The other issue with the hollow bars is that if enough weight was placed on a spot they would begin to bend. The issue became so bad that a 90 day warranty was put in place by most manufacturers of these frames. Another issue the black metal frames suffered from were bending stretcher bars or rails. Again the hollow nature of these strecther rails presented issues with breakage and bending.
However, the rigidity is quite low. A futon mattress made from a mixture of cotton and foam is much lighter and less firm than that of one made from 100% cotton. The rigidity of a cotton and foam futon mattress is quite high, so is ideal for futons that are going to be used mainly as a sofa. A futon mattress made from cotton and polyester is also light and not too firm. Its rigidity is less than that of 100% cotton or cotton and foam mattress.
Early designs involved a steel tooth design that would fit into pocket welds on the arms. These would snap off over use. The alternative design was to run a bolt through the arms and into the rails. While better it still did not address the issue of bending stretcher rails. Bent hinges also added another issue that would happen from use over time. While not as common as the other problems this issue still led to the failure of many black metal frames.
Any content, trademark/s, or other material that might be found on this site that is not this site property remains the copyright of its respective owner/s. In no way does Hilosylanas claim ownership or responsibility for such items, and you should seek legal consent for any use of such materials from its owner.