Precautions

The most versatile brazing alloys are those based on the silver-copper-cadmium-zinc or silver-copper-zinc systems. They are all distinguished by their low melting points and good flow properties. They should never be overheated. Overheating is bad brazing practice and is likely to result in poor joints and increased evolution of fume. Metal and metal oxide fumes are irritating and can be harmful to health. Cadmium oxide fumes are particularly poisonous.
Operator well-being and safety will result from following the precautions given in this data sheet and those basic rules of safe brazing practice summarised on the last page.

Potential health and safety problems in brazing may arise in the following areas:-

1. Metal and metal oxide fumes from the brazing alloys
2. Fumes from heating the flux
3. Fumes from brazing torches
4. Equipment used to effect the brazed joint

Metal and metal oxide fumes

All brazing operations raise the temperature of the filler metal above its melting point hence it is unavoidable that metal fume (as the oxide of the elements present) will be evolved.

Cadmium Oxide

Cadmium Oxide fume will always be evolved to some extent during brazing with alloys from the silver-copper-cadmium-zinc range. Regulations list the exposure limits for Cadmium Oxide as a MAXIMUM EXPOSURE LEVEL (MEL) which must never be exceeded. The level present in the workplace must always be as low as practicable. The use of local extraction is virtually obligatory when brazing with cadmium containing alloys.

Short exposures to very high levels of cadmium oxide fume can lead to pulmonary oedema and may be fatal. Prolonged or repeated over exposure to cadmium oxide fume is reported as causing renal damage. There is a symptomless latent period and any person thought to have been over exposed to cadmium oxide fume should be kept under observation for 48 hours.

Cadmium Oxide fume is reported as carcinogenic and may cause cancer by inhalation. The likelihood of any problems occurring under normal brazing conditions is very limited and are normally the result of extremely poor brazing practice. These conditions would include severe overheating of the molten alloy using an intense heat source such as oxy-acetylene, brazing in an enclosed or ill ventilated area where fume build up is possible; or brazing without flux cover.

If cadmium containing alloys are felt likely to cause a health hazard then consideration should be given to the use of a cadmium free alloy from the Probraze Silver-flo range. These alloys may still contain cadmium as an impurity, but at a very low controlled limit of 0.025% maximum. This level allows brazing to be carried out under normal conditions of ventilation without the need for local exhaust ventilation as far as cadmium oxide fume is concerned. There could, of course, be other factors which would make local exhaust ventilation necessary.

If brazing is to be carried out where ventilation is poor, such as an enclosed pipe joint or any similar situation, then brazing of any kind, or welding, must be carried out with the operator using breathing equipment, in conformance to factory regulations for working in confined spaces.

Copper Oxide & Zinc Oxide

Copper and zinc oxide fumes under normal conditions are unlikely to be a problem but, if excessive, are irritating and can cause metal fume fever. Symptoms of metal fume fever are similar to those of influenza and often appear after a latent period of up to 10 hours; they will normally disappear after 24 hours with rest. Zinc oxide can also be irritating to the nose, mouth and throat.

Diphosphorus Pentoxide

On overheating corrosive diphosphorus pentoxide fumes may be evolved which are irritating to mucous membranes, the respiratory system, eyes and skin. Contact between the fume and perspiration may produce a mildly acidic reaction causing irritation of the eyes, skin and mucous membrane.

Atmospheric Sampling

Workshop personnel who may be exposed to excessive fumes during brazing operations should undergo tests of their working zone using personal air sampling equipment to ensure that MELs are not exceeded. Alternatively portable detection devices may be used to monitor the atmosphere during brazing operations. There are an increasing number of companies specialising in environmental monitoring who can undertake the necessary testing. Where local exhaust ventilation is installed regular checks on air flows and capture velocities should be made.

FLUXES

Skin Contact

The Probraze Range of brazing fluxes is based on fluorides, fluoroborates, borates, fluorosilicates and chlorides of potassium with additions of boric acid and borax.

On prolonged contact, these fluxes are moderately irritating to skin. Extra care should be taken if the skin is broken as immediate irritation will occur. If the irritation becomes a problem, operators should use barrier creams. Any cuts or abrasions, however slight, should be covered with an adhesive dressing. The use of flux paste eliminates the contact which could occur when mixing a flux powder with water before use. The use of impervious gloves e.g. rubber or latex is recommended to prevent skin contact.

Tests have shown the fluxes are irritant to the eyes. If flux does come into contact with the eyes they should be irrigated immediately with water or isotonic saline for up to 20 minutes. Medical attention should be sought if there is any suspicion of eye damage.

