Rubber Bonding tips for when the rubber type is unknown

People often ask me what I do for a living. When I say that I work for an engineering company stickers, more often than not I am presented with an empty look and the question: “what’s that?” I answer “you know, glue, sticks stuff together …” “Ah, Yes, glue … “, then they quickly change the conversation.

So when someone needs advice on rubber bonding, given the lack of knowledge, excitement and interest in glue, I do not know where to start with the selection of adhesive. Then play into the mix that they are not a rubber / materials specialist and they are really frustrated.

 

 

Types of Rubber

Now, I am no rubber expert and struggle to identify one type to another as well, but here are some basic types:

ACRILONYTRILE BUTADIENE RUBBER– this is very common and can be found frequently in applications such as hoses, O-rings, gaskets, conveyor belts, cable coating and printing rollers.

BUTYL RUBBER – This material is very flexible and is used for things like linings, inner tubes, seals and lids, as well as valve seating.

POLYURETHAN EDGE – often used for things like moulding and modelling.

NATURAL RUBBER – often used for mountings and carpet backing.

SILICONE RUBBER – This material has excellent resistance to high temperatures, making it a popular choice for O-rings, gaskets, cookware, kitchenware, medical appliances and prosthetics.

EPDM RUBBER– hoses, seals, etc.

There are plenty of other rubbers like SBR latex, chloroprene, etc … too many to mention.


Rubber Bonding

Before attempting rubber bonding, it is recommendable to carry out a solvent degrease. Surfaces may have mould release, slip additives or other lubricant processing on them, so a quick clean using isopropanol is a good idea. Acetone can be very aggressive as certain types of rubber are vulnerable to attack.

Even after you have cleaned the surface, the rubbers may contain plasticizers that can resurface again over time and can cause boning at a later date (but not all adhesives are affected by it, so do not panic!).

Instant adhesive cyanoacrylate is usually your best bet for rubber bonding; Epoxies are not usually recommended – the rubber is easily peeled off.

Cyanoacrylate adhesive cures in seconds, so you can find out very quickly whether it will work or not! Less cyanoacrylate is more to use only a small drop and make sure that the components are pressed together firmly. If the joint falls apart after enough curing time, it indicates that it may be a harder to bond rubber (like EPDM or natural rubber) or could be dealing with silicone rubber rubber.

For EPDM bonding and natural rubber, an easy solution is to simply use a specialized hard rubber adhesive like Permabond 105. This eliminates the need to use a primer cyanoacrylate. For silicone it would be necessary to use a primer such as Permabond POP in combination with 105 or, if a little more desired flexibility, use the cyanoacrylate POP and Permabond 2050.

Permabond 2050 is very useful, especially for bonding together Soft O-rings as it maintains its flexibility in the joint so it is difficult to detect the joint (usually the adhesive may feel a little “crunchy” on the joint, but the 2050 keeps a uniform seal).


Other Bonding options

It may be very restrictive to consider cyanoacrylate adhesives as the only option for bonding rubber; This is not necessarily the case.

The advantages are obviously a good grip (usually to the point that if you try to pull the rubber side link will break) and fast curing speed make cyanoacrylates ideal for fast assembly processes on production lines, but there are drawbacks.

Cyanoacrylates

Do not allow time to re-align the joints due to curing in seconds. In addition, they offer a limited gap fill (maximum 0.5 mm) and cannot extend over large areas (they will bond the spreader or roller). Its pungent odour can be unpleasant.

Contact adhesives

Can be used instead, especially offering a practical solution to large areas (but again, it may be a bit smelly!), But they can also be difficult to realign well. An alternative, low-cost method of joining is solvent based rubber bonders.

Silicone based products

Can be used for bonding a silicone, but some find them messy and slow to cure, so they are not practical for small item assembly on a fast production line.

Permabond TA4605 and TA4610 are two-part acrylic structures for bonding difficult plastics like polypropylene, polyethylene and PTFE which also demonstrate the quality of designs such as EPDM.

EPDM rubber contains polypropylene, so it is understandable that these products are used to connect this rubber. Structural acrylic adhesives offer the possibility of accurate alignment and spreading due to their slower cure time than cyanoacrylates.

The odour is less pungent than many adhesives, and are not solvent based. TA4605 and TA4610 have excellent environmental durability, therefore they can be used in applications that are submerged in water.

For more help and quotation services, please contact Antala.

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