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Processes
Moulding process
Injection
Preparation
The material is received in the form of raw rubber, called "masterbach". If necessary, curing agents, accelerators and activators are mixed in the raw rubber with the help of two rollers. After several runs through the rollers, the material acquires its homogeneity, is calibrated in thickness and cut into strips.
The masterbach
It consists of an elastomer base mixed with plasticizers and carbon black (or mineral fillers, usually for coloured mixtures). Semi-finished material acquires its properties of process-ability and hardness. Curing agents, accelerators and activators will need to be added for the moulding process. The use of masterbach can extent the storage period of raw.
Vulcanisation
A strip of elastomer material is inserted into an endless conveyer screw. The mixture is then heated and liquefied channels to go and fill up the cavities of the tool. Vulcanisation can now take place. Vulcanisation (or reticulation) is the trigger of the chemical reactions during wich the monomer bases bind and form a cross-linked chain. The solidified result forms a cluster consisting of the parts and the fedding channels. During the finishing process, the parts will nedd to be separated from the rubber residues of channels and deflashed.
Injection tools
The cavities of the injection tool are fed with material thanks to secondary feeding channels via an injection point, or feeding area. These channels are themselves connected to the press's injection nozzle.
The tools are usually equiped with a thermoregulation system in order to maintain a homogenous temperature in the different cavities.
The injection point of feeding area may leave a raised mark or a hollow depending on the dimensions of the parts. The maximum sizes are listed in the ISO 3601-3:2005 grade N.
Tolerances
The tolerances on finished parts are in accordance with ISO 3302 grade M2.
Workflow
Compression
Preparation
The procedure of reception and mixing of the masterbach is the same as by injection moulding.
The masterbach is cut into strips. The weight of those strips is 100% controlled to ensure that the operators have the exact needed quantity.
Vulcanisation
With the help of a specific tool, the operator places the strips into open mould. When the mould shuts the vulcanisation begins.
Vulcanisation (or reticulation) is the trigger of the chemical reactions during which the monomer bases bind and form a cross-linked chain. The solidified result forms a sheet consisting of the parts and a linking membrane (also called "flash").
Tolerances
The tolerances on finished parts are in accordance with ISO 3302 grade M1 or M2 depending of customers' needs..
Compression tools
Compression tools are usually composed of the plates (upper and lower plate). The cavities are machined without any feeding channels, thereby increasing the number of cavities.
The mould's temperature is regulated by resistors in contact with plates. Thanks to the simplicity of its design, the tool easily gets a homogeneous temperature.
The mould is positioned horizontally (vertical opening) in order to guarantee an accurate closing: parting line offset due to tool upper and lower plates misalignment is minimal. To create complicated shapes, theoretically un-extractable, Techné offers a multi-plates tool conception.
Workflow
Transfert moulding
Transfert moulding uses a press similar to the one used for compression moulding. It is generally chosen to manufacture parts with bounded or over-moulded metal inserts.
Preparation
To obtain such parts, a 3-plates tool is manufactured: a lower plate, a middle plate and a perforated upper plate. The cavities are machined in the middle and lower plates.
Vulcanisation
The metal inserts are placed on the lower plate. The middle plate is placed on the latter. The rubber strips are placed on the middle plate just above the holes, which are used as injections feeding channels. The upper plate the shuts the tool.
As a result of the closing pressure, and of the temperature, the material melts, passes through the holes and fills the cavities.
Tolerances
The tolerances on finished parts are in accordance with ISO 3302 grade M2.
Workflow
Similar to compression moulding concerning the preparation of the material, it differs howerver in the moulding method.
Moulding tolerances
Techné's moulded parts are made according to ISO 3302. Depending on the selected process, feasibility and customer requirements, a M1 grade (precision part) or a M2 grade will be applied. Even tighter tolerances can be proposed on specific request.
Deflashing process
Cryogenic deflashing
The parts in the form of either clusters or sheets, are placed in a rotating sieve, and are sprayed with polymer balls or pellets.
The sieve rotates and the temperature is lowered to -50°C or -70°C depending on the material. The balls and pellets are therefore projected on the parts and break up the sheets or clusters. Thus the parts are separated from the flashes.
A polishing tribofinition is usually done to complete cryogenic deflashing.
Manual delfashing
To perform a manual deflashing, a properly adapted tool must be used. During the manufacture of the mould, the "rubber cutting lozenges" are placed around the cavities. During the deflashing process, the operator pulls on the "rubber cutting lozenges". The forces are transmitted, due to the lozenge profile, on a fragility line, so that parts can be torn off from the sheet.
Automatic deflashing
In some cases, Techné does an automatic deflashing by cutting, called "trimming".
This especially applies on circumferential parts.
To do so, the parts is rotated, and a knife comes and cuts of the excess material. A sharp angle is obtained. The part is free from any residual burrs. This is the method used in the manufacture of oil seals.
Cutting process
To manufacture gaskets (flat seals), Techné and its division, Chromex, use an automatic process to cut rubber sheets.
The gaskets (flat seals) are widely used for static sealing. Two different processes exist: with a cutting blade or with a punch press.
Blade cutting
Preparation
The material is placed on the cutting table and is kept in place thanks to a vacuum system. The material comes either in rolls or in sheets. The maximum thickness is 15mm. The cutting table's size are 1500 x 3000mm.
Cutting
Depending on the machine's program or the CAD drawing (*.DXF), the cutting head supporting the blade, moves over the table and cuts the rubber. To optimise the scrap ratio, optical material localisation sofware is used. This type of cutting is suitable for seals as unique parts, or cutting is suitable for seals as unique parts, or in small and medium series, with no additional tool cost.
Tolerances
The general cutting tolerances are of +/- 0.2mm
Press cutting
Preparation
The material comes either in rolls or in sheets and is placed on the cutting table.
Cutting
The press is equiped with a cutting tool made specifically according to the wished 2D profile. The piston moves down and the tool separates the parts from the rubber sheet. This process is suitable for medium and large series.
Machning process
Turning
Preparation
The raw material is stored in the form of extrusion rods in an automatic air conditioned storage tower. The rods are vulcanized to a hardness of 83+/-5 IRHD.
Techné has a large number of rods of different diameters available on stock, in order to meet short delivery time expectations. The use of a rod nearest to the dimensions of the finished parts helps to optimize production costs and to reduce material waste, and therefore the environmental impact.
Machining
The rod is placed in the chuck of the lathe spindle, and tools specific to rubber maching, cut out the requested shape.
This process is dedicated to circumferential parts. It is used to manufacture small series, or spare parts based on a model, as well as technical developments.
The machining of elastomers provides a flexible and quick option for the production of prototypes.
Fore more information, see Techné catalogue, "Machined parts" :
Comparison of methods
