MOLD Cleaning Techniques

Mold Cleaning Techniques

INTRODUCTION

History of mold release agent is as old as moulding of rubber itself.In general all rubber compounds tend to stick to the curing mold surfaces. Mold release agents of mold lubricants are often used in the rubber industry to prevent the above sticking and also to facilitate removal of the rubber product from the mold.

Mold release agents, normally implies that these are external agents. truly they are not always external chemical or product, sometimes they can be used internally along with the compound as well. example if stearic acid is used between 2- 4 parts in butyl inner tube compound or in curing bladder formulation, the product release from the curing mold is faster and also it prolongs the process on mold dirtiness problem.Incidentally stearic acid does not require functioning as co activator in butyl rubber. Since stearic acid has got the above advantages, many metallic stearates are there in the market as claiming release agents when added in the compound.

Resons for Mold Cleaning:

As the technological break through is happening every year, there is also increase in trend towards manufacturing of intricate smaller rubber products with more complex parts. Mould fouling is a major problem faced by tyre manufacturers all over the world , where typical residue build up on the curing mould surfaces caused primarily by the chemical reactions betweeen sulphur, zinc oxide and organo metallic accelerators under hear and pressure. Excessive fouling in the bead area of a tyr bead surface that the tyre might not seal properly on a wheel rim.

Other reasons for mould cleaning are a vast majority of the tyre mould in use today have vents or micro vents to expel air trapped between the green tyre surface and the  mould surface as the bladder expands the green tyre into the mould cavity during cure,
another area of concern is keeping mould surfaces cleaned which mate or come into intimate contact during cure, free of residue buildup. For two piece tyre moulds these are the surfaces bewteen the two mould halves that comes into contact when mould is closed and that produce a parting line in the mid cross section of the tread pattern.

If too much residue is allowed to build up in this area of the mould the mould halves will not meet together completely even under the extreme pressure of the press.. This might result in flash arounthe circumference in the middle of the tread pattern on the finished tyre.

Segmented moulds

For tyres cured in segemented moulds flash can be very noticeable and rejection because it occurs partly on the sidewalls and across the tread pattern.Also a build up of residue on the mating mould surfaces can causes high mechanical stresses in the fasteners which attach the segments and sidewall rings to the press.          

Mould vents and Microvents:

Mould fouling must be cleaned at a regular intervals to achieve continuously global surface of finished products. At the same time there is also development of different types of moulds with different metal alloys to reduce mould fouling.

Typically the mold vents are 1 mm to 2 mm in diameter. Both types can't be extended an inch or more in depth inside the mould. A typical passenger car Tyre mould contains thousands of these vents.
 The problem lies in that the bladder expansion pressure,combined with the elevated curing Temperature causes some of the tyre surface rubber to extrude into these vents.

When the cure cycle is over and the tyre us relased from the mould most of the extrude rubber in these vents remains attached to the cured tyre and pulls back out tibform the familiar rubber Whisker's on new tyres.

However not all of the mi to vents release their extruded Whisker's but when this happens air trapped in the mould begins to cause surface irregularities and other faults on the finished tyres, which ultimately increases the production scrap rate. Such moulds need to be cleaned immediately for getting quality products.

This process repeats to clog a few more vents each cure cycle. The traditional vent cleaning method has been to remove the mould from the press grit blast the side wall and tread surfaces, the drill the cured rubber out of each vent hole with very small drill bits and air tools.

A subset of the clogged vent problem occurs when these very fragile drill bits break off to permanently plug the vents.Thus the vent must be removed and replaced with a vent insert.Typical passenger car and light truck tyre moulds contains thousands of events or micro vents.the labour required to drill out the clogged vents and the hundreds of drill bits consumed per month add the cost to the manufacturing much.

Drilling vents

Drilling through mould vents is applicable whne vents or micro vents are blocked and can not be cleaned in usual blasting methods.It is a pricessbof drilling the cured rubber out of each vent hole with very small drill bits and air tools..the vents are blocked with rubber products is over cured or under cured in the mould.

Ventless moulds

A major quality driver in the tyre industry is aesthetic specifically product appearance.The trend today is to produce tyres devoid of the Whisker's produced by very tiny vents or micro vents.Typically the micro vents are between 0.5 mm to 1.0 mm or even less than 0.5 mm in diameter. 

Traditional  tyre mold cleaning methods.

Traditionally there are two types of traditional tyre mould cleaning methods.

Mechanical Cleaning:

This is also known as hand cleaning or chemicals cleaning and essentially include organic solvents, melting, pickling, alkaline Cleaning methods.These methods are easy to use and they are low in capital investment costs.However prolonged use of the above methods can causes changes in mould dimensions may also cause mould corrosion, which directly affects the product appearance and quality.

Currently the method is mainly used for small scale rubber products business. With the continuous  development some new technologies being developed and applied.

It is safe mode if mould cleaning since history of rubber products

 Hand Cleaning is time consuming.With different types of spray cleaner, solvents, chemicals and brushes etc, they all required handling each piecebof tooling several times, so none resultednin significant savings in cost or labour.

