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QUALITY
Our products are constantly monitored throughout the production process and stand out on the market for their quality, which starts with the excellence of the materials used. Spaggiari Industria Gomma controls the entire production process by means of a quality management system, which has awarded us the highest recognitions from the main certification bodies for over 30 years.
PROCESS
PROCESS GENERAL PRINCIPLES Thousands of products are created from a large selection of raw materials, of which polymers are only a part. The areas of application of the products are numerous and very different. What we produce is not primarily determined by materials or processes; our aim is instead to solve our customers' problems. In this respect, rubber technology is only part of the solution.
1. CONTROL AND STORAGE OF RAW MATERIALS
After receiving the raw materials, random samples are taken for comparison with certificates from the supplier. Sometimes, for example, the viscosity and moisture content may have changed due to incorrect transport. Storage conditions must be respected in order to avoid problems in the manufacturing process. Most raw materials can be stored at room temperature while some materials should be stored in refrigerated and/or humidity-free areas.
2. DOSING
Each product has a special formula mix and therefore the number and type of raw materials used is different. The ingredients taken from the silos or bags are weighed with high precision according to the predefined recipe. Any error or inaccuracy at this stage could prove fatal to the whole process. Each raw material container is marked to identify its ingredients and weight.
3. MIXING
Mixing is carried out either in open or closed mixers. In both cases, the objective is to distribute and disperse the rubber ingredients through mechanical processing.
4. COMPOUND STORAGE
Each batch of material is controlled according to specifications and the time limit for its storage is also indicated.
5. THE MOULD
The first step in the material production of a product is the design of the mould. On the basis of the desired article, thermal shrinkage must also be taken into account according to the material used. The designer needs to know the compound to be used beforehand. In the case of large articles, the orientation of the molecules can influence the shrinkage of the material. The mould is normally manufactured from hardened steel to produce an exceptionally solid article. In many cases, an initial mould with fewer cavities is created for prototype production.
6. RUBBER BONDING
An important property of rubber is the opportunity it offers for bonding to other materials such as metal, plastics, glass fibres, natural and synthetic fibres and other types of rubber. The adhesion between the two materials depends on the type of rubber and the bonding materials used.
RUBBER-METAL BONDING
This is a widely used combination, as metal gives the necessary rigidity and the possibility of placing the product in its intended location, while rubber gives elasticity and dampens stress. Steel and aluminium are the metals that give the best results. For alloys such as brass and bronze, the result depends very much on the composition of the alloy. During production, the metal must be smooth and free of rust and other impurities. The metal is prepared by degreasing and/or sandblasting. Finally, before moulding, a bonding agent is sprayed onto the metal and, after drying, the rubber is vulcanised together with the metal insert.
RUBBER-FABRIC BONDING
Some products are reinforced with fabric, threads or yarns. The fibre can be polyester, polyamide, aramid, glass and, to a certain extent, cotton can also be used. The textile or metal filament in tyres is the part that gives the tyre its mechanical strength.
WATERPROOF SPREADING
At the beginning of the development of the rubber industry, back in the 1800s, waterproofing of textiles was a popular process. To achieve this, rubber was dissolved in an organic solvent and spread onto the designated fabric with a spatula. Once the solvent has evaporated, a thin film of rubber remains on the fabric and the article is cured in a hot oven.
7. TYPES OF RUBBER CURING
EXTRUSION
This is used for the production of items requiring considerable lengths such as profiles and tubes. The extruder used has the same principle of operation as a meat grinder, a screw feeds the compound through a die. The compound, inside a compartment, is heated by friction. Once the profile passes through the die it takes on the desired shape. It can then be vulcanised in a microwave oven or in a salt bath. If the rubber is to be vulcanised in an autoclave, it is left to cool in water.
CALENDERING
The calendering technique can be used for the production of rubber sheets. Typical products are parts for tyres, conveyor belts, hoses, sheets and mats. The calender is a machine consisting of two or more rotating rollers between which the material to be processed is passed. The number of rollers and the configuration depend on the type of operation to be carried out. The compound is preheated in a mixer or extruder. The rollers, rotating in opposite directions, compress the compound forcing it to the narrow passage. Once a sheet of the desired thickness has been obtained, the rubber is air-cooled before being wound on rollers or sheared into smaller sheets.
COMPRESSION MOULDING
The oldest method is compression moulding, a mould consisting of two parts is mounted in a press. A block of preformed rubber is placed inside the cavity and when the press is closed, the rubber fills the mould cavity. To ensure that the product is perfect, there must be a very slight excess of material. The curing time is rather long and generates substantial flash. The advantage is determined by the simplicity of the method and it is well suited to larger products. The requirements of the compounds to be used are less than in other moulding methods.
TRANSFER MOULDING
Some of the drawbacks of compression moulding are overcome by transfer moulding. The compound is placed in a third part of the mould (heating chamber) and when the press is closed, the rubber is injected into the cavity by means of a piston. The preheating of the material makes the curing process shorter and reduces the risk of porosity in the article. Flash can be reduced by maintaining the correct injection pressure. This process is also used for rubber-metal products. The moulds are more complex and therefore more expensive.
INJECTION MOULDING
The compound is extruded through a screw into a closed cavity. Extrusion pre-heats the rubber and therefore reduces the curing time. The process places high demands on the compound in terms of flow properties and compound curing. The biggest advantage associated with injection moulding is the possibility it offers to automate the process and control the flash. An injection moulding machine is rather complicated and the whole process is technically complex.
8. POST-CURING
Rubber products cool slowly and vulcanisation continues even after the product has been removed from the mould. The post-curing process is normally about 10% of the total curing time. Some special compounds require post-curing in hot air for several hours, sometimes up to a maximum of 24 hours.
9. FINISHING OPERATIONS
We have the mixing of the compound, the moulding and the post-curing of the product. To complete the manufacturing process, some products have to be cut, engraved or moulded. Other products have to be assembled with other materials or rubber components. All moulded parts have a certain amount of flash. The rubber is removed mechanically or manually by cutting or tearing. An alternative method used for deflashing small parts is to freeze the rubber with liquid nitrogen, which facilitates the removal of flash.
10. SURFACE TREATMENT
In some cases, the surface of rubber is treated to reduce friction. For example, this may be the case with chlorination and UV radiation. Other types of treatment may be necessary to better bond the rubber with other materials.
A certified choice
COMPANY CERTIFICATIONS, QUALITY AND RELIABILITY
Company certifications attest to the creation, application and maintenance of a management and work organisation system that complies with specific national and international reference standards.
ISO UNI EN 2015 : 9001
ISO 9001 certification demonstrates that the company’s quality management system has been recognised as conforming to a standard of excellence.
EC REGULATION No 1935/2004
Material suitable for contact with foodstuffs in accordance with the EC Regulation no. 1935/2004 of the European Parliament and of the Council dated 27 October 2004
BFR
Product conforming to the BfR European Standard (Chap. XXI, cat. 3)
CE
Product conforming to the European legislation
FDA
Material made in total conformity with the American FDA standard.