1, the cracking phenomenon
Cracking approach is generally grouped into two situations:
1) From the inside corner weld angle horns start;
2) compare the law in a straight line along the weld cracking.


2, "weld cracking" Cause and Prevention of the resulting "
Weld cracking caused by reasons more unified view of the industry, mainly because of problems of welding process, weld strength to achieve their value, resulting in welding angle cracking.
The following aspects of the welding process will produce a direct impact on the strength of welded corners, cracks also have an important impact on the welds, are worth noting:
1) molding material geometry precision, such as tolerance diagonal length, angle, frame and fan must ensure that within the 2 n ~ 3 coffee to avoid welding and soldering melting capacity margin uneven weld strength decreases, while avoiding excessive fillet of internal stress.
2) the quality of welding plates and welding temperature settings. The temperature must be evenly distributed weld plate, welded plate set temperature and the actual temperature of the agreement is better; the heating temperature is set too high or too low will reduce the weld strength.
3) Feed pressure setting. Fillet weld strength of the relationship between the feed pressure should be: as feed pressure increases, the weld strength increases, the feed pressure exceeds an optimal value, but decreased strength welding angle j Also note that pressure before and after the pressure clamp Profiles should be set to ensure no distortion, no displacement, once displaced profiles, weld strength will be severely degraded during the welding process.
4) profiles by adjusting plate and use. Must be adjusted by the straightness and verticality of the plate, and by the relative position of the inside edge of the jaw plates, profiles on board adjusted properly, will produce profiles partial dislocation and partial melting solder, a serious impact on the fillet weld strength profiles. Profiles on board height should be coordinated with the profile height (former lower), some assembly plants by the board is not complete, with profiles on board to weld large width of small series of profiles, which is not desirable.
5) welding quality and cleaning cloth. Has expired or has been perforated welding cloth should be replaced for life, and should pay attention to maintaining clean cloth welding, there is adhesive material should be promptly removed. Some assembly plant in order to save time, having a good strip and then welded sections, resulting in viscose cloth welding, welding cloth made of a black plastic material, which is a pursuit of efficiency rather than just the pursuit of quality practice. In addition, not using the same profile or different profiles manufacturers of welding process parameters different varieties and specifications.


3, "material cracking" reasons
The stress profiles generated "material cracking" and profile itself suffered stress and profiles of both relationship, when the external stress is greater than the internal stress, profiles will have a "material cracking."
1) In the design, production process, to produce profiles "material cracking" of negative factors 1) small end welding angle cracking problem. It was through simulation test welding angle cracking of the corners of retractable stainless steel doors do destructive test pressure profiles easy to crack, the following conclusions: easy to crack profile, their experimental fillet weld strength is usually low. The low profile fillet weld strength and more concentrated in the small end sections, profiles and thus more prone to small end fillet cracking. Thus, the small end sections of steel production frames, when doors, its size should not be too large.
2) the same kinds of profiles at room temperature solderability general difference is not great, but when the ambient temperature is below 15 ℃ is not the case, the lower the temperature, weld strength values drop more different formulations Great, we recommend that the assembly plant by comparison test, use at low temperatures and good weldability profiles.
3) Extrusion processing of plastics. It was found by experiment, material cracking profiles with plastics of a clear relationship between profiles, bad or overly plasticized plastics profiles are easy to produce. Material cracking. "So in the profile production process, manufacturers should strictly control the production process, to grasp the degree of fit of plastics, so the profile to achieve better performance, has the best ability to withstand external stresses.


2 welding and assembly of "material cracking" the impact of its preventive measures in addition to the second point in this article, there are several aspects of the profile of the "material cracking" has a significant impact.
1) Welding ambient temperature. Low temperature welding environment (≤15 ℃) the welding box, fan fillet more prone to cracking the case, which is generated during welding profiles stress related. When profiles welding, end welded plate is heated to a molten state, but near the end face of the profile is at a room temperature, so that between the pads and a temperature gradient profiles zone distribution area is formed. In the cooling process, the cooling profile will be due, uneven shrinkage is generated within the internal stress of the small region, the welding temperature and ambient temperature the greater the difference, the greater the internal stress. Including stress joint action with the external stress, the fillet from this small region will crack, but more often than not starting from the weld cracking. Therefore, the conditional assembly plant welding car asked ambient temperature must be maintained at above 16 ℃, and winter outdoor ambient temperature is relatively low, the material must be stored indoors for more than 24 h. No terms of the assembly plant in front sections welded should think of ways to profiles, welding platform and press pliers preheating.
2) clearance angle work. In the clean-up box when the fan inside corners weld, should avoid using the flat blade Gouge and generates marks, the marks will be generated after the procedure to install caulking stress concentration worst parts.
3) aluminum rails and layering is expected to open size. To prevent the fit between the layering or aluminum frame rails and a gap, a lot of assembly plants in determining the layering and aluminum rails dimensions often do not get to take the high low, if the pressure of the size and aluminum rails than excessive, often leads installation box, fan angle portion is split brace. Recommends layering and aluminum slide sizes of materials per actual size jamb frame, fan operation.


4, the impact on the "material cracking" installation and preventive measures
1) install retractable doors in the winter, the work should reduce outdoor jobs. One can avoid the box fan is floating in the corners when installing caused cracking, on the other hand to avoid the cold crisp cold outdoor environment affect the material.
2) stainless steel retractable door openings must be smooth vertical and horizontal position, the hole size appropriate. Hole skew is not standardized, resulting angle between two adjacent frames is not equal to 90. That box, the corners of increased stress fan.
3) fixing method should preferably be fixed piece fixation, try not to use the included expansion screw fixation, and the fixing piece mounted spacing should meet the national standard requirements. Since the expansion screw fastening action and non-deformation characteristics, it will not be able to mitigate and eliminate the stress frame, or even increase stress, causing fillet cracking.
4) it must be used within telescopic joints between the door and the entrance of foam or other resilient material filling, to avoid affecting the dimensional change of the plastic door changes in temperature.
Effect of stainless steel retractable door welding angle cracking more complex factors, both may be inherent quality profile, it may be the problem retractable door stainless steel assembly and installation, this requires profile production companies and assembly plants and other users enhance technical exchanges cooperation on all fronts at the same time manpower, to take reasonable measures to deal with it may reach the objective of reducing and preventing the occurrence of cracking fillet weld profiles.