Oral Ingestion

Fluxes are harmful if ingested. They should be kept out of the reach of children and away from food, drink and animal feeding stuffs. It is advisable not to smoke when using these materials. Before meals, hands must be washed and fingernails cleaned. In the event of flux being swallowed, a doctor should be called and, meanwhile, the patient should drink plenty of water or milk with calcium carbonate (chalk) mixed in. Do not induce vomiting. If powder fluxes are used, they should be mixed in a special flux tray. Flux should never be put in a container such as a cup, a mug or a bottle which might be used for drinking or other purposes. Empty flux containers must not be used for the storage of foodstuffs e.g. sugar, coffee, powdered milk etc.

Fumes

On heating, flux will fume slightly. With overheating, the fume will increase. Fumes generated include Hydrogen Fluoride, Fluorine and Boron Trifluoride. Without adequate ventilation, or as the result of bad brazing practice, fume can cause irritation of nasal passages and eyes.
The workpiece should not be overheated and operators should avoid standing directly over the work. Any annoyance from fumes can be minimised by using workshops with high roofs, good local ventilation and efficient extraction systems.

Inhalation

In acute cases, remove to fresh air, apply artificial respiration and oxygen and summon medical aid. Continue observation for 48 hours. (Note: Poisoning by inhalation may also result from brazing metal fume or torch gases).

FUMES AND BRAZING TORCHES

Torch fumes will be burnt gases, primarily oxides of carbon and nitrogen which are unlikely to cause problems in well ventilated conditions.

BRAZING EQUIPMENT

Although brazing is a reliable, simple and safe method of joining metal components, there are a number of basic precautions to follow when brazing.

• Brazing stations should be made from non flammable materials and suitable refractory brick.
• Hot brazed components must only be handled with pliers or tongs unless gloves are worn.

Hand & Fixed Torch Brazing

A torch should always be pointed away from the operator or other people when being lit. Fixed torches should be lit from the side or from below. Do not reach over one unlit torch to light another. It is usual for all the torches in a system to light simultaneously, and very severe burns to the forearm can result.

Induction Brazing

Never touch the work coil while the machine is working. Although work coils are often water-cooled, when machines have been recently switched off the coils retain enough heat to cause a minor burn if they are touched. Hands should never be inserted into a work coil if a ring, a watch, a metal bracelet or any other metal object is worn. The object will heat up rapidly and cause an extremely severe burn.

Furnace Brazing

Controlled atmosphere furnaces usually have a curtain of burning gases at the inlet and outlet doors. Since these flames are often colourless and virtually invisible, a piece of iron or steel gauze should be hung in the flame path, this will glow brightly when a flame is present. Care should be taken when components are removed from a furnace or from a conveyor belt or container, since they may still be hot.

Resistance Heating

The hot electrodes should never be touched. The electrical apparatus and the equipment which regulates the flow of a controlled atmosphere gas (if one is used) should be set and adjusted only by competent personnel.

Salt Bath Brazing

The parts must be completely clean and dry before they are immersed in the bath. Any water on them is converted immediately into steam, causing a minor explosion in the bath and throwing out droplets of molten salt. The salt sticks to virtually anything it touches and can cause very severe skin burns. The components should be lowered very slowly into the bath to avoid splashing the molten salt. Salt residues should be scrubbed off the hands before meals and at the end of the day. The controls that govern the heat input to the salt bath should be set and adjusted only by competent personnel.

General

Mechanised brazing operations should always be set and adjusted by competent personnel. If machines fail to operate or operate incorrectly local supervision should always be notified immediately.

SAFETY PRECAUTIONS

Operator well-being and safety will result from observing the following basic precautions:

* Wear suitable protective clothing. Gloves are recommended to prevent skin contact with flux powders and pastes.

* Always wear safety glasses or goggles. Suitable tinted glasses should be worn if glare from brazing torches is a problem.

* Local extraction should always be used when brazing with cadmium containing alloys. Good ventilation is essential in all brazing operations.

* Avoid standing with the face directly over the work-piece. All brazing atmospheres should be monitored to ensure MEL’s are not being exceeded.

* Welding techniques must not be used when brazing. For example, the direct heating of a pool of molten brazing alloy must be avoided.

* Brazing in confined spaces should only be carried out using suitable breathing apparatus.

NOTE:The above is a brief summary and more detail is available on request . Probraze Metals(Pty) Limited cannot anticipate all conditions under which this information and our products are used. Probraze disclaims any liability for any loss, damage or injury howsoever arising (including in respect of any claim brought by any third-party) incurred using this information.

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