Whether the frame is good or bad can be seen from several points of the frame structure and the frame welding bead, and I will give you a detailed introduction below!
1. Look at the frame structure
As we all know, the frame is the soul of our bicycles. However, the frame is often doomed when it is designed. Whether it is a good frame or not, let’s not talk about the angle today. Let’s analyze it from the strength. After 5 years of work QC test experience, the model with the easiest to break the ordinary frame Women's city bike, as shown in the picture.
Where is the easiest place for this kind of women's city bike to break? ——The middle tube, the place where the middle tube and the upper tube are combined is the most vulnerable point of this type of model. Why is this?
The force of the bumps during riding is upward for the bicycle. However, the gap above the middle tube of this type of model is too large, and it is easy to deform after riding. Often we vibrate 10,000 times when the head tube reaches the middle when we do the relevant JIS test The distance between the tubes starts to shorten, and then all the force of the upper tube is applied to the middle tube, and the middle tube is the most vulnerable at this time.
Of course, professional factories still have a solution. Put a liner inside the middle pipe, and weld it with the outer middle pipe before assembling! Thus making up for its absence!
2. The combination of the hook and the upper fork is not tight enough.
Why is the combination of this kind of claw and upper fork fragile? Because when the upper fork is preparing materials, the arc openings on the left and right sides (where the upper fork and the rear hook meet) tend to be inconsistent from left to right, resulting in one side being longer and one side being shorter when assembling.
From this picture, it is obvious that the upper fork pipe material is not fully connected with the hook claw at the joint of the upper fork. ! In order to save costs, many factories directly divide the welding into two times, and the first time fills the gap and grinds. Solder 1 more time at the end to create a false impression! In fact, this kind of bike has no problem pressing the road, such as mountain climbing, off-roading is worth sweating!
Since the picture of the frame is hard to find, we will talk about the above two points for the structural strength.
Second, look at the frame weld bead
The weld bead is the most important part of the aluminum alloy frame. It tells us that our scattered pipe materials are combined by high temperature melting! So what kind of weld bead is a qualified weld bead?
The weld beads on our frames can be easily divided into two categories.
1. Fish scale welding - as the name suggests, it looks like fish scales, piece by piece!
The standard of fish scale welding is: bead width 7-8MM, one inch is 9-11 pieces, clear, full, no pinholes, sand holes, false welding and other phenomena, the finishing point should be placed at 5 o'clock or 7 o'clock position! As shown in the picture:
I know that many bosses and riders think that a good frame should be a flat-welded frame. In fact, it is not the case. The flat-welded frame is blown open by high-voltage current on the basis of fish scale welding, and after grinding, the pipe material and the pipe material are separated. The union between them is like one.
Mountain bike frames have higher strength requirements. If there is flat welding, it should be on the head tube and two places in the middle tube. The dropouts and bottom bracket cannot be flat welded! Because flat welding is easy to cause metal fatigue and stress gaps after two high temperatures, many factories do not even follow the most basic common sense in order to achieve the so-called beauty! Misleading consumers, as shown in the figure:
What's more, even the bottom bracket is flat-welded, and it is still under the guise of passing the test to deceive consumers!
2. Flat welding, the full name is Italian flat welding: In fact, flat welding is mostly used for road vehicles, track vehicles, and roads with less demanding strength requirements!
First of all, let’s talk about the weld bead standard of flat welding!
The standard width of the flat welding bead is 11-13mm, and the surface is uniform without pinholes, pores, undercuts, false welding, etc.
In fact, there are not many factories in China that can really do flat welding. Why is this? Because the welding flat welding frame should be in a relatively clean environment! There should be no wind blowing against it, so that there will be no small sand particles attached to the weld bead. A small sand particle is often a small pit after baking paint!
There are not many factories that really have these conditions! So it’s not that this frame is flat welded, we judge it to be a good frame! This frame is fish scale welding is not good! The real big names of mountain bikes are almost all the fish scale welding method, which not only ensures the strength, but also improves the weld bead level and solves the problem of weld bead appearance!
