how we made custom rubber extrusions for clients

Custom rubber extrusions are made to be small size flexible strips or large size straight bars/profiles,often made by EPDM,silicone rubber etc, the finished products series are

• weatherstrip seals for vehicle,door and window(sunlight,rainstorm, cold,wind,ozone,UV etc)
• edge trims for guard protection or rough parts decoration(e.g.sheet metal)
• sponge/foam rubber extrusions for anti impact/vibration/collision/hard-wearing
• industrial use rubber tubing,rubber waterstop strip/sheet,extruded large profiles

custom rubber extrusions manucturing workflow chart

1.Raw material preparation–compounding

Mix all raw materials to a certain proportion except ultra accelerator and vulcanizator,for the first stage mixing:banbury internal mixing. Most of the rubber extrusions requires two stage mixing/plastication:

• banbury internal mixing
• open mixing

2.Banbury internal mixing

Mix uniformly the crude rubber with the compounding ingredients e.g. vulcanizing agent,oil-softener,fortifier etc,and stash it for 8 hours or so,to make it

• Recover the fatigue
• release mechanical stress
• Reduce shrinkage
• Compounding diffusing uniformly
• Bound rubber reinforcement between carbon black and rubber with cross-linking matrix structure

first stage rubber mixing machine–banbury mix machine

Notes:

• One of the ingredients Kerosene is to change the plasticity and flexibility to be more machinable;
• The largest 3 synthetic rubber producing country are: USA/Japan/Korea,especially for EPDM rubber;
• Rubber straining machine can effectively wipe off the impurities of the compounding rubber

EPDM rubber straining machine to wipe off impurities

3. Open Mixing

Compounding with accelerant,prepare the material to be next process-calendaring molding

second stage open mixing-epdm rubber mixer machine

4. Extruding

The exhaust type pin cold feed extruder is the most popular extruding machine,or thread cold feed extruder is another option,for general custom rubber extrusions. Extruding Die design moulds to determine the cross section shapes,which makes extruded rubber items to be a continuous bar with constant lateral section shape.

extrusion die moulds and its cross section shapes

5. Vulcanization

Closely followed by vulcanization(or sulfidation),via a series of curing equipment—micro wave vulcanister,hot air culcanister,hauling machine and cooling equipment.

rubber extrusions manufacturing vulcanization equipment

rubber extrusions assembly line

6. Packaging (cutting or coiling)

After cooling then make dry,the rubber extrusions item can be cut to be a given length or packed in a roll. Small size extruded rubber items is flexible,we often call it “rubber strips”(including small diameter rubber tubing),it can be curled in a roll,then every 200~300meters per carton;

small size rubber extrusions-flexible rubber strip packed in rolls

Large size extruded rubber items are not easy to bend,it is more like straight bars,we often call them “rubber profiles”,rubber extrusions profiles are usually cut into centain length bars,such as anti-collision rubber profiles;

large size rubber extrusions-straight bar profiles cut into certain length

7.Or deep processing as per clients’ special requirement below:

• Hole punching
• Butt jointing
• Angle Adjancent
• Flocking/Pile coating
• Adhesive Backing

rubber extrusions flocking equipment-pile coating machine

angle acjacent moulds for extruded rubber seals

8.Required Properties for Automotive rubber extrusions

Working conditions of automotive rubber seals are required strictly conditional especially for weathering aspect,the service life of the finished product are up to the performance index of rubber extrusion items. Important parameters of automotive rubber extrusions:

• Temperature range: typical value: -35℃ to 70℃
• Hardness
• Tensile strength: typical value >=7Mpa
• Enlongation at break   Typical value 250~350
• Compression set(compression load)
• Anti-ozone aging
• Atmospheric aging
• Resistant to paint(coating properties)
• Low-temperature properties (low-temp elasticity)    typical value:keep resilient at -35℃
• Installation performance(insert/pull out force)
• Flocking resistance
• Cohesiveness
• Extrusion force for edge trims
• Brittleness temperature    typical value -35℃

The above properties and its typical value applies to custom rubber extrusions for common projects of industrial use rubber extrusions, such as u channel rubber edge trims,epdm rubber tubing,house door window rubber strip seals,etc