It is the key to ensure service life of roller press by overlaying and maintenance timely to roller surface. The manufacturing and overlaying remanufacturing process requirements for squeeze roller include that there should be no crack in welding process, the hardness of roller surface is no less than HRC55, roller press works properly , abrasion resistance of roller surface and integration should be good and roller press are worn evenly in operation.

For normal wear, excessive wear, peeling off in large areas, overload operation, and other different failure modes caused by poor performance of roller itself and foreign material introduced to roller, usually three remanufacturing processes can be applied including on-line repair welding, on-line overlaying, off-line overhaul repair according to customers’ particular circumstances (Whether spare squeeze roller of roller press is available and repair is needed.),. Off-line overlaying welding will be introduced as following.

Various application cases show that key technology of overlaying squeeze roller lies in reasonable design to wear-resisting material and raised pattern of roller surface, and the overlaying process for partial or whole roller surface.

① Condition for off-line overlaying
For squeeze roller which is worn excessively, over damaged or overloaded in operation, the scientific method to deal with it is to disassemble for off-line overlaying, because after 5-6 times direct repair welding for roller, tiny welding crack will develop continuously and a certain thickness of fatigue layer will appear on the surface due to repeatedly high crushing stress on parent roller. And if the roller is repair welded directly at this time, it’s easy to peel off among layers. Therefore, it is needed to completely clear up fatigue layer before the whole overlaying. Meanwhile, stress of roller can be eliminated by appropriate heat treatment.

When the roller is off-line overlaid, the quality is well guaranteed due to better heating and mechanical process condition. If condition permits, by using lathe to remove transition layer, bottom layer and the fusion layer of parent material and bottom layer to make sure that the fatigue layer can be removed more thoroughly. Besides, heat treatment can be used, thus the fatigue stress of roller can be eliminated completely and the ductility and toughness of roller can be recovered. Therefore, after off-line overhaul repairing, the roller is comparable with a new roller. Its wear resistance is even better than new roller, which can guarantee safe run in a long term. Due to good wear-resisting property, 8,000h of running time or even more can be ensured after off-line overlaying.

② Process for off-line overlaying
The basic processes of off-line welding are as follows: firstly, clear up the roller before welding, and then preheat the roller to a certain temperature. Secondly, overlay bottom layer and repair roundness of the roller, then shape it on a lather to get further the roundness of the roller. After that, overlay transition layer, hardfacing layer and emboss layer successively. Finally, after overlaying is completed, preheat the roller again, and carefully wrap the roller with thermal insulation material, then cool down slowly.

According to working condition, the combination of auto/semi-auto welding of gas shielded arc welding and self-shielded arc welding or of submerged arc welding and open arc welding can be used.

③ Process and control measures
Thereinafter, off-line overlaying process for squeeze roller of Beijing ARC Xinxing Science & Technology Co., Ltd is taken as example to detail process and control measures.

a. Pre-welding treatment

To ensure the overlaying quality of squeeze roller, the remove of fatigue layer is very important. For overlaying remanufacturing of worn roller, the time taken to clearing up and overlaying is almost half-and-half; even more time is taken to the former. Thorough remove of the fatigue layer is the prerequisite to produce overlaying layer with excellent integration.

The first step of off-line overlaying is to remove fatigue layer by the process of carbon arc gouging or electric smelting gouging, then lathe the remained fatigue layers or layer with mixed carbon caused by gouging. After remove there should be no crack in the roller. Then polish the surface of roller to expose the metallic luster. Secondly, conduct ultrasonic detection and penetration inspection to make sure that there is no crack. After inspection, repair roundness of roller surface, use heater, like oxyacetylene or ceramic electric heater to preheat roller. The preheating temperature is 300℃, rate of temperature increase is 60℃/min, and make heat preservation for 10 hours.

b. Overlaying process

According to the damage degree of workpiece, overlay successively bottom, transition, hardfacing and emboss layer.
The welding speed can be adjusted appropriately according to overlaying layer thickness. Once the welding operation begins, it cannot discontinue since the temperature of roller must be kept to avoid the appearance of cracks (Crack is the main factor that causes roller peel off.).
During the whole process of welding, crack, pore, slag inclusion, incomplete penetration, etc., should not exist and the surface must be cleared up. The temperature of the roller should not be lower than 200℃.Thickness of each wear-resisting layer should be even and meet requirements of drawing design to make squeeze roller keep round all along.

c. Post-weld Treatment

Temper in the furnace with temperature of 580℃～600℃ and preserve heat for 24 hours.

Clean up, polish, correct and balance.

Measure the distance between two rollers to ensure there is no big or small end.

Measure the roller surface and control height difference in ±2mm.

After welding, wrap the roller with thermal insulation blanket and prohibit welding the roller again after cooling down.