What is the common failure of rubber expansion joints?

Common failures on rubber expansion joints

SHANGHAI SONGJIANG JINGNING SHOCK ABSORBER CO.,LTD.

1，Bubble

Bubble mainly appears on the outside of rubber bellows.It’s a bubble start in the middle layer.See the pictures following:

The reasons and how to avoid:

1,The rubber and nylon didn’t combine well.It’s because of bad rubber material and inappropriate rubber formula.

All the material JINGNING use in our process are recommended by a tire factory who cooperate with Dunlop.We buy from the same company as the tire factory.And we commissioned the tire factory to analysis the material.

Rubber formula is also a very important factor. JINGNING rubber bellows have 3 different rubber formula for outside layer, inside layer,Nylon layer.We regularly test the extraction force of nylon and rubber.

2,Nylon cord exposed to working medium.Nylon is not water resistant. When exposed,the water will flow along nylon cord into the middle layer.When pressure high, it caused the bubble.

It’s easy to test after the vulcanized process.We will pick out the bad one to the scrap box.Some companies didn’t realize this reason. They will repair it with glue then sell again.It has a big risk.

3,The rubber’s gas-tightness is not good.It’s caused by bad quality rubber and chemicals.Even some companies use reclaimed rubber.

There are many gaps between the rubber molecules, which need to be filled with chemical materials.Reclaimed rubber’s granule are large, and the gap is difficult to fill.Carbon black is the most suitable chemicals to fill the gap.But some companies may use calcium carbonate instead to reduce cost.

We use large quantity carbon black per month.

2，Pull out

The rubber bellows may be pulled out of flange when work under pressure.

The reasons and how to avoid:

1,Installed not well.

If the bolt is not tightened as required, it will be pulled out easily.

We have install instruction for this.

2,Rubber bellows and flange didn’t fit well .

If the flange is too floating , it means the gap is too large,it has the risk of pull out.

We also use floating flange, but our rubber bellows and flange are designed a little tight to avoid this failure.

3，Sealing surface damage

The reasons and how to avoid:

1,The rubber and nylon didn’t combine well.

2,Rubber toughness is bad.

They are caused by unsuitable rubber formula or bad raw material as mentioned in the bubble failure.

JINGNING rubber has very high toughness. It’s very hard to pull the rubber strip down.

4，Leakage

The Water may leak a little from the neck of rubber bellows.

The reasons are the same with the Bubble failure reason 2,and 3.

5，Crack

The reasons and how to avoid:

1,Rubber aging.

Rubber aging is inevitable.But we can use chemicals to delay rubber aging.We use sufficient anti-aging chemicals.Our rubber bellows’ surface are designed smooth to protect its inner from aging .  So our JINGNING products can work a long life.

2,Nylon cord damage.Because it’s too fracture to with standard pressure.

The nylon cord quality and numbers of layers is the most important factor.

You can see the combination of rubber and nylon.We use sufficient  numbers of layers.