This video explains a way to make a welding for a round PU belt. A DIY tool is shown and proposed for that, and it includes measurement of the temperature of the heating surface for the belt ends.
0:00 Introduction to the round PU belt material
0:50 Principle of the welding process
1:22 Description of the welding tool
2:03 Preferred temperature to be used
2:35 Instrument to measure temperature
3:54 Holders of the belt ends
4:44 Guide to other videos about welding on KZitem
5:16 Actual welding of a belt
6:12 Heating the belt ends
6:31 Steel heating is removed and belt ends are connected
7:06 Removal of belt holders
7:33 Excess material is removed from belt
8:06 Finished welding
8:18 End of video
Round PU belt material is a cheep and easy way to make a belt for a vintage sewing machine. However, the friction power losses are significantly higher than what you can get with black V-belts. You may also be able to make use of timing belts, and they got even lower power losses. But round PU belts are a cheap and easy possibility to use.
In order to measure the welding temperature, a K-type Thermocouple Digital Thermometer is used. You can find many suppliers for such instruments. The thermometer used in this video is sold here:
www.aliexpress.com/item/32816...
I suggest this improvement of the tool: You make the base plate of plywood a bit larger and add another wooden strip on top to the other side. Then you do not need to remove the steel block before you connect the ends, but you move the two holders against the opposite list and connect the ends. It is important to keep the time short from heating the ends to connecting the ends.
Below, you will find some nice references about the welding process:
This is a link to a scientific paper describing this welding method:
www.ncbi.nlm.nih.gov/pmc/arti...
This link prefer a welding temperature of 250 C:
www.aliexpress.com/item/10050...
These three links prefer a welding temperature of 260 C:
www.fennerdrives.com/FetchFil... www.mafdel-belts.com/prod/bel...
• Extruded round belts e...
These links prefer a welding temperature of 290-300 C:
• BEHAbelt FZ02/3 & EErg...
• Optibelt Material Hand...
IMPORTANT NOTE ON PU MATERIAL QUALITY:
I made a survey of about 120 green rough round PU-belts on Ebay, AliExpres and Amazon. Most sellers do not provide technical information about the material used. None on Amazon. About 10 % of the sellers on Ebay and AliExpres provide information about the hardness of material used according to the Shore A method. Here you got two kinds with a harness of 75 +/-5 or in range 85-95. A higher number means a harder more rigid product. Youngs Module (Elasticity module) will be higher with a harder product, and I have seen 21 MPa and 42 MPa. I suppose, that the harder product will be better for sewing machines, but I do not know. But I recommend, that you buy from a seller, that at least specify hardness or Youngs Module.
I tried to order from another ebay Chinese seller of hardness 85-95. Unfortunately I got no way to check hardness, but my best guess is, that the received hardness was actually 75. I can measure Youngs Module, at it was 19 MPa. I guess you need to buy from a professional seller of these belts, if you want to be sure about material properties.
Please like the video if you find it useful. You are free to leave your questions and comments below.
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