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Matters Needing Attention of Titanium - Steel Composite Board Container Equipment Manufacture

I. Acceptance of the Material

1. When the ultrasonic inspection is carried out on the composite rate of the titanium - steel composite board, instead of the lubricant coupling agent, water or water glass shall be used.
2. The quality of titanium plate, steel plate shall meet BG/T3621-94 standard; the quality of titanium - steel composite plate should meet GB8546-87, GB8547-87 standard or be made as the agreement between the two parties of supplier and demander; the quality of titanium pipe shall meet GB/T3624- 95 standard; the selected titanium wire shall comply with the provisions of GB/T3623-1998.
3. The inspection of the outline dimension and surface quality of the composite board shall be carried one by one and the measurement of the thickness of the composite board is allowed to be carried on one sheet for each batch.

II. Matters Needing Attention in Cutting

The titanium materials and titanium - steel composite board may be cut by flame, plasma, punching or machinery processing method.
1.When the flame cutting, plasma cutting are applied, because the titanium is susceptible to oxidation above 300 ℃, and its thermal conductivity is low, the titanium is easier to cut than general steels. Thus, the gas-cutting speed shall be 4-5 times faster than the steel plate. After gas-cutting of the titanium, there is gas contamination layer on the cut surface with the depth of about 2mm, which shall be removed mechanically.
2. When the titanium - steel composite board is cut mechanically, the primary layer shall be downward; when cut by flame or plasma, the composite board shall keep enough height from the ground, with the cladding layer upward or downward, and the oxidizing layer of the cut must be cleared before the welding.
3. The bevel surface of cutting shall not have cracks, delaminating and slag inclusion defects.
4. Determination of the cutting size of the cylinder must be based on the actual size formed of the shell cover.

III. Welding of the Titanium - Steel Composite Board

1. If the tungsten pole encountered the weld metal during gas tungsten arc welding, i.e. touching tungsten occurred, stop immediately the welding operation and remove the source of pollution. Replace the tungsten pole and then carry out the job.
2. Welding seam in welding operation shall be as long as possible; when stopping welding takes place in the middle and re-welding is conducted, welding seam shall overlap about 10mm.
3. Random arc striking is not allowed in welding. Conduct self-check after the accomplishment of welding, and timely deal with any problem found. After welding, carefully clean welding beading, welding slag, splash and other contaminations on the surface of weldment, if necessary, conduct local finishing
4. When process welding seam defects, firstly use grinding wheel for thinning and cleaning, and then use calico dipping acetone to conduct scrubbing and cleaning; after cleaning is finished, further conduct rework processing. The number of overhaul times is not inadvisable more than two times; if over two times, it shall be approved by technical director of the unit before rework.
5. Weld inspection: welding seam forming shall be uniform, dense and extremely smooth, not allowed the appearance of cracks, gas porosity, tungsten inclusion, non amalgamation, oxidation (mainly see the color change of welding seam), excessive undercut, crater and other defects, and titanium welding seam surface is not allowed the appearance of obvious scoring.
6. If base steel needs to weld ear or conduct reinforcement, welding current shall be small, and after each welding, it needs a time lag to conduct next welding to prevent that the excessive large amount of heat input lead to titanium composite bed thermal oxidation discoloration.
7. Winter construction shall attentively maintain ambient temperature because titanium metal is more brittle; if temperature is too low and cooling rate is too fast, crack will very easily appear. Ambient temperature should be timely increased; welding seam zone shall be conducted appropriate preheating within 80mm of periphery, with temperature not below 15℃ and preheating from base steel.
8. Welding seam is strictly prohibited melting parent metal, not adding welding wire, which will lead to welding seam strength depression and dehiscence in cooling.
Judge weldment quality by welding seam and heat affected zone color:

Welding and heat affected zone surface colorArgon shield situationQualification JudgmentProcessing method
Silver-white colorGoodQualifiedNot need processing
Golden yellow (densification)Still goodQualifiedAble to not process
BlueSomewhat lessCan only be used for non-critical partsRemove blue
PurpleWorseCan only be used for commonly used containerRemove purple, and if not removed off, rework
Dark grayBadUnqualifiedRework
OffwhiteVery badUnqualifiedRework
Yellow powderVery badUnqualifiedRework

III. Formation of Shell Cover and Cylinder

1. Titanium-steel composite board shell cover forming can apply be hot or cold stamping postheating check type (allowing the use of cold stamping). Titanium clad steel plate shell cover shall apply cold stamping as much as possible; if applying hot forming, its heating temperature shall be controlled within 550--650℃.
2. Before hot forming of shell cover, all oily soil and other attachments on workpiece surface shall be removed fully. When workpiece no longer passed mechanical working after high temperature (above 350℃) hot working, its surface can be coated with thermostable coating material to prevent the surface from being oxidized and polluted.
3. Heating generally applies electric furnace; if applying gas heating furnace, such kind of furnace must be a box type furnace, and the atmosphere in the furnace must be maintained micro-oxidability, not allowed reducibility. The sulfur content of heating fuel shall be low. Heating shall be uniform, and not allowed making heating flame and solid fuel directly contact with the titanium surface.
4. To prevent the workpiece from being scratched or sticky touch in the stamping procedure, the titanium surface should be coated with a lubricant with low friction coefficient.
5. Main dimensional tolerance of elliptical and butterfly-shaped shell covers are as follows

Shell Cover Diameter

Diameter Tolerance

Difference between Maximum Diameter and Minimum Diameter

Surface Convexconcave

Surface Height Tolerance

Straight Edge

IV. Cylinder Forming

Cylinder forming can apply hot roll forming or cold roll forming.
1. Before cold roll of cylinder, both sides of titanium plate shall be decided semidiameter prespringing on mold and then plate is rolled. As for titanium clad steel plate cylinder with smaller rolling curvature radius, once press amount shall not be too large to prevent the gaffing of multiple coat. Meanwhile, in rolling circle, it is not allowed to remain in non-composite parts, in order to avoid the enlargement of loosening area. Lapping machine roller surface shall be cleaned up and burnished smooth, or in rolling, pad a thin layer of galvanized iron sheet or stainless steel thin sheet on titanium plate to prevent titanium plate surface.
2. Wall thickness of cylinder is not allowed to be less than design thickness provided by the drawing after hot rolling.

Problems Which Should Be Paid Attention in Manufacture of Pressure Vessel with Composite Board

1. Cutting and Groove Processing

Composite board cutting applies air plasma cutting, ensuring not only good quality of incision but also less quench hardening of incision surface. As for manufacture of pressure vessel using composite board, lineation control of sheet bar, especially the control of perimeter geometric dimension, is very important. Because this dimension will directly affect the contra-aperture unfitness of butt joint of shell circular seam, it must be strictly controlled. As for vessel with band convex shell cover, its cylinder cutting shall be decided as actual dimension after the forming of shell cover. In addition, in lineation, the control of sheet bar diagonal line dimension is also very necessary so that it can ensure rolling circle back shell ring end's declivity and mismatch amount as small as possible, so as to make shell ring group against back welding seam gap uniform, laying a foundation for the welding quality. As for groove processing of composite board, there was not any difference from conventional single plywood a few years ago; however, fairsized changes have generated in recent years, from pattern in Figure 1a to pattern in Figure 1b, while pattern in Figure 1b can better ensure welding quality and reliability of equipment used. As for groove processing methods, applying edge planer processing is more ideal. Speaking for fillet welding seam, groove processing is appropriate to apply air plasma cutting. After cutting, remove dross; burnish quench hardening layer with grinding wheel; and conduct dye check inspection on groove surface.

2. Forming and Assembly

As for the forming of composite board, under the conditions accessible for equipment capacity, apply cold processing as much as possible. Key problem in forming course is the protection of cladding surface because the thickness of claddings is generally very thin. It may lead to mechanical damage to partial surface with little attention, which affects the corrosion effect of the cladding layer. The effective method to prevent this situation is to regrind the curved roller and mold surface to be smooth and tidy, so as to play a role of protective coatings. When composite board need to apply hot forming, attentively protect the termination temperature and cooling rate, in forming; heating times shall not be more than twice, and plate shall be uniformly heated in order to maintain the corrosion resistance of cladding material. There is not much difference for composite board shell assembly from assembly principle of unilayer shell, just with more strict requirements for composite board shell in counterpart unfitness control. It is not decided by the whole thickness of sheet bar but by the thickness of cladding, providing that it is not allowed to exceed 1/2 thickness of cladding, not more than 2mm. Because of this, in above cutting and groove processing, it gives special emphasis on indispensable strict control of perimeter dimension and diagonal line dimension in cutting and planning, with the purpose to ensure that assembly counterpart unfitness meets the requirements. At the same time, it can also avoid forcing grouping. In addition, such appurtenances as ear and clip are prohibited to be spot-welded on the cladding to avoid damage to the cladding. If spot welding is necessary, in removal, burr, crater etc must be conducted repair welding and re-grinded to be flush with parent metal; and then conduct dye check on the surface of such parts to prevent such opening defects left as microcrack which will leave hidden danger to the safe usage of equipment.

3. Welding

Welding of composite board must apply three kinds of materials, namely base welding material, transition layer welding material and cladding welding material. Speaking its methods, it not only can apply manual welding, but also can apply unionmelt welding for base while cladding and transition layer apply manual welding. Practice has proved that, in the welding course of composite board, applying small line energy interlayer temperature control is necessary, particularly in welding course of transition and cladding layer, interlayer temperature control becomes more important. If interlayer temperature is too high at that moment, after welding, multiple coats along welding seam heat affected zone is very easily to crack. Therefore, in welding course, interlayer temperature should not exceed 50℃.