 Even extremely caustic cleaners such as sodium hydroxide, sulfuric acid baths were limited in the amount  of rust build up they would remove on unplayed surfaces in a specific time frame. Hand cleaning is an effective cleaning method. However for areas of plastic moulds that normally have the most corrosion and contaminant building up in use front and rear clamp plates that directly contact thr press platens Bubbler places ( Non stainless) Bushings and wear plate grease groove

Choosing the wrong type of cleaning system or having repair technicians reject the new method can cause disastrous repercussions so they vaping making a change. Heavy brust buildup of needs prevention thought more frequent cleanings  usevof stainless steel plates and corrosion resistant platic and consistent application of spray on rust inhibitors.

Abrasive blasting:

Abrasive blasting cleaning method involves high speed sand particles or other  solid particles like glass beads over dirty mold clean the mould surface.Sand blasting is a process during which abrasive industrial Cleaning materials are quickly propelled at equipment.This can also be useful for purposely roughening a smooth surface for bonding application.

This is the operation of forcibly propelling a stream of abrasive material against a surface under high pressure to smooth a rough surface, roughen a smooth surface, shape a surface or remove surface contaminants.A pressurized fluid typically air or a centrifugal wheel is used to propel the variants of the process such a s bead blasting, sand blasting,soda blasting and shot blasting etc.

Bead blasting:

Bead blasting is the process of removing surface deposits by applying fine glass beads at a high pressure without damaging the surface.Other than glass beads, hard alumina bead is also used for the purpose.It is used to clean calcium deposits from pool tiles remove embedded fungus and brighten grout colour.It is used in auto body work to remove paint.In removing paint for auto body work bead blasting is preferred over sand blasting.

Sand Blasting:

Sand blasting is a process during which the abrasive industrial Cleaning materials can be useful for purposely roughening smooth surface

Pressure sand blasting machine

Wheel blasting:

In wheel blasting a wheel uses centrifugal force abrasive against an object.It is typically categorized as an airless blasting operation because there is a propellent used. The wheel machine is a high power , high efficiency blasting operation with recyclable abrasive or stainless steel shot. Specialised wheel blast machines propel plastic abrasive in a cryogenic chamber and is usually used for deflashing plastic and rubber components

                                                    Table wheel blasting

Micro abrasive blasting:

Micro abrasive blasting is dry abrasive blasting process that uses small nozzles. Typically 0.25 mm to 1.5 mm diameter to deliver a fine stream of abrasive accurately to a small part or small area on a larger part. Generally vthe area to be blasted is from about 1 mm to 2mm This is also known as pencil blasting the fine jet of abrasives is accurate enough to write directly on glass and delicate enough to cut a pattern in an eggshell.

The abrasive medial particle sizes ranges from 10 to 150 micro meters. Higher pressure are often required in this process .The most common micro abrasive blasting system are commercial bench mounted units consisting of a power supply and mixer, exhaust hood, nozzle and gas supply.The noZle can be hand held or fixture mounted for automatic operation.

Hydro blasting:

 Hydro blasting commonly known as water blasting is commonly used because it usually requires only one operator. In hydro blasting a highly pressured strean of water is used to remove old paint, chemicals or buildupbwithiyt damaging the original surface.

This method is ideal for cleaning internal and external surfaces because the operator is generally able to send the stream of water into places that are difficult to reach using other methods. Another benefit of hydro blastin is the ability to recapture and reuse the water.

Hydroblasting

Dry ice blasting / Cleaning:

Dry ice cleaning or solid Co2 cleaning technology is used to remove particles,ionic contamination and organic residues from complex components and assemblies to improve performance and reliability of the systems within which they are employed.This process do not require to dismantle the moulds and cleaning.Dry ice blasting is a portable devices and can. Be brought near any type of mould and can be cleansed faster with out generating any pollution effect on the environment.

When Co2 is compressed it directly concerts intonsolid ice and in room temperature is sublimates into gaseous state directly.Dry ice is Co2 in solid state.

Ice blasting is a non abrasive cleaning method developed in the 1940 s.thatvforst became popular among automotive rubber moulders because of its ability to clean moulds in the press, while the mould is hot without causing an appreciable secondary waste strean of its own.

 Solid carbon di oxide pellets are about the size of a grain of rice or shaving about the size of a grain of sugar are introduced into an air stream and are shot out at high velocity through a variety of state if art aerodynamically designed nozzles to remove residue quickly band harmlessly from mould plates and tooling.

 For larger equipment and machinery that has been affected by dirt, rust and other contaminants , technologies that use industrial Cleaning materials such as dry ice blasting and sand blasting can provide an effective cleaning solution.However dry ice blasting is a technologically advanced process that produces a non abrasive superior clean that reduces the frequency of routine cleanings decrease downtime.

Dry ice blasting can simply and effectively remove contaminant without damaging equipment costs.These systems can utilize blast nozzles up to six inches wide at the low pressure and kinetic energy level required for the coatedvmoulds. Cleaning coated passenger, light truck and even larger commercial truck and rear farm vehicle coated tyre moulds will be fast and easy at very low noise, air pressure and dry ice pellet flow rates by employing the very wide nozzles available only with single hose systems.

Carbon dioxide precision cleaning technology has been employed high reliability and high volume manufacturing application mitigate contamination yield problems.Surface contamination are dislodged by the force of frozen carbon di oxide particle hitting at high velocity and also by slight shrinkage of metal due to freezing which disrupts adhesion bonds.The dry ice sublimates leaving no residue to lean up other