What is Sandblasting and Shot Blasting

Created on 08.19

Between polishing and electrostatic spraying, sandblasting and shot blasting are an indispensable link for slide metal parts. For the slides which are mainly made up of galvanized steel pipe, through the rust, oil and other remaining impurities on the surface of galvanized steel pipe removed by shot blasting, get a proper roughness directly used for coating, so as to improve the coating film adhesion of the final product.

1. Principle.

The rust on galvanized steel pipes is mostly white rust induced by oxidation of zinc film or localized rust on iron matrix. The rust layer is brittle but strongly bonded to the zinc layer. High-speed abrasive particles strike the galvanized surface with certain kinetic energy. The impact force on the galvanized surface breaks up the oxidized rust layer while damaging as little as possible of the intact galvanized substrate. The rust removal on ordinary steel is different from that on galvanized steel pipes. The impact intensity on galvanized steel pipes should be strictly controlled to remove the rust and impurities on the zinc layer as possible as to preserve the intact zinc layer as protective substrate to.

2. Abrasives.

The characteristics of galvanized steel pipes demand that abrasives should have low damage resistance and high cleaning power. In actual use, round or sub-round abrasives are preferred. Cast steel shot is the preferred abrasive. The roundness of abrasives can reduce the damage to the galvanized layer by scratches through rolling impact. The hardness of abrasives is HRC40-50. The rust layer on the galvanized steel pipe is broken up and the intact galvanized substrate is avoided from excessive abrasion. For the local serious rust, a small amount of angular steel grit can be added. The cut action removes the rust. In actual use, the proportion of steel grit should be strictly controlled within the range of less than 20%, so as to avoid the excessive loss of zinc layer. There are also clear requirements for the selection of abrasive grit. Generally, medium grit is used, namely, the grit size is 0.3-0.8mm. Φ0.5mm steel shot is widely used. The abrasives remove the rust on the galvanized steel pipe efficiently and form uniform and fine pits on the galvanized surface to give the ideal roughness to the plastic spraying.

3.Equipment.

Grit blasting and shot blasting equipment for galvanized steel pipes.As for the jet mechanism, usually the shot blasting equipment adopts the low-speed impeller (the speed is 1500-2000 rpm), which can decrease the ejected velocity of the abrasive and weaken the impact intensity of the abrasion. Sandblasting equipment should strictly control the compressed air pressure (0.3-0.5 MPa). The abrasive circulation system should be installed with a high-precision screening device, which can timely separate the broken abrasive and avoid the sharp objects damaging the galvanized coating. The dust removal system should be upgraded into the high-efficiency cartridge-type dust collector. Generally, the particles of the zinc dust generated by the rust removal on the galvanized coating are finer and harder to separate from the original abrasive by the bag filter used in ordinary dust collectors. High-efficiency dust removal can not only protect the working environment but also avoid the possibility that the zinc dust settles on the treated surface and affects the coating adhesion.

4. Process.

The grit blasting parameter for galvanized steel pipes should follow the principle of "protecting the zinc coating first and achieving rust removal later". The blasting distance should be controlled into the range of 200-300mm and avoid the abrasion impact on the zinc coating caused by the high kinetic energy of the abrasive. The blasting angle should be controlled into the range of 30-45° to avoid the vertical impact on the surface and causing the falling off of the local zinc layer. The treatment time should be dynamically controlled according to the degree of rust. The mild white rust can be removed in 10-15 seconds. Localized ferrous rust should be treated in no more than 30 seconds. The intermittent blasting should be adopted and multiple short blasting cycles replace the continuous blasting. After completing the process, the cleanliness of the surface should reach at least Sa 2.5 according to the international standard ISO 8501-1. This international standard requires the surface should be free of visible grease and dirt, scale and rust. If there is any residue, it should be the minimal streak or speckled shadow. In addition, the retention rate of the zinc coating should be strictly controlled.

Get in touch

Let's take your business to the moon.

By signing up to our newsletter you agree to our Term of Service and Privacy Policy.

Contact Us

Wechat