Baker Pacific successfully use cast iron skid bars to support wire mesh ovens bands, (for example Z47, Z 47R and Ashworth U66-48-1718 PGLW). The skid bars are used on ovens of up to 100m length. Where the products and oven conditions are very dry, some graphite skid bars can be added to reduce friction . Skid bars are trouble free and do not require maintenance, except annual checks and cleaning.
Skid bar with access port before oven band installation
Cast iron skid bars are placed inside the baking chamber with a pitch of 0.8 – 1.2m. They are supported in frames and are removable for cleaning. Apart from cleaning, which is infrequent, skid bars do not require any maintenance.
The skid bars are cast from iron with a graphite content which reduces friction. The material and casting are critical to the performance and the skid bars are supplied to suitable specifications, for example International ISO/DIS 185 Grade 200 / 250. The chemical composition, casting process, shape of the mould and cooling rate are important to achieve the optimum low friction and durability of the skid bars in operation.
The surface of the skid bar has a microstructure of a pearlitic matrix with evenly spread type A graphite flakes to ASTM A247 standard with no hard particles. Maximum allowed amount of ferrite is 10%. No ledeburite is allowed. The sliding surface of the skid bar is machined after casting by removing the surface layer (1.0mm), which contains ferrite and would result in scratching of the band. The final surface should have a roughness of Rmax 3.0um
The installation of the skid bars is critical to good band tracking. The bars must be level and at right angles to the direction of band travel. Levelling is best done optically with a laser instrument.
Baker Pacific skid bar support with levelling adjustment and access port
Return band supports
On the return below the baking chamber, the band is supported on rollers. A proportion of these, usually one in three, may have spring loaded guide discs. These are very effective in keeping the band in its central position.
Baker Pacific spring loaded return band support roller
Heavy mesh band supports
Heavy mesh bands are supported on rollers, which will carry heavy bands with low friction. The design of the supports and adjustment for levelling and the specification of the bearings are critical as the rollers operate at baking temperatures. If the rollers seize, they will quickly cause wear to the oven band. The ends of the rollers are therefore exposed for inspection and high temperature bearings must be used. The bearings are mounted outside the baking chamber and are insulated from the chamber.
Bearing assembly with SKF bearing type Y – V228 sealed for life and suitable for operating temperatures of up to 350